E.coli Gone Electric: Glucose Oxidase Based Anodic Catalyst Mediated by Gold Nanowires for High Performance Microbial Fuel Cell
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 (GOx) is a flavoprotein oxoreductase that catalyzes the oxidation of glucose by using oxygen as the electron acceptor to produce glucono-β-lactone (glucanolactone) and hydrogen peroxide. GOx is a homodimeric enzyme, with a flavin adenine dinucleotide (FAD) molecule noncovalently bound at the active site of each subunit. 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, 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. (1)
Aim: Our goal is to design an environmentally friendly and efficient biofuel cell that will maximize electron shuttling using various glucose oxidase mutants derived from Aspergillus niger. Glucose oxidase from Aspergillus Niger provides high specificity, activity, and stability compared to other glucose oxidizing enzymes (Cosnier, Gross, et al.) Additionally, we will try to take MtrCAB operons from Shewanella to make E. coli electric. We plan to accomplish this by presenting these mutants with an anode with gold nanowires adhered to it. We hypothesize that anode nanowires wires will connect to the Shewanella nanowires generating a path for direct electron transfer.
Purpose/Significance: Increasing the efficiency of the overall biofuel-cell will allow for many advances in the field of medicine and technology. Biofuel cells can be used as portable power sources for miniaturize electronics as well as self power implanted medical devices to improve health. For example, biofuel cells have promise to power continuous glucose monitors (CGMs). According to the CDC and the American Diabetes Association, diabetes is the seventh leading cause of death in the U.S. Albeit, diabetes is believed to actually be an underreported cause of death due to its many comorbidities. Either way, current blood glucose monitoring is very cumbersome and relies heavily on an external power source. The promise of a self powered glucose biosensor implant would tremendously help patients monitor blood glucose levels without using any invasive techniques. Biofuel cells may also be able to power cardiac pacemakers. Conventional cardiac pacemakers are powered by lithium batteries which only last between five to eight years. The replacement of these devices requires open heart surgery. This highly invasive surgery has significant surgical costs and may pose a risk to the patient. Hypothetically, a glucose biofuel cell could be implanted in vivo. The fuel cell would reside within the heart and would utilize the glucose present in the blood stream to power the pacemaker. As long as there is a continuous supply of glucose, the fuel cell would provide a theoretically limitless supply of electricity. Overall, glucose biofuel cells are a promising alternative power source that may be able to power ultra-low power devices and decrease our reliance on conventional batteries. Implemented correctly in medical devices, glucose biofuel cells may also be able to provide energy for long periods of time without the need for surgical replacements.
Future Research: In the future, we hope to continue our work and vision of making make clean energy reality for all. We are interested in improving the efficiency of our fuel cell by testing new mutants, possibly generated from error prone PCR or from documented and established glucose oxidase mutant libraries. We are also interested in pursuing the possibility of integrating solar power. Most importantly, we aim to prioritize and troubleshoot for cost-effectiveness.
References:
- Chung, Yongjin, et al. "Amide Group Anchored Glucose Oxidase Based Anodic Catalysts for High Performance Enzymatic Biofuel Cell." Journal of Power Sources, vol. 337, 01 Jan. 2017, pp. 152-158. EBSCOhost, doi:10.1016/j.jpowsour.2016.10.092.
- Cosnier, Serge, et al. "Recent Advances on Enzymatic Glucose/Oxygen and Hydrogen/Oxygen Biofuel Cells: Achievements and Limitations." Journal of Power Sources, 2016, p. 252. EBSCOhost, doi:10.1016/j.jpowsour.2016.05.133.
- Zhang, Kaiyue. “CHINA_CD_UESTC.” Team:CHINA CD UESTC/Design, 2015.igem.org/Team:CHINA_CD_UESTC/Design.
