Silver Nanoparticles and its Antibacterial Activity

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*Corresponding Author: M.Dhanalakshmi, Email: dhana_booma@yahoo.co.in, Phone No: +91-9443873051
ISSN 0976 – 3333
REVIEW ARTICLE
Available Online at www.ijpba.info
International Journal of Pharmaceutical & Biological Archives 2013; 4(5): 819 - 826
Silver Nanoparticles and its Antibacterial Activity
M.Dhanalakshmi*, S.Thenmozhi, K.Manjula Devi, S.Kameshwaran
Swamy Vivekanandha College of Pharmacy, Thiruchengode, Namakkal (Dist), Tamil Nadu, India
Received 09 May 2013; Revised 20 Sep 2013; Accepted 29 Sep 2013
ABSTRACT
Nanotechnology is the creation and utilization of materials, devices, and systems through the control of
matter on the nanometer-length scale (a nanometer is one billionth of a meter). The size of nanomaterials
is similar to that of most biological molecules and structures; therefore, nanomaterials can be useful for
both in vivo and in vitro biomedical research and applications. The nanoparticles of silver showed high
antimicrobial and bactericidal activity. All major pharmaceutical companies are currently investing
significantly in the development of medicines with a nanotechnology component. Such research promises
therapeutic drugs with greater efficacy and a wider range of clinical indications. In the current global
financial crisis such systems are likely to become increasingly attractive. The importance of bactericidal
nanomaterials study is because of the increase in new resistant strains of bacteria against most potent
antibiotics. This has promoted research in the well known activity of silver nanoparticles. Silver
nanoparticles exhibiting bactericidal properties are reviewed and discussed.
Key words: Nanoparticles ; Silver nanoparticles; antibacterial effect; Application of silver nanoparticles
1. INTRODUCTION
Nanotechnology is the science of the small with
big potential it will revolutionize our world.
Nanotechnology involves the production,
manipulation and use of materials ranging in size
from less than a micron to that of individual atoms
[1]. Nanotechnology often referred as the
manipulation of matter at the atomic molecular
level. The word ‘nano’ derives from the greek
nanos, which means dwarf. A nanometer is the
one billionth of a meter, or roughly 75,000 times
smaller than the width of a human hair.
Approximately 3 to 6 atoms can fit inside a
nanometer (nm), depending upon the atom.
Nanotechnology involves the study, manipulation,
creation and use of materials, devices and systems
typically with dimensions smaller than 100 nm [2].
The term "nanotechnology" was first defined by
Tokyo Science University, Norio Taniguchi in a
1974 paper as follows: "'Nano-technology' mainly
consists of the processing of, separation,
consolidation, and deformation of materials by
one atom or one molecule [4]
1. "Wet" nanotechnology is the study of
biological systems that exist primarily in a
water environment. The functional
nanometer-scale structures of interest here
are genetic material, membranes, enzymes
and other cellular components. The
success of this nanotechnology is amply
demonstrated by the existence of living
organisms whose form, function, and
evolution are governed by the interactions
of nanometer-scale structures.
. Nanotechnology and
nanoscience got a boost in the early 1980s with
two major developments: the birth of cluster
science and the invention of the scanning
tunneling microscope (STM).
Nanotechnology is expected to open some new
aspects to fight and prevent diseases using atomic
scale tailoring of materials. The ability to uncover
the structure and function of biosystems at the
nanoscale, stimulates research leading to
improvement in biology, biotechnology, medicine
and healthcare.
This development led to the discovery of
fullerenes in 1985. There are three distinct
nanotechnologies:
2. "Dry" nanotechnology derived from
surface science and physical chemistry
focuses on fabrication of structures in

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carbon (for example, fullerenes and
nanotubes), silicon, and other inorganic
materials. Unlike the "wet" technology,
"dry" techniques admit use of metals and
semiconductors. The active conduction
electrons of these materials make them too
reactive to operate in a "wet" environment,
but these same electrons provide the
physical properties that make "dry"
nanostructures promising as electronic,
magnetic, and optical devices. Another
objective is to develop "dry" structures
that possess some of the same attributes of
the self-assembly that the wet ones exhibit.
