(260p) Fabrication of Enzyme-Based Coatings on Intact Multi-Walled Carbon Nanotubes As Highly Effective Electrodes in Biofuel Cells

Carbon nanotubes (CNTs) need to be well dispersed in aqueous solution for their successful use. Most methods to disperse CNTs rely on tedious and time-consuming acid-based oxidation reactions. Here, we report the simple dispersion of intact CNTs by adding them directly into an aqueous solution of glucose oxidase (GOx), resulting in simultaneous CNT dispersion and facile enzyme immobilization through sequential enzyme adsorption, precipitation and crosslinking (EAPC). The EAPC approach achieved high enzyme loading and stability in the form of crosslinked enzyme coatings on intact CNTs, while obviating the chemical pretreatment that can damage the electron conductivity of CNTs. Initial EAPC-driven GOx activity is ca. 4.5- and 11-times higher than those of covalently-attached GOx (CA) on acid-treated CNTs (ox-CNTs) and simply-adsorbed GOx (ADS) on intact CNTs, respectively. EAPC showed no decrease of GOx activity in aqueous buffer at room temperature for 270 days, while under identical conditions the half-lives of CA and ADS were 20 and 19 days, respectively. EAPC was employed to prepare the enzyme anodes for biofuel cells, and the EAPC anode produced 7.5-times higher power output than the CA anode. Even with a higher amount of bound non-conductive enzymes, the EAPC anode showed 1.7-fold higher electron transfer rate than the CA anode, revealing the reduced electron conductivity of CNTs upon acid treatment. The EAPC approach has potential for effective immobilization of various other enzymes on CNTs that can improve both enzyme loading and stability together with key routes of electron transfer important in biosensing and bioelectronics devices.