Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
Synthesis of metal Nanoparticles
Synthesis of MNPs is carried out by several physical and chemical methods that
include laser ablation, ion sputtering, solvothermal synthesis, chemical
reduction and sol-gel method. Basically, there are two approaches for
nanoparticle synthesis, the top-down and bottom-up. Top-down approaches seek
to create nanoscale objects by using larger, externally-controlled microscopic
devices to direct their assembly, while bottom-up approaches adopt molecular
components that are built up into more complex assemblies. The top-down
approach often uses microfabrication techniques where externally controlled
tools are used to cut, mill, and shape materials into the desired shape and size.
Micropatterning techniques, such as photolithography and inkjet printing are
well known examples of top-down approach. On the other hand, bottom-up
approaches use the self-assembled properties of single molecules into some
useful conformation. Different commonly used physical and chemical methods
are described in the following paragraphs.
Laser ablation
Laser ablation enables to obtain colloidal nanoparticles solutions in a variety of
solvents. Nanoparticles are formed during the condensation of a plasma plume
produced by the laser ablation of a bulk metal plate dipped in a liquid solution.
This technique is considered as a ‘green technique’ alternative to the chemical
reduction method for obtaining noble MNPs. However, the main drawbacks of
this methodology are the high energy required per unit of MNPs produced and
the little control over the growth rate of the MNPs
Inert gas condensation
Inert gas condensation (IGC) is the most widely used methods for MNPs
synthesis at Laboratory-scale. (Gleiter (1984) introduced the IGC technique in
nanotechnology by synthesizing iron nanoparticles. In IGC, metals are
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
evaporated in ultra high vacuum chamber filled with helium or argon gas at
typical pressure of few hundreds pascals. The evaporated metal atoms lose their
kinetic energy by collisions with the gas, and condense into small particles.
These particles then grow by Brownian coagulation and coalescence and finally
form nano-crystals. Recent application of this technique includes size-controlled
synthesis of Au/Pd NPs and hetero-sized Au nanoclusters for non-volatile
memory cell applications.
Sol-gel method
The sol-gel process is a wet-chemical technique developed recently in
nanomaterial synthesis. The inorganic nanostructures are formed by the sol-gel
process through formation of colloidal suspension (sol) and gelation of the sol
to integrated network in continuous liquid phase (gel). Size and stability control
quantum-confined semiconductor, metal, and metal oxide nanoparticles has
been achieved by inverted micelles polymer blends , block copolymers porous
glasses and ex-situ particle-capping techniques However,the fundamental
problem of aqueous sol-gel chemistry is the complexity of process and the fact
that the as-synthesized precipitates are generally amorphous. In non-aqueous
sol-gel chemistry the transformation of the precursor takes place in an organic
solvent. The nonaqueous (or non-hydrolytic) processes are able to overcome
some of the major limitations of aqueous systems, and thus represent a powerful
and versatile alternative. The advantages are a direct consequence of the
manifold role of the organic components in the reaction system (e.g., solvent,
organic ligand of the precursor molecule, surfactants, or in situ formed organic
condensation products). Nowadays, the family of metal oxide nanoparticles are
synthesized by non-aqueous processes and ranges from simple binary metal
oxides to more complex ternary, multi-metal and doped systems.
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
Hydrothermal and solvothermal synthesis
The hydrothermal and solvothermal synthesis of inorganic materials is an
important methodology in nanomaterial synthesis. In hydrothermal method, the
synthetic process occurs in aqueous solution above the boiling point of water,
whereas in solvothermal method the reaction is carried out in organic solvents at
temperatures (200-300°C) higher than their boiling points. Though development
of hydrothermal and solvothermal synthesis has a history of 100 years, recently
this technique has been applied in material synthesis process. Normally,
hydrothermal and solvothermal reactions are conducted in a specially sealed
container or high pressure autoclave under subcritical or supercritical solvent
conditions. Under such conditions, the solubility of reactants increases
significantly, enabling reaction to take place at lower temperature. Among
numerous
examples,
TiO2
photocatalysts
were
synthesized
through
hydrothermal process Because of low cost and energy consumptiom,
hydrothermal process can be scale-up for industrial production. Solvothermal
process enables to choose among numerous solvents or mixture thereof, thus
increasing the versatility of the synthesis. For example, well-faceted
nanocrystals of TiO2 with high reactivity were synthesized in a mixture of the
solvents Hydrogen fluoride (HF) and 2-propanol.
