Rosalba Rincon

Entrapment of Enzymes and Carbon Nanotubes in Biologically Synthesized Silica: Glucose Oxidase-Catalyzed Direct Electron Transfer

This work demonstrates a new approach for building bioinorganic interfaces by integrating biologically derived silica with single-walled carbon nanotubes to create a conductive matrix for immobilization of enzymes. Such a strategy not only allows simple integration into biodevices but presents an opportunity to intimately interface an enzyme and manifest direct electron transfer features. Biologically synthesized silica/carbon nanotube/enzyme composites are evaluated electrochemically and characterized by means of X-ray photoelectron spectroscopy. Voltammetry of the composites displayed stable oxidation and reduction peaks at an optimal potential close to that of the FAD/FADH(2) cofactor of immobilized glucose oxidase. The immobilized enzyme is stable for a period of one month and retains catalytic activity for the oxidation of glucose. It is demonstrated that the resulting composite can be successfully integrated into functional bioelectrodes for biosensor and biofuel cell applications.

Enzymatic fuel cells: Integrating flow-through anode and air-breathing cathode into a membrane-less biofuel cell design

One of the key goals of enzymatic biofuel cells research has been the development of a fully enzymatic biofuel cell that operates under a continuous flow-through regime. Here, we present our work on achieving this task. Two NAD(+)-dependent dehydrogenase enzymes; malate dehydrogenase (MDH) and alcohol dehydrogenase (ADH) were independently coupled with poly-methylene green (poly-MG) catalyst for biofuel cell anode fabrication. A fungal laccase that catalyzes oxygen reduction via direct electron transfer (DET) was used as an air-breathing cathode. This completes a fully enzymatic biofuel cell that operates in a flow-through mode of fuel supply polarized against an air-breathing bio-cathode. The combined, enzymatic, MDH-laccase biofuel cell operated with an open circuit voltage (OCV) of 0.584 V, whereas the ADH-laccase biofuel cell sustained an OCV of 0.618 V. Maximum volumetric power densities approaching 20 μW cm(-3) are reported, and characterization criteria that will aid in future optimization are discussed.

Gold-Decorated Flow-Through Electrodes: Effect of Electrochemical Time Constant on Electrodeposition of Au Particles on Reticulated Vitreous Carbon

Here, we investigate the effect of the time constant on the ED of Au particles on RVC substrates. Potentiostatic ED was performed on two RVC samples with electrochemical accessible surface areas of 1.0 and 750 cm 2 . Progressive nucleation was observed on both substrates. At the same applied potentials, the large ohmic drop on the high surface area sample (750 cm 2 ) cannot be neglected and results in a significantly reduced nucleation density (∼30%) and a larger mean diameter. Knowledge of how the electrochemical cell time constant (resistance-capacitance time constant) affects particle coverage and size allows one to optimize ED conditions on substrates with high surface areas. The scaling of ED conditions is important for several technological applications.