Green Synthesis of Silver Nanoparticles and their applications

www.wjpps.com Vol 5, Issue 7, 2016. 730
Rawat et al. World Journal of Pharmacy and Pharmaceutical Sciences
A REVIEW ON GREEN SYNTHESIS AND CHARACTERIZATION OF
SILVER NANOPARTICLES AND THEIR APPLICATIONS: A GREEN
NANOWORLD.
Jagpreet Singh1
, Gurleen Kaur1
, Pawanpreet Kaur1
, Rajat Bajaj1
and Mohit Rawat1
*
1
Department of Nanotechnology, Sri Guru Granth Sahib World University, Fatehgarh
Sahib, Punjab.140406.
ABSTRACT
Nanoparticles are the spearheads of the rapidly expanding field of
nanotechnology. An array of physical and chemical methods is used
for the synthesis of nanoparticles. The development of immaculate
protocols for the synthesis of highly monodisperse nanoparticles of
various sizes, geometries and chemical composition is one of the most
challenging obstructions in the field of nanotechnology. The use of
toxic chemicals and non-polar solvents in synthesis leads to the
inability to use nanoparticles in clinical fields. Therefore, development
of clean, non-toxic, biocompatible and eco-friendly method for
synthesis of nanoparticles deserves recognition. Silver nanoparticles
are of interest because of the unique properties (e.g., size and shape
depending optical, electrical and magnetic properties) which can be
incorporated into antimicrobial applications, biosensor materials, composite fibers, cryogenic
superconducting materials, cosmetic products, and electronic components. Several physical
and chemical methods have been used for synthesizing and stabilizing silver nanoparticles.
The present review explores the immense plant diversity to be employed towards rapid and
single step protocol preparatory method with green principles over the conventional ones and
describes the antimicrobial activities of silver nanoparticles.
KEYWORDS: size and shape depending optical, electrical and magnetic properties, silver
nanoparticles, antimicrobial etc.
WORLD JOURNAL OF PHARMACY AND PHARMACEUTICAL SCIENCES
SJIF Impact Factor 6.041
Volume 5, Issue 7, 730-762 Review Article ISSN 2278 – 4357
*Corresponding Author
Mohit Rawat
Assistant Professor,
Department of
Nanotechnology, Sri Guru
Granth Sahib World
University, Fatehgarh
Sahib, Punjab.140406.
Article Received on
09 May 2016,
Revised on 29 May 2016,
Accepted on 19 June 2016
DOI: 10.20959/wjpps20167-7227

Graphical Abstract
INTRODUCTION
Nanotechnology can be defined as the understanding of phenomena and manipulation of
matter of matter at the atomic, molecular or macromolecular levels at dimensions between
approximately 1–100 nanometer. Due to its small size, it produces structures, devices, and
systems with atleast one novel/superior characteristic property. These properties may differ in
important ways from the properties of bulk materials and single atoms and molecules.
Currently, there are two main approaches for the synthesis of nanomaterials and fabrication
of nanostructure: “top down” and “bottom up” approaches.
Top-down approach is a physical method and also refers to microfabrication method where
tools are used to cut, mill and shape materials into the desired shape and order. Integrated
circuits is an example. It include preparation by lithographic techniques, etching, grinding in
a ball mill, sputtering, etc. However, the most acceptable and effective approach for
nanoparticle preparation is the „„bottom up‟‟ approach, where devices are „„grown‟‟ from
smaller building blocks such as atoms or molecules by self assembly. In this way, it is
possible to control the size and shape of the nanoparticle depending on the subsequent
application through variation in precursor concentrations, reaction conditions (temperature,
pH, etc.), functionalizing the nanoparticle surface, using templates, etc. Thus, it produces
products with high precision accuracy. Colloidal dispersion is an example.

