A Review on Concept of Nanotechnology in Veterinary Medicine

ES Food Agrofor., 2021, 4, 28-60

 ES Food and Agroforestry
 DOI: https://dx.doi.org/10.30919/esfaf481

A Review on Concept of Nanotechnology in Veterinary
Medicine
Rai Dhirendra Prasad,1 Naresh Charmode,2 Om Prakash Shrivastav,3 Saurabh R Prasad,4 Asha Moghe,5 Anant Samant,6 Prashant D
Sarvalkar7 and Neeraj R Prasad7,*

Abstract
Nanoscience and technology is an exciting and rapidly emerging branch of science and technology which work at the atomic,
molecular and macromolecular levels. Nanotechnology deals with manipulation and use various tools and functional materials
at nanoscale. The concept of nanotechnology was first time proposed by American Nobel laureate Richard Feynman in 1959.
However, the basic idea of definition and popularization was explored much more in 1980s. Nanotechnology has opened up
new panoramas for applications in molecular biology, biotechnology in revolutionizing almost all the disciplines of veterinary
and animal sciences by providing new, small scale tools and materials that are beneficial for living organisms. The different
types nanomaterials are being used for disease diagnosis, treatment, drug delivery, animal nutrition, animal breeding. The
various types of nanoparticles are used such as metallic nanoparticles, quantum dots, carbon nanotubes, magnetic nanoparticles,
fullerenes, liposomes and dendrimers Therefore, scientists, doctors, engineers and biologists should work at the cellular and
molecular levels for significant benefits and there should be public awareness about the potential risks.
Keywords: Drug delivery; Liposomes; Polymeric nanoparticles; Carbon nanotubes; Micelle.
Received: 26 April 2021; Accepted: 10 June 2021.
Article type: Review article.

1. Introduction to concept of nanotechnology 1.1 Science at nanoscale
Richard Feynman cast a glance on the new horizon of physics The word nano is of Greek origin which means small or dwarf.
(Nanoscience) on December 29, 1959 at annual meeting of Scientifically, nano is 10⁻9 m. Nano technology is art and
American physical society at Caltech by quoting ‘There is science of manipulating materials at nano-scale.[1] The
plenty of room at the bottom’ According to him we can emerging field of nano-science and nano-engineering are
manage individual atoms. Herein, glimpses of various aspects leading to unexpected understanding and control over the
of nanoparticles such as their synthesis, physico-chemical fundamental building blocks of all physical matters. This is
properties, characterization and possible applications in likely to revolutionize the way almost everything from vaccine
different domain. The role of nature as a source of inspiration to computers to automobile to object yet imagined is designed
for synthesizing nanoparticles by novel economical and eco- and made. Nanostructured science and technology is a broad
friendly method are well described here. and interdisciplinary area of research and development
 activities that has been growing explosively worldwide in past
 1 Bihar Veterinary College, Patna and Retired Gazetted officer few years. It has potential in revolutionizing the ways in which
 Government of Maharashtra, India. materials and products are created and the range and nature of
 2 Nagpur Veterinary College, Nagpur and Retired Gazetted officer
 functionalities that can be accessed. The term nanotechnology
 Government of Maharashtra, India. has entered into general and scientific vocabulary only
 3 Retired Principal Scientist IARI, Pusa, Bihar.
 recently but was first time used by Japanese scientist Nario
 4 DKTE College of Engineering, Ichalkaranji.
 Taniguchi in 1974. Fig. 1 reveals lotus effect responsible to
 5 Medical Officer, Primary Health Centre, Jaysingpur, India.
 self-cleaning properties that are a result of super-
 6 Formerly at J J Magdum Ayurveda College, Jaysingpur.
 hydrophobicity as exhibited by lotus leaves and flower surface.
 7 School of Nanoscience and Technology, Shivaji University,
 Dirt particles are pulled out by water droplets due to the micro-
 Kolhapur, India. and nanoscopic structure on the surface. This is a technology
 *Email: neeraj_prasad21@rediffmail.com (N. R. Prasad) where the dimensions and tolerance are in the range of 0.1 nm

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 One who performs his duty without attachment
 ,surrendering the results unto the supreme god, is not
 affected by sinful action, as the lotus leaf is untouched by
 water Chapter 5, text 10
 Geeta

 Fig. 1 Glimpses of Nanotechnology.

to 100 nm.[3] surface tension often dominate over forces such as gravity.[9]
 Human beings have used nano materials since long back.
The first report of existence of nano material is described in 1.3 Viscosity
Ayurveda that dates back to 5000 years.[4] In Ayurveda The force F needed to move a sphere of mass m, density ρ,
formation of various bhasma i.e. ashes e.g. Suvarna Bhasma, radius R at a velocity v through a viscous medium of viscosity
Rajat bhasma, Tamra bhasma etc. are well described. Dr. η (Stoke’s Law) is given by:
Samuel Hahnemann discovered new therapy of medicine i.e. = 6 (1)
Homeopathy. In this therapy, it is believed that as the When the sphere reaches terminal velocity Vt , the force on it
concentration of medicine decreases its effectiveness due to gravity (F = mg) is balanced by the retarding force due
increases.[5] There are number of homeopathic medicine like to the viscosity of the medium:
 4
Argentinum, Cuprum metallium in which metals are in nano 6 V = 3 (2)
 3
form.[6] V ∝ 2 (3)
 Michel Faraday had synthesized colloidal solution of gold Since velocity is proportional to the radius squared, it is
in 1857. This colloidal solution is kept in British Museum. clear that small particles fall very much more slowly. Note that
Even today the gold particles have not settled down thus it is the above treatment is only valid under conditions of
supposed that Michel faraday was the first person of modern streamline flow, for small particles and low velocities. This
period to have synthesized nanoparticle.[7] condition is met when the Reynolds Number (Re) is less than
 The synthesis and study of nanoparticles was difficult in about 2000, where Re is a non-dimensional quantity that
earlier days. This is because the nanoparticles could not be describes the type of flow in a fluid defined by:
visualized and manipulated but, after discovery of electron = 2 /η (4)
microscope by Knoll and Ruska in 1931, it became possible to As size decreases, the ratio of inertia forces to viscous
visualize and manipulate particles at nanoscale. The forces within the fluid decreases and viscosity dominates.
nanoparticles do not obey the law of classical or Newtonian Hence, micro/nano-scale objects moving through fluids are
mechanics but they do obey the law of quantum mechanics.[8] dominated by viscous forces, and their motion is characterized
The beginnings and developments of nanotechnology, the by a low Reynolds number. This means that nanoparticles
application of nanoscience, are unclear. The first “feel” the viscosity (or ‘gooeyness’) of the fluid much more
nanotechnologists may have been medieval glass workers than we do.
using medieval forges, although the glaziers naturally did not
understand why what they did to gold made so many different 1.4 Historical perspectives
colors. When nanocomposites are prepared in glassy or ceramic
 matrices, the particles are so produced, precipitated in situ or
1.2 Classical physics at nanoscale otherwise included into the matrix. Some of the synthesis and
At the scale of nano- and micro-particles, we can adequately application of such nanocomposites are nothing new. For
describe many physical phenomenon’s with classical physics. example, the synthesis and use of metallic nano-particles in a
We often ask questions such as: Why do dust particles float in glassy phase is a well-known ancient technique. During the
the air instead of falling to the ground? Why does a small drop study of a Roman mosaïc, the "Thomas Panel" found at
of water not spread but remain round? Why do micron-sized Faiyum, 100 km southwest away from Cairo, R. H. Brill and
wheels have so little inertia? At this scale, the behavior of D. Whitehouse discovered that the Romans embedded fine
objects is different from what we experience in our daily lives. gold particles to impart color some of their glass. The colors
This is because at the small scale, forces such as friction and obtained ranged from bright red to purple. The finest example

