Prof.P. Ravindran, -...

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

Disperse systems

Pharmaceutical Suspension-Definition

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!

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

The velocity of the Brownian motion is defined by a property known

as the translational diffusion coefficient (usually given the symbol,

Stokes-Einstein relationship

No spherical particles

Hydrodynamic diameter is calculated based on the equivalent

sphere with the same diffusion coefficient

Zetasizer Nano ZS

Malvern

He-Ne Laser

= 633 nm

Brownian motion and scattering

Intensity of the scattered light fluctuates

Small particles- noisy curve

Large particles- smooth curve

Determining particle size

Determined autocorrelation function

Depend

Correlation function Correlograms

Correlogram from a

sample containing large

particles

Correlogram from a

sample containing small

particles

Data interpretation - Correlograms

concentration turbidity is linear with

concentration

concentration Particles are so close together

that the scattered radiation is

re-scattered by other particles.

Optical arrangement in

backscatter detection

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)

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

d1- Number

V= 4r3

r = d/2

V= 4(d/2)3 = 4d3

By the Mie theory it is possible to convert

intensity distribution into volume

Two population of spherical nanoparticles :

5 nm and 50 nm

(in equal number)

Which of these distributions should I use?

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

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.

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.

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).

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.

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.

1) laser; 2) attenuator; 3) cell; 4) compensation optics;

5) computer

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.

SEM: Scanning Electron Microscope;

SPM: Scanning Probe Microscop; AFM:

Atomic Force Microscope.

The grey box displays the dimensional

range of nanomaterials.

1. Dimensional Nanometrology

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.

TEM: scheme

http://www.nobelprize.org/educational/physics/microscopes/tem/index.html

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.

SEM: Scheme

http://www-archive.mse.iastate.edu/microscopy/path2.html

SEM image of Co3O4 nanoparticles in cluster

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.

AFM: Scheme

AFM image of Co3O4 nanoparticles

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.

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.

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.

SAXS: Scheme

(http://pubs.usgs.gov/of/2001/of01-041/htmldocs/xrpd.htm)

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)

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/

4f. SANS: Small Angle Neutron Scattering

Basics: A neutron source generates a collimated beam;

neutrons are scattered by the sample, placed in the

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.

SANS: Scheme

(http://www.ncnr.nist.gov/instruments/usans/)

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

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

Bio-uptake of NM and accumulation in food chain

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

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

Human Respiratory Tract

Proximal Alveolar Region SWCNT Day 3

Silver-enhanced gold-labeled aggregate SWCNT, 40 ug aspiration,

perfusion fixed. Mercer - NIOSH

Pharyngeal aspiration of 40ug SWCNT in C57BL/6 mice

Mercer - NIOSH

SWCNT Response 7 Days

Collagen

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

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

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

Functionalization of NM

Different chemical groups added to the

surface of CNT changed CNT properties

and decreased their toxicity (Sayes et al.

Addition of water-soluble functional groups

can decrease the toxicity of pristine C60

(Sayes et al. 2004)

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

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

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?

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

Physicochemical Properties

ChemicalsStructure

Solubility

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

Charge

Surface Chemistry

Surface Area

Agglomeration State

Zeta Potential

Diversity of Zinc Oxide NanoparticlesPhotos adapted: Dr. Z Wang, Georgia Tech

Size Dependent Bandgap in Quantum Dots

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 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

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

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.

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

Extinction spectra calculated using Mie theory for gold

nanospheres with diameters varying from 5 nm to 100 nm.

Detecting Biomolecules with Gold Nanocrystals

Self Assembly and Plasmon Coupling

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.

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