Evaluation of polycation-stabilized lactate oxidase in a silica sol-gel as a biosensor platform

Whereas glucose oxidase and related proteins are encapsulated readily in silica sol-gels, alpha-hydroxy enzymes such as lactate oxidase (LOx), are reported to be damaged by electrostatic interaction with these matrices. Based on a previous report, poly(ethyleneimine), PEI, was evaluated as a protecting compound under conditions suited to analytical measurements. With LOx and PEI co-encapsulated in a silica sol-gel, the enzyme retained 62% of its initial activity after 20 days. In the absence of PEI, activity was lost during the processing. Batch analytical measurements with enzyme-doped sol-gel yielded a linear response over the range 0.5-2.0 mM lactate and a detection limit of 0.03 mM lactate. Both simple incorporation of LOx in a silica sol-gel and an alternative protection method, blocking the ion-exchange sites on silica with La(III), failed. These negative results supported the hypothesis that the efficacy of PEI was related to its formation of a protective sheath around the enzyme.