World Journal of Nano Science and Engineering, 2011, 1, 93-98
doi:10.4236/wjnse.2011.14015 Published Online December 2011 (http://www.SciRP.org/journal/wjnse)
Green Synthesis and Characterization of Gold
Nanoparticles Using Onion (Allium cepa) Extract
Umesh Kumar Parida1, Birendra Kumar Bindhani2, Padmalochan Nayak*
1P. L. Nayak Research Foundation, Manorama Bhavan, Cuttack, India
2KIIT School of Biotechnology, KIIT University, Patia Bhubaneswar, India
Received September 28, 2011; revised November 3, 2011; accepted November 12, 2011
Abstract
In the present research program, cost effective and environment friendly gold nanoparticless were synthe-
sized using the onion (Allium cepa) extract as the reducing agent. The nanoparticless were characterized us-
ing UV-visble, XRD, and SEM, TEM methods. The absorption peak at 540 nm was found to be broaden
with increase in time indicating the polydispersity nature of the nanoparticles. The XRD results suggested
that the crystallization of the bio-organic phase occurs on the surface of the gold nanoparticles or vice versa.
The broadening of peaks in the XRD patterns was attributed to particle size effects. The internalization of
nanoparticles within cells could occur via processes including phagocytosis, fluid-phase endocytosis and re-
ceptor mediated endocytosis.
Keywords: Biosynthesis, Gold Nanoparticles, Allium cepa, Green-Gold
1. Introduction
The field of nanotechnology is one of the most active
areas of research in modern material sciences. Nanotech-
nology is a field that is developing day by day, making an
impact in all spheres of human life and creating a grow-
ing sense of excitement in the life sciences especially
biomedical devices and biotechnology. Recently, the
green chemistry which aims to reduce or eliminate sub-
stances hazardous to human health and the environment
in the design, development and implementation of chemi-
cal processes and products is becoming more and more
important [1,2]. To comply with the 12 principles of
green chemistry, many researches tried to avoid or re-
duce the uses of hazardous chemicals and solvents, such
as using natural materials instead of traditional toxic
chemicals [3-5].The use of nanoparticles is gaining im-
portance in the present century as they possess definite
chemical, optical and mechanical properties. Metal nano-
particles are of importance due to their potential applica-
tions in catalysis, photonics, biomedicine, antimicrobial
activity and optics [6,7] Nanotechnology is expected to
open new avenues to fight and prevent disease using
atomic scale tailoring of materials.This is indeed a chal-
lenging field of research with unlimited future prospects.
The use of phytochemicals in the synthesis of nanopar-
ticles is an important symbiosis between nanotechnology
and green chemistry [8-10]. As the nano revolution un-
folds, it is imperative to develop “nano-naturo” connec-
tions between nanotechnology and green domains of the
nature. Production of nanoparticles under nontoxic green
conditions is of vital importance to address growing con-
cerns on the overall toxicity of nanoparticles for medical
and technological applications [11-13]. The power of phy-
tochemicals, which initiate varieties of chemical trans-
formations within biological systems, is well known [12,
14-16]. For example, a high level of genistein found in
soybeans is both a phytoestrogen and antioxidant, and
has been extensively used to treat conditions affected by
estrogen levels in the body [17,18]. Polyphenolic flavo-
noid in tea, of which epigallocatechin gallate (EGCG) is
the major constituent, has anticarcinogenic activity [19,
20]. Cinnamon a common household spice is known to
have potential properties to treat diabetes mellitus [21,
22]. While the tremendous health benefits of chemical
cocktails present within tea, soya, cinnamon is beyond
doubt, the actual applications of the chemical reduction
power of the myriad of chemicals present in herbs and
spices is still in infancy.
Many biotechnological applications such as remedia-
tion of toxic metals employ microorganisms such as
bacteria [23] and yeast [24] for the synthesis of nanopar-

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94
ticles. Nair and Pradeep [25] have synthesized nanopar-
ticles of gold, silver and their alloys by the reaction of
the corresponding metal ions within cells of lactic acid
bacteria present in buttermilk. The bacteria [26] and al-
gae [27] have been used for the synthesis of gold na-
noparticle.
