Colloids and Surfaces B: Biointerfaces 105 (2013) 342–352
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Colloids and Surfaces B: Biointerfaces
journal homepage: www.elsevier.com/locate/colsurfb
Review
Biofunctionalized silver nanoparticles: Advances and prospects
Aswathy Ravindran ∗ , Preethy Chandran, S. Sudheer Khan
Center for Nanotechnology and Advanced Biomaterials (CeNTAB), School of Chemical and Biotechnology, SASTRA University, Tirumalaisamudram,
Thanjavur 613401, Tamilnadu, India
a r t i c l e
i n f o
Article history:
Received 23 February 2012
Received in revised form 24 July 2012
Accepted 29 July 2012
Available online xxx
Keywords:
Biofunctionalization
Biocompatibility
Nanotechnology
Silver nanoparticles
a b s t r a c t
The unique size-dependent properties of nano scale materials have significantly impacted all spheres of
human life making nanotechnology a promising field for biomedical applications. Metal nanoparticles like
silver have gained significant interest over the years due to their remarkable optical, electrical and antimicrobial properties. However, the toxic nature and aggregation of these nanoparticles has limited its use in
more optimized applications. Rational selection of therapeutically active biomolecules for functionalizing
the surface of these particles will certainly increase the biocompatibility and biological applicability. The
current review attempts to stress on the application domains of silver nanoparticles and also extends an
overview on the current strategies involved in biofunctionalizing these particles for specific applications.
This review is divided into three sections. The first section emphasizes the importance of silver
nanoparticles and its biomedical applications. The need for functionalization and the various concepts
and techniques involved in creating surface modified silver nanoparticles will be described in the second section; and the last section throws light on the various applications of the functionalized silver
nanoparticles.
© 2012 Elsevier B.V. All rights reserved.
Contents
1.
2.
3.
4.
Silver nanoparticles: an overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.1.
Synthesis of silver nanoparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2.
Applications of silver nanoparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2.1.
Tuning the optical properties of silver for diagnosis and imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2.2.
Antimicrobial properties of nano silver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2.3.
Anti inflammatory effects of nano silver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Need for surface modification of nanoparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.
Biomolecule-mediated nanoparticle organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.1.
Proteins and antibodies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1.2.
DNA based nanoparticle systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.
Biotemplating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.1.
Peptides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.2.
Bacterial and fungal surface layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Applications of the functionalized silver nanoparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1.
Biofunctionalized silver nanoparticles as bioanalyzers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2.
Biomedical applications of functionalized silver nanoparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Conclusion and perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
∗ Corresponding author. Tel.: +91 4362264667; fax: +91 4362264120.
E-mail address: [email protected] (A. Ravindran).
0927-7765/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.colsurfb.2012.07.036
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A. Ravindran et al. / Colloids and Surfaces B: Biointerfaces 105 (2013) 342–352
1. Silver nanoparticles: an overview
The bright and fascinating colors of noble metal nanoparticles [1,2] have attracted significant interest as a novel platform
for nanobiotechnology and biomedicine [3,4]. The applications of
nanotechnology have broadened due to convenient surface bioconjugation with molecular probes and remarkable optical properties
related with the localized plasmon resonance [5]. The frequency of
the surface plasmon resonance lies in the visible spectral range and
depends on several factors like shape, size, dielectric properties of
the particle environment, and interparticle interactions. This frequency also depends on the electron density in the metal and can
be blue- or red-shifted depending on injection or withdrawal of
electrons from the nanoparticles by varying the applied potential
in an electrochemical environment [6–9].
The use of silver as a metal can be traced back to times even
before Neolithic revolution. Moyer first recorded the medicinal
use of silver during 8th century [10]. In recent times, the tunable photophysical attributes of silver nanoparticles [11–13], their
efficient addressability via optical and spectroscopic techniques,
and rapid advances in nanoparticle synthesis and fabrication [14]
have brought these nanoparticles to the forefront of nanotechnology research directed toward applications ranging from photonics
[15,16] to biomedicine [17–21].
1.1. Synthesis of silver nanoparticles
Numerous methods for the synthesis of silver nanoparticles
have been reported which includes chemical reduction [22], thermal decomposition [23], laser ablation [24], and sonochemical
synthesis [25]. Among these, chemical reduction method and laser
ablation method are the most commonly employed synthetic
routes. The chemical reduction method involves the reduction of
metal salt like silver nitrate in an appropriate medium using various
reducing agents like citrate, borohydride, etc. to produce colloidal
suspensions integrated by nanoparticles [26]. In the citrate reduction method described by Lee and Meisel, silver nitrate (90 mg) was
dissolved in 500 mL of distilled water and brought to boiling. A solution of 1% sodium citrate (10 mL) was added and the solution was
kept on boiling for 1 h. The resulting colloid was greenish yellow
and had absorption maximum at 420 nm [22]. Another method,
commonly referred to as the Creightons method uses sodium borohydride as the reducing agent instead of citrate [27]. In this method,
0.00386 g of sodium borohydride (NaBH4 ) was diluted with water
to 50 mL in a volumetric flask. Before proceeding with the reaction, nitrogen was bubbled through the above solution and then
kept in an ice bath to prevent degradation. Next a solution was
made by weighing out 0.00442 g of silver nitrate, which was diluted
with water in a 25 mL volumetric flask. The final step was to add
12 mL of the ice cold prepared aqueous solution of NaBH4 to 4 mL of
the silver nitrate solution with vigorous stirring. This resulted in a
color change to light yellow. Stirring was continued until the reaction reached room temperature. This synthesis procedure routinely
yields particles of narrow size distribution.
Silver nanoparticles can be successfully synthesized by irradiation. For example, laser irradiation (Nd3+ –YAG 500 nm) of an
aqueous solution of silver salt and surfactant can fabricate silver
nanoparticles with a well-defined shape and size distribution [24].
No chemical reducing agent is required in this method.
A quest for environmentally sustainable synthesis processes
has led to a few biomimetic approaches [28]. Such an approach
must be evaluated based on a green chemistry perspective which
includes (1) selection of a suitable solvent medium, (2) selection of
environmentally benign reducing and capping agent which comprises extracts from plants or bio organisms or a combination of
biomolecules found in these extracts such as enzymes/proteins,
343
amino acids, polysaccharides, and vitamins and (3) selection of
nontoxic substances to stabilize the particles [29].
1.2. Applications of silver nanoparticles
The surface plasmon resonant properties of silver nanoparticles have recently been examined for agglomeration, uptake, and
interaction in a variety of live cells with a high illumination system
[30]. Antibacterial properties of metallic silver and its derivatives
are known from time immemorial. In small concentrations, silver is safe for human cells but lethal for the majority of bacteria
and viruses and hence widely used in disinfection of water and
food in everyday life and in the infection control in medicine [31].
Optical properties of silver nanoparticles have also received much
attention due to their potential in advanced photonic and sensor
applications [32]. Herein, we have discussed some of the unique
properties of silver nanoparticles which make them the ultimate
nanoscale material for bio medical applications.
1.2.1. Tuning the optical properties of silver for diagnosis and
imaging
Silver nanoparticles are known for their excellent optoelectronic properties. These unique optical properties originate from
the collective oscillations of conduction electrons termed as surface
plasmon resonance. The factors that contribute to these oscillations
are: (1) acceleration of the conduction electrons by the electric field
of incident radiation, (2) presence of restoring forces that result
from the induced polarization in both the particle and surrounding medium, and (3) confinement of the electrons to dimensions
smaller than the wavelength of light. These properties depend on
their size, shape, composition and their environment including
the spatial ordering of particles. The size-dependent absorbance
of silver nanoparticles was explored to demonstrate how the composition, size, and nanostructure can be employed to adjust the
optical properties [17,33]. According to the reports of Emory and
Nie, silver nanoparticles of varying sizes and shapes exhibited
enhancement signals in the order of 1014 to 1015 . These particles
had a very narrow size range where the enhancement properties were standardized for a given excitation wavelength. Their
results strongly support the idea that size-dependent localized surface plasmon resonance contributes to surface enhanced Raman
signals intense enough to detect single molecules [11]. The detection of various biomolecular analytes using plasmonic sensors is an
area that has received significant attention. The plasmonic properties of silver actively contribute to the large intensities observed
in surface enhanced Raman spectroscopy (SERS). In particular, the
Raman signal of an analyte of interest can be drastically amplified
by adsorbing it onto hot-spots regions of the nanoparticles such
as gaps and junctions resulting in an enhancement signal strong
enough to allow single-molecule detection [34].
