pH- and Solvent-Stable Zn ^II /Cd ^II Metal–Organic Frameworks with 2,1,3-Benzothiadiazole Derivative for Turn-On Fluorescence Sensing Dipicolinic Acid and Thiamine in Living Cells

The rapid detection of specific biological substances and biomarkers has the potential to contribute to the early identification, diagnosis, and prevention of diseases. Two examples of structurally similar luminescent metal-organic frameworks based on the same mixed ligands, namely {[M(BTBD)₂(bptc)_0.5]·H₂O}_n (M = Zn (<b>JXUST-48</b>) and Cd (<b>JXUST-49</b>), BTBD = 4,7-bis(1<i>H</i>-1,2,4-triazol-1-yl)-2,1,3-benzothiadiazole, H₄bptc = 3,3',5,5'-biphenyltetracarboxylic acid), have been successfully constructed using solvothermal methods. Both remain stable when immersed in organic solvents and aqueous solutions with varying pH values of 1-14 for 24 h. Interestingly, <b>JXUST-48</b> can detect 2,6-pyridine dicarboxylic acid (DPA) and thiamine (vitamin B1, VB1) by fluorescence enhancement and red-shift effect, whereas <b>JXUST-49</b> is able to detect DPA and VB1 by fluorescence enhancement effect. The practical applicability of the sensors was validated using spiked recovery experiments, achieving recovery rates between 96.6% and 105.5%. More importantly, <b>JXUST-48</b> and <b>JXUST-49</b> have good biocompatibility and low cytotoxicity, while simultaneously achieving the capacity for fluorescence imaging and sensing of exogenous DPA and VB1 in vivo in living cells. This work provides some guidance for the development of MOF-based fluorophores based on different metal ions.