Immobilization of Specific Binding Sites

This section pertains particularly to proteins and other biomolecules that are used as specific binding sites in biosensors. For that purpose, these molecules have to be retained in the selective layer or at the selective surface of the sensors. Because they are usually large, one possibility is to use entrapment in a matrix. Both organic and inorganic matrices have been used for this purpose (Lev et al., 1995). However, this is not a preferred approach due to the poor control of the porosity of the matrix. 

A simple, one-step immobilization technique is bulk cross-linking of the functional protein with bovine serum albumin (BSA) using glutaraldehyde as the cross-linking agent (Fig. 2.19). It is popular because of its simplicity, but it usually leads to reduction of the biological activity of the biomolecule. A cleaner and preferable approach is the two-step carbodiimide route. A partial summary of the various immobilization options was shown in Table 2.3. 

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