Nanoparticles have a surprisingly long history.
Proteins, polysaccharides, viruses among others are the organic nanoparticles
occurring naturally whereas iron oxyhydroxides, metals are examples of
inorganic nanoparticles. The inorganic nanoparticles are produced due to
weathering, volcanic eruptions or microbial
processes. This is how we know that
nanoparticles have been existing in nature for a
long time and not just produced in the
laboratories by modern synthesis Heiligtag F.C. and
Niederberger M., 2013.
Its history dates back to the 9th Century
in Mesopotamia, the artisans used nanoparticles to
generate a glittery effect on the surface of pots.
This lustre over pots was due to a metallic
film that was placed over its surface. This lustre
is seen due to the presence of silver and
copper nanoparticles present in the film. The
nanoparticles were made by adding cooper and
silver salts and oxides together with vinegar, ochre
and clay on the surface of the pot Dr.
Mandal A., 2014.
In nature variety of nanomaterials are synthesised
naturally by biological processes.
R. Nithya and R. Ragunathan, 2009.
Presently, microorganisms have acquired metabolic
and genetic changes such that they have
developed resistance against the drugs that are used
for the treatment of common infectious
diseases. These drug resistant microbes are more pathogenic
and are proved to be fatal
resulting in high mortality rate. This pose a great
challenge in pharmaceutical and healthcare
industry. Thus, providing a need for development of
alternative and novel drugs Kumar G.,
et al., 2011. Recent studies have shown that metal
oxide nanoparticles have good, broad
target range antimicrobial activity and microbes are
less prone to develop resistance against
these nanoparticles as they do in case of
conventional narrow target range antibiotics R.
Nithya and R. Ragunathan, 2009. This is because
mode of action of nanoparticles is by
direct contact with the bacterial cell wall, and
hence is not required to penetrate the cells
thereby causing modification in the cell components
Beyth N., et al., 2015.
A nanoparticle is a microscopic particle whose size
varies from 1-100 nm (nanometer). It is
also called as a nanopowder or nanocluster.
Nanoparticles inculcate completely new or
enhanced properties based on its characteristic
size-distribution and morphology of the
particles Vidya C., et al., 2013. They are often
referred to as clusters, nanospheres,
nanorods and nanocups ranging in size from 1 to
100nm, Rupiasih N.N., et al., 2013
crystalline or amorphous in nature Zia M., et al., 2016.
The term “nano” is derived from
Greek word synonymous to dwarf (meaning extremely
small). Bionanotechnology has
emerged as an integration between biotechnology and
nanotechnology which is employed
with use of biosynthetic and environmental-friendly
technology for synthesis of
nanoparticles. Sivakumar J., et al., 2011. The
optical and electronic properties of
nanoparticles depends on the size and shape of the
particle R. Nithya and R. Ragunathan,
The use of metallic nanoparticles are most
encouraging as they show good antimicrobial
properties because of their large surface area to
volume ratio Sivakumar J., et al., 2011. UV/
Visual/ IR spectroscopy are used for identifying,
characterizing, and studying nanoparticles
due to its optical properties that are sensitive to
size, shape, concentration, agglomeration
state, and refractive index near the nanoparticle
surface. Nanoparticles made from metals
such as gold and silver, strongly interact with
specific wavelengths of light and the unique
optical properties of these materials is the
foundation for the field of plasmonics.
1.3.1. ANTIOXIDANT PROPERTY
Free radical derivatives of oxygen also called as
reactive oxygen species (ROS) are highly
reactive oxygen containing molecules such as singlet
oxygen, superoxide, peroxyl, radicals,
hydroxyl radicals, nitric oxide radical and
hypochlorite radical. These free radicals maybe
produced by physiological, biochemical process or by
pollutions and other endogenous
sources P. Jayanthi and P. Lalitha, 2011. These
radicals are continuously produced in the
human body, but overproduction of these radicals
causes an imbalance between ROS
production and antioxidant defence termed as
“oxidative stress” Ansari A.Q., et al., 2013.
This imbalance deregulates the cellular function and
causes chronic human diseases like
diabetes mellitus, cancer, atherosclerosis,
arthritis, and neurodegenerative diseases. Fayaz
P.P and Ramachandran H.D., 2014. Antioxidants
prevents this damage caused by ROS
imbalance by neutralizing the free radicals by its
free radical scavenging activity. Plants are
rich source of antioxidants as they contain free
radical scavenging molecules such as vitamins, terpenoids, phenolic acids,
lignins, stilbenes, tannins, flavanoids, quinones,
coumarins, alkaloids, amines, betalains etc. P.
Jayanthi and P. Lalitha, 2011. Synthesis of
metal nanoparticles uses this antioxidant property
where biomolecules (e.g., enzymes,
proteins, amino acids, vitamins, polysaccharides,
and organic acids such as citrates) from
plant extract are reduced Barman G., et al., 2013.
Types of nanoparticles are broad divided in two
Organic nanoparticles: these are polymeric
nanoparticles which kill microorganisms either by
releasing antibiotics, antimicrobial peptides or by
contact with cationic surface such as
quaternary ammonium compounds, alkyl pyridiniums or
Inorganic nanoparticles: this include metal and
metal oxide nanoparticles.
Silver- they are widely used metal nanoparticles and
are effective antimicrobial agent against
bacteria, fungi and viruses. They are photolytic and
can induce ROS. They show antibacterial
action on both gram positive and gram negative
bacteria Beyth N., et al., 2015. Exposure to
silver have risk of causing agyrosis and argyria
Sivakumar J., et al., 2011.
Iron oxide and gold Hasan S., 2015.
Magnesium oxide ,Supraparamagnetic iron oxide,Nitric
Aluminium oxide Beyth N., et al., 2015.
1.5. MODE OF
Bacterial membrane is made up of sulphur containing
proteins, nanoparticles get attached to
this cell membrane. Some also penetrate inside the bacteria
and form low molecular weight
region in the center of the bacteria thus protecting
the DNA from the silver ions.
Nanoparticles release silver ions in the bacterial
cell which enhances the bactericidal activity
and causes cell death. The reactivity of
nanoparticles is increased by the electronic effect
which is produced by interaction of smaller
nanoparticles (smaller than 10nm) with the
bacterial cells. Therefore, bactericidal effect of
silver nanoparticles is size dependent
Sivakumar J., et al., 2011.
Synthesis of nanparticles can be carried out by
various physical and chemical methods such
as (i) coprecipitation; (ii) sol-gel processing;
(iii) hydrothermal/solvothermal; (iv) microwave
synthesis; (v) sonochemical synthesis; (vi) inert
gas condensation; (vii) pulsed laser ablation;
(viii) spark discharge generation; (ix) micro
emulsions chemical vapour synthesis; (x)
thermal plasma synthesis; (xi) laser pyrolysis/
photochemical synthesis; (xii) spray pyrolysis;
and (xiii) flame spray pyrolysis. However,
limitations coming across while using these
processes are synthesising nanoparticles using these
methods are expensive and can have
toxic substances absorbed onto them. Therefore,
there is a growing need for development of
eco-friendly and economical procedures for synthesis
of nanoparticles. This can be achieved
by using biological methods for the synthesis of
nanoparticles. This method includes the use
of all life forms such as bacteria, fungi and plants
for biosynthesis of nanoparticles by direct
reduction of ions present Zia M., et al., 2016.