Master of Science (M.Sc.)
Conjugated polymer nanoparticles (CPN) doped with a mercury sensitive dye are able to detect ion concentrations as low as a parts-per-billion within an aqueous environment. Select forms of spirolatam rhodamine dye are capable of selectively undergoing a ring-opening reaction in response to Hg2+ ions. The initial closed form presents as a colorless, non-fluorescent, compound while the opened form results in a colored and highly fluorescent form. The CPNs are also fluorescent, yet at a lower wavelength and can transfer of their energy into the dye molecules via Förster resonance energy transfer. The dye’s reaction with Hg2+ goes unhindered by the presence of CPNs, and their transfer of energy increases the dye molecule’s sensitivity to mercury. The CPNs provide the additional functionality of stabilizing the hydrophophic dye, enabling sensing in aqueous environments. The two fluorescent peaks can be compared, enabling the system to be used as a ratiometric sensor for Hg2+ sensing. The proposed system previously showed great potential reaching publication in 2012 with a “turn-on” mercury selective fluorescence probe. The initial system increased detection sensitivity 10-fold, detecting mercury concentrations as low as 700 parts per trillion. With a proof-of-concept staked work continued with alternate dyes, rhodamine B S2, capable of switching between an on and off state, and rhodamine B 1NI, a derivative of the original dye. Unable to reproduce the results of the initial study, work shifted into isolating the cause of a new fluorescence quenching phenomenon and procedural refinement of the CPN synthesis. Unable to rectify the cause of the quenching phenomenon, work shifted to alternate uses for the CPN system. Preliminary testing of a rhodamine B spirolactam, sensitive to pH changes has shown potential as fluorescent pH probe. Synthesis has begun on a dye that would maximize the overlap between its pKa and the CPNs’ window of pH viability.
© The Author
McCarron, Matthew August, "Ratiometric Fluorescent Sensors in Aqueous Environments" (2018). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1530192824.