UCLA

Enzymes have been employed as molecular recognition elements in electrochemical sensors, enabling the selective detection and continuous monitoring of small molecules across wearable, implantable, and ingestible platforms. Beyond molecular recognition, however, enzymes possess diverse catalytic and regulatory capabilities that remain underexplored in bioelectronic systems. This thesis investigates how enzymes can perform multiple functional roles to facilitate the operation of electrochemical devices in vivo. Two principal domains are addressed: expanding enzymatic biosensing capabilities and engineering microenvironments to support reliable device performance under physiologically challenging conditions.Chapter 1 addresses key limitations in dehydrogenase-based electrochemical sensors, including the need for cofactor immobilization, limited interfacial reaction kinetics, inefficient electron transfer, and the high oxidation potential typically required for reduced nicotinamide adenine dinucleotide (NADH). Acid-treated single-walled carbon nanotubes were engineered to provide a conductive and electrocatalytically active interface for low-potential NADH oxidation. Building upon this material platform, we developed a tandem metabolic reaction-based sensing architecture in which enzymes perform complementary functions, including metabolite recognition, intermediation, and interference inactivation. By integrating these functions into coordinated enzymatic cascades, this strategy offers a generalizable framework for extending continuous electrochemical sensing beyond the limited range of metabolites accessible through conventional oxidase-based designs.Chapter 2 demonstrates that enzymes can also actively regulate the microenvironment surrounding electrochemical devices. Dynamic and highly acidic physiological environments can suppress enzymatic activity, destabilize molecular components, alter electrode responses, and compromise analytical performance. To address these challenges, we developed an enzymatic buffer-generation system inspired by microbial acid-survival mechanisms. Through the localized conversion of endogenous or externally supplied substrates, the system generates buffering species within the device microenvironment and establishes a self-regulated, near-neutral pH without requiring a large reservoir of conventional buffer. Two complementary configurations were investigated: interfacial buffering, which directly stabilizes the sensing interface, and peripheral buffering, which regulates the surrounding environment before acidic species reach the device.Collectively, this work expands the role of enzymes from passive recognition elements to multifunctional components capable of target conversion, signal transduction, reaction mediation, interference management, and microenvironmental regulation. This thesis establishes a broader framework for developing robust electrochemical devices for continuous in vivo molecular monitoring.