Review Article Optical Fiber Sensors Based on Nanoparticle...

Review ArticleOptical Fiber Sensors Based onNanoparticle-Embedded Coatings

Aitor Urrutia Javier Goicoechea and Francisco J Arregui

Nanostructured Optical Devices Laboratory Department of Electrical and Electronic Engineering Public University of NavarreCampus Arrosadıa SN 31006 Pamplona Spain

Correspondence should be addressed to Aitor Urrutia aitorurrutiaunavarraes

Received 21 May 2015 Accepted 26 July 2015

Academic Editor Wojtek J Bock

Copyright copy 2015 Aitor Urrutia et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The use of nanoparticles (NPs) in scientific applications has attracted the attention of many researchers in the last few yearsThe useof NPs can help researchers to tune the physical characteristics of the sensing coating (thickness roughness specific area refractiveindex etc) leading to enhanced sensors with response time or sensitivity better than traditional sensing coatings AdditionallyNPs also offer other special properties that depend on their nanometric size and this is also a source of new sensing applicationsThis review focuses on the current status of research in the use of NPs within coatings in optical fiber sensing Most used sensingprinciples in fiber optics are briefly described and classified into several groups absorbance-based sensors interferometric sensorsfluorescence-based sensors fiber grating sensors and resonance-based sensors among others For each sensor group specificexamples of the utilization of NP-embedded coatings in their sensing structure are reported

1 Introduction

For the last few decades optical fiber sensors have exper-imented an important growth and relevance in sensingtechnologies field Recently many applications have beendeveloped to monitor or detect a wide range of parametersin different fields such as biomedicine aeronautics envi-ronmental control and other industries This interest of thescientific community in optical fiber sensors is motivatedby their already well-known advantages as immunity toelectromagnetic interferences remote sensing small dimen-sions low weight biocompatibility real time monitoring ormultiplexing capabilities [1 2]

Currently optical fiber sensors field has increased in itsresearch lines and possibilities with the use of nanocoat-ing deposition techniques Nanostructured thin films andnanocoatings have been applied to the diverse optical fiberconfigurations for the fabrication of new sensors Thanksto these combinations many devices have been developedobtaining the detection and monitoring of multiple param-eters such as a wide range of gases [3 4] pH [5] temperature[6] humidity [7 8] ions [9] and biomolecules [10 11]

One of the latest steps in the search for improved novelsensors is the inclusion of nanoparticles (NPs) within coat-ings In diverse new researches it has been demonstrated thatselected NP-embedded coatings enhance some parameters ofprevious devices for example sensitivity [12 13] dynamicrange robustness and lifetime On one hand these improve-ments are due to the fact that NPs can provide additionalspecial properties in coatings (mesoporosity higher rough-ness antibacterial behavior etc) Thus higher surface areain sensitive regions allows reaching lower limits of detection(LoD) in biosensing On the other hand the intrinsic prop-erties of certain NPs cause diverse phenomena by their ownfor example localized surface plasmon resonances (LSPR) orquantum confinement

In the following sections most used sensing principlesand optical fiber configurations will be described and thentheir combination with diverse NP-embedded coatings willalso be presented The optical fiber sensors described in thispaper are classified into several groups depending on theirdetection method Intensity-based sensors interferometricsensors fluorescence-based sensors fiber grating sensorsand resonance-based sensors are the most typical ones

Hindawi Publishing CorporationJournal of SensorsVolume 2015 Article ID 805053 18 pageshttpdxdoiorg1011552015805053

2 Journal of Sensors

2 Intensity- and Absorbance-Based Sensors

21 Introduction Intensity-based optical fiber sensors havebeen reported since the 70s in literature and their devel-opment has been widely used to these days Generallythe underlying phenomenon of such sensors is the lighttransmission-absorption in materials Absorbance is basedon the attenuation of light due to the characteristics of thematerial that light is guided through The sensitive materialschange the absorbance in presence of a specific parameteror analyte and therefore a change on the guided lightcan be observed The absorption mechanisms are describedby the Lambert-Beer Law where the transmission of thelight through an analyte material or sensitive region (119879called transmittance) represents the relation between the lightintensity before (119868

119900) and that after (119868) passing through this

sensitive region expressed by the following equation

119879 =119868

119868119900

= 10minus120572119871

= 10120576119862119871

(1)

where 119871 is the length of interaction within the absorbingregion (optical path) and120572 is the absorption coefficient whichcan be denoted as the product of the molar absorptivity (120576)and the concentration (119862) of the target This transmittancenomenclature can also be transferred to absorbance termssuch that

119860 = minuslog10

119868

119868119900

= 120572119871 = 120576119862119871 (2)

where absorbance (119860) is the magnitude commonly used inthis kind of optical fiber sensors

The incorporation of sensitive materials to optical fibersensors can be performed by embedding them into coatingsor thin films The propagation of light through the opticalfiber presents two contributions the guided field in the coreand the evanescent field in themedium surrounding this coreThis evanescent field is not accessible in unmodified standardcladded fibers and therefore it is not relevant to sensingThereby the externalmediumcannot interactwith the guidedlight through the core nor the evanescent contribution inthe cladding Nevertheless when the cladding is intentionallyreplaced by sensitive coatings there could be a significantinteraction between the external medium and the evanescentfield to the guided lightThe optical properties of the selectedcoating materials determine the changes in this evanescent-field interaction In many cases optical configurations aredeveloped to enlarge this interactionwith the evanescent fieldby removing the cladding bending or tapering the fiber asit is shown in Figure 1 thus improving their sensitivity to thechanges in the external media

22 Cladding-Removed Optical Fiber Sensors Cladding-removed optical fiber (CROF) is one of the simplest struc-tures used in optical fiber sensing (shown in Figure 1(a)) Ashort distance of the cladding of the fiber is removed and thenreplaced by the deposition of a selected nanostructured coat-ing which interacts with the surroundings This coating actsas sensitive region and therefore its composition and fabrica-tion parameters are thoroughly studied in order to improve

sensitivity or other desirable sensing values Thin film fab-rication techniques such as Layer-by-Layer (LbL) assem-bly Langmuir-Blodgett sol-gel or spin-coating are used tocreate these coatings where in some cases NPs are embeddedinside them

During the last two decades many CROF based ap-proaches have been developed Nevertheless as it was pre-viously commented the use of NPs in coatings has not beenreported until the last few years

CROF sensors with NP-based coatings have beenreported in several works detecting humidity [14 15]ethanol [16] ammonia [17] methanol [18] and other gases[19 20] For instance Kodaira et al [20] coated an opticalfiber with SiO

2NPs and poly(diallyldimethyl ammonium

chloride) to createmesoporous overlays by LbLThe resultantcoating morphology allows allocating functional chemicalcompounds for diverse gases detection Another relevantapproach is reported by Mariammal et al [16] using SnO

2

and CuOSnO2

NPs for ethanol detection The use ofCuOSnO

2NPs based coatings presented an enhancement

of 3 times in sensitivity with respect to previously reportedsensors based on pure SnO

2NPs

23 Bent Optical Fiber Sensors Bent optical fiber sensors canbe considered as a particular case of the CROF sensors whenthemodified fragment of the fiber is submitted to a significantbending (see Figure 1(b)) Sometimes these devices are alsoreported as U-shape fiber sensors [21] The intentionallybending effect provides higher losses in the transmitted lightand dramatically increases the evanescent-field depth [8 22]Khijwania et al demonstrated the notable enhancement insensitivity presented by a U-probe in comparison with astraight probe due to a larger evanescent field and absorp-tion coefficient [8] Included in this classification there aredifferent devices which have sensitive coatings without NPsfor humidity [8 23 24] or pH [25] However the use ofcoatings with NPs has appeared more recently Thus Guoand Tao reported ammonia sensing devices [26] based on AgNPs within silica coatings with a theoretical limit of detec-tion (LoD) of 61 ppb Vijayan et al developed optical fiberhumidity sensors based on a Co NPs-embedded polyanilinecoating [27] Their sensors showed a quick response of 8 s ina broad dynamic range of 20ndash95 in relative humidity termsAnother humidity device with MgO NPs was presented byShukla et al [28] using the sol-gel technique Also U-bentfibers have been coated with Au NPs to develop resonance-based sensors [29 30] as it will be described in Section 6

24 Tapered Optical Fiber Sensors and Other Special FiberSensors An alternative strategy for exposing the evanescentfield to an external sensitive coating is fiber tapering Thistechnique modifies the optical fiber geometry and its struc-ture (see Figure 1(c)) thus obtaining an increment of theinteraction of light with the sensitive region and thereforeproviding higher variations in the magnitude of the evanes-cent field The length and waist diameter of the taper therefractive indices and other fiber parameters were analyzedby Ahmad and Hench using a ray model The influence ofthese factors on the penetration depth of the evanescent

Journal of Sensors 3

Cladding

Core

NP-embedded coating

Surroundingmedium

Evanescentfield

(a)

NP-embeddedcoating

Surrounding medium

Cladding

Core

Evanescentfield

(b)

NP-embedded coating

Surroundingmedium

Cladding

Core

Tapered region

Evanescentfield

(c)

Figure 1 Schematic of the most used optical configurations used for the development of absorbance-based sensors with NP-embeddedcoatings (a) cladding-removed fiber (b) U-shape or bent fiber (c) tapered fiber Evanescent field is also depicted as tails that penetrate andinteract within the coating

field was studied [31] They concluded that the longest tapersprovided the largest evanescent field and that penetrationdepth can be augmented three times with a convenient waistdiameter depending on the original fiber diameter accordingto other studies [32 33]

Recently tapered optical fiber sensors with AgNPs-basedcoatings have been developed for ammonia sensing [34]ethanol levels [35] and bacteria detection [36] Anotherexample of this type of devices was presented by Monzon-Hernandez et al for hydrogen sensing using PaAu NPs [37]

The combination of diverse special fibers with NPs-embedded coatings is also reported Examples of this aresuch as hollow core fibers with Fe

3O4NPs for magnetic field

sensing and optical filter purposes [38] polished fibers withTiO2NPs [39] or photonic crystal fibers (PCFs) in junction

with Au NPs [40] and Fe3O4NPs [41] for temperature

sensing D-fibers also have been coated with silica NPscoatings to develop other sensing approaches [42] PCFs andmicrostructured optical fibers (MOFs) are recently used inthe development of new sensors with metallic NPs basedon metal-enhanced fluorescence (MEF) or surface-enhancedRaman scattering (SERS) (reported in Sections 4 and 5 resp)

3 Interferometric-Based Sensors

31 Introduction Optical fiber interferometers have beenwidely used in the development of optical fiber sensors

They can be mainly classified into four types Fabry-PerotMach-Zehnder Michelson and Sagnac [43] Their sensingprinciples and then some examples of each type of sensorswith NP-embedded coatings will be described below

32 Fabry-Perot Interferometers The fabrication of Fabry-Perot interferometers (FPI) in optical fibers has provideddifferent sensing structures There are numerous works thatuse the simplest FP configuration an air gap between twoperpendicularly cleaved optical fibers [44 45] A modifi-cation of this basic structure involves the fabrication of apolymer-based nanocavity onto the cleaved end-face of theoptical fiber These FPI nanocavities based on nanostruc-tured coatings have been commonly performed by meansof the LbL technique in the last decade [46 47] Thusthe obtained optical system is composed of three differentmaterials in terms of refractive index the optical fiber (119899

119891)

the nanocavity (119899119888) and the surroundingmedium (119899

119890)When

the transmitted light passes through the structure the twomedia interfaces (fiber-coating and coating-air) act as partialmirrors where part of the optical power is transmitted andthe other part is reflected (see Figure 2) The reflected powerdepends on the RI of the three materials and the nanocoatingthickness (cavity length)

This reflective phenomenon has been used for sensingapplications Some of them have performed Fabry-Perotcavities including NPs within thin films For instance silica


Cladding

CoreSurrounding

mediumIncident light

Reflected light

Cavity length

NP-embedded coating

nenc

nf

Figure 2 Schematic of the Fabry-Perot interferometer configura-tion in optical fiber sensing

NPs were used in FPI based sensors for humidity [48 49]Moreover FPI based sensors with embedded Au NPs orTiO2NPs have been published for biological applications

such as rabbit immunoglobulin detection [50] or even as aprecision refractometry for refractive index (RI) monitoring[51] Another example is the addition of carbon nanotubesbased nanocomposites in Langmuir-Blodgett overlays todetect volatile organic compounds (VOCs) reported byConsales et al [52] Furthermore Yin et al presented a novelpH sensor whose nanocavity was composed of polymericoverlays combined with complex NPs [53] In another reportAg NPs were allocated in zeolite thin films to detect Hg2+cations in aqueous solutions [54]

33 Mach-Zehnder Interferometers The multiple configura-tions provided by the Mach-Zehnder (MZ) interferometershad led to a wide variety of sensing applications At theirbeginning these types of interferometers were composed oftwo separate light paths or arms the sensing path and thereference path The light entered into the device and wassplit into two beams by a fiber coupler Then light passedthrough both paths reaching to another fiber coupler wherelightbeams were reunited and both contributions create theinterference The traditional MZ structure was scaled downas it was applied to optical fiber devices In Figure 3 differentapproaches to MZ configurations are shown

Since the introduction of fiber gratings in sensing manysensors have been performed including them in the MZconfiguration [55 56] shown in Figure 3(a) As it will bedetailed in Section 6 the periodic perturbation of the gratingproduces the coupling of some core modes to cladding-propagating modes thus obtaining two virtual paths for thetransmitted light in a single optical fiber To recombine bothlight contributions a second grating is placed behind thefirst one obtaining the desirable interference The sensingmechanism of the fiber grating is described in Fiber GratingSensors One experimental work based on this configurationis presented by James et al [57] coating two Long-PeriodGratings with embedded SiO

2NPs in polymeric thin films

by LbL In this study the response of the system to theenvironmental perturbations was investigated to measurethe changes for temperature and RI and also to detectammonia concentrations

