The concept of molecules recognising and binding to other molecules can be understood by considering the most common binding agent used commercially - Antibodies.

Antibodies (Ab) are produced naturally as a response to foreign substances (antigens). We all have the potential to recognise an unlimited set of foreign molecules.  Though the general structure of all antibodies is very similar, a small region at the tip of the protein is extremely variable, allowing millions of antibodies with slightly different tip structures, or antigen-binding sites, to exist. This region is known as the hypervariable region. Each of these variants can bind to a different antigen. This enormous diversity of antibody antigen-binding fragments allows the immune system to recognize an equally wide variety of antigens

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Due to their ability to bind to other molecules with high specificity Abs have been used in numerous applications including therapeutics and diagnostics. While there are over 500,000 different antibodies on the market, it has been reported that up to 75% have either not been validated, show a low level of validation or simply do not perform adequately in certain applications