Spectroelectrochemical sensor for metal speciation and bead-based immunoassay for Bacillus anthracis spores in finished water

The work presented in this dissertation is the development of a chemical and a biological sensor to detect analytes in water. First, the feasibility of spectroelectrochemical sensing for detecting a metal in different oxidation states is presented. The speciation sensor concept is illustrated with iron in the ferrous (Fe2+) and ferric (Fe3+) oxidation states as the model metal ion. The sensor consists of an indium tin oxide optically transparent electrode (ITO OTE). The ITO side of the electrode is coated with a thin film of cation exchange polymer, Nafion and is loaded with the ligand 2,2'-bipyridine (bipy). Fe2+ in the sample partitions into the film and forms Fe(bipy)32+. The optical response at 520 nm associated with the electrochemical modulation of the Fe(bipy) 32+/3+ complex in the film is measured by attenuated total reflectance spectroscopy. The corresponding change in absorbance (DeltaA) is proportional to the concentration of Fe2+ in the film, which in turn is proportional to the bulk concentration of Fe2+ in the sample. Fe3+ has more complex coordination chemistry than Fe2+ and is detected indirectly. Fe3+-bipy complexes formed in the film are reduced to Fe(bipy)32+. The corresponding DeltaA at 520 nm is proportional to the Fe3+ in the film which in turn is proportional to the concentration of Fe 3+ in the sample. Careful manipulation of the applied potential enables speciation of a mixture of Fe2+ and Fe3+. Optimizing film thickness and ligand concentration with respect to the sensor response yields a detection limit of 0.6 x 10-6 M for Fe2+ and 2 x 10-6 M for Fe3+ and a sensor response time of 6 minutes under kinetic measurements.; The second part of the work presents the development of a bead-based enzyme immunoassay to detect the bacterial spores, Bacillus anthracis Sterne strain (Ba). The immunoassay was built by linking biotinylated goat anti Ba antibody to streptavidin coated magnetic beads. Next, gamma-irradiated Ba spores were captured by the Ab-coated capture beads. Then beta-D-galactosidase conjugated goat anti Ba antibody was attached to the spores to complete the immunoassay.; A small volume electrochemical detection method was developed by using a gold rotating disk electrode. As an alternative method to electrochemical detection, a fluorescence method was also developed. (Abstract shortened by UMI.)...