Regarding the rest of MZ configurations there are somerelevant works for diverse applications For instance Li et al

CladdingCore

LPG 1 LPG 2

(a)

CladdingCore

Taper 1 Taper 2

(b)

CladdingCore

PCF segment

(c)

Figure 3 Schematic of themainly usedMZconfigurations in opticalfiber sensing (a) based on Long-Period Gratings (LPGs) (b) basedon tapered fibers and (c) based on a PCF

[58] presented one MZ based sensor using ultra-abrupttapered fibers to detect N

2 with an improved RI sensitivity

with respect to a conventional MZ interferometer In anotherapproach Socorro et al have reported a theoretical andexperimental study of the multimode interferences createdby a single mode-multimode-single mode fiber structureobtaining a sensitivity enhancement controlling the thicknessof thin films [59] However until these days as in the FPIsituation the use of NPs in the MZ based approaches is notvery common

34 Michelson Interferometers Another interesting type ofinterferometers is that called Michelson interferometers(MI) Their optical structure is quite similar to the MZdevices but in this case the light is reflected at the end ofeach arm by a mirror addition Also this approach can bedeveloped in a compacted configuration commonly knownas in-line Michelson interferometers As in the case ofMZ interferometers LPGs have been mainly used in MIconfigurations There are recent advances in MZ with NP-embedded coatings for concretes applications One of themost relevant works is reported by Carrasquilla et al whodesign a LPG based MI interferometer [60] LPGs werecoated with Au NPs entrapped in a sol-gel matrix to createa platform for the immobilization of functional structure-switching DNA aptamer molecules

35 Sagnac Interferometers Sagnac interferometers presentan interesting alternative to other sensing structures due toadvantages as easy fabrication and simple set-up and robust-nessThese types of interferometers consist of an optical fiberloop along which two beams are propagating in counterdirections with different polarization states providing thedesired interference A more detailed description of thoseinterferometers can be found in the bibliography [61]MainlySagnac interferometers are commonly fabricated using highbirefringent fibers or polarization maintaining (PM) fibersto obtain a higher sensitivity although more recently theyhave been developed using PCFs or PM-PCFs reducing theirtemperature dependency


Sagnac interferometers designed with NP-embeddedcoatings have not been reported However there are someadvances where the sensing fiber has been coated withpolymers Hence humidity sensors based in chitosan [62] orpolyvinyl(alcohol) [63] or salinity sensing devices based inpolyimide [64] have been published

4 Fluorescence-Based Sensors

41 Introduction The use of fluorescence as a sensing mech-anism for optical fiber sensors has been studied for decadesbecause of two main reasons On one hand fluorescencehas been a daily life tool for scientific disciplines such asmicrobiology and therefore researchers have an abundantrepertoire of different fluorescent labels and dyes and a goodknowledge of how to bond them to other target moleculesOn the other hand the optical nature of the fluorescent signalis ideal to be collected and transmitted through a mediumsuch as an optical fiber The wide variety of fluorescent dyestogether with the benefits of the optical fiber as transmissionmedium (low losses wide broadband multiplexing smallsize biocompatibility etc) has encouraged the research inthis field for decades

Although there are a lot of works in the bibliographythat reports fluorescent based optical fiber sensors [65ndash69]not all of them describe optical sensing approaches in whichnanoparticles are present Most of the traditional approachesfor fluorescent optical fiber sensors describe the use of regularfluorescent organic molecules that experience a variation intheir emission efficiency due to the presence of the analyteStrictly speaking most of them are intensity-based sensorsalthough it is possible to find other approaches such as phase-fluorescence sensors [70 71] Nevertheless there have beentwo fields where nanoparticles have brought a significantimprovement of the fluorescent properties of the materialsand it is possible to use it in the field of sensors the use ofsemiconductor quantum dots and the fluorescence enhance-ment in the surroundings of certain metallic particles Themain contributions and trends are summarized in the nextsubsections

42 Quantum-Dot Based Sensors As it was commented inthe previous introduction one of the main advantages offluorescence-based sensors is that after decades of researchin fields such as microbiology there is an enormous availablediversity of available fluorophores [72 73] and there arealso well-known tools for manipulating those moleculesincluding selectively binding to other molecules and struc-tures Nevertheless traditional organic fluorophores havesome important drawbacks usually they show short lifetimesand very restricted excitation wavelength ranges too closefrom the fluorescence emissionmaximum(small Stokes shiftstypically around 10ndash20 nm) These two limitations are veryimportant when a sensor is being designed and implementedbecause they negatively impact in the sensitivity and in thelifetime of the sensors Quantum dots overcome those criticallimitations of the organic fluorophores

Fluorescent quantum dots (QDs) are nanoparticles ofsemiconductor material with a diameter of typically around

3ndash8 nm Such nanosize of the semiconductor particle inducesthe phenomenon of the quantum confinement The excitedelectron-hole pair behaves as a quasiparticle called excitonand this quasiparticle has some physical dimensions relatedto its Bohr radius that depend on the specific properties of thesemiconductormaterialWhen the exciton size is constrainedby potential barriers the density of energy state distribution(DOS) is significantly altered changing from a continuousDOS distribution of the bulk materials to a discrete DOS typ-ical of the QDs [74] One of the most important advantagesof QDs is that their absorption spectrum is very broad andremains almost unaltered as the size of the QD decreasesand at the same time the narrow fluorescence emission peakshows a significant blue-shift as the quantum confinement isincreased (with smaller QDs) This absorbance and emissioncharacteristic is very useful since it overcomes the problem ofthe small Stokes shift of the traditional organic fluorophoresand allows adjusting the excitation wavelength and intensityso it is possible to avoid spectral overlapping between theexcitation and the emission

Depending on the size of the QD nanoparticles thefluorescence emission can be tuned from the near infraredto the blue region of the visible spectrum Although thereare different approaches for achieving quantum confinementand consequently the QDs the wet-synthesis routes ofsemiconductor nanoparticles are the most used ones Suchwet chemistry approaches are reproducible and cost-effectiveand currently there are several synthesis routes availableusing organic solvents or even water-based approaches Typ-ically QDs are chalcogenide semiconductors most of themfrom group VI CdTe CdSe ZnSe ZnS and so forth Oneof the most important advantages of nanoparticle QDs is thatthey can be easily functionalized usingwell developed surfacechemistry and they can be embedded or bonded to a widevariety of surfaces and matrices [75]

There are a lot of sensing applications based on QDsluminescence Their high quantum yield has made possibleapplications such as single particle tracking using fluores-cence microscopy [76] very useful for intracellular dynamicsresearch Functionalized QDs have been used successfully inselective cell identification techniques both in vitro [77] andin vivo [78] Other sensing applications have been reportedbased on colloidal dispersions of QDs that selectively graftto biological molecules such as proteins [79 80] or evensensing mechanisms based on the variation of the fluores-cent signal using biologically triggered Forster ResonanceEnergy Transfer (FRET) quenching [81 82] Optical fibersensors have also been reported using quantum dots Theirhigh quantum yield and small size make them suitable forembedding into sensitive thin films over the optical fibers Itis possible to find coatings for transmission tapered fibers andd-shaped or similar approaches using a tapered end fiber in areflection arrangement [83] The versatility of QDs allowedbeing incorporated into thin films created inside the innerholes of PCFs to create a fluorescent temperature opticalsensor [84] (Figure 4)

43 Fluorescence Enhancement Using Metallic NanoparticlesThere is another phenomenon that involves fluorescence


3000

2000

1000

0

Emiss

ion

inte

nsity

(au

)

600 700

minus40∘Cminus30∘Cminus20∘Cminus10∘C

0∘C10∘C20∘C30∘C

40∘C50∘C60∘C70∘C

Wavelength (nm)

Figure 4 Temperature sensor using CdSe QDs embedded into LbLthin films fabricated inside the inner holes of a PCF Reprinted withpermission from [84]

that is a direct consequence of the nanostructure of certainparticles This phenomenon is known as metal-enhancedfluorescence (MEF) and it is caused by the alteration ofthe normal radiative and nonradiative decay rates causedby the close proximity of metal nanoparticles The MEFphenomenon is caused by the singular concentration of thelocal electrical field in the surroundings of certain metallicnanoparticles as a consequence of a resonant phenomenonknown as localized surface plasmon resonance (LSPR) LSPRis the collective oscillation of the free electrons of metallicnanoparticles due to their resonant coupling with incidentlight at a specific wavelength More detailed informationabout the nature and applications of the LSPR phenomenoncan be found in the bibliography [85] The LSPR absorptionpeaks of metallic nanoparticles have been widely used in thedevelopment of optical fiber sensors [15 86]

The electrical field in the medium surrounding themetallic nanoparticles is altered and as it is shown in Figure 5when two nanoparticles come very close one to the other adramatic enhancement of the local electrical field is causedin the nanoparticles gap If a fluorophore molecule is placedin this region its emission properties of fluorophores aresignificantly enhanced by both the excitation and emissionmodifications

It has been probed that the distance of the fluorophoresto the nanoparticles surface is a critical parameter to achieveMEF The fluorophore is needed to be close enough to theplasmonic nanostructure since the field enhancement decaysnearly exponentially with distance from the metallic surfaceNevertheless if the fluorophore is too close to the NP (lessthan 5 nm) its fluorescence would be quenched significantlydue to the nonradiative decay through energy andor chargetransfer to the metal Consequently the distance of the

40

20

0

minus20

minus40

minus40 minus20 0 20 40

y(n

m)

x (nm)

6

4

2

0

Figure 5 Electric field intensity in the vicinity of two Ag NPs of25 nm diameter separated 30 nm between centers Simulated usingGreensym It is possible to see that the region between both particles(pointed to with an arrow) shows a significant increasing in theelectrical field intensity

fluorophores should be controlled in a range of 5 to 30 nmin general

Liursquos group had reported aDNA-detecting platformbasedonMEF using AgNPs PDDAPSS LbL films and conjugatedpolyelectrolytes [87 88] But the polyelectrolytes can also playa significant role in the development of optical sensors asfar as the MEF could be manipulated in an in situ way byexternal stimuli such as pH or temperature variations Basedon this concept pH sensitive poly(acrylic acid)PDDA spacerlayers over Ag NPs that change their thickness with theirionization degree have been reported and consequently theMEF is altered [89]

It has also been demonstrated that sharp shapes andedges of metallic nanoparticles induce more intense elec-tromagnetic field concentrations and consequently higherMEF rates Consequently nonspherical nanoparticles arefrequently used in the development of optical sensors basedon MEF For example gold nanorods have been successfullyused to create glucose sensors [90] among other applicationsGabudean et al even have demonstrated that gold nanorodscan be used as dual probes forMEF and for surface-enhancedRaman spectroscopy (SERS) [91] (Figure 6) SERS sensingmechanism and applications will be commented in thefollowing paragraphs

5 Surface-Enhanced RamanSpectroscopy (SERS)

Sensors are devices designed for the quantitative identifica-tion of analytes but there are other applications in which thequalitative characterization of the analyte is crucial such as inmolecule identification In such applications there are severalanalytic techniques available (High Pressure Liquid Chro-matography (HPLC) and other chromatography techniques)that helps to determine the composition of the chemicals


MEF

SERS

(a)

Emiss

ion

(au

)

520 560 600 640 680

Wavelength (nm)

(b)

Figure 6 (a) Schematic configuration of a gold nanorod dual MEF and SERS probe (b) Fluorescence spectra showing a 2-fold enhancementof the Rose Bengal emission Reprinted with permission from [91] copy (2012) American Chemical Society

present in the sample Nevertheless there are techniques thatprovide information about the structure chemical bonds orpresence of certain functional groups and moieties as far asthey are based on the excitation of the natural vibrationalfrequencies of the moleculesThemost used ones are FourierTransform Infrared (FTIR) and Raman spectroscopy In factRaman spectroscopy is especially useful because it makes itpossible to distinguish between very similar structures butgenerally it requires powerful lasers and long acquisitiontimes to get a weak Raman scattering signal

As it is has been previously commented the electricalfield concentrations in the vicinity of metallic nanoparticlesby means of LSPR coupling allow the apparition of two dif-ferent enhancement phenomena MEF and SERS Thereforewhen the LSPR induced electromagnetic field concentrationoccurs near metallic nanoparticles the molecules nearby thesurface experiment an enhancement in their Raman scat-tering cross section making more efficient their excitationEnhancements up to 8 orders of magnitude in the Ramanscattering emission are typically observed from themoleculessurrounding the metallic nanoparticles [92]

The very first approaches used highly rough metallicsubstrates obtained by several oxidation-reduction cycles ofthe surface of the metal but the electrical field concentrationspots were randomly distributed throughout the surface andthis made difficult the utilization of SERS as a tool forquantitative determination of chemical species

More sophisticated structures such as the so-calledNano-sphere Lithography (NSL) technique or the Metal Film OverNanosphere (MFON) have been successfully used to fabricatethe metallic structures that allow the electromagnetic fieldconcentrations that make the SERS phenomenon possible(Figure 7) Both techniques have been widely used but bothof them have been used over planar substrates and not overoptical fibers where the geometry is muchmore complicated

Although most of the applications are focused on planarsubstrates for Lab-On-a-Chip (LOC) applications [95 96]optical fiber approaches have been also reported usingnanoparticle decorated tapered optical fibers [94 97ndash100]Another example can be found in [94] where it is reported

that silver nanoplates were deposited on the tapered surfaceof an optical fiber with the LbL technology (Figure 8)

6 Fiber Grating Sensors

61 Introduction Fiber gratings are optical fibers that presenta periodic perturbation of their optical properties namelythe core refractive index Since the 80s decade fiber gratingshave contributed to the development of many devices fordiverse applications in research fields such as communica-tions instrumentation and sensing There are several tech-niques for fabricating optical fiber gratings based onUV laser[101] CO

