Biosynthesis of Au nanoparticles using cumin seed powder extract.

Abstract

Cumin seed was investigated for synthesis of gold nanoparticles. Polydispersed particles were obtained at pH 3 and 30 degrees C, and the effect of temperature and pH on synthesis of gold nanoparticles was analyzed. TEM images showed that amount of platelets formed were predominant at lower temperature where as more number of monodispersed spherical particle of size 1-10 nm were perceived at high temperatures. The gold nanoparticles particles formed at higher pH were stable, uniform and spherical in shape. XPS analysis showed the presence of pure gold nanoparticles.

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catalysis to diagnostics. Numerous chemical synthetic
routes have been used for synthesis of AuNPs. Due to the
employment of harmful chemicals, the usage of chemically
synthesized nanoparticles to biological applications is lim-
ited. This snag has lead biological synthesis routes to gain
considerable attention in the recent past.1Even though
number of reports are available on nanoparticle synthesis
by microbes, usage of plants to synthesize has continued
to flourish in order to materialize their use in large scale
production, since they are non pathogenic, easily avail-
able and easy to use.2Although plants such as Coriander
leaf, Alfalfa, Aloe vera, Neem, Cinnamomum camphora,
Emblica offincianalis, lemon grass and tamarind have been
reported as potent biological materials for synthesis of
AuNPs, the available resources are yet to be completely
explored.3Toting up to these plants we have used Cumin
seed for biosynthesis of AuNPs. Cumin is an herbaceous
plant grown in Mediterranean climate and is known for its
stimulant, antispasmodic and carminative properties.
Cumin’s distinctive flavor and strong, warm aroma are
due to its essential oil content.4
Present study describes for the first time use of
cumin seed powder for synthesis of gold nanoparticle
and nanoplatelets. We have also scrutinized the effect
RESEARCH ARTICLE
Copyright © 2011 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 11, 1811–1814, 2011
Biosynthesis of Au Nanoparticles Using
Cumin Seed Powder Extract
Krishnamurthy Sneha1, Muthuswamy Sathishkumar2?3, Shi Yn Lee1,
Min A. Bae2, and Yeoung-Sang Yun1?2?∗
1Department of Bioprocess Engineering and Department of New Paradigm for BIN Fusion Technology,
Chonbuk National University, Jeonju 561-756, Korea
2Division of Semiconductor and Chemical Engineering, Chonbuk National University, Jeonju 561-756, Korea
3Singapore-Delft Water Alliance, National University of Singapore, Singapore 117577, Singapore
Cumin seed was investigated for synthesis of gold nanoparticles. Polydispersed particles were
obtained at pH 3 and 30?C, and the effect of temperature and pH on synthesis of gold nanoparticles
was analyzed. TEM images showed that amount of platelets formed were predominant at lower
temperature where as more number of monodispersed spherical particle of size 1–10 nm were
perceived at high temperatures. The gold nanoparticles particles formed at higher pH were stable,
uniform and spherical in shape. XPS analysis showed the presence of pure gold nanoparticles.
Keywords: Gold Nanoparticle, Cumin Seed, XPS.
1. INTRODUCTION
Gold nanoparticles (AuNPs) have attracted significant
attention owing to its wide range of applications from
∗Author to whom correspondence should be addressed.
of temperature and pH, followed by investigation on the
chemical state of the nanoparticles formed, using X-ray
photoelectron spectroscopy (XPS).
2. EXPERIMENTAL DETAILS
2.1. Preparation of Cumin Seed
Powder Extract (CSE)
Cumin seeds purchased from a local market were washed
to remove any impurities and powdered in a mixer, and
sieved through a 20-mesh sieve, to obtain uniform size
particles. 2.5 g of the sieved powder was added to 100 mL
sterile distilled water in a 500 mL Erlenmeyer flask and
boiled for 2 min. This was then allowed to cool to room
temperature and filtered using sterile Wattman No. 1 filter
paper to obtain CSE.
