Selective Determination of Cu2+ and ClO− Ions in Aqueous Media by Dual-Channel Colorimetric and Fluorescent “Turn-on” Probe

Abstract

The dual-responsive colorimetric and fluorescent “turn-on” sensor, RhNPS, was synthesized and characterized using elemental analysis, FT-IR, LC-MS/MS, and NMR (1-H and 13-C) spectroscopies. UV–Vis absorption and fluorescence titration experiments were conducted to investigate the probe's optical response to disturbances caused by various metal ions and anions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Cr³⁺, Fe³⁺, Al³⁺, Hg²⁺, Mn²⁺, Zn²⁺, Pb²⁺, Fe²⁺, Cu²⁺, Co²⁺, Sr²⁺, Ni²⁺, Cd⁺², Ag⁺, and F⁻, Cl⁻, Br⁻, I⁻, ClO⁻, S²⁻, CN⁻, CO₃²⁻, SO₃²⁻, SO₄²⁻, NO₂⁻, H₂PO₄⁻, AcO⁻). Among the eighteen metal ions tested, only copper induced a detectable color change in the RhNPS probe in buffer solution, shifting it from colorless to purple. Furthermore, significant increases were observed in both absorption and fluorescence emission, with peaks centered at 558 and 590 nm, respectively. Besides that, RhNPS demonstrated considerable sensitivity and selectivity to ClO⁻ in the presence of thirteen anion species, exhibiting broad-band emission and absorption spectra at 549 and 581 nm, respectively. According to the Job's plot approach, it was possible to demonstrate that RhNPS and Cu²⁺ could form a 1:1 complex. Additionally, the detection limits for ClO⁻ and Cu²⁺ were also calculated to be 2.6 × 10⁻⁷ and 5.4 × 10⁻⁸ M, respectively. Consequently, a robust binding interaction between Cu²⁺ and RhNPS was deduced from the reversible ring-opening mechanism of spirolactam. Spectroscopic analyses demonstrated the efficacy of the chromogenic and fluorogenic chemosensor RhNPS as a highly sensitive and selective probe for Cu²⁺ and ClO⁻ within aqueous environments.