As one of the widely accepted SERS active substrates, silver
nanoparticles have proved its role to obtain million fold enhancements in Raman scattering making it a highly sensitive tool for trace
analysis and for probing single molecules [11]. Since the current
antibody based techniques lack in terms of sensitivity for the low
level detection of virus particles, SERS has emerged as a strong tool
which broadens its possibilities in vibrational spectroscopy. In a
recent work carried out by Huang et al. [13] substrates composed
of silver nanorods were used to determine the Raman spectra of
Respiratory Syncytial Virus (RSV) making use of SERS. The power
of SERS was further demonstrated in its use in immunoassays for
the detection of immunoglobulins, peptides, proteins, etc. [14]. The
excellent sensing properties of these nanoparticles as biosensors
[15] are being increasingly exploited and typical examples of these
will be discussed in the later sections of this review.
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A. Ravindran et al. / Colloids and Surfaces B: Biointerfaces 105 (2013) 342–352
1.2.2. Antimicrobial properties of nano silver
Silver is a metal known for its broad spectrum antimicrobial
activity against Gram-positive and Gram-negative bacteria, fungi,
protozoa and certain viruses. The persistence of antibiotic-resistant
bacteria has exploited the anti microbial properties of silver and
silver-based compounds, including silver nanoparticles [16].
1.2.2.1. Nano silver as a potent bactericidal agent. Understanding
the antibacterial mechanism of designed nanoparticles is important for achieving the synergistic effects with biomolecules. In
general the mechanism of cellular toxicity exhibited by metal
nanoparticles is through the release of reactive oxygen species
(ROS) [35]. The anti bacterial properties of silver nanoparticles are
associated with its slow oxidation and liberation of Ag+ ions to
the environment making it an ideal biocidal agent. Moreover, the
small size of these particles facilitates the penetration of these particles through cell membranes to affect intracellular processes from
inside. Additionally, the excellent antibacterial properties exhibited by the nanoparticles are due to their well developed surface
which provides maximum contact with the environment [17].
A better understanding of the bactericidal action of nanosilver would require a proper examination of the membrane-bound
and intracellular nanoparticles. Silver nanoparticles were found to
penetrate into the bacterial cell causing membrane damage and
ultimately the death of the organism. For example, Duran et al.
reported the potential antibacterial activities of silver nanoparticles synthesized using Fusarium oxysporum [19]. The antibacterial
properties exhibited by nano silver can be extended to the textile industry as well [20]. The nanoparticles synthesized using
bio-based approaches were found to have excellent antibacterial
properties over Escherichia coli when impregnated on cotton disks
[18]. There are reports, which have discussed about the synthesis
of metal nanoparticle embedded paints using vegetable oils in lieu
of their excellent antibacterial properties [21].
1.2.2.2. Nano silver in anti fungal therapy. Fungal infections have
become more common in the recent years and silver nanoparticles have emerged itself in use as potential anti fungal agents. In
particular, fungal infections are most commonly found in immune
compromised patients because of cancer chemotherapy or human
immunodeficiency viral infections [22]. There are many reports
showing the anti microbial effects of silver nanoparticles but
the anti fungal effects of silver nanoparticles remain unexplored.
According to the reports of Kim et al., silver nanoparticles exhibited excellent anti fungal activity on Candida albicans by disrupting
the cell membrane and inhibiting the normal budding process [36].
In order to compare the anti fungal effects of silver nanoparticles, amphotericin B, an antifungal agent used to treat serious
systemic infections was used as a positive control [37]. Silver nanoparticles showed remarkable antifungal activity against
Trichophyton mentagrophytes and Candida species. Remarkably,
these particles exhibited similar activity with amphotericin B, but
more potent activity than fluconazole toward all the fungal strains
examined.
1.2.3. Anti inflammatory effects of nano silver
There is an urgent need for the development of new inflammatory drugs as most of the inflammatory diseases are not responsive
to the available drugs. The challenge for the development of efficient anti-inflammatory drugs lies in finding appropriate targets
that are mostly dispensable for host defense against pathogens.
The discovery of potent drugs is expected to revolutionize the
treatment of several inflammatory diseases. Nanocrystalline silver
dressings had wound healing properties by virtue of its size and it
is used as commercial antimicrobial dressings since 1998 [38,39].
2. Need for surface modification of nanoparticles
Appropriate surface functionalization strategies are often a
prerequisite for every possible application as these interactions
ultimately affect the colloidal stability of the particles, and may
yield to a controlled assembly or to the delivery of nanoparticles to a
target, e.g. by appropriate functional molecules on the particle surface. One of the key issues is that the interaction mechanisms and
the nanoscale effects about nanoparticles and bio-macromolecules
have not been well understood. According to Ruckenstein and Li
although many nanoparticles possess excellent physical and chemical properties they do not possess suitable surface properties for
specific applications [40]. Hence, functionalizing the surface of the
nanoparticles in a controlled manner with biomolecules changes
the surface composition, structure and morphology of a material,
leaving the bulk mechanical properties intact. Furthermore, surface
modification of nanomaterials is essential where the surface layer
facilitates the reduction of surface energy simultaneously providing
a protective coating that prevents nanoparticles from agglomeration thus increasing their long term [41]. In short, the process of
bioconjugation or biofunctionalization can be referred to as the
‘natural’ extension of the described concepts of ligand exchange
and chemical functionalization of the biomolecules.
2.1. Biomolecule-mediated nanoparticle organization
The interaction of biomolecules with various types of nanoparticles in a controlled manner has turned toward a number of
biological applications such as biosensing, imaging and hyperthermia treatment. The process creates an interface that is compatible
with the environments of real biological systems [42]. Many
approaches are available which enables the formation, modification and organization of metal nanoparticles. The most commonly
employed methods are the incorporation of these particles onto
glassy surfaces, the use of biomolecules as linker molecules, incorporating bivalent linker compounds, and the deposition of the
particles on structured surfaces. The strategies for the conjugation
of biomolecules to nanoparticles generally fall into four classes:
• Binding of the biomolecule to the surface of the inorganic particle
core through ligand mediated binding, commonly by chemisorption, e.g. thiol groups.
• Electrostatic
interactions
between
positively
charged
biomolecules to negatively charged nanoparticles or vice
versa.
• Covalent binding by conjugation chemistry, exploiting functional
groups on both particle and biomolecules.
• Non-covalent, affinity-based receptor–ligand systems.
Nanoparticles require a suitable surface functional group for
conjugating with various biomolecules. A huge large variety of
organic molecules of different composition, size and complexity
are available in nature that provides structure and function for the
various biological processes and organisms. Examples include, on
the one hand, small molecules like lipids, vitamins, peptides, sugars and larger ones such as natural polymers including proteins,
enzymes, DNA and RNA. Most biomolecules have a carboxylic acid,
primary amine, alcohol, phosphate, or a thiol group on their surfaces [43,44] and hence any number of molecules can be attached to
the nanoparticle surface to make the surface of the metal nanoparticle functional.
Selected examples are discussed below:
According to Ravindran et al. [45] the interaction of silver
nanoparticles with an important circulatory protein bovine serum
albumin (BSA) helped in stabilizing the particles via chemisorption and the modified particles could be more amenable toward
A. Ravindran et al. / Colloids and Surfaces B: Biointerfaces 105 (2013) 342–352
Fig. 1. Binding of thiol groups on the surface of silver nanoparticles.
biosensing application. The wet-chemical preparation of the silver
nanoparticles is mostly carried out in the presence of stabilizing agents like citrate or thiols, which readily binds to the atoms
exposed on the surface of the nanoparticles. For example, the
synthesis of silver nanoparticles with minor modifications in the
borohydride reduction method yielded well-dispersed particles
[46]. One of the commonly employed attachment group is a thiol
group (Fig. 1), which has a strong affinity for both gold and silver
surfaces, and a huge research effort has succeeded in adding a large
range of biological molecules to nanoparticles. The formation of self
assemblies of silver nanoparticles revealed that the interactions of
silver nanoparticles with cysteine lead to a rapid aggregation of
the particles. Under acidic conditions, the functional groups of cysteine were protonated favoring the attachment of the thiol groups
of cysteine to silver surface through ligand exchange reactions. The
positive amine group of cysteine formed salt bridges through electrostatic interaction with carboxylate groups, which resulted in the
aggregation of the particles [47].
