Hierarchical MOF@MOF Ratiometric Probe for Ultrasensitive On-Site Detection of Norfloxacin in Food and Environmental Samples

Norfloxacin (NFX) residues in food and environmental samples threaten human health, necessitating rapid on-site detection. A hierarchical MOF@MOF probe (Ag-MOF-74/NH₂-MIL-53(Al) for ratiometric NFX sensing has been fabricated, in which NH₂-MIL-53(Al) enhances NFX emission via hydrogen bonding and energy transfer, while Ag-MOF-74 provides a stable reference, enabling self-calibration. The probe achieves ultrasensitive detection (6 nM) with high selectivity and reproducibility. A smartphone-based platform was designed for on-site quantification within minutes. Validated in milk, soil, and water, it showed excellent accuracy (98–102% recovery) and precision (RSD < 2.86%). This MOF@MOF strategy offers a robust on-site screening tool and a versatile design paradigm for food safety and environmental monitoring.