2[102] infrared [103] lasers or electric arc [104] It is

possible to find twomain kinds of optical fiber gratings FiberBragg Gratings (FBGs) and Long-Period Gratings (LPGs)LPGs are characterized by the long periodicity of their per-turbation which ranges from 100 um to 1000 um In the FBGscase the perturbation has a shorter period than LPGs (tens ofmicrons)This difference in period results in different opticalphenomena that yield different spectral behavior when whitelight is guided through the grating In LPGs certain nonprop-agating core modes are visible in the transmission spectrumat wavelengths where there is a coupling between the core andthe copropagating cladding modes whereas in FBGs thereis a coupling between propagating and counterpropagatingcoremodes Each attenuation bandpresented in the spectrumis a consequence of an optical resonance of the guided lightand the grating structure so it is frequent to refer to thosetransmission minima as resonance wavelengths

On one hand for FBGs the resonance wavelength obeysthe Bragg condition described as [105]

120582bragg = 2119899eff coreΛ 119892 (3)

More details about FBGs can be found in relevant worksreported by Hill and Meltz [105] Kersey et al [106] orErdogan [107]

On the other hand for LPGs the resonance condition isgiven by [108]

120582res = (119899eff core minus 119899eff clad) Λ 119892 (4)


250

0

(nm

)

10120583m

(a)

600nm

(b)

Figure 7 (a) AFM image of a silver coated assembly of polystyrene nanospheres of 540 nm diameter A continuous metallic film was createdover the nanospheres (b) 3D reconstruction of the AFM micrography where the sharp edges in the metallic film can be observed It is inthose regions where SERS takes place Reprinted with permission from [93] copy (2002) American Chemical Society

(A) (B)

200120583m

(a)

1000 1200 1400 18001600

Raman shift (cmminus1)

Inte

nsity

(au

)

(D)(C)

(B)(A)

70000

60000

50000

40000

30000

20000

10000

0

(b)

Figure 8 (a) (A) low- and (B) high-magnification SEM images of a SERS probe made from a tapered optical fiber It is possible to see therough profile of the silver nanoparticles synthesized onto the surface of the taper (b) SERS spectra of 4-ATP (10minus7M) detected by the taperedfiber probes with different cone angles (A) 35 (B) 96 (C) 158 and (D) 226 Reproducedwith permission from [94] copy (2014) AIP PublishingLLC


core

Cladding

Λg = grating period

L = grating length

NP-embedded coating

Figure 9 Illustration of a LPG coated with aNP-embedded coating

where 120582res is the resonance wavelengths 119899eff core and 119899eff cladare the effective refractive indices of the core and thecladding respectively and Λ

119892represents the grating period

along the fiber axis (see Figure 9) LPG theory and some ofits optical sensing applications are found in the bibliography[109 110]

Both FBGs and LPGs have been widely used for the fab-rication of optical fiber sensor devices and sensor networksThe following sections describe and enumerate briefly severalresearch works based on FBGs and LPGs Also several recentapplications with the use of NPs within coatings as sensitiveregions onto these fibers are presented

62 FBG and Tilted FBG Sensors withNP-Embedded CoatingsFBG sensors have been widely reported in literature duringthe last 25 years for the monitoring of numerous physicalparameters including vibration [111] strain [112] bendingtemperature [113] and pressure [114]

An important particular type of FBGs is the tilted FBGs(TFBGs) where their grating has a shift in angle with respectto the fiber axis [115] TFBGs based sensors have been alsodeveloped tomeasure strain and temperature [116 117] vibra-tion [118] bending [119] torsion [120] external refractiveindex [121] or humidity [122] among other parameters

All FBG sensors reported in the two previous paragraphsdo not present NPs in their coatings or even in some casesthey do not have any coating as sensitive region Works withcoated FBGs as sensor have also been reported recently withgold nanofilms [123] for biosensing and with ZnO thin films[124] for an enhancement in RI sensitivity Thus Paladino etal [125] studied the effect of the thickness of the coating andthe RI in TFBG sensors As in other fiber optics structuresensors the use of NPs into optical fiber sensing applicationsis very recent and it was during the last few years whenmost of the applications were reported In the particularFBG sensors case there are few works which add NPs ornanocomposites For example Lepinay et al introduced goldNPs to create novel biosensors based on TFBGs [12] The AuNPs were coated onto the TFBG thus providing an enhancedsensing platform for protein detection Another work whichpresents a novel refractometer with an improvement insensitivity is reported by Bialiayeu et al [126] where aTFBG was coated with silver nanowires obtaining a 35-fold increase in sensitivity with respect to the uncoatedTFBG

63 LPG and Coated LPGs Sensors without NPs As in FBGsthe inherent LPG structure also permits the developmentof sensors for temperature bending strain or external RIdepending on their fabrication settings [63] The sensitivityto a particular measurand is dependent upon the period ofthe LPG and the order of the cladding mode to which theguided optical power is coupled and thus is different for eachattenuation band These characteristics make them attractivefor sensing purposes

Cusano et al studied theoretically and experimentallythe effects of the cladding modes along the LPG struc-ture when this was coated with nanoscale overlays [127]The variations of the external RI and the thickness of thecoating were analyzed showing relevant improvements inthe surrounding RI in terms of amplitude variation andwavelength shift in the attenuation bands [83 84] As a resultof these investigations several optochemical sensors based onpolystyrene nanocoatings have been reported by the sameresearch group [128ndash130] Langmuir-Blodgett [131] LbL [132]and sputtering [133] deposition techniques were used for thefabrication of diverse thin film coatings over the LPGs forsensing various physical and chemical magnitudes such ashydrogen [134 135] pH [136] humidity [137] VOCs [138]or the study of sensitive improvements [139 140] Anotherrelevant study was reported by Shu et al [141] presentingthe so-called turning points in LPGs These turning pointsappeared for LPGs with specific grating periods and providetwo resonance wavelengths for each cladding mode thusallowing the fabrication of high sensitivity devices [142]

64 LPG Sensors with NPs-Embedded Coatings During thelast few years the inclusion of NPs in coated LPGs hasbeen also reported for different sensing applications InTable 1 some of these works are presented including targettype of nanoparticles included coating composition andfabrication method used A wide variety of substances havebeenmonitored such as ethanol ammonia proteins or otherlow-molecular analytes One of the most used depositiontechniques for LPG sensitive coating fabrication is LbLbecause this method allows a controllablemanagement of thethickness and theNP composition of the fabricated thin films

An interesting work about how to improve the sensitivityin humidity LPG sensors is reported byViegas et al [13]Theydemonstrated that the use of SiO

2nanospheres in polymeric

thin films as intermediate structural coatings enhanced thehumidity sensitivity by a factor of 15 at a RH asymp 30 whichwas improved to a value of 35 when dealing with RH around70 (shown in Figure 10)

7 Resonance-Based Optical Fiber Sensors

71 Introduction Resonance-based sensors are another im-portant group within optical fiber sensing field Their devel-opment has been reported for more than 20 years Whenan optical waveguide is coated by a nanostructured coatingthe transmission of light along the overall structure can beaffected Depending on the properties of the different mate-rials involved in the system (the waveguide the coating and


Table 1 Summary of optical fiber sensors with NP-embedded coatings based on LPGs Specific terms of sensitivity parameters relativehumidity (RH) limit of detection (LoD) parts per billion (ppb) refractive index units (RIU) and enhancement with respect to the samedevice without NPs (ENH)

Target Nanoparticles Deposition technique Sensitivity parameters ReferenceHumidity SiO

2NPs LbL 02 nmRH [143]

Ion chloride Au colloids LbL 046 nmRH [13 144]Ethanol ZnO nanorods Aqueous chemical growth LoD asymp 004 [145]Ammonia SiO

2NPs LbL mdash [146]

Low-molecular chemicals TiO2NPs LbL LoD = 140 ppb [147 148]

RI SiO2NPs LbL 10minus7M [149]

Proteins SiO2and Au NPs LbL 1927 nmRIU [150]

Aromatic carboxylic acids SiO2NPs LbL 19 nM [151]

Low-molecular analytes Au NPs Sol-gel 1 nM [152]Corrosion Fe and SiO

2NPs Dip-coating sim2- and sim25-fold ENH for ATP and QDNA [60]

Sucrose RI Au NPs LbL mdash [153 154]Copper Cibacron blue LbL 20 nm ENHRIU [155]

16

14

12

10

8

6

4

2

0

20 30 40 50 60 70 80

Relative humidity ()

Reso

nant

wav

eleng

th sh

ift (n

m)

Intermediate + sensitive coatingSensitive coating

Figure 10 Resonancewavelength shift dependencewith the humid-ity for LPG with (black spots) and without (white spots) SiO

2NPs

intermediate coatings [13] from the journal ldquoSENSORSrdquo

the surrounding medium) three different kinds of electro-magnetic resonances can be recognized To distinguish thesetypes of resonances the relationship of the permittivity ofthe coating (120576

2) composed of real and imaginary part is

considered (see Figure 11)The first resonant phenomenon happens when the real

part of 1205762satisfies the following three conditions it must be

negative it must be higher in magnitude than its respec-tive imaginary part and it must be higher in magnitudethan both the waveguide permittivity and the surroundingpermittivity as well Under these conditions the producedresonance is called SPR This kind of resonance consists inthe coupling of the energy of certain resonant wavelengthsof the incident light to a surface electrical current in a

metallic-semiconductor interface When such resonanceoccurs the energy is transferred from photons to electronsand therefore suchwavelengths are not observable in the finaltransmitted light

The second type of resonance occurs when the realpart of 120576

2satisfies these other three conditions it must be

positive it must be higher in magnitude than its respectiveimaginary part and itmust be higher inmagnitude than boththe waveguide permittivity and surrounding permittivityas well see Figure 11 Some studies demonstrated that thepropagation of light in semiconductor cladded waveguidesexhibits some attenuation maxima for specific thicknessvalues of the semiconductor cladding and also at certainwavelengths of incidence values [170] This is due to acoupling betweenwaveguidemodes and a specific lossymodeof the semiconductor thin film [171] Because of that inthese cases resonances are denoted as lossy mode resonances(LMRs) [156 172] In this resonance the light couples intoa different propagating medium and it is lost from thetransmitted light

Finally a third case happens when the real part of 1205762is

close to zero and its imaginary part is large This particularcase named as long-range surface exciton polariton (LRSEP)has not been applied to the development of optical fibersensors and will not be reported in this review

According to the optical structure resonance-based sen-sors could be englobed as a subgroup of absorbance sensorsgrating sensors or interferometric sensors if their coatingssatisfy the concrete resonance conditions Generally in lit-erature resonance-based sensors are considered as a groupby themselves because of the importance of the resonancephenomena However they could also be classified as CROFsensors U-shape sensors tapered sensors LPG sensors FBGsensors and so forth depending on their optical configura-tion

As the SPR and LMR based sensors with NP-embeddedcoatings have being widely reported in the last few years theywill be described in separate sections


T T

120582 120582

Input white light spectrum External medium

(air) 1205761 = 1

External medium(air) 1205761 = 1

Optical waveguide core (lossless)1205763 = 1205769984003

Nanostructured coating1205762 = 1205769984002 + j1205769984009984002

Output mode resonance spectrum

SPR conditions LMR conditions

1205769984002 lt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|

1205769984002 gt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|

Figure 11 Schematic of a waveguide coated with a nanostructured film and the required conditions to generate SPR andor LMR Adaptedfrom [156] Copyright (2014) with permission from Elsevier

400 500 600 700 800 900 1000

00010203040506070809101112

30 bilayersLMR 1

LMR 1

LSPR

30 bilayers25 bilayers20 bilayers


Abso

rban

ce (a

u)

Wavelength (nm)

25 bilayers

(a)

500 600 700 800 90007

08

09

10

11

12


37 bilayers36 bilayers

LMR 2

Abso

rban

ce (a

u)

Wavelength (nm)

LMR 3

(b)

Figure 12 UV-Vis absorption of the sensor in function of the number of LbL bilayers (a) 1ndash30 bilayers (b) 35minus40 bilayers Reprinted from[157] Copyright (2012) with permission from Elsevier

72 SPR and LSPR Based Sensors Since the introductionof optical fiber technology in the research of the techniqueof SPR fiber-optic SPR sensors have presented a lot ofadvancements Jorgenson and Yee published in 1993 [173] oneof the earliest optical fiber sensors based on SPRThey studiedthe changes of the transmission spectrum varying the keyparameters the film thickness the film refractive index andthe length of the coated area After that many devices basedon SPR phenomenon were reported thanks to the metallicthin coatings onto the fiber being an essential reference inbiochemical sensing in the last decade [174] However thesemetallic coatings mainly composed of silver or gold films donot contain NPs and consequently there are not SPR basedsensors with NP-embedded coatings

The unique optical properties of metal NPs have alsoattracted the sensor community to develop LSPR basedsensors [175] In the LSPR phenomenon the conductive NPsinteract with the light which goes through the coatingsgenerating resonance wavesThis occurs when the dimensionof the NPs is smaller than the wavelength of light Thecreated localized resonances depend on the size geometryand composition ofNPs and their distribution in the coatingsLSPR based sensors have few advantages over SPR basedsensors such as higher surface area and it is now whenthey are becoming relevant [176] as they are improvingsensitivity ratios or limit of detection values [12] or selectivityNevertheless further studies will be required Hence Caoet al [177] performed a comparative study between a LSPR


Table 2 Summary of optical fiber sensors based on LSPR and LMR phenomena

Resonancephenomenon Target Coating Deposition technique Sensitivity parameters Reference

LSPR HF Au NPs and silica matrix Sol-gel 1 to 5 [158]

LSPR Hydrogen peroxide Ag NPs embedded inpolyvinyl(alcohol) Dipping and sintering 10minus8M [159]

LSPR ProteinsAPTMS

glutaraldehydecysteamine+ Au NPs (nanocages or

nanospheres)

LbL 11 pM (nanospheres)8 pM (nanocages) [12]

