Sensitive fluorescent assay for copper(ii) determination in aqueous solution using quercetin-cyclodextrin inclusion

Environmentally friendly probe materials for detecting copper ions were studied in this research. Fluorescent emission of quercetin (Q) was observed in the buffer solution (pH = 7.40), and (2-hydroxypropyl)-β-cyclodextrin (CD) could enhance the fluorescence intensity of Q. The UV/Vis spectrum showed that the Q-CD system was formed. After adding copper ions into the Q-CD system, the fluorescent emission intensity of Q-CD system generated quenching, and other metal ions could not bring change, which meant the Q-CD system showed good selectivity to copper ions. The fluorescence titration spectra showed that the concentration of copper ions was inversely proportional to fluorescence intensity, and gave a good linear change in fluorescence emission intensity in response to the concentration of copper ions ranging from 5.0 × 10^-8 to 8.3 × 10^-6 mol L^-1. The calibration curve of the relationship between the intensity and copper ions concentration was y = -9.24x + 844.51 (R ² = 0.997). The detection limit of copper ions was measured to be 2.3 × 10^-8 mol L^-1. The probable mechanism was studied by UV/Vis spectrum and Job's plot method. The results indicated that Q-CD-Cu(ii) complex was formed and intramolecular charge transfer (ICT) took place. At last, the probe was successfully applied for determination of copper ions in water bodies, vegetables and fruits with good recovery. The study showed that Q-CD system could detect copper ions as a fluorescent probe with high selectivity, sensitivity and larger linearity range.