Selective detection of Zn2+ and Cd2+ ions in water using a host-guest complex between chromone and Q[7]

In this paper, the host-guest interaction of cucurbit7]uril (Q7]) and chromone (CMO) has been developed as a fluorescent probe for the highly selective detection of Zn²⁺ and Cd²⁺ in water based on a chelation-enhanced fluorescence (CHEF) mechanism. There was a good linear relationship between the fluorescence intensity of the CMO@Q7] probe and the concentration of Zn²⁺ or Cd²⁺ in the range of 0–3.0 × 10^–5 mol/L and the detection limit for Zn²⁺ and Cd²⁺ was found to be 2.03 × 10^–6 mol/L and 1.89 × 10^–6 mol/L, respectively. The X-ray crystal structure indicated that different coordination fashions were triggered by Zn²⁺ and Cd²⁺ in the CMO@Q7] complexes, respectively. However, both metal ions coordinated with the carbonyl oxygen of CMO, which was encapsulated in the cavity of Q7], thus leading to the enhancement of recognition fluorescence emission of CMO.