Detection strategies with membrane-based electrochemical sensing systems and mechanistic studies of ethanol oxidation at ordered electrode surfaces

The first part of this dissertation describes the use of surface refunctionalized fluorinated ethylene propylene (FEP) membranes in biosensors based on the Clark-type oxygen sensor. FEP membranes, partially hydroxylated by exposure to a radio frequency glow discharge plasma, were aminated by treatment with ({dollar}gamma{dollar}-aminopropyl)triethoxysilane. Measurement of the permeability and diffusion coefficients for oxygen in non-modified, hydroxylated, and aminated FEP showed that modifications did not alter the oxygen transport characteristics of the membranes. In subsequent experiments, biosensors were constructed by using aminated FEP as the gas-permeable membrane of a Clark-type oxygen sensor. The respiration of mouse neuroblastoma cells (NB2a) was monitored with an oxygen sensor following cell attachment to the sensor membrane through natural growth processes. Another biosensor was constructed by linking glucose oxidase to an aminated oxygen sensor membrane with albumin and glutaraldehyde. Sensor response to glucose was linear between 0.1 mM and 6.5 mM.; In a second study, a sensing system for ethanol was developed. The sensor was designed to extract ethanol vapor through an expanded poly(tetrafluoroethylene) detection schemes were used to monitor ethanol levels. Cyclic voltammograms and pulsed amperometric detection response curves recorded with a rotated platinum disk electrode were used to optimize pulsed potential waveforms employed in a static electrolyte drop behind a membrane. A four step waveform was insensitive to solution hydrodynamics and sensitive to ethanol concentration between 0.02 mM and 1.7 M. Response characteristics of this sensing system enabled the direct determination of ethanol in non-diluted alcoholic beverages.; In concluding studies, platinum single crystal electrodes with (111), (557), and (335) surface orientations were used to probe the effects of electrode surface step density on ethanol electrooxidation to acetic acid. Cyclic voltammetry demonstrated the sensitivity of ethanol voltammetry to electrode surface structure. Chronocoulometry was coupled with ion chromatography to quantify acetic acid produced during ethanol oxidation as a function of electrolysis potential and electrode surface step density. Results showed increased surface step density inhibits ethanol oxidation to acetic acid and promotes carbon-carbon bond cleavage pathways.