Visual-Based Platform Using Sustainable Intrinsic Fluorescent Zn-Based Metal–Organic Framework for Detection of Folic Acid in Pharmaceutical Formulations

In the present work, intrinsic fluorescent zinc-based metal–organic framework (FMOF-5) was prepared and used for folic acid (FA) detection. The intrinsic emission of zinc-based MOFs without encapsulation and/or functionalization of the ligand and/or the MOF is not very common. Here, the intrinsic emission of FMOF-5 is triggered by the coordination-induced emission of weakly fluorescent organic ligand in the framework structure. FMOF-5 showed fluorescence emission at 440 nm when excited at 300 nm. Common characterization techniques were used to investigate the size, morphology, and optical properties of the FMOF-5. The fluorescence emission of the prepared MOF was quenched by the internal filter effect, which gives us an opportunity to design a novel on-off mode sensor for the detection of FA. The conventional fluorometric-based assay and the smartphone-assisted visual detection mode were developed and validated. The visual-mode linearity was from 30 to 270 µM with limit of detection about 4.3 µM. The on-off sensor was successfully applied for detection of FA in pharmaceutical formulations with excellent recovery and reproducibility. The visual on-off mode using intrinsic fluorescent MOFs is highly appealing for pint of care testing applications.