William Case, PhD, Converse College
PROJECT TITLE: Xerogel based amperometric biosensing for the detection of diagnostic markers
This project involves the development of a 1st generation amperometric biosensor for the detection of clinically relevant molecules. The initial aim of the project was to develop a biosensor for the detection and quantification of galactose, with potential applications in the diagnosis of galactosemia. This disease is a genetic disorder associated with a comprised ability to metabolize the galactose sugar and can be fatal if not detected early. Galactose served as a model system, and our research showed the ability to successfully detect and quantify this molecule. Since then my research group has aimed to detect other clinically relevant molecules using a similar 1st generation sensing strategy.
The specific aims of the work are given below:
The Use of Xerogels as Enzyme Immobilization Scaffolds. First generation sensing schemes require an oxidase enzyme to be functional within a given matrix. Inevitably, selecting a scaffold that preserves an enzyme’s native structure and function is paramount to sensor performance. Xerogels (sol-gels in which solvent has been evaporated) have found previous use as enzyme scaffolds for first generation sensing. Their viability as matrices for oxidase enzymes was investigated. Different silane precursors, each containing a different “R” group, were used to create xerogels of differing size, polarity and porosity. Platinum electrodes deposited with enzyme doped xerogel layers were then tested as potential biosensors. Results obtained for key sensing parameters were used to determine if certain silane precursors are more effective than others. The use of multiple xerogel layers (in which one layer contains an oxidase enzyme while the other does not) was also envisioned as a means of exploring a “layer-by-layer” (L-B-L) approach with respect to biosensor design. The performance of biosensors comprised of multiple xerogel layers was compared to those containing a single, enzyme-doped layer.
Drying/Aging Conditions for Xerogels. Sol-gel formation involves competing hydrolysis and condensation reactions. A stable xerogel matrix is crucial for first generation sensing strategies, thus necessitating the need to identify optimum aging/drying conditions associated with xerogel formation. Experiments were performed to test the effect that different drying times and humidity levels may have on the performance of xerogel biosensors, with an ultimate goal of identifying a set of “universal” conditions that could be adopted for all subsequent xerogels doped with a specific oxidase enzyme.
Effects of Outer Layer Membranes on Biosensor Selectivity. Perhaps the most important aspect of first generation biosensors is the ability to signal the target analyte without being influenced by other interfering species. The use of outer layer membranes created from polyurethane (PU) blends was explored as potential outer layers capable of enhancing signal selectivity. The PU layer was added as an outer membrane during biosensor construction, and its effectiveness at precluding possible interferent molecules was investigated through the calculation of selectivity coefficients.
I am a Developmental Research Project Program (DRP) Target Faculty Member through SC INBRE. The funding provided through this program was essential for me to begin my research at Converse College. Converse is a private, women’s liberal arts college with ~900 undergraduates. I began as a faculty member at Converse in August 2015. That summer I applied for the DRP grant and was successful in obtaining funding for 18 months from October 2015 through June 2017. Converse can only offer limited startup funds to new faculty (under $5,000 for new faculty). My research ideas would have simply been a dream had I not received DRP funding. In my time at Converse I have mentored five undergraduate students, one high school teacher and one high school student. All of these individuals were provided significant research experiences thanks to the funding provided. Thus, in addition to the scientific advances made, this grant has enabled the continued training of undergraduates and colleagues, an opportunity very valued at a women’s liberal arts institution.
We have developed a tunable template for the detection of different target molecules through slight modifications in the biosensor’s design. This approach expands upon current technology in the field, yet presents a mechanistically simple strategy for the detection of clinically relevant molecules. In addition, the biosensor template has been shown to be tunable, thus providing a platform for detecting a variety of diagnostic markers by making slight modifications to the design.
My collaborator and I are both working on developing a 1st generation amperometric biosensor for the detection of an array of clinically relevant molecules. Together, we have shown that our design is suitable for detecting several different small molecules implicated in human health (e.g. glucose, galactose, uric acid, xanthine and hypoxanthine) by making slight modifications to the template design. The miniaturization of this technology could lead to advances in clinical diagnostics.
Publications as a result of SC INBRE funding for this project include:
Case, W.; et. al. A 1st Generation Amperometric Galactose Biosensor (in press)
Case, W. & Ezell, D. The Art of Chemistry. The Science Teacher (accepted). This publication is a result of my participation in the Research Experience for Teachers (RET) Program, an outreach program through SC INBRE.
December 8, 2017