2.2. Biosynthesis of Gold Nanoparticles
Chloroauric acid was purchased from Sigma-Aldrich,
USA. AuNPs were synthesized from CSE by adding
50 mL of 1 mM AuCl−
pared CSE in a 250 mL Erlenmeyer flask and incubated in
shaker at 160 rpm at 30?C for 24 h. Followed by visual
observations, after 24 h the biogenic nanoparticles were
collected by centrifuging the samples at 10000 rpm for
15 min. The effects of pH and temperature on biosynthe-
sis were performed at various initial pH ranging from 1–9
and temperature ranging from 0 to 100?C.
4solution to 5 mL of freshly pre-
J. Nanosci. Nanotechnol. 2011, Vol. 11, No. 2
1533-4880/2011/11/1811/004doi:10.1166/jnn.2011.3414
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reaction. It is well known that gold nanoparticles exhibit
a ruby-red color in aqueous solution due to the excita-
tion of surface plasmon resonance in AuNp’s. Therefore,
the appearance of a ruby red color clearly indicated the
presence of AuNPs.5Visual observation was followed by
UV-Vis-NIR spectroscopy, which shows the characteristic
surface plasmon resonance (SPR) of AuNPs at 560 nm
(Fig. 1 inset). TEM image depicts the presence of polydis-
persed triangular, octahedral and spherical nanoparticles of
size ranging form 5 nm to 400 nm (Fig. 1). The ample
range of shapes and sizes of Au NPs obtained by incuba-
tion at room temperature and at natural pH (pH 3±0?05)
of metal solution, pressed for further studies to analyze the
effects of temperature and pH on the nanoparticle forma-
tion. For the investigation of the above mentioned param-
eters on synthesis of AuNPS, the CSE-AuCl−
mixes were incubated at temperatures 0?C, 20?C, 40?C,
60?C, 80?C and 100?C. Observations by UV-Vis-NIR
spectroscopy indicate that the rate of synthesis increased
with increase in temperature from 0 to 100?C. Rai et al.6
previously reported the effect of temperatures from 30?C
to 100?C on the size and shape of the AuNPs synthesized
using lemon grass extract.
Reports are available that the anisotropic and flat AuNPs
absorb the wavelength in the NIR region of the elec-
tromagnetic spectrum which accounts for the in plane
RESEARCH ARTICLE
Biosynthesis of Au Nanoparticles Using Cumin Seed Powder Extract
Sneha et al.
2.3. Characterization of AuNPs
The UV-Vis-NIR region was measured using JASCO V-
670 double beam spectrophotometer using 0.1 mL of the
sample, diluted to 2 mL with sterile de-ionised water.
The synthesized AuNPs suspension was centrifuged and
the sample was subjected to TEM analysis. TEM sam-
ples of biogenic AuNPs were prepared by placing a drop
of the suspension on carbon-coated copper grids and the
films on the TEM grids were allowed to stand for 2 min,
after which the surplus solution was removed using a
blotting paper and the grid was allowed to dry prior
to measurement. TEM observations were performed on
a HITACHI-JP/H7600 instrument (Japan) operated at an
accelerating voltage of 100 kV. The residual metal ion
concentration after bioreduction was analysed using ICP
(Agilent 7500). X-ray photoelectron spectroscopy (XPS)
analysis, for determining the chemical state of the biogenic
AuNPs was performed on AXIS-NOVA (Kratos Inc) with
monochromatic Al K? (1486.6 eV) X-ray as source, base
pressure 8?5×10−9Torr, pass energy 160 eV (wide scan),
20 eV (narrow scan), dwell time-100 ms and no surface
treatment.
3. RESULTS AND DISCUSSION
3.1. Biosynthesis of Gold Nanoparticles
Addition of CSE to 10−3M aqueous HAuCl−
lead to the formation of ruby red color in about 6 h of
4solution,
4reaction
400500 600 700 800
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Absorbance
Wavelength (nm)
Fig. 1.
