SERS in Bio Medical Diagnostics

8/6/2019 SERS in Bio Medical Diagnostics

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SERS in Biomedical Diagnostics

Presented by;

Bibi Mohanan

M.Tech, OEC

Roll No: 7


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Motivation

The development of practical and sensitive devices for

screening multiple genes related to medical diseases and

infectious pathogens is critical for early diagnosis and

improved treatments of many illness. An important factor in medical diagnostics is rapid, selective

and sensitive detection of biochemical substances, biological

species or living systems at ultra-trace levels in biological

samples, which often requires a detection method that is

capable of identifying and differentiating a large number ofbiochemical constituents in complex samples simultaneously.


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Raman spectroscopy is rapid, nondestructive and highly

compound-specific. It has multi-component analysis potential

and requires little sample preparation, which allows on-line

and in-field analysis Raman scattering efficiency can be enhanced by factors >108

when a compound is adsorbed on or near special metal

surfaces. The enhancement provided by surface-enhanced

Raman scattering helps to bridge the sensitivity gap between

the fluorescence and Raman techniques, therefore, the SERSgene probes could offer a unique combination of performance

capabilities and analytical features of merit.


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Principle of Raman spectroscopy


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Raman scattering intensity , p = E

p = 1st order transition electric dipole

= Transition polarizability of the molecule

E = Incident electric field magnitude

Raman effect forms a characteristic Raman spectrum ineffect a molecular fingerprint

A limitation of normal Raman spectroscopy is low sensitivity

Raman scattering efficiency can be enhanced by

factors >108 when a compound is adsorbed on or near specialmetal surfaces, a phenomenon known as SERS.


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Mechanisms of Plasmonics and Surface-

Enhanced Raman Scattering (SERS)

Plasmonics refers to the research area of enhancedelectromagnetic properties of metallic nanostructures.

The term plasmonics is derived from plasmons, which are thequanta associated with longitudinal waves propagating in matter

through the collective motion of large numbers of electrons. Incident light irradiating these surfaces excites conduction

electrons in the metal, and induces excitation of surfaceplasmons leading to enormous electromagnetic enhancement ofspectral signatures [such as surface-enhanced Raman scattering(SERS) and surface-enhanced fluorescence (SEF)] for ultra

sensitive biological detection and imaging


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Electromagnetic Enhancement (E Factor)

Incident radiation (primary field) induces oscillationof conductance electrons in the metal surface,generating a secondary field

When incident radiation at the plasma frequency, aresonant response of conductance electrons (surfaceplasmons) generates an enhanced secondary field

Plasma Frequency Factors:

Type of metals Size of metal nanoparticle

Shape of the metal nanoparticle


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Molecular Enhancement ( factor)

Charge transfer between the metal and adsorbate can

enhance the transition polarizability


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SERS-active dyes and nanostructures


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Application of Raman (SERS)

techniques to bioanalysisAdvantages:

Nonradioactive

High

spectral selectivity- Very narrow bands (


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Surface-enhanced Raman scattering

(SERS) SERS provides scattering enhancement factor of up

to 108, making it competitive with fluorescence for

certain trace analysis applications

SERS results from the adsorption of chemicals on a

sub-micron textured surface

Resonance can also enable up to 106 factor

enh

ancement


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Instrumental system for SERS

Two detection systems:-

a. Spectral recording of individual spots

b. Imaging of the entire 2-D hybridization array plate


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Schematic diagram of optical system for

SERS detection


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Spectral recording of individual spots

Individual spot corresponds to an individual microdot on a hybridizationplatform

Focused, low power laser beam is used to excite an individual spot

He-Ne laser:

632.8 nm, 5 mw power BPF:

isolate the 632.8 nm line prior to sample excitation

Signal collection optical module:

collect SERS signal at 1800 w.r.to propagation of incident laser beam

Include Raman holographic filter: Rejects the Rayleigh scattered radiation before it enters the collection fiber


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Collection fiber is coupled to a spectrograph:

Contain red- enhanced intencified CCD (RE-ICCD)

detection system

Signal collection module can be directly coupled to

spectrograph,bypassing the optical fiber


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Imaging of the entire 2-D hybridization array

plate

Reduce analysis time

Precludes the need for platform scanning

Accomplished through multispectral imaging (MSI)


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Modes of imaging and spectroscopy and their

combination for multispectral imaging

IMAGING:

Intensity is recorded for every pixel at one single

wavelength


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SPECTROSCOPY:

Intensity is recorded for a single spot at multiple

wavelengths


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MULTISPECTRAL IMAGING:

Intensity is recorded at multiple wavelengths for

every pixel


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Instrumental system for 2-D multispectral

imaging of a SERS gene array platform


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Expanded, collimated laser beam is used to stimulate a0.5 cm dia region of the assay array platform

Krypton ion laser,25 to 50 mw

AOTF: tunable wavelength selection with image preserving

capability

450-700 nm

Spectral resolution of 2 A0

diffraction efficiency- 70%

Tunable RF signal is applied for wavelength tuning


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BPF:

Isolate 647.1 nm line of laser

Spatial filter /beam expansion module:

Expand and collimate laser beam

Imaging optical module:

Is a microscope

Collect and project the image of through an AOTF to a CCD

camera

Holographic notch filter:

Infront ofCCD detector for rejecting laser Rayleigh scatter


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Reference

Biomedical photonics Handbook, Tuan Vo-Dinh

SurfaceEnhanced Raman Scattering ((SERS)) Gene

probes forMedical Diagnostics,Vo-Dinh

Laboratory,Fitzpatrick Institute for Photonics, Duke

University, Durham,NorthCarolina, USA

SERS in Bio Medical Diagnostics

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