The intrinsic metal-chelating properties of cysteine and glutathione enable them to form high-affinity metal–ligand clusters
[48], which serve as excellent matrixes. This is due to the ability
of the corresponding biomolecule to effectively compete for metal
binding sites and thereby restricting the incorporation of inorganic sulfide during the process of metal-sulfide nucleation. The
ability of cysteine and glutathione to dictate the formation of metalsulfide nanoparticles has enabled the thiol containing biomolecules
to mediate the formation of silver sulfide (Ag2 S) nanoparticles.
Attempts to synthesize colloidal Ag2 S nanoparticles were difficult owing to the tendency of Ag2 S to aggregate into bulk. Aryal
et al. had recently reported a simple and reproducible route for
the synthesis of colloidal Ag2 S capped with glutathione and cysteine [49]. Carboxylic acids or thiol containing amino acids confer
additional advantages through which the surface states of these
molecules could be controlled with solution pH, thus providing a
convenient mechanism for modifying the surface states of bifunctionally capped nanoparticles [50]. Ag2 S nanoparticles coated with
dodecanethiol formed self-assembled hexagonal two-dimensional
layers and highly ordered face-centered cubic three-dimensional
structures [51]. Hence from the above examples it is clear that the
surface chemistry and functionality of the particles during modification greatly depends on the ligands and the functional groups
acting on the surface of the particle.
2.1.1. Proteins and antibodies
Functionalization of nanoparticles with amino acids and peptides has been another effective way to enhance specificity and
efficacy of nanoparticle based delivery systems. Proteins are comprised of amino acids (in addition to other naturally occurring or
synthetic amino acids) linked together by amide bonds and possess
different side-chain residues. Each peptide or protein is composed
of a carboxylic and primary amino group at its ends while the amino
345
acid side chains attach additional functional groups or properties
depending on their molecular structure [52].
Furthermore special classes of proteins comprising enzymes and
antibodies can be considered as ideal candidates for surface modification and molecular recognition. Enzymes are highly specialized
molecules that are responsible for metabolism and catalyzing
important biochemical reactions. Antibodies (immunoglobulins)
on the other hand are large Y-shaped proteins that have the ability
to specifically bind to antigens mediated by molecular recognition.
Conjugation of proteins to nanoparticles has tremendous applications in sensing, imaging, delivery, catalysis, therapy and control
of protein structure and activity. Therefore, characterizing the
nanoparticle–protein interface is of great importance. Several
approaches are available for conjugation of proteins to nanoparticles. Non-specific adsorption is one such mechanism in which
the nanoparticles are incubated with the protein, which adsorbs
to the surface of the particles by electrostatic attraction, provided
both partners are oppositely charged. In such cases the molecules
are held together to the surface of the particle by van der Waals
forces, hydrogen bridges, Ag–thiol bonds (from cysteine residues)
or by hydrophobic interaction, e.g. when the pH is close to the pI (iso
electric point) of the protein or the nanoparticle so that the electrostatic repulsion is reduced. Sastry et al. have utilized amino acids for
the development of water-dispersible nanoparticles, wherein they
used the amino acid cysteine (for Ag) [53] or lysine (for Au) [54]
to modify the surface of nanoparticles. According to them amino
acid-capped nanoparticles could be assembled through hydrogen
bonding between amino and carboxylic acid functional groups.
A variety of covalent and non-covalent linking mechanisms have
been reported for the attachment of the nanoparticles (Fig. 2).
Non-covalent interactions mostly take place by the process of
physisorption when the ligand adsorbs to the surface of the
nanoparticle via non-covalent forces, including electrostatic interactions, hydrogen bonding, and hydrophobic interactions. Steric
stabilization is another process that helps in binding capping agents
such as polymers or surfactants to the nanoparticle surface through
non-covalent interactions. In such cases the biomolecules can be
linked directly to the particles through exchange reactions with
stronger binding ligands. The surface coating stabilizes individual
nanoparticles, and at the same time, the steric repulsion inhibits
agglomeration by keeping the nanoparticle dispersion intact. For
instance, gold and silver nanoparticles, which are produced by the
citrate method, have been functionalized with IgG molecules at
high pH values that are slightly above the isoelectric point of the
citrate ligand [55]. This enables an active binding of the positively
charged amino acid side chains of the protein to the negatively
charged citrate groups on the colloids. A flocculation assay can be
used to determine the optimal coupling ratio. On the addition of
an electrolyte to gold and silver nanoparticles, a shielding of the
repulsive double layer occurs which leads to flocculation. Adsorption of proteins on the metal particle stabilizes and steric repulsion
prevents flocculation of the particles. To determine the amount
of stabilizer needed to prevent flocculation the concentration of
the electrolyte is increased in various nanoparticle preparations
that are previously coated with distinct amounts of proteins. In
cases when nanoparticles are functionalized with primary amines,
carboxylic acids and thiol surface groups, they are covalently conjugated with biomolecules via amide, disulfide and ester bonds.
This method is usually applied for coating silver nanoparticles with
immunoglobulins (IgG) and serum albumins that have cysteine
residues accessible for the heterogeneous interphase coupling.
Shenton et al. [55] functionalized gold and silver nanoparticles with
immunoglobulin’s of class G and E (IgG and IgE, respectively). Thus
the functionalized particles had a specificity directed against either
the d-biotin or the dinitrophenyl (DNP) group. Kathiravan et al.
[56] studied the interaction between colloidal AgTiO2 nanoparticles
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A. Ravindran et al. / Colloids and Surfaces B: Biointerfaces 105 (2013) 342–352
Fig. 2. Surface modification of silver nanoparticles through covalent and non-covalent approaches.
and BSA by various spectroscopic measurements. Their results
clearly indicated that colloidal AgTiO2 nanoparticles quench the
fluorescence of BSA through a static mechanism. The binding
constants, quenching rate constants and the number of binding
sites were also calculated. From the synchronous fluorescence
data it was confirmed that the conformational change of BSA was
induced by the interaction of colloidal AgTiO2 nanoparticles with
the tyrosine moiety of BSA. This study would be of importance to
study the interaction of BSA with metal nanoparticles especially in
the field of pharmacy, pharmacology and biochemistry.
Murawala et al. have described [57] a simple method for the synthesis of silver and gold nanoparticles at room temperature using
BSA. Their studies revealed that BSA was able to reduce silver ions
to silver nanoparticles. Hence the synthesized particles were water
soluble and could with stand high salt concentrations. The studies on the interaction of serum albumins with silver nanoparticles
by Shen et al. exhibited a twofold hysteresis effect with the coverage of aggregated silver nanoparticles and the conformational
transition of serum albumins, respectively. Their study states that
this hysteresis theory could be helpful in the application of silver
nanoparticles in biodetection and bioanalysis [58]. However the
functionalization of silver nanoparticles with proteins and amino
acids still needs an intensive study.
2.1.2. DNA based nanoparticle systems
Metal DNA and metal nucleotide interactions have been an
intensive area of study. DNA is considered as the most appropriate molecule that can serve as a construction material in
nanosciences. Regardless of its simplicity, the enormous specificity
of the adenine–thymine (A T) and guanine–cytosine (G C) bonding allows the convenient programming of artificial DNA receptors.
By modifying the number of sequences and conformations, DNA
can be used as the structural element and building block of artificial structures. Hence the ability to synthesize and amplify any
DNA sequence from microscopic to macroscopic quantities by automated methods enhances the power of DNA as a molecular tool.
The great mechanical rigidity of the double helices and the high
physicochemical stability that DNA possesses makes it the most
suitable biomolecule for modifying the surface of nanoparticles.
