workingelectrode relativeto the referenceelectrode.A voltammetricdevicealso
consistsof one or severalworkingelectrodesand a referenceelectrode,but instead
a fixedelectrodepotentialis appliedto drivean electrontransferreaction,and the
resultingcurrentis measured. Thesizeof the electrodepotentialdetermines
whetherthe targetmoleculeswillloseor gainelectrons.Thus,electroactive
chemicalspeciesare measured.The techniquemaybe usedfor measuringions,
redoxactivecompounds,heavymetals,chargedparticles,conductivityand pH.
Anotherway of usingvoltammetry is by largeor smallamplitudepulsingof
the potential(Winquistet al., 2003). These two techniques generate complex
multivariate output dataand requirechemometricsfor the dataprocessingand
analysis. Piezoelectric sensors suchas the SAWdeviceshavealso beenapplied
to aqueous phases (Kondohand Shiokawa, 1994;Yamazakiet al., 2000).
19.2.3 Biosensors
Biosensors,in contrast to the sensors in sections19.2.1and 19.2.2,represent
a self-contained analyticaldevice that incorporates a biologically active
material (e.g.enzyme,DNA,antibody, or microorganism)in intimate
contactwithan appropriate transductionelement (e.g.electrochemical,
thermal,optical,or acoustic)for the purposeof detecting (reversibly
and selectively)the concentrationor activity of chemicalspeciesin any
typeof sample(Arnoldand Meyerhoff,1998).Clarkand Lyons developedthe first biosensor, an enzyme-basedglucose sensor,
in 1962.Sincethen,hundredsof biosensors havebeendevelopedin many
research laboratoriesaround the world. Over a thousand research papersabout
biosensors, including reviewsand books,havebeenpublished since1995.Their
authorsclassifiedsensors according to theirbiologicalor transduction element,
which is used in this chapter (see below; Fig. 19.3) to illustrate these
Fig. 19.2 Generalconstructionof an electronictongue.Improvinghygieniccontrol by sensors 293