Biosensors incorporate a biological sensing element that converts a change
in an immediate environment to signals conducive for processing. Biosensors
have been implemented for a number of applications ranging from environmen
tal pollutant detection to defense monitoring. Biosensors have two intrigui
ng characteristics: (1) they have a naturally evolved selectivity to biolog
ical or biologically active analytes; and (2) biosensors have the capacity
to respond to analytes in a physiologically relevant manner. In this paper,
molecular biosensors, based on antibodies, enzymes, ion channels, or nucle
ic acids, are briefly reviewed. Moreover, cell-based biosensors are reviewe
d and discussed. Cell-based biosensors have been implemented using microorg
anism, particularly for environmental monitoring of pollutants. Biosensors
incorporating mammalian cells have a distinct advantage of responding in a
manner that can offer insight into the physiological effect of an analyte.
Several approaches for transduction of cellular signals are discussed; thes
e approaches include measures of cell metabolism, impedance, intracellular
potentials, and extracellular potentials. Among these approaches, networks
of excitable cells cultured on microelectrode arrays are uniquely poised to
provide rapid, functional classification of an analyte and ultimately cons
titute a potentially effective cell-based biosensor technology. Three chall
enges that constitute barriers to increased cell-based biosensor applicatio
ns are presented: analytical methods, reproducibility, and cell sources. Po
ssible future solutions to these challenges are discussed. (C) 1999 Biomedi
cal Engineering Society. [S0090-6964(99)01406-X].