Gold nanoparticless can be successfully synthesized
by traditionally chemical and physical methods. How-
ever, these methods strongly depend on severe reaction
conditions, for example, aggressive agents like sodium
borohydride, hydrazinium hydroxide, cetyltriethylamm-
nonium bromide, and harmful solvent system to envi-
ronment and ecology, higher temperature and higher
pressure have been used. To pursue a healthy life and
space, it is imperative to develop a clean synthetic ap-
proach using the concept of “green chemistry” to obtain
nanomaterials targeted for different applications, espe-
cially in biomedical fields.
In recent years, plant-mediated biological synthesis of
nanoparticles is gaining importance due to its simplicity
and eco-friendliness. Recently the biosynthesis of gold
nanoparticles by plants such as Terminalia catappa [28],
tea [29], lemongrass [30] has been reported. On a more
fundamental level, it would be interesting to study the
nature of nanoparticles formed using extracts from dif-
ferent parts of the plant [31-35]. A survey of the litera-
ture reveals that onion extract has not been used for the
synthesis of gold nanoparticles.
In the present research program, we wish to report the
green synthesis of gold nanoparticles using the extract of
onion (Allium cepa). The gold nanoparticles were char-
acterized by using UV-visible spectra, SEM, XRD and
TEM.
2. Experimental
2.1. Reagents and Chemicals
Tetrachloroauric acid (HAuCl4·XH2O) was obtained from
Sigma Chemicals. Freshly prepared triple distilled water
was used throughout the experimental work.
2.2. Biological Synthesis of Gold Nanoparticles
The broth used for the reduction of Au3+ ions to Au0 was
prepared by taking 10 g of thoroughly washed and finely
cut onion (Allium cepa) in a 500 ml Erlenmeyer flask
with 40 mL of sterile distilled water and was boiled for
15 min. In a typical experiment, 0.2 ml of broth was
added to 50 ml of 10–3 M aqueous chloroauric acid
(HAuCl4) solution. Within an hour cherry yellowish red
color solution was obtained (Figure 1). The gold nano
particles so prepared were stabilized by adding 2% of
(a)
(b)
Figure 1. (a) Allium cepa; (b) Picture of aqueous solution of
10–3 mM AuCl3 with Allium cepa.
aqueous chitosan solution.Onion juice contains vitamin
C which reduces the Au3+ to Au0 [36].
3. Cell Culture
MCF-7 breast cancer cells and were obtained from SCB
Medical Cuttack, India and MCF-7 cells were main-
tained in MEM with nonessential amino acids, 10 pg·ml–1
phenol red, 10 mM HEPES, 6 ngml-1 insulin, 100 units
ml–1 penicillin, 100 pg·ml–1 streptomycin, and 5% char-
coal-stripped calf serum (maintenance medium).
4. Cell Internalization Procedure
About 16,000 cells (MCF-7) were plated into each well
in a 6 well plate and were incubated at 37˚C for 20.0 hr
to allow the cells to recover. The medium from each well
was aspirated and 4 ml of fresh growth medium was
added per each well. Cells were allowed to grow until

U. K. PARIDA ET AL.
95
they reached confluence by changing the medium every
alternate day. To the confluent cell layer, 150 μl of
AuNps solution was added and further incubated for 4
hrs at 37˚C. The medium was then aspirated from each
well and the cell layer was rinsed 3 times with complete
growth medium to remove any traces of uninternalized
AuNps. The cell layer was washed with CMFH-EDTA
(Calcium-Magnesium-Free-Hank’s + HEPES-EDTA) so-
lution to remove all traces of serum, a trypsin inhibitor.
About 0.5 ml of 0.1 M Trypsin-EDTA solution was ad-
ded to each well to detach the cell layer. Detached cells
were dispersed in 4 ml of complete growth medium and
gently pipetted out of the well. The cell suspension was
transferred into a centrifuge tube and centrifuged at ap-
proximately 125 × g for 5 minutes. Supernatant solu-
tion was discarded and cell pellet was fixed with 0.1 M
Na-Cacodylate buffer containing 2% glutaraldehyde and
2% paraformaldehyde. The pellets were post-fixed with
1% osmium tetraoxide, dehydrated and embedded in Epon/
Spurr’s resin and 80 nm sections were collected.