CSE at 30?C and pH 3.
TEM image of AuNPs produced after 24 h using 2.5 mL of
vibration component (longitudinal component of SPR
band).5?6Similarly, the UV-Vis-NIR spectrum illustrates
the increase in intensity of the out of plane (transverse)
SPR band. A broad SPR band from 800 to 1200 nm indi-
cates the formation of anisotropic nanoparticles, as incuba-
tion temperature increased to 20?C.7Drastic changes were
observed as the incubation temperature increased to 100?C
(Fig. 2). The UV-Vis-NIR data represents the shift of the
in plane SPR band towards lower wavelength and this is
assigned to the decrease in the edge length of triangu-
lar nanoparticles. This result corresponds to the increasing
percentage of spherical nanoparticles relative to triangu-
lar platelets and other anisotropic nanoparticles, with the
increase in the increase in temperature.6At 100?C a single
absorption band at 562 nm is observed with little evidence
of the peak in NIR region, indicating the presence of only
spherical nanoparticles.6The peak is initially centered at
540 nm. A slight red shift to 562 is observed with increase
in temperature probably due to the increase in the size of
spherical nanoparticles.
TEM images also mirror the consistent decrease of
nanoplatelets and increase in spherical nanoparticles, with
rise in temperature, which is consistent with the UV-
Vis-NIR spectrum of AuNPs. This temperature dependent
behavior of nanoparticles synthesis can be attributed to the
fact, that at low temperature the formation of nanoparticles
in a self possessed kinetically driven process which collars
the formation of nanoplatelets, whereas at high tempera-
tures the rate of reduction is high. Higher rate of reduction
thereby leads to enhanced nucleation rate, due to which
secondary reduction is arrested.5?6However at lower tem-
perature, the rate of formation may be slow enough which
enables the aggregation of spherical nanoparticles in order
to form nanoplatelets.7
pH studies also revealed similar effect on the syn-
thesis of nanoparticles. It is observed from the UV-Vis-
NIR spectrum that little or no nanoparticles are formed
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0 °C
RESEARCH ARTICLE
Sneha et al.
Biosynthesis of Au Nanoparticles Using Cumin Seed Powder Extract
40 °C
60 °C
80 °C
Control
0 °C
400600
Wavelength (nm)
800 1000 1200
100 °C
80 °C
60 °C
40 °C
20 °C
20 °C
100 °C
Absorbance
Fig. 2.
Effects of temperature on AuNPs biosynthesis.
at pH 1 whereas a wide range of spherical nanoparti-
cles and anisotropic nanoparticles were formed at pH 3
(with a prominent broad SPR band in the NIR region)
(Fig. 3).
In contrast to lower pH, it is observed that with increase
in pH, the intensity of SPR band in the NIR region
decreases. The noted changes in the UV-Vis-NIR spec-
trum could be due to the increasing concentration of
spherical nanoparticle and decrease in the aspect ratio
of nanoplatelets as pH increases.6The TEM images cast
back the results noticed by UV-Vis-NIR spectrum. The
increase of pH value to 9 resulted in the observation of
spherical nanoparticles which is concurrent with a dis-
crete single peak obtained for the same. pH 9, exhibits the
presence of nanoparticles ranging from 4 nm to 30 nm
(Fig. 3). Spherical nanoparticles of smaller size were
observed at alkaline pH, but no precipitation was noticed
and the nanoparticles remained suspended in solution. This
embarks the stability of nanoparticles at alkaline pH. The
results are concomitant with that obtained by Shipway
et al.,9where in it is stated that AuNPs are well stable at
pH 1 pH 5
pH 9
400600
Wavelength (nm)
8001000 1200
pH 5
Absorbance
pH 3
pH 1
pH 9
pH 7
Fig. 3.
