UC Irvine

Chemical sensors and biosensors are important devices that are capable of providing real-time analytical information, widely applicable to problems ranging from point-of-care diagnostics to the detection of explosive or toxic gases. This dissertation will discuss a few different liquid- and gas-phase sensors developed during my time in the Penner Lab. Electrodeposition and electropolymerization have emerged as versatile tools for the fabrication of chemical sensors and biosensors. Electropolymerization allows for the ability to entrain receptors such as antibodies, engineered virus particles, and metal chelating agents into a conductive polymer sensing element and has proven to be a versatile method of preparing sensors for a variety of analyses. Meanwhile, electrodeposition has been utilized to fabricate nanostructured metal indicator microelectrodes as well as for rapid and sensitive hydrogen gas sensors. Chapter 2 will discuss the optimization of the Virus BioResistor (VBR) to allow for the detection of larger proteins. The VBR is a conductive polymer thin-film biosensor utilizing an electropolymerized virus-PEDOT composite bioaffinity layer, engineered specifically to bind proteins of interest. The VBR previously demonstrated fast and reproducible response to small proteins, but larger proteins, such as antibodies, exhibited minimal signal responses. An electrochemical overoxidation process to unlock the ability for the VBR to detect two different IgG antibodies is described and discussed. Chapter 3 details the fabrication of a nanojunction pH sensor, where a nanogap is fabricated within a single gold nanowire and is then subsequently bridged via the electropolymerization of polyaniline (PANI), which is pH responsive. The nanogap is created in a facile manner via electromigration, and thefabricated nanojunction sensor is able to reliably detect a range of pH from 1 to 9 within 30 s via impedance. This serves as a first step towards fabricating a VBR that is on the nanometer scale in all three dimensions. Chapter 4 then explores chemiresistive gas sensing for the detection of ethylene gas utilizing a single platinum nanowire, fabricated using lithographically patterned nanowire electrodeposition (LPNE). Platinum nanowires exhibit a reversible decrease in resistance upon exposure to H2 due to the increase in the specularity of electron surface scattering by the formation of Pt – H. We test if this surface scattering modality is also observed to also occur in the presence of ethylene exposure. A simple platinum nanowire transducer capable of detecting ppm concentrations of ethylene in air is described and a mechanism involving the combustion of ethylene causing changes in electron surface scattering is proposed. Finally, Chapter 5 details a unique and collaborative urology project investigating the encrustation of ureteral stents. Stents are an indispensable tool in the medical field to relieve obstruction and preserve kidney function. However, these devices lose their efficacy over time as they become obstructed by encrustation. In this final chapter, I describe and compare the encrustation formation on 2-hydroxyethy methacrylate (HEMA)-coated Pellethane to that formed on commercially available polymer-based stents.