Antibodies
Antibodies are proteins that show outstanding selectivity.
They are produced by b-lymphocytes in response to
antigenic structures, that is, substances foreign to the
organism. Molecules larger than about 10 kDa can
stimulate an immune response. Smaller molecules like
vitamins or steroids can be antigenic (also called haptens)
but they do not cause an immune response unless they are
conjugated to larger ones like bovine serum albumin.
Many antibodies are commercially available and
commonly used in immunoassays. Antibodies are usually
immobilized on the surface of the transducer by covalent
attachment by conjugation of amino, carboxyl, aldehyde,
or sulfhydryl groups. The surface of the transducer must be
previously functionalized with an amino, carboxyl,
hydroxyl, or other group. A review of conjugation
techniques can be found elsewhere.[20] Antibodies share
similar limitations with enzymes. Furthermore, binding
may not be reversible and regeneration of the surface may
require drastic changes in conditions like low pH, high
ionic strength, detergents, etc. Therefore, efforts are being
made to produce low cost, single use sensors. Probably the
main potential advantage of immunosensors over
traditional immunoassays is that they could allow faster
and in-field measurements. Immunosensors usually
employ optical or acoustic transducers.