Chapter 16 - Biosensors based on immobilization of biomolecules in sol-gel matrices

Abstract

This chapter highlights the advantages, recent developments, biosensing applications, and future perspectives of sol–gel entrapped biomolecules. The sol–gel process involves hydrolysis of alkoxide precursors under acidic or basic conditions, followed by condensation and polycondensation of the hydroxylated units, which then lead to the formation of porous gel. Different sol–gel matrices such as inorganic, organically modified (ormosils), hybrid sol–gels, and interpenetrating polymer networks have been used for encapsulation. Inorganic sol–gels are good in optical transparency; chemical robustness but brittleness and low porosity in xerogels are their major limitations. Similarly organically modified sol–gels have good tunable porosity and electrochemical activities, but are relatively fragile and have limited optical transparency. Various proteins such as Mb, hemoglobin (Hb), cyt c, bacteriorhodopsin (bR), lactate oxidase, alkaline phosphatase (AP), GOD, HRP, urease, superoxide dismutase, tyrosinase, and acetylcholinesterase have been immobilized into different sol–gel matrices. The inherent features of the sol–gel matrices such as optical transparency, high surface area, tunable porosity, chemical and photochemical inertness, and the ability to obtain any desired shape such as monoliths, thin films, powders, and fibers enable the design of biosensors. Sol–gel-derived electrochemical biosensors rely on two basic configurations: conductive ceramic composites and electrode surface coatings. Compared to enzymes, fewer reports are available on immobilization of antibody (Ab) in sol–gels and their applications in immunosensing, and like other immunoassays, sol–gel-based immunosensors can entrap either antigen or antibody.