Even though many reports are available on the functionalization
of gold nanoparticles with DNA for biomedical applications, very
limited literature discusses on silver nanoparticles. Fig. 3 shows a
typical model of a DNA–silver nanoparticle conjugate. DNA acts as
counter ions and may interact with metal ions non covalently to
balance the negative charge of the phosphate backbone. A covalent interaction may also occur with DNA at different binding sites
including the nitrogen centers in nucleobases, sugars and the phosphates. Based on DNA metal studies, Eichorn proposed that Ag+ ion
binds more strongly with nucleobases than phosphates [59].
The work done by Basu et al. describe the synthesis of silver
nanoparticles using borohydride reduction method and its interaction with various bases of DNA. The interaction resulted in the
aggregation of the particles and it was quantified using surface
Fig. 3. Shows a typical model of a DNA–silver nanoparticle conjugate.
A. Ravindran et al. / Colloids and Surfaces B: Biointerfaces 105 (2013) 342–352
plasmon resonance spectroscopy and surface enhanced Raman
scattering [60]. The fabrication of silver nanoparticle ring by plasmid DNA [61] was made possible through electrostatic assembling
of 4-aminothiophenol (4-ATP) capped silver nanoparticles on predefined extended circular plasmid pBR322 DNA. The resulting
silver nanoparticles ring was about 1.5 mm in length and about
2.2 nm in height. For example, a 16 mm DNA molecule with two
cohesive ends was used as a bridge between two gold microelectrodes separated by a distance of about 12 ± 16 mm synthesized
by conventional photolithography [62]. Successful interconnection of the electrodes was confirmed by optical microscopy of
the fluorescent labeled ␭-DNA. Next, the sodium ions bound to
the phosphate backbone of the ␭-DNA were exchanged with Ag
ions, and the latter were chemically reduced by hydroquinone.
This led to the formation of silver nanoparticles on the DNA backbone which then behaved as catalytic sites for reductive deposition
leading to the formation of a silver nanowire. Furthermore, Zheng
et al. [63] reported on the interaction of silver nanoparticles and
nucleic acids in the presence of cetyltrimethylammonium chloride. The interaction mechanism was studied using transmission
electron spectroscopy (TEM), circular dichroism (CD), fluorometry
and UV spectrometry. The fresh silver nanoparticles were adopted
as Rayleigh light scattering (RLS) probes for the determination of
nucleic acids at nanogram levels. The produced probe showed high
selectivity and sensitivity toward the detection of nucleic acid.
2.2. Biotemplating
Biologically inspired nanoparticle synthesis is currently a
rapidly expanding area of research, which draws on many different disciplines. Here we make use of the derived supramolecular
complexes of bio macromolecules and their electrostatic and
topographic properties to synthesize and assemble organic and
inorganic compounds. Peptides, proteins which are produced by
bacteria and fungi, components of nucleic acids, hollow biological
compartments like virus particles, plants, etc. are typically used to
construct stable nanostructures [49,66–68].
2.2.1. Peptides
The concept of using peptides for synthesis and stabilization
of metal nanoparticles was first reported by Naik et al. who synthesized peptide conjugated silver nanoparticles [64]. According to
them the peptides with the amino acid moieties reduced the silver
ions at the interface between the peptide and the metal forming
silver nano crystals. Peptides comprising amino acid moieties of
arginine, cysteine, methionine and lysine are found to favor the
reaction. Similarly it has been observed that under alkaline conditions, ionization of the phenolic group in tyrosine residues reduced
silver ions to a semi-quinone structure.
The interaction of the tyrosine residues in proteins or peptides
with the metal surface occurred through the free N terminus of the
peptide [65]. The above studies indicate that appropriate pH conditions and selection of suitable amino acid moieties in the peptide
can result in the synthesis of stable nanoparticles.
2.2.2. Bacterial and fungal surface layers
Bacteria are known to produce inorganic materials either intracellularly or extra cellularly. Microorganisms are considered as a
potential biofactory for the synthesis of nanoparticles like gold,
silver and cadmium sulfide. Magnetotactic bacteria (synthesizing
magnetic nanoparticles) and S-layer bacteria (produce gypsum and
calcium carbonate layers) are a few among the well-known examples of bacteria synthesizing inorganic materials [49]. By treating
dried cells of Corynebacterium sp. with diamine silver complex,
10–15 nm sized silver nanoparticles were produced. The ionized
carboxyl group of amino acid residues and the amide of peptide
347
chains trapped Ag(NH3 )2+ onto the cell wall and some reducing
groups such as aldehyde and ketone were involved in subsequent
bioreduction. But it was found that the reaction progressed slowly
and could be accelerated in the presence of OH− [67].
Extracellular secretion of the microorganisms, which are free
from other cellular proteins associated with the organism serves
as one of the best templates for the synthesis of nanoparticles
[68]. Silver nanoparticles were synthesized extracellularly using
the mycelia free spent medium of the fungus, Cladosporium cladosporioides. It has been hypothesized that the fungus secretes
various organic acids, proteins and polysaccharides that directs the
growth of different crystal shapes and extended spherical crystals.
Khan et al. [69–74] have done significant amount of work on the
use of bacterial surfaces for the surface modification of nanoparticles. According to them, the adsorption of exopolysaccharides on
the surface of the particles is strongly dependent on zeta potential
[69,70,74]. A possible mechanism suggesting the influence of zeta
potential on the adsorption of biomolecules on nanoparticles at different pH is shown in Fig. 4. According to the figure, adsorption is
favored at a lower pH where the nanoparticles exhibit a net positive
charge. In another set of study, the exopolysaccharides produced
by Aeromonas punctata acted as a capping agent and helped in the
stabilization of the particles [69]. The exopolysaccharides capped
particles showed less toxicity to E. coli, Staphylococcus aureus and
Micrococcus luteus when compared to the uncapped ones suggesting that capping of nanoparticles by bacterially produced EPS acts
as a probable physiological defense mechanism [71].
3. Applications of the functionalized silver nanoparticles
The excellent absorption and scattering properties of noble
metal nanocrystals has made them a novel class of optical and
spectroscopic tags for biological sensing [75,76]. It is well established that the plasmon properties is strongly dependent on the
dielectric properties of the local environment of the nanoparticles [77] including substrate, solvent, and adsorbates [76]. In the
case of silver nanoparticles, the negative real part of the dielectric constant increases with increasing wavelength in the visible
range which is reflected as a red shift in the plasmon band. Thus, by
monitoring the SPR wavelength in response to adsorbate-induced
changes in the local environment of the nanoparticle, a nanoscale
chemical or biosensor can be developed [75]. Wei et al. [78] has
done a significant work by making use of the plasmonic properties
where in the coating of silver nanoparticles was done using adenine during the in situ synthesis using silver nitrate and sodium
borohydride in an aqueous medium at room temperature. The
characterization studies of the as prepared silver nanoparticles
were carried out using TEM, UV–visible spectroscopy, etc. Due
to electrostatic interactions silver nanoparticles easily interacted
with polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS), and
this was fabricated onto mercaptopropyltrimethoxysilane/silver
nanoparticle functionalized indium tin oxide (ITO) substrate via the
layer-by-layer self-assembly technique. Furthermore using a probe
molecule like p-aminothiophenol, the ITO substrates which were
coated with multilayers of different thicknesses were investigated
as surface enhanced Raman scattering active substrates. Surface
enhanced resonance Raman scattering has also shown its role in
the quantitative detection of dye labeled DNA. It is said to be generally three orders of magnitude more sensitive than fluorescence
for the detection of dye labeled oligonucleotide.
