Design and Characterization of Hybrid Biological-Inorganic Systems

Abstract

Hybrid biological-inorganic systems have been designed to drive fine chemical syntheses and to interrogate fundamental biology. These systems couple electronic signals to cellular activity, allowing the unique chemistries of materials and biological sciences to work synergistically. Towards synthetic goals, engineered bacteria have been cultured with electrochemical catalysts to achieve artificial photosynthesis with yields greater than those of nature. In the fields of therapeutics and electrophysiology, nanomaterials have been interfaced with mammalian cells to deliver drugs and map neural signal propagation. The cellular and material modularity of these hybrid systems leaves a great deal of unexplored chemical space to perform new reactions and discover new biological processes. This thesis encompasses a series of studies into bacterial metabolism and nanomaterial surface design to electrically power living systems. Efforts began with the engineered bacterial synthesis of medium chain fatty acid biofuels in biphasic growth media. Hydrogen-oxidizing chemolithoautotroph Cupriavidus necator was transformed with a chimeric thioesterase to produce saturated and monounsaturated octanoic acid, precursors to biodiesel. Continuous extraction of octanoic acids from the aqueous bacteria layer enabled high yields with no observable loss in cell viability. Next, Xanthobacter autotrophicus, another chemolithoautotroph with the ability to fix nitrogen in addition to carbon dioxide, was investigated for its ability to accumulate phosphorus. As a potential biofertilizer, the bacterium was shown to synthesize and utilize cyclic metaphosphates, with this study detailing the first spectroscopic evidence of biological cyclic phosphates. These unique phosphates were found to comprise 40% of whole cell X. autotrophicus polyphosphates, suggesting these compounds may exist with yet uncharacterized functions in other species and kingdoms. Development of hybrid biological-inorganic systems was then expanded to mammalian cells through the nanofabrication of electrodes. Polymer-coated silicon nanowire arrays were charged with molecular cargo to deliver molecules into human endothelial cells upon electrical input. Reduction of cargo-loaded polymer on nanowires saw molecular delivery with more than ten times the efficacy of solution-based methods when normalized to mass. Covalent silicon modification methods were next explored to modulate the cell-nanowire interface. Surface silanization procedures were developed to attach proteins, electrocatalysts, and quantum dots. Quantum dot modification and cell dyes were investigated to construct a fluorescent readout of cellular nanowire internalization. Lastly, nano-spaced electrodes were designed to probe the electric field effects and coupling kinetics of electrochemical syntheses.