A dual-signal Mn(Ⅱ)-MOF fluorescent sensor for detection of water pollutants, food additives, and their induced sweat metabolic biomarkers

5,5'-(diazene-1,2-diyl)bis(2-hydroxybenzoic acid) (H 2 L ) is used as a ligand precursor for a high-performance metal-organic framework (MOF)-based fluorescent probe, due to its dye characteristic group. The hydrothermal reaction of H 2 L and 4, 4ʹ-bipyridine (4,4ʹ-bipy) with Mn(II) salt led to a MOF Mn 3 ( L ) 4 (4,4ʹ-bipy) 2 (H 2 O) 2 ·Mn(4,4ʹ-bipy) 2 (H 2 O) 2 ·4H 2 O (MOF- 1 ). MOF- 1 features a 3D net with 1D square channels (12.50 Å × 15.36 Å), where L 2− ligands link trinuclear Mn clusters via bis-bridging and bis-monodentate carboxylate groups. MOF- 1 has good chemical stability across a wide pH range and strong blue luminescence. It enables quantitative detection of Fe 3+ , MnO 4 − , dehydroacetic acid sodium salt (SDH), and hydrocortisone (HC) via fluorescence turn-off effect, and Pb 2+ , tartaric acid (TA), and ascorbic acid (AA) through fluorescence turn-on effect, with high selectivity, good reusability, and low limits of detection (LODs). The sensing of Fe 3+ and MnO 4 − involves the competitive absorption (CA) and the resonance energy transfer (RET) mechanisms. The sensing of Fe 3+ also relies on the weak interactions with uncoordinated O sites in carboxylate groups. The detection of Pb 2+ primarily relies on its weak interactions with benzene moieties of L 2− ligands. Orbital energy theoretical calculations reveal that the fluorescence changes of MOF- 1 for SDH, HC, TA, and AA mainly stem from photoinduced electron transfer (PET). The CA process also plays an important role for SDH detection. The detection of water pollutants in real water samples (tap, spring, and Hunhe River) and of HC and AA in 100-fold diluted real sweat is achieved with corresponding recoveries of 98.00–103.70 %, 100.1 %, and 104.10 %. MOF- 1 fabricated into test strips can rapidly detect HC and AA in sweat. These results highlight the potential of MOF- 1 as a dual-signal sensor for detecting water pollutants and food additives, and for sensing specific sweat biomarkers to evaluate exposure to these substances.