Figure 1: Top-down and Bottom-up synthesis approaches. Reprinted from Sci. Tot.
Environ., Vol. 400 (1-3), Ju-Nam, Y. and Lead, J.R., Manufactured nanoparticles: An
overview of their chemistry, interactions and potential environmental implications,
pp396-414, Copyright 2008 with permission from Elsevier.
Figure 2: Different approaches of synthesis of silver nanoparticles.
Green Chemistry of the Synthesis of Nanomaterials
The growing demand in the chemical industries is due to the ample benefits of nanomaterials
and preparation of nanomaterials include chemicals such as solvents, raw materials, reagents,
and template materials. Such chemicals have engendered the noxious intermediates and
products. To deminsh the undesirable products, the concept of green chemistry was brought
in the chemical industries.[1]
The advantages of green synthesis of nanoparticles over the
physical and chemical methods are:
a) Clean and eco-friendly approach, as toxic chemicals are not used;
b) the active biological component itself act as reducing and capping agent , therefore
reduction the overall cost of synthesis process;

c) can be used at large scale production of nanoparticles;
d) external experimental conditions like high energy and high pressure are not required,
leads to energy saving process.
Elemental Silver and Silver Nanoaprticles
Elemental or metallic silver (Ag) is a chemical element which is malleable and ductile
transition metal with a white metallic luster appearance. Of all metals, silver has.[2,3]
 highest electrical conductivity(higher than copper that is currently used in many electrical
applications)
 thermal conductivity
 lowest contact resistance
 high optical reflectivity.[4]
Silver is stable in pure air and water. The presence of ozone or hydrogen sulfide or sulfur in
the air or water may result in silver tarnishing[5]
due to the formation of silver sulfide. Silver
can be present in four different oxidation states: Ag0
, Ag2+
, Ag3+
. The former two are the
most abundant ones, the latter are unstable in the aquatic environment.[6]
Silver has many
isotopes with 107
Ag being the most common. Although acute toxicity of silver in the
environment is dependent on the availability of free silver ions, investigations have shown
that these concentrations of Ag+ ions are too low to lead toxicity.[7]
Metallic silver appears to
pose minimal risk to health, whereas soluble silver compounds are more readily absorbed and
have the potential to produce adverse effects.[8]
The reduction in the size of silver to
nanosized silver increases its ability to control bacteria and fungi. Due to the large surface
area of nanomaterials leads to increased contact with bacteria and fungi which increases its
effectivity. Nanosilver, when in contact with bacteria and fungus, adversely affects the
cellular metabolism of the electron transfer systems and the transport of substrate in the
microbial cell membrane. Bacteria and fungi causes itchiness, infection, odor, sores, the use
of nanosilver repress the proliferation of bacteria and fungi. Nanosilver have been widely
used due to its antibacterial microbial activity for the development of products containing
siver include food contact materials (such as cups, bowls and cutting boards), odor-resistant
textiles, electronics and household appliances, cosmetics and personal care products, medical
devices, water disinfectants, room sprays, children‟s toys, infant products and „health‟
supplements.

Properties of Silver Nanoparticles
Surface effects and quantum effects are two factors which differentiate nanomaterials from
bulk.[9]
Due to these effects there significant change in chemical, mechanical, optical,
electrical and magnetic properties of materials. Therefore nanosilver has unique optical and
physical properties that are not present in bulk silver, and which are very useful in medical
applications. Mainly the properties of silver nanoparticles are antibacterial, antifungal[10]
Antiviral[11]
., anti-inflammatory.[12]
etc.
Antibacterial properties
Nanosilver kill the gram- positive and gram- negative bacteria very effectively, so it can
called as killing agent.[13,14,15]
, including antibiotic-resistant strains.[16]
Gram-negative bacteria
are the bacteria which retain the colour of the stain even after washing with alcohol or
acetone and include genera such as Acinetobacter, Escherichia, Pseudomonas, Salmonella,
and Vibrio. Acinetobacter species are associated with nosocomial infections, i.e., infections
that are the result of treatment in a hospital or a healthcare service unit, but secondary to the
patient‟s original condition. Gram-positive bacteria are those which lose the colour of the
stain after wash with alcohol or acetone and include many well-known genera such as
Bacillus, Clostridium, Enterococcus, Listeria, Staphylococcus and Streptococcus. Antibiotic-
resistant bacteria are the bacteria that are not controlled or killed by antibiotics which include
strains such as methicillin-resistant and vancomycin-resistant Staphylococcus aureus and
Enterococcus faecium. To enhance the antibacterial activity of various antibiotics[17]
,
penicillin G, amoxicillin, erythromycin, clindamycin and vancomycin against Staphylococcus
aureus and Escherichia coli. silver nanoparticles (diameter 5-32 nm, average diameter 22.5
nm) play very prominent role. Size-dependent (diameter 1-450 nm) The antimicrobial activity
of silver nanoparticles depends on their size[18]
and Gram-positive bacteria. Small
nanoparticles with a large surface area to volume ratio provide a more efficient means for
antibacterial activity even at very low concentration. Also the antimicrobial activity of silver
nanoparticles depend upon the concentration and shape.[19]
The different shapes silver
nanoparticles of (spherical, rod-shaped, truncated triangular nanoplates) have been developed
by synthetic routes. Due to their large surface area to volume ratios, truncated triangular
silver nanoplates display the strongest antibacterial activity.

