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
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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
2
Disperse systems
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
3
Pharmaceutical Suspension-Definition
P.Ravindran, Nanomaterials and Nanotechnology, Spring 2016: Importance of Nanoparticle distribution – selection, assembly, measurements
4
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
-
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
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.