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A new glucose biosensor was developed based on the sandwich con®guration of organically modi®ed sol-gel glasses. The new sol-gel glass was developed using 3-aminopropyltrimethoxy silane and 2-(3,4-epoxycyclohexyl)-ethyltrimethoxy silane. Two types of sol-gel glasses were used to develop glucose biosensors that differ in absence (A) and the presence of graphite powder [particle size 1±2 m] (B). An additional additive (polyethylene glycol, Mol. wt. 6000) was also incorporated in both types of the upper sol-gel glass layer. The new sol-gel matrix with immobilized glucose oxidase was analyzed by scanning electron microscopy (SEM).The sandwich con®guration was developed using a bilayer of sol-gel glasses having a layer of glucose oxidase in between the bilayer. This electrode with special con®guration was used to form a layer of sol-gel glass of ca. 0.2 mm thickness. The performance of sol-gel glasses (A & B) was analyzed based on cyclic voltammetry using ferrocene monocarboxylic acid. The results show a diffusion limited condition of ferrocene across the sol-gel matrix. The characterization of sol-gel glass based biosensor was recorded based on the cyclic voltammograms in absence and presence of glucose. The results show an increase in anodic current which is also characteristic of hydrogen peroxide oxidation in both cases (A & B). The responses of the sol-gel glasses based biosensors were analyzed based on chronoamperometric measurements. An ampli®ed signal on the addition of the same concentrations of glucose was recorded with the B-type sol-gel glass electrode which was attributed to its relatively high porosity and better conductivity of the graphite loaded sol-gel glass. These observations were in accordance with the results on the diffusion of ferrocene and the magnitude of anodic current resulting from hydrogen peroxide oxidation. The calibration plots for glucose analysis using both type of sensors are reported. Data on the mediated electrochemical oxidation of glucose oxidase using soluble ferrocene were also reported based on cyclic voltammograms and amperometric measurement.

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A new, organically modified sol‐gel glass electrode is reported using 3‐aminopropyltriethoxy 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 glass modified glucose electrodes are made in acidic medium having common sol‐gel precursors and: 1) glucose oxidase, 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 regeneration of immobilized glucose oxidase within sol‐gel glasses are studied in these four systems. The nonmediated regeneration is achieved in the presence of oxygen as electron donor whereas mediated regeneration involves soluble ferrocene monocarboxylic acid as electron donor in each system. The electrochemical performance of sol‐gel glass based biosensors is compared on the basis of cyclic voltammetry and amperometry. This leads to the observations: i) all four systems reach a diffusion limited condition associated with the transport of soluble ferrocene monocarboxylic acid as well as for dissolved oxygen within the sol‐gel matrix, ii) the relative rate of diffusion of these analytes increases from system 1 to system 4, iii) both nonmediated and mediated amperometric responses at suitable potentials are based on the oxidation of H2O2 and enzymatically reduced soluble ferrocene with relatively amplified electrochemical signal of system 4. Data on the reduction of oxygen at conventional graphite disk electrode and at typical sol‐gel glass modified electrode are reported.

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Two new sol-gel glass systems with immobilized ferrocene are developed using two different types of sol-gel precursors. System (1) is developed using ferrocene carboxaldehyde and a mixture of two silanes (3-aminopropyltriethoxy silane and 2-(3,4-epoxycyclohexyl)-ethyltrimethoxy silane). System (2) is developed using ferrocene monocarboxylic acid and a mixture of 3-glycidoxypropyltrimethoxysilane and trimethoxysilane. The surfaces of the sol-gel glasses are analyzed based on scanning electron microscopy (SEM). The electrochemistry of ferrocene in system 1 and system 2 is characterized based on cyclic voltammetry. System 1 shows capacitive CV at slow scan rate whereas system 2 shows good reversible electrochemistry of ferrocene. The potentiometric response of the ferrocene immobilized sol-gel glass (system 1) is studied in 10 mM Tris-HCl buffer pH 7.0. A reproducible potential difference of system 1 to the order of À30 mV is recorded for 2 months with respect to a double junction SCE reference electrode. An ion sensing membrane is assembled over the ferrocene immobilized sol-gel glass using plasticized PVC matrix membrane containing dibenzo-18-crown-6. A typical potentiometric response of the ion sensor is reported. The response of the ion-sensor shows better response time, high reproducibility and relatively better slope for potassium analysis as compared to earlier reported solid-state K ion-sensor based on dibenzo-18-crown-6 neutral carrier. The reproducibility, detection limit and relative response of the ion sensor to Na and NH 4 ions are reported.

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