Environmental Engineering Reference
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microcontroller (output systems). The conceptual diagram of biosensing principle is
shown in Figure 13.2. The most common forms of biosensing by these biological
recognition elements/bioreceptors are: i) antibody/antigen interaction, ii) nucleic
acid/nucleic acid interaction, and iii) cellular interaction. The commonly employed
transducers are based on: i) optical measurements, ii) electrical/electrochemical
measurements, and iii) mechanical measurements.
Antibody-Antigen interaction
B ioreceptor
Transducer
A m p lifie r
Display
Figure 13.2
Schematic illustrating the general principle used in most micro- and nano-
sensors.
13.3.2 Biomolecular Interactions Exploited in Sensors
There are two main classes of biomolecule interactions that have been exploited
more than others to detect waterborne pathogens: i) antibody/antigen, ii) nucleic
acid/nucleic acid. Specificity i.e., the ability to discriminate between two different
closely related targets is governed by this interaction. Nucleic acid/nucleic acid based
interactions have better specificity than the antibody/antigen (immunological) based
interactions. The antibody/antigen interaction is analogous to lock and key mechanism
(Figure 13.3), where the antigen-specific antibody interacts with the antigen in a highly
specific manner. This interaction is exploited in various immunosensors, where the
antibodies are generally immobilized on the surface of a substrate, which interacts with
the specific antigens to produce biological signals. The antibody/antigen binding can be
detected by a change in fluorescent intensity, refractive index, or reflectivity.
Antibody/antigen interaction is mainly dependent on the immobilization strategy. Bio-
molecule immobilization is considered to be an important step in the development of
sensors. Immobilizations that result in disoriented or overcrowded antibodies are known
to induce non-specific antibody/antigen interactions. The most popular method to
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