Advancing Generation-Collection Methodologies at Chip-Based Electrode Arrays for Biochemical Sensing Applications

Professor Ingrid Fritsch, Ph.D., Department of Chemistry and Biochemistry, University of Arkansas

Abstract

Developing a device capable of electrochemical detection in small spaces with high sensitivity, selectivity, speed, and kinetics resolution is an ongoing challenge. Applications that motivate interest in pursuing these capabilities include lab-on-a-chip platforms for chemical analysis and in vivo sensing. In conventional electroanalytical chemistry, the electrochemical experiment consists of at least two electrodes: one serves as the working electrode where detection of analyte is of interest and the other serves to complete the electronic/ionic current circuit. 

Generation-collection experiments host at least two working electrodes, where one, designated as the “generator” is held at a potential that oxidizes or reduces the electrochemically active analyte. A nearby second working electrode, designated as the “collector” and positioned within the diffusion layer (<10 µm) of the generator, is simultaneously held at a different potential to revert the generated species back to its original form, enabling redox cycling. As the gap between the generator and collector electrode diminishes, the concentration gradient of the two forms of the redox couple increases and the current at both electrodes amplifies. This approach has been used to quantify electroactive analytes at low concentrations and to map the chemical reactivity of conductive surfaces through electroactive mediators.

Both experimental and computer simulation studies will be presented that focus not just on two working electrodes, but on an array of individually addressable microband electrodes. Strategic selection of potentials of individual and groups of electrodes at various locations in the array acting as generators and collectors can lead to various outcomes, and the experiments can be tailored for maximized generation or collection depending on the goals of the study. It is the unique electrochemical responses of each chemical species resulting from its individualized thermodynamics, heterogeneous electron transfer kinetics, and following chemistry (i.e. intramolecular cyclization and bimolecular reaction mechanisms) that can also allow differentiation at the electrode array. Model redox compounds (e.g., hexacyanoferrate(III) and hexaammineruthenium(III)) validate simulations and guide interpretation of electrochemical responses. Applications are demonstrated with biologically-relevant analytes, including catecholamine neurotransmitters, dopamine, norepinephrine, and epinephrine, their precursors and metabolites. (The roles of these species are linked to a variety of neurological functions).

Biographical Statement

Dr. Ingrid Fritsch is a Professor in the Department of Chemistry and Biochemistry at the University of Arkansas.  She received a B.S. degree from the University of Utah and a Ph.D. from the University of Illinois at Urbana-Champaign and was a postdoctoral associate at the Massachusetts Institute of Technology.  Dr. Fritsch has advanced the field of redox-magnetohydrodynamic microfluidics and developed multifunctional miniaturized analytical devices and sensors, including protein and DNA-hybridization microarrays interfaced to electrochemical detection. This work is important in developing portable devices for environmental and point-of-care chemical analysis. She is the recipient of the Society of Electroanalytical Chemistry Young Investigator Award, a National Science Foundation Career Award and an NSF Special Creativity Extension.  She is a Fellow of the National Academy of Inventors and of the American Association for the Advancement of Science and has received the University of Arkansas Alumni Distinguished Faculty Award in Research. She holds ten issued U.S. patents and co-founded two startup companies. Invested in the future of our society and planet, Dr. Fritsch is passionate and engaged in science outreach with kids in grades K-12, and is an American Chemical Society (ACS) Ambassador, Science Coach, and Local ACS Section Coordinator for the National Chemistry Olympiad.