A Novel Bio-inspired Materials Fabrication Method and Its Potential Applications
Thomas S. T. Tan
Laboratory of Bio-Nanotechnology, Institute of Biotechnology, National Tsing Hua University, Hsinchu
Contract No：甲-91-E-FA04-1-4
Period：4/1/2005-3/31/2006
give rise to a devise with controlled arrangement of metal
Abstract
particles with a defined size and interparticle distance. Such
New strategies for materials fabrication are of
fundamental importance in the advancement of science and
a device has potential use in the fabrication of ultrasmall
electronic components.
technology [1-5]. In my laboratory certain bio-molecules
One extensively studied S-layer is the hexagonally
were found to be potentially useful in fabrication of novel
packed intermediate (HPI) layer of the major cell envelope
metal-based nanomaterials. This report presents tangible
protein of the radioresistant bacterium
results and potential applications based on S-layer-protein
radiodurans. The HPI layer has been extensively studied by
modified silicon wafers.
conventional electron microscopy and scanning force
Introduction
Deinococcus
microscopy [12-14]. Its stability is remarkable: even after
drying in air it exhibits a relatively well preserved structure
Bacterial S-layers. The outer surface of a number of species
showing a hexagonal lattice (a = b = 18 nm) of rosette-like
of bacteria comprises of a porous crystalline membrane
units connected by six spokes. The thickness of single HPI
called an S-layer, which is made up of protein monomers [6].
layers was about 7 nm whereas stable double layers
Isolated S-layer proteins (SLPs) have the intrinsic property
exhibited a thickness of about 17 nm.
to reassemble in vitro into S-layer on the surface of a broad
D. radiodurans S-layer. We have previously demonstrated
spectrum of materials such as wafers, metals and
that the in vitro self-assembly capacity of D. radiodurans IR
biomembranes [7-11]. Several important applications can be
SLPs in suspension [15]. The self-assemblies were sheet
derived
S-layers.
structures and several micronmeters in size. This report
Ultrafiltration membranes can be made from SLPs. The
shows that (1) under certain conditions the HPI proteins can
advantage of S-layer-based membrane is that the isoporous
assemble into several-hundred-micrometer to millimeter
membrane could give a very sharp molecular exclusion
sized membranes on silicon wafer, and (2) the large-scale
limits. Functional ligands can be immobilized to S-layer
protein nanomembranes could be used as a tool to fabricate
site-specifically to be utilized in future biomedical devices
silver nano/microstructures of various dimensions directly
such
on a silicon wafer surface. Based on these findings, possible
as
from
those
these
for
unique
DNA
properties
detection
of
and
analysis,
immunoassays and proteomics. SLPs can be reassembled
advanced
bio-metal
onto liposomes to strengthen and to improve the
applications are proposed.
physicochemical resistance of the liposomes. This will
nanocomposites
and
potential
Methods
enhance the usage of liposomes in medicine. Because of the
periodic structure and constant spacing of the identical pores
Bacterial strain. D. radiodurans IR, originally isolated from
and morphological units, S-layer can be used as the template
γ– irradiated chicken meat, has been characterized
for the in vitro deposition of metal nanoparticles. This will
previously [16].
Isolation of SLPs. It is well documented that SLPs have the
further exploration of integration and functionality As
intrinsic tendency to reassemble into two-dimensional
summarized in Fig, 6, possible advanced nanostrutures may
arrays after removal of the disrupting agent, such as
include interconnects, switch, array, and living electric
guanidine hydrochloride (GHCl) and urea, used in the
circuit (i.e., living cells are interconnected).
S-layer dissolution procedure. Cells of D. radiodurans IR,
Applications.
washed and suspended in phosphate buffer, were broken by
method may find potential industrial applications in
sonication.
production of
The
cell-wall
fraction,
collected
by
centrifugation, washed and suspended in Tris-HCl buffer
The
novel
bio-inspired
nanofabrication
(1) ultrasensitive sensors, (2) miniturizd
devices, and (3) smart drug delivery systems.
Conclusions
(50 mM, pH 7.4), was treated with deoxyribonuclease I (1
mg/ml), ribonuclease A (0.5 mg/ml), and Triton X-100
We have established novel methods using bacterial
(0.5%). The partially purified S-layer preparation was
S-layer proteins to functionalize wafer surface in large areas.
suspended in Tris-HCl buffer for further use.
We have successfully established that our S-wafer products
have potential uses in the synthesis of not only
Microscopy. The S-layer preparation was treated with 5 M
zero-dimensional
but
also
one-dimensional
silver
GHCl to dissolve the SLPs. The GHCl extract was stored at
4℃ before use. Samples were observed with confocal laser
nanostructures. For examples, one of the products was
capable of transforming silver ions into silver nanocubes.
scanning microscopy, atomic force microscopy, and electron
Another product can even help fabricate silver nanowires
microscopy when appropriate.
under certain conditions.
Results and Discussion
Atomic force microscopy. The atomic force micrograph of
the HPI-protein-based self-assemblies on a silicon wafer
(S-wafer) suggested a nonrandom arrangement of the
HPI-protein-based nanoparticles (with a morphological unit
sized around 50 – 100 nm) (Fig. 1).
Confocal laser scanning microscopy. By using confocal
laser scanning microscopy, we noted that in some area on
the wafer several self-assembly sheets further formed
multi-layered structures (Fig. 2). A layer appeared to serve
as the template for the next one with smaller size, thus
forming a layered cake-like structure.
Fabication of silver nanostructures. We have produced a
number of S-layer modified wafers by different procedures.
One of the products was found to effectively transform
silver ions into silver nanocubes under certain reaction
conditions (Fig. 3). Use of another protocol resulted in the
synthesis and simultaneous immobilization of silver
nanowires directly on wafer surfaces (Fig. 4 & 5).
Possible
advanced
nanostructures.
More
advanced
fabrication work is currently being conducted with a view to
Fig. 1. Atomic force micrograph of a S-wafer.
Fig. 4. SEM micrograph showing silver nanowires
on an S-wafer.
Fig. 2. Scanning laser confocal micrograph
showing multi-layered self-assembly. Bar =
100 μm.
Fig. 5. A silver nanobridge on an S-wafer.
Fig. 3. Silver nanocubes on an S-wafer.
Fig. 6. Possible advanced bio-metal nanocomposites.
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