DEVELOPMENT OF ELECTROCHEMICAL MICROSENSORS TO USE IN BIOELECTROCHEMICAL SYSTEMS
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The objective of this dissertation was to develop electrochemical microsensors to quantify microscale gradients within biofilms grown in bioelectrochemical systems (BESs). In BESs, generally three electrodes are used: an anode accepting electrons from the biofilms, a cathode donating electrons to biofilms or generating biocides, and a reference electrode. The anodic biofilms are grown for energy and biochemical production. In addition, some BESs are used to generate biocides at the cathodes. When biofilms are used for energy generation, the electron donor gradients play a critical role and can control electron transfer rates as well as energy generation. On the other hand, when the cathodes of BESs are used to generate hydrogen peroxide to prevent biofilm growth, its concentration is critically needed to understand the applicability of this technology. Currently, there is no electrochemical microsensors which can operate in BESs. This dissertation focuses on the development and applications of electrochemical microsensors to quantify electron donor and electron acceptor concentrations on electrodes employed in BESs. A hydrogen peroxide microelectrode was developed to measure hydrogen peroxide concentrations on cathodically polarized surfaces. We found that the maximum hydrogen peroxide concentration on cathodically polarized surfaces was ~25 µM which was enough to eliminate biofilms. This discovery allowed us to develop an electrochemical technology to eliminate unwanted biofilms on cathodically polarized surfaces. Then, we developed two microbiosensors (acetate and fumarate) which were operated based on similar principles. The working principle of the acetate microbiosensor was based on the correlation between the acetate concentration in the vicinity of the microbiosensor and the current generated during acetate oxidation by Geobacter sulfurreducens acting as a transducer in the microbiosensor. When we used it in anodic biofilms, we found that the acetate was limiting in the biofilm and the bottom of the biofilm was serving as a scaffold for the top layer. The fumarate microbiosensor used G. sulfurreducens acting as a transducer for the cathodic reactions. When we used fumarate microbiosensor in cathodic biofilms, we found that fumarate can be reduced while an electrode is used as an electron donor and the fumarate reduction was potential-dependent in the biofilm.