ACTION OF SILVER NANOPARTICLES ON MICROBES
Silver nanoparticles are able to physically interact with the cell surface of various bacteria.
This is particularly in the case of Gram- negative bacteria where numerous studies have been
observed the adhesion and accumulation of AgNPs to the bacteria surface. Silver
nanoparticles have the ability to anchor to the bacterial cell wall and subsequently penetrate
it, thereby causing structural changes in the cell membrane which renders bacteria more
permeable. AgNPs accumulate on the membrane cell creates gaps in the integrity of the
bilayer which predisposes it to a permeability increase and finally bacterial cell death. There
have been electron spin resonance spectroscopy studies that suggested that there is formation
of free radicals by the silver nanoparticles when in contact with the bacteria and these free
radicals have the ability to damage the cell membrane and make it porous which can
ultimately lead to cell death.[20]
It is likely that a combined effect between the activity of the
nanoparticles and the free ions contributes in different ways to produce a strong antibacterial
activity of broad spectrum. It has also been proposed that there can be release of silver ions
by the nanoparticles[21]
and these silver ions can interact with the thiol groups of many vital
enzymes and inactivate them.[22]
The bacterial cells in contact with silver take in silver ions,
which inhibit several functions in the cell and damage the cells. Then, there is the generation
of reactive oxygen species(ROS), forming free radicals with a powerful bactericidal action,
which are produced possibly through the inhibition of a respiratory enzyme by silver ions and
attack the cell itself. Silver ions have the tendency to enter the microbial body causing
damage to its structure. As a consequence, ribosomesmay be denatured with inhibition of
protein synthesis, as well as translation and transcription can be blocked by the binding with
the genetic material o the bacterial cell. Protein synthesis has been shown to be altered by
treatment with AgNPs and proteomic data have shown an accumulation of immature
precursors of membrane proteins resulting in destabilization of the composition of the outer
membrane. Silver is a soft acid, and there is a natural tendency of an acid to react with a base,
in this case, a soft acid to react with a soft base. The cells are majorly made up of sulfur and
phosphorus which are soft bases. The action of these nanoparticles on the cell can cause the
reaction to take place and subsequently lead to cell death. Another fact is that the DNA has
sulfur and phosphorus as its major components; the nanoparticles can act on these soft bases
and destroy the DNA which would definitely lead to cell death.[23]

Figure 3: Various modes of action of silver nanoparticles on bacteria
Applications of Silver Nanoparticles
Scientific Applications
Due to the surface Plasmon resonance (SPR)[24,25]
and surface enhanced raman scattering
(SERS) properties of silver nanoparticles, they have many applications such as sensing
applications including detection of DNA sequences.[26]
laser desorption/ionization mass
spectrometry of peptides[27]
, colorimetric sensors for Histidine[28]
, enhanced IR absorption
spectroscopy, biolabeling and optical imaging of cancer.[29]
biosensors for detection of
herbicides[30]
and glucose sensors for medical diagnostics.[31]
Medical Applications
Nanosilver is used for coating such as incorporated in wound dressings, diabetic socks,
scaffolds, sterilization materials in hospitals, medical textiles etc. One website claims that
“the number of people using colloidal silver as a dietary supplement on a daily basis is
measured in the millions”.

