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

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 PPESO3 could be quenched by Cu(II) due to the strong electrostatic interaction and electron transfer between PPESO3 and Cu2+. 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 PPESO3 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 PPESO3–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.