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from this period however is the Lycurgus Cup (4th century 1.5 Evolution of nanotechnology
AD), 165mm tall, with decorations in very intense red color The existence and use of nanoparticles goes long back. The
achieved by gold and silver nanoparticles contained in the first relationship between human life and nano-scale was
glassy phase.[10] Since the XIIth century, copper and silver have developed in Ayurveda, which is about 5000 years old Indian
been used to color stained glass windows of cathedrals in red system of medicine. Ayurveda had some knowledge of nano
and yellow, respectively. The insertions of these nanoparticles medicine synthesis and its effects even before the term
were done either in the bulk or at the surface of the glass, nanotechnology was coined. The process of formation of
depending on the desired luminosity. Later, during the XVIIIth bhasmas, a kind of metallic nano-particle is well described in
century in China, under the reign of K'angHsi, the famous pink ancient Ayurveda literature RasRatnakar authored by
Chinese porcelain where gold nanoparticles are embedded in Nagarjuna in 50 BC.[11] Ayurveda describes this process as
enamel, were manufactured. These porcelains had great shodhan i.e. purification and maran i.e. killing the metallic
success and were widely used in Europe. The development in properties so that it becomes digestible and suitable for
nanotechnology are summarized in the Table 1. medicinal use. Also, the modern therapy of medicine
 Homeopathy developed by Dr. Samuel Hahnemann uses
 Table 1. Evolution of Nanotechnology. alcoholic solution of metallic nanoparticles for curing the
 Period Development in Nanoscience and Technology diseases. In Homeopathic book “Organon of Medicine”, Dr.
 5000 years ago, Ayurveda system of medicine describes use of Samuel Hahnemann mentions number of homoeopathic
 nanoparticles in medicine medicines in which metal is in nano form e.g. Aurum
 1857 Michel Faraday synthesized colloidal solution of metallicum (nano gold), Argentium (nano Silver) etc. In fact
 gold Homeopathic way of treatment has a strong belief that by
 1905 Einstein publishes his study on the dimension of lowering the concentration the property changes and the
 sugar molecule, approximately 1 nm product can be used to cure diseases.[12]
 1959 R. Feynman, in his lecture at the annual meeting History claims that nanoparticles have been around us for
 of American Association of a long time. Presumably the use of nanoparticles was reported
 Physical Sciences, claims that There is Plenty of in 1570 as aurum potable (potable gold) and Luna potable
 Room at the Bottom (potable silver) which alchemist used as elixirs. Unfortunately,
 1974 Norio Taniguchi introduced the term they did not make the consumer immortal, as is evident by the
 nanotechnology fact that those alchemists are not among us today. However,
 1981 E. Drexler designs molecular machines that one of the oldest application of nanoparticles that we come
 mimic enzymes and ribosomes across in literature is the use of gold nano particles for staining
 1984 1984 The first description of the term glasses, a famous example of which is Lycurgus cup that dates
 “dendrimer” by D.A. Tomalia and the back to 4th century AD.[13] The origin of unusual optical
 preparation method of PAMAM dendrimers properties of nano-structured materials however could be
 1991 The discovery of carbon nanotubes (CNTs) dated back to 17th century when the brilliant color of some of
 1994 Drug delivery systems these nanoparticles was used advantageously to make stained
 1995 FDA approved Doxil (liposomal doxorubicin) glass window of cathedrals. Faraday explained the origin of
 1997 FDA approved AmBisome (liposomal their color owing to presence of metallic gold nanoparticles
 amphotericin B) especially in colloidal form. Mie theoretically explained the
 1998 DNA nanoparticles for controlled gene delivery origin of color of these nanoparticles by applying Maxwell’s
 2000 The first FDA approval of medicinal product equation.[14]
 based on the technology of However, research on nanomaterials has got attention only
 Liquid Crystals (NanoCrystal Technology) and during last few decades. This is because of the development of
 the solid dose formulation of electron microscope which could reveal the structure of
 the immunosuppressant sirolimus – Rapamune nanomaterials. In the present age indeed, the nano-technology
 2005 FDA approves Abraxane, the nanotechnological mania is sweeping through essentially all the fields of science
 formulation of paclitaxel and technology and public is practically experiencing the
 2008 In market: PEG-Certolizumabpegol (trade name, meaning of quote of Nobel Laureate Richard Smalley: “Just
 Cimzia) anti-TNF Fab for rheumatoid arthritis wait – the next century is going to be incredible.[15] We are
 and Crohn’s disease about to build things that works on smallest possible length
 2012 Biomimetic drug delivery systems: the first scales, atom by atom. These little nano-things will
 publications in literature July 2015 Successful revolutionize our industries and our lives.” This is becoming
 clinical trials of Thermo Dox (lyso- more and more evident in the form of potential applications of
 thermosensitive liposomal doxorubicin) nanoparticles which extend to a wide range of areas such as
 October 2015 FDA approves Onivyde (irinotecan liposomal) catalysis, biosensors, solar cells, super capacitors, smart
 for advanced pancreatic cancer windows and in medical sciences. A remarkable aspect of

