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Biosensor Technologies for Biochips
Biosensors incorporate a biological sensing element that converts a change in an
immediate environment to signals that can be processed. Biosensors have been
implemented for a number of applications ranging from environmental pollutant
detection to defense monitoring. Biosensors have two intriguing characteristics: (1)
they have a naturally evolved selectivity to biological or biologically active ana-
lytes; and (2) biosensors have the capacity to respond to analytes in a physiologi-
cally relevant manner. Molecular biosensors are based on antibodies, enzymes, ion
channels, or nucleic acids. In theory, nucleic acid analysis provides a higher degree
of certainty than traditional antibody technologies because antibodies occasionally
exhibit cross reactivity with antigens other than the analyte of interest. In practice,
however, development of nucleic acid sensor systems has been hampered by the
challenges presented in sample preparation. Nucleic acid isolation remains the rate-
limiting step for all of the state-of-the-art molecular analyses.
Almost all analytical systems combine sensing (i.e. detection) and transducing
components. The distinct feature of biosensors is that the two functions are coupled
in a single physical entity. A biosensor’s input is a specifi c biological event (e.g.,
binding of an antigen to an antibody). Its output is a measurable signal that corre-
sponds to the input. Basic plan of a biosensor is shown in Fig. 2.5.
A biosensor’s biological component provides specifi city, the ability to selec-
tively recognize one type of chemical or event. Its transducer confers sensitivity, the
ability to transform the very low energy of the biological event into a measurable
signal. In other words, a biosensor converts a biological event into an electrical
signal. Biosensors would be useful in personalized medicine as feedback about sta-
tus of biomarkers can guide therapeutics, e.g., glucose biosensors to monitor and
guide insulin therapy according to individual requirements.
TRANSDUCERNO
SIGNALSIGNALBIOLOGICAL
SENSING© Jain PharmaBiotechFig. 2.5 Basic principle of a biosensor. The compound of interest ( black circles ) in a mixture of
substances specifi cally interacts with the biological sensing part of the sensor. The resulting bio-
logical signal is converted into a physical signal (e.g., electric or optical) by a transducer. Substances
which are not capable of interacting with the biological component ( hollow circles ) will not pro-
duce any signal
2 Molecular Diagnostics in Personalized Medicine