Page 301 - Microsensors, MEMS and Smart Devices - Gardner Varadhan and Awadelkarim

BIO(CHEMICAL) SENSORS 281

Figure 8.48 Basic components of a bio(chemical) sensor: analyte molecules, chemically sensitive
layer, and transducer. After Gardner and Bartlett (1999)

Figure 8.49 Basic mechanisms of a biochemical sensor: (a) reversible binding of the analyte A
to a site at the chemically sensitive layer and (b) irreversible reaction of the analyte A at a site to
produce molecule B at the chemically sensitive layer. After Gardner and Bartlett (1999)

reaction is in fact more common and its sensitivity and selectivity varies with the shape
and charge distributions of the analyte molecule and sensitive layer. The most selective
reactions tend to be those like the key-lock mechanism that operates in a biological sensor
(biosensor), such as a glucose sensor. However, the poor stability of biological materials
makes them unsuitable for use in a real sensor that operates many thousands or millions
of times with a lifetime of a year or more but more suited to a single measurement, that
is, a disposable sensor. For this reason, we concentrate predominantly here on the field
of chemical sensors; anyone interested specifically in biosensors is referred to books by
Cass (1990) and Taylor and coworkers (1996).
Figure 8.50 shows the main types of bio(chemical) sensors classified according to the
operating principle of the sensitive layer, that is, the signal transduced. The signals that are