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nanomaterials is that a number of factors can influence their those linked with health called as bio-inspired nanotechnology)
properties which are their size, shape, surface composition, used for the prosperity of mankind.
dielectric environment and the inter-particle interactions.[16] The field of nanoscience and nanotechnology has primarily
 There has been a saying since a long time “Necessity is the been a motivation to mimic the synthesis and manipulation of
mother of invention.” Hence people have been passionate materials at similar length scale by the nature. The interesting
enough to nurture science and transform it into fruitful properties and appealing structures of biomaterials have
technology. From ancient times human beings are using inspired the scientists for the synthesis of novel nanomaterials
materials to meet their needs. Materials have always been an with precise control over their morphology and dimensions.
integral part in the progress of human civilization. Material These nano scale materials possess novel size and shape
science is one of the areas where the continuous changes are dependent properties useful for diverse applications in various
taking place and its growth is an indication of civilization e.g. fields of science and engineering. Accordingly, recent
stone age about 5000 BC, copper age 5000-800 BC, bronze technological developments makes it possible to generate
age 300 - 00 BC, iron age 800 BC to 40 AD, plastic age since structures or devices which are less than 100 nanometers in
1907 i.e. after the discovery of Bakelite. Gold was probably size with noteworthy functional advantages over conventional
the first elemental metal used by mankind. After gold, the next devices leading towards the threshold of revolution. It is
metal used by mankind was copper. The evidence of this is having the potential to change the entire scenario of present
obtained from archeological study of Indus valley civilization. technology. Indeed, promises are so high that it can even cope-
Material scientists and Engineers now have focused on up with the millennium goal of achieving affordable amenities
tailored materials from the atomic scale upwards to obtain to all human beings. Nanotechnology finds increasing
desired properties. A new age in materials known as the applications in various products such as food, electronics, cars
tailored material age has been used to describe the and clothing as well as in different biomedical applications.[20]
revolutionary changes in material science and engineering as In recent years, research in nanotechnology is emerging as
well as their impact on society.[17] cutting-edge technology interdisciplinary with Physics,
 Man had endeavored to discover techniques for producing Chemistry, Biology, Material Science and Veterinary
materials possessing properties superior to those occurring Medicine. The Greek word nano identifies a material whose
naturally. One of the possibilities to alter the properties of size has been reduced to 10-9 m, which is 1000 times smaller
materials is by heat treatment and alloying which can improve than one micron. It is obvious that nanoscience, nano-
the strength and durability of materials. The development of engineering and nanotechnology all deal with very small sized
different advanced technologies makes life easier. For objects and systems. Structures on nano scale are considered
example, in early days the materials used in aircraft and at the border line of the smallest of human made devices and
automobiles were mostly metallic. As the metals possess the largest molecule of living system. Our ability to control
higher densities, therefore those automobiles were very heavy. and manipulate nanostructure will make it possible to exploit
Thus it was difficult to achieve high speed. Due to new physical, biological and chemical properties of system
advancements in technology the metallic parts are being that are intermediate in size between single atoms and bulk
replaced by composite materials and the vehicles or materials. Presently nanotechnology and its associated
automobiles manufactured using composite material are light research discipline together constitute the complete spectrum
and can achieve very high speed.[18] of activities towards the promised next industrial revolution.[21]
 Material science is a scientific discipline which involves Nanotechnology has been defined in various ways by
investigation of the relationship between the structures, different scientists. According to Hunt, “Nanomaterials are an
processing and properties of materials. When the knowledge enabling component of the popularly labelled area of
of material is applied to prepare a technical product, then it nanotechnology”. Nanotechnology as described by Scientific
gives rise to an engineering discipline known as Material Americana; “The field is a vast grab bag of stuff that has to do
Engineering. Progress in advanced materials has been deemed with creating tiny things that sometimes just happen to be
to be one of the major engineering accomplishments of the last useful. It borrows liberally from condensed matter physics,
century. The cutting edge research activity places particular engineering, molecular biology, and large swaths of
emphasis on material related to nanotechnology and chemistry”. However, a more comprehensive definition is
nanoscience. In addition to main requirements engineering given by the US National Nanotechnology Initiative (NNI) as:
materials also require various qualities such as stability, (i) research and technology development at the atomic,
durability, chemical resistance, corrosion resistance, wear molecular, or macromolecular levels, approximately 1-100
resistance, impact resistance, thermal and shock resistance.[19] nano-meters in length, (ii) creation and use of structures,
 Research on nanomaterials is driven by two motivating devices, and systems that have novel properties and functions
factors: because of their small and intermediate size, and (iii) ability to
 (1) They exhibit interesting properties at nanometer size control or manipulate on the atomic scale. Another definition
scale which is different from bulk material and given by The Royal Society and The Royal Academy of
 (2) Applications of these properties in devices (especially Engineering is “nanotechnology is the design,

