In addition to the onslaught of environmental challenges posed by the warming climate, eutrophication is encouraging the growth of the cyanobacteria that cause harmful algal blooms (HABs) and release toxins that threaten human, wildlife, and environmental health. To track the emergence of and protect against cyanobacterial toxins, as well as to inform remediation processes, a robust and real-time detection system is first required. Here, I design, construct, and evaluate a sensor system that integrates Shewanella oneidensis’ naturally occurring extracellular electron transport (EET) pathways with nanobodies’ capacity for antigen-specific binding to digitize information on contamination events via a modulated electrical signal. This report outlines the expression, purification, and binding-capability assessment of the biological components for such a real-time bioelectronic detection device. In addition to creating a biohybrid device to detect microcystin-LR – a well-characterized cyanobacterial toxin within the microcystin family – I also designed a model system to detect green fluorescent protein (GFP) and validate the approach to cell-surface binding. The final design relied on the direct display of nanobodies on the surface of S. oneidensis for target detection. After confirming target binding to the cells via microscopy, I performed an electrochemical analysis of the sensor in response to target exposure. This preliminary study indicated that the engineered strain of Shewanella underpinning the sensor design demonstrates a change in current distinct from that of the control strain in both chronoamperometry and cyclic voltammetry experiments upon addition of the target.

Bioelectrochemical systems (BESs) interface bacterial metabolic processes with electronic systems for purposes including biosensing, bioremediation, and modulating biological activity. A key bottleneck that currently hinders development of these systems is the difficulty of interfacing bacteria with electronics, resulting in the limited mutual transfer of charge associated with the contact between the bacteria's natural biofilms and an electrode surface. I developed a formulation using biocompatible conductive polymers and designed a device in which to electropolymerize an engineered living hydrogel that incorporates electrically active microbes into its polymer matrix, increasing the surface area contact between the bacteria and the electrode. With a connected potentiostat, the device allows for repeatable, consistent electrochemical systems for hydrogel synthesis and measurement via cyclic voltammetry and chronoamperometry. Engineering a new bridge between biology and electronics requires material that can syncretize the two worlds and an engineering design-build-test-learn cycle that can fine-tune this bridge to create a path toward more environmentally-friendly energy production in the future.