3. Computational nanotechnology permits
the modeling and simulation of complex
nanometer-scale structures. The predictive
and analytical power of computation is
critical to success in nanotechnology:
nature required several hundred million
years to evolve a functional "wet"
nanotechnology; the insight provided by
computation should allow us to reduce the
development time of a working "dry"
nanotechnology to a few decades, and it
will have a major impact on the "wet" side
as well.
These three nanotechnologies are highly
interdependent. The major advances in each have
often come from application of techniques or
adaptation of information from one or both of the
others [4]
Nanoparticles are defined as particulate
dispersions or solid particles with a size in the
range of 10-1000nm. The drug is dissolved,
entrapped, encapsulated or attached to a
nanoparticle matrix. Depending upon the method
of preparation, nanoparticles, nanospheres or
nanocapsules can be obtained. Nanocapsules are
systems in which the drug is confined to a cavity
surrounded by a unique polymer membrane, while
nanospheres are matrix systems in which the drug
is physically and uniformly dispersed. In recent
years, biodegradable polymeric nanoparticles,
particularly those coated with hydrophilic polymer
such as poly(ethylene glycol) (PEG) known as
long-circulating particles, have been used as
potential drug delivery devices because of their
ability to circulate for a prolonged period time
target a particular organ, as carriers of DNA in
gene therapy, and their ability to deliver proteins,
peptides and genes
.
2. NANOPARTICLES
[5-8]. The use of nanoparticles
in biological applications is being widely explored
eg: polymeric nanoparticles, metallic
nanoparticles and quantum dots have been found
applicable in drug delivery, bioimaging and
biosensing [9-11].
The major goals in designing nanoparticles as a
delivery system are to control particle size,
surface properties and release of
pharmacologically active agents in order to
achieve the site-specific action of the drug at the
therapeutically optimal rate and dose regimen.
Though liposomes have been used as potential
carriers with unique advantages including
protecting drugs from degradation, targeting to
site of action and reduction toxicity or side effects,
their applications are limited due to inherent
problems such as low encapsulation efficiency,
rapid leakage of water-soluble drug in the
presence of blood components and poor storage
stability. On the other hand, polymeric
nanoparticles offer some specific advantages over
liposomes. For instance, they help to increase the
stability of drugs/proteins and possess useful
controlled release properties. The advantages of
using nanoparticles as a drug delivery system
include the following:
1. Particle size and surface characteristics of
nanoparticles can be easily manipulated to
achieve both passive and active drug
targeting after parenteral administration.
2. They control and sustain release of the drug
during the transportation and at the site of
localization, altering organ distribution of
the drug and subsequent clearance of the
drug so as to achieve increase in drug
therapeutic efficacy and reduction in side
effects.
3. Controlled release and particle degradation
characteristics can be readily modulated by
the choice of matrix constituents. Drug
loading is relatively high and drugs can be
incorporated into the systems without any
chemical reaction; this is an important
factor for preserving the drug activity.
4. Site-specific targeting can be achieved by
attaching targeting ligands to surface of
particles or use of magnetic guidance.
5. The system can be used for various routes
of administration including oral, nasal,
parenteral, intra-ocular etc [12,13]
Nanoparticles can be prepared from a variety of
materials such as proteins, polysaccharides and
synthetic polymers. The selection of matrix
.
2.1 Preparation of Nanoparticles
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materials is dependent on many factors including:
(a) size of nanoparticles required; (b) inherent
properties of the drug, e.g., aqueous solubility and
stability; (c) surface characteristics such as charge
and permeability; (d) degree of biodegradability,
biocompatibility and toxicity; (e) Drug release
profile desired; and (f) Antigenicity of the final
product [14]
For centuries silver has been in use for the
treatment of burns and chronic wounds. As early
as 1000 B.C. silver was used to make water
potable
.