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characterization, production, and application of structures, nanomaterial is allowed to grow in 2 dimensional vectors e.g.
devices, and systems by controlling shape and size at the nano- quantum sheets.[26] In 3D nanostructures, nanomaterial is
meter scale”. Thus, improvement of properties of materials by allowed to grow in all 3 dimensional vectors e.g. fullerene,
controlling their nanoscale structures is the heart of silica NPs.[27] This concept is shown in Fig. 2.
nanotechnology.[22,23] Similarly, core-shell nanoparticles constitute another class
 Nanomaterials can be classified based on their of nanomaterials having chemical composition different on the
dimensionality. Let us consider the three-dimensional space surface compared to the core region. Non-metallic
vectors for a specific nanomaterial. If the size of nanomaterial nanoparticles are another class consisting of non-metals and
is within the critical regime of 1-100 nm in all three dimension organic molecules which exhibits interesting electrical
vectors, they can be known as 0-dimensional particles or behaviour which can be tuned to be insulating or conducting
quantum dots[24] e.g. spherical nanoparticles of Au, Ag, CdS, based on size and composition. The most familiar example of
CdSe etc. Similarly, if the growth of nanomaterial is restricted non-metallic nanoparticle is Fullerenes which finds
within the critical regime of 1-100 nm in two spatial applications in super-conductors and in medicine.[28] Carbon
dimensional vectors allowing nanomaterial to grow only in the nanotubes constitute another celebrated class of nanomaterials
third direction, then the resultant nanomaterial is known as 1D that can be metallic or semiconducting depending on their
nanostructure e.g. quantum wires, nano-rods, nano-wires, diameter and chirality. The dimensionality in nanomaterials
single walled carbon nanotubes etc.[25] In 2D nanostructures, can be represented in Table 2 as below:
only one dimension is restricted to that critical regime and

 Table 2. Dimensions of Materials at Nanoscale.
 Dimension Properties Examples
 Materials wherein all the dimensions
 0-Dimensional are measured within the nanoscale. ( no Nanoparticles
 dimension or 0-D is larger than 100nm)
 Materials wherein one dimension is
 1-Dimensional outside the nanoscale. This means two Nanotubes, Nanorods, Nanowires
 dimensions are within the nano region.
 Materials wherein two dimensions are
 outside the nanoscale. This means one
 2-Dimensional dimension is within the nano region. Nanofilms, Nanolayers, Nanocoating
 Such type of nano-materials exhibits
 plate like shapes.
 Dispersion of Nanoparticles, bundles of
 Materials wherein all three dimensions
 3-Dimensional nanowires and nanotubes as well as
 are outside the nanoscale.
 multinanolayers

 Fig. 2 Different dimensions of nanomaterial.

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1.6 Engineering trends in materials by nano-technological routes. Materials used in robotics and
The knowledge of nanotechnology has been exploited to yield bio-chemicals analysis also belong to smart materials category.
different improved engineering materials. Advanced and Nanotechnology is now days a buzz word and became
improved aerospace alloys such as Nickel-base super alloys indispensable tool for researchers from various fields, such as
are constantly being researched for increased high temperature physics, chemistry, mechanical engineering, microbiology and
strength and corrosion resistance. The alloys are used in medical sciences. In fact, nanotechnology has dissolved the
engine components and increased engine efficiency can be boarders of scientific disciplines. This is because the
obtained at high operating temperature. Polymeric materials nanoparticles are not said to obey the law of classical
have been the fastest growing material in the world over the mechanics but follows quantum mechanics. All the materials
past few years and they have substituted for metals, glass and retain their properties up to the size of micro level. But below
packaging papers. Similarly, nanotechnology has been applied this the properties of materials are different from the bulk
for the development of improved ceramic materials that fulfill material and their properties can be steered by controlling their
the demand for engineering applications where high size and morphology. John Dewey has said in his Quest for
temperature and high wear environment exists. Some certainty, “Every Great advancement in science has emerged
nanotechnology based smart materials have come into from a new audacity of imagination”. Nano-scale is thus
existence in last few years which are used in sensors and imagination of world of the small where one nanometer refers
actuators.[29] to one billionth of a meter. Thus there would be an obvious
 question i.e. up to what length scale shall we speak of
1.7 Smart or intelligent materials nanometer, 10nm, 100 nm or 1000 nm. The answer to this
Smart materials are the materials that respond favorably to question is debatable, but most of the scientists feel that the
change in temperature, pH, moisture or electromagnetic fields. particles ranging in between 1nm-100nm in any dimension
Smart materials have the ability to change their shape and size and having at least one property different from their bulk form
simply by providing little heat to them. Also they can change are known as nanoparticles.[30] The practical idea about size of
from liquid to solid almost instantly when placed near the few nanomaterials can be obtained by comparing them with
magnet. Smart materials have one or more properties that can biologically occurring substance or species and that is given
be dramatically changed. Now, in today’s era material in Fig. 3.
scientists are actively engaged in designing the new materials

Fig. 3 Picture representing the relative size of the various naturally occurring objects/species and artificial materials. Courtesy: Josh
Wolfe’s report on nanotechnology, www.forbeswolfe.com.

