A new fluorescence “off–on” chemodosimeter for l-cysteine based on water-soluble polythiophene

A novel water-soluble cationic conjugated polymer, denoted as poly 2,5-[3-(1,1-dimethyl-4-piperidine methylene)thiophene] chloride（PDPMT-Cl）was a novel fluorescent material. Fluorescence can be quenched by [AuCl4]− effectively. On addition of l-cysteine (l-Cys) in [AuCl4]−-PDPMT-Cl, fluorescence recovered. A new method to detect l-Cys was established successfully by designing a fluorescent “off-on” probe. The method showed good sensitivity and selectivity. Under optimized condition, the fluorescence intensity was linear to l-Cys concentration varying from1.0×10−8 M to 6.0×10−5 M (γ=0.9982). The detection limit (3σ) was 1.39×10−10 M. The method was successfully used for the determination of l-Cys in human serum and compound amino acid injection.