Date of Award


Document Type

Union College Only

Degree Name

Bachelor of Science






The purpose of this research was to develop a fiber-optic sensor for sulfite via immobilizing Methylene Blue (MB) within a sol-gel matrix. MB is a redox-indicating dye. In the oxidized form, the dye is a blue color, but reduction causes a change to the colorless, leuco form. This property is advantageous for the detection of reducing agents, such as sulfite. In solution, leuco-MB reverts to its blue form in the presence of an oxidizing agent. The method of MB immobilization is through the use of sol gels. The environment of a sol gel is chemically inert and small analytes can easily diffuse into a thin-film matrix. In this study, the sol-gel matrix was formed via the hydrolysis and polycondensation of tetraethoxysilane (TEOS) as well as organically-modified orthosilicates. Blue MB is converted to leuco-MB in both solution and in the thin-film coated fiber upon exposure to sulfite. In the sol gel, however, blue-MB is not regenerated in the presence of oxidizing agents. Hence, the sensor cannot be regenerated and is currently only satisfactory for a single use. Fundamental studies of the spectroscopic properties, including absorbance and fluorescence spectra, of the sol gel environment were also performed as the sol gel aged.