Colloidal methods
The crystallographic control over the nucleation and growth of noble-metal
nanoparticles has most widely been achieved using colloidal methods . In
general, metal nanoparticles are synthesized by reducing metal salt with
chemical reducing agents like borodride, hydrazine, citrate, etc, followed by
surface modification with suitable capping ligands to prevent aggregation and
confer additional surface properties. Occasional use of organic solvents in this
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
synthetic process often raises environmental questions. At the same time, these
approaches produce multi-shaped nanoparticles requiring purification by
differential centrifugation and consequently have low yield. Thus, the
development of reliable experimental protocols for the synthesis of
nanomaterials over a range of chemical compositions, sizes, and high
monodispersity is one of the challenging issues in current nanotechnology.
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
Bio-inspired nanomaterial synthesis (Green Synthesis)
Global efforts to reduce generation of hazardous waste and to develop energyeffective production routes, ‘green’ chemistry and biochemical processes are
progressively integrating with modern developments in science and technology.
Hence, any synthetic route or chemical process should address the fundamental
principles of ‘green chemistry’ by using environmentally benign solvents and
nontoxic chemicals.
The green synthesis of MNPs should involve three main steps based on green
chemistry perspectives:
(1) The selection of a biocompatible and nontoxic solvent medium,
(2) The selection of environmentally benign reducing agents,
(3) The selection of nontoxic substances for stabilization of the nanoparticles.
Employing these principles in nanoscience will facilitate the production and
processing of inherently safer nanomaterials and nanostructured devices.
Green nanotechnology thus aims to the application of green chemistry
principles in designing nanoscale products, and the development of
nanomaterial production methods with reduced hazardous waste generation and
safer applications.
Further, biochemical process can occur at low temperatures, because of the high
specificity of the biocatalysts. Hence, a synthetic route that include one or more
biological steps will result in consistent energy saving and lower environmental
impact with respect to conventional methods. To optimize safer nanoparticle
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
production, it would be desirable to employ bio-based methods, which could
minimize the hazardous conditions of materials fabrication and use. Inspiration
from nature, where living organisms produce inorganic materials through
biological guided process known as biomineralization, is adopted as a superior
approach to nanomaterials assembly. The biomineralization processes exploit
biomolecular templates that interact with the inorganic material at nanoscale,
resulting in extremely efficient and highly controlled syntheses. Typical
examples of biomineralized products include siliceous materials synthesized by
diatoms and sponges, calcite or aragonite (calcium carbonates) in invertebrates,
and apatite (calcium phosphates and carbonates) in vertebrates.
These biominerals are the phosphate and carbonate salts of calcium that form
structural entities such as sea shells and the bone in mammals and birds in
conjunction with organic polymers. The structures of these biocomposite
materials are highly controlled both at nano- and macroscale level, resulting in
complex architectures that provide multifunctional properties. Simpler
organisms, such as bacteria, algae, and fungi, have also developed during
hundreds of millions of years of evolution highly specialized strategies for
biominerals synthesis. The role of the templating molecule in biomineralization
is to provide a synthetic microenvironment in which the inorganic phase
morphology is tightly controlled by a range of low-range interactions
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
Biosynthesis of Nanoparticles by Microorganisms
Nanoparticles produced by a biogenic enzymatic process are far superior, in
several ways, to those particles produced by chemical methods. Despite that the
latter methods are able to produce large quantities of nanoparticles with a
defined size and shape in a relatively short time, they are complicated, outdated,
costly, and inefficient and produce hazardous toxic wastes that are harmful, not
only to the environment but also to human health. With an enzymatic process,
the use of expensive chemicals is eliminated, and the more acceptable “green”
route is not as energy intensive as the chemical method and is also environment
friendly.
