Biomedical Engineering Reference
In-Depth Information
compact disk with a gold rel ective layer (CDtrode) [35]. h e NPGE
was fabricated in two consecutive stages as follows [36]. Firstly, a step
potential is ramped up from open circuit potential to +3.6 V vs Ag/AgCl
for 3 min, leading to the gold surface of rel ective layer of CD being
anodized in a phosphate buf er solution (pH 7.4). While gas evolution
is accomplished an oxide i lm is grown on the gold substrate until the
anodizing process is terminated. Under these conditions only oxygen
evolution can be done and the produced bubbles at the anode are oxy-
gen which is removed by striking the cell during the anodizing. In the
second step, ascorbic acid is applied as a nontoxic and low-cost reducing
agent to reduce gold oxide to metallic gold. h e reduction is performed by
incubating the anodized gold substrate in a 1.0 M ascorbic acid solution
for 5 minutes. h e gold CDtrode surface area before and at er the anod-
izing process is measured using cyclic voltammetry in dilute sulfuric acid,
by assuming a specii c charge of 386 C/cm for the reduction peak of gold
electrode surfaces. h e surface areas before and at er anodization/reduc-
tion process are 0.19 ± 0.01 and 0.69 ± 0.02 cm
2
respectively. Ferrocene
carboxylic acid is used as molecular reporter in the assay and covalently
attached to the amino-modii ed probe DNA using EDC/NHS chemistry.
h e direct oxidation problem of the ferrocene on the electrode surface has
also been solved by covalent attachment of the redox reporter molecules
on the top of DNA. Taking the advantage of signal enhancing strategy
using nanoporous gold, the sensitivity of the biosensor is improved and
the dif erent single-base mismatches, including the thermodynamically
stable G-A and G-T mismatches, can be easily distinguished. h is sensi-
tive biosensor is able to detect complementary target DNA in subnano-
mole scales.
Zhong
et al.
have also reported a NPGE which is prepared using
square-wave oxidation- reduction cycle method [37]. h e procedure was
done in two steps, i rstly, a gold oxide layer was produced on the gold
electrode immersed in 0.5M H
2
SO
4
by applying repetitive square-wave
potential pulses over a range of −0.8V to 2.5V (versus Ag/AgCl electrode)
at 2000 Hz for 5 min. h en, the potential was held at −0.8V until the com-
plete electroreduction of the gold oxide layer was done [38]. h e surface
area of nanoporous gold electrode was ~10 times larger than the bare
one. h is NPGE has been applied for the fabrication of a DNA biosen-
sor for the detection of promyelocytic leukemia/retinoic acid receptor α
fusion gene in acute promyelocytic leukemia using Methylene Blue (MB)
as an electroactive intercalator. h e hybridization reaction on the probe-
modii ed electrode was monitored using dif erential pulse voltammetry.
Hybridization of the probe with target DNA resulted in the decrease of