3.1. Biofunctionalized silver nanoparticles as bioanalyzers
Nanoparticle based colorimetric sensors have gained significant
attention due to their simplicity, rapidity, high sensitivity and ease
348
A. Ravindran et al. / Colloids and Surfaces B: Biointerfaces 105 (2013) 342–352
Fig. 4. A possible mechanism suggesting the influence of zeta potential on the adsorption of biomolecules on silver nanoparticles at different pH.
of measurement. Surface modification acts as a key to develop
metal nanoparticles as colorimetric detecting probes. As described
in the previous sections, the introduction of organic ligands onto
the surface of metal nanoparticles stabilizes these nanoentities in
different solvents as well as the desired surface functionality. The
extremely high extinction coefficients and the strongly distancedependent optical properties of metallic nanoparticles allow them
to be utilized as ideal color reporting groups for colorimetric sensor
design due to their surface plasmon properties [77]. For example,
dispersed silver nanoparticles are slightly yellow in color, while
aggregated ones are red. In cases where the interaction between
a nanoparticle and the analyte of interest is weak, a metal ion is
added which bind with both the nanoparticle and the analyte of
interest through cooperative ligand mediated interactions [Fig. 5
(the figure is derived from sensing strategy developed by Ravindran et al. [79])]. This phenomenon was used for the development
of a visual colorimetric sensing method that is capable of detecting
cysteine using Cr3+ [79]. Surface plasmon resonance properties of
silver nanoparticles and the interaction of silver–cysteine complex
with chromium ions (Cr3+ ) in a ratio of 2:1 decides the efficacy of
the process. In the presence of Cr3+ , cysteine was able to induce
the aggregation of these particles thereby resulting in a change
in yellow color of the silver colloid to purple. The reported probe
has a lowest limit of detection of 1 nM which is the best reported
detection range for the colorimetric detection of cysteine. Moreover, a noteworthy characteristic of this method is that it is a simple
technique which exhibits high selectivity to cysteine over the other
tested amino acids. Selected examples of surface modified silver
nanoparticles in use as bioanalyzers is listed in Table 1 [79–85].
3.2. Biomedical applications of functionalized silver nanoparticles
The various applications of silver nanoparticles in the field of
biomedical science are an exciting area of research. Glutathione
stabilized water soluble silver nanoparticles were allowed to bind
covalently with a model protein BSA [86]. The optical properties
of the silver nanoparticles were extremely sensitive to their size
and the surface modification, thereby suggesting a potential in the
biomedical analysis and detection.
Silver nanocrystals have promising antibiotic and antiviral properties in biological systems. The biological distribution of silver
nanostructures when injected into animals in vivo is an area that
remains still unexplored. However, Ocanas et al. functionalized the
silver nanocrystals with BSA and injected the same in live rats to
elucidate their fate in several organs including liver, heart and brain
[87]. A very remarkable accumulation of the particles was found out
and it was confirmed by inductively coupled mass spectroscopy
(ICPMS) and transmission electron microscopic techniques on the
A. Ravindran et al. / Colloids and Surfaces B: Biointerfaces 105 (2013) 342–352
349
Fig. 5. Schematic representation of the visual colorimetric sensing strategy with nanoparticles and metal ions.
The figure is derived from sensing strategy developed by Ravindran et al. [79].
liver and heart. On the contrary the brain tissue did not reveal the
evidence of particles. Their findings suggest that Ag+ permeated
across the blood–brain barrier (BBB), and followed swift clearance
from the organ.
The antibacterial effects of norvancomycin capped silver
nanoparticles, suggests the use of nanobiocomposites as novel
bactericidal agents [88]. In an investigation carried out by Faulds
et al., the detection of dye labeled DNA was possible using surface enhanced resonance Raman scattering (SERRS) from silver
nanoparticles [89]. Their studies reported the SERRS detection limit
for four dye labeled oligonucleotide at two excitation frequencies.
The obtained results were consistent and showed a range of labels
for use in quantitative DNA. Silver/PVA surfaces were used to detect
labeled DNA corresponding to breast cancer gene using the dye
rhodamine B [90].
Coupled with silver nanoparticles, gold nanoparticle probes are
employed to analyze the combinatorial DNA arrays and the selectivity and sensitivity of this probe exceeds those of the existing
fluorescence methods [91]. Silver Nano (Silver Nano Health System)
is a trademark name of an antibacterial technology, which uses
silver nanoparticles in washing machines, refrigerators, air conditioners, air purifiers and vacuum cleaners introduced by Samsung
in April 2003. In another set of studies, Elechiguerra demonstrated a
dose-dependent and a size dependent interaction of silver nanoparticles with HIV, in which silver nanoparticles in the range of
1–10 nm were attached to the virus, thereby effectively inhibiting
the virus from binding to host cells [92]. Detailed studies on the
development of silver coated plastic catheters were carried out
using silver nitrate and N,N,N ,N -tetramethylethylenediamine as
a reducing agent. The hence developed catheters had efficient anti
microbial activities [93]. These studies exhibit the enhanced use of
biofunctionalized silver nanoparticles in biomedical applications.
The surface modified silver nanoparticles have proved to have
improved biocompatibility and intracellular uptake for drug delivery. The plasmonic nature of noble metal nanoparticles, such as
silver, is useful for imaging and targeting the surface of certain cell
types or specific areas within individual cells for applications in
imaging and cancer therapies [94]. The photodynamic properties
of silver nanoparticles may be considered useful, in the case of targeted cancer cell or tumor destruction. The studies performed by
Hussain et al. [95] showed that low concentrations (<25 ␮g mL−1 )
of silver nanoparticles can effectively provide biological labeling in live cells due to their intense plasmon-resonant properties
that can be readily detected by a high illumination system. The
silver nanoparticles coated with a biocompatible polysaccharide
readily bind to the surface of living cells while allowing the maintenance of normal cell morphological features such as neurite
extensions.
In an effort to prevent the direct interaction between the
nanoparticle surface and the cell and at the same time increase dispersion, the surface chemistry of metal and other nanoparticles,
such as quantum dots or carbon nanotubes, can be engineered.
It has been shown that the incorporation of silver nanoparticles
into polymers [96–98] or other materials for biomedical applications such as bone cement [99] does not alter its toxic effect on
bacteria and viruses. Other studies have found that the incorporation of silver nanoparticles into polymers creates more stable
dispersions in solution, which is important for applications such
as imaging probes or for the deposition of thin films [100]. Therefore, studies on the interactions between silver nanoparticles and
live cells have been made possible taking advantage of both the
intense plasmon-resonant properties of silver nanoparticles and
the enhanced resolution obtainable with the high illumination system in physiological solutions.
Table 1
Depicts the typical examples of biofunctionalized silver nanoparticles (Ag NP) in use as bioanalyzers.
Biomolecule
Bioanalyzer
Limit of detection
Reference
Ag NP + Cr3+
Ag NP + thio disuccinic acid
Ag NP + Glu
Ag NP
Ag NP + Cys
Ag NP
Ag NP + PMAA
Cysteine
Lead
Nickel
Berberine hydrochloride
Histidine
Cysteine
Cysteine
1 × 10−9 M
8 × 10−5 M
7.5 × 10−5 M
0.05–0.4 ␮M
3.0 × 10−5 M
1.6 × 10−7 M
2.5 × 10−8 M
[79]
[80]
[81]
[82]
[83]
[84]
[85]
350
A. Ravindran et al. / Colloids and Surfaces B: Biointerfaces 105 (2013) 342–352
4. Conclusion and perspectives
We hereby provide glimpse of a rapidly emerging research area
that is located at the crossroads of materials research, nanosciences,
and molecular biotechnology. The nanomaterials exhibit great
prospects in biomedical applications since their dimensions match
those of biological molecules and entities. The surface modified silver nanoparticles have proved to have improved biocompatibility
and intracellular uptake for drug delivery and other biomedical
applications. The nano bioconjugates of silver in particular have
also proved its role as efficient bionalyzers for the detection of
various analytes in solution.
This review creates an insight into the efforts and approaches
for the bio functionalization of silver nanoparticles. The excellent
optoelectronic and plasmonic properties of silver nanoparticles
have brought them to the forefront of nanotechnology research
directed toward applications ranging from sensing to biomedical
applications. The first section gives an overview of the synthesis
and applications of silver nanoparticles and the need for modifying
the surface of these particles. Although any number of biomolecules
can be coupled to nanoparticles by means of various methods, there
is still a great demand for mild and selective coupling techniques
for the preparation of thermodynamically stable and well-defined
bioconjugate hybrid nanoparticles. Hence, the second part of the
review discusses on the various functionalities like protein- or
nucleic acid based recognition elements for bioconjugation of silver
nanoparticles. In both the systems, a large number of complementary binding pairs along with a wide variety of free energy
associations are available. It therefore remains to be seen whether
protein-based conjugation might offer advantages over nucleic acid
based assembly. Consequently, combinations of the two fundamental biological systems, nucleic acids and proteins, are very
promising to synergistically cooperate and thus allow novel functions and applications. Another crossover of biotechnology and
materials science concerns utilizing properties of biological components for templating the spatial assembly of nanoparticles. Hence
the paradigm that encompasses the use of bacterial and fungal layers, for bioconjugation of silver nanoparticles and the mechanisms
involved is also discussed. Toward the end (Section 3), the various
prospects and the application of biofunctionalized silver nanoparticles in the field of biomedicine and as bioanalyzers is summarized.