Table 1: Emerging applications of nanosilver in medical products. (Reprinted from
Nanotoxicology, Vol. 3 (2), Wijnhoven, S.W.P., Peijnenburg, W.J.G.M., Herberts, C.A.,
Hagens, W.I., Oomen, A.G., Heugens, E.H.W., Roszek, B., Bisschops, J., Gosens, I., van
de Meent, D., Dekkers, S., de Jong, W.H., van Zijverden, M., Sips, A.J.A.M., Geertsma,
R.E., Nanosilver – a review of available data and knowledge gaps in human and
environmental risk assessment, pp109-138, Copyright 2009 with permission from
Informa Healthcare).
Medical domains Examples References
Anesthesiology
Coating of breathing mask and endotracheal tube
for mechanical ventilatory support
Patent -
Dentistry
Silver-loaded SiO2 nanocomposite resin filler as
aadditive in polymerizable dental materials
[32]
Diagnostics
Nanosilver pyramids for enhanced biodetection
Ultrasensitive and ultrafast platform for clinical
assays for diagnosis of myocardial infarction
Fluorescence-based RNA sensing Magnetic
core/shell Fe3O4/Au/Ag nanoparticles with turnable
plasmonic properties
[33]
Drug delivery
Remote laser light-induced opening of
microcapsules
[34]
Eye care Coating of contact lens [35]
Imaging
Silver dendrimer nanocomposite for cell labeling
Fluorescent core-shell Ag@SiO2 nanoballs for
cellular imaging Molecular imaging of cancer cells
[36]
Neurosurgery Coating of catheter for cerebrospinal fluid drainage [37]
Orthopedics
Additive in bone cement Implantable material using
clay-layers with starch-stabilized silver
nanoparticles Coating of intramedullary nail for
long bone fractures Coating of implant for joint
replacement Orthopedic stockings
[38]
Patient care Superabsorbent hydrogel for incontinence material [39]
Pharmaceutics
Treatment of dermatitis Inhibition of HIV-1
replication Treatment of ulcerative colitis Treatment
of acne
[40]
Industrial Applications
Catalysis
The silver nanomaterials and silver nanocomposites are used as catalyst in many such as CO
oxidation, benzene oxidation to phenol, photodegradation of gaseous acetaldehyde and the
reduction of the p-nitrophenol to p-aminophenol.[41]
To catalyze the reduction of dyes by
sodium borohydride (NaBH4), silver nanoparticles immobilized on silica spheres[42]
etc.

Electronics
Nanosilver has high electrical and thermal conductivity along with the enhanced optical
properties leads to various applications in electronics. In nanoelectronics, silver nanowires
are used as nanoconnectors and nanoelectrodes.[43]
Other applications include),
optoelectronics, nanoelectronics (such as single-electron transistors and electrical
connectors), data storage devices, the preparation of active waveguides in optical devices
high density recording devices, intercalation materials for batteries, making micro-
interconnects in integrated circuits (IC) and integral capacitors etc.
Plant Extract Mediated Green Synthesis of Silver Nanoparticles
There is growing imposition of silver nanoparticles in the field of medicine, optics,
biotechnology, microbiology, environmental remediation and material science has lead to
increasing demand in chemical industry. For the production of silver nanoparticles, various
reducing agents are reported such as H2 gas[44]
, sodium borohydride[45]
, hydrazine[46]
,
ethanol[47]
, ethylene glycols[48]
, Tollen‟s reagent[49]
, ascorbic acid[50]
and aliphatic amines.[51]
Depending on the strength of the reducing agents the particle size can be controlled. Hence
umpteen number of toxic chemicals have been utilized to blend the silver nanoparticles as a
reducing and stabilizing agent and poly (ethylene glycol) block copolymers are used to
reduce the Ag+
ions into Ag nanoparticles in aqueous or non- aqueous solution. Although
these methods may successfully manufacture the well defined nanoparticles but they are quiet
expensive and dangerous to environment. Thus, the concept of green chemistry was
introduced to nanoparticles synthesis with the elimination or decline tradition of toxic
chemicals. In previous study, plants and herbs antioxidant are present as a phytochemical
constituents in seeds, stems, fruits and in leaves. The plant-based phytochemicals in the
synthesis of nanoparticles creates a meaningful symbiosis between natural/plant science and
nanotechnology. This connection provides a green approach to nanotechnology, referred to as
“green nanotechnology” or Green Synthesis. The major foredeal of using plant extracts for
silver nanoparticle preparation is that they are easily available, safe and nontoxic in most
cases, have a broad variety of metabolites that can aid in the reduction of silver ions and
quicker than microbes in the synthesis. The main mechanism considered for the route is
plant-assisted reduction due to phytochemicals. The main phytochemicals involved are
terpenoids, flavones, ketones, aldehydes, amides and carboxylic acids. Flavones, organic
acids and quinones are water-soluble phytochemicals that are responsible for the instant
reduction of the ions and formation of nanoprticles. Studies have revealed that xerophytes

