Water-Induced Structural Instability in Zinc Coordination Polymers for Dual-Channel Fluorescent Sensing of Cu²⁺ and Cysteine

Coordination polymers (CPs) have gained significant attention due to their unique structural tunability and broad application prospects. However, their instability in water remains a key challenge for practical applications. This study presents a dual-channel fluorescent sensor based on water-unstable zinc coordination polymers (Zn-CPs) for the sensitive detection of copper ions (Cu²⁺) in water and cysteine (Cys) in serum. Zn-CPs underwent structural collapse in water, deactivating matrix coordination-induced emission (MCIE) and quenching blue fluorescence. pH adjustment activated the aggregation-induced emission (AIE) of the ligand, turning on green fluorescence. The introduction of Cu²⁺ facilitated the formation of zinc-copper co-coordination polymers (Zn/Cu-CPs), improving water stability while preserving blue fluorescence and inhibiting green fluorescence activation. In contrast, Cys competitively coordinated with Cu²⁺, preventing the formation of Zn/Cu-CPs, resulting in blue fluorescence quenching and green fluorescence activation. The sensor exhibited a linear detection range of 0.01-0.25 mg/L for Cu²⁺ (limit of detection: 0.0162 mg/L) and 0.5-14 μM for Cys (limit of detection: 0.4380 μM). Unlike conventional approaches that focus on enhancing water stability, this study highlights the potential of water-unstable coordination polymers in environmental and bioanalytical applications and provides new insights into the design of fluorescence sensors based on structural transformations.