UC Santa Barbara

Electrochemical biosensors offer a platform to build miniaturizable and easy to use sensing technology with high levels of accuracy and sensitivity. This has led to applications across many industries, including in the food industry, for environmental monitoring, pharmaceutical production, and healthcare. Though there are a wealth of biomolecules which can provide specificity, enzymatic electrochemical biosensors (EEBs) have thus far proved most commercially successful. The central principle of EEBs is the coupling of the enzyme reaction to a change in redox active species near an electrode which can be electrochemically quantified. The continuous glucose monitor (CGM) is the foundational example of an EEB and has enabled the benefits associated with higher frequency of use and intervention in patients with diabetes. However, as the frontiers of medicine and healthcare, there has been substantial need to improve EEBs – expanding the substrates they interact with, increasing the time for which operation is stable, pursuing lower limits of detection, etc.In this dissertation, I describe my work which focuses on understanding how the contexts of biosensors – especially including electrode modifying materials towards reaching the needs of next generation medicine- influence the enzyme behavior and how it displays in electrochemical measurements. I first measure the reaction rates of glucose oxidase in solution to determine descriptive thermodynamic and kinetic variables, using a simple system without using a modified electrode or external mediator via chronoamperometric measurements at a platinum microelectrode. By examining how those variables change with the reaction condition, I delineate a set of guidelines to decouple pure electrochemical effects from changes to enzyme behavior, serving to aid investigations which seek to improve EEBs. Following this, I discuss the current capabilities for electrochemistry to elucidate the behavior of single enzymes, which represents both the ultimate limit of detection in healthcare settings but also a means to further our fundamental understanding of enzymes their behavior in the presence of an electrode. Finally, I will describe some of my efforts to treat enzyme-conductive polymer mixtures as a hybrid material, measuring how the presence of enzyme alters the conductivity of thin-films of PEDOT:PSS and how PEDOT:PSS films influence enzyme kinetics. These measurements are coupled with a discussion of how conductive polymers can play a role in the future of biosensing, highlighting organic electrochemical transistors (OECTs) as transduction method for enzymes at low sensitivity limits. In total, my work aims to further the potential of EEBs in the next generation of medicine, and to provide my insights after much thought and learning about the electrochemistry behind these wonderful systems.