Walter Scott, Jr. College of Engineering

Graduate Exam Abstract

Sean Pieper
M.S. Final
Feb 14, 2008, 12pm (noon)
Engineering E103
Optical Characterization of Photoluminescent Dyes for Biosensor Transducer Applications
Abstract: Environmental health and safety concerns motivate groundwater monitoring of chlorinated hydrocarbons (CHC), chlorinated ethenes, and toluene. These toxic compounds are found in such items as organochlorine pesticides, industrial chemicals, degreasing agents, dry cleaning industry, and chlorine waste products. These toxic compounds persist and bioaccumulate in the food chain. Conventional methods for monitoring these substances are slow and cumbersome. For example, multiple samples must often be transported to laboratory locations for analysis. Optical characterization of photoluminescent dyes for use as a transducer in biosensors for water quality monitoring is presented. Initial measurements of the amount of fluorosceinamine (FLA) in a poly vinyl alcohol (PVA) matrix applied to the tip of a plastic optical fiber to form an optode and act as a pH sensitive transducer is considered. A method to optically measure the absorption spectra of this transducer using a double transmission pass setup is presented. Results of this work found the absorption coefficient of FLA-PVA transducers to be 9.5 cm-1 for this dye / matrix transducer. The saturation intensity, photobleaching, and decay lifetime of tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) chloride (Ru(dpp)3) are investigated. The saturation point was estimated to be 11.8 W/cm2 using a measured decay lifetime of 4.19 µs and subsequently measured to be 11.5 W/cm2. Photobleaching of this dye at a peak absorbance equivalence of 6.6 W/cm2 is observed over two days resulting in a 14% decrease in phosphorescent emission power within 20 minutes and 47% decrease over two days yielding an unacceptably short operational lifetime under saturated conditions. Lower optical excitation levels at 159 µW/cm2 currently used in the application of oxygen sensitive phosphorescent type fiber optic enzymatic biosensor systems yield acceptable photobleaching rates of 3.3 % decrease in emission power over two days. Photoluminescence emission power and lifetime temperature dependence for Ru(dpp)3 / silicone transducer layer is investigated in sparged water and gas surroundings for two different sets of optodes. From near freezing to 40°C studies show a negative linear response to temperature of 0.03 µs/ºC and 7.5 pW/cm2/ºC for decay lifetime and phosphorescent emission power respectively. For optodes stored in a dark space in air at room temperature for four months the unquenched to quenched ratio for phosphorescent emission power decreases by 20 % while the unquenched to quenched ratio of decay lifetime only reduces by 5 %. Relating phosphorescent emission power to decay lifetime shows that the radiative lifetime of Ru(dpp)3 is temperature independent suggesting the temperature dependence lies within nonradiative recombination processes.
Adviser: Dr. Kevin L. Lear
Co-Adviser: NA
Non-ECE Member: Dr. Kenneth Reardon (Department of Chemical and Biological Engineering)
Member 3: Dr. Randy Bartels
Addional Members: NA
Program of Study: