Sensitive and selective fluorometric determination and monitoring of Zn²⁺ ions using supermicroporous Zr-MOFs chemosensors

We report the fabrication of water-stable, supermicroporous fluorescent chemosensors (MFCs) using Zr-based metal-organic frameworks (MOFs) as scaffolds for selective fluorescent determination of the ultra-traces of heavy metals, such as Zn²⁺ ions from water resources. The MFCs structures was developed by direct decoration of hydrophobic fluorescent probes (2,2′-((1Z,12Z)-5,9-dithia-2,12-diazatrideca-1,12-diene-1,13 diyl) diphenol), (S1) into the Zr-based metal-organic frameworks (MOFs). Significantly, the MFCs design with uniform super-microgroove pores, long-range intergrowing crystal, and dense decoration of fluorescent probes, leading to create active hook surface sheaths as sensitive and selective chemosensors platforms for ultra-trace monitoring of Zn²⁺ ions. The MFCs supermicro-crystal structures have shown synergistic enhancement in selective sensing assay associated with low-detection limit up to part-per-billion (ppb), wide-range determination (0.5 ppb to 2000 ppb) and fast response monitoring in the order of second during the binding of Zn²⁺ ion target. The selectivity of Zn²⁺ ions fluorometric sensing process in a heterogeneous mixture of inorganic cations and anions was mainly dependent on the structure of the fluorescent probe, pH condition, competitive ion system composition, and Zn-to-fluorescent probe binding procedure. Our developed MFCs showed a wide range of detection of Zn²⁺ ions with a considerably low detection limit of approximately 10⁻⁹ mol/L, in optimal working condition. The long-term stability of MFCs with fluorescent surface functionality enabled the practical and multiple reuse/cycles of Zn²⁺ ion determination.