Quinoline-imidazole based hydrophilic “turn-on” fluorescent probe for specific detection of Pb2+ and viscosity

Herein, a novel dual-response fluorescent chemosensor (HPI-Qu) based on quinoline and imidazole moieties with aggregation-induced emission enhancement (AIEE) properties and good water-solubility was developed for the detection of Pb²⁺ and viscosity. The probe exhibits a remarkable “turn-on” fluorescence response at 620 nm upon binding Pb²⁺ in aqueous media and has the advantages of fast response time (<20 s), high selectivity and excellent anti-interference ability for Pb²⁺, and the binding constant (Ka) was 0.75 × 10⁶ M⁻¹. The low detection limit for Pb²⁺ was found to be 0.08 μM, which is far below the maximum allowable value of Pb²⁺ in drinking water fixed by the World Health Organization (WHO). The binding mechanism of the probe HPI-Qu toward Pb²⁺ was determined by Job's plot, FTIR Spectral, ¹H NMR titration experiments, ESI-HRMS spectrometry, and theoretical calculation. Additionally, HPI-Qu displays significant turn-on viscosity-dependent behavior and a perfect linear relationship with viscosity in the range of 1.01–1412 cP. Furthermore, the probe HPI-Qu exhibits good cell permeability and biocompatibility, and could be applied for detecting Pb²⁺ and viscosity in the living cells. This indicates that the probe HPI-Qu has potential application prospects for monitoring Pb²⁺ and viscosity in environmental and biological systems.