LSPR Anti-IgG Amino silane + Au NPs Silanization 08 nM [160]

LSPR ProteinsPoly(ethyleneimine)AuNPs + poly(sodium4-styrenesulfonate)

LbL mdash [161]

LSPR Blood glucose Au NPs + glucose oxidase LbL Blood min volume sim150120583L [162]

LSPR Explosive vapoursAu NPs functionalized with4-mercaptobenzoic acidl-cysteine and cysteamine

Silanization with APTES lt100 nM (23 ppb)LoD sim 5ndash10 ppb [30]

LSPR DNA sequences Au NPs functionalized witholigonucleotides LbL lt100 nM [163]

LSPR amp LMR HumidityPoly(allylamine

hydrochloride)poly(acrylicacid) + Ag NPs

LbL sim1 nmRH [157]

LSPR amp LMR RIPoly(allylamine

hydrochloride)poly(acrylicacid) + Au NPs

LbL 4037 nmRIU LMR 21906 nmRIU LMR 3 [164]

LMR RI TiO2NPspoly(sodium

4-styrenesulfonate) LbL 287273 nmRIU1987 nmRIU [165 166]

LMR Humidity TiO2NPspoly(sodium

4-styrenesulfonate) LbL 143 nmRH LMR 1097 nmRH LMR 2 [167]

LMR HumidityPoly(allylamine


LbL 0455 nmRH [168]

LMR VOCsPoly(allylamine

hydrochloride)Au-Agnanocompound + sodium

dodecyl sulfate

LbL 0131 nmppm for methanol [169]

based sensor withAu nanorods coating and SPR based sensorwith a thin Au layer giving the second one higher sensitivity

73 LMR Based Sensors with NP-Embedded Coatings LMRtheory is very recent and its development in sensing has beenreported since 2009 by some authors [156 178 179] Thusthe use of NPs in these sensors is being a hot-point at thismoment

In these few years LMR based sensors with embeddedNPs have been published to measure parameters such asthe surrounding RI [165] relative humidity [167] or volatileorganic compounds (VOCs) [169] using the LbL technique

Rivero et al have recently developed the first sensorwhereboth LSPR and LMR phenomena appear [157] thanks to aself-assembled polymeric coating with Ag NPs In this workthe appearance and evolution of the LSPR caused by the AgNPs and LMRs caused by the overall coating during theLbL deposition process were observed (shown in Figure 12)

As a result the created coating and its swelling propertiesproduced important changes in the mode resonances shift-ing their respective LMR peaks according to the humiditychanges (Figure 13)Their results had a sensitivity of 1 nm perRH from the first LMRThey also show another sensor with0943 nm per RH for the second LMR

The same research group also developed another refrac-tometer based on both types of resonances here usingAuNP-embedded coatings [164] Last works in LMR based sensorsindicate that this sensing mechanism and its potential usehave a promising future in the next years

Finally a summary with different approaches of fiber-optic sensors based on LSPR and LMR is shown in Table 2

8 Conclusions

In this review a classification of optical fiber sensors basedon nanoparticle-embedded coatings is proposed this list


0 100 200 300 400 500 600

0

10

20

30

40

50

60

Time (min)

LSPR

LMR 1

RH ()

10

20

30

40

50

60

70

Δ120582max

Relat

ive h

umid

ity (

)

Figure 13 Dynamic response of the sensorThewavelength shifts ofboth LSPR and LMR 1 are monitored simultaneously to RH cyclesfrom 20 to 70 RH at 25∘C Reprinted from [157] Copyright (2012)with permission from Elsevier

of sensors has been ordered according to their sensingprinciples which are briefly described in separated sectionsAbsorbance interferometry fluorescence gratings and reso-nances phenomena were briefly reported The introductionof new specialty fibers combined to these coatings hasplenty of potential applications Moreover LSPR and LMRtechnologies in fiber sensing are experiencing a great degreeof development these days All these advances are likely todrive future trends in the research and development of opticalfiber sensors

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work was supported in part by the Spanish Ministryof Economy and Competitiveness CICYT-FEDER TEC2013-43679-R Research Grant and a UPNA predoctoral researchgrant

References

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[2] B Culshaw ldquoOptical fiber sensor technologies opportunitiesandmdashperhapsmdashpitfallsrdquo Journal of Lightwave Technology vol22 no 1 pp 39ndash50 2004

[3] A Abdelghani J M Chovelon N Jaffrezic-Renault et alldquoOptical fibre sensor coated with porous silica layers for gas andchemical vapour detectionrdquo Sensors and Actuators B Chemicalvol 44 no 1ndash3 pp 495ndash498 1997

[4] V P Minkovich D Monzon-Hernandez J Villatoro and GBadenes ldquoMicrostructured optical fiber coated with thin filmsfor gas and chemical sensingrdquoOptics Express vol 14 no 18 pp8413ndash8418 2006

[5] J Lin ldquoRecent development and applications of optical andfiber-optic pH sensorsrdquo TrAC Trends in Analytical Chemistryvol 19 no 9 pp 541ndash552 2000

[6] F J Arregui I R Matıas K L Cooper and R O Claus ldquoSimul-taneousmeasurement of humidity and temperature by combin-ing a reflective intensity-based optical fiber sensor and a fiberbragg gratingrdquo IEEE Sensors Journal vol 2 no 5 pp 482ndash4872002

[7] C Bariain I R Matıas F J Arregui and M Lopez-AmoldquoOptical fiber humidity sensor based on a tapered fiber coatedwith agarose gelrdquo Sensors and Actuators B Chemical vol 69 no1 pp 127ndash131 2000

[8] S K Khijwania K L Srinivasan and J P Singh ldquoAn evanes-cent-wave optical fiber relative humidity sensor with enhancedsensitivityrdquo Sensors and Actuators B Chemical vol 104 no 2pp 217ndash222 2005

[9] S C Warren-Smith S Heng H Ebendorff-Heidepriem A DAbell and T M Monro ldquoFluorescence-based aluminum ionsensing using a surface-functionalized microstructured opticalfiberrdquo Langmuir vol 27 no 9 pp 5680ndash5685 2011

[10] M El-Sherif L Bansal and J Yuan ldquoFiber optic sensors fordetection of toxic and biological threatsrdquo Sensors vol 7 no 12pp 3100ndash3118 2007

[11] O S Wolfbeis ldquoFiber-optic chemical sensors and biosensorsrdquoAnalytical Chemistry vol 76 no 12 pp 3269ndash3284 2004

[12] S Lepinay A Staff A Ianoul and J Albert ldquoImproved detec-tion limits of protein optical fiber biosensors coated with goldnanoparticlesrdquo Biosensors and Bioelectronics vol 52 pp 337ndash344 2014

[13] D Viegas J Goicoechea J L Santos et al ldquoSensitivity improve-ment of a humidity sensor based on silica nanospheres on along-period fiber gratingrdquo Sensors vol 9 no 1 pp 519ndash5272009

[14] R Aneesh and S K Khijwania ldquoZinc oxide nanoparticle basedoptical fiber humidity sensor having linear response throughouta large dynamic rangerdquo Applied Optics vol 50 no 27 pp 5310ndash5314 2011

[15] P J Rivero A Urrutia J Goicoechea F J Arregui and I RMatıas ldquoHumidity sensor based on silver nanoparticles embed-ded in a polymeric coatingrdquo International Journal on SmartSensing and Intelligent Systems vol 5 no 1 pp 71ndash83 2012

[16] R N Mariammal K Ramachandran B Renganathan and DSastikumar ldquoOn the enhancement of ethanol sensing by CuOmodified SnO

2nanoparticles using fiber-optic sensorrdquo Sensors

and Actuators B Chemical vol 169 pp 199ndash207 2012[17] L R ShobinD Sastikumar and SManivannan ldquoGlycerolmed-

iated synthesis of silver nanowires for room temperature ammo-nia vapor sensingrdquo Sensors and Actuators A Physical vol 214pp 74ndash80 2014

[18] B Renganathan D Sastikumar S G Raj and A R GanesanldquoFiber optic gas sensors with vanadium oxide and tungstenoxide nanoparticle coated claddingsrdquo Optics Communicationsvol 315 pp 74ndash78 2014

[19] B Renganathan D Sastikumar G Gobi N R Yogamalar andAC Bose ldquoGas sensing properties of a cladmodified fiber opticsensor with Ce Li and Al doped nanocrystalline zinc oxidesrdquoSensors and Actuators B Chemical vol 156 no 1 pp 263ndash2702011

[20] S Kodaira S Korposh S-W LeeW J Batty SW James and RP Tatam ldquoFabrication of highly efficient fibre-optic gas sensorsusing SiO

2polymer nanoporous thin filmsrdquo in Proceedings of

the 3rd International Conference on Sensing Technology (ICSTrsquo08) pp 481ndash485 December 2008

[21] S K Khijwania and B D Gupta ldquoMaximum achievable sen-sitivity of the fiber optic evanescent field absorption sensor


based on theU-shaped proberdquoOptics Communications vol 175no 1 pp 135ndash137 2000

[22] D Littlejohn D Lucas and L Han ldquoBent silica fiber evanescentabsorption sensors for near-infrared spectroscopyrdquo AppliedSpectroscopy vol 53 no 7 pp 845ndash849 1999

[23] R Jindal S Tao J P Singh and P S Gaikwad ldquoHigh dynamicrange fiber optic relative humidity sensorrdquo Optical Engineeringvol 41 no 5 pp 1093ndash1096 2002

[24] Z Zhao and Y Duan ldquoA low cost fiber-optic humidity sensorbased on silica sol-gel filmrdquo Sensors and Actuators B Chemicalvol 160 no 1 pp 1340ndash1345 2011

[25] F Surre B Lyons T Sun et al ldquoU-bend fibre optic pH sen-sors using layer-by-layer electrostatic self-assembly techniquerdquoJournal of Physics Conference Series vol 178 Article ID 0120462009

[26] H Guo and S Tao ldquoSilver nanoparticles doped silica nanocom-posites coated on an optical fiber for ammonia sensingrdquo Sensorsand Actuators B Chemical vol 123 no 1 pp 578ndash582 2007

[27] A Vijayan M Fuke R Hawaldar M Kulkarni D Amalnerkarand R C Aiyer ldquoOptical fibre based humidity sensor using Co-polyaniline cladrdquo Sensors and Actuators B Chemical vol 129no 1 pp 106ndash112 2008

[28] S K Shukla G K Parashar A PMishra et al ldquoNano-like mag-nesium oxide films and its significance in optical fiber humiditysensorrdquo Sensors and Actuators B Chemical vol 98 no 1 pp 5ndash11 2004

[29] C-H Chen T-C Tsao W-Y Li et al ldquoNovel U-shape goldnanoparticles-modified optical fiber for localized plasmon res-onance chemical sensingrdquoMicrosystem Technologies vol 16 no7 pp 1207ndash1214 2010

[30] R Bharadwaj and S Mukherji ldquoGold nanoparticle coated U-bend fibre optic probe for localized surface plasmon resonancebased detection of explosive vapoursrdquo Sensors and Actuators BChemical vol 192 pp 804ndash811 2014

[31] M Ahmad and L L Hench ldquoEffect of taper geometries andlaunch angle on evanescent wave penetration depth in opticalfibersrdquo Biosensors and Bioelectronics vol 20 no 7 pp 1312ndash13192005

[32] S Guo and S Albin ldquoTransmission property and evanescentwave absorption of cladded multimode fiber tapersrdquo OpticsExpress vol 11 no 3 pp 215ndash223 2003

[33] A G Mignani R Falciai and L Ciaccheri ldquoEvanescent waveabsorption spectroscopy by means of bi-tapered multimodeoptical fibersrdquo Applied Spectroscopy vol 52 no 4 pp 546ndash5511998

[34] D Rithesh Raj S Prasanth T V Vineeshkumar and C Sudar-sanakumar ldquoAmmonia sensing properties of tapered plasticoptical fiber coated with silver nanoparticlesPVPPVAhybridrdquoOptics Communications vol 340 pp 86ndash92 2015

[35] A Aziz H N Lim S H Girei et al ldquoSilvergraphene nano-composite-modified optical fiber sensor platform for ethanoldetection in water mediumrdquo Sensors and Actuators B Chemicalvol 206 pp 119ndash125 2015

[36] M I Zibaii H Latifi Z Saeedian and Z Chenari ldquoNonadia-batic tapered optical fiber sensor for measurement of antimi-crobial activity of silver nanoparticles against Escherichia colirdquoJournal of Photochemistry and Photobiology B Biology vol 135pp 55ndash64 2014

[37] DMonzon-Hernandez D Luna-Moreno D M Escobar and JVillatoro ldquoOptical microfibers decorated with PdAu nanopar-ticles for fast hydrogen sensingrdquo Sensors and Actuators BChemical vol 151 no 1 pp 219ndash222 2010

[38] X Yang Y Liu F Tian et al ldquoOptical fiber modulator derivatesfrom hollow optical fiber with suspended corerdquo Optics Lettersvol 37 no 11 pp 2115ndash2117 2012

[39] H Lu Z Tian H Yu et al ldquoOptical fiber with nanostructuredcladding of TiO

2nanoparticles self-assembled onto a side

polished fiber and its temperature sensingrdquo Optics Express vol22 no 26 pp 32502ndash32508 2014

[40] N J Florous K Saitoh and M Koshiba ldquoNumerical modelingof cryogenic temperature sensors based on plasmonic oscilla-tions in metallic nanoparticles embedded into photonic crystalfibersrdquo IEEE Photonics Technology Letters vol 19 no 5 pp 324ndash326 2007

[41] Y Miao B Liu K Zhang Y Liu and H Zhang ldquoTemperaturetunability of photonic crystal fiber filled with Fe

