Biosensors for the Detection of Waterborne Pathogens - Waterborne Pathogens: Detection Methods and Applications - page 184

7.2. RECOGNITION ELEMENTS
In the early stages of biosensor research, the recognition elements
employed were biological materials, such as antibodies and enzymes. In
recent years, novel materials have emerged, either derived from biological
materials e.g. antibody fragments, or designed to mimic biological materi-
als (biomimetics). These new recognition elements have been developed
in order to offer advantages in terms of cost, stability, long-term storage,
sensitivity, or selectivity. However, antibody- and nucleic acid-based sensors
remain the most popular. Perhaps this will change in the future as the new
materials become more established.
Evidently, the choice of recognition element depends upon the exact
application and involves a trade-off between various performance charac-
teristics. The immobilization of this material on the sensor surface is also
of critical importance for biosensor performance. This section concentrates
on antibodies as the most popular type of recognition element, followed
by a brief discussion of other recognition elements employed as well as the
consideration of surface immobilization techniques.
7.2.1. Antibodies
Antibodies (immunoglobulins, or Igs) are molecules produced by biological
systems in response to a contaminating agent (antigen). Antibodies (Abs),
which were first applied to detection in the 1950s, 8 are the most widely
used biorecognition elements thanks to their proven sensitivity and speci-
ficity. 9 Antibodies can be used to detect the whole pathogen (their sur-
face proteins) or some of the pathogen components (lysate, enzymes, toxin,
spore, pili). Antibody-based methods have been used extensively to detect
bacteria, virus, toxins, and spores alike. 1 Highly selective and sensitive anti-
bodies are readily available for many pathogens, and there are a number
of well-established methods to conjugate antibodies and perform surface
immobilization.
Two categories of antibodies are used in biosensors: monoclonal and
polyclonal, which are produced, or “raised against” the pathogen of inter-
est, in different ways. Monoclonal antibody (mAb) solutions are produced
in vitro from hybridoma cell lines and consist of an identical, well-defined
population of antibodies that bind to a single epitope. Polyclonal antibod-
ies (pAbs) are produced in vivo and consist of a suite of antibodies that
bind to a number of epitopes on the antigen, which is time-consuming.