1

The critical parameters of a nanoparticulate formulation to set and monitor

quality standards have to be based on simplicity (for routine analysis),

reliability and correlation to the in vivo performance.

Journal of Biomedical Nanotechnology. 1 (2005) 235-258

Nanomedicine: Nanotechnology, Biology and Medicine 2(2006) 127-136

o Particle size, shape

o Zeta potential

o Polydispersity Index

o pH of the suspension

o Aggregation

o Assay of the incorporated drug

o Maximum allowable limit of solvents

Dynamic light scattering

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Particles, emulsions & molecules in suspension undergo Brownian motion.

If the particles are illuminated with laser, the intensity of scattered light

fluctuates.

Analysis of these intensity fluctuations yields the particle size(radius, rk) using

Stokes- Einstein relationship,

rk =kT/6πηD where k = Boltzmann’s constant

T = Temperature

η = Viscosity

D = Diffusion coefficient

Basic principle

(Movie courtesy of Dr. Eric R. Weeks,

Physics Department, Emory University.)

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What does Dynamic Light Scattering

measure?

The diameter measured in DLS is called the hydrodynamic diameter and refers to how a

particle diffuses within a fluid. The diameter obtained by this technique is that of a sphere

that has the same diffusion coefficient as the particle being measured.

The diffusion coefficient will depend not only on the size of the particle “core”, but also on

any surface structure, as well as the concentration and type of ions in the medium.

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Transmission Electron Microscopy

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The crystalline sample interacts with the

electron beam mostly by diffraction rather

than by absorption.

The intensity of the diffraction depends on

the orientation of the planes of atoms in a

crystal relative to the electron beam.

A high contrast image can be formed by

blocking deflected electrons which produces

a variation in the electron intensity that

reveals information on the crystal structure.

This can generate both ‘bright or light field’

& ‘dark field’ images.

Basic principle

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TEM enables Direct 2-D imaging of particle size, shape & surface

characteristics.

Changes in nanoparticle structure as a result of interactions with gas,

liquid & solid-phase substrates can also be monitored.

Sample must be able to withstand the electron beam & also the high

vacuum chamber.

Time consuming.

It needs an analysis by image treatment & must be performed on a

statistically significant large no. of samples.

Atomic Force Microscopy

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Basic principle

In AFM, a probe consisting of a sharp tip(~ 10 nm) located near the end of

a cantilever beam is raster scanned across the surface of a specimen using

piezoelectric scanners.

Changes in the tip specimen interaction are often monitored using an opticallever detection system, in which a laser is reflected off the cantilever & onto aposition-sensitive photodiode.

A particular operating parameter is maintained at a constant level & imagesare generated through a feedback loop between the optical detection system& the piezoelectric scanners.

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Qualitative analysis

The AFM offers visualization in three dimensions. Resolution in the vertical,

or Z, axis is limited by the vibration environment of the instrument,

whereas resolution in the horizontal, or X-Y, axis is limited by the diameter

of tip utilized for scanning.

Typically, AFM instruments have vertical resolutions of less than 0.1 nm and

X-Y resolutions of around 1 nm.

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Quantitative analysis

For individual particles, size information (length, width, and height) and other

physical properties (such as morphology and surface texture) can be measured.

Figure: A wood particle scanned with an AFM to measure roughness. Paper products containing such

wood fibers can vary in quality based on the physical properties of the particulates.

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SEM and AFM images

Fig. SEM & AFM images of Cu Nanowires

R. Adelung et al.

Courtesy of F. Ernst

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Zeta potential is a scientific term for electrokinetic potential in colloidal

dispersions, is usually denoted ζ-potential. From a theoretical

viewpoint, the zeta potential is the electric potential in the interfacial

double layer (DL) at the location of the slipping plane relative to a point

in the bulk fluid away from the interface.

It is widely used for quantification of the magnitude of the charge. The

zeta potential is a key indicator of the stability of colloidal dispersions.

Zeta potential [mV] Stability

from 0 to ±5, Rapid coagulation or flocculation

from ±10 to ±30 Incipient instability

from ±30 to ±40 Moderate stability

from ±40 to ±60 Good stability

more than ±61 Excellent stability

Zeta potential is not measurable directly but it can be calculated using

theoretical models and an experimentally-determined electrophoretic

mobility or dynamic electrophoretic mobility.

ζ-potential

DSC: differential scanning calorimetry

Technique that allows to study the phase transition of lipids around the Melting

Temperature (Tm) by increasing the temperature of the sample and measuring the

entalpy (∆H).

DIFFERENTIAL SCANNING CALORIMETRY (DSC)