Hollow Bioelectrodes Based on Buckypaper Assembly. Application to the Electroenzymatic Reduction of O₂

A new concept of hollow electrode based on the assembly of two buckypapers creating a microcavity which contains a biocatalyst is described. To illustrate this innovative concept, hollow bioelectrodes containing 0.16-4 mg bilirubin oxidase in a microcavity were fabricated and applied to electroenzymatic reduction of O₂ in aqueous solution. For hemin-modified buckypaper, the bioelectrode shows a direct electron transfer between multi-walled carbon nanotubes and bilirubin oxidase with an onset potential of 0.77 V vs. RHE. The hollow bioelectrodes showed good storage stability in solution with an electroenzymatic activity of 30 and 11% of its initial activity after 3 and 6 months, respectively. The co-entrapment of bilirubin oxidase and 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) in the microcavity leads to a bioelectrode exhibiting mediated electron transfer. After 23 h of intermittent operation, 5.66 × 10^-4 mol of O₂ were electroreduced (turnover number of 19,245), the loss of catalytic current being only 54% after 7 days.