Effects of pH on synthesis of AuNP.
higher pH. It is also evident from the TEM images that
the particles are or more or less monodispersed at higher
pH in contrast to the polydispersed particles formed at
lower pH.
Consequently, higher population of metal nanoparticles
can be obtained on increasing the reaction temperature and
pH, whereas higher population of triangular nano-platelets
can be acquired at lower pH and low incubation tempera-
ture. Nanotriangles have a wide range of applications from
use on cantilevers to drug delivery.10Since at lower tem-
perature, more number of nanoplatelets was formed; XPS
studies were performed for biogenic AuNPs obtained at
20?C to quantify the elemental composition and electronic
configuration. Wide scan spectrum of AuNPs reveals the
presence of C, O, Au elements. The existence of these
peaks is due to the use of biomaterial and no other peaks
are observed from the spectrum which reveals highly pure
AuNPs. The inset Figure 4 (i) represents Au4f doublet nar-
row scan spectrum AuNPs. The binding energies observed
at 85.15 and 88.8 eV represent 4f 7/2 and 4f 5/2 energy
states of Au particles, respectively. The obtained binding
0 200400
Binding energy (eV)
60080010001200
0
10000
20000
30000
Intensity (a.u)
8284 86 88 90
(i)
92
0
500
1000
1500
2000
Intensity (a.u)
Binding energy (eV)
Fig. 4.
XPS analysis of AuNPs formed at 20?C.
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for synthesis of spherical and non spherical nanoparticles.
Nevertheless, the use of plant extracts for biological syn-
thesis of nanoparticles can be a definite retreat for conven-
tional methods of nanoparticles fabrication.
RESEARCH ARTICLE
Biosynthesis of Au Nanoparticles Using Cumin Seed Powder Extract
Sneha et al.
energies are higher than that of bulk gold particles (84 eV)
but are closer to the binding energies of AuI(84.9 eV).
On the other hand, Zhang and Sham11reported that the
electron donated from the surface of gold atoms to thio-
late lead to the high binding energy shift of the material
Au0(4f) energy state. A plausible reason for the shift in
binding energy of CSE-synthesized AuNPs may be due
the capping of AuNPs by the polyols present in the CSE.
Electron donated from the gold atom to the capping agent
or the un-reacted precursor may have lead to a high bind-
ing energy shift.
The peak positions, shapes, and peak to peak distance
(3.65 eV) observed for the prepared material are consis-
tent with the identical spectrum of the gold oxidation state
Au0. XPS study shows the pure and crystalline form of
CSE-synthesized AuNPs. Shankar et al.10stated that the
reduction of chloroaurate ion may have been caused by
the reducing sugars present in lemon grass extract and that
the formation of nanoplatelets may be due to the the inter-
action between AuNPs and aldehydes/ketones. It has also
been suggested that enzymatic reduction of metal nanopar-
ticle can occur in the presence of NADH-reductase and
nitroreductases enzymes.5Previous studies have revealed
that various polyols such as terpenes, flavonoids and other
polysaccharides may act as reducing and capping agent in
nanoparticle biosynthesis. However, the exact mechanism
of reduction is yet to be explored.2Similar mechanisms
may have assisted the synthesis of AuNPs using CSE
and can prove to be a low cost, efficient, green approach
4. CONCLUSION
In summary, the study reveals that AuNPs thus obtained
are pure; and stable in nature over a period of 1 month at
room temperature. Nanoplatelets can be produced at 20?C
and spherical AuNPs can be synthesized at 100?C. Poly-
dispersed AuNPs can be obtained at pH 3 and room tem-
perature. These biogenic AuNPs are water soluble and this
property widens their scope in various applications. XPS
studies show the pure and crystalline nature of biogenic
nanoparticles.
Acknowledgment: This work was supported by NRF
(2009-0083194) and KEITI Grants funded by the Korean
Government.
References and Notes
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Received: 6 November 2009. Accepted: 31 March 2010.
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