3. Silver as antimicrobial agent
[15,16]. Silver nitrate was used in its solid
form and was known by different terms like,
“Lunar caustic” in English, “Lapis infernale” in
Latin and “Pierre infernale” in French [17]. In
1700, silver nitrate was used for the treatment of
venereal diseases, fistulae from salivary glands,
and bone and perianal abscesses [17,18]. In the 19th
century granulation tissues were removed using
silver nitrate to allow epithelization and promote
crust formation on the surface of wounds. Varying
concentrations of silver nitrate was used to treat
fresh burns [16,17]. In 1881, Carl S.F. Crede cured
opthalmia neonatorum using silver nitrate eye
drops. Crede's son, B. Crede designed silver
impregnated dressings for skin grafting [17,18]. In
the 1940s, after penicillin was introduced the use
of silver for the treatment of bacterial infections
minimized [19-21]. Silver again came in picture in
the 1960s when Moyer introduced the use of 0.5%
silver nitrate for the treatment of burns. He
proposed that this solution does not interfere with
epidermal proliferation and possess antibacterial
property against Staphylococcus aureus,
Pseudomonas aeruginosa and Escherichia coli
[22,23]. In 1968, silver nitrate was combined with
sulfonamide to form silver sulfadazine cream,
which served as a broad-spectrum antibacterial
agent and was used for the treatment of burns.
Silver sulfadazine is effective against bacteria like
E. coli, S. aureus, Klebsiella sp., Pseudomonas
sp.It also possesses some antifungal and antiviral
activities [24].Recently, due to the emergence of
antibiotic-resistant bacteria and limitations of the
use of antibiotics the clinicians have returned to
silver wound dressings containing varying level of
silver [25,21]
The exact mechanism of action of silver on the
microbes is still not known but the possible
mechanism of action of metallic silver, silver ions
and silver nanoparticles have been suggested
according to the morphological and structural
changes found in the bacterial cells.
.
3.1 Mechanism of action
3.1.1 Mechanism of action of silver
The mechanism of action of silver is linked with
its interaction with thiol group compounds found
in the respiratory enzymes of bacterial cells.
Silver binds to the bacterial cell wall and cell
membrane and inhibits the respiration process [17].
In case of E. coli, silver acts by inhibiting the
uptake of phosphate and releasing phosphate,
mannitol, succinate, proline and glutamine from
E. coli cells [26-30].
3.1.2. Mechanism of action of silver
ions/AgNO3
The mechanism for the antimicrobial action of
silver ions is not properly understood however,
the effect of silver ions on bacteria can be
observed by the structural and morphological
changes. It is suggested that when DNA
molecules are in relaxed state the replication of
DNA can be effectively conducted. But when he
DNA is in condensed form it loses its replication
ability hence, when the silver ions penetrate inside
the bacterial cell the DNA molecule turns into
condensed form and loses its replication ability
leading to cell death. Also, it has been reported
that heavy metals react with proteins by getting
attached with the thiol group and the proteins get
inactivated [31,32].
3.1.3 Mechanism of action of silver
nanoparticles
The silver nanoparticles show efficient
antimicrobial property compared to other salts due
to their extremely large surface area, which
provides better contact with microorganisms. The
nanoparticles get attached to the cell membrane
and also penetrate inside the bacteria. The
bacterial membrane contains sulfur-containing
proteins and the silver nanoparticles interact with
these proteins in the cell as well as with the
phosphorus containing compounds like DNA.
When silver nanoparticles enter the bacterial cell
it forms a low molecular weight region in the
center of the bacteria to which the bacteria
conglomerates thus, protecting the DNA from the
silver ions. The nanoparticles preferably attack the
respiratory chain, cell division finally leading to
cell death. The nanoparticles release silver ions in
the bacterial cells, which enhance their
bactericidal activity [32-35]
The apparatus used in the experiment is shown in
(Fig 1). Added 50 ml silver nitrate solution (1.0 ×
.
