Role of Organic Solvents in Immobilizing Fungus Laccase on Single-Walled Carbon Nanotubes for Improved Current Response in Direct Bioelectrocatalysis.

Improving bioelectrocatalytic current response of redox enzymes on electrodes has been a focus in the development of enzymatic biosensors and biofuel cells. Herein a mediatorless electroreduction of oxygen is effectively improved in terms of a remarkable enhancement by ca. 600% in maximum reductive current by simply adding 20% ethanol into laccase solution during its immobilization onto single-walled carbon nanotubes (SWCNTs). Conformation analysis by circular dichroism and attenuated total reflectance infrared spectroscopy demonstrate promoted laccase-SWCNTs contact by ethanol, thus leading to favorable enzyme orientation on SWCNTs. Extended investigation on acetone-, acetonitrile-, N,N-dimethylformamide (DMF)-, or dimethyl sulfoxide (DMSO)-treated laccase-SWCNTs electrodes shows a 400% and 350% current enhancement at maxima upon acetone and acetonitrile treatment, respectively, and a complete diminish of reductive current by DMF and DMSO. These results together reveal the important role of organic solvents in regulating laccase immobilization for direct bioelectrocatalysis by balancing surface wetting and protein denaturing.