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 Richard Feynman, also regarded as Father of was subsequently written as a novel of the same title by Isaac
Nanotechnology, was the first visionary who drew attention Asimov, based on the screenplay. Fantastic Voyage II:
towards this possibility in his talk on 29th December 1959 and Destination Brain was written by Isaac Asimov as an attempt
made a famous statement, “There is a plenty of room at the to develop and present his own story apart from the 1966
bottom”. This has initiated a new branch of science which is screenplay. Fantastic Voyage: Microcosm is a third
presently known as nanoscience and technology where interpretation, written by Kevin J. Anderson, and published in
everything depends upon our ability to manipulate and design 2001. This version updates the story with modern ideas of
materials atoms by atom and molecule by molecule at nano- nanotechnology, but uses the same theme of miniaturizing a
scale. The term nanotechnology was coined by Japanese crew of scientists, doctors and technicians to investigate a
scientist Norio Taniguchi in year 1974. According to him body.[33] We have seen from the earlier sections that the motion
“Nanotechnology mainly consists of the process of separation, of a Nano boat in a fluid would be complex and difficult to
consolidation and deformation of materials by one atom or one control. The viscosity of the fluid is greatly enhanced at the
molecule.[31] The nano-sized materials possess novel size and nanoscale making design of the propulsion system a major
shape dependent properties useful for diverse applications in engineering challenge. Brownian motion would cause a
the field of science and technology.” constant random shaking that would also make engineering
 design difficult. Furthermore, surface forces at the nanoscale
1.8 Properties of nanomaterials become significant, resulting in the Nano boat sticking to any
It is observed that the material at nano-scale show different surface it comes into contact with. Nevertheless, we can use
properties than bulk state. Due to possible favorable variation these effects to our advantage by getting inspiration from
in optical, mechanical, thermal and electrical properties of Nature.[34] After all, living organisms such as viruses and
nanoparticles, they remain point of interest for scientist from bacteria are able to find their way into human cells. If we can
all branches of science. The materials sustain their regular design molecules with sticky and non-sticky areas, then the
physical and chemical properties up to micrometer level. But agitation caused by Brownian motion will eventually lead to
as their size goes down the micro-level, interestingly they start molecules sticking together in very well-defined ways.[35]
exhibiting astonishingly exotic properties. But the properties Such random stochastic processes are the basis of all
of nanoparticles are not only dependent upon the size but they chemical reactions, and indeed of the biochemistry of life
also depend upon other factors like shape, stabilizing agent, itself. So far we have been describing physics at the nanoscale
method of preparation etc. For example, the changes in optical, using purely classical physics. However, quantum mechanical
thermal, electrical, electronic, magnetic and mechanical effects become significant when we consider even smaller
properties are noticeable at nanoscale. These properties are entities such as the electron. Indeed changes in energy levels
briefly discussed below.[32] occur when electrons are confined to nano-sized objects,
 altering the electronic and optical properties of the material.
1.8.1 Brownian motion of nanoscale objects The temperature at which the atoms, ions or molecules in a
We consider Brownian motion of a nanoparticle in an substance have enough energy to overcome intermolecular
incompressible Newtonian Fluid medium with fluctuating forces that hold them in a fixed position in a solid
hydrodynamic approach. In 1827, the English botanist Robert
Brown noticed that pollen grains suspended in water jiggled 1.8.3 Melting point
about under the lens of the microscope, following a zig-zag At macroscopic length scale, the melting of material is size
path like the one pictured in Fig. 3. It was only in 1905 when dependent. For example, an ice cube and a glacier both melt at
Einstein succeeded in stating the mathematical laws governing the same temperature. Thermal conduction is another vital
the movements of particles on the basis of the principles of the mechanical property of nanoscale structure with immense
kinetic-molecular theory of heat. According to this theory, scientific and technological significances. Heat generation,
microscopic bodies suspended in a liquid perform irregular conduction and dissipation in transistor are major challenges
thermal movements called Brownian molecular motion. in electronics industries. At cryogenic temperature, heat
Brownian motion became more generally accepted because it conduction engineering of micro-bolometer is a basic
could now be treated as a practical mathematical model. Its constituent for sensitive detection of radiation and energetic
universality is closely related to the universality of the normal particles. Improvement in figure of merit is achieved in
(Gaussian) distribution. quantum dot super-lattice. In scientific research, heat
 conduction through a mechanical point contact measures the
1.8.2 Motion at the nanoscale universal quantum of thermal conductance. The melting
It has been often hypothesized that in the not-too-distant- point of nanoparticles is below the melting point of bulk
future, micron-sized medical nanorobots will be able to material. The reduced melting point can be graphically
navigate through our bloodstream to destroy harmful viruses represented in Fig. 4.
and cancerous cells. This is reminiscent of the 1966 science From above graph of melting point (Tm) vs size of particle
fiction film Fantastic Voyage written by Harry Kleiner, which (D), it can be seen that by decreasing the size of particle, the

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melting point decreases. At nano-scale, there is a drastic mechanical strength decreases with increase in material
decrease in melting point below 3-4nm size. The relationship defects. The strength and hardness of the material depends on
between melting point of nanoparticles and particle size is grain size. Due to small cross section and less number of
given by following equation: imperfections, Nano material like Nano rod, carbon Nano
 1
 = (1 − ) (5) tubes or Nano wire exhibit improved mechanical strength.
 However, the capability of nanomaterials to undergo extensive
where Tm is the melting point of the nanomaterial, and D is
 tensile deformation without destroying the structure has been
their dimension. The reason behind the decrease in the melting
 well reported and is called as super-plasticity. The large
point of the nanoparticles is described as: In solid phase, the
 surface to volume ratio of nanoparticles results in a generation
surface atoms are coordinatively unsaturated and therefore
 of different local environment for the surface atoms that alters
high amount of surface energy is associated with them.
 the magnetic coupling and interaction with neighboring atoms
Surface energy is always lower in liquid phase than the solid
 and thereby changing mechanical properties. Unlike bulk
phase. The process of melting starts from the surface and thus
 ferromagnetic materials, which usually form multiple
the nanoparticle system is much more stable in the liquid
 magnetic domains, their nanoparticles could consist of only a
phase due to reduced surface energy. The nanoparticles whose
 single magnetic domain. The particle having single magnetic
size decreases below 3-4 nm undergo drastic decrease in
 domain can be used in super-para-magnetism, in which the
melting point.
 magnetizations of the particles are randomly distributed and
 they are aligned only under an applied magnetic field, and the
 alignment disappears once the external field is withdrawn.
 These could be used in various applications such as in ultra-
 compact information storage where the size of the domain
 determines the limit of storage density.
 The nanomaterials may be stronger than bulk. The
 relationship between the material strength and grain size can
 be given by Hall-Petch effect,
 
 = 0 + (6)
 √ 
 where σy is the yield stress, σo is the material constant, ky is the
 strengthening coefficient and d is the average grain diameter.
 Theoretically a material could be made infinitely strong if the
 grain size is made infinitely small.