4.SYNTHESIS OF SILVER
NANOPARTICLES
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10-3 mol L-1) into a 500 ml flask (A), which was
placed into a constant temperature water bath on a
magnetic stirrer. Then 50 mL ammonia solution
(1.0 mol L-1) was added into another 500 ml flask
(D). Flasks A and D were connected with glass
tubes and short pieces of rubber tubes, through
which the ammonia gas in flask D volatilized and
diffused slowly into the flask A and reacted with
the silver nitrate solution. In all stirring
procedures of preparing silver nanoparticles, the
vessel was exposed to the light of a daylight lamp
(40 W) at a distance of 100 cm. The whole
experiment lasted 54 hours. The detailed
procedure of preparing silver nanoparticles
contained five steps: (1) keep the reaction 11
hours under stirring (~39 ºC water bath); (2) keep
the reaction for 13 hours without stirring and
heating; (3) keep the reaction for 10 hours
(conditions are same as step 1); (4) repeat the step
2; (5) keep the reaction for 7 hours [36]
Figure 1: Apparatus for silver nanoparticles synthesis (A.
conical flask with AgNO3 solution; B. constant temperature
water bath; C. magnetic stirrer; D. conical flask with
NH3.H2O).
5.SILVER NANOPARTICLES AS
ANTIBACTERIAL AGENT
.
Over the past few decades, inorganic
nanoparticles, whose structures exhibit
significantly novel and improved physical,
chemical, and biological properties, phenomena,
and functionality due to their nanoscale size, have
elicited much interest. Nanophasic and
nanostructured materials are attracting a great deal
of attention because of their potential for
achieving specific processes and selectivity,
especially in biological and pharmaceutical
applications [37,38]. Discoveries in the past decade
have demonstrated that the electromagnetic,
optical, and catalytic properties of noble-metal
nanocrystals are strongly influenced by shape and
size [39,40]. This has motivated an upsurge in
research on the synthesis routes that allow better
control of shape and size [41-43], with projected
applications in nanoelectronics and spectroscopy
[44-46]. Recent studies have demonstrated that
specially formulated metal oxide nanoparticles
have good antibacterial activity [47], and
antimicrobial formulations comprising
nanoparticles could be effective bactericidal
materials [48,49]. Among inorganic antibacterial
agents, silver has been employed most extensively
since ancient times to fight infections and control
spoilage. The antibacterial and antiviral actions of
silver, silver ion, and silver compounds have been
thoroughly investigated [50-52]. However, in minute
concentrations, silver is nontoxic to human cells.
The epidemiological history of silver has
established its nontoxicity in normal use. Catalytic
oxidation by metallic silver and reaction with
dissolved monovalent silver ion probably
contribute to its bactericidal effect [53]. Microbes
are unlikely to develop resistance against silver, as
they do against conventional and narrow-target
antibiotics, because the metal attacks a broad
range of targets in the organisms, which means
that they would have to develop a host of
mutations simultaneously to protect themselves.
Thus, silver ions have been used as an
antibacterial component in dental resin composites
[54], in synthetic zeolites [55], and in coatings of
medical devices [56]. Recent literature reports
encouraging results about the bactericidal activity
of silver nanoparticles of either a simple or
composite nature [57,33].It is found that silver
nanoparticles undergo a size-dependent
interaction with human immunodeficiency virus
type 1, preferably via binding to gp120
glycoprotein knobs [58]. The size-dependent
interaction of silver nanoparticles with gram-
negative bacteria has also been reported by the
same group [34]
The silver nanoparticle showed high antimicrobial
and bactericidal activity against gram positive
bacteria such as Escherichia Coli, Pseudomonas
aureginosa and Staphylococcus aureus. Colloidal
silver nanoparticles inhibited the growth and
multiplication of the tested bacteria, including
highly multiresistant bacteria such as methicillin-
resistant Staphylococcus aureus,. Escherichia coli
and Pseudomonas aeruginosa. Such high
antibacterial activity was observed at very low
total concentrations of silver below 6.74 μg/ml
.
[4].
