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Chemistry Letters Vol.36, No.10 (2007)
A Novel Method for Fabrication of Unique Cobalt Nanostructures
Shiyong Sun,ꢀ1 Jun Li,2 Ying Xiong,1 Huijie Yu,1 and Nan Tao1
1Hefei National Laboratory for Physical Sciences at Microscale and Department of Materials Science and Engineering,
USTC, Hefei 230026, P. R. China
2Department of Oncology, Affiliated Hospital and Teaching Section of Anhui Medical University,
Hefei 230022, P. R. China
(Received June 5, 2007; CL-070605; E-mail: shysun@mail.ustc.edu.cn)
˚
In this article, a novel method has been developed for
(ꢁ ¼ 1:5418 A).
extracellular prepared of amorphous ring and chain cobalt nano-
structures using Staphylococcus epidermidis in combination
with PVP as template. The nanostructures consist of cobalt
nanoparticles with the average particle size of 50 nm. The mor-
phological difference between chain and ring nanostructures is
determined by the interaction between PVP and bacteria. Extrac-
ellular prepation of nanostructures using bacteria as template
opens up a new possibility to fabricate metal-based nanostruc-
tures in biological system.
The high yield of cobalt chain nanostructures was achieved
by the addition of 1 g of PVP to bacterial suspension before
reduction. The detailed chain nanostructures are showed in
Figures 1a and 1b. The chains are disorderly wrapped together.
The chain consists of Co nanoparticles with the average particle
size of 50 nm. The X-ray diffraction pattern (see Supporting
Information S1)14 of as-prepared product shows only one broad
peak at the 2ꢂ range from 40 to 55ꢂ, which indicates that chain
nanostructures may be amorphous. The TEM image (Figure 1c)
confirms that the cobalt chains are linked by bacteria. The select-
ed area electron diffraction (SAED) pattern (insert of Figure 1c)
exhibits a diffuse ring, which further confirms that the chain
nanostructures are amorphous.
A sample was made without washing so that PVP chains re-
mained in structures. Then Co nanoparticles were removed off
by H2O2. The remained PVP chains were bound to bacterial
surface (see Supporting Information S2).14 It confirms that
PVP chains can link to the capsular polysaccharide molecules
on S. epidermidis surface. The control experiments, in which
the samples were prepared in the absence of bacteria, have
shown that only separate Co nanoparticles were obtained with-
out the existence of chain-like structures. On the contrary, when
the samples were prepared by the addition of bacteria and in the
absence of PVP, Co nanoparticles deposited on the bacterial sur-
face and formed the disordered flakes with pleated structures
(see Supporting Information S3).14 These results verify our
deduction that S. epidermidis in combination with PVP chains
can provide the template for chain nanostructure formation.
The nanoscale magnetic materials have a wide variety of
applications such as the high density magnetic recording media,1
catalysts,2 and biomedicine.3 Currently, there are considerable
interests in synthesis of materials with unique nanostructures.
Living microorganisms such as bacteria, fungi and virus have
been developed as the biotemplate for preparetion of nanoparti-
cles.4–6 We considered that whether bacteria can be developed
as the reactor for fabrication of metal nanostructures, in which
bacterial surface provided the biotemplate for nanostructure
formation and the bound metal ions were reduced by the agents
like NaBH4. However, it seems that bacteria6 cannot provide the
template for extracellular fabrication of nanostructures, unlike
DNA or virus which is well suitable to assemble one-dimension-
al nanostructure because of their sizes and well-organized struc-
tures. An encapsulated Staphylococcus epidermidis strain, which
bacteria are enclosed within a capsule layer, has been obtained
from a clinical specimen when we cultured tumor cell. Herein,
we show a novel method for extracellular fabrication of cobalt
nanostructures using PVP in combination with encapsulated S.
epidermidis as template.
.
Then, PVP solution was added into a CoCl2 6H2O solution
and ultrasonically dispersed 15 min before exposure to bacteria.
Representative AFM images of products prepared by the addi-
.
The S. epidermidis (1 ꢁ 106 per mL) for experiment was
cultured overnight in the Dulbecco minimum essential medium
(DMEM) with supplement of 5% the fetal bovine serum
(FBS). The whole process was carried out at room temperature
under the nitrogen atmosphere. In a typical reaction, 5 mL of
1 ꢁ 106 per mL living-state bacteria was added to the 25 mL of
aqueous solution containing 1 g of polyvinylpyrrolidone (PVP,
tion of 212.5 mg of CoCl2 6H2O and 10 g of PVP are shown
in Figure 2. Cobalt nanoparticles encircled the bacteria and
formed the ring-like nanostructures. These encircling Co nano-
particles as the magnetic dipoles formed the bistable flux closure
.
K-30, Mw ¼ 49000), then 25 mL of 53.125-g CoCl2 6H2O solu-
tion was added in, and magnetically stirred for 30 min.
Following this was the addition of 20 mL of 16 mM NaBH4.
The as-prepared products were collected, washed several times
with absolute alcohol, and finally dried in a vacuum oven at
room temperature. The morphology of as-prepared products was
observed by FESEM (JEOL-6700F), TEM (H-800, Hitachi) and
AFM (AJ-III). TEM observation was performed at 200 kV. The
phase of the as-synthesized products was determined by an
X-ray diffractometer with monochromatized Cu Kꢀ radiation
Figure 1. (a), (b) FESEM images of cobalt chain nanostruc-
tures. (b) detailed images of cobalt chain nanostructures. (c)
TEM images of detailed chain structures; insert in (c): SAED
pattern of cobalt chain.
Copyright Ó 2007 The Chemical Society of Japan
Sun, Shiyong
