Biology Reference
In-Depth Information
using the thiol-gold chemistry. Successful discrimination between
complementary andmismatched target DNA was demonstrated.
Other examples of CMOS-based field-effect sensor arrays are
used for the monitoring of extracellular electrophysiological signals
orpHchanges[56].ThosedevicesnormallyinvolveonlyISFETsand
hencearelesscomplicatedinstructurethanthoserequiredforDNA
or protein arrays.
AC techniques such as EIS, which demand high electronic
performance, have also been shown on CMOS circuits integrated
with biosensor arrays. Unlike with potentiometric techniques,
the signal of current sensing techniques such as amperometry
and EIS naturally decreases with the electrode size. In addition,
EIS detection requires currents to be measured for a range of
frequencies, which could make the time needed to read the signals
from the entire microarray impractically long. The use of a wide
band stimulus coupled with a fast Fourier transform algorithm has
been proposed to overcome this problem [57]. A saving feature is
that the frequency range to bemeasured is below 100 Hz.
The aforementioned examples with CMOS processes achieved
success to a certain level, either in the electronic performance or
in measurements with actual biological samples. However, due to
the different fabrication factors, applications and characterization
methods, it is impractical to compare the performance of the
biosensorarrays.
The use of TFTs in electronic biosensor array is still limited.
Various TFT-based DNA and protein transducers have been devel-
opedeitherwithpoly-SioramorphoussiliconTFTs[4,58].Although
proved to be successful as sensor transducers, working TFT-based
sensor arrays have not reported in the literature. This is largely
attributed to the fact that TFT foundries are mostly specialized
for the manufacturing of LCD backplanes and not commercially
availableto researchers.
6.5.4
Fabrication Technologies and Future Trends
From the point of view of electronic biosensor array appli-
cations, both CMOS and TFT technologies clearly have advan-
tages and disadvantages. CMOS represents the state-of-the-art for