The “biogenic” approach is further supported by the fact that the majority of the
bacteria inhabit ambient conditions of varying temperature, pH, and pressure.
The particles generated by these processes have higher catalytic reactivity,
Greater specific surface area, and an improved contact between the enzyme and
metal salt in question due to the bacterial carrier matrix .Nanoparticles are
biosynthesized when the microorganisms grab target ions from their
environment and then turn the metal ions into the element metal through
enzymes generated by the cell activities. It can be classified into intracellular
And extracellular synthesis is according to the location where nanoparticles are
formed. The intracellular method consists of transporting ions into the microbial
cell to form nanoparticles in the presence of enzymes. The extracellular
synthesis of nanoparticles involves trapping the metal ions on the surface of the
cells and reducing ions in the presence of enzymes. The biosynthesized
nanoparticles have been used in a variety of applications including drug carriers
for targeted delivery, cancer treatment, gene therapy and DNA analysis,
antibacterial agents, biosensors, enhancing reaction rates, separation science,
and magnetic resonance imaging (MRI).
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
Biological Synthesis of Nanoparticles by Microorganisms
Biological entities and inorganic materials have been in constant touch with
each other ever since inception of life on the earth. Due to this regular
interaction, life could sustain on this planet with a well-organized deposit of
minerals. Recently scientists become more and more interested in the
interaction between inorganic molecules and biological species. Studies have
found that many microorganisms can produce inorganic nanoparticles through
either intracellular or extracellular routes. This section describes the production
of various nanoparticles via biological methods following the categories of
metallic nanoparticles including gold, silver, alloy and other metal
nanoparticles, oxide nanoparticles consisting of magnetic and nonmagnetic
oxide
nanoparticles,
sulfide
nanoparticles,
and
other
miscellaneous
nanoparticles.
Metallic Nanoparticles : Some typical metal nanoparticles produced by
microorganisms
Biological synthesis of NPS by Bacteria ,Fungus and Yeast :
Gold nanoparticles (AuNPs) have a rich history in chemistry, dating back to
ancient Roman times where they were used to stain glasses for decorative
purposes. AuNPs were already used for curing various diseases centuries ago.
The modern era of AuNPs synthesis began over 150 years ago with the work of
Michael Faraday, who was possibly the first to observe that colloidal gold
solutions have properties that differ from bulk gold. Biosynthesis of
nanoparticles as an emerging bionanotechnology (the intersection of
nanotechnology and biotechnology) has received considerable attention due to a
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
growing need to develop environment-friendly technologies in material
synthesis .
Among the microorganisms, prokaryotic bacteria have received the most
attention in the area of biosynthesis of nanoparticles.
Bacillus subtilis is able to reduce Au3+ ions to produce octahedral gold
particles of nanoscale dimensions (5–25 nm) within bacterial cells by incubation
of the cells with gold chloride
under ambient temperature and pressure
conditions. Organic phosphate compounds play a role in the in vitro
development of octahedral Au possibly as bacteria–Au-complexing agents.
Fe(III)-reducing bacteria Shewanella algae can reduce Au(III) ions in
anaerobic environments .
In the presence of S. algae and hydrogen gas, the Au ions are completely
reduced, which results in the formation of 10- to 20-nm gold nanoparticles.
Sastry and coworkers have reported the extracellular synthesis of gold
nanoparticles
by
fungus
Fusarium
oxysporum
and
actinomycete
Thermomonospora sp.The intracellular synthesis of gold nanoparticles by
fungus Verticillium sp. as well .
Southam and Beveridge have demonstrated that gold particles of nanoscale
dimensions may readily be precipitated within bacterial cells by incubation of
the cells with Au3+ ions . Monodisperse gold nanoparticles have been
synthesized by using alkalotolerant Rhodococcus sp. under extreme biological
conditions like alkaline and slightly elevated temperature conditions .
