Prof.P. Ravindran, -...
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P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
http://folk.uio.no/ravi/cutn/NMNT2016
Prof.P. Ravindran, Department of Physics, Central University of Tamil
Nadu, India
&Center for Materials Science and Nanotechnology,
University of Oslo, Norway
Importance of Nanoparticle distribution –
selection, assembly, measurements
1
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
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Disperse systems
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
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Pharmaceutical Suspension-Definition
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
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Particle Measurements
Nanoparticle General Sampling Practices Look at outdoor concentrations for sources and variability Ventilation system plays a role – Evaluate the effect Background / baseline measurementsMass Measurements - Background
Traditional workplace exposure limits are mass based– No regulations currently exist specifically for nanoparticles
Mass of one 10 µm particle= 106 times the mass of one 100 nm particle= 109 times the mass of one 10 nm particle
Traditional gravimetric methods are not effective for nanoparticles since toxicity data is based on large particles
It takes ~1,000,000,000 (1 billion) 10 nm particles to equal the mass of one 10 µm particle!
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
If the particles or molecules are illuminated with a laser, the
intensity of the scattered light fluctuates at a rate that is
dependent upon the size of the particles
Analysis of these intensity fluctuations yields the velocity of the
Brownian motion and hence the particle size using the Stokes-
Einstein relationship.
Principle of Measurement
Measurement of the particles size by the PCS technique
Particles, emulsions and molecules in suspension undergo Brownian motion.
This is the motion induced by the bombardment by solvent molecules that
themselves are moving due to their thermal energy
Temperature and viscosity must be known
PCS – Photon correlation spectrascopy
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
The velocity of the Brownian motion is defined by a property known
as the translational diffusion coefficient (usually given the symbol,
D).
Stokes-Einstein relationship
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
No spherical particles
Hydrodynamic diameter is calculated based on the equivalent
sphere with the same diffusion coefficient
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Zetasizer Nano ZS
Malvern
He-Ne Laser
= 633 nm
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Brownian motion and scattering
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Intensity of the scattered light fluctuates
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Intensity of the scattered light fluctuates
Small particles- noisy curve
Large particles- smooth curve
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Determining particle size
Determined autocorrelation function
Depend
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Correlation function Correlograms
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Correlogram from a
sample containing large
particles
Correlogram from a
sample containing small
particles
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Data interpretation - Correlograms
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Low
concentration turbidity is linear with
concentration
High
concentration Particles are so close together
that the scattered radiation is
re-scattered by other particles.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Optical arrangement in
173°
backscatter detection
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Information
Size by:
- Intensity I d6
Rayleigh Scattering
(For nanoparticles less than d =λ/10 or around 60nm
the scattering will be equal in all
Directions-isotropic)
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
This particles will scatter 106 (one million) times
more light than the small particle (8 nm)
The contribution to the total light scattered by
the small particles will be extremely small
8 nm80 nm
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
8 80
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
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Volum
e
d3
d1- Number
V= 4r3
r = d/2
V= 4(d/2)3 = 4d3
8
By the Mie theory it is possible to convert
intensity distribution into volume
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Two population of spherical nanoparticles :
5 nm and 50 nm
(in equal number)
Which of these distributions should I use?
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
1. Size determination: PSD for particles (GSD, Grain Size Det., for polycrystalline materials)
2. Surface Specific Area, SSA
3. Z potential, hydrodynamic radius and electrophoretic mobility
4. Surface and 3D imaging, lattice properties
Step by step
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
1. PSD, Particle Size Distribution
Photon Correlation Spectroscopy.
Fluctuations of the light scattered from dispersed objects in
suspension are due to Brownian motion and are proportional to
the size of these objects.
Smaller particles move faster, causing a rapid decay of
scattering
This method of measurement is standardised according to ISO
13320-1.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Dynamic Scatter Light:
In the exemple the powder contains 50% of nanparticles
sized 5 nm and 50% of their aggregates, sized 50nm. The
number and the volume of particles, and the intensity of the
scattered light are shown.
