Biological Routes to Gold Nanoplates
Jianping Xiea, Jim Yang Lee* a,c, Daniel I.C. Wanga,b and Yen Peng Tingc
a
Singapore-MIT Alliance, 4 Engineering Drive 3, National University of Singapore, Singapore 117576.
Department of Chemical Engineering, M.I.T., 77 Massachusetts Ave., Cambridge, MA 02139, USA.
c
Department of Chemical and Biomolecular Engineering, National University of Singapore, 10 Kent
Ridge Crescent, Singapore 119260.
b
Abstract—Gold nanoplates are promising for optical and
electronic applications; but their synthesis is complex, often
requiring a seeded growth process or spherical to triangle
morphology transformation. We have discovered a biological
protocol to promote the anisotropic growth of different crystal
planes under ambient conditions. Thin, flat, single-crystalline
gold nanoplates were produced when aqueous chloroaurate
ions reacted with the mycelia-free spent medium. While the
exact mechanism for this shape-controlled synthesis is not
clear at this time, the possibility of achieving nanoparticle
shape control in a fungal based system is exciting.
magnetic nanoparticles in magnetotactic bacteria, and the
formation of various other biogenic minerals by bacteria,
algae, and fungi.6 The growing interest in the biomimetic
synthesis of nanoparticles is inspired by nature’s
effectiveness and the selectivity of the biological systems.7
Herein we report the discovery that the mycelia-free spent
medium of Aspergillus niger, when reacted with
chloroaurate ions, could form gold nanoplates at high yield.
It is possible to develop a biological protocol for the sizeand shape- controlled synthesis of nanoparticles using this
fungal based biological system.
Index Terms —Gold, Nanoparticle, Nanoplates, Triangular,
Aspergillus niger, Mycelia-free spent media.
II. EXPERIMENTAL
I. INTRODUCTION
Much effort has been devoted to the synthesis of
inorganic nanoparticles with different shapes. This includes
zero-dimensional nanospheres,1 one dimensional nanorods,2
and two-dimensional nanoplates.3 Compared to zero and
one dimensional nanostructures, the synthesis of
two-dimensional nanostructures in high yield has always
been a challenge, often requiring complex and
time-consuming steps such as morphology transformation
from the nanospheres,4 or the seeded growth process.5
Meanwhile, biological organisms have evolved the ability to
direct the synthesis and assembly of crystalline inorganic
materials under environmentally benign conditions with
good control of chemical composition, size and morphology.
Examples include the formation of iron oxides by bacteria,
silica deposition in diatoms, calcification in cyanobacteria,
Manuscript received November 17, 2006.
Prof. Jim Yang Lee is with Department of Chemical and Biomolecular
Engineering, National University of Singapore, Singapore-119260 and also
a Fellow of Singapore-MIT Alliance, National University of Singapore,
Singapore-117576. (phone: 65-6874-2899; fax: 65-6779-1936; e-mail:
cheleejy@nus.edu.sg).
Prof. Daniel I.C. Wang is with Department of Chemical Engineering,
M.I.T., 77 Massachusetts Ave., Cambridge, MA 02139, USA and also a
Fellow of Singapore-MIT Alliance, National University of Singapore,
Singapore-117576.
Prof. Yen Peng Ting is with Department of Chemical and Biomolecular
Engineering, National University of Singapore, Singapore-119260.
Jianping Xie is with Singapore-MIT Alliance, National University of
Singapore, Singapore-117576.
Aspergillus niger was obtained from Dr H. Brandl
(University of Zurich, Switzerland) and was cultured
according to the protocol of Bosshard et al8. The fungus was
grown in 250mL flasks, each containing 100mL media with
the following composition (g/L): 100 sucrose (Biorad), 1.5
NaNO3 (Merck), 0.5 KH2PO4 (Merck), 0.025 MgSO4.7H2O
(Merck), 0.025 KCl (Merck), and 1.6 yeast extract (Difco).
The culture was incubated in an incubator at 30oC with
rotary shaking at 120rpm. After 4 days of fermentation, the
mycelia-free spent medium was separated from the culture
broth by filtration through Whatman Autovials (0.45μm).
HAuCl4 was added to 10mL mycelia-free spent medium to a
an overall Au(III) concentration of 1 × 10-3M. The final pH
was 3. The mixture was gently agitated with a magnetic
stirrer, and the reaction was carried out at room temperature
(25oC). Aliquots of the reaction mixture were removed at
regular intervals and analyzed by UV-vis spectroscopy and
TEM imaging. UV-vis spectroscopy was performed on a
Shimadzu UV-2450 spectrophotometer operating at 1 nm
resolution. TEM analysis was carried out on a JEOL
JEM2010 microscope operating at 200kV.
III. RESULTS AND DISCUSSION
On mixing the mycelia-free spent medium with the
aqueous solution of chloroaurate ions, the color of the latter
changed from yellow to red purple in 3 hours, signaling the
formation of gold nanoparticles. The gold nanoparticles
obtained were characterized by TEM and UV-visible
1
600
700
800
900
Wavelength (nm)
Fig. 2 UV-visible spectrum of gold nanoparticles formed in mycelia-free
spent medium.
IV. CONCLUSION
In conclusion, a biological protocol for the synthesis of
gold nanoplates using mycelia-free spent medium of
Aspergillus niger was demonstrated. The metabolic
products secreted by A.niger such as proteins, organic acids
and polysaccharides, are believed to be able to differentiate
different crystal faces and directed the growth into extended
flat crystals. The strong absorption at ~856nm due to SPR is
close to the femtosecond laser pulse wavelength (720-780
nm) and we expect these nanoplates to have promising
non-linear optical properties.
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Fig. 1 A) Representative TEM image of gold nanoparticles formed in
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Au triangular with the electron beam perpendicular to the [111] plane.
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