Page 208 - Analytical Electrochemistry 2d Ed - Jospeh Wang
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6-3 SOLID-STATE DEVICES 193
was developed for continuous monitoring of glucose in body ¯uids (72). The theory
and mode of operation of ISFETs have been reviewed (73).
6-3.1 Microfabrication of Solid-State Sensor Assemblies
Other miniaturized solid-state sensors can be fabricated by coupling microelec-
tronics and chemically sensitive layers. In particular, Wrighton and co-workers (74)
fabricated diode and transistor structures by combining a conducting polymer with
lithographically de®ned interdigitated microarray electrodes. Such devices have been
responsive to redox species such as oxygen or hydrogen. Interesting biosensing
applications of this molecular electronic switching device involved the addition of an
enzyme layer (75,76). Changes in the conductivity of the polymer resulting from pH
changes (associated with the enzymatic reaction) have been exploited for monitoring
the corresponding substrate (e.g., Figure 6-20). Miniaturized and disposable
amperometric biosensors can be achieved by coupling microfabricated oxygen
electrodes with various biocomponents (77).
6-3.2 Microfabrication Techniques
Microfabrication technology has made a considerable impact on the miniaturization
of electrochemical sensors and systems. Such technology allows replacement of
traditional bulky electrodes and ``beaker-type'' cells with mass-producible, easy-to-
use sensor strips. These strips can be considered as disposable electrochemical cells
onto which the sample droplet is placed. The development of microfabricated
electrochemical systems has the potential to revolutionize the ®eld of electroanaly-
tical chemistry.
FIGURE 6-20 Con®guration of a penicillin sensor based on an microarray electrode coated
with a pH-responsive polypyrrole. V G gate voltage; V D drain voltage; I D drain current;
PS potentiostat; CE and RE counter and reference electrodes, respectively. (Reproduced
with permission from reference 76.)
