Multimodal Cyclotriguaiacylene-Fluorescein Supramolecular Sensor for Field-Deployable Monitoring of Strontium in Complex Environmental Waters.

Selective quantification of dissolved Sr2+ in chemically complex environmental waters remains a significant analytical challenge because of the closely related physicochemical properties of alkaline-earth ions and the matrix complexity of natural waters. Herein, a fluorescein-functionalized cyclotriguaiacylene macrocycle (CTG-FL) was developed as a preorganized supramolecular sensor for the optical determination of Sr2+. The rigid, oxygen-rich binding cavity enables preferential Sr2+ recognition, while coordination perturbs the intramolecular charge-transfer pathway, producing static fluorescence quenching through a nonemissive ground-state complex. Integrated spectroscopic, thermodynamic, NMR, and density functional theory (DFT) investigations established a spontaneous 1:1 host-guest binding mechanism driven predominantly by enthalpic ion-dipole interactions, with a binding affinity (Ka) of 1.49 × 107 M-1. CTG-FL exhibited ultratrace sensitivity (LOD = 1.66 nM), rapid response (<30 s), and excellent discrimination against competing alkaline-earth ions while retaining selectivity in hypersaline media, artificial seawater, and chemically complex environmental matrices. This supramolecular recognition strategy was translated into complementary fluorometric, smartphone-assisted colorimetric, cellulose-based test strip, and paper-based microfluidic sensing formats spanning both solution-phase and solid-state operation for portable quantitative analysis. Quantification of native Sr2+ in authentic river water, groundwater, seawater, and industrial wastewater demonstrated excellent agreement with ICP-MS, establishing CTG-FL as a mechanistically validated platform for decentralized Sr2+ monitoring that complements established laboratory-based elemental analysis.