Fluorescence sensing of phytate in water using an isothiouronium-attached polythiophene

A water-soluble isothiouronium-attached polythiophene (1(poly)) is prepared for the first time by the oxidative polymerization of 3-(3-(N-(2-methoxyethoxy)ethyl-N-methyl-S-isothiouronio)propoxy-4-methylthiophene (1) with FeCl(3). The gel-permeation chromatography analysis allows us to estimate the number average molecular weight (M(n)) and the polydispersity index (PDI) to be 5.68x10(5) and 1.4, respectively. The polymers (excited at 438 nm) show an absorption band at 438 nm and fluorescence at 546 nm, with 1.2 % fluorescence quantum yield when fluorescein was used as a reference. The pH-dependent absorption spectra at varying pH, indicates that aggregation starts at neutral conditions. At pH 5.5, 1(poly) exhibits a significant quenching in the fluorescence upon the addition of phytate (IP(6)), as a plausible analyte. This response is higher than that in the case of other anions such as adenosine 5-triphosphate (ATP), pyrophosphate (PPi), cis,cis-1,3,5-cyclohexanetriol triphosphate (CTP(3)), and H(2)PO(4)(-). As inferred from the SEM measurement, the phytate-induced spectral change has been explained on the basis of the pi-stacked aggregation of the polymer.