Chapter 6
Affinity-Based Recognition
6.1 General Principles
Affinity interactions are based on multiple noncovalent interactions between two species leading to the formation of a molecular aggregate usually called a complex. Such interactions are very common in living organism, being associated with important physiological functions. The strength of the complex arises from the multiplicity of the noncovalent bonds and is quantified by its stability constant, often termed the affinity constant. At the same time, the noncovalent character of the interaction imparts reversibility to the affinity association process. Finally, affinity interactions are very specific as a result of the steric and structural complementarity of the reactant.
The high specificity of biological affinity interactions prompted the development of a broad range of analytical applications in which one affinity reagent acts as a recognition receptor, whereas the second, target compound functions as the analyte. Inspired by natural affinity reactions, various synthetic receptors have been developed in the field of supramolecular chemistry [1, 2]. Synthetic receptors are often more stable and cheaper than the natural ones but the latter are well established and will be further employed on a large scale.
From the standpoint of analytical applications, immunoassay is the most common analytical methods in this class. It is based on antibodies that are secreted by higher organisms in defense against pathogens. Biological ...
