Biocatalytic Composite Electrodes for Biofuel Cell Applications
Daniel Appel
Eldorado High School
Albuquerque, NM
Abstract
Enzymes are biological catalysts critical to life functions and operate in mild environments with high specificity. Researchers are attempting to immobilize enzymes on or in robust matrices for biofuel cells, biosensors, bioreactors, etc. for future nanotechnology applications. Enzyme immobilization must occur without protein denaturation. Sol-gel glass is used because of its porosity, strength, heat resistance, transparency, hydrophobicity, and low temperature fabrication. It is also possible to use polymers (e.g., polyvinyl alcohol) to entrap enzymes.
This project's purpose was to evaluate silicate and polymeric matrices for enzyme immobilization. I hypothesized that silica sol-gels would encapsulate and retain more viable enzyme than polymers; and that immobilized enzyme anodes would generate electricity in biofuel cells (but less than in vitro microorganisms). A mixtures designed experiment was performed to optimize sol-gel fabrication. Glucose oxidase was then entrapped in the silica gels and polymers. Protein assays were performed to spectrophotometrically quantify captured enzyme and measure reactivity to determine the better immobilization medium. A biofuel cell was then designed and constructed with glucose oxidase immobilized on the anode. Fuel cell voltage was then recorded over time. Results showed that PVA-based polymer retained more viable protein, possibly due to larger porosity (macromolecule entrapment and reactant access). The poorer sol-gel performance was perhaps attributable to diffusion limitations. The biofuel cell with immobilized enzyme on the anode successfully oxidized glucose, generating electricity within published millivolt ranges. Further work is needed using more sophisticated porosimetry and spectrographic assay equipment, precious metal mediators and electrode substrates, micromultimeter, and biofuel cell miniaturization.
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