What within the Nano capsules or coated onto

What is Nano-characterization? Discuss the purpose of
microscopic analysis of soil.

 

Characterization
of nanoparticles is based on the size, morphology and surface charge, using
such advanced microscopic techniques as atomic force microscopy (AFM), scanning
electron microscopy (SEM) and transmission electron microscopy (TEM).
Properties such as the size distribution, average particle diameter, charge
affect the physical stability and the in vivo distribution of the
nanoparticles. Properties like surface morphology, size and overall shape are
determined by electron microscopy techniques. Features like physical stability
and redispersibility of the polymer dispersion as well as their in vivo performance
are affected by the surface charge of the nanoparticles. Different
characterization tools and methods for nanoparticles are mentioned in Table.
Therefore, it’s very important to evaluate the surface charge during
characterization of nanoparticles.

 

·        
Surface charge

 

Surface charge and intensity
determines the interaction of nanoparticles with the biological environment as
well as their electrostatic interaction with bioactive compounds. Stability of
colloidal material is usually analysed through zeta potential of nanoparticles.
Zeta potential is an indirect measure of the surface charge. It can be obtained
by evaluating the potential difference between the outer Helmholtz plane and
the surface of shear. Thus, zeta potential of colloidal based dispersion
assists in directly evaluating its storage stability. Zeta potential values
(high zeta potential values, either positive or negative) are achieved to
ensure stability and avoid aggregation of the particles. Zeta potential values
can be utilized in evaluating surface hydrophobicity and the nature of material
encapsulated within the Nano capsules or coated onto the surface.

 

 

The
purpose of microscopic analysis of soil is to characterize it according to its
properties. And for the characterization following microscopic technologies are
use:

 

1.      Photon-Correlation
Spectroscopy (PCS) or Dynamic Light Scattering (DLS)

 

The fastest and most popular techniques
like photon-correlation spectroscopy (PCS) or dynamic light scattering (DLS),
widely used to determine the size of Brownian nanoparticles in colloidal
suspensions in the Nano and submicron ranges. In this technique solution of
spherical particles in Brownian motion causes a Doppler shift when they = are
exposed against shining monochromatic light (laser). Such monochromatic light
exposure hits the moving particle which results in changing the wavelength of the incoming light. Extent of this
change in wavelength determines the size of
the particle. This parameter assists in evaluation of the size distribution, particle’s motion in the medium, which may
further assist in measuring the diffusion
coefficient of the particle and using the autocorrelation function. Dynamic light scattering (DLS) offer the most frequently
used technique for accurate estimation of the
particle size and size distribution.

 

2.     
Scanning Electron Microscopy
(SEM)

 

This electron microscopy based
technique determines the size, shape and surface morphology with direct
visualization of the nanoparticles. Therefore, scanning electron microscopy
offer several advantages in morphological and sizing analysis. However, they
provide limited information about the size distribution and true population
average. During the process of SEM characterization, solution of nanoparticles
should be initially converted into a dry powder. This dry powder is then
further mounted on a sample holder followed by coating with a conductive metal
(e.g. gold) using a sputter coater. Whole sample is then analysed by scanning
with a focused fine beam of electrons. Secondary electrons emitted from the
sample surface determine the surface characteristics of the sample. This
electron beam can often damage the polymer of the nanoparticles which must be
able to withstand vacuum. Average mean size evaluated by SEM is comparable with
results obtained by dynamic light scattering. In addition, these techniques are
time consuming, costly and frequently need complementary information about
sizing distribution.

 

3.     
Transmission Electron
Microscope

 

Experimental difficulties in
studying nanostructures stem from their small size, which limits the use of
traditional techniques for measuring their physical properties. Transmission
electron microscopy techniques can provide imaging, diffraction and
spectroscopic information, either simultaneously or in a serial manner, of the specimen
with an atomic or a sub-nanometre spatial resolution. TEM operates on different
principle than SEM, yet it often brings same type of data. The sample preparation
for TEM is complex and time consuming because of its requirement to be ultra-thin
for the electron transmittance. High-resolution TEM imaging, when combined with
Nano diffraction, atomic resolution electron energy-loss spectroscopy and nanometre
resolution X-ray energy dispersive spectroscopy techniques, is critical to the
fundamental studies of importance to nanoscience and nanotechnology. During the
TEM characterization nanoparticles dispersion is deposited onto support grids
or films. After dispersion, they are fixed using either a negative staining material
(phosphotungstic acid or derivatives, uranyl acetate, etc., or by plastic embedding).
This is done to make nanoparticles withstand against the instrument vacuum and
facilitate handling. Alternatively, nanoparticles sample can also be exposing
to liquid nitrogen temperatures after embedding in vitreous ice. When a beam of
electrons is transmitted through an ultra-thin sample it interacts with the sample
as it passes through the surface characteristics of the sample are obtained.
TEM imaging mode has certain benefits compared with the broad-beam illumination
mode:

 

• Collection of the
information about the specimen using a high angular annular dark field (HAADF)
detector (in which the images registered have different levels of contrast related
to the chemical composition of the sample)

• It can be utilized for the
analysis of biological samples is its contrast for thick stained sections,
since high angular annular dark field images (samples with thickness of 100–120
nm) have better contrast than those obtained by other techniques.

• Combining HAADF-TEM imaging
leads to imaging the atomistic structure and composition of nanostructures at a
sub-angstrom resolution.

• Availability of sub-nanometre
or sub-angstrom electron probes in a TEM instrument, due to the use of a field
emission gun and aberration correctors, ensures the greatest capabilities for
studies of sizes, shapes, defects, crystal and surface structures, and
compositions and electronic states of nanometre-size regions of thin films,
nanoparticles and nanoparticle systems.

 

 

 

4.     
Atomic Force Microscopy

 

This technique is also known
as scanning force microscopy (technique that forms images of surfaces using a probe
that scans the specimen), very high-resolution type of scanning probe
microscopy, with reported resolution on the order of fractions of a nanometre,
more than 100 times better than the optical diffraction limit. The atomic force
microscopy is based on a physical scanning of samples at sub-micron level using
a probe tip of atomic scale and offers ultra-high resolution in particle size
measurement. Depending upon properties, samples are usually scanned in contact
or noncontact mode. During contact mode, the topographical map is generated by
tapping the probe on to the surface across the sample and probe hovers over the
conducting surface in non-contact mode. One of the prime advantage of AFM is its
ability to image non-conducting samples without any specific treatment. This feature
allows the imaging of delicate biological and polymeric Nano and
microstructures. Moreover AFM (without any mathematical calculation) provides the
most accurate description of size, size distribution and real picture which
helps in understanding the effect of various biological conditions.

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