contain emodin, an anthraquinone that undergoes tautomerization, leading to the formation of
the silver nanoparticles.
Mechanism of Plant Mediated Synthesis of Silver nanoparticles
In plants the abundant compunds are Ascorbic acid (C6H8O6) and polyphenols. The acid has
functions in photosynthesis as an enzyme cofactor (including synthesis of ethylene,
gibberellins and anthocyanins) and in the control of cell growth. Also in plants the widely
chemicals are polyphenol or hydroxyphenol are found which are used as a reducing agents
for one pot synthesis of silver nanoparticles nature, polyphenol is one of the most important
chemicals in many reductive biological reactions widely found in plants and animals.
Figure 4: Ascorbic acid reduction mechanism of gold and silver ions to obtain Ag0
and
Au0
nanoparticles.
Figure 5: Mechanism of Plant mediated synthesis of Silver nanoparticles

Table 2: Plants extract mediated synthesis of silver nanoparticles
Plants Size(nm) Plants’s part Shape References
Alternanthera dentate 50–100 Leaves Spherical [52]
Acorus calamus 31.83 Rhizome Spherical [53]
Boerhaavia diffusa 25 Whole plant Spherical [54]
Tea extract 20–90 Leaves Spherical [55]
Tribulus terrestris 16–28 Fruit Spherical [56]
Cocous nucifera 22 Inflorescence Spherical [57]
Abutilon indicum 7–17 Leaves Spherical [58]
Pistacia atlantica 10–50 Seeds Spherical [59]
Ziziphora tenuior 8–40 Leaves Spherical [60]
Ficus carica 13 Leaves - [61]
Cymbopogan citrates 32 Leaves - [62]
Acalypha indica 0.5 Leaves - [63]
Premna herbacea 10–30 Leaves Spherical [64]
Calotropis procera 19–45 Plant Spherical [65]
Centella asiatica 30–50 Leaves Spherical [66]
Argyreia nervosa 20–50 Seeds - [67]
Psoralea corylifolia 100–110 Seeds - [68]
Brassica rapa 16.4 Leaves - [69]
Coccinia indica 10–20 Leaves - [70]
Vitex negundo 5 & 10–30 Leaves Spherical & fcc [71]
Melia dubia 35 Leaves Spherical [72]
Portulaca oleracea <60 Leaves - [73]
Thevetia peruviana 10–30 Latex Spherical [74]
Pogostemon benghalensis >80 Leaves - [75]
Trachyspermum ammi 87, 99.8 Seeds [76]
Swietenia mahogany 50 Leaves [77]
Musa paradisiacal 20 Peel [78]
Moringa oleifera 57 Leaves [79]
Garcinia mangostana 35 Leaves [80]
Eclipta prostrate 35–60 Leaves Triangles, pentagons, hexagons [81]
Nelumbo nucifera 25–80 Leaves Spherical, triangular [82]
Acalypha indica 20–30 Leaves Spherical [83]
Allium sativum 4–22 Leaves Spherical [84]
Aloe vera 50–350 Leaves Spherical, triangular [85]
Citrus sinensis 10–35 Peel Spherical [86]
Eucalyptus hybrid 50–150 Peel [87]
Memecylon edule 20–50 Leaves Triangular, circular, hexagonal [88]
Nelumbo nucifera 25–80 Leaves Spherical, triangular [89]
Datura metel 16–40 Leaves Quasilinear superstructures [90]
Carica papaya 25–50 Leaves [91]
Vitis vinifera 30–40 Fruit [92]

