Biomedical Engineering Reference
In-Depth Information
lead wire (covered
with photoresist)
10mm
electrode
800 m
m
2
)
Fig. 4.6.
The microelectrode array (electrode area 200
×
200
μ
First, we fabricated a microelectrode array and then the DNA probes were
synthesized and had thiol group placed at the 5'-phosphate ends for covalent
binding with the surface of each gold electrode. By using a microarrayer,
each DNA probe was selectively arrayed on each electrode. The fixed probes
were complementarily bound with targeted 20 mer oligonucleotides chosen
from the conservative region of HIV and HCV genes, as shown later. After
a hybridization process with target DNA, an electrochemically active DNA
intercalator specifically binds with the duplexed DNA. Then electrochemical
signals were obtained from the intercalators fixed with DNA on the electrode.
The electrochemical signal provides a correlation with the amount of DNA
duplex formation.
The 32 individually addressable gold electrodes were arranged on a glass
plate (Fig. 4.6). Each electrode measured 200
m
2
. Each microelectrode
was connected to an external potentiostat by an insulated gold track. The
fabrication procedure of the microelectrodes is shown in Fig. 4.7. At first,
a 200 nm gold layer was deposited over a 20 nm chromium adhesion layer
on a glass chip by vacuum evaporation. Next, the chip was spin-coated with
photoresist and was irradiated with UV light. Each metal layer was etched to
form electrodes, lead wires, and their connections. The lead wires were pho-
tolithographically covered with photoresist for insulation. Only the electrode
region was open to the solution.
Figure 4.8 shows a cyclic voltammogram of intercalator, Hoechst 33258,
which consists of piperazine and imidazole derivative. This has been reported
to be a DNA minor groove binder and an electrochemically active dye. This
×
200
μ
