Enzyme adsorption, precipitation and crosslinking of glucose oxidase and laccase on polyaniline nanofibers for highly stable enzymatic biofuel cells

Enzymatic biofuel cells have many great features as a small power source for medical, environmental and military applications. Both glucose oxidase (GOx) and laccase (LAC) are widely used anode and cathode enzymes for enzymatic biofuel cells, respectively. In this paper, we employed three different approaches to immobilize GOx and LAC on polyaniline nanofibers (PANFs): enzyme adsorption (EA), enzyme adsorption and crosslinking (EAC) and enzyme adsorption, precipitation and crosslinking (EAPC) approaches. The activity of EAPC-LAC was 32 and 25 times higher than that of EA-LAC and EAC-LAC, respectively. The half-life of EAPC-LAC was 53 days, while those of EA-LAC and EAC-LAC were 6 and 21 days, respectively. Similar to LAC, EAPC-GOx also showed higher activity and stability than EA-GOx and EAC-GOx. For the biofuel cell application, EAPC-GOx and EAPC-LAC were applied over the carbon papers to form enzyme anode and cathode, respectively. In order to improve the power density output of enzymatic biofuel cell, 1,4-benzoquinone (BQ) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) were introduced as the electron transfer mediators on the enzyme anode and enzyme cathode, respectively. BQ- and ABTS-mediated enzymatic biofuel cells fabricated by EAPC-GOx and EAPC-LAC showed the maximum power density output of 37.4μW/cm², while the power density output of 3.1μW/cm² was shown without mediators. Under room temperature and 4°C for 28 days, enzymatic biofuel cells maintained 54 and 70% of its initial power density, respectively.