There is enormous room at the surface awaiting exploration for effective surface coupling chemistry to give bioactive and stable interfaces. Hence this review would provide
standing information for the development of more useful
nanobiocomposites. In future the functionalized nanoparticles
will offer a better platform in various fields of science and
medicine.
References
[1] E. Boisselier, D. Astruc, Gold nanoparticles in nanomedicine: preparations, imaging diagnostics, therapies and toxicity, Chem. Rev. 38 (2009)
1759–1782.
[2] L.A. Dykman, V.A. Bogatyrev, Gold nanoparticles: preparation, functionalisation and applications in biochemistry and immunochemistry, Russ. Chem.
Rev. 76 (2007) 181–194.
[3] S.Y. Shim, D.K. Lim, J.M. Nam, Ultrasensitive optical biodiagnostic methods
using metallic nanoparticles, Nanomedicine 3 (2008) 215–232.
[4] N.R. Panyala1, E.M. Pena-Mendez, J. Havel, Gold and nano-gold in
medicine: overview, toxicology and perspectives, J. Appl. Biomed. 7 (2009)
75–91.
[5] U. Kreibig, M. Vollmer, Optical Properties of Metal Clusters, Springer, Berlin,
New York, 1995, pp. 483–525.
[6] M.A. El-Sayed, Some interesting properties of metals confined in time
and nanometer space of different shapes, Acc. Chem. Res. 34 (2001)
257–264.
[7] S. Link, M.A. El-Sayed, Shape and size dependence of radiative, non-radiative
and photothermal properties of gold nanocrystals, Int. Rev. Phys. Chem. 19
(2000) 409–453.
[8] K.L. Kelly, E. Coronado, L.L. Zhao, G.C. Schatz, The optical properties of metal
nanoparticles: the influence of size shape, and dielectric environment, J. Phys.
Chem. B 107 (2003) 668–677.
[9] P.K. Jain, K.S. Lee, I.H. El-Sayed, M.A. El-Sayed, Calculated absorption and
scattering properties of gold nanoparticles of different size, shape, and composition: applications in biological imaging and biomedicine, J. Phys. Chem.
B 110 (2006) 7238–7248.
[10] C.A. Moyer, Treatment of burns, Trans. Stud. Coll. Physicians Phila. 33 (1965)
53–103.
[11] S. Nie, S.R. Emory, Probing single molecules and single nanoparticles by
surface-enhanced Raman scattering, Science 275 (1997) 1102–1106.
[12] A. Henglein, Physicochemical properties of small metal particles in solution:
microelectrode reactions, chemisorption, composite metal particles, and the
atom-to-metal transition, J. Phys. Chem. 97 (1993) 5457–5471.
[13] Y.F. Huang, H.T. Chang, W.H. Tan, Cancer cell targeting using multiple
aptamers conjugated on nanorods, Anal. Chem. 80 (2008) 567–572.
[14] K. Shrivas, H.F. Wu, Modified silver nanoparticle as a hydrophobic affinity
probe for analysis of peptides and proteins in biological samples by using
liquid micro extraction coupled to AP-MALDI-Ion trap and MALDI-TOF mass
spectroscopy, Anal. Chem. 80 (2008) 2583–2589.
[15] S. Schultz, D.R. Smith, J.J. Mock, D.A. Schultz, Applications of silver nanoparticles in biosensor, Proc. Natl. Acad. Sci. U.S.A. 97 (2000) 996.
[16] L.S. Nair, C.T. Laurencin, Silver nanoparticles: synthesis and therapeutic applications, J. Biomed. Nanotechnol. 3 (2007) 301–316.
[17] Y.A. Krutyakov, A. Kudrinskiy, A. Yu Olenin, G.V. Lisichkin, Synthesis and properties of silver nanoparticles: advances and prospects, Russ. Chem. Rev. 77 (3)
(2008) 233–257.
[18] A. Tripathy, N. Chandrasekaran, A.M. Raichur, A. Mukherjee, Antibacterial applications of silver nanoparticles synthesized by aqueous extracts
of Azadirachta indica (neem) leaves, J. Biomed. Nanotechnol. 5 (2009)
93–98.
[19] N. Duran, P.D. Marcato, G.I.H. De Souza, O.L. Alves, E. Esposito, Antibacterial
effect of silver nanoparticles produced by fungal process on textile fabrics and
their effluent treatment, J. Biomed. Nanotechnol. 3 (2007) 203–208.
[20] N. Vigneshwaran, A.A. Kathe, P.V. Varadarajan, P.R. Nachane, R.H. Balasubramanya, Biomimetics of silver nanoparticles by white rot fungus
Phaenerochaete chrysosporium, Colloids Surf. B 53 (2006) 55–59.
[21] A. Kumar, P. Kumar, M.P. Ajayan, G. John, Silver nanoparticle embedded antimicrobial paints based on vegetable oil, Nat. Mater. 7 (2008)
236–241.
[22] P.C. Lee, D. Meisel, Adsorption and surface-enhanced Raman of dyes on silver
and gold sols, J. Phys. Chem. 86 (1982) 3391–3395.
[23] Y. Yang, S. Matsubara, L. Xiong, Solvothermal synthesis of multiple shapes
of silver nanoparticles and their SERS properties, J. Phys. Chem. 111 (2007)
9095–9104.
[24] A.V. Simakin, V.V. Voronov, N.A. Kirichenko, G.A. Shafeev, Nanoparticles produced by laser ablation of solids in liquid environment, Appl. Phys. A 79 (2004)
1127.
[25] R.A. Salkar, P. Jeevanandam, S.T. Aruna, Y. Koltypin, A. Gedanken, The sonochemical preparation of amorphous silver nanoparticles, J. Mater. Chem. 9
(1999) 1333–1335.
[26] D.D. Evanoff, G. Chumanov, Synthesis and optical properties of silver nanoparticles and arrays, Chem. Phys. Chem. 6 (2005) 1221–1231.
[27] J.A. Creighton, C.G. Blatchford, M. Grant Albrecht, Plasma resonance enhancement of Raman scattering by pyridine adsorbed on silver or gold sol particles
of size comparable to the excitation wavelength, J. Chem. Soc. Faraday Trans.
75 (1979) 790.
[28] P. Raveendran, J. Fu, S.L. Wallen, Completely “green” synthesis and stabilization of metal nanoparticles, J. Am. Chem. Soc. 125 (2003) 13940–13941.
[29] K. Kalimuthu, R.S. Babu, D. Venkataraman, B. Mohd, S. Gurunathanm, Biosynthesis of silver nanocrystals by Bacillus licheniformis, Colloids Surf. B 65 (2008)
150–153.
[30] A.H. Groll, P.M. Shah, C. Mentzel, M. Schneider, G. Just-Nuebling, K. Huebner,
Trends in the postmortem epidemiology of invasive fungal infections at a
University Hospital, J. Infect. 33 (2006) 23–32.
[31] I.K. Batarseh, Anomaly and correlation of killing in the therapeutic properties of silver (I) chelation with glutamic and tartaric acids, J. Antimicrob.
Chemother. 54 (2004) 546–548.
[32] A.D. McFarland, R.P. Van Duyne, Single silver nanoparticles as real-time optical sensors with zeptomole sensitivity, Nano Lett. 3 (8) (2003) 1057–1062.
[33] J.J. Mock, M. Barbic, D.R. Smith, D.A. Schultz, S. Schultz, Shape effects in plasmon resonance of individual colloidal silver nanoparticles, J. Chem. Phys. 116
(6755) (2002).
