1. bio-synthetic methods for nanomaterials offers some important contribution

1.
Bio-synthetic nanoparticles
The
application of nanoscale materials structures in the range of 1 to 100nm is a
new up and
coming area of
nanoscience and nanotechnology. Nanomaterials provide different solutions to
technological and
environmental challenges in the field of solar energy conversion, catalysis,
biology, biomedical
science, and water treatment. Nanoparticles have a very high surface to
volume ratios. So,
due to this property nanoparticles can be utilized in various scientific
fields,
where large surface
area is required. For example, in mostly catalytic industry nanoparticles have
been confirmed
excellent catalysts 1.
There are quite a lot of physical and biochemical methods
for nanoparticles
synthesis but there is a lot of requirement to introduce bio-synthetic
processes
for nanoparticles
production due to their abnormal optical 2,
chemical 3, photoelectrochemical
4 and electronic 5 properties
.The synthesis and congregation of nanoparticles would be
beneficial for the
development of fresh, nontoxic and eco-friend environmentally acceptable
“green chemistry” most likely involving organisms like bacteria,
fungi and even plants 6, 7 .
Both unicellular and
multicellular organs are considered as well-known to manufacture inorganic
materials either
intra- or extracellular purposes. The Verticillium sp. fungal biomass when
exposed to aqueous
AgNO3 solution resulted in the intracellular formation
of silver nanoparticles,
while Fusarium
oxysporum biomass resulted in the extracellular silver nanoparticles 8.
The study of
bio-synthetic methods for nanomaterials offers some important contribution to
materials chemistry.
Microorganisms have gained more attention in biosynthesis of nanoparticles.
Earlier
investigations expose that the microbes have the ability to reduce Au3+ ions
to generate
octahedral gold
particles of nanoscale size (i.e., 5–25 nm) and is incubated with gold chloride
in
the bacterial cell
body under ambient temperature and pressure conditions 9, 11.
Micro-organisms
like yeast, bacteria
and even fungi plays important role in remedy of toxic metals by reduction of
metals. Thus
bio-synthetic processes are considered interesting in nanofactories 12.
The
following figure
shows different techniques and sources for nanocompounds synthesis.
2
Fig. 1 synthesis of
nanoparticles from different methods
1.1 Use of
micro-organism for nanoparticles synthesis
There
is a constant touch between biological entities and inorganic materials since
from the
beginning of life on
earth. Due to this usual relation, life could only sustain on earth with an
efficient deposition
of minerals. Now scientists turn into more and more concerned with the
interaction between
inorganic nanoparticles and biological species. Recently studies have
revealed that many
microorganisms can be used for the production of inorganic nanoparticles
either by
intracellular or by extracellular routes. Here, is summarizing some of the
organisms that
are used in the
biosynthesis of nanomaterials and describing some of their properties that
should
be innate for the
synthesis of nanoparticles of preferred characteristics.
1.2 Bacterial use for nanoparticles
synthesis
Pseudo.
Stutzeri AG259 extracted from silver supplies has been used for production of
Ag Nps.
13, 14 MTB (polyphyletic groups of bacteria) can be
used to synthesize magnetic nanoparticles 15.
Magnetotactic
bacteria such as “Gram- negative Magnetospiril. Magneticum” used to
manufacture two types
of particles; some generate magnetic iron (II III) oxide nanoparticles in
chains structure and
some construct iron (II III) sulphide nanoparticles, while some other
bacterial cell used
to produce both categories of Nps. In the same way sulphate-reducing bacteria
DS desulfuricans
NCIMB 8307, exogenous electron donor, has been found to synthesize
palladium
nanoparticles 16, 17. L. bacillus strains
present in buttermilk helps in the growth of
3
well-defined
morphological nanoparticles of Au, Ag, and Au-Ag alloy. Recently, bacterial
cell
such as Pseudo.
Aeruginosa was used for biosynthesis of gold nanoparticles via extracellular
route which can
reduce gold ions 18.The formation silver nanoparticles via
intracellular and
extracellular route
from bacteria (Esch. coli, Pseudo. stut. AG259, S. typhus V cholerae, Phoma
specie 3.2883,
Pseudo. Aerug., and Staphylo. aureus) have been demonstrated by reaction of
cells with silver (I)
nitrate (AgNO3) 19, 22.
The suggested mechanisms for the bio reduction of
silver by bacteria
involve (DNA) or sulfur-containing proteins 19.
Another achievement in better
control on size and
polydispersity of nanoparticles is by cell filtrate. Further, it has been
explained that by
using cell filtrate for extracellular synthesis of nanoparticles would be more
beneficial rather
than intracellular synthesis.
Another method to
control over the shape of gold nanoparticles synthesis has been developed by
utilizing Plect.
Bory. UTEX 485, a filamentous cyanobacterium. When they reacted with
aqueous soln. of Au
(S2O3)23- and
AuCl4- at temperature range from 25–100o C
for up to one
month and for a
single day at 200o C resulted in the formation of cubic gold
nanoparticles and
octahedral gold
platelets precipitates, respectively 23.
The mechanisms of gold bioassemilation
of cyanobacteria
(Plectonema boryanum UTEX 485) with gold (III) chloride solutions form
octahedral platelets.
This mechanism involves two steps, in the first cyano-bacteria interact with
aqueous gold(III)-chloride
to form precipitates of nanoparticles of amorphous gold(I)-sulfide at
the cell walls, and
finally in the other step deposited metallic gold octahedral (III) platelets
close
to cell surfaces and
in solutions24. Elemental gold can be produce by gold(I)-tiosulfate
by
enrichment of
sulfate-reducing bacteria and this mechanism may have three steps including
iron
sulfide, metabolism
and contained reducing conditions 25.
1.3 Actinomycetes
roll in nanoparticles formation
It
has been examined that when microbes i. e extremophilic actinomycete, Thermomo.
Specie
reacted with gold
ions, metal ions are reduced extracellularly, giving gold nanoparticles of
greatly better
polydispersity 26. However, in searching a mechanism or favourable
conditions
for the synthesis of
nanoparticles with desired characteristics, 27 a
reaction was carried out for
the reduction of AuCl4 ions
through extremophilic Thermomonospora specie biomass that has
been proved efficient
method for the formation of monodisperse gold nanoparticles. It might be
believed that metal
ion reduction and nanoparticles stability was due to enzymatic process
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