Functionalized Metal-Organic Framework for Selective Fluorometric Detection of Sodium Dodecyl Sulfate and Vitamin B12 Using MOF@Cotton Composites and Lewis Base-Catalyzed Condensation Reaction.

A zirconium(IV)-based metal-organic framework (MOF) fluorophore containing the 2,5-diaminoterephthalic acid (H2BDC-(NH)2) linker was synthesized and characterized. The physicochemically stable, porous (SBET = 504 m2 g-1) MOF (1') exhibited selective and sensitive fluorescence turn-on behavior toward the sodium dodecyl sulfate (SDS) surfactant and turn-off response toward vitamin B12. This is the first ever reported MOF-based dual optical sensor of SDS and vitamin B12. Other competitive analytes did not interfere in the detection of both the analytes. Along with the lowest ever reported limit of detection (LOD) values (LOD for SDS = 108 nM and LOD for vitamin B12 = 45.3 nM), 1' displayed short response time for SDS (50 s) and vitamin B12 (5 s) detection. The MOF was able to detect SDS in various real water samples and vitamin B12 in various bio-fluids (urine and serum) and pH media. A MOF-coated cotton composite was fabricated, which displayed a visible color change under UV light even after treating it with a nanomolar concentration of both the analytes. The sensor displayed excellent reusability up to five cycles of sensing. Various experimental outcomes evidenced that the electrostatic interaction between the -NH2 groups of the linker and the -SO3- group of SDS is the possible reason for the selective SDS sensing. For vitamin B12, the energy transfer from the probe to vitamin B12 resulted in fluorescence quenching. In addition, the catalytic performance of 1' was investigated in the condensation reaction between benzaldehyde derivatives with cyanoacetamide with high yields in ethanol at 70 °C. The solid was used for three cycles with no decrease in its activity and selectivity. PXRD and FESEM analysis before and after the reaction suggested the retention of the crystallinity of 1', thus indicating catalyst stability.