Layer-by-layer self-assembled osmium polymer-mediated laccase oxygen cathodes for biofuel cells: the role of hydrogen peroxide.

High potential purified Trametes trogii laccase has been studied as a biocatalyst for oxygen cathodes composed of layer-by-layer self-assembled thin films by sequential immersion of mercaptopropane sulfonate-modified Au electrode surfaces in solutions containing laccase and osmium-complex bound to poly(allylamine), (PAH-Os). The polycation backbone carries the Os redox relay, and the polyanion is the enzyme adsorbed from a solution of a suitable pH so that the protein carries a net negative charge. Enzyme thin films were characterized by quartz crystal microbalance, ellipsometry, cyclic voltammetry, and oxygen reduction electrocatalysis under variable oxygen partial pressures with a rotating disk electrode. New kinetic evidence relevant to biofuel cells is presented on the detection of traces of H(2)O(2), intermediate in the O(2) reduction, with scanning electrochemical microscopy (SECM). Furthermore the inhibitory effect of peroxide on the biocatalytic current resulted in abnormal current dependence on the O(2) partial pressure and peak shape with hysteresis in the polarization curves under stagnant conditions, which is offset upon stirring with the RDE. The new kinetic evidence reported in the present work is very relevant for the operation of biofuel cells under stagnant conditions of O(2) mass transport.

Redox molecule based SERS sensors.

We describe a general framework to design nanobiosensors based on a wired enzyme coupled to a redox molecule and integrated with SERS Au core-shell nanoparticles and ordered nanocavities. The response of the proposed sensor is based on the different electronic resonant Raman behavior of the oxidized or reduced electronic states of the molecular wire, and on the surface plasmon amplification induced by the tailored metallic substrate. The nanobiosensors can be interrogated remotely through the resonant Raman scattering intensity recovery or spectral variation of the redox molecule, an Os-complex, when the latter varies its oxidation state. Alternatively, we show through two-color spectro-electrochemistry that Raman scattering is also finely sensitive to oxidation state changes of flavin, a biomimetic system that mimics the active center of many flavoprotein enzymes. We show that multiple sample spectroscopic ellipsometry gives access to the spectral dependence of the optical constants of single redox-molecule layers, and through it to the electronic resonances of the system. All the components for selective molecular recognition and for the generation of an optical amplified signal, are self-contained in the proposed biosensor. As proof of concept a compact SERS sensor responsive to glucose with millimolar concentration in solution is demonstrated.

Macroporous ultramicroelectrodes for improved electroanalytical measurements.

Recent work on the preparation of highly organized macroporous electrodes and nanoporous ultramicroelectrodes has been combined and extended to elaborate macroporous ultramicroelectrodes (UMEs) by template synthesis using colloidal crystals and following two different and complementary methods. On the one hand, arched porous UMEs were prepared, and on the other hand, cylindrical porous UMEs were obtained by using cavity UMEs. These macroporous UMEs have an active surface area which is up to 2 orders of magnitude higher compared to that of a classical disk UME as characterized by cyclic voltammetry. To study their analytical performance, the macroporous UMEs have been modified with a redox-active thiol and also a model bioelectrocatalytical system containing a redox mediator, a cofactor, and glucose-dehydrogenase. In both cases the electrochemical signal is amplified by up to 2 orders of magnitude, which increases significantly the analytical performance of such electrodes and therefore opens up new applications for this kind of miniaturized electrochemical system.