3O4nanoparti-

cle fluidrdquoApplied Physics Letters vol 98 no 2 Article ID 0211032011

[42] J Canning L Moura L Lindoy et al ldquoFabricating nanoporoussilica structure on D-fibres through room temperature self-assemblyrdquoMaterials vol 7 no 3 pp 2356ndash2369 2014

[43] BH Lee YH Kim K S Park et al ldquoInterferometric fiber opticsensorsrdquo Sensors vol 12 no 3 pp 2467ndash2486 2012

[44] A Wang H Xiao J Wang Z Wang W Zhao and RG May ldquoSelf-calibrated interferometric-intensity-based opticalfiber sensorsrdquo Journal of Lightwave Technology vol 19 no 10pp 1495ndash1501 2001

[45] X Chen F Shen Z Wang Z Huang and A Wang ldquoMicro-air-gap based intrinsic Fabry-Perot interferometric fiber-opticsensorrdquo Applied Optics vol 45 no 30 pp 7760ndash7766 2006

[46] F J Arregui Y Liu I R Matias and R O Claus ldquoOptical fiberhumidity sensor using a nano Fabry-Perot cavity formed by theionic self-assembly methodrdquo Sensors and Actuators B Chemi-cal vol 59 no 1 pp 54ndash59 1999

[47] M Jiang Q-S Li J-N Wang et al ldquoOptical response offiber-optic Fabry-Perot refractive-index tip sensor coated withpolyelectrolyte multilayer ultra-thin filmsrdquo Journal of LightwaveTechnology vol 31 no 14 pp 2321ndash2326 2013

[48] J M Corres I RMatiasM Hernaez J Bravo and F J ArreguildquoOptical fiber humidity sensors using nanostructured coatingsof SiO

2nanoparticlesrdquo IEEE Sensors Journal vol 8 no 3 pp

281ndash285 2008[49] S Dass R K Gangwar S M Nalawade and T M Bhave

ldquoA novel optical fiber humidity sensor coated with superhy-drophilic silica nanoparticlesrdquo AIP Conference Proceedings vol1391 no 1 pp 428ndash430 2011

[50] Y-T Tseng Y-J Chuang Y-C Wu C-S Yang M-C Wangand F-G Tseng ldquoA gold-nanoparticle-enhanced immune sen-sor based on fiber optic interferometryrdquoNanotechnology vol 19no 34 Article ID 345501 2008

[51] M Jiang Q-S Li J-N Wang et al ldquoTiO2nanoparticle thin

film-coated optical fiber Fabry-Perot sensorrdquo Optics Expressvol 21 no 3 pp 3083ndash3090 2013

[52] M Consales A Crescitelli M Penza et al ldquoSWCNT nano-composite optical sensors for VOC and gas trace detectionrdquoSensors and Actuators B Chemical vol 138 no 1 pp 351ndash3612009

[53] M Yin B Gu Q Zhao et al ldquoHighly sensitive and fast respon-sive fiber-opticmodal interferometric pH sensor based on poly-electrolyte complex and polyelectrolyte self-assembled nano-coatingrdquo Analytical and Bioanalytical Chemistry vol 399 no10 pp 3623ndash3631 2011


[54] N Liu L Li G Cao and R Lee ldquoSilver-embedded zeolite thinfilm-based fiber optic sensor for in situ real-time monitoringHg2+ ions in aqueous media with high sensitivity and selectiv-ityrdquo Journal of Materials Chemistry vol 20 no 41 pp 9029ndash9031 2010

[55] O Duhem J F Henninot and M Douay ldquoStudy of in fiberMach-Zehnder interferometer based on two spaced 3-dB longperiod gratings surrounded by a refractive index higher thanthat of silicardquo Optics Communications vol 180 no 4 pp 255ndash262 2000

[56] J Yang L Jiang S Wang et al ldquoHigh sensitivity of taper-basedMach-Zehnder interferometer embedded in a thinned opticalfiber for refractive index sensingrdquo Applied Optics vol 50 no28 pp 5503ndash5507 2011

[57] S W James S Korposh S-W Lee and R P Tatam ldquoAlong period grating-based chemical sensor insensitive to theinfluence of interfering parametersrdquo Optics Express vol 22 no7 pp 8012ndash8023 2014

[58] B Li L Jiang S Wang L Zhou H Xiao and T Hai-LungldquoUltra-abrupt tapered fiber mach-zehnder interferometer sen-sorsrdquo Sensors vol 11 no 6 pp 5729ndash5739 2011

[59] A B Socorro I Del Villar J M Corres F J Arregui and I RMatias ldquoSensitivity enhancement in a multimode interference-based SMS fibre structure coated with a thin-film theoreticaland experimental studyrdquo Sensors and Actuators B Chemicalvol 190 pp 363ndash369 2014

[60] C Carrasquilla Y Xiao C Q Xu Y Li and J D BrennanldquoEnhancing sensitivity and selectivity of long-period gratingsensors using structure-switching aptamers bound to gold-doped macroporous silica coatingsrdquo Analytical Chemistry vol83 no 20 pp 7984ndash7991 2011

[61] H Y Fu H Y Tam L-Y Shao et al ldquoPressure sensorrealized with polarization-maintaining photonic crystal fiber-based Sagnac interferometerrdquo Applied Optics vol 47 no 15 pp2835ndash2839 2008

[62] L H Chen C C Chan T Li et al ldquoChitosan-coated polariza-tion maintaining fiber-based sagnac interferometer for relativehumidity measurementrdquo IEEE Journal on Selected Topics inQuantum Electronics vol 18 no 5 pp 1597ndash1604 2012

[63] J Wang H Liang X Dong and Y Jin ldquoA temperature-insensitive relative humidity sensor by using polarizationmain-taining fiber-based sagnac interferometerrdquoMicrowave andOpti-cal Technology Letters vol 55 no 10 pp 2305ndash2307 2013

[64] CWu B-O Guan C Lu andH-Y Tam ldquoSalinity sensor basedon polyimide-coated photonic crystal fiberrdquoOptics Express vol19 no 21 pp 20003ndash20008 2011

[65] O SWolfbeis Fiber Optic Chemical Sensors and Biosensors vol1 CRC Press 1991

[66] B D MacCraith C M McDonagh G OrsquoKeeffe et al ldquoFibreoptic oxygen sensor based onfluorescence quenching of evanes-cent-wave excited ruthenium complexes in sol-gel derivedporous coatingsrdquo Analyst vol 4 no 118 pp 385ndash388 1993

[67] D J Monk and D R Walt ldquoOptical fiber-based biosensorsrdquoAnalytical andBioanalytical Chemistry vol 379 no 7-8 pp 931ndash945 2004

[68] K L Brogan andD RWalt ldquoOptical fiber-based sensors appli-cation to chemical biologyrdquo Current Opinion in Chemical Bio-logy vol 9 no 5 pp 494ndash500 2005

[69] A Leung P M Shankar and R Mutharasan ldquoA review of fiber-optic biosensorsrdquo Sensors and Actuators B Chemical vol 125no 2 pp 688ndash703 2007

[70] T Yamauchi H Iwai and Y Yamashita ldquoLabel-free imaging ofthe dynamics of cell-to-cell string-like structure bridging in thefree-space by low-coherent quantitative phase microscopyrdquo inOptical Coherence Tomography and Coherence Domain OpticalMethods in Biomedicine XVII vol 8571 of Proceedings of SPIEMarch 2013

[71] H Deng Y Bai J Xiao and Q Wu ldquoPrecision estimate offluorescence quenching based fiber optical oxygen sensorrdquoOptical Technique vol 41 pp 124ndash127 131 2015

[72] R W Sabnis Handbook of Fluorescent Dyes and Probes JohnWiley amp Sons Hoboken NJ USA 2015

[73] J A Kiernan ldquoClassification and naming of dyes stains andfluorochromesrdquo Biotechnic and Histochemistry vol 76 no 5-6pp 261ndash277 2001

[74] J Goicoechea F J Arregui and I R Matias ldquoQuantum dotsfor sensingrdquo in Sensors Based on Nanostructured Materials F JArregui Ed pp 131ndash181 Springer New York NY USA 2008

[75] J M Costa-Fernandez ldquoOptical sensors based on luminescentquantumdotsrdquoAnalytical and Bioanalytical Chemistry vol 384no 1 pp 37ndash40 2006

[76] M Dahan S Levi C Luccardini P Rostaing B Riveau andA Triller ldquoDiffusion dynamics of glycine receptors revealed bysingle-quantum dot trackingrdquo Science vol 302 no 5644 pp442ndash445 2003

[77] L Zhu S Ang andW-T Liu ldquoQuantum dots as a novel immu-nofluorescent detection system for Cryptosporidium parvumand giardia lambliardquo Applied and Environmental Microbiologyvol 70 no 1 pp 597ndash598 2004

[78] X Michalet F F Pinaud L A Bentolila et al ldquoQuantum dotsfor live cells in vivo imaging and diagnosticsrdquo Science vol 307no 5709 pp 538ndash544 2005

[79] R Bakalova Z Zhelev H Ohba and Y Baba ldquoQuantum dot-based western blot technology for ultrasensitive detection oftracer proteinsrdquo Journal of the American Chemical Society vol127 no 26 pp 9328ndash9329 2005

[80] S C Makrides C Gasbarro and J M Bello ldquoBioconjugationof quantum dot luminescent probes for Western blot analysisrdquoBioTechniques vol 39 no 4 pp 501ndash505 2005

[81] A R Clapp I L Medintz J M Mauro B R Fisher M GBawendi and H Mattoussi ldquoFluorescence resonance energytransfer between quantum dot donors and dye-labeled proteinacceptorsrdquo Journal of the American Chemical Society vol 126no 1 pp 301ndash310 2004

[82] A M Dennis W J Rhee D Sotto S N Dublin and GBao ldquoQuantum dot-fluorescent protein fret probes for sensingintracellular pHrdquo ACS Nano vol 6 no 4 pp 2917ndash2924 2012

[83] G de Bastida F J Arregui J Goicoechea and I R MatiasldquoQuantum dots-based optical fiber temperature sensors fabri-cated by layer-by-layerrdquo IEEE Sensors Journal vol 6 no 6 pp1378ndash1379 2006

[84] B Larrion M Hernaez F J Arregui J Goicoechea J Bravoand I R Matıas ldquoPhotonic crystal fiber temperature sensorbased on quantum dot nanocoatingsrdquo Journal of Sensors vol2009 Article ID 932471 6 pages 2009

[85] M E Stewart C R Anderton L B Thompson et al ldquoNanos-tructured plasmonic sensorsrdquo Chemical Reviews vol 108 no 2pp 494ndash521 2008

[86] X Li L Jiang Q Zhan J Qian and S He ldquoLocalized surfaceplasmon resonance (LSPR) of polyelectrolyte-functionalizedgold-nanoparticles for bio-sensingrdquo Colloids and Surfaces APhysicochemical and Engineering Aspects vol 332 no 2-3 pp172ndash179 2009


[87] Y Wang B Liu A Mikhailovsky and G C Bazan ldquoConju-gated polyelectrolyte-metal nanoparticle platforms for opticallyamplified dna detectionrdquo Advanced Materials vol 22 no 5 pp656ndash659 2010

[88] J Geng J Liang YWang G G Gurzadyan and B Liu ldquoMetal-enhanced fluorescence of conjugated polyelectrolytes with self-assembled silver nanoparticle platformsrdquo Journal of PhysicalChemistry B vol 115 no 13 pp 3281ndash3288 2011

[89] N Ma F Tang X Wang F He and L Li ldquoTunable metal-enhanced fluorescence by stimuli-responsive polyelectrolyteinterlayer filmsrdquo Macromolecular Rapid Communications vol32 no 7 pp 587ndash592 2011

[90] J Zhang N Ma F Tang Q Cui F He and L Li ldquopH- andglucose-responsive core-shell hybrid nanoparticles with con-trollable metal-enhanced fluorescence effectsrdquo ACS AppliedMaterials and Interfaces vol 4 no 3 pp 1747ndash1751 2012

[91] A M Gabudean M Focsan and S Astilean ldquoGold nanorodsperforming as dual-modal nanoprobes via metal-enhancedfluorescence (MEF) and surface-enhanced Raman scattering(SERS)rdquo Journal of Physical Chemistry C vol 116 no 22 pp12240ndash12249 2012

[92] C L Haynes and R P Van Duyne ldquoPlasmon-sampled surface-enhanced Raman excitation spectroscopyrdquo Journal of PhysicalChemistry B vol 107 no 30 pp 7426ndash7433 2003

[93] L A Dick A DMcFarland C L Haynes and R P VanDuyneldquoMetal film over nanosphere (MFON) electrodes for surface-enhanced Raman spectroscopy (SERS) improvements in sur-face nanostructure stability and suppression of irreversible lossrdquoJournal of Physical Chemistry B vol 106 no 4 pp 853ndash8602002

[94] J Cao D Zhao X Lei Y Liu and QMao ldquoOne-pot hydrother-mal synthesis of silver nanoplates on optical fiber tip for surface-enhanced Raman scatteringrdquo Applied Physics Letters vol 104no 20 Article ID 201906 2014

[95] L X Quang C Lim G H Seong J Choo K J Do and S-K Yoo ldquoA portable surface-enhanced Raman scattering sensorintegratedwith a lab-on-a-chip for field analysisrdquo Lab on aChipvol 8 no 12 pp 2214ndash2219 2008

[96] A Walter A Marz W Schumacher P Rosch and J PoppldquoTowards a fast high specific and reliable discrimination ofbacteria on strain level by means of SERS in a microfluidicdevicerdquo Lab on a ChipmdashMiniaturisation for Chemistry andBiology vol 11 no 6 pp 1013ndash1021 2011

[97] Z Chen Z Dai N Chen et al ldquoGold nanoparticles-modifiedtapered fiber nanoprobe for remote SERS detectionrdquo IEEEPhotonics Technology Letters vol 26 no 8 pp 777ndash780 2014