Lengke et al.claimed the synthesis of gold nanostructures in different shapes
(spherical, cubic, and octahedral) by filamentous cyanobacteria from Au(I)thiosulfate and Au(III)-chloride complexes and analyzed their formation
mechanisms.
Some
bymicroorganisms
other
typical
gold
nanoparticles
produced
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
Silver Nanopaticles :
Silver nanoparticles, like their bulk counterpart, show effective antimicrobial
activity against Gram-positive and Gram-negative bacteria, including highly
multi resistant strains such as methicillin resistant Staphylococcus aureus .
The secrets discovered from nature have led to the development of biomimetic
approaches to the growth of advanced nanomaterials.
Recently, scientists have made efforts to make use of microorganisms as
possible eco-friendly nanofactories for the synthesis of silver nanoparticles.
Various microbes are known to reduce the Ag+ ions to form silver
nanoparticles, most of which are found to be spherical particles.
 Silver is highly toxic to most microbial cells. Nonetheless, several
bacterial strains are reported as silver resistant and may even accumulate
silver at the cell wall to as much as 25% of the dry weight biomass, thus
suggesting their use for the industrial recovery of silver from ore material.
The silver resistant
bacterial strain Pseudomonas stutzeri AG259
accumulates silver nanoparticles, along with some silver sulfide, in the
cell where particle size ranges from 35 to 46 nm ). Larger particles are
formed when P. stutzeri AG259, isolated from a silver mine, is placed in
a concentrated aqueous solution of silver nitrate.Nanoparticles of welldefined
size, ranging from a few to 200 nm or more, and distinct
morphology are deposited within the peri plasmic space of the bacteria.
 Cell growth .
 Metal incubation conditions.
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
The reasons for the formation of different particle sizes. The exact
reaction mechanisms leading to the formation of silver nanoparticles by
this species of silver resistant bacteria is yet to be elucidated.
The ability of microorganisms to grow in the presence of high
metal concentrations might result from specific mechanisms of
resistance.
Such mechanisms include the following:
 Efflux systems, alteration of solubility and toxicity by changes in the
redox state of the metal ions,
 Extracellular complexation or precipitation of metals,
 The lack of specific metal transport systems.
AgNPs were synthesized in the form of a film or produced in solution or
accumulated on the surface of its cell when fungi, Verticillium, Fusarium
oxysporum,or Aspergillus flavus, were employed.
Alloy Nanoparticle :
Alloy nanoparticles are of great interest due to their applications in catalysis,
electronics, as optical materials, and coatings.
 Bacteria not normally exposed to large concentrations of metal ions may
also be used to grow nanoparticles. The exposure of Lactobacillus strains
which are present in buttermilk, to silver and gold ions resulted to the
large-scale production of metal nanoparticles within the bacterial cells.
Moreover, the exposure of lactic acid bacteria present in the whey of
buttermilk to mixtures of gold and silver ions can be used to grow alloy
nanoparticles of gold and silver .
The synthesis of bimetallic Au-Ag alloy by F.oxysporum and argued that the
secreted cofactor NADH plays an important role in determining the composition
of Au-Ag alloy nanoparticles.
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
Au-Ag alloy nanoparticles biosynthesized by yeast cells. Fluorescence
microscopic and transmission electron microscopic characterizations indicated
that the Au-Ag alloy nanoparticles were mainly synthesized via an extracellular
approach and generally existed in the formof irregular polyg onal nanoparticles.
Electrochemical investigations revealed that the vanillin sensor based on Au-Ag
alloy nanoparticles modified glassy carbon electrode was able to enhance the
electrochemical response of vanillin for at least five times.
Sawle et al. demonstrated the synthesis of core-shell Au-Ag alloy nanoparticles
from fungal strains Fusarium semitectum and showed that the nanoparticle
suspensions are quite stable for many weeks
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
Other Metallic Nanoparticles.
Heavy metals are known to be toxic to microorganism life. In nature, microbial
resistance to most toxic heavy metals is due to their chemical detoxification as
well as due to energy-dependent ion efflux from the cell by membrane proteins
that function either as ATPase or as chemiosmotic cation or proton
antitransporters.
