The Minteer Research Group is currently focused on studying bioelectrocatalysis. We have two main projects: enzyme cascades for bioelectrocatalysis and organelle bioelectrocatalysis for sensing and energy conversion applications. Our research in enzymatic bioelectrocatalysis is focused on both the bioengineering of natural enzymatic metabolic pathways for bioanodes for biofuel cells as well as enzyme discovery and enzyme engineering for non-natural complete oxidation pathways for biofuels. Our research in organelle-based bioelectrocatalysis is focused on the use of mitochondria to catalyze the complete oxidation of pyruvate and fatty acids at the anode of fuel cells as well as the unique biochemical actuation properties of mitochondria that allow for the use of mitochondria for self-powered explosive sensing.
Biofuel cells are a type of fuel cell where a biocatalyst is used as the catalyst for converting the chemical energy of a fuel into electrical energy, instead of a traditional metallic catalyst. Our research group has made advances in enzymatic fuel cell lifetimes over the last decade due to the development of a novel enzyme immobilization membrane that three-dimensionally constrains the enzyme while providing a buffered pH and a hydrophobic environment that mimics the cellular environment. However, in order to effectively utilize biofuel cells as energy conversion devices, it is essential to be able to use enzyme cascades to allow for complete oxidation of complex biofuels and, thereby, high energy densities, as well as coupling to an air breathing biocathode to ensure high current densities. In a living cell, complex fuels/substrates are completely oxidized to carbon dioxide utilizing the enzymatic cascades of metabolic pathways, such as: the Kreb's cycle, glycolysis, etc. These metabolic pathways can be used to oxidize fuels in a biofuel cell, but require the immobilization of over 20 enzymes at a bioanode, whereas only 6 of these enzymes are dehydrogenase (i.e. electron producing enzymes). We have employed metabolic engineering to design and study these systems. However, we are also developing enzymatic cascades for complete oxidation of a variety of biofuels by employing non-specific PQQ-dependent dehydrogenases. We have previously shown the ability to do this for the complex alcoholic fuels: ethylene glycol and glycerol.
Mitochondria are considered the "powerhouse" of the cell and contain enzymes and enzymatic pathways that can completely oxidize biofuel sources, such as: pyruvate. Recently, our research group has developed a biofuel cell that employs mitochondria as the anode catalyst which is responsible for oxidizing fuel. As with any fuel cell, this fuel cell will only produce electrical energy in the presence of fuel, but mitochondria are different than most traditional catalyst in that there are a number of inhibitors (e.g. the antibiotic oligomycin) that can stop mitochondria functioning, which in turn will stop the electrical power generation. However, this mitochondrial function (metabolism of fuel) can be returned by the addition of an uncoupler or uncoupler. It is important to note that nitroaromatic compounds are common explosive materials, but are also selective uncouplers for mitochondrial inhibition. Therefore, we have been studying the use of inhibited mitochondria as sensors for nitroaromatic explosives. This is a self-powered sensor, because there will be no power produced in the absence of the explosive material, but after the nitroaromatic explosive is present, it will decouple the inhibited mitochondria and allow for the mitochondria to catalyze the oxidation of pyruvate fuel to carbon dioxide. This oxidation at the anode of a biofuel cell in combination with the reduction of oxygen to water at the cathode produces power that can then be used for signaling the presence of the explosive.