Note that for particles of larger size the intensity is greater:
in fact, smaller particles move faster, causing a rapid decay
of scattering.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
2. SSA, Specific Surface Area
The specific surface area, or the total surface area per gram of material,
is one of the main properties characterizing nanomaterials, in which it is
very larger than in bulk materials.
Measurement
The material is inserted in a closed container, under
nitrogen. The gas adsorption to the surface causes a drop of
the pressure of nitrogen proportional to the surface Area
(B.E.T. method).
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
3a. Z potential and hydrodynamic radius
An electrical double layer sorrounds charged particles in liquid
suspensions. Around them, two regions differentiate: one (the
lighter layer) where charges are diffuse, another (darker) where
the charges are stricly bonds (Stern layer).
It moves together with the atoms forming the sorrounded sphere and
represents the hydro-dynamic radius.
The electric potential at the boundary between Stern and diffuse radius
is called Z potential.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Measuring the Z potential.
A laser beam passes through a cell containing the
nanoparticles suspension.
When an electric field is applied to the cell, the charged
particles moves.
When interfering with the laser beam, they cause the
laser intensity fluctuate: the recorded signal is
proportional to the particle speed.
Decrease in Z potential is followed by dramatical
aggregation of nanoparticles, big aggregates does not
move in the beam light.
A scheme of the apparatus follows.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
1) laser; 2) attenuator; 3) cell; 4) compensation optics;
5) computer
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
3b. Electrophoretical mobility.
Uε = 2 ε ζ f (k a) / 3 η
The Henry’s equation for measuring the electrophoretical mobility
(Uε) includes the following variables:
ε: dielectric constant
ζ : Z potential
η: viscosity
F (k a) : Henry’s function
Environmental variables, as pH, concentration of ions and of
sufractant-acting molecules, including polymers and organics, affects
the Z potential.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
SEM: Scanning Electron Microscope;
SPM: Scanning Probe Microscop; AFM:
Atomic Force Microscope.
The grey box displays the dimensional
range of nanomaterials.
1. Dimensional Nanometrology
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
4a. TEM: Transmission Electron Microscopy
Basics: The electrons interacts with the ultra thin specimen and are
transmitted through that, than recorded, The image corresponding to
the transmitted electrons is magnified on a screen, a photographic
layer or another sensor.
The tomographic reconstruction provides 3D images, diffraction
methods give informations about the crystalline state of the
sample, and the cryo-vitrification shows the macromolecule
assemblies inside the sample.
Resolution: depth: 200nm, lateral resolution: 2-20nm.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
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TEM: scheme
http://www.nobelprize.org/educational/physics/microscopes/tem/index.html
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
4b. SEM: Scanning Electron Microscopy
Basics: SEM uses a high-energy beam of electrons. The beam
is condensed and directed at the sample surface. The
interactions occurring during the scanning are recorded.
Resolution: depth: 1nm-5μm, lateral
resolution: 1-20nm.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
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SEM: Scheme
http://www-archive.mse.iastate.edu/microscopy/path2.html
SEM image of Co3O4 nanoparticles in cluster
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
4c. AFM: Atomic Force Microscopy
Basics: The tip of a probe (cantilever) is slowly scanned
across the surface. A laser beam, focused on the
cantilever, records on a photodetector the deflection of
the cantilever, caused by the interaction of its atoms with
those on the sample surface.
Resolution: depth: 0.5nm-5nm; lateral resolution: 0.2-
130 nm.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
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AFM: Scheme
AFM image of Co3O4 nanoparticles
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
AFM techniques and applications
Contact Mode (CM): The signal is the movement of the tip, or the
adjustments needed to maintain the deflection constant. The stiffness
of the lever must be lower than the interatomic forces at the sample
surface (1 - 10 nN/nm). For topological recordings.