Table 3: Antimicrobial activities of silver nanoparticles synthesized using plant extracts.
Literature Review
Green Synthesis of Silver nanoparticles using plant extract is a very simple and cost-
effective way that satisfies the demand of research community and eliminates the possibility
of environment hazards simultaneously. Till date several groups had reported the synthesis of
silver nanoparticles using plant extract which are listed in Table 2. such as bioreduction of
silver ions to yield metal nanoparticles with the help of living plants, geranium, Neem leaf,
Aloevera plant extracts, Emblicaofficinalis (amla, Indian Gooseberry. The green synthesis of
silver nps using Capsicum annuum leaf extract has been reported. These biogenic silver
nanoparticles show high antimicrobial activity against gram-positive and gram-negative
bacteria. Table 3.
In a recent report, these nanoparticles have been synthesized on irradiation using an aqueous
mixture of Ficuscarica leaf extract.[104]
The silver nanoparticles were formed after three hour
of incubation at 370
C using aqueous solution of 5mM silver nitrate. Cymbopogan citratus
(DC) stapf (commonly known as lemon grass) a native aromatic herb from India and also
Biological entity Test microorganisms Method References
Alternanthera dentate
Escherichia coli, Pseudomonas
aeruginosa, Klebsiella pneumonia
and Enterococcus faecalis
[93]
Boerhaavia diffusa
Aeromonas hydrophila, Pseudomonas
fluorescens and Flavobacterium
branchiophilum
[94]
Tea E. coli [95]
Tribulus terrestris
Streptococcus pyogens, Pseudomonas
aeruginosa, Escherichia coli, Bacillus
subtilis and Staphylococcus aureus
Kirby-Bauer [96]
Cocous nucifera
Klebsiella pneumoniae, Bacillus
subtilis, Pseudomonas aeruginosa and
Salmonella paratyphi
[97]
Aloe vera E. coli Standard plate count [98]
Solanus torvum
P. aeruginosa, S. aureus, A. flavus
and Aspergillus niger
Disc diffusion [99]
Trianthema decandra E. coli and P. aeruginosa Disc diffusion [100]
Argimone mexicana
Escherichia coli; Pseudomonas
aeruginosa; Aspergillus flavus
Disc diffusion for
bacteria and food
poisoning for fungi
[101]
Abutilon indicum
S. typhi, E. coli, S. aureus and B.
substilus
[102]
Cymbopogan citratus
P. aeruginosa, P. mirabilis, E. coli,
Shigella flexaneri, S. somenei and
Klebsiella pneumonia
Disc diffusion [103]

cultivated in other tropical and subtropical countries showed strong antibacterial effect
against P. aeruginosa, P. mirabilis, E. coli, Shigella flexaneri, S. Somenei and Klebsiella
pneumonia.[105]
Many plants such as Pelargonium graveolens[106]
, Medicagosativa[107]
,
Azadirachta indica[108]
, Lemongrass[109]
, Aloevera[110]
, Cinnamomum Camphora[111]
, Emblica
officinalis[112]
, Capsicum annuum[113]
, Diospyros kaki[114]
, Caricapapaya[115]
, Coriandrum
sp.[116]
, Boswellia ovalifoliolata[117]
, Tridax procumbens, Jatropha curcas, Solanum
melongena, Datura metel, Citrus aurantium[118]
and many weeds[129,120]
have shown the
potential of reducing silver nitrate to give formation of AgNPs.
The bio-synthesis of silver nanoparticles from a silver nitrate solution using two medicinal
plant extract namely Ocimum tenuiflorum(Ag NP1) and Catharanthus roseus(Ag NP2)
has been reported by Dulen Saikia.[121]
The plant leaf extracts were prepared by mixing 5 g
of dried leaves in 100 ml of deionized water in an Erlenmeyer flask, boiled for 30 minutes at
desired temperature and then filtered through a Whatman 42 no. filter paper. In a typical
reaction, 9 mL of the leaf extracts was added to the desired amount of aqueous AgNO3
solution (1×10 -3
mol dm-3
, 2×10 -3
mol dm-3
, 3×10-3
mol dm-3
, 4×10-3
mol dm-3
and 5×10 -3
mol
dm-3
AgNO3) and the reaction mixture was left at room temperature for the reduction process
to take place. When the leaf extract was mixed in the aqueous solution of the silver ion
complex, it started to change colour (within 30 minutes) from brown to reddish brown.

