Enzymatic and non-enzymatic bioanodes: novel materials for glucose oxidase and polyviologen biosensors and biofuel cells

Abstract

A fundamental study of the interaction of iodide and glucose oxidase (GOx) was carried out, showing that the iodide acts as a direct mediator with GOx in enzymatic glucose biosensors. This direct mediation may be happening in parallel with the known electron transport chain through hydrogen peroxide. The aqueous I-/I3-/I2 redox reactions are discussed and studied through the use of cyclic voltammetry and chronoamperometry in conjunction with glucose and GOx. These results are compared with water soluble ferrocenyl salts known to mediate GOx biosensors. This study shows that iodide can mediate GOx in the presence and absence of oxygen, making this the first work, to our knowledge, to show iodide can act as a direct mediator, rather than an indirect mediator for GOx. Layer-by-layer (LBL) modification of gold electrodes with GOx has been an effective way to make enzymatic electrochemical glucose bioanodes for biofuel cells and biosensors. The use of a cystamine attachment layer is usually used to establish a functionalizable initial layer upon which to build up more material for these systems. While this is an easy and fast way to functionalize gold, it was unknown how this attachment layer affects access to the electrode surface. This work explores the use of carbon disulfide (CS2) substituted linear- and branched-polyethylenimine (LPEI and BPEI respectively) as the first layer of these LBL bioanodes. The dithiocarbamate groups attached to the polymer allows it to react with the gold surface and establish a polymeric-first layer. This work shows that the polymeric first layer immobilizes ~2.5 times more material than the first three layers of the cystamine-modified electrodes. The inclusion of ferrocenyl groups in the first-layer PEI also wires the upper layers to the electrode resulting in a ~6 fold increase in current density in the 3-layer system. The Fc-CS2-LPEI- and Fc-CS2-BPEI-based electrodes are also more stable than the cystamine-first layer electrodes. The 9L Fc-CS2-LPEI anode was found to produce 978 µA/cm2 current density, and 271 µW/cm2 peak power at saturating glucose conditions as a biofuel cell while the 19L Fc-CS2-BPEI anode was found to produce 2.1 mA/cm2 current density, and 677 µW/cm2 peak power. Under physiological glucose concentrations the Fc-CS2-LPEI had a sensitivity of 47 µA/cm2 mM while the Fc-CS2-BPEI anode had a sensitivity of 64 µA/cm2 mM, making these some of the most sensitive enzymatic glucose bio-anodes made to date. This work also explores electropolymerization techniques for the fabrication cucurbit[7]uril (CB7)/Polyviologen-based bioanodes. This non-enzymatic electrode was fabricated using cyclic voltammetry, constant potential and pulsed potentials. It was found that the cyclic voltametric method was the best technique to fabricate functional glucose anodes. This method was used to functionalize the high surface-area material carbon felt, and highly stable glucose electrodes were made that produced ~20 µW/cm2 peak power and were able to also utilize sucrose as a fuel source.