Biosensor-Based Technologies for the Evaluation of Quality - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 426

Complementarity determining regions

Heavy chain

Light chain

V H

V L

Intrachain disulphide bond

C H1

C L

Hinge region

Interchain
disulphide bond

C H2

Carbohydrate

C H3

Fig. 20.5 A general schematic diagram of an IgG antibody. The following terms are used in the diagram: V H ,
variable heavy region; V L , variable light region; C H , constant heavy region; C L , constant light region. The location
of the carbohydrate moiety attached to the C H2 constant region is also shown.

antibodies (Fig. 20.5) have a Y-shaped backbone with four polypeptide chains located in two
identical chains that are covalently attached through disulfide bonds. The innermost chains
are referred to as the heavy chains because they are approximately double the molecular
weight of the outer arms (termed the light chains). The recognition sites of the antibody
(which interact with an epitope on an antigen) are located at the ends of the V H (variable
heavy) and V L (variable light) regions of the heavy and light chains. They are commonly
referred to as the complementarity-determining regions (CDRs). Each arm of an antibody
can bind to one antigen, so one IgG molecule can theoretically bind to two antigens. The
strength of an antibody-antigen interaction is referred as the “affinity” of the antibody.
This is important when using an antibody in an immunosensor-based system to detect the
presence or absence of an antigen in a fruit or vegetable sample.
There are three main methods for generating antibodies that may be implemented in
biosensor-based platforms.
The production of polyclonal antibodies involves the immunization of animal hosts to
generate an immune response toward a particular antigen. Blood samples are subsequently
collected, and the antibodies generated are purified from the serum of the animal. These
typically consist of a variety of different serotypes with varying affinities/specificities toward
the epitope in question. Any large animal, including guinea pigs, rabbits, goats, sheep, and
donkeys, is capable of producing these antibodies (Leenaars and Hendriksen, 2005).
The second method of generating antibodies is by using hybridoma technology to pro-
duce monoclonal antibodies (Kohler and Milstein, 1975; Nelson et al., 2000; Hudson and