A novel “on–off–on” near-infrared fluorescent probe for Cu2+ and S2− continuous detection based on dicyanoisoflurone derivatives, and its application in bacterial imaging

Abstract

We have successfully synthesized a near-infrared fluorescent probe for the continuous detection of copper and sulfur ions. The probe has good selectivity and anti-interference ability against Cu²⁺ and S²⁻. The results show that after adding Cu²⁺ to the DL solution of the near-infrared fluorescent probe, Cu²⁺ forms a [DL + Cu²⁺] complex with the probe, which leads to fluorescence quenching due to the paramagnetism of Cu²⁺. The probe can be used for the quantitative detection of Cu²⁺ with a detection limit of 1.26 × 10⁻⁹ M. According to the Job's plot curve the binding stoichiometry between DL and Cu²⁺ is 1 : 1. Subsequently, S²⁻ was added to the [DL + Cu²⁺] solution, because the precipitation dissolution equilibrium constant of CuS was K_sp = 1.27 × 10⁻³⁶, so the binding capacity between Cu²⁺ and S²⁻ was stronger, CuS precipitation was formed, and red fluorescence was re-released, and the quantitative detection of S²⁻ was realized, and the detection limit was 3.50 × 10⁻⁸ M. Through bacterial imaging experiments, we found that the probe can accomplish the fluorescence imaging experiments of Staphylococcus aureus, indicating that the probe has good biopenetration and biocompatibility, and has application prospects in bioimaging and environmental monitoring. In addition, the probe DL has good suitability for Cu²⁺ and S²⁻ detection in real samples.