Recognition Units

At the heart of any chemosensor or biosensor is its recognition unit (receptor). It is constructed for providing selective target binding from a mixture of different and sometimes closely related compounds. The high specificity and affinity of this unit is achieved by its appropriate structures allowing multi-point non-covalent interactions with the target. Such highly selective binding is called molecular recognition. In this chapter we discuss different binding units and the principles of their design and construction.

Some targets are small molecules and ions and for their recognition various coordination compounds can be used. Many of the targets, however, are larger molecules such as enzyme substrates, proteins, nucleic acids, macromolecular assemblies or even living cells. Their immense number requires a great variety of means for specific detection. All of these receptors or recognition units must be transformed into sensors by coupling a dye or nanoparticle to respond to the presence of the target without affecting the binding affinity. Therefore our goal is to achieve optimal binding and efficient labeling of the binder but to still maintain the target binding properties intact while adding the reporter function.