Biosensors – Design, Development, and Application to Cell, Protein, and Nucleic Acid Detection Blake N. Johnson Advisor: Dr. Mutharasan Background A great number of problems with both scientific and practical importance hinge on sensitive measurement of biological targets. However, important targets are typically present in a liquid background with high levels of interfering biological species. Recently, device-‐based techniques have been applied with success to create biotechnology geared toward biological detection, termed biosensors. They are now being applied in diverse areas including medical diagnostics, food and environmental monitoring, and bio-‐separations, where important targets range from biomarkers to pathogens. The field is highly interdisciplinary, involving a combination of applied physics, biochemistry, chemical and mechanical engineering, and microbiology. The biosensors examined in this Thesis are based on piezoelectric property of materials which creates coupling between mechanical and electrical effects. Ultimately, bio-‐MEMS devices based on piezoelectric cantilevers are the primary focus of this research along with various supporting analytical and characterization techniques useful in such biotech development (e.g. surface characterization, microscopy, chemical analysis). Research Research thus far has revealed a variety of new and important results in the field which can mainly be separated into areas related to: (1) design and characterization (electromechanical coupling, modal mechanics, and fluid-‐structure interaction) which better helps understand how the device operates, (2) biosensing (protein orientation, surface regeneration) which focuses on optimizing and understand factors that influence molecular architecture and demonstrating diagnostic application for detection of small RNA targets difficult to detect with standard techniques in human serum (microRNA biomarkers), and (3) critical review of biosensing applications of cantilever-‐based devices. Ongoing research involves two primary focuses: (1) integration of additional sensing signals for simultaneous and complementary measurement, (2) examining effects of surface vibration on non-‐ specific binding, and (3) detection of environmental pathogens by rRNA markers in environmental source waters. We are also writing a criticalreviewoftechniquesformicroRNAdetection. Inthefirstaim,wearecurrentlyexploringthe integration of electrochemical sensing capability by incorporating additional circuitry for probing the electrochemical properties of immobilized or captured biomolecules. In the second aim, we are using a variety of measurements to triangulate the effect vibration plays in affecting non-‐ specific protein adsorption as this work seeks to address the important and impeding phenomena of biofouling in many surface-‐based applications. In the third aim, we are currently exploring use of species-‐specific 16S rRNA genes for detection of toxin-‐producing cyanobacteria.