The critical parameters for evaluating nanoparticle formulations include particle size, shape, zeta potential, polydispersity index, pH, aggregation, drug content, and solvent levels. Dynamic light scattering measures hydrodynamic diameter to assess size, while transmission electron microscopy and atomic force microscopy directly image particles for size, shape, and surface characteristics. Zeta potential indicates stability, and differential scanning calorimetry analyzes phase transitions by measuring enthalpy changes with temperature. Together, these techniques set quality standards and predict in vivo performance of nanoparticle drugs.

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.
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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
Journal of Biomedical Nanotechnology. 1 (2005) 235-258
Nanomedicine: Nanotechnology, Biology and Medicine 2(2006) 127-136

2. Dynamic light scattering
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3. Basic principle
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
(Movie courtesy of Dr. Eric R. Weeks,
Physics Department, Emory University.)
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4. 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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5. Transmission Electron Microscopy
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6. Basic principle
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.
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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.

8. Atomic Force Microscopy
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9. Basic principle
A Changes In particular AFM, in a the probe operating tip consisting specimen parameter interaction of a sharp is maintained tip(~ are often 10 at nm) monitored a constant located using near level the an & images
optical
end of
are a lever cantilever generated detection beam through system, is raster a in feedback which scanned a laser loop across is between reflected the surface the off optical the of cantilever a detection specimen & system
onto using
a
position-piezoelectric & the piezoelectric sensitive scanners.
photodiode.
scanners.
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10. 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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11. 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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12. SEM and AFM images
Fig. SEM &AFM images of Cu Nanowires
R. Adelung et al.
Courtesy of F. Ernst
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13. ζ-potential
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.

14. 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 (ΔH).

15. DIFFERENTIAL SCANNING CALORIMETRY (DSC)