Biomedical Engineering Reference
In-Depth Information
in fields such as health care, the food industry, and environmental monitoring. The attraction to
biosensors stems from their accurate, precise, and reproducible measurements in a cheap, small,
and portable manner.
A biosensor is commonly defined as a device that detects, records, and transmits information
regarding a physiological change or process. Biologically derived recognition entities (enzymes,
antibodies, microorganisms, cell receptors, cells, etc.) are coupled to a transducer that detects the
biological reaction and converts it into a signal, which can be physicochemical, optical, electro-
chemical, thermometric, or magnetic (Figure 5.1).
Biosensing technology has spread throughout many disciplines due to its great specificity, sensi-
tivity, and diversity in uses. Molecular and enzymatic biosensors were among the first to be intro-
duced in the late 1960s (Updike and Hicks 1967; Guilbault and Montalvo 1969) with thermal,
optical, and electrochemical biosensors following shortly thereafter (Mosbach and Danielsson 1974;
Clemens et al. 1976; Weaver et al. 1976; Volkl et al. 1980).
Planar microelectrode biosensors, used to monitor cellular behavior, were first introduced by
Thomas et al. in 1972 to monitor the electrical activity of contracting embryonic, chick heart cells
(Thomas et al. 1972). Since then, microelectrode biosensors have been used to study cell cultures
in
vitro
under different conditions. For instance, Gross et al. used a microelectrode biosensor to moni-
tor and eventually stimulate neuronal cell activity
in vitro
from the brain and spine (Gross et al.
1977, 1982, 1993). Other uses include monitoring metabolism (McConnell et al. 1992), fluorescent
probes and reporter genes (Zysk and Baumbach 1998), and electrophysiology (DeBusschere and
Kovacs 20 01).
Whole-cell impedance-based biosensors, pioneered by Giaever and Keese (1984) were devel-
oped to monitor the proliferation and motion of a population of anchorage-dependent cell cultures.
By monitoring whole-cell activity, one can monitor changes in membrane receptors, channels, and
enzymes that may be expressed by the cell. Morphological changes can also be monitored using
electrical impedance sensing (EIS) biosensors, since cellular membranes exhibit dielectric proper-
ties (Pancrazio et al. 1999). EIS biosensors are especially beneficial for monitoring the behavior of
the whole cell because they provide information about the total physiological responses of cells to
external stimuli. Biosensors that incorporate whole cells can have an advantage over other biosensors
for certain applications because they can provide functional information without damaging the cells.
Most current biosensors are used to detect enzymes, DNA/RNA (deoxyribonucleic acid), and immu-
nological components, converting the biological phenomena into electrical signals (Katz and Willner
2003; Song et al. 2006; Luong et al. 2008) and allowing for specifically targeted results.
Enzyme
Antibody
Amplifiers
Electroactive
material
pH change
Electrode
Filters
Semiconducting
pH electrode
Termistor
Nucleic acid
Multiplexers
Electrical
signal
Bacteria
Heat
Analog-to-
digital
converters
Cell
Tissue
Light
Mass change
Photodetector
Linearizers
Compressors
Piezoelectric
medium
Organelle
Sample
analyte
Bioreceptors or
molecular
recognizers
Signal
transducers
Signal-
conditioning
circuits
FIGURE 5.1
Schematic of the biosensor.
