Disassembly-activated fluorescence switching in salamo-Cu(II) polymer for phosphate detection: From pharmaceutical analysis to environmental monitoring

Excessive orthophosphate (PO₄³⁻) in aquatic environments is a primary cause of eutrophication, promoting algal blooms that lead to oxygen depletion upon decay, resulting in hypoxia and ecosystem degradation. To tackle this challenge, we designed a new 1D copper-based coordination polymer (Cu-CP) fluorescent probe, self-assembled from Cu²⁺ and a bis-Salamo-ligand (H₄L). This probe exhibits a pronounced fluorescence turn-on response toward PO₄³⁻ upon 365 nm irradiation, demonstrating ultrahigh sensitivity (LOD = 2.09 μM), broad pH stability (4-11), and excellent selectivity against competing species. HR-MS/XPS studies reveal a disassembly-induced sensing mechanism, whereby PO₄³⁻ triggers the release of highly fluorescent H₄L ligand. The probe can be regenerable for at least three cycles with consistent performance. Time-resolved fluorescence lifetime measurements further corroborate the sensing pathway. Portable test strips integrated with smartphone-based fluorescence readout enable on-site, semiquantitative detection, and the system has been successfully applied to environmental water and pharmaceutical samples. However, the practical application in pure aqueous media is currently constrained by the limited solubility of Cu-CP. Future efforts will aim to enhance hydrophilicity through structural modification or carrier immobilization to broaden its utility.