 1.8.5 Optical properties
 Many of the optical properties are closely related to the
 Fig. 4 Size dependent melting point of materials. electrical and electronic properties of the materials. But as we
 shall see other factors also come into the picture when dealing
1.8.4 Mechanical properties with optical properties. When we are concerned with optical
A very interesting and yet not well explored aspect of properties, we usually refer to interaction of electromagnet
nanotechnology is the mechanical properties of Nano- radiation with matters.[36] The particles are so small that
materials. A Nano electromechanical device is different from electrons are not free to move about as in bulk. Because this
its bulk counterparts. Because of small size, displacement and movement is restricted the particles react differently with light.
force involved in nanoscale mechanical motion, the operation Optical properties have specifically gained an indispensable
of NEMS depends sensitively on its immediate environment. status in the study of the noble metallic nanostructures. This is
In addition to traditional mechanical parameters such as due to the fact that they show size, shape, surrounding medium
Young’s modulus and elasticity mechanical motion of NEMS and composition dependent absorption profile and exhibit the
is affected by surface quality, surface adsorbent, chemical phenomenon of surface Plasmon resonance.[37] Metal
environment etc. At the nanoscale surface and interface forces nanoparticles show different optical properties from their bulk.
become dominant. For example, adhesive forces, capillary The optical properties are size dependent. Gold which is
forces, strain forces. These forces can exceed forces that are yellowish color metal can be obtained in different colors in the
dominant at macroscopic length scale. Grain boundary plays a form of its colloidal solution. The different color of butterfly
significant role in material properties. Changes in grain size is due to the way in which the nanostructure interacts with
result in a high density of incoherent interfaces or other lattice light. The absorption profile of nanoparticles varies from
defects such as dislocation, vacancies etc. Mechanical strength visible region to NIR region depending on the size and shape
of the material depends on various parameters such as of nanoparticles.[38] Gold, Silver and Copper nanoparticles are
dislocation, impurity and surface to volume ratio etc. The known to exhibit unique optical properties in visible and NIR

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region within certain size limit of particle. The size dependent solvent can be calculated from optical constant of the bulk
optical properties of nanomaterials are depicted in Fig. 5. In metal. The absorption spectrum of spherical particles of sizes
this figure, different colors are observed due to different size between 3 to 20 nm does not strongly depend upon particle
and morphology of nanomaterials dissolved in the solvent.[39] size. This is because the particles are below size at which
 higher order terms in the Mie formula for the absorption
 constant becomes significant thus one has to regard only the
 dipole terms, which depends upon the total metal
 concentration in the solution and not on particle size. Higher
 order modes become more dominant with increasing particle
 size, causing the Plasmon absorption band to red shift and
 resulting in increased bandwidth. In case of large particle size,
 the light cannot polarize the nanoparticles homogeneously and
 Fig. 5 Size dependent optical properties of nanoparticles. retardation effects lead to the excitation of higher order modes.
 Within the size range of 25nm, the nanoparticles can be treated
 It finds that the band gap and the size of nanoparticles have within the dipolar approximation and the absorption profile
inverse relation. Because of quantum confinement effect band does not much depend on the particle size. Though, it has been
gap is getting higher as the size of nanoparticles decrease. reported that below the size limit of 10nm the particle start
When we synthesize the nanoparticles from bulk the density showing size dependence of the Plasmon resonance band and
of state in conduction band changes. To excite the electron ultimately disappear for particle size below 2 nm.[47]
from valance band to conduction need more energy because
the spacing of band gap and electronic levels are increase with
decrease in particle size. As the particle size increases it
observes the red shift and although the band gap is decreases.
[40-41]

1.8.6 Surface plasmon resonance
It appears due to the interaction of electromagnetic radiation
with the electron cloud present on the surface of metal
nanoparticles. Surface plasmon resonance (SPR) is the Fig. 6 Schematic of Surface Plasmon oscillations for a sphere
collective oscillation of electrons in a solid or liquid stimulated showing the displacement of the conduction electrons charge
by incident electromagnetic radiation. The resonance cloud relative to the nuclei.
condition is established when frequency of photons matches
the natural frequency of surface electrons oscillating against To explain the optical absorption of the cylindrical and
the restoring force of positive nuclei. The SPR in oblate nanoparticles, Gans theory extended the Mie theory
nanomaterials is also called localized surface plasmon within the dipole approximation. The Plasmon resonance of
resonance. SPR is the basis of many standard tools for Nano-rods shows two discrete energy levels; one is the high
measuring absorption of material onto planar metal surfaces energy band for the out of phase transverse Plasmon resonance
or onto the surface of metal nanoparticles. It is the and another is low energy band corresponding to in phase
fundamental principle behind many color-based biosensor longitudinal Plasmon resonance along the axis of Nano-rods.
applications and different lab-on-a-chip sensor.[42] The transverse Plasmon band shows a linear relationship with
 Atoms present on the surface of nanoparticles contribute the aspect ratio and dielectric constant of the medium. With an
electron cloud. As shown in Fig. 6 the movement of these free increase in aspect ratio, the energy separation between the two
electrons under the influence of electric field vector of the Plasmon bands also increases. Similarly, triangular
incoming electromagnetic radiation leads to a dipole nanoparticles also show two absorption bands corresponding
excitation in the nanoparticle.[43] This induces positive to transverse and longitudinal Plasmon resonance. In certain
polarization charge on cationic lattice. This charge acts as a cases, another peak in between two Plasmon peaks has also
restoring force, and brings back electron cloud to its original been reported which has been attributed to the in- phase
position, thus causing the oscillation of electrons.[44] quadruple mode of Plasmon resonance.[48]
 Thus the oscillation of surface electrons, whose thickness Several attempts have been made towards successful
is nearly equal to the screening length of a few angstrom’s, synthesis of anisotropic metal nanostructures such as rods,
takes place whereas the electron density in the interior of the disks, triangular prisms, multi-pods, cubes and Nano-shells
particle remains constant.[45] This distinguishing property of and their optical properties has been studied. Some noble
nanoparticles is called Surface Plasmon resonance, and is first metal nanoparticles such as Gold and Silver possess transverse
explained by Mie in 1908, based on the Maxwell’s equation of plasmon absorption on the visible region of electromagnetic
scattering.[46] The absorption spectrum of particle in a given radiations.[49]