Figure 6: Colour change of AgNO3 solution with the change in concentration of AgNO3
solution (1mM to 5mM) containing Ocimum tenuiflorum leaf extract; (b) Colour
change of AgNO3 solution with the change of concentration of AgNO3 solution (1mM to
5mM) containing Catharanthus roseus leaf extracts; (c) UV-Vis absorption spectra of
AgNP1 using different concentrations of aqueous AgNO3 solution; (1) 1×10-3
mol dm-3
,
(2) 2×10-3
mol dm-3
, (3) 3×10-3
mol dm-3
, (4) 4×10-3
mol dm-3
, (5) 5×10-3
mol dm-3
; (d) UV-
Vis absorption spectra of AgNP2 using different concentrations of aqueous AgNO3
solution; (1) 1×10-3
mol dm-3
, (2) 2×10-3
mol dm-3
, (3) 3×10-3
mol dm-3
, (4) 4×10-3
mol dm-
3
, (5) 5×10-3
mol dm-3
Figure 7: (a) XRD pattern of AgNP1 (b) XRD pattern of AgNP2

Figure 8: (a) TEM images of AgNP1 and (b) AgNP2
RESULTS
The reduction of the silver ions through leaf extracts leading to the formation of AgNPs of
fairly well-defined dimensions is being demonstrated in UV-Vis, XRD analysis. The XRD
pattern reveals the face-centred crystal structure of AgNPs. The average grain size obtained
for AgNP1 is 29 nm and for AgNP2 is 19 nm.
In another study, Sunlight-induced rapid and efficient biogenic synthesis of silver
nanoparticles using aqueous leaf extract of Ocimum sanctum Linn. With enhanced
antibacterial activity has been reported by Goutam Brahmachari et.al.[122]
In this study the
O.sanctum leaf extracts of varying concentrations (10%, 7%, 5% and 3%) transferred (5mL
each) into four different 100-mL conical flasks containing 45mL of 10−30M silver nitrate
solution leads to final volumes of 50mL each. The resulting solutions were kept under direct
sunlight; gradual colour change was then noticed as an indication of silver nanoparticle
formation (Figure 9) and confirmed by UV-Vis spectrophotometer studies at a regular
interval of time. The nanoparticles were characterized with the help of UV-visible
spectrophotometer and transmission electron microscopy (TEM). The prepared silver
nanoparticles exhibited considerable antibacterial activity.

Figure 9: Optical image. (A) Gradual colour change for the formation of AgNPs by 7%
of O. sanctum leaf extract at different time intervals. (B) AgNPs formation with O.
sanctum leaf extract at different concentrations (10%, 7%, 5% and 3%) measured at 60
min.
Figure 10: (a) UV-visible spectra for different concentrations of O. sanctum Linn. leaf
extract (PLE) with 10−3M AgNO3 measured at 60 min. (b) UV-visible spectra of 7%
aqueous leaf extract (PLE) of three different plants (Curve A) Ocimum sanctum Linn.
(Curve B) Citrus limon L (Curve C) Justicia adhatoda L with 10−3 M AgNO3
measured at 60 min.

Figure 11: (a) TEM image of biosynthesized silver nanoparticles using O. sanctum leaf
extract at 100 nm scale (b) Effect of the treatment of actively growing cells. With AgNPs
(dispersed in the aqueous leaf extract) formed by 7% leaf extracts of O. Sanctum on
growth pattern of Staphylococcus aureus [(●—●) for untreated and (○—○) for treated]
and Pseudomonas aeruginosa [(▲—▲) for untreated and (Δ—Δ) for treated]. All
values are means of three sets of experimental data.
In one more study, the Green Synthesis of Silver nanoparticles by Mulberry Leaves Extract
has been reported by Akl M. Awwad1, Nidà M. Salem[123]
by utilizing the reduced property
of mulberry leaves extract and silver nitrate to synthesize a silver nanoparticles (Ag NPs) at
room temperature and characterized by using UV-visible absorption spectroscopy, scanning
electron microscopy (SEM) and X-ray diffraction (XRD). Further, silver nanoparticles
showed effective antibacterial activity toward Staphylococcusaureus and Shigella sp.

