Biomedical Engineering Reference
In-Depth Information
Fig. 3
Different steps of technological integration
2.1 Biosensors and Biochips
The concept of biosensors has a long history; usually Clark's glucose electrode
proposed in 1962 is named as the birth of the technology [
6
]. Biosensors were
defined by IUPAC in 1992; a biosensor is ''a device that uses specific biochemical
reactions mediated by isolated enzymes, immune systems, tissues, organelles or
whole cells to detect chemical compounds usually by electrical, thermal or optical
signals'' [
12
]. By this definition classical biosensors are made from two compo-
nents, the biological receptor molecule and the transducer, which are responsible
for linking a biochemical reaction to a readout that may be quantified such as an
optical or electronic signal.
Having a look at the technological side, in the early days of biosensors, there was
a clear separation between the receptor molecules and the transducer which was
made by physical entrapment of the receptor molecule within a membrane. The
membrane itself was also used as a separation tool which only allows the analyte of
interest to pass through. The next step in the process of integration was the
generation of biosensors in which the membrane, the receptor molecule, and the
transducer were all combined in one compartment [
19
]. Hence, the process of
separation, binding, and transduction were located next to each other enabling
faster electron transfer, better biosensor response, and higher sensitivities. These
so-called membrane sensors where then replaced by second-generation biosensors
in which the membrane was no longer necessary. This could be accomplished by
new and more specific recognition elements which made the first separation step
redundant. As fabrication technologies in microelectronics and microsystems
progressed in the later 1980s smaller and affordable production of microelectronic
and mechanical systems (MEMS) was achieved and thus the integration of receptor
molecules, transducer, and the electronics necessary for data generation could be
combined. The convergence of now three components led to the production of
third-generation biosensors which were sometimes also termed ''biochips'' [
19
].