The microorganisms such as bacteria, yeast and
now fungi play an important role in remediation
of toxic metals through reduction of the metal
ions, this was considered interesting as
nanofactories very recently. A new generation of
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M.Dhanalakshmi et al. / Silver Nanoparticles and its Antibacterial Activity
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dressing incorporating antimicrobial agents like
silver was development to reduce or prevent
infections. Extracellular production of silver
nanoparticles by F. oxysporum strain and its effect
bactericide in cotton and silk cloth against S.
aureus. Antibacterial activity was observed when
silver nanoparticles were incorporated in cotton
cloth. It is reported successfully that biological
synthesized silver nanoparticles incorporated in
materials with the objective to make them sterile
[59]
Silver nanoparticles dispersed in chitosan solution
can be directly applied in antimicrobial fields,
including antimicrobial food packaging and
biomedical applications. The silver nanoparticles
exhibited antimicrobial activities against
Escherichia coli and Staphylococcus aureus Silver
nanoparticles were prepared by γ ray irradiation–
reduction under simple conditions, i.e., air
atmosphere, using chitosan as a stabilizer. The
obtained silver nanoparticles dispersed in a 0.5%
(w/v) γ ray irradiated chitosan–aqueous acetic
acid solution were stable for more than 3 months
without tendency to precipitate
.
[60]. Antibacterial
properties of differently shaped silver
nanoparticles against the gram-negative bacterium
Escherichia coli, both in liquid systems and on
agar plates and successfully reported that silver
nanoparticles undergo a shape-dependent
interaction with the gram-negative organism E.
coli. Silver nanoparticles undergo shape-
dependent interaction with the gram-negative
bacterium E. coli. The interactions of silver
nanoparticles with biosystems are just beginning
to be understood, and these particles are
increasingly being used as microbicidal agents. It
may be speculated that silver nanoparticles with
the same surface areas but with different shapes
may also have different effective surface areas in
terms of active facets [61]
The preparation of silver nanoparticles in the
range of 10–15 nm with increased stability and
enhanced anti-bacterial potency. The antibacterial
effect was dose dependent and was more
pronounced against gram-negative bacteria than
gram-positive organisms. The antibacterial effect
of nanoparticles was independent of acquisition of
resistance by the bacteria against antibiotics. The
major mechanism through which silver
nanoparticles manifested antibacterial properties
was by anchoring to and penetrating the bacterial
cell wall, and modulating cellular signaling by
dephosphorylating putative key peptide substrates
on tyrosine residues
.
[62]. Wound healing is
accelerated by silver nanoparticles. Furthermore,
through quantitative PCR, immunohistochemistry,
and proteomic studies, showed that silver
nanoparticles exert positive effects through their
antimicrobial properties, reduction in wound
inflammation, and modulation of fibrogenic
cytokines. The actions of silver nanoparticles and
have provided a novel therapeutic direction for
wound treatment in clinical practice (63).Silver
nanoparticles (Ag-NPs) have been known to have
inhibitory and bactericidal effects. The
antibacterial activities of penicillin G, amoxicillin,
erythromycin, clindamycin, and vancomycin were
increased in the presence of silver nanoparticles
against both test strains. The highest enhancing
effects were observed for vancomycin,
amoxicillin, and penicillin G against S. aureus [64]
1. Prashant Mohanpuria,Nisha K Rana and
Sudesh Kumar Yadav,Biosynthesis of
Nanoparticles: Technological Concepts
and Future
Applications,J.Nanopart.Res.,10 2008
:507-517.
.
6. CONCLUSION
In Summary, it can be concluded that among
different types of antibacterial agents, silver found
to be effective. Silver nanoparticles have been
extensively reviewed and it is seen that silver
nanoparticles are non-toxic to human in minute
concentrations. Silver nanoparticles have also
found its application in wound dressings, medical
devices etc.Silver nanoparticles found to be
effective against various bacteria.
Thus, it can be concluded from the review that,
silver nanoparticles can be extensively used as an
antibacterial agents. The following questions has
to be yet addressed.1.The exact mechanism of
interaction of nanoparticles with the bacterial
cells.2.Toxicity if any of silver dressings.
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