Figure 12: (a) Effect of contact time on AgNPs synthesised by mulberry leaves extract
(b) FT-IR spectra of Mulberry leaves powder.
Figure 13: (a) XRD pattern of AgNPS synthesized by mulberry leaves extract (b) SEM
image of silver nanoparticles.

Figure14: Activity of silver nanoparticles against: (a) Staphylococcus aureus and (b)
Shigella sp.
DISCUSSION
It was found that the average size of silver nanoparticles was 20 ± 2.8 nm that was calculated
by using Debye-Scherer equation. The presence of structural peaks in XRD patterns and
average crystalline size around 20nm clearly illustrates the crystalline nature of AgNPs.
The SEM image of silver nanoparticles, showed cubical and relatively uniform shape of
nanoparticle formation with diameter range 20-40 nm. The larger silver particles may be due
to the aggregation of the smaller ones.
In this study, Banerjee et al.[124]
, proposed a Leaf extract mediated green synthesis of silver
nanoparticles from widely available Indian plants: Musa balbisiana (banana), Azadirachta
indica (neem) and Ocimum tenuiflorum (black tulsi) and their synthesis, characterization,
antimicrobial property and toxicity analysis. This study investigates an efficient and
sustainable route of AgNP preparation from 1mM aqueous AgNO3 using leaf extracts of
three indian plants. The Ag NPs were characterized by UV-visible spectrophotometer,
particle size analyzer (DLS), scanning electron microscopy (SEM), transmission electron
microscopy (TEM) and energy-dispersive spectroscopy (EDS), Fourier transform infrared
spectrometer (FTIR) to determine the nature of the capping agents in each of these leaf
extracts. Ag NPs showed significantly higher antimicrobial activities against Escherichia coli
(E. coli) and Bacillus sp. in comparison to both AgNO3 and raw plant extracts. Additionally,

a toxicity evaluation of these Ag NPs containing solutions was carried out on seeds of Moong
Bean (Vigna radiata) and Chickpea (Cicer arietinum). Results depicts the treatment of seeds
with Ag NPs solutions exhibited better rates of germination and oxidative stress enzyme
activity (nearing control levels), though detailed mechanism of uptake and translocation are
yet to be analyzed.
Figure 15: UV–Vis absorption spectrum of silver nanoparticles. From (A) banana, (B)
neem and (C) Tulsi leaf extracts.
Figure 16: Graphs obtained from FTIR analysis of AgNPs. Curve: (A)- Banana, (B)-
Neem and (C)- Tulsi leaf extracts respectively.

Figure17: SEM images of silver nanoparticles formed by the reaction of 1 mM silver
nitrate and 5% leaf extract of (A) banana. (B) neem and (C) tulsi leaves respectively.
Figure 18: TEM images of silver nanoparticles formed by the reaction of 1 mM silver
nitrate and 5% leaf extract of (A) banana. (B) neem and (C) tulsi leaves respectively.

Table 4: Showing zone of inhibitions found in Bacillus and E. coli cultures
CONCLUSION
As metal nanoparticles seems to fascinate for the future diverse industry due to their enrich
chemical, electrical and physical properties. Metal nanoparticles are synthesized
predominantly by wet chemical methods, where the chemical used are toxic and flammable.
So there is need of eco friendly nanoparticles synthesis approach. Green nanotechnology
accomplish this need by synthesize the metal nanoparticles without using any toxic chemical
as a reducing agent. Plant extract mediated biological synthesis of nanoparticles is known as
Green Synthesis or Green Nanotechnology and these nanoparticles are known as biogenic
nanoparticles. Green synthesis provides benefits over chemical and physical method as it is
cost effective. eco friendly, more stable and there is no need any high energy, pressure,
temperature and toxic chemicals.
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