An anionic polythiophene as a water-soluble fluorescent sensor.

Anionic conjugated polymers are promising cation sensors, offering bright fluorescence and superior fluorescence-quenching response upon analyte binding, due to highly efficient intramolecular energy transfer along the polymer chain. We have investigated the sensing capability of a commercially available polythiophene, poly[2-(3-thienyl)ethoxy4-butylsulfonate] (Mw = 1,000,000 g/mol), in aqueous solution, using methyl viologen ([MV.sup.2+]) as quencher. A detection limit of 5.0 '[10.sup.-8] M methyl viologen was determined for polymer solutions ~[10.sup.-4] M in monomers. In studies with varying concentrations of SSC buffer, increasing buffer-ion concentration resulted in decreased quenching efficiency. This confirmed that quenching occurs by a static mechanism, involving ground-state polymer-ion complexation. Stern-Volmer kinetic analysis yielded a [K.sub.SV] value of 2.0 ' [10.sup.6] [M.sup.-1], similar to the published value for a related polythiophene. Unfortunately, poor polymer solubility limited sensitivity. Addition of the cationic surfactant CTAB resulted in a 6-fold increase in polymer fluorescence intensity and a narrowed, blue-shifted polymer absorption spectrum, suggesting that interaction with surfactant helped to break up polymer aggregates. The polymer-surfactant solution showed a weak quenching response to methyl viologen ([K.sub.SV] = 7.0 ' [10.sup.1] [M.sup.-1]), as the surfactant prevented polymer-[MV.sup.2+] binding. Future efforts will focus on related polymers with different side chains to improve solubility. * Supported by Winthrop University Research Council Grant 529078