Laccase electrodes

The fuel cell described above exhibited three key flaws. First, the anode redox mediator operates at a redox potential well above that of glucose oxidase, raising the operating potential of the anode and lowering the achievable cell potential. Second, the cell operates at pH 5, near-optimal for the laccase electrode but suboptimal for the current-limiting glucose... 

Figure 12. Effect of electrode thickness on performance of an oxygen-reducing laccase electrode (a) optimum current density, imax, at 0.5 V vs SHE and (b) optimum support porosity (e) and relative gas-phase porosity (eg/e) for carbon fiber supported electrodes optimized for (—) gas...

A laccase electrode for the determination of the lignin content of wood has been described by Malovik et al. (1983). The samples were extracted with organic solvent and the extracts directly injected into the measuring cell. 

Fig. 61. Concentration dependence of the current of hydroquinone (H2Q) conversion at a laccase electrode. At +100 mV H2Q not converted enzymatically is directly oxidized at the anode whereas at -100 mV only the product of the enzymatic reaction is indicated.

Fig. 3.7 Schematic representation of a LDH-ABTS laccase electrode b SWCNT- LDH-ABTS laccase mixed coating and c two layers configuration based on an inner SWCNT deposit modified by a LDH-ABTS laccase coating...

Vaz-Dominguez C, Campuzano S, Rudiger O, Pita M, Gorbacheva M, Shleev S, Fernandez VM, De Lacey AL. Laccase electrode for direct electrocatalytic reduction of O2 to H2O with high-operational stability and resistance to chloride inhibition. Biosens Bioelectron 2008 24(4) 531-537. 

A novel application for ionic hquids in the preparation of functional materials has also served as a pre-immobilization strategy for a robust laccase electrode. In this case, the enzyme was first adsorbed to an ioiuc liquid-functionalized cellulose acetate that was then incorporated into a carbon paste electrode. The approach served to produce a device with acceptable levels of accuracy for methyldopa determination in pharmaceutical samples. In a similar manner, microencapsulation of laccase from T. versicolor in polyethylenimine (PEI) was demonstrated as a prior treatment for creating a coating on a paper support. Although first attempts showed a deleterious effect of PEI on laccase because of negative conformafional changes that reduced the activity of the encapsulated enzyme [28], optimized microencapsulation conditions resulted in superior stabihty compared with free enzyme [27]. 

Fameth WE, D Amore MB. Encapsulated laccase electrodes for fuel cell cathodes. J Electroanal Chem 2005 581 197-205. 

Attachment Strategies It has been shown that a film of adsorbed laccase will exchange electrons directly with a PGE electrode, leading to electrocatalytic O2 reduction, but the adsorbed film is very unstable [Blanford et al., 2007]. Several approaches have been employed to generate films of laccase that are stable for many days and show higher electrocatalytic current density. 

Figure 17.6 Redox hydrogel approach to immobilizing multiple layers of a redox enzyme on an electrode, (a) Structure of the polymer, (b) Voltammograms for electrocatalytic O2 reduction by a carbon fiber electrode modified with laccase in the redox hydrogel shown in (a) (long tether) or a version with no spacer atoms in the tether between the backbone and the Os center (short tether). Reprinted with permission fi om Soukharev et al., 2004. Copyright (2004) American Chemical Society.

Figure 17.7 Electrocatalysis of O2 reduction by Pycnoporus cinnabarinus laccase on a 2-aminoanthracene-modified pyrolytic graphite edge (PGE) electrode and an unmodified PGE electrode at 25 °C in sodium citrate buffer (200 mM, pH 4). Red curves were recorded immediately after spotting laccase solution onto the electrode, while black curves were recorded after exchanging the electrochemical cell solution for enzyme-fiiee buffer solution. Insets show the long-term percentage change in limiting current (at 0.44 V vs. SHE) for electrocatalytic O2 reduction by laccase on an unmodified PGE electrode ( ) or a 2-aminoanthracene modified electrode ( ) after storage at 4 °C, and a cartoon representation of the probable route for electron transfer through the anthracene (shown in blue) to the blue Cu center of laccase. Reproduced by permission of The Royal Society of Chemistry fi om Blanford et al., 2007. (See color insert.)...

While direct electron transfer to laccases may help elucidate the mechanism of action of these enzymes it is unlikely that this process will supply sufficient power for a viable implantable biocatalytic fuel cell, because of difficulties associated with the correct orientation of the laccase and the two-dimensional nature of the biocatalytic layer on the surface. However, a recent attempt to immobilize laccase in a carbon dispersion, to provide electrodes with correctly oriented laccase for direct electron transfer, and a higher density of electrode material shows promise [53],... 

An alternative strategy for co-immobilization of mediator and GOx is based on adsorption of enzyme, cross-linked, as was described for the laccase-based biocatalytic cathodes [30, 37 42], to an osmium-based redox polymer film, on carbon electrodes [1-3, 54],... 

Palmore et al. first demonstrated the use of ABTS in a biofuel cell cathode, combining it with laccase from Pyricularia oryzae ABTS was dissolved at 2 mM in oxygen-saturated 0.2 M acetate buffer, pH 4, 25 °C. With a glassy carbon working electrode, an open-circuit potential of 0.53 V vs SCE was observed, reflecting the presence of HABTS in low-pH solution. Protonation of ABTS shifts the redox potential to 0.57 V vs SCE. With negligible stirring, current densities of 100 / A/cm were achieved at an electrode potential of 0.4 V vs SCE. 

Potentials vs SHE. High-surface-area carbon supports in 02-saturated buffer. Catalyzed by bilirubin oxidase in the presence of chloride. Catalyzed by fungal laccase, chloride absent. Moderate stirring by bubbled gas. Strong stirring by rotating disk electrode at 4 krpm. 

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