A biomimetic Fe(<scp>iii</scp>)–metal–organic framework nanosphere-based dual modal probe for aqueous and intracellular sensing of nicotine and its metabolite cotinine

Integration of novel biocompatible nanostructures as effective sensing platforms is still of great significance for robust and rapid analysis. Herein, novel iron(III) metal-organic framework (Fe-MOF) nanospheres with the formula [Fe₃(μ₃-O)(C₇O₂H₅)₆(COO)₂(H₂O)·2DMF] were successfully developed and characterized by single crystal X-ray diffraction (SXRD) studies. Interestingly, fluorescence studies reveal that Fe-MOF is an effective multi-functional turn-on sensor for nicotine and cotinine that exhibits a blue shift, a low detection limit, notable recyclability, and good anti-interference ability. This material satisfies essential biological criteria by being minimally toxic to living cells (L929 and A549 cell lines) and retaining structural stability in water across a broad pH range (3-11), enabling its successful application in biological imaging of nicotine and cotinine in living cells. To our knowledge, this is the first report of fluorescence enhancement for cotinine detection with a metal-organic framework. Density functional theory (DFT) calculations and ultraviolet-visible (UV-vis) absorption studies have elucidated the plausible sensing mechanism. This study significantly expands the potential of Fe-MOF in sensing and biological applications.