ABSTRACT
Higher loading of enzymes on electrodes and efficient electron transfer from the enzyme to the electrode are urgently needed to enhance the current density of biofuel cells. The two-dimensional nature of the electrode surface limits the enzyme loading on the surface, and unfavorable interactions with electrode surfaces cause inactivation of the enzyme. Benign biohydrogels are designed here to address enzyme degradation, and the three-dimensional nature of the biohydrogel enhanced the enzyme density per unit area. A general strategy is demonstrated here using a redox active enzyme glucose oxidase embedded in a bovine serum albumin biohydrogel on flexible carbon cloth electrodes. In the presence of ferricyanide as a mediator, this bioelectrode generated a maximum current density (jmax) of 13.2 mA·cm-2 at 0.45 V in the presence of glucose with a sensitivity of 67 µA·mol-1·cm-2 and a half-life of >2 weeks at room temperature. A strong correlation of current density with water uptake by the biohydrogel was observed. Moreover, a soluble mediator (sodium ferricyanide) in the biohydrogel enhanced the current density by â¼1000-fold, and citrate-phosphate buffer has been found to be the best to achieve the maximum current density. A record 2.2% of the loaded enzyme was electroactive, which is greater than the highest value reported (2-fold). Stabilization of the enzyme in the biohydrogel resulted in retention of the enzymatic activity over a wide range of pH (4.0-8.0). We showed here that biohydrogels are excellent media for enzymatic electron transfer reactions required for bioelectronics and biofuel cell applications.
