Novel ionic liquid–Schiff base grafted on NH2-MIL-53(Al) hybrid sensor for selective and sensitive Zn2+ fluorescent sensing in complex matrices

A novel hybrid sensor was constructed by grafting 1-(salicyl)-2,4-lutidinium hexafluorophosphate (Sal(lut⁺PF₆⁻) onto NH₂−MIL-53(Al) via a Schiff base reaction (Sal@MIL) for the highly selective and sensitive detection of Zn²⁺ ions. The chemical structure of Sal (Lut⁺PF₆⁻) was confirmed using ¹H, ¹³C, ³¹P, ¹⁹F NMR and FT-IR spectroscopy, while NH₂−MIL-53(Al) and the Sal@MIL sensor were characterized using XRD, BET surface area analysis, FT-IR, SEM, and XPS techniques. The Sal@MIL sensor exhibited a broad Zn²⁺ recognition capability. Under optimal conditions, it achieved a remarkable low limit of detection (0.11 ppb) and limit of quantification (0.36 ppb), along with excellent selectivity against potentially interfering metal ions. The sensing mechanism relies on the inhibition and destruction of CN isomerization and excited-state intramolecular proton transfer (ESIPT) upon Zn²⁺ binding, resulting in a significant fluorescence response. Practical applications were successfully demonstrated through accurate Zn²⁺ quantification in diverse real-world matrices including tap water, seawater, human blood serum, and various medications with results rigorously validated by ICP-MS analysis. The Sal@MIL sensor offers a high sensitivity, selectivity, and rapid response for Zn²⁺ ion detection in complex matrices.