Designing of cathodes modified with enzymes for the biofuel cell applications

Maciej Klis 1Jerzy Rogalski 2Marcin Karbarz 1Zbigniew Stojek 1Renata Bilewicz 1

1. Warsaw University, Faculty of Chemistry, Pasteura 1, Warszawa 02-093, Poland
2. Maria Curie Sklodowska University, Department of Biochemistry, Pl. Sklodowskiej 3, Lublin 20-031, Poland

Abstract

Biocatalysts are employed in biofuel cells for the conversion of chemical energy to electrical energy. The enzymes can be used in one of two ways. Either the biocatalysts can generate the fuel substrates for the cell by biocatalytic transformations or metabolic processes, or the biocatalysts may participate in the electron transfer chain between the fuel substrates and the electrode surfaces. Unfortunately, most of redox enzymes do not take part in direct electron transfer with the conductive supports, and therefore a variety of electron mediators are used for the electrical wiring of the biocatalyst to the electrode.

biofuelcell.jpg

An important condition for the progress in biotechnology is to understand the electrochemical reactions of redox proteins and to control their interactions with gold substrates. Gold is often used as the electrode material due to its inertness. One of the crucial steps in the development of electrodes for biofuel cells is the appropriate immobilization of the enzyme on gold, since its biological activity as well as electrical contact have to be preserved.
Laccase (EC 1.10.3.2) is a blue multi-copper enzyme which catalyses the oxidation of a variety of phenolic and amine compounds simultaneously with the four-electron reduction of molecular oxygen to water. The enzyme active site contains four copper atoms of types I, II, and III, which play different roles in the enzymatic process. Substrates are oxidized near the T1 site, and the electrons are transferred to the T2/T3 cluster, where molecular oxygen is reduced.
We employed several strategies to immobilize laccase on gold, such as electrostatic adsorption on gold clusters, entrappment of the enzyme in poly(N-isopropylacrylamide) gel (NIPA) and covalent attachment to self-assembled organothiols monolayers (SAMs).

Lcs_on_SAM.jpg

In case of NIPA gel matrix the immobilized laccase showed electroactivity at 0.360 V vs. NHE, however, upon binding to 11-mercaptoundecanoic acid (MUA) the Cu center is electroactive at a more positive potential (590 V vs. NHE). The catalytic current of oxygen reduction was observed in case of Au cluster/laccase modified electrode. For the MUA/laccase electrode, for both mediatorless and mediated with 1,1'-ferrocenedimethanol processes, the catalytic oxygen reduction was observed. Hence, best results obtained so far are those based on 11-mercaptoundecanoic acid (MUA) as the molecular bridge.
 

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Presentation: Poster at SMCBS'2005 Workshop, by Maciej Klis
See On-line Journal of SMCBS'2005 Workshop

Submitted: 2005-07-31 16:22
Revised:   2009-06-07 00:44