Lateral Force Microscopy (LFM): The twisting of the cantilever is a
function of the friction levels in different areas of the sample surface.
Force Modulation (FM): The tip (or the sample) is oscillated at a high
frequency and pushed into the repulsive regime. The slope of the
force-distance curve is correlated to the sample's surface elasticity.
Phase Imaging: The phase shift of the oscillating tip is related to
specific properties of the sample, such as friction, adhesion, and
viscoelasticity.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
4d. NMR: Nuclear Magnetic Resonance
Basics: NMR studies a magnetic nucleus by aligning it
with a very powerful external magnetic field and
perturbing this alignment using an electromagnetic field.
The relaxation spectra is a function of nuclear identity,
3D structure of macromolecules in solution or pore
dimensions.
Resolution: in the nm range.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
4e. SAXS: Small Angle X RayScattering
Basics: X ray is incident on to a sample and scattered electrons from the sample are analyzed
at very low angles.The lattice interplanar spacing of the crystal is a function of the wavelength and of the incidence
angle of the x-ray.
Resolution: between 1 nm and >200 nm.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
SAXS: Scheme
(http://pubs.usgs.gov/of/2001/of01-041/htmldocs/xrpd.htm)
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
SAXS: Scheme
BRAGG law:
2d(sinΘ) = λo
d = lattice interplanar spacing of the crystal
Θ = x-ray incidence angle (Bragg angle)
λ = wavelength of the characteristic x-ray
(http://pubs.usgs.gov/of/2001/of01-041/htmldocs/xrpd.htm)
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Two-dimensional small-angle X-ray scattering image.
Nanostructure of two styrene-
diene-styrene triblock
copolymers.
Left: a lamella-forming triblock
showing a biaxial texture (four-
spot pattern).
Right: a cylinder-forming
triblock showing a single-crystal
texture (six-spot pattern).
Images: Sasha Myers, http://www.princeton.edu/cbe/news/archive/
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
4f. SANS: Small Angle Neutron Scattering
Basics: A neutron source generates a collimated beam;
neutrons are scattered by the sample, placed in the
beam.
A position sensitive neutron detector detects scattered
neutrons with 0.05° ≤ 2θ ≤ 3°.
The scattered intensity is a function of position.
Resolution: between 0.5 nm and 500 nm.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
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SANS: Scheme
(http://www.ncnr.nist.gov/instruments/usans/)
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Manufacturing
Nanomaterial
manufacturing
TransportationTransportation
Nano- Intermediate
Manufacturing
Nano-enabled product
manufacturing
Transportation Use
End of life
TransportationDisposal
Sewage
Landfill
Life Cycle of Nanomaterials
From: L. Gibbs 2006
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Health, Safety, and Environmental Concerns Regarding NM
Human implications NM toxicity not yet well understood; nano-size materials do
not behave like their bulk counterparts
Reactivity of NM due to large surface area
Potential for bioaccumulation
Environmental implications Contamination of water and soil from improper disposal of
NM
Bio-uptake of NM and accumulation in food chain
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Nanotoxicology
Nanotoxicology – Science of engineered nanodevices and nanostructures that deals with their effects in living organisms (Oberdorster et al. 2005 )
Potential NM exposure routes include: Inhalation
Dermal contact
Ingestion
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Research Approaches to
Understand NM Toxicity
In vitro and in vivo approaches allow study of the mechanisms and biological effects of NM on cells and tissues under controlled conditions
In vivo models include: Inhalation chambers Intratracheal instillation Nose-only inhalation Pharyngeal aspiration
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Human Respiratory Tract
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Proximal Alveolar Region SWCNT Day 3
Silver-enhanced gold-labeled aggregate SWCNT, 40 ug aspiration,
perfusion fixed. Mercer - NIOSH
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Pharyngeal aspiration of 40ug SWCNT in C57BL/6 mice
Mercer - NIOSH
SWCNT Response 7 Days
SWCNT
Collagen
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Translocation/Bioaccumulation
of Nanomaterials
Nanoparticles can cross alveolar wall into bloodstream
Absence of alveolar macrophage response
Distribution of NM to other organs and tissues
Inhaled nanoparticles may reach brain through
olfactory nerve
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
In Vitro NM Studies
Monteiro-Riviere et al. 2006 - Isolated porcine skin flap model and HEK
– MWCNT, substituted fullerenes, and QD can penetrate intact skin
– Cytotoxic and inflammatory responses
Tinkle et al. 2003 - Human skin flexion studies and beryllium exposures
– Penetration of dermis with 0.5μm an 1μm fluorescent beads
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
In Vitro NM Studies
Fullerenes can interact with cell membranes and specifically with membrane lipids (Isakovic et al. 2006; Sayes et al. 2004; 2005; Kamat et al. 2000).
