Polyethylene glycol capped ZnO quantum dots as a fluorescent probe for determining copper(II) ion

As an important heavy metal ion, copper has the negative influence on otherwise healthy individuals, so establishing a valid way for the highly efficient, sensitive, and quantitative determination of Cu 2+ ion becomes an emergency in the environmental analysis. In the present work, water-soluble luminescent ZnO quantum dots (QDs) capped by polyethylene glycol (PEG) have been synthesized by a simple solution method. The PEG capped ZnO QDs (PEG@ZnO QDs) showed yellow fluorescence. High-resolution transmission electron microscopy, UV–vis absorption spectroscopy, Fourier transform infrared spectroscopy, and luminescence spectroscopy were applied to elucidate the properties of the PEG@ZnO QDs. In addition, the yellow fluorescence of the PEG@ZnO QDs was quenched when Cu 2+ ion was added to the PEG@ZnO QDs solutions. Therefore, a novel fluorescent probe was designed to detect Cu 2+ in water solution. The linear relationships were 10–200   nM and 2–10   μM, respectively, with the detection limit for Cu 2+ at 3.33   nM according to 3σ/slope (where σ denotes the standard deviation of the blank measures). The proposed sensor of the PEG@ZnO QDs has also been used in natural water samples to examine the availability of this method. In addition, the quenching mechanism was discussed, which may be attributed to the aggregation induced quenching.