Water-soluble conjugated polymer–Cu(II) system as a turn-on fluorescence probe for label-free detection of glutathione and cysteine in biological fluids

Abstract In this paper, a new one-step turn-on sensor was developed for the detection of glutathione (GSH) and cysteine (Cys). The photoluminescence (PL) intensity of the water-soluble fluorescent conjugated polymers PPESO 3 could be quenched by Cu(II) due to the strong electrostatic interaction and electron transfer between PPESO 3 and Cu 2+ . In the presence of biothiols, such as GSH and Cys, Cu(II) preferred to react with biothiols to form the Cu(II) S bond due to the strong affinity between Cu(II) and thiols. The recovered PL intensity of PPESO 3 was proportional to the concentration of GSH or Cys in the concentration ranges of 1.0 × 10 −7 to 1.5 × 10 −5  mol/L and 1.0 × 10 −7 to 2.0 × 10 −5  mol/L, respectively. The detection limit for GSH and Cys were 4.0 × 10 −8 and 4.5 × 10 −8  mol/L, respectively. The established method shows a high selectivity for biothiols compared with other twelve amino acids without thiols group. Furthermore, the PPESO 3 –Cu(II) system as a fluorescence probe was successfully used for fluorescence imaging of biothiols in the HepG2 cells, which presents a potential application in bioimaging field.