Interactions can produce lipid peroxidation and leaky cell membranes that result in the release of cellular enzymes.
Proposed mechanism of damage is that fullerenes generate superoxide anions
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Functionalization of NM
Different chemical groups added to the
surface of CNT changed CNT properties
and decreased their toxicity (Sayes et al.
2006)
Addition of water-soluble functional groups
can decrease the toxicity of pristine C60
(Sayes et al. 2004)
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Ingestion Pathway
Ingestion exposures can occur through direct
intake of food or materials containing NM
and secondary to inhalation or dermal
exposures
Some evidence suggests that ingested NM
may pass through to lymphatics
Little research to date about Ingestion
exposures and the potential for distribution
of NM to other tissues.
Workplace Studies
From Maynard 2005
Handling Raw
SWCNT
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Workplace Studies
Maynard and coworkers (2004) determined
that aerosol concentrations of NM during
handling of unrefined NM material were low
More energetic processes likely needed to
increase airborne concentrations of NM
Gloves were contaminated with NM
Results indicated importance of dermal contact
as potential exposure route Handling Raw SWCNT
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Environmental Risk Concerns
Regarding NM
What happens to NM after product use and disposal?
What is the fate of NM in the environment?
Do NM degrade?
Will NM accumulate in the food chain?
How to evaluate real world exposures to NM?
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
NM and Ecotoxicology
Exposures of largemouth bass to fullerenes
for 48 hr produced lipid damage in brain
tissues (E Oberdorster 2004)
Exposures of Daphnia to uncoated, water
soluble fullerenes for 48 hr indicated an LC50
of 800 ppb (E Oberdorster 2004)
Daphnia –water flea
Largemouth bass
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Physicochemical Properties
ChemicalsStructure
pKa
Solubility
log P
3-D Molecular Structure
3-D Crystal Structure
Illustrations reproduced with permission from
Herr’s Carbon Fullerene Gallery
http://www.vincentherr.com/cf/nanomain.html
NanomaterialsChemical Structure
Core Particle Composition
Size
Shape
Charge
Surface Chemistry
Surface Area
Agglomeration State
Zeta Potential
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Diversity of Zinc Oxide NanoparticlesPhotos adapted: Dr. Z Wang, Georgia Tech
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Size Dependent Bandgap in Quantum Dots
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Size Dependent Bandgap in Quantum Dots
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
SIZE DEPENDENT OPTICAL ABSORPTION SPECTRA OF CAPPED CdSe
NANOCLUSTERS, SYNTHESIS AND CHARACTERIZATION OF NEARLY
MONODISPERSE CdE (E = S, Se, Te) SEMICONDUCTOR
NANOCRYSTALLITES, MURRAY CB, NORRIS DJ, BAWENDI MG, JOURNAL
OF THE AMERICAN CHEMICAL SOCIETY 115 (19): 8706-8715 SEP 22 1993)
Size Dependent Bandgap in Quantum Dots
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
SIZE AND COMPOSITION DEPENDENCE OF THE OPTICAL EMISSION
SPECTRA OF CAPPED InAs (RED), InP (GREEN) AND CdSe (BLUE), BRUCHEZ,
M.JR; MORONNE, M.; GIN, P.; WEISS, S.; ALIVISATOS, A.P.