[34] M. Potara, M. Baia, C. Farcau, S. Astilean, Chitosan-coated anisotropic silver
nanoparticles as a SERS substrate for single-molecule detection, Nanotechnology 23 (2012), 055501 (10 pp.).
[35] A.E. Nel, L. Mädler, D. Velegol, T. Xia, E.M.V. Hoek, P. Somasundaran, F. Klaessig,
V. Castranova, M. Thompson, Understanding biophysicochemical interactions
at the nano–bio interface, Nat. Mater. 8 (2009) 543–557.
[36] K.J. Kim, W.S. Sun, B.K. Suh, S.K. Moon, J.S. Choi, J.G. Kim, D.G. Lee, Antifungal activity and mode of action of silver nanoparticles on Candida albicans,
Biometals 22 (2009) 235–242.
[37] S. Hartsel, J. Bolard, Amphotericin B: new life for an old drug, Trends Pharmacol. Sci. 17 (1996) 445–449.
[38] J.B. Wright, K. Lam, A.G. Buret, M.E. Olson, R.E. Burrell, Early healing events in
a porcinemodel of contaminated wounds: effects of nanocrystalline silver on
A. Ravindran et al. / Colloids and Surfaces B: Biointerfaces 105 (2013) 342–352
[39]
[40]
[41]
[42]
[43]
[44]
[45]
[46]
[47]
[48]
[49]
[50]
[51]
[52]
[53]
[54]
[55]
[56]
[57]
[58]
[59]
[60]
[61]
[62]
[63]
[64]
[65]
[66]
[67]
[68]
matrix metalloproteinases, cell apoptosis, and healing, Wound Repair Regen.
10 (2002) 141–151.
K.C. Bhol, J. Alroy, P.J. Schechter, Anti-inflammatory effects of topical
nanocrystalline silver cream on allergic contact dermatitis in a guinea pig
model, Clin. Exp. Dermatol. 29 (2004) 282–287.
E. Ruckenstein, Z.F. Li, Surface modification and functionalization through the
self assembled monolayer and graft polymerization, Adv. Colloid Interface Sci.
113 (2005) 43–63.
V. Labhasetwar, D.L. Leslie-Pelecky, Biomedical Applications of Nanotechnology, John Wiley & Sons Inc., Hoboken, NJ, 2007.
R.A. Sperling, W.J. Parak, Surface modification, functionalization and bioconjugation of colloidal inorganic nanoparticles, Phil. Trans. R. Soc. A 368 (2010)
1333–1383.
N. Marie-Alexandra, I. Schubert, Surface modification, functionalization of
metal and metal oxide nanoparticles by organic ligands, Monatsh. Chem. 139
(2008) 183–195.
R. Gref, P. Couvreur, G. Barratt, E. Mysiakine, Surface-engineered nanoparticles for multiple ligand coupling, Biomaterials 24 (2003) 4529.
A. Ravindran, A. Singh, A.M. Raichur, N. Chandrasekaran, A. Mukherjee, Studies
on interaction of colloidal Ag nanoparticles with bovine serum albumin (BSA),
Colloids Surf. B 76 (2010) 32–37.
A. Ravindran, S.P. Dhas, N. Chandrasekaran, A. Mukherjee, Differential
interaction of silver nanoparticles with cysteine, J. Exp. Nanosci. (2012),
http://dx.doi.org/10.1080/17458080.2011.577100.
A. Ravindran, N. Chandrasekaran, A. Mukherjee, Studies on differential behavior of silver nanoparticles towards thiol containing amino acids, Curr. Nanosci.
8 (2012) 141–149.
C.B. Michael, Z.Z. Jin, N. Liem, K.M. Rajesh, Synthesis, Ultrafast study of
cysteine- and glutathione-capped Ag2 S semiconductor colloidal nanoparticles, J. Phys. Chem. A 103 (1999) 10194–10201.
S. Aryal, B.K. Remant, B. Narayan, C.H. Kim, H.Y. Kim, Study of electrolyte
induced aggregation of gold nanoparticles capped by amino acid, J. Colloid
Interface Sci. 299 (2006) 191–197.
D. Lawless, S. Kapoor, D. Meisel, Bifunctional capping of CdS nanoparticles
and bridging to TiO2 , J. Phys. Chem. 99 (1995) 10329.
L. Motte, M.P. Pileni, Influence of length of alkyl chains used to passivate
silver sulfide nanoparticles on two- and three-dimensional self-organization,
J. Phys. Chem. B 102 (1998) 4104–4109.
M.D. Marco, S. Shamsuddin, K. Abdul Raza, A.A. Aziz, C. Devaux, E. Borghi, L.
Levy, C. Sadun, Overview of the main methods used to combine proteins with
nanosystems: absorption, bioconjugation, and encapsulation, Int. J. Nanomed.
5 (2010) 37–49.
S. Mandal, A. Gole, N. Lala, R. Gonnade, V. Ganvir, M. Sastry, Studies on the
reversible aggregation of cysteine-capped colloidal silver particles interconnected via hydrogen bonds, Langmuir 17 (2001) 6262–6268.
P.R. Selvakannan, S. Mandal, S. Phadtare, R. Pasricha, M. Sastry, Capping of
gold nanoparticles by the amino acid lysine renders them water-dispersible,
Langmuir 19 (2003) 3545.
W. Shenton, S.A. Davies, S. Mann, Directed self-assembly of nanoparticles into
macroscopic materials using antibody–antigen recognition, Adv. Mater. 11
(1999) 449–452.
A. Kathiravan, R. Renganathan, S. Anandan, Interaction of colloidal
AgTiO2 nanoparticles with bovine serum albumin, Polyhedron 28 (2005)
157–161.
P. Murawala, S.M. Phadnis, R.R. Bhonde, B.L.V. Prasad, In situ synthesis of water
dispersible bovine serum albumin capped gold and silver nanoparticles and
their cytocompatibility studies, Colloids Surf. B 73 (2009) 224–228.
X. Shen, Q. Yuan, H. Liang, H. Yan, X. He, Hysteresis effects of the interaction
between serum albumins and silver nanoparticles, Sci. China: Ser. B 46 (2008)
387–398.
G.L. Eichorn, Metal ions in genetic information transfer, in: Inorganic Biochemistry, Elsevier/North Holland, New York, 1973, p. 34.
S. Basu, J. Subhra, P. Surojit, P. Tarasankar, Interaction of DNA bases with silver
nanoparticles: assembly quantified through SPRS and SERS, J. Colloid Interface
Sci. 321 (2008) 288–293.
L. Sun, G. Wei, Y. Song, Z. Liu, L. Wang, Z. Li, Fabrication of silver nanoparticles
ring templated by plasmid DNA, Appl. Surf. Sci. 252 (2006) 4969–4974.
E. Braun, Y. Eichen, U. Sivan, G. Ben-Yoseph, DNA templated self-assembly of
a conductive wire connecting two electrodes, Nature 391 (1998) 775–778.
J. Zheng, X. Wu, M. Wang, D. Ran, W. Xu, J. Yang, Study on the interaction between silver nanoparticles and nucleic acids in the presence of
cetyltrimethylammonium bromide and its analytical application, Talanta 74
(2008) 526–532.
R.R. Naik, S.J. Stringer, G. Agarwal, S.E. Jones, M.O. Stone, Biomimetic synthesis
and patterning of silver nanoparticles, Nat. Mater. 1 (2002) 169–172.
R.R. Bhattacharjee, A.K. Das, D. Haldar, S. Si, A. Banerjee, T.K. Mandal, Peptideassisted synthesis of gold nanoparticles and their self-assembly, J. Nanosci.
Nanotechnol. 5 (2005) 1141–1147.
S.S. Shankar, A. Rai, A. Ahmad, M. Sastry, Rapid synthesis of Au, Ag and bimetallic Au core–Ag shell nanoparticles using neem (Azadirachta indica) leaf broth,
J. Colloid Interface Sci. 275 (2004) 496–502.
M. Fu, Q. Li, D. Sun, Lu He, X. Deng, H. Wang, J. Huang, Rapid preparation
process of silver nanoparticles by bioreduction and their characterizations,
Chin. J. Chem. Eng. 14 (2006) 114–117.
