Immobilization of Enzymes in 3-D Inorganic Hosts

Immobilization of Enzymes in 3-D Inorganic Hosts 15.4.2.1 Immobilization in Si02 

Since it is the major constituent of the Earth s crust, silica is very abundant in nature in amorphous or crystalline forms. Silica can be manufactured, for instance, by high-temperature processing (glasses) or by the sol-gel process. This latter occurs through a two-step reaction hydrolysis followed by condensation. Silica gels are good candidates for use in enzyme immobilization. They display good optical and 

A wide range of additives can also be introduced into the sol-gel matrices in order to modulate the hydrophobicity of the materials and to improve enzyme stability, activity and accessibility, leading to hybrid or even composite sol-gel matrices. Polymers [157,179,180] such as polyethyleneglycol, polyvinylpyrrolidone, polyvinylalcohol, polyglycidol, polyethyleneimine, polyacrylate have been simultaneously entrapped with enzymes in a siloxane matrix, as well as organic additives (sugar, amino add) 

With regard to biosensor applications, a wide variety of electrochemically active species (ferrocene, ruthenium complexes, or carbon and metal (Pt, Pd, Au...) [185,186] were also introduced into the sol-gel matrices or adsorbed to improve the electron transfer from the biomolecules to the conductive support [187,188]. For instance, glucose oxidase has been trapped in organically modified sol-gel chitosan composite with adsorbed ferrocene to construct a low-cost biosensor exhibiting high sensitivity and good stability [189]. 

Since both are negatively charged, a first coating of the capsules surface with L-polylysine is needed. 

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