SEMICONDUCTOR NANOCRYSTALS AS FLUORESCENT BIOLOGICAL
LABELS, SCIENCE 1998, 281, 2013
Size Dependent Bandgap in Quantum Dots
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
GOLD ATOMIC
DISCRETE STATES
GOLD CLUSTER
DISCRETE MOLECULE
STATES
GOLD QUANTUM DOT
CARRIER SPATIAL AND
QUANTUM
CONFINEMENT
GOLD COLLOIDAL
PARTICLE SURFACE
PLASMON – 1850
MICHAEL FARADAY
ROYAL INSTITUTION
GB PIONEER OF
NANO!!!
BULK GOLD PLASMON
Size dependence of Plasmonics – Metal Nano particles
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Plasmonics Basics – Size Effects
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Plasmonics Basics – Size Effects
What is surface plasmon resonance of gold nanostructures?. On the top left corner is shown how the electron cloud of free-electrons in the gold respond to an oscillating electromagnetic field, depending on the shape and orientation of the particle. The formation of a dipole causes the emergence of a resonance at a specific wavelength, as shown on the right by the representative absorbance spectra. In the case of spherical particles the plasmon resonance occur at a single frequency, while for elongated nanocrystals you can have two resonance frequencies related with the two dipole oscillation modes (longitudinal or transverse).
In the bottom part of the Figure is shown the origin of the absorbance features according to the Mie theory. The absorbance A is expressed as the product of two terms. The first term is scattering-related and has a 1/l dependence, while the second term is exclusively dependent on the dielectric constants of the metal and the surrounding medium. This last term represent the resonant plasmon mode which is shown as a peak centered at the surface plasmon resonance wavelength lSPR. The product of the two terms is the spectrum observed experimentally.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Extinction coefficient from Mie theory is the exact solution to Maxwell’s electromagnetic field equations for a plane wave interacting with a homogenous sphere of radius R with the same dielectric constant as bulk metal (scattering and absorption contributions).
em is the dielectric constant of the surrounding medium – sensitive to environment
e = e1 + ie2 is the complex dielectric constant of the particle
Resonance peak occurs whenever the condition e1 = -2em is satisfied – sensitive to change in em of environment hence use as a surface plasmon sensor
This is the SPR peak which accounts for the brilliant colors of various metal nanoparticles – form factors can be introduced to account for non-spherical shape – Gansmodification of Mie theory.
SURFACE PLASMON RESONANCE MIE THEORY
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Extinction spectra calculated using Mie theory for gold
nanospheres with diameters varying from 5 nm to 100 nm.
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Detecting Biomolecules with Gold Nanocrystals
Self Assembly and Plasmon Coupling
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
Detecting Biomolecules with Gold NanocrystalsSelf Assembly and Plasmon Coupling
The coupling of plasmons can be used for the detection of oligonucleotides in solution. Gold nanocrystals can be produced with thiol-functionalized oligonucleotides bound to their surface – a construct which we call the probe. The oligonucleotides on the nanocrystals are synthesized to be complementary to the ones one wants to detect. The ultraspecific binding of oligonucleotides for their complementary strand allows the particles to bind very efficiently to the analytes in solution. Such binding of two nanocrystals to the same analyte brings the nanocrystals very close together thus enabling the coupling of the plasmons.
As shown in the diagram below, once the nanocrystals are close the dipole can extend over the ensemble of the two nanocrystals (as in resonance r2) while for single isolated particle the dipole is confined to the particle itself (resonance r1). The simultaneous presence of r1 and r2 resonances leads to an effective red shift of the absorbance peak of the nanocrystals thus changing their color, as shown in the photos thereby enabling detection of a specific oligonucleotide which shows complementary Watson-Crick base pairing.