[98] D Jin Y Bai H Chen et al ldquoSERS detection of expired tetra-cycline hydrochloride with an optical fiber nano-proberdquo Ana-lytical Methods vol 7 no 4 pp 1307ndash1312 2015

[99] C Liu S Wang G Chen et al ldquoA surface-enhanced Ramanscattering (SERS)-active optical fiber sensor based on a three-dimensional sensing layerrdquo Sensing and Bio-Sensing Researchvol 1 pp 8ndash14 2014

[100] C Liu S Wang C Fu H Li S Xu and W Xu ldquoPreparation ofsurface-enhanced Raman scattering(SERS)-active optical fibersensor by laser-induced Ag deposition and its application inbioidentification of biotinavidinrdquoChemical Research inChineseUniversities vol 31 no 1 pp 25ndash30 2015

[101] ADragomir DNNikogosyan K A Zagorulko P G Kryukovand E M Dianov ldquoInscription of fiber Bragg gratings byultraviolet femtosecond radiationrdquoOptics Letters vol 28 no 22pp 2171ndash2173 2003

[102] Y-J Rao Y-P Wang Z-L Ran and T Zhu ldquoNovel fiber-opticsensors based on long-period fiber gratings written by high-frequency CO

2laser pulsesrdquo Journal of Lightwave Technology

vol 21 no 5 pp 1320ndash1327 2003[103] Y Kondo K Nouchi T Mitsuyu MWatanabe P G Kazansky

and K Hirao ldquoFabrication of long-period fiber gratings byfocused irradiation of infrared femtosecond laser pulsesrdquoOpticsLetters vol 24 no 10 pp 646ndash648 1999

[104] A Malki G Humbert Y Ouerdane A Boukhenter and ABoudrioua ldquoInvestigation of the writingmechanism of electric-arc-induced long-period fiber gratingsrdquo Applied Optics vol 42no 19 pp 3776ndash3779 2003

[105] K O Hill and G Meltz ldquoFiber Bragg grating technologyfundamentals and overviewrdquo Journal of Lightwave Technologyvol 15 no 8 pp 1263ndash1276 1997

[106] A D Kersey M A Davis H J Patrick et al ldquoFiber gratingsensorsrdquo Journal of Lightwave Technology vol 15 no 8 pp1442ndash1462 1997

[107] T Erdogan ldquoFiber grating spectrardquo Journal of Lightwave Tech-nology vol 15 no 8 pp 1277ndash1294 1997

[108] A M Vengsarkar P J Lemaire J B Judkins V Bhatia TErdogan and J E Sipe ldquoLong-period fiber gratings as band-rejection filtersrdquo Journal of Lightwave Technology vol 14 no 1pp 58ndash64 1996

[109] S W James and R P Tatam ldquoOptical fibre long-period gratingsensors characteristics and applicationrdquo Measurement Scienceand Technology vol 14 no 5 pp R49ndashR61 2003

[110] V Bhatia ldquoApplications of long-period gratings to single andmulti-parameter sensingrdquoOptics Express vol 4 no 11 pp 457ndash466 1999

[111] X-K Zeng and Y-J Rao ldquoSimultaneous static strain tempera-ture and vibration measurement using an integrated FBGEFPIsensorrdquo Chinese Physics Letters vol 18 no 12 pp 1617ndash16192001

[112] Z C Zhuo and B S Ham ldquoA temperature-insensitive strainsensor using a fiber Bragg gratingrdquoOptical Fiber Technology vol15 no 5-6 pp 442ndash444 2009

[113] J Jung H Nam B Lee J O Byun and N S Kim ldquoFiberBragg grating temperature sensor with controllable sensitivityrdquoApplied Optics vol 38 no 13 pp 2752ndash2754 1999

[114] H Ahmad W Y Chong K Thambiratnam et al ldquoHighsensitivity fiber Bragg grating pressure sensor using thin metaldiaphragmrdquo IEEE Sensors Journal vol 9 no 12 pp 1654ndash16592009

[115] X Dong H Zhang B Liu and Y Miao ldquoTilted fiber bragggratings principle and sensing applicationsrdquo Photonic Sensorsvol 1 no 1 pp 6ndash30 2011

[116] S C Kang S Y Kim S B Lee SWKwon S S Choi andB LeeldquoTemperature-independent strain sensor system using a tiltedfiber bragg grating demodulatorrdquo IEEE Photonics TechnologyLetters vol 10 no 10 pp 1461ndash1463 1998

[117] E Chehura S W James and R P Tatam ldquoTemperature andstrain discrimination using a single tilted fibre Bragg gratingrdquoOptics Communications vol 275 no 2 pp 344ndash347 2007

[118] T Guo A Ivanov G Chen and J Albert ldquoTemperature-independent tilted fiber grating vibration sensor based oncladding-core recouplingrdquo Optics Letters vol 33 no 9 pp1004ndash1006 2008

[119] S Baek Y Jeong and B Lee ldquoCharacteristics of short-periodblazed fiber Bragg gratings for use as macro-bending sensorsrdquoApplied Optics vol 41 no 4 pp 631ndash636 2002


[120] X Chen K Zhou L Zhang and I Bennion ldquoIn-fiber twistsensor based on a fiber Bragg grating with 81∘ tilted structurerdquoIEEE Photonics Technology Letters vol 18 no 24 pp 2596ndash2598 2006

[121] C-L Zhao X Yang M S Demokan andW Jin ldquoSimultaneoustemperature and refractive index measurements using a 3∘slanted multimode fiber Bragg gratingrdquo Journal of LightwaveTechnology vol 24 no 2 pp 879ndash883 2006

[122] YMiao B Liu H Zhang et al ldquoRelative humidity sensor basedon tilted fiber Bragg grating with polyvinyl alcohol coatingrdquoIEEE Photonics Technology Letters vol 21 no 7 pp 441ndash4432009

[123] V Voisin J Pilate P Damman P Megret and C CaucheteurldquoHighly sensitive detection of molecular interactions withplasmonic optical fiber grating sensorsrdquo Biosensors and Bioelec-tronics vol 51 pp 249ndash254 2014

[124] J-M Renoirt C Zhang M Debliquy M-G Olivier P MegretandCCaucheteur ldquoHigh-refractive-index transparent coatingsenhance the optical fiber cladding modes refractometric sensi-tivityrdquo Optics Express vol 21 no 23 pp 29073ndash29082 2013

[125] D Paladino A Cusano P Pilla S Campopiano C Caucheteurand P Megret ldquoSpectral behavior in nano-coated tilted fiberBragg gratings effect of thickness and external refractive indexrdquoIEEE Photonics Technology Letters vol 19 no 24 pp 2051ndash20532007

[126] A Bialiayeu A Bottomley D Prezgot A Ianoul and J AlbertldquoPlasmon-enhanced refractometry using silver nanowire coat-ings on tilted fibre Bragg gratingsrdquo Nanotechnology vol 23 no44 Article ID 444012 2012

[127] A Cusano A Iadicicco P Pilla et al ldquoMode transition in highrefractive index coated long period gratingsrdquo Optics Expressvol 14 no 1 pp 19ndash34 2006

[128] A Cusano A Iadicicco P Pilla et al ldquoCoated long-period fibergratings as high-sensitivity optochemical sensorsrdquo Journal ofLightwave Technology vol 24 no 4 pp 1776ndash1786 2006

[129] A Cusano P Pilla L Contessa et al ldquoHigh-sensitivity opticalchemosensor based on coated long-period gratings for sub-ppm chemical detection in waterrdquo Applied Physics Letters vol87 Article ID 234105 pp 1ndash3 2005

[130] P Pilla A Iadicicco L Contessa et al ldquoOptical chemo-sensorbased on long period gratings coated with 120575 form syndiotacticpolystyrenerdquo IEEE Photonics Technology Letters vol 17 no 8pp 1713ndash1715 2005

[131] G Decher ldquoFuzzy nanoassemblies toward layered polymericmulticompositesrdquo Science vol 277 no 5330 pp 1232ndash1237 1997

[132] X Zhang H Chen and H Zhang ldquoLayer-by-layer assemblyfromconventional to unconventionalmethodsrdquoChemical Com-munications pp 1395ndash1405 2007

[133] P Sigmund ldquoElements of sputtering theoryrdquoNanofabrication byIon-Beam Sputtering Fundamentals and Applications pp 1ndash402012

[134] A Trouillet E Marin and C Veillas ldquoFibre gratings forhydrogen sensingrdquo Measurement Science and Technology vol17 no 5 pp 1124ndash1128 2006

[135] X Wei T Wei H Xiao and Y S Lin ldquoNano-structured Pd-long period fiber gratings integrated optical sensor for hydrogendetectionrdquo Sensors and Actuators B Chemical vol 134 no 2pp 687ndash693 2008

[136] J M Corres I Del Villar I R Matias and F J Arregui ldquoFiber-optic pH-sensors in long-period fiber gratings using electro-static self-assemblyrdquoOptics Letters vol 32 no 1 pp 29ndash31 2007

[137] J M Corres I Del Villar I R Matias and F J ArreguildquoTwo-layer nanocoatings in long-period fiber gratings forimproved sensitivity of humidity sensorsrdquo IEEE Transactions onNanotechnology vol 7 no 4 pp 394ndash400 2008

[138] S M Topliss S W James F Davis S P J Higson and R PTatam ldquoOptical fibre long period grating based selective vapoursensing of volatile organic compoundsrdquo Sensors and ActuatorsB Chemical vol 143 no 2 pp 629ndash634 2010

[139] I Del Villar I R Matias and F J Arregui ldquoEnhancement ofsensitivity in long-period fiber gratings with deposition of low-refractive-index materialsrdquo Optics Letters vol 30 no 18 pp2363ndash2365 2005

[140] I Del Villar M Achaerandio I R Matıas and F J ArreguildquoDeposition of overlays by electrostatic self-assembly in long-period fiber gratingsrdquo Optics Letters vol 30 no 7 pp 720ndash7222005

[141] X Shu L Zhang and I Bennion ldquoSensitivity characteristics oflong-period fiber gratingsrdquo Journal of LightwaveTechnology vol20 no 2 pp 255ndash266 2002

[142] C S Cheung S M Topliss S W James and R P TatamldquoResponse of fiber-optic long-period gratings operating nearthe phase-matching turning point to the deposition of nanos-tructured coatingsrdquo Journal of the Optical Society of America BOptical Physics vol 25 no 6 pp 897ndash902 2008

[143] D Viegas J Goicoechea J M Corres et al ldquoA fibre optichumidity sensor based on a long-period fibre grating coatedwith a thin film of SiO

2nanospheresrdquoMeasurement Science and

Technology vol 20 no 3 Article ID 034002 2009[144] D Viegas M Hernaez J Goicoechea et al ldquoSimultaneous

measurement of humidity and temperature based on an SiO2-

nanospheres film deposited on a long-period grating in-linewith a fiber Bragg gratingrdquo IEEE Sensors Journal vol 11 no 1pp 162ndash166 2011

[145] J-L Tang and J-N Wang ldquoMeasurement of chloride-ionconcentration with long-period grating technologyrdquo SmartMaterials and Structures vol 16 no 3 pp 665ndash672 2007

[146] M Konstantaki A Klini D Anglos and S Pissadakis ldquoAnethanol vapor detection probe based on a ZnO nanorod coatedoptical fiber long period gratingrdquo Optics Express vol 20 no 8pp 8472ndash8484 2012

[147] S Korposh R Selyanchyn W Yasukochi S-W Lee S WJames and R P Tatam ldquoOptical fibre long period grating witha nanoporous coating formed from silica nanoparticles forammonia sensing in waterrdquo Materials Chemistry and Physicsvol 133 no 2-3 pp 784ndash792 2012


[149] R-Z Yang W-F Dong X Meng et al ldquoNanoporousTiO2polyion thin-film-coated long-period grating sensors for

the direct measurement of low-molecular-weight analytesrdquoLangmuir vol 28 no 23 pp 8814ndash8821 2012

[150] S Korposh S-W Lee S W James and R P Tatam ldquoRefractiveindex sensitivity of fibre-optic long period gratings coated withSiO2nanoparticlemesoporous thin filmsrdquoMeasurement Science

and Technology vol 22 no 7 Article ID 075208 2011[151] L Marques F U Hernandez S Korposh et al ldquoSensitive

protein detection using an optical fibre long period gratingsensor anchored with silica core gold shell nanoparticlesrdquo in23rd International Conference on Optical Fibre Sensors vol 9157of Proceedings of SPIE Santander Spain June 2014


[152] S Korposh T Wang S James R Tatam and S-W Lee ldquoPro-nounced aromatic carboxylic acid detection using a layer-by-layer mesoporous coating on optical fibre long period gratingrdquoSensors and Actuators B Chemical vol 173 pp 300ndash309 2012

[153] Y Huang Z Gao G Chen and H Xiao ldquoLong periodfiber grating sensors coated with nano ironsilica particles forcorrosion monitoringrdquo Smart Materials and Structures vol 22no 7 Article ID 075018 2013

[154] Y Huang F Tang X Liang G Chen H Xiao and F AzarmildquoSteel bar corrosion monitoring with long-period fiber grat-ing sensors coated with nano ironsilica particles and poly-urethanerdquo Structural Health Monitoring vol 14 pp 178ndash1892015

[155] J-L Tang and J-NWang ldquoChemical sensing sensitivity of long-period grating sensor enhanced by colloidal gold nanoparti-clesrdquo Sensors vol 8 no 1 pp 171ndash184 2008

[156] F J Arregui I Del Villar J M Corres et al ldquoFiber-optic lossymode resonance sensorsrdquo Procedia Engineering vol 87 pp 3ndash82014

[157] P J Rivero A Urrutia J Goicoechea and F J Arregui ldquoOpticalfiber humidity sensors based on Localized Surface PlasmonResonance (LSPR) and Lossy-mode resonance (LMR) in over-lays loaded with silver nanoparticlesrdquo Sensors and Actuators BChemical vol 173 pp 244ndash249 2012

