The work described in this dissertation was done as a part of a project to further develop spectroelectrochemical sensors for detection of biomarkers of human exposure to polycyclic aromatic hydrocarbons, pyrene metabolites 1-hydroxypyrene [1-PyOH] and 1-hydroxypyreneglucuronide [1-PyO-glu] and to develop a down-well spectroelectrochemical sensor. The second part of this work is focused on the development of a lab-on-a-chip sensor for zinc detection in serum by anodic stripping voltammetry.
The spectroelectrochemical sensor developed in our research group offers high analyte selectivity. Most of the sensors developed by other members of our group include a glass waveguide coated by an optically transparent indium tin oxide [tin-doped indium oxide or ITO] electrode. An optically transparent thin layer electrochemical [OTTLE] cell and holder that can be used with a conventional spectrophotometer for both absorbance and luminescence measurements was optimized and characterized as a part of this project. This OTTLE cell consists of an ITO electrode and a quartz cover slide. The holder is designed to hold the OTTLE at 45° to the incident light and has dimensions of 1 x 1 x 4 cm which allows the holder to fit most conventional spectrophotometers. The reference and auxiliary electrodes are fixed in space in the opposite corners of the holder. The cell was characterized by thin-layer cyclic voltammetry and coulometry of ferricyanide/ferrocyanide. Spectroelectrochemistry of tris- 2, 2'-bipyridine ruthenium [II] chloride and 1-hydroxypyrene was done with commercially available bench-top absorbance and fluorescence spectrophotometers. The good correlation between the results obtained and the known properties of each compound demonstrate that the OTTLE cell and holder provide an effective means for making spectroelectrochemical measurements in bench-top absorbance and fluorescence spectrophotometers.
Spectroelectrochemical sensing in an optically transparent thin layer electrode cell was used for detecting the polycyclic aromatic hydrocarbon [PAH] biomarkers 1-hydroxypyrene and 1-hydroxypyrene-glucuronide in phosphate buffer and artificial urine. This approach uses selective electrochemical modulation of a fluorescence signal by sequentially oxidizing the analytes in an optically transparent thin layer electrode to distinguish between their overlapping fluorescence spectra. This technique allows for complete oxidation and signal modulation in approximately 15 min for each analyte; a mixture of 1-pyOH and its glucuronic acid conjugate can be analyzed in 30 min. Calibration curves consisting of the fluorescence change vs. analyte concentration for 1-pyOH and 1-pyOglu yielded linear ranges from 10 nM to 1 µM and from 1 nM to 1 µM, respectively.
The second part of this work focuses on the detection of zinc by anodic stripping voltammetry [ASV] on electrodeposited bismuth electrodes. The electrochemical sensor is a three-electrode system consisting of the electrodeposited bismuth film working electrode, the electrodeposited Ag/AgCl reference electrode, and a Au counter electrode. The working potential window of the bismuth film electrode was investigated by cyclic voltammetry, while square wave ASV was used for measurement of Zn in acetate buffer and blood serum. Conditions critical to sensing, such as preconcentration potential, preconcentration time, and buffer pH were optimized for Zn detection. The sensor was successfully calibrated with pH 6 acetate buffer in the physiologically-relevant range of 5 µM to 35 µM. Detection of Zn in unspiked and spiked serum samples was done by two digestion methods. The initial 0.2 M HCl digestion method allowed for Zn detection in serum but did not exhibit adequate reproducibility. The second digestion method resulted in the expected Zn stripping peaks for post digestion spikes but peaks could not be obtained for Zn spikes prior to digestion.
|Commitee:||Baldwin, Michael, Stalcup, Apryll|
|School:||University of Cincinnati|
|School Location:||United States -- Ohio|
|Source:||DAI-B 72/11, Dissertation Abstracts International|
|Subjects:||Toxicology, Surgery, Analytical chemistry|
|Keywords:||Polycyclic aromatic hydrocarbons, Spectroelectrochemical sensors, Voltammetry|
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