Dual-Mode Luminescent Microporous Zn-MOF for Food Safety: Turn-On/Off Detection of Primamycin Ia and Toxic Ions

In this study, two Zn-based metal–organic frameworks (ZnMOF<inf>1</inf> with 1,10-phenanthroline and ZnMOF<inf>2</inf> with 4,4′-bipyridine as co-ligands) were synthesized via a solvothermal method and used as fluorescent sensors for the detection of cations (Pb²⁺, Cu²⁺, Ni²⁺, Co²⁺, Hg²⁺, Cr³⁺, and Al³⁺), anions (Cr<inf>2</inf>O<inf>7</inf>²⁻, CrO<inf>4</inf>²⁻, SO<inf>4</inf>²⁻, OH⁻, Cl⁻, H<inf>2</inf>PO<inf>4</inf>⁻, and NO<inf>3</inf>⁻), and primamycin Ia antibiotic in both milk and dairy products. The characterization results using FTIR, XRD, SEM, BET, and TG-DTA methods confirmed the successful formation of MOFs with uniform morphologies. When the fluorescence sensing performances were evaluated, it was concluded that both materials exhibited similar fluorescence responses; however, ZnMOF<inf>1</inf> demonstrated superior sensing performance. The results revealed that ZnMOF<inf>1</inf> enables the selective molecular recognition of Cu²⁺, Pb²⁺, OH⁻, and primamycin Ia, exhibiting a “turn-on” luminescence response for OH⁻ and primamycin Ia, and a “turn-off” response for Cu²⁺ and Pb²⁺. In milk samples, the limits of detection (LOD) were determined to be 472, 235, 698, and 757 µM for Cu²⁺, Pb²⁺, OH⁻, and primamycin Ia, respectively. These results show that ZnMOF<inf>1</inf> can be used as a promising fluorescence sensor for rapid, sensitive, and selective monitoring of both ionic and antibiotic contaminants in dairy products, providing a practical tool for food safety applications.