A novel fluorescent probe with high sensitivity and selectivity for "On-Off-On" sensors for Cu²⁺ cations and CN^-...

A novel fluorescent probe NIPF was synthesized by the Suzuki reaction to recognize Cu²⁺ and CN^-. With the addition of Cu²⁺, NIPF exhibited strong fluorescence quenching (90 % for NIPF) with a K_sv value of 3.4 × 10⁶ M^-1 and a detection limit of 9.04 × 10^-10 M. Subsequently, CN^- was added to the NIPF-Cu²⁺ solution, and [Cu(CN)_x]^n- was formed due to the strong interaction between Cu²⁺ and CN^- leading to fluorescence recovery (89 % for NIPF-Cu²⁺). In addition, a detection limit of 3.6 × 10^-8 M was obtained by fluorescence titration. Meanwhile, it was demonstrated that the sensor achieved 93 %-105 % recovery of Cu²⁺ in the tested environmental samples, and the practicability of Cu²⁺ and CN^- detection were verified using hydrogels test, with significant color changes observed under 365 nm light. Accordingly, the fluorescent probe NIPF was used to recognize Cu²⁺ and CN^- by the "on-off-on" sensors.