Biosurfactant functionalized single-walled carbon nanotubes to promote laccase bioelectrocatalysis

Abstract

Fast oxygen (O₂) reduction at high positive potential is essential to obtain effective green energy conversion systems. Here, in an attempt to develop a desirable O₂ reduction biocathode for fuel cells using laccase (Lac), we modify the surface of single-walled carbon nanotubes (SWCNTs) with various biosurfactants to obtain fast direct electron transfer from the SWCNTs to Lac, resulting in O₂ reduction starting from a potential close to the redox equilibrium potential of the oxygen/water couple. We found that pyranoside- and sugar-type surfactants behaved as effective modifier layers of SWCNTs to facilitate Lac bioelectrocatalysis. In particular, SWCNTs modified with the pyranoside-type surfactant n-octyl-β-D-glucopyranoside and the sugar-type surfactant n-decanoyl-N-methyl-D-glucamine exhibited electron transfer rates between the type-1 Cu site of Lac and the modified electrodes of 4000 and 2500 s⁻¹, respectively. The number of modifier layers adsorbed onto SWCNTs strongly influenced its effect on Lac bioelectrocatalysis.