Ultrasensitive fluorescent responses of water-soluble, zwitterionic, boronic acid-bearing, regioregular head-to-tail polythiophene to biological species.

Water-soluble regioregular head-to-tail zwitterionic fluorescent conjugated boronic acid-bearing polythiophene (polymer 2) was prepared through a postpolymerization quaternization of a pyridine group of 3-pyridineboronic acid with bromide groups of regioregular head-to-tail poly(3-bromohexylthiophene) (polymer 1). Titration of monosaccharides, lactose, ascorbic acid, or dopamine with 0.1 M phosphate buffer (pH 7.4), containing 4.0 microM of polymer 2, results in significant concentration-dependent quenching of the polymer fluorescence. The polymer displays an optimum response to the biological species at pH 7.0. The binding constants of polymer 2 with mannose, fructose, glucose, galactose, vitamin C, dopamine, and lactose are 3.33 x 10(4), 1.13 x 10(5), 1.23 x 10(5), 1.69 x 10(5), 3.17 x 10(5), 3.27 x 10(5), and 4.60 x 10(5), respectively.