Bioelectrocatalytic O2 reduction with a laccase-bearing film of the copolymer of 3-methylthiophene and thiophene-3-acetic acid

• A novel laccase-bearing biocathode was fabricated with a conducting polymer film.
• Bioelectrocatalytic O2 reduction was carried out with the biocathode.
• The biocathode gave a large current due to efficient O2 reduction.
• The large O2 reduction current was attributed to the orientation of laccase molecules.

Biocathodes bearing laccase as an O2-reducing enzyme have a problem involved in electrical wiring between the enzyme and the electrode. We report on efficient wiring of the enzyme molecules to the surface of a conducting polymer film for fabrication of a biocathode having high performance in O2 reduction. Laccase was immobilized by adsorption on the conducting film prepared by electrochemical copolymerization of 3-methylthiophene and thiophene-3-acetic acid. The biocathode obtained thus with the copolymer film formed at an applied potential of +2.2 V vs. Ag/AgCl with passed charge of 1.0C cm−2 showed the onset potential of O2 reduction corresponding to the redox potential of the T1 site of laccase (+0.62 V vs. Ag/AgCl at pH 4.5) and gave a large O2 reduction current (87 μA cm−2). This value of the O2 reduction current is 1.7 times as large as that given by the biocathode fabricated with the film of 3-methylthiophene homopolymer (52 μA cm−2). An increasing amount of passed charge through the electrochemical copolymerization led to an increase in the O2 reduction current, which reached 158 μA cm−2 when the biocathode was fabricated with the copolymer prepared with the passed charge of 2.0 C cm−2. The O2 reduction current was found to depend on the conductivity of the copolymer film, which was relevant to the composition of the copolymer.

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