Functionalized CdS quantum dots-based luminescence probe for detection of heavy and transition metal ions in aqueous solution

Abstract

Strong luminescence CdS quantum dots (QDs) have been prepared and modified with l-cysteine by a facile seeds-assistant technique in water. They are water-soluble and highly stable in aqueous solution. CdS QDs evaluated as a luminescence probe for heavy and transition metal (HTM) ions in aqueous solution was systematically studied. Five HTM ions such as silver(I) ion, copper(II) ion, mercury(II) ion, cobalt(II) ion, and nickel(II) ion significantly influence the photophysics of the emission from the functionalized CdS QDs. Experiment results showed that the fluorescence emission from CdS QDs was enhanced significantly by silver ion without any spectral shift, while several other bivalent HTM ions, such as Hg 2+, Cu 2+, Co 2+, and Ni 2+, exhibited effective optical quenching effect on QDs. Moreover, an obvious red-shift of emission band was observed in the quenching of CdS QDs for Hg 2+ and Cu 2+ ions. Under the optimal conditions, the response was linearly proportional to the concentration of Ag + ion ranging from 1.25 × 10 −7 to 5.0 × 10 −6 mol L −1 with a detection limit of 2.0 × 10 −8 mol L −1. The concentration dependence of the quenching effect on functionalized QDs for the other four HTM ions could be well described by typical Stern–Volmer equation, with the linear response of CdS QDs emission proportional to the concentration ranging from 1.50 × 10 −8 to 7.50 × 10 −7 mol L −1 for Hg 2+ ion, 3.0 × 10 −7 to 1.0 × 10 −5 mol L −1 for Ni 2+ ion, 4.59 × 10 −8 to 2.295 × 10 −6 mol L −1 for Cu 2+ ion, and 1.20 × 10 −7 to 6.0 × 10 −6 mol L −1 Co 2+ ion, respectively. Based on the distinct optical properties of CdS QDs system with the five HTM ions, and the relatively wide linear range and rapid response to HTM ions, CdS QDs can be developed as a potential identified luminescence probe for familiar HTM ions detection in aqueous solution.