S. Balaji, S. Basavaraja, R. Deshpande, D.B. Mahesh, B.K. Prabhakar,
A. Venkataraman, Extracellular biosynthesis of functionalized silver
[69]
[70]
[71]
[72]
[73]
[74]
[75]
[76]
[77]
[78]
[79]
[80]
[81]
[82]
[83]
[84]
[85]
[86]
[87]
[88]
[89]
[90]
[91]
[92]
[93]
[94]
[95]
[96]
[97]
351
nanoparticles by strains of Cladosporium cladosporioides fungus, Colloids Surf.
B 68 (2009) 88–92.
S.S. Khan, A. Mukherjee, N. Chandrasekaran, Interaction of colloidal silver nanoparticles (SNPs) with exopolysaccharides (EPS) and its adsorption
isotherms and kinetics, Colloids Surf. A 381 (2011) 99–105.
S.S. Khan, A. Mukherjee, N. Chandrasekaran, Studies on interaction of colloidal
silver nanoparticles (SNPs) with five different bacterial species, Colloids Surf.
B 87 (2011) 129–138.
S.S. Khan, E.B. Kumar, A. Mukherjee, N. Chandrasekaran, Bacterial tolerance to
silver nanoparticles (SNPs): Aeromonas punctata isolated from sewage environment, J. Basic Microbiol. 51 (2011) 183–190.
S.S. Khan, A. Mukherjee, N. Chandrasekaran, Silver nanoparticles tolerant bacteria from sewage environment, J. Environ. Sci. 23 (2) (2011)
346–352.
S.S. Khan, P. Srivatsan, N. Vaishnavi, A. Mukherjee, N. Chandrasekaran, Interaction of silver nanoparticles (SNPs) with bacterial extracellular proteins
(ECPs) and its adsorption isotherms and kinetics, J. Hazard. Mater. 192 (2011)
299–306.
S.S. Khan, A. Mukherjee, N. Chandrasekaran, Impact of exopolysaccharides on
the stability of silver nanoparticles in water, Water Res. 45 (2011) 5184–5190.
A.J. Haes, D.A. Stuart, S. Nie, R.P. Van Duyne, Using solution-phase nanoparticles surface-confined nanoparticle arrays and single nanoparticles as
biological sensing platforms, J. Fluoresc. 14 (2004) 355.
A.J. Haes, R.P. Van Duyne, A nanoscale optical biosensor: sensitivity and selectivity of an approach based on the localized surface plasmon resonance of
triangular silver nanoparticles, J. Am. Chem. Soc. 124 (2002) 10596.
K.L. Kelly, E. Coronado, L.L. Zhao, G.C. Schatz, The optical properties of metal
nanoparticles: the influence of size shape, and dielectric environment, J. Phys.
Chem. B 107 (2003) 668.
H. Wei, J. Li, Y. Wang, E. Wang, Silver nanoparticles coated with adenine:
preparation, self-assembly and application in surface-enhanced Raman scattering, Nanotechnology 18 (2007) 610–615.
A. Ravindran, V. Mani, N. Chandrasekaran, A. Mukherjee, Selective colorimetric sensing of cysteine in aqueous solutions using silver nanoparticles in the
presence of Cr3+ , Talanta 85 (2011) 533–540.
L. Wei, Z. Yuping, C. Chengxing, C. Wentao, L. Runqiang, Q. Lingbo, Measuring
technology and mechatronics automation (ICMTMA), Third Int. Conf. 3 (2011)
1013–1016.
L. Haibing, C. Zhimin, H. Cuiping, Glutathione-stablilized silver nanoparticles as colorimetric sensor for Ni2+ ion, Sens. Actuators 143 (2009)
87–92.
J. Ling, Y. Sang, C.Z. Huang, Visual colorimetric detection of berberine
hydrochloride with silver nanoparticles, J. Pharm. Biomed. Anal. 47 (2008)
860–864.
L. Haibing, B. Yinghui, Selective colorimetric sensing of histidine in aqueous
solutions using cysteine modified silver nanoparticles in the presence of Hg2+ ,
Nanotechnology 20 (2009) 145502.
T. Wu, Y.F. Li, C.Z. Huang, Selectively colorimetric detection of cysteine with
triangular silver nanoprisms, Chin. Chem. Lett. 20 (2009) 611–614.
L. Shang, S. Dong, Sensitive detection of cysteine based on fluorescent silver
clusters, Biosens. Bioelectron. 24 (2009) 1569–1573.
W. Qingzhi, C. Huaqiang, L. Qiuying, Z. Jiyong, W. Zhao, H. Jamie, A.
Warner, A.R. Watt, Biomolecule-assisted synthesis of water-soluble silver
nanoparticles and their biomedical applications, Inorg. Chem. 47 (13) (2008)
5882–5888.
L.G. Ocanas, D.A. Ferrer, J. Burt, L.A.D. Torres, M.R. Cabrera, V.T. Rodriguez,
R.L. Rangel, R. Romanovicz, M.J. Yacaman, Biodistribution and long-term fate
of silver nanoparticles functionalized with bovine serum albumin in rats,
Metallomics 2 (2010) 204–210.
W.Q. Shan, J. Jian, F.J. Hong, S.J. Cong, Norvancomycin-capped silver nanoparticles: Synthesis and antibacterial activities against E. coli, Sci. China Ser. B 50
(2006) 418–424.
K. Faulds, L. Stewart, W. Smith, D. Graham, Quantitative detection of dye
labelled DNA using surface enhanced resonance Raman scattering (SERRS)
from silver nanoparticles, Talanta 67 (2005) 667–671.
L.R. Allain, T. Vo-Dinh, Surface-enhanced Raman scattering detection of the
breast cancer susceptibility gene BRCA1 using a silver-coated microarray platform, Anal. Chim. Acta 469 (2002) 149–154.
T.A. Taton, C.A. Mirkin, R.L. Letsinger, Scanometric DNA array detection with
nanoparticle probes, Science 289 (2000) 1757–1760.
J.L. Elechiguerra, J.L. Burt, J.R. Morones, A. Camacho-Bragado, X. Gao, H.H. Lara,
M.J. Yacaman, Interaction of silver nanoparticles with HIV-1, J. Nanobiotechnol. 3 (2005) 6.
R. David, K. Balu, B.S. Nathan, G. Bruce, R. Jean-Baptiste, Antimicrobial surface
functionalization of plastic catheters by silver nanoparticles, J. Antimicrob.
Chemother. 61 (2008) 869–876.
S. Kumar, N. Harrison, R. Richards-Kortum, K. Sokolov, Plasmonic nanosensors for imaging intracellular biomarkers in live cells, Nano Lett. 7 (2007)
1338–1343.
S.M. Hussain, K.L. Hess, J.M. Gearhart, K.T. Geiss, J.J. Schlager, In vitro toxicity
of nanoparticles in BRL-3A rat liver cells, Toxicol. In Vitro 19 (2005) 975–983.
L. Balogh, D.R. Swanson, D.A. Tomalia, G.A. Hagnauer, A.T. McManus,
Dendrimer–silver complexes and nanocomposites as antimicrobial agents,
Nano Lett. 1 (2001) 18–21.
S.Y. Yeo, H.J. Lee, S.H. Jeong, Preparation of nanocomposite fibers for permanent antibacterial effect, J. Mater. Sci. 38 (2003) 2143–2147.
352
A. Ravindran et al. / Colloids and Surfaces B: Biointerfaces 105 (2013) 342–352
[98] S.H. Jeong, Y.H. Hwang, S.C. Yi, Antibacterial properties of padded PP/PE
nonwovens incorporating nano-sized silver colloids, J. Mater. Sci. 40 (2005)
5413–5418.
[99] V. Alt, T. Bechert, P.S. Ucker, M. Wagener, P. Seidel, E. Dingeldein, E. Domann,
R. Schnettler, An in vitro assessment of the antibacterial properties and
cytotoxicity of nanoparticulate silver bone cement, Biomaterials 25 (2004)
4383–4391.
[100] L. Balogh, D.R. Swanson, D.A. Tomalia, G.L. Hagnauer, A.T. McManus,
Dendrimer–silver complexes and nanocomposites as antimicrobial agents,
Nano Lett. 1 (2001) 18–21.