Background: Energy has become a necessity to sustain our society and to further its advancement. The depletion of fossil fuels and the need for clean electricity production has called attention to biofuel cells which convert chemical energy into electrical energy by electro enzymatic reactions. This source of energy is sustainable, renewable, and does not emit CO2. Conventional fuel cells are generally cost-ineffective in regards to energy production. In addition, once one of the active masses in a conventional fuel cell is fully consumed, the current-producing reaction ceases.
Many scientists have shown glucose powered biofuel cells to hold much promise. As a resource, glucose is energy dense, cost-efficient, and readily abundant. It also represents a clean source of power. The redox enzymes used to power biofuel cells are renewable and less expensive compared to the precious metal catalysts used in conventional fuel cells. In addition, these enzymes are optimized in neutral pH buffers, making them an attractive candidate to power ultralow power consuming implantable medical devices.
Glucose oxidase is a relatively large enzyme, with an average diameter of about 8 nm. This enzyme comes with both advantages and disadvantages. The enzyme has highly stable catalytic activity, most likely due to the fact that its redox center is insulated by a protein shell. The shell effectively buries the active site, flavin adenine dinucleotide (FAD), in a deeply embedded protein matrix. As a result, glucose oxidase generally requires mediators such as nanotube based materials to achieve successful electron transfer to the electrode because of the long electron tunneling distances and the steric constraints. The two mediators that have been given the most attention are carbon nanotubes and gold nanoparticles because of their large active surface area and exceptional electrical properties. Carbon nanotube has been commonly used as a mediator for direct electron transfer from the FAD site within glucose oxidase because it lowers overpotential. Carbon nanotubes; however, are toxic to the human body and has hard immobilization with glucose oxidase molecules because of its hydrophobic feature. Gold nanoparticles (GNP) are not poisonous to the human body, and can aid long term stability of GOx molecules (Chung, Ahn, et al.)