Alteration in solubility also plays a role in microbial resistance . Konishi and
coworkers reported that platinum nanoparticles were achieved using the metal
ion-reducing bacterium Shewanella algae Resting cells of S. algae were able to
reduce aqueous PtCl6 2− ions into elemental platinum at room temperature and
neutral pH within 60min when lactate was provided as the electron donor.
Platinum nanoparticles of about 5 nm were located in the periplasm. Sinha and
Khare demonstrated that mercury nanoparticles can be synthesized by
Enterobacter sp. Cells . The culture conditions (pH 8.0 and lower concentration
of mercury) promote the synthesis of uniform-sized 2–5 nm, spherical, and
monodispersed intracellular mercury nanoparticles. Pyrobaculum islandicum,
an anaerobic hyperthermophilic microorganism, was reported to reduce many
heavy metals including U(VI), Tc(VII), Cr(VI), Co(III), and Mn(IV) with
hydrogen as the electron donor. The palladium nanoparticles could be
synthesized by the sulphate reducing bacterium, Desulfovibrio desulfuricans,
and metal ion-reducing bacterium, S. oneidensis
OxideNanoparticles. Oxide nanoparticle is an important type of compound
nanoparticle synthesized by microbes. the biosynthesized oxide nanoparticles
from the two aspects: magnetic oxide nanoparticles and nonmagnetic oxide
nanoparticles. Most of the examples of the magnetotactic bacteria used for the
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
production of magnetic oxide nanoparticles and biological systems for the
formation of nonmagnetic oxide nanoparticles
Magnetic Nanoparticles: Magnetic nanoparticles are recently developed new
materials, due to their unique micro configuration and properties like super
paramagnetic and high coercive force, and their prospect for broad applications
in biological separation and biomedicine fields. Magnetic nanoparticles like
Fe3O4 (magnetite) and Fe2O3 (maghemite) are known to be biocompatible.
They have been actively investigated for targeted cancer treatment (magnetic
hyperthermia), stem cell sorting and manipulation,guided drug delivery, gene
therapy, DNA analysis, and magnetic resonance imaging (MRI).
Magnetotactic bacteria synthesize intracellular magnetic particles
comprising iron oxide, iron sulfides, or both . In order to distinguish these
particles from artificially synthesized magnetic particles (AMPs), they are
referred to as bacterial magnetic particles (BacMPs) . BacMPs, which are
aligned in chains within the bacterium, are postulated to function as biological
compass needles that enable the bacterium to migrate along oxygen gradients in
aquatic environments, under the influence of the Earth’s geomagnetic field .
BacMPs can easily disperse in aqueous solutions because they are enveloped by
organic membranes that mainly consist of phospholipids and proteins.
Furthermore, an individual BacMP contains a single magnetic domain or
magnetite that yields superior magnetic properties
Magnetotactic bacteria in 1975 , various morphological types including
cocci,spirilla, vibrios, ovoid bacteria, rod-shaped bacteria, and multicellular
bacteria possessing unique characteristics have been identified and observed to
inhabit various aquatic environments . Magnetotactic cocci, for example, have
shown high diversity and distribution and have been frequently identified at the
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
surface of aquatic sediments. The discovery of this bacterial type, including the
only cultured magnetotactic coccus strain MC-1, suggested that they are
microaerophilic. In the case of the vibrio bacterium, three facultative anaerobic
marine vibrios—strains MV-1, MV-2,and MV-4—have been isolated from
estuarine salt marshes.
These bacteria have been classified as members of α-Proteobacteria, possibly
belonging to the Rhodospirillaceae family, and observed to synthesize BacMPs
of a truncated hexa-octahedron shape and grow chemoorganoheterotrophically
as
well
as
chemolithoautotrophically.
The
members
of
the
family
Magnetospirillaceae, on the other hand, can be found in fresh water sediments.