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1.8.7 Magnetic properties semi-conductor crystal. This leads to many unique optical and
The noble metallic nanomaterials exhibit different magnetic transport properties. A typical quantum dot has a diameter in
properties than that of bulk in two ways. The one of the reason the range of 2-10 nm. Quantum dots are usually regarded as
for above mentioned property is the high surface to volume semiconductors. Quantum dots are band gap tunable by size
ratio that results in generation of different local environment which means their optical and electrical properties can be
for the surface atoms in their magnetic coupling/interaction engineered to meet their specific applications. Metals do not
with neighboring atoms. The second reason behind this is have band gap, so quantum confinement is only observed at
unlike bulk ferromagnetic materials which usually form dimensions below 2 nm. The quantum dot can be made by
multiple magnetic domains; several small ferromagnetic various methods such as lithography, colloidal synthesis and
particles could consist of only a single magnetic domain. The epitaxy. Quantum dot technology is one of the promising
super magnetism occurs in single particle in which candidates for use in solid state quantum computation. By
magnetization of the particles are randomly distributed and applying small voltage to the leads, the flow of electrons
they are aligned only under the influence of an applied through quantum dot can be controlled and thereby precise
magnetic field and the alignment disappears once the magnetic measurement of the spin and other properties therein can be
field is withdrawn. This effect is applied in several commercial made. With several entangled quantum dots, or qubits, plus a
and scientific applications such as optical recording or storage way of performing operations, quantum calculations and the
medium, super-magnets etc. The magnetic properties have computation and the computers that would perform them
been in focus of much research in recent days due to their wide might be possible. Here electrons and holes confined in all
application in various areas such as catalysis, biomedicine, three dimensions of space by surrounding materials with a
magnetic resonance imaging, magnetic particle imaging, data large band gap. Quantum confinement is represented in Table
storage, environmental remediation, optical filters etc.[50] 3.
 Table 3. Quantum confinement effect on all three-dimensional
1.8.8 Biocompatibility property
 nanostructures.
Nanoparticles are known to play an important role in many
processes of life sciences and pharmaceutical sciences. Quantum Confinement Description
Nanoparticles affect the cytotoxicity levels in living systems 0-D or quantum dots Systems in which carriers are confined
and that is an important aspect in the study of nanoscience and in all directions and no free carriers
nanotechnology. Nanoparticles have been used for various 1-D or quantum wires The carriers are free to move down the
biological applications and in other fields also. They have directions of the wire
found the potential future in the field of bio-diagnostics, 2-D or quantum wells The carriers act as free carriers in the
therapeutics, drug delivery, bio-imaging, immune-staining and plane. First observed in semi-conductor
bio-sensing. Thus, it becomes an important issue to study the systems.
short- and long-term effects of size, shape and surface 3-D All carriers act as free carriers in all
functional groups on the bioavailability, sub-cellular three directions.
distribution, metabolism and degradation of these different Researchers are trying to develop flexible and transparent
nanostructures. Some of the efforts made towards this aim are coatings that conduct electricity particularly well.[52-55]
the studies using carbon nanostructures, CdSe quantum dots
and gold nanoparticles. Shastry et al. have studied the uptake 1.8.10 Catalytic Properties
of gold nanoparticles by mammalian cells by pinocytosis and As the particle size decreases, the fraction of surface atoms
its compartmentalization in lysosomal bodies. With high significantly increases; for example, 3 nm particles would
scattering cross section of gold nanoparticles in the NIR region, have 45% of its atoms on the surface and a 1 nm particle would
they are also being considered for use as intravenous contrast have 76% of the atoms on its surface. As any reaction takes
enhancer in medical imaging.[51] place at the surface therefore small particle sized nanomaterial
 having high percentage of surface atoms make them a good
1.8.9 Electrical properties catalyst. Gold is considered to be a noble metal in bulk state
At Nano scale the material are showing different electrical but the nanoparticles of gold dispersed in alumina or iron
properties. The metals that are known for their good oxide was found to be excellent catalysts for oxidation of
conductance behave as semiconductor at Nano-level. As carbon monoxide. Apart from the particle size, the other
explained earlier the size can have drastic effects on the factors controlling the rate of chemical reaction are surface
properties of samples in Nano scale range. At Nano level, structure, shape of the nanomaterial, electronic state of atoms
electrons are confined within a small radius. Single electron in nanomaterial, and work function of a nanoparticle etc. The
tunneling is one of the most remarkable effects exhibited by reactant molecules show differential affinity in adsorption
quantum dots. The capacitance of a dot can be changed towards different faces of the catalyst. Hence metal
drastically simply by the addition of a single extra electron as nanoparticles of different shapes covered by different faces
a result of one electron tunneling. Quantum dot is nano sized could be used to increase the selectivity of a catalyst. Hence

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surface reactivity tailored in such a way by varying the shape complete its valency and the unoccupied bond is known as
of the nanoparticle could help in designing molecular specific dangling bond, which makes the surface more reactive.
catalyst.[56,57] Therefore, the nanoparticles are unstable as compared to its
 counter bulk parts.[59]
1.8.11 Electronic properties
When the particle size enters Nano meter level, electronic
motion is restricted to a smaller space compared to mean free
path of electrons leading to the stronger confinement of
electronic motion (spatial confinement). These materials do
not follow the classical theory of electronic motion which
exhibit quantum effect. The quantization of electronic motion
in metallic nanoparticles restricts them into certain discrete
energy levels making the valence and conduction band no
longer in-separable. The energy gap between valence band and
conduction bond (Kubo gap) becomes comparable to or larger
than thermal energy (KBT) at certain size regime and hence
metallic nanoparticles become semiconductor and further
reduction of size causes higher confinement and reaches a
stage when the material becomes an insulator. At these stage
materials behave differently towards various perturbations and
exhibit properties not achievable from its individual
counterparts or from the bulk. Apart from the size dependence Fig. 7 Surface to volume ratio vs size of the particle.
of various properties of nanomaterials, they also exhibit
interesting shape dependence due to the execution of
 1.9.2 Forces
electronic motion in different dimensions. For example,
 The magnitude of the forces (gravitational, electrostatic etc)
electronic tunneling phenomenon is observed for 0-D
 between objects decides their size and the distance between
nanostructures which is the key concept used for building
 them. At the Nano-scale, gravitational forces are so weak that
artificial atoms and devices like single electron transistors.
 they can be neglected.[60] This is just similar to escape velocity
Similarly, the electron can oscillate in two distinct ways in 1-
 i.e. at extremely high speed of 11.3 km/s gravitational force
D nanostructures under electromagnetic field, namely in
 becomes ineffective. At the same time the nuclear force is
longitudinal and transverse modes. The way electrons execute
 strong but its range is so smaller that it can be neglected.[61] At
its motion alters their various properties and thus Nano-rods
 nano-scale particular importance are gained by several forces
and Nano-tubes give rise to Surface Plasmon absorption peaks
 (e.g. Van der Walls force) that are electrostatic in origin. They
due to the two different types of electronic motion.[58]
 are especially important for self-assembly. The main focus of
 this thesis is the development of new methods for the synthesis
1.9 Change in property at nanoscale
 of noble metallic nanoparticles in different media with varying
As discussed earlier the change in properties at nanoscale is
 size, shape and sustained stability. The next section follows the
attributed to the following reasons.
 methods of preparation of metal nanoparticles and its stability.
1.9.1 High aspect ratio
 1.10 Stability of nanoparticles
Nanoparticles are having high aspect ratio i.e. surface to
 Nanoparticles are inherently unstable and they tend to form
volume ratio. For example for a spherical particle, surface area
 agglomerate but for any kind of application we need stable
= 4 2 and volume = 4/3 π r3 Then,
 nanoparticles.[62] Monolayer or mixed monolayer of different
 4 2 
 = 4 3 (7) molecules having different functionalities at both ends has
 
