Biomedical Engineering Reference
In-Depth Information
and tested the conducting capability of the resulting wires. These efforts col-
lectively open a new direction in the fabrication of electronic nanomaterials.
3.4.2
Templates for Nanowires: DNA for Nano-Electronics
The DNA molecule has been suggested as a template for making nanoscale
wires for the emergent field of nano-electronics. This is due to the regularity
of the width of the DNA double helix and its robust mechanical properties.
Several groups have succeeded in coating DNA molecules with metallic par-
ticlesandhaveshowndataontheconductivepropertiesofthesebiotemplated
materials. Braun et al. non-covalently bound a stretch (16
µ
m) of bacterio-
phage
-DNA between two gold electrodes by allowing it to hybridize with
short DNA fragments that had been covalently attached to those surfaces [84].
Electrical measurements indicated that the wires were non-conducting at
low voltage bias, with resistances greater than the experimentally measurable
10
13
. Furthermore, the shape of the I-V curve obtained was dependent on
the voltage scan direction. Richter et al. employed a similar strategy to pro-
duce DNA-templated nanowires that showed relatively low resistances under
low-voltage bias [85]. They reduced palladium on
λ
-DNA and immobilized
thenanowireongoldelectrodes.Theresistancesobtainedwerelowerthan
1 kv, with the specific conductivity approximately one order of magnitude
lower than bulk palladium. Subsequently, the resistances of these palladium
nanowires [86] were studied at low temperatures which discovered that the
palladium metals reduced on a DNA template showed the expected quantum
mechanical behavior, with their resistances increasing at low temperatures.
This behavior is similar to that of thin palladium films and shows that wires
templated with DNA molecules behave normally.
Mertig et al. discovered conditions in which fine and regular platinum
clusters formed on DNA molecules by using first-principle molecular dynam-
ics (FPMD), which ultimately yielded a faster rate of growth and finer metal
clusters on the template [87]. Another metal that has been investigated for
surface templating of DNA is gold. Harnack et al. investigated the binding
and reduction of tris(hydroxymethyl) phosphine derivatized gold particles on
calf-thymus DNA [88]. The rapidly formed nanowires show electrical con-
ductivities about 1
λ
1000th that of gold, which the authors attributed to the
graininess of the material.
Patolsky et al. modified
N
-hydroxysuccinimide-gold nanoparticles with
a nucleic-acid intercalating agent, amino psoralen [89]. In addition, Belcher
and colleagues [75, 90-92] took a very different approach toward not only
discovering, but also fabricating, electronic and magnetic materials, depart-
ing sharply from traditional materials process technology. Such approaches
for producing finer and finer features at the nanoscale, with increasing dens-
ity and in finite areas, may prove complementary to the microcontact printing
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