[158] I-C Chen S-S Lin T-J Lin and J-K du ldquoDetection of hydro-fluoric acid by a SiO

2sol-gel coating fiber-optic probe based on

reflection-based localized surface plasmon resonancerdquo Sensorsvol 11 no 2 pp 1907ndash1923 2011

[159] P Bhatia P Yadav and BD Gupta ldquoSurface plasmon resonancebased fiber optic hydrogen peroxide sensor using polymerembedded nanoparticlesrdquo Sensors and Actuators B Chemicalvol 182 pp 330ndash335 2013

[160] VV R Sai TKundu and SMukherji ldquoNovelU-bent fiber opticprobe for localized surface plasmon resonance based biosensorrdquoBiosensors andBioelectronics vol 24 no 9 pp 2804ndash2809 2009

[161] R Dahint E Trileva H Acunman et al ldquoOptically responsivenanoparticle layers for the label-free analysis of biospecificinteractions in array formatsrdquo Biosensors and Bioelectronics vol22 no 12 pp 3174ndash3181 2007

[162] S K Srivastava V Arora S Sapra and B D Gupta ldquoLocalizedsurface plasmon resonance-based fiber optic u-shaped biosen-sor for the detection of blood glucoserdquo Plasmonics vol 7 no 2pp 261ndash268 2012

[163] A Candiani A Bertucci S Giannetti et al ldquoLabel-freeDNA biosensor based on a peptide nucleic acid-functionalizedmicrostructured optical fiber-Bragg gratingrdquo Journal of Biomed-ical Optics vol 18 no 5 Article ID 057004 2013

[164] P J Rivero M Hernaez J Goicoechea I R Matias and FJ Arregui ldquoOptical fiber refractometers based on localizedsurface plasmon resonance (LSPR) and lossy mode resonance(LMR)rdquo in 23rd International Conference on Optical FibreSensors vol 9157 of Proceedings of SPIE International Societyfor Optical Engineering Santander Spain June 2014

[165] M Hernaez C R Zamarreno I Del Villar I R Matias and FJ Arregui ldquoLossy mode resonances supported by TiO

2-coated

optical fibersrdquo Procedia Engineering vol 5 pp 1099ndash1102 2010[166] M Hernaez I D Villar C R Zamarreno F J Arregui and I

R Matias ldquoOptical fiber refractometers based on lossy moderesonances supported by TiO

2coatingsrdquoApplied Optics vol 49

no 20 pp 3980ndash3985 2010[167] C R Zamarreno M Hernaez P Sanchez I Del Villar I R

Matias and F J Arregui ldquoOptical fiber humidity sensor based

on lossy mode resonances supported by TiO2PSS coatingsrdquo

Procedia Engineering vol 25 pp 1385ndash1388 2011[168] P J Rivero A Urrutia J Goicoechea I R Matias and F J

Arregui ldquoA Lossy Mode Resonance optical sensor using silvernanoparticles-loaded films for monitoring human breathingrdquoSensors and Actuators B Chemical vol 187 pp 40ndash44 2013

[169] C Elosua F J Arregui C R Zamarreno et al ldquoVolatile organiccompounds optical fiber sensor based on lossy mode reson-ancesrdquo Sensors and Actuators B Chemical vol 173 pp 523ndash5292012

[170] T E Batchman and G M McWright ldquoMode coupling betweendielectric and semiconductor planar waveguidesrdquo IEEE Journalof Quantum Electronics vol 18 no 4 pp 782ndash788 1982

[171] MMarciniak J Grzegorzewski andM Szustakowski ldquoAnalysisof lossy mode cut-off conditions in planar waveguides withsemiconductor guiding layerrdquo IEE proceedings Part J Optoelec-tronics vol 140 no 4 pp 247ndash252 1993

[172] IDelVillar C R ZamarrenoMHernaez F J Arregui and I RMatias ldquoGeneration of lossy mode resonances with absorbingthin-filmsrdquo Journal of Lightwave Technology vol 28 no 23 pp3351ndash3357 2010

[173] R C Jorgenson and S S Yee ldquoA fiber-optic chemical sensorbased on surface plasmon resonancerdquo Sensors and Actuators BChemical vol 12 no 3 pp 213ndash220 1993

[174] X D Hoa A G Kirk and M Tabrizian ldquoTowards integratedand sensitive surface plasmon resonance biosensors a reviewof recent progressrdquo Biosensors and Bioelectronics vol 23 no 2pp 151ndash160 2007

[175] B Sepulveda P C Angelome L M Lechuga and L M Liz-Marzan ldquoLSPR-based nanobiosensorsrdquo Nano Today vol 4 no3 pp 244ndash251 2009

[176] B D Gupta and R K Verma ldquoSurface plasmon resonance-based fiber optic sensors principle probe designs and someapplicationsrdquo Journal of Sensors vol 2009 Article ID 97976112 pages 2009

[177] J Cao E K Galbraith T Sun and K T V Grattan ldquoCross-comparison of surface plasmon resonance-based optical fibersensors with different coating structuresrdquo IEEE Sensors Journalvol 12 no 7 pp 2355ndash2361 2012

[178] I Del Villar C R Zamarreno P Sanchez et al ldquoGeneration oflossy mode resonances by deposition of high-refractive-indexcoatings on uncladded multimode optical fibersrdquo Journal ofOptics vol 12 no 9 Article ID 095503 2010

[179] N Paliwal and J John ldquoTheoretical modeling of lossymode res-onance based refractive index sensors with ITOTiO

2bilayersrdquo

Applied Optics vol 53 no 15 pp 3241ndash3246 2014

International Journal of

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RoboticsJournal of

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Active and Passive Electronic Components

Control Scienceand Engineering

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Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design



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Civil EngineeringAdvances in

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Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks



2 Intensity- and Absorbance-Based Sensors

21 Introduction Intensity-based optical fiber sensors havebeen reported since the 70s in literature and their devel-opment has been widely used to these days Generallythe underlying phenomenon of such sensors is the lighttransmission-absorption in materials Absorbance is basedon the attenuation of light due to the characteristics of thematerial that light is guided through The sensitive materialschange the absorbance in presence of a specific parameteror analyte and therefore a change on the guided lightcan be observed The absorption mechanisms are describedby the Lambert-Beer Law where the transmission of thelight through an analyte material or sensitive region (119879called transmittance) represents the relation between the lightintensity before (119868

119900) and that after (119868) passing through this

sensitive region expressed by the following equation

119879 =119868

119868119900

= 10minus120572119871

= 10120576119862119871

(1)

where 119871 is the length of interaction within the absorbingregion (optical path) and120572 is the absorption coefficient whichcan be denoted as the product of the molar absorptivity (120576)and the concentration (119862) of the target This transmittancenomenclature can also be transferred to absorbance termssuch that

119860 = minuslog10

119868

119868119900

= 120572119871 = 120576119862119871 (2)

where absorbance (119860) is the magnitude commonly used inthis kind of optical fiber sensors

The incorporation of sensitive materials to optical fibersensors can be performed by embedding them into coatingsor thin films The propagation of light through the opticalfiber presents two contributions the guided field in the coreand the evanescent field in themedium surrounding this coreThis evanescent field is not accessible in unmodified standardcladded fibers and therefore it is not relevant to sensingThereby the externalmediumcannot interactwith the guidedlight through the core nor the evanescent contribution inthe cladding Nevertheless when the cladding is intentionallyreplaced by sensitive coatings there could be a significantinteraction between the external medium and the evanescentfield to the guided lightThe optical properties of the selectedcoating materials determine the changes in this evanescent-field interaction In many cases optical configurations aredeveloped to enlarge this interactionwith the evanescent fieldby removing the cladding bending or tapering the fiber asit is shown in Figure 1 thus improving their sensitivity to thechanges in the external media

22 Cladding-Removed Optical Fiber Sensors Cladding-removed optical fiber (CROF) is one of the simplest struc-tures used in optical fiber sensing (shown in Figure 1(a)) Ashort distance of the cladding of the fiber is removed and thenreplaced by the deposition of a selected nanostructured coat-ing which interacts with the surroundings This coating actsas sensitive region and therefore its composition and fabrica-tion parameters are thoroughly studied in order to improve

sensitivity or other desirable sensing values Thin film fab-rication techniques such as Layer-by-Layer (LbL) assem-bly Langmuir-Blodgett sol-gel or spin-coating are used tocreate these coatings where in some cases NPs are embeddedinside them

During the last two decades many CROF based ap-proaches have been developed Nevertheless as it was pre-viously commented the use of NPs in coatings has not beenreported until the last few years

CROF sensors with NP-based coatings have beenreported in several works detecting humidity [14 15]ethanol [16] ammonia [17] methanol [18] and other gases[19 20] For instance Kodaira et al [20] coated an opticalfiber with SiO

2NPs and poly(diallyldimethyl ammonium

chloride) to createmesoporous overlays by LbLThe resultantcoating morphology allows allocating functional chemicalcompounds for diverse gases detection Another relevantapproach is reported by Mariammal et al [16] using SnO

2

and CuOSnO2

NPs for ethanol detection The use ofCuOSnO

2NPs based coatings presented an enhancement

of 3 times in sensitivity with respect to previously reportedsensors based on pure SnO

2NPs

23 Bent Optical Fiber Sensors Bent optical fiber sensors canbe considered as a particular case of the CROF sensors whenthemodified fragment of the fiber is submitted to a significantbending (see Figure 1(b)) Sometimes these devices are alsoreported as U-shape fiber sensors [21] The intentionallybending effect provides higher losses in the transmitted lightand dramatically increases the evanescent-field depth [8 22]Khijwania et al demonstrated the notable enhancement insensitivity presented by a U-probe in comparison with astraight probe due to a larger evanescent field and absorp-tion coefficient [8] Included in this classification there aredifferent devices which have sensitive coatings without NPsfor humidity [8 23 24] or pH [25] However the use ofcoatings with NPs has appeared more recently Thus Guoand Tao reported ammonia sensing devices [26] based on AgNPs within silica coatings with a theoretical limit of detec-tion (LoD) of 61 ppb Vijayan et al developed optical fiberhumidity sensors based on a Co NPs-embedded polyanilinecoating [27] Their sensors showed a quick response of 8 s ina broad dynamic range of 20ndash95 in relative humidity termsAnother humidity device with MgO NPs was presented byShukla et al [28] using the sol-gel technique Also U-bentfibers have been coated with Au NPs to develop resonance-based sensors [29 30] as it will be described in Section 6

24 Tapered Optical Fiber Sensors and Other Special FiberSensors An alternative strategy for exposing the evanescentfield to an external sensitive coating is fiber tapering Thistechnique modifies the optical fiber geometry and its struc-ture (see Figure 1(c)) thus obtaining an increment of theinteraction of light with the sensitive region and thereforeproviding higher variations in the magnitude of the evanes-cent field The length and waist diameter of the taper therefractive indices and other fiber parameters were analyzedby Ahmad and Hench using a ray model The influence ofthese factors on the penetration depth of the evanescent


Cladding

Core

NP-embedded coating

Surroundingmedium

Evanescentfield

(a)

NP-embeddedcoating

Surrounding medium

Cladding

Core

Evanescentfield

(b)

NP-embedded coating

Surroundingmedium

Cladding

Core

Tapered region

Evanescentfield

(c)













119891)


119890)When




Cladding

CoreSurrounding


Reflected light

Cavity length

NP-embedded coating

nenc

nf









CladdingCore

LPG 1 LPG 2

(a)

CladdingCore

Taper 1 Taper 2

(b)

CladdingCore

PCF segment

(c)



















3000

2000

1000

0

Emiss

ion

inte

nsity

(au

)

600 700


0∘C10∘C20∘C30∘C

40∘C50∘C60∘C70∘C

Wavelength (nm)





40

20

0

minus20

minus40


y(n

m)

x (nm)

6

4

2

0








MEF

SERS

(a)

Emiss

ion

(au

)

520 560 600 640 680

Wavelength (nm)

(b)













120582bragg = 2119899eff coreΛ 119892 (3)





250

0

(nm

)

10120583m

(a)

600nm

(b)


(A) (B)

200120583m

(a)

1000 1200 1400 18001600


Inte

nsity

(au

)

(D)(C)

(B)(A)

70000

60000

50000

40000

30000

20000

10000

0

(b)



core

Cladding


L = grating length

NP-embedded coating






























16

14

12

10

8

6

4

2

0

20 30 40 50 60 70 80


Reso

nant

wav

eleng

th sh

ift (n

m)



2NPs
















T T

120582 120582


(air) 1205761 = 1






1205769984002 lt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|

1205769984002 gt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|


400 500 600 700 800 900 1000

00010203040506070809101112

30 bilayersLMR 1

LMR 1

LSPR



Abso

rban

ce (a

u)

Wavelength (nm)

25 bilayers

(a)

500 600 700 800 90007

08

09

10

11

12



LMR 2

Abso

rban

ce (a

u)

Wavelength (nm)

LMR 3

(b)









LSPR ProteinsAPTMS


nanospheres)




LbL mdash [161]







LbL sim1 nmRH [157]










LbL 0455 nmRH [168]



dodecyl sulfate









8 Conclusions



0 100 200 300 400 500 600

0

10

20

30

40

50

60

Time (min)

LSPR

LMR 1

RH ()

10

20

30

40

50

60

70

Δ120582max

Relat

ive h

umid

ity (

)





Acknowledgments


References


















































3O4nanoparti-














































































































































2-coated




















2bilayersrdquo




RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










Cladding

Core

NP-embedded coating

Surroundingmedium

Evanescentfield

(a)

NP-embeddedcoating

Surrounding medium

Cladding

Core

Evanescentfield

(b)

NP-embedded coating

Surroundingmedium

Cladding

Core

Tapered region

Evanescentfield

(c)













119891)


119890)When




Cladding

CoreSurrounding


Reflected light

Cavity length

NP-embedded coating

nenc

nf









CladdingCore

LPG 1 LPG 2

(a)

