Nanostructured Microelectrodes for High-Activity Electrochemistry in Biosensing and CO2 Recycling

Electrochemical biosensors are promising candidates for point-of-care (POC) diagnostics, since they require neither costly instrumentation nor expert operators. However, for them to become widely used in a clinical setting, biosensors must be enhanced in sensitivity without increasing costs or compromising the speed of detection. The goal of this thesis is to realize this vision by promoting high-activity redox reactions via rational design of the size, shape and structure of electrodes. Incorporating nanostructures on the surface of microelectrodes greatly increases their surface area and reaction rates, while maintaining efficient diffusion of analytes to electrode surfaces. Here, by coupling optimized electrode morphology with an enzyme-based assay, I report on a new class of ultra-sensitive biosensors. I showcase the applicability of these sensors for POC diagnostics by incorporating them on a platform designed to isolate rare cells in biological samples. The integrated device is the first example of an electrochemical sensing platform capable of detecting cancer cells with clinically-relevant sensitivity and specificity. Decreasing the cost of POC diagnostic devices is vitally important for their adoption in low-resource settings. To that end, I advance a strategy to decrease the costs associated with the fabrication of nanostructured microelectrodes (NMEs). I present an image-reversal soft lithography (IRSL) technique based on an elastomeric stamping protocol, eliminating the need for costly photolithographic fabrication steps. The distinct morphology of the sensors made by IRSL improves access to the surface of the electrodes leading to enhanced performance in the detection of biomolecules. Overall, the strategies presented in this thesis can guide the development of low-cost, sensitive, and rapid diagnostic systems. Outside of biosensing, NMEs have potentially important applications in CO2 recycling. Realizing efficient CO2 conversion to chemical fuels is an important step towards reducing the atmospheric concentration of CO2 and decreasing the carbon footprint of energy. Recently, our group reported highly-efficient electroreduction of CO2 to CO using nano-sharp Au structures. Here, I improve upon the performance of these structures by increasing the density of honed needle-like features on the surface of NMEs and demonstrate a 15-fold improvement in the reaction rates relative to the previously reported best results.Ph.D