Studies on glucose biosensors based on nonmediated and mediated electrochemical oxidation of reduced glucose oxidase encapsulated within organically modified sol-gel glasses

A new, organically modified sol-gel glass electrode is reported using 3-ami nopropyltriethoxy silane and 2-(3,4-epoxycyclohexyl)-ethyltrimethoxy silane as sol-gel precursors for the construction of electrochemical biosensors. Four different systems of new sol-gel grass modified glucose electrodes are made in acidic medium having common sol-gel precursors and: 1) glucose oxi dase, 2) glucose oxidase along with polyethylene glycol, 3) glucose oxidase and graphite powder, and 4) glucose oxidase along with polyethylene glycol and graphite powder. Both nonmediated and mediated electrochemical regener ation of immobilized glucose oxidase within sol-gel glasses are studied in these four systems. The nonmediated regeneration is achieved in the presenc e of oxygen as electron donor whereas mediated regeneration involves solubl e ferrocene monocarboxylic acid as electron donor in each system. The elect rochemical performance of sol-gel glass based biosensors is compared on the basis of cyclic voltammetry and amperometry. This leads to the observation s: i) all four systems reach a diffusion limited condition associated with the transport of soluble ferrocene monocarboxylic acid as well as for disso lved oxygen within the sol-gel matrix, ii) the relative rate of diffusion o f these analytes increases from system I to system 4, iii) both nonmediated and mediated amperometric responses at suitable potentials are based on th e oxidation of H2O2 and enzymatically reduced soluble ferrocene with relati vely amplified electrochemical signal of system 4. Data on the reduction of oxygen at conventional graphite disk electrode and at typical sol-gel glas s modified electrode are reported.