 3 been used to functionalize gold nanoparticles. In these
where, σ is surface area factor of the given shape w.r.t. sphere methods, reduction of metal ions by weak reducing agents was
and is volume factor of the given shape w.r.t. sphere performed in the presence of capping molecules.[63] During the
 (8) synthesis of nanoparticles, size of nanoparticles depends on
 3 1
 = ( ) 
 the stoichiometric ratio of metal ion to capping ligands
As shown in Fig. 7, if → 0, → ∞ concentration. It can be further modified to different
 Atoms are having coordination with surrounding. In bulk functional molecules with the help of ligand exchange
material all the atoms are able to complete its coordination reactions. Many times surface modified nanoparticles may
number with surroundings, while surface atoms are not able to lose stability due to ionic strength of solutions and strong inter-
complete its coordination number. Thus surface atom does not molecular interaction between capping agents.

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 To overcome this problem, new capping molecules with resulting in the maxima in the potential energy diagram. This
different amino acid sequence have been developed which maximum is the repulsion energy barrier between two
mimic the principles of naturally occurring non aggregating nanoparticles. Potential barrier depends upon the thickness of
proteins. These capping ligands readily attach to the surface the double layer formed around the nanoparticles. Greater the
and form well packed passivating surface with hydrophilic thickness of the double layer, higher is the potential energy
terminus, which makes it soluble and stable even in the barrier.[67] If this barrier is greater than the certain value,
presence of salt in aqueous phase. This ability to control the nanoparticles solutions remain stable. Electrostatic
properties of surfaces of nanoparticles can be used to stabilize stabilization is the kinetic stabilization process and it is useful
nanoparticles.[64] Use of nanoparticles have been shown in only in the case of dilute solution. Additions of electrolytes
various applications such as solution-based sensors, electronic screen the double layer charge leading to aggregation.[68]
devices, and drug delivery systems. Surface modification has
two advantages; it protects nanoparticles from agglomeration
and provides various functionalities to the nanoparticles
surface.

1.10.1 Surface modification of nanoparticles
Surface modification of nanoparticles is a very important
factor for stability and designed functionality. Atoms on the
surface possess less co-ordination number than the bulk atoms.
Thus it experiences inward force and tries to achieve
maximum co-ordination number. It results in smaller bond
length with its immediate atomic layer than bulk atoms. As the
nano particle size decreases, more and more atoms are
exposed to the surface leading to decrease in the bond length
with its next layer of atoms. At such a small scale, large
numbers of atoms are present on the surface and as Fig. 8 Scheme showing the stabilization of metal nanoparticles
consequence of these lattice parameters of nanoparticles by electrostatic interaction.
changes. Energy required to bring back these atoms to its
original position is nothing but surface energy.[65] As the 1.10.3 Stability of nanoparticles by capping agents
particle size of the nanoparticles decreases their surface energy Capping of nanoparticles with suitable ligands can overcome
increases significantly. Increase in the surface energy also the above-mentioned disadvantages. As mentioned earlier,
results in the increase in the Gibb’s free energy. According to lithographic technique can be used for the synthesis of two as
the law of thermodynamics, every system always tries to attain well as three dimensional nanostructures. But these techniques
minimum Gibb’s free energy; therefore, it loses its nanoness have inherent limitations of two dimensionality of lithographic
and exotic properties related to it. Hence it is very important step. Surface modification of nanomaterials gives freedom of
to stabilize the nanoparticles against the aggregation. There controlling the interactions around its surface, which can be
are many ways by which nanoparticles can be stabilized.[66] used to build three dimensional structures. Capping agents
 also minimize surface energy of nanoparticles and prevents
1.10.2 Electrostatic stabilization uncontrolled growth of the nanoparticles.[69]
During the synthesis of the noble metallic nanoparticles Stability is always an important issue when metal
specifically, the particles formed are surrounded by the nanoparticles are synthesized in solvent since small particles
electronic double layer due to adsorption of reactant ions on are unstable and tends towards aggregation to form bulk in
the surface of nanoparticles. Simultaneously there are two order to acquire the stability. At short inter-particle distance,
factors acting on the nanoparticles; first the Van der Waals two particles would be attracted to each other that will lead to
forces of attraction, and second the electrostatic force of aggregation which would be countered by the repulsive double
repulsion due to the charged ions on the surface. Stability of layer and steric interactions. In the case of nanoparticle
nanoparticles is dependent on the combined effect of these two synthesized in aqueous medium, an aqueous double layer is
forces. formed by adsorption of precursor ions which surrounds
 Fig. 8 shows the graph of potential energy versus distance nanoparticles. This layer of ions is immediately surrounded by
between the nanoparticles. At far distance electrostatic counter ions resulting in columbic repulsion between particles.
repulsion and Van der Waals forces of attraction are zero. At As nanoparticles are having some charge their aggregation is
zero distance there is deep minimum in the potential energy prevented. Under solution condition if there is low ionic
curve due to strong dominating Van der Waals forces of strength and moderate surface potentials the electrostatic
attraction. As nanoparticles go away from each other repulsion between the particles is sufficient to prevent
electrostatic force starts dominating the force of attraction attractive forces causing the particles to aggregates.[70]

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