Immobilization of glucose oxidase into polyaniline nanofiber matrix for biofuel cell applications

Glucose oxidase (GOx) was immobilized into the porous matrix of polyaniline nanofibers in a three-step process, consisting of enzyme adsorption, precipitation, and crosslinking (EAPC). EAPC was highly active and stable when compared to the control samples of enzyme adsorption (EA) and enzyme adsorption and crosslinking (EAC) with no step of enzyme precipitation. The GOx activity of EAPC was 9.6 and 4.2 times higher than those of EA and EAC, respectively. Under rigorous shaking at room temperature for 56 days, the relative activities of EA, EAC and EAPC, defined as the percentage of residual activity to the initial activity, were 22%, 19% and 91%, respectively. When incubated at 50 °C under shaking for 4 h, EAPC showed a negligible decrease of GOx activity while the relative activities of EA and EAC were 45% and 48%, respectively. To demonstrate the feasible application of EAPC in biofuel cells, the enzyme anodes were prepared and used for home-built air-breathing biofuel cells. The maximum power densities of biofuel cells with EA and EAPC anodes were 57 and 292 μW/cm2, respectively. After thermal treatment at 60 °C for 4 h, the maximum power density of EA and EAPC anodes were 32 and 315 μW/cm2, representing 56% and 108% of initially obtained maximum power densities, respectively. Because the lower power densities and short lifetime of biofuel cells are serious problems against their practical applications, the present results with EAPC anode has opened up a new potential for the realization of practical biofuel cell applications.