Sensors and Signal Conditioning, 2nd Edition

9.6   BIOSENSORS

Biosensors are devices that incorporate biological sensing elements. They provide a specific and sensitive response to chemical species, particularly molecules of biological relevance. Figure 9.23 shows their simplified structure. There is an external membrane that must be permeable to the target analyte but exclude other substances. The biological element inside the biosensor interacts with the analyte and yields a response that is detected by a common sensor. Hence, the biological element behaves as primary sensor. It may convert the analyte to a different chemical species through a biochemical reaction, release a chemical product in response to the analyte stimulus, or change its electrical, mechanical, or optical properties. The permeability of the internal membrane near the output sensor, if present, may be different from that of the external membrane. The output sensor may be a conventional electrochemical sensor (Section 6.5), a ChemFET (Section 9.2), a piezoelectric or SAW sensor (Section 8.2.2), an optical sensor, a thermal sensor, or other [22].

Figure 9.23   Basic structure of a biosensor. The biological element reacts to the analyte (black dots) that diffuses through the semipermeable external membrane and yields a product (circles) or undergoes a change that is detected by a common (output) sensor.

Biosensors often drift because proteins or other substances ...