4.1. UV-Vis Spectroscopy Studies
UV-vis spectroscopy measurements of the gold nanotri-
angles were carried out on a UV-vis Spectrophotometer
(UV-245 Shimadzu).
4.2. X-Ray Diffraction (XRD) Measurement
XRD measurements of the were done on a Phillips PW
1830 instrument operating at a voltage of 40 KV and
current of 20 mA with Cu K radiation.
4.3. SEM Analysis of Gold Nanoparticles
Scanning Electron Microscopic (SEM) analysis was done
using Hitachi S-4500 SEM machine. Thin films of the
sample were prepared on a carbon coated copper grid by
just dropping a very small amount of the sample on the
grid, extra solution was removed using a blotting paper
and then the film on the SEM grid were allowed to dry
by putting it under a mercury lamp for 5 min.
4.4. TEM Measurements
TEM measurements were performed on a JEOL model
1200EX instrument operated at an accelerating voltage at
80 kV.
5. Results and Discussion
Onion contains vitamin C as one of its constituents. Vi-
tamin C is responsible for the reduction of Au3+ to Au0.
5.1. UV-Vis Spectra Analysis
The reduction of aqueous HAuCl4 ions during reaction
with the Allium cepa extract was followed by UV-vis
spectroscopy. Figure 2 show the UV-vis absorption spec-
tra recorded from the Allium cepa extract, prepared from
aqueous gold nanoparticle solution. A strong resonance
at 540 nm is clearly seen and arises due to the excitation
of surface plasmon vibrations in the gold nanoparticles.
5.2. X-Ray Diffraction Studies
Structural characterization has been performed using
XRD analysis and the typical XRD pattern for gold na-
noparticles is shown in Figure 3. In addition to these
three peaks there are some unidentified peaks appeared
in the XRD pattern. The characteristic peaks correspon-
ding to (111), (200), (220) of Au are located at 2θ = 38.29˚,
44.43˚ and 64.68˚, respectively. The result indicates that
the sample is composed of crystalline gold.
Figure 2. UV-vis absorption spectra of gold nanoparticles.
Figure 3. XRD of gold nanoparticle.

U. K. PARIDA ET AL.
96
5.3. Scanning Electron Microscopy of Gold Nano
Particles
The SEM photograph of gold nanoparticles are shown in
Figure 4. SEM photograph of gold nanoparticles clearly
indicates that in the room temperature synthesized sam-
ples the size the average size of the nanoparticles is ~100
nm, with spherical and cubic shape.
6. Cellular Internalization Studies
TEM images of breast tumor (MCF-7) cells treated with
AuNPs unequivocally validated our hypothesis. Signifi-
cant internalization of nanoparticles via endocytosis
within the MCF-7 was observed (Figures 5). The inter-
nalization of nanoparticles within cells could occur via
processes including phagocytosis, fluid-phase endocyto-
sis, and receptor mediated endocytosis. The viability of
Figure 4. SEM image of gold nanoparticles.
Figure 5. TEM Images of different MCF-7 cells showing
uptake of Allium cepa—AuNps.
and MCF-7 cells post-internalization suggests that the
phytochemical coating renders the nanoparticles non-
toxic to cells. Such a harmless internalization of AuNps
will provide new opportunities for probing cellular proc-
esses via nanoparticulate-mediated imaging.
7. Conclusions
The rapid green synthesis of gold nanoparticles using
Allium cepa extract has been demonstrated. The nanopar-
ticles were stabilized using aqueous chitosan solution.
The reduction of gold nanoparticles takes place because
of the presence of vitamin C in onion extract. The UV-
visible spectra measurements were carried out at 540 nm
with sharp peak. The surface of the nanoparticle was as-
certained from the SEM and crystallinity was observed
from the XRD spectra. The viability of and MCF-7 cells
post-internalization suggests that the phytochemical coat-
ing renders the nanoparticles non-toxic to cells.
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