With the use of growth medium and magnetic isolation techniques established, a
considerable number of the magnetotactic bacteria isolated to date have been
found to be members of this family. The Magnetospirillum magnetotacticum
strain MS-1 was the first member of the family to be isolated ,while the
Magnetospirillum gryphiswaldense strain MSR-1 is also well studied with
regard to both its physiological and genetic characteristics. Magnetospirillum
magneticum AMB-1 isolated by Arakaki et al. was facultative anaerobic
magnetotactic spirilla.
A number of new magnetotactic bacteria have been found in various aquatic
environments since 2000. Uncultured magnetotactic bacteria have been
observed in numerous habitats. Most known cultured magnetotactic bacteria are
mesophilic and tend not to grow much above 30◦C. Uncultured magnetotactic
bacteria were mostly at 30◦C and below. There are only a few reports describing
thermophilic magnetotactic bacteria. Lef`evre et al. reported that one of
magnetotactic bacteria called HSMV-1 was found in samples from springs
whose temperatures ranged from 32 to 63◦C
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
Nonmagnetic Oxide Nanoparticles. Beside magnetic oxide nanoparticles, other
oxide nanoparticles have also been studied including TiO2,Sb2O3, SiO2,
BaTiO3, and ZrO2 nanoparticles . Jha and co-workers found a green low-cost
and reproducible Saccharomyces cerevisiae mediated biosynthesis of Sb2O3
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
nanoparticles . The synthesis was performed akin to room temperature. Analysis
indicated that Sb2O3 nanoparticles unit was a spherical aggregate having a size
of 2–10nm . Bansal et al. used F. Oxysporum (Fungus) to produce SiO2 and
TiO2 nanoparticles from aqueous anionic complexes SiF6 2− and TiF62−,
respectively. They also prepared tetragonal BaTiO3 and quasi spherical
ZrO2 nanoparticles from F. oxysporum with a sizerange of 4-5nm and 3–11 nm,
respectively.
Sulfide Nanoparticles: oxide nanoparticles,sulfide nanoparticles have also
attracted great attention in both fundamental research and technical applications
as quantum-dot fluorescent biomarkers and cell labeling agents because of their
interesting and novel electronic and optical properties. CdS nanocrystal is one
typical
type of sulfide nanoparticle and has
been synthesized
by
microorganisms.
Cunningham and Lundie found that Clostridium
thermoaceticum could
precipitate CdS on the cell surface as well as in the medium from CdCl2 in the
presence of cysteine hydrochloride in the growth medium where cysteine most
probably acts as the source of sulfide . Klebsiella pneumoniae exposed to Cd2+
ions in the growth medium were found to form 20–200nm CdS on the cell
surface [99]. Intracellular CdS nanocrystals, composed of a wurtzite crystal
phase, are formed when Escherichia coli is incubated with CdCl2 and Na2SO4.
Nanocrystal formation varies dramatically depending on the growth phase of the
cells and increases about 20-fold in E. coli grown in the stationary phase
compared to that grown in the late logarithmic phase. Dameron et al. have used
S. pombe and C. Glabrata (yeasts) to produce intracellular CdS nanoparticles
with cadmium salt solution.
ZnS and PbS nanoparticles were successfully synthesized by biological systems.
Rhodobacter sphaeroides and Desulfobacteraceae have been used to obtain ZnS
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat
nanoparticles intracellularly with 8 nm and 2–5 nm in average diameter,
respectively. PbS nanoparticles were also synthesized by using Rhodobacter
sphaeroides,whose diameters were controlled by the culture time .
Ahmad et al. have found Eukaryotic organisms such as fungi to be a good
candidate for the synthesis of metal sulphide nanoparticles extracellularly .
Some stable metal sulphide nanoparticles, such as CdS, ZnS, PbS, and MoS2,
can be produced extracellularly by the fungus F. oxysporum when exposed to
aqueous solution of metal sulfate. The quantum dots were formed by the
reaction of Cd2+ ions with sulphide ions which were produced by the enzymatic
reduction of sulfate ions to sulfide ions.
Class Notes for Nano biotechnology MNTF 405 by Er. Mohit Rawat