CladdingCore

Taper 1 Taper 2

(b)

CladdingCore

PCF segment

(c)



















3000

2000

1000

0

Emiss

ion

inte

nsity

(au

)

600 700


0∘C10∘C20∘C30∘C

40∘C50∘C60∘C70∘C

Wavelength (nm)





40

20

0

minus20

minus40


y(n

m)

x (nm)

6

4

2

0








MEF

SERS

(a)

Emiss

ion

(au

)

520 560 600 640 680

Wavelength (nm)

(b)













120582bragg = 2119899eff coreΛ 119892 (3)





250

0

(nm

)

10120583m

(a)

600nm

(b)


(A) (B)

200120583m

(a)

1000 1200 1400 18001600


Inte

nsity

(au

)

(D)(C)

(B)(A)

70000

60000

50000

40000

30000

20000

10000

0

(b)



core

Cladding


L = grating length

NP-embedded coating






























16

14

12

10

8

6

4

2

0

20 30 40 50 60 70 80


Reso

nant

wav

eleng

th sh

ift (n

m)



2NPs
















T T

120582 120582


(air) 1205761 = 1






1205769984002 lt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|

1205769984002 gt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|


400 500 600 700 800 900 1000

00010203040506070809101112

30 bilayersLMR 1

LMR 1

LSPR



Abso

rban

ce (a

u)

Wavelength (nm)

25 bilayers

(a)

500 600 700 800 90007

08

09

10

11

12



LMR 2

Abso

rban

ce (a

u)

Wavelength (nm)

LMR 3

(b)









LSPR ProteinsAPTMS


nanospheres)




LbL mdash [161]







LbL sim1 nmRH [157]










LbL 0455 nmRH [168]



dodecyl sulfate









8 Conclusions



0 100 200 300 400 500 600

0

10

20

30

40

50

60

Time (min)

LSPR

LMR 1

RH ()

10

20

30

40

50

60

70

Δ120582max

Relat

ive h

umid

ity (

)





Acknowledgments


References


















































3O4nanoparti-














































































































































2-coated




















2bilayersrdquo




RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










Cladding

CoreSurrounding


Reflected light

Cavity length

NP-embedded coating

nenc

nf









CladdingCore

LPG 1 LPG 2

(a)

CladdingCore

Taper 1 Taper 2

(b)

CladdingCore

PCF segment

(c)



















3000

2000

1000

0

Emiss

ion

inte

nsity

(au

)

600 700


0∘C10∘C20∘C30∘C

40∘C50∘C60∘C70∘C

Wavelength (nm)





40

20

0

minus20

minus40


y(n

m)

x (nm)

6

4

2

0








MEF

SERS

(a)

Emiss

ion

(au

)

520 560 600 640 680

Wavelength (nm)

(b)













120582bragg = 2119899eff coreΛ 119892 (3)





250

0

(nm

)

10120583m

(a)

600nm

(b)


(A) (B)

200120583m

(a)

1000 1200 1400 18001600


Inte

nsity

(au

)

(D)(C)

(B)(A)

70000

60000

50000

40000

30000

20000

10000

0

(b)



core

Cladding


L = grating length

NP-embedded coating






























16

14

12

10

8

6

4

2

0

20 30 40 50 60 70 80


Reso

nant

wav

eleng

th sh

ift (n

m)



2NPs
















T T

120582 120582


(air) 1205761 = 1






1205769984002 lt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|

1205769984002 gt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|


400 500 600 700 800 900 1000

00010203040506070809101112

30 bilayersLMR 1

LMR 1

LSPR



Abso

rban

ce (a

u)

Wavelength (nm)

25 bilayers

(a)

500 600 700 800 90007

08

09

10

11

12



LMR 2

Abso

rban

ce (a

u)

Wavelength (nm)

LMR 3

(b)









LSPR ProteinsAPTMS


nanospheres)




LbL mdash [161]







LbL sim1 nmRH [157]










LbL 0455 nmRH [168]



dodecyl sulfate









8 Conclusions



0 100 200 300 400 500 600

0

10

20

30

40

50

60

Time (min)

LSPR

LMR 1

RH ()

10

20

30

40

50

60

70

Δ120582max

Relat

ive h

umid

ity (

)





Acknowledgments


References


















































3O4nanoparti-














































































































































2-coated




















2bilayersrdquo




RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation





















3000

2000

1000

0

Emiss

ion

inte

nsity

(au

)

600 700


0∘C10∘C20∘C30∘C

40∘C50∘C60∘C70∘C

Wavelength (nm)





40

20

0

minus20

minus40


y(n

m)

x (nm)

6

4

2

0








MEF

SERS

(a)

Emiss

ion

(au

)

520 560 600 640 680

Wavelength (nm)

(b)













120582bragg = 2119899eff coreΛ 119892 (3)





250

0

(nm

)

10120583m

(a)

600nm

(b)


(A) (B)

200120583m

(a)

1000 1200 1400 18001600


Inte

nsity

(au

)

(D)(C)

(B)(A)

70000

60000

50000

40000

30000

20000

10000

0

(b)



core

Cladding


L = grating length

NP-embedded coating






























16

14

12

10

8

6

4

2

0

20 30 40 50 60 70 80


Reso

nant

wav

eleng

th sh

ift (n

m)



2NPs
















T T

120582 120582


(air) 1205761 = 1






1205769984002 lt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|

1205769984002 gt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|


400 500 600 700 800 900 1000

00010203040506070809101112

30 bilayersLMR 1

LMR 1

LSPR



Abso

rban

ce (a

u)

Wavelength (nm)

25 bilayers

(a)

500 600 700 800 90007

08

09

10

11

12



LMR 2

Abso

rban

ce (a

u)

Wavelength (nm)

LMR 3

(b)









LSPR ProteinsAPTMS


nanospheres)




LbL mdash [161]







LbL sim1 nmRH [157]










LbL 0455 nmRH [168]



dodecyl sulfate









8 Conclusions



0 100 200 300 400 500 600

0

10

20

30

40

50

60

Time (min)

LSPR

LMR 1

RH ()

10

20

30

40

50

60

70

Δ120582max

Relat

ive h

umid

ity (

)





Acknowledgments


References


















































3O4nanoparti-














































































































































2-coated




















2bilayersrdquo




RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










MEF

SERS

(a)

Emiss

ion

(au

)

520 560 600 640 680

Wavelength (nm)

(b)













120582bragg = 2119899eff coreΛ 119892 (3)





250

0

(nm

)

10120583m

(a)

600nm

(b)


(A) (B)

200120583m

(a)

1000 1200 1400 18001600


Inte

nsity

(au

)

(D)(C)

(B)(A)

70000

60000

50000

40000

30000

20000

10000

0

(b)



core

Cladding


L = grating length

NP-embedded coating






























16

14

12

10

8

6

4

2

0

20 30 40 50 60 70 80


Reso

nant

wav

eleng

th sh

ift (n

m)



2NPs
















T T

120582 120582


(air) 1205761 = 1






1205769984002 lt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|

1205769984002 gt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|


400 500 600 700 800 900 1000

00010203040506070809101112

30 bilayersLMR 1

LMR 1

LSPR



Abso

rban

ce (a

u)

Wavelength (nm)

25 bilayers

(a)

500 600 700 800 90007

08

09

10

11

12



LMR 2

Abso

rban

ce (a

u)

Wavelength (nm)

LMR 3

(b)









LSPR ProteinsAPTMS


nanospheres)




LbL mdash [161]







LbL sim1 nmRH [157]










LbL 0455 nmRH [168]



dodecyl sulfate









8 Conclusions



0 100 200 300 400 500 600

0

10

20

30

40

50

60

Time (min)

LSPR

LMR 1

RH ()

10

20

30

40

50

60

70

Δ120582max

Relat

ive h

umid

ity (

)





Acknowledgments


References


















































3O4nanoparti-














































































































































2-coated




















2bilayersrdquo




RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










250

0

(nm

)

10120583m

(a)

600nm

(b)


(A) (B)

200120583m

(a)

1000 1200 1400 18001600


Inte

nsity

(au

)

(D)(C)

(B)(A)

70000

60000

50000

40000

30000

20000

10000

0

(b)



core

Cladding


L = grating length

NP-embedded coating






























16

14

12

10

8

6

4

2

0

20 30 40 50 60 70 80


Reso

nant

wav

eleng

th sh

ift (n

m)



2NPs
















T T

120582 120582


(air) 1205761 = 1






1205769984002 lt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|

1205769984002 gt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|


400 500 600 700 800 900 1000

00010203040506070809101112

30 bilayersLMR 1

LMR 1

LSPR



Abso

rban

ce (a

u)

Wavelength (nm)

25 bilayers

(a)

500 600 700 800 90007

08

09

10

11

12



LMR 2

Abso

rban

ce (a

u)

Wavelength (nm)

LMR 3

(b)









LSPR ProteinsAPTMS


nanospheres)




LbL mdash [161]







LbL sim1 nmRH [157]










LbL 0455 nmRH [168]



dodecyl sulfate









8 Conclusions



0 100 200 300 400 500 600

0

10

20

30

40

50

60

Time (min)

LSPR

LMR 1

RH ()

10

20

30

40

50

60

70

Δ120582max

Relat

ive h

umid

ity (

)





Acknowledgments


References


















































3O4nanoparti-














































































































































2-coated




















2bilayersrdquo




RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










core

Cladding


L = grating length

NP-embedded coating






























16

14

12

10

8

6

4

2

0

20 30 40 50 60 70 80


Reso

nant

wav

eleng

th sh

ift (n

m)



2NPs
















T T

120582 120582


(air) 1205761 = 1






1205769984002 lt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|

1205769984002 gt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|


400 500 600 700 800 900 1000

00010203040506070809101112

30 bilayersLMR 1

LMR 1

LSPR



Abso

rban

ce (a

u)

Wavelength (nm)

25 bilayers

(a)

500 600 700 800 90007

08

09

10

11

12



LMR 2

Abso

rban

ce (a

u)

Wavelength (nm)

LMR 3

(b)









LSPR ProteinsAPTMS


nanospheres)




LbL mdash [161]







LbL sim1 nmRH [157]










LbL 0455 nmRH [168]



dodecyl sulfate









8 Conclusions



0 100 200 300 400 500 600

0

10

20

30

40

50

60

Time (min)

LSPR

LMR 1

RH ()

10

20

30

40

50

60

70

Δ120582max

Relat

ive h

umid

ity (

)





Acknowledgments


References


















































3O4nanoparti-














































































































































2-coated




















2bilayersrdquo




RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation






















16

14

12

10

8

6

4

2

0

20 30 40 50 60 70 80


Reso

nant

wav

eleng

th sh

ift (n

m)



2NPs
















T T

120582 120582


(air) 1205761 = 1






1205769984002 lt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|

1205769984002 gt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|


400 500 600 700 800 900 1000

00010203040506070809101112

30 bilayersLMR 1

LMR 1

LSPR



Abso

rban

ce (a

u)

Wavelength (nm)

25 bilayers

(a)

500 600 700 800 90007

08

09

10

11

12



LMR 2

Abso

rban

ce (a

u)

Wavelength (nm)

LMR 3

(b)









LSPR ProteinsAPTMS


nanospheres)




LbL mdash [161]







LbL sim1 nmRH [157]










LbL 0455 nmRH [168]



dodecyl sulfate









8 Conclusions



0 100 200 300 400 500 600

0

10

20

30

40

50

60

Time (min)

LSPR

LMR 1

RH ()

10

20

30

40

50

60

70

Δ120582max

Relat

ive h

umid

ity (

)





Acknowledgments


References


















































3O4nanoparti-














































































































































2-coated




















2bilayersrdquo




RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










T T

120582 120582


(air) 1205761 = 1






1205769984002 lt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|

1205769984002 gt 0

|1205769984002| gt |1205769984009984002 |

|1205769984002| gt |1205769984003|


400 500 600 700 800 900 1000

00010203040506070809101112

30 bilayersLMR 1

LMR 1

LSPR



Abso

rban

ce (a

u)

Wavelength (nm)

25 bilayers

(a)

500 600 700 800 90007

08

09

10

11

12



LMR 2

Abso

rban

ce (a

u)

Wavelength (nm)

LMR 3

(b)









LSPR ProteinsAPTMS


nanospheres)




LbL mdash [161]







LbL sim1 nmRH [157]










LbL 0455 nmRH [168]



dodecyl sulfate









8 Conclusions



0 100 200 300 400 500 600

0

10

20

30

40

50

60

Time (min)

LSPR

LMR 1

RH ()

10

20

30

40

50

60

70

Δ120582max

Relat

ive h

umid

ity (

)





Acknowledgments


References


















































3O4nanoparti-














































































































































2-coated




















2bilayersrdquo




RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation














LSPR ProteinsAPTMS


nanospheres)




LbL mdash [161]







LbL sim1 nmRH [157]










LbL 0455 nmRH [168]



dodecyl sulfate









8 Conclusions



0 100 200 300 400 500 600

0

10

20

30

40

50

60

Time (min)

LSPR

LMR 1

RH ()

10

20

30

40

50

60

70

Δ120582max

Relat

ive h

umid

ity (

)





Acknowledgments


References


















































3O4nanoparti-














































































































































2-coated




















2bilayersrdquo




RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










0 100 200 300 400 500 600

0

10

20

30

40

50

60

Time (min)

LSPR

LMR 1

RH ()

10

20

30

40

50

60

70

Δ120582max

Relat

ive h

umid

ity (

)





Acknowledgments


References


















































3O4nanoparti-














































































































































2-coated




















2bilayersrdquo




RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation

































3O4nanoparti-














































































































































2-coated




















2bilayersrdquo




RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation






































































































































2-coated




















2bilayersrdquo




RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









Review Article Optical Fiber Sensors Based on Nanoparticle...

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Transcript of Review Article Optical Fiber Sensors Based on Nanoparticle...