Page 213 - Analytical Electrochemistry 2d Ed - Jospeh Wang

198 ELECTROCHEMICAL SENSORS

FIGURE 6-25 The ¯ow of information in the array-based arti®cial nose. (Reproduced with
permission from reference 94.)

useful when high-speed analysis is required (88). Arrays of voltammetric electrodes
can be based on the use of different electrode materials (89) or catalytic surface
modi®ers (84) (with different voltammetric characteristics), on the use of partially
selective coated electrodes (each covered with a different permselective ®lm) (90), or
on the use of different operating potentials or surface pretreatments (91,92).
Microlithographic techniques are often used for the construction of such ampero-
metric array electrodes, with multielectrode potentiostats controlling the potentials of
the individual electrodes. A single (common) reference electrode is normally used
with these arrays. Novel arrays of polymeric chemoresistors or metal oxide sensors
have been used in connection with computer-assisted pattern-recognition algorithms
for monitoring the ¯avor of beers (93) or for detecting various odorants (94).
Changes in the resistivity of a series of conducting polymers upon the adsorption of
different volatile compounds have been particularly useful for creating the response
patterns. The distinct yet partially overlapping signals are achieved by preparing the
individual polymers from modi®ed monomer units or with different counter ions
(dopants). Such arrays serve as electronic analogues for the human nose. The
information ¯ow in such arrays is displayed in Figure 6-25. Practical applications of
electrode arrays have been facilitated by the availability of inexpensive multichannel
data-acquisition cards for personal computers. The development of sensor arrays has
been reviewed by Diamond (95). New advances are expected based on the
development of user-friendly software, of new statistical tools, and of novel
sensor fabrication technology.

REFERENCES

1. G. Sittamplam and G.S. Wilson, J. Chem. Educ., 59, 70 (1982).
2. I. Willner, E. Katz, and B. Willner, Electroanalysis, 9, 965 (1997).
3. L. Gorton, Electroanalysis, 7, 23 (1995).