16-10-2012, 05:07 PM
Electrochemical biosensors – principles and applications
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INTRODUCTION
Electrochemical biosensors have been the subject
of basic as well as applied research for nearly fifty
years. Leland C. Clark introduced the principle of
the first enzyme electrode with immobilized
glucose oxidase at the New York Academy of
Sciences Symposium in 1962 (Clark and Lyons was
the YSI 23A Blood Glucose Analyzer; Yellow
POTENTIOMETRIC BIOSENSORS
Potentiometric biosensors are based on
ion-selective electrodes (ISE) and ion-sensitive
field effect transistors (ISFET). The primary
outputting signal is possibly due to ions
accumulated at the ion-selective membrane
interface. Current flowing through the electrode is
equal to or near zero. The electrode follows the
presence of the monitored ion resulting from the
enzyme reaction (Kauffmann and Guilbault 1991).
For example, glucose oxidase can be immobilized
on a surface of the pH electrode. Glucose has only
minimal influence on pH in the working medium;
however, the enzymatically formed gluconate
causes acidification.
AMPEROMETRIC BIOSENSORS
Amperometric biosensors are quite sensitive and
more suited for mass production than the
potentiometric ones (Ghindilis et al. 1998). The
working electrode of the amperometric biosensor is
usually either a noble metal or a screen-printed
layer covered by the biorecognition component
(Wang 1999). Carbon paste with an embedded
enzyme is another economic option (Cui et al.
2005). At the applied potential, conversion of
electroactive species generated in the enzyme layer
occurs at the electrode and the resulting current
(typically nA to μA range) is measured (Mehrvar
and Abdi 2004). The principle of the previously
mentioned YSI 23A (Magner 1998) can serve as an
example:
CONCLUSION
Electrochemical biosensors have existed for nearly
fifty years and seem to possess great potential for
the future. This technology gains practical
usefulness from a combination of selective
biochemical recognition with the high sensitivity of
electrochemical detection. Thanks to current
technological progress, such biosensors profit from
miniaturized electrochemical instrumentation and
are thus very advantageous for some sophisticated
applications requiring portability, rapid
measurement and use with a small volume of
samples. Numerous commercial applications
confirm the attractive advantages of
electrochemical biosensors.