A MOF chemosensor for highly sensitive and ultrafast detection of folic acid in biofriendly medium, paper strips and real samples

Abstract

A new zirconium-based dansyl anchored metal–organic framework (MOF) bearing the University of Oslo – 66 (UiO-66) topology was synthesised by a solvothermal procedure. The synthesised material (UiO@Dansyl) shows excellent structural integrity. The as-synthesised and activated form of the material was stable up to 215 °C, and structural integrity remained unaltered in common organic solvents as well as in a wide pH range (2–12). UiO@Dansyl has a specific BET surface area of 1026 m² g⁻¹. FT-IR, FE-SEM and EDX studies with UiO@Dansyl confirmed that the material was pure enough for application purposes. The activated material was utilised for the fluorogenic detection of folic acid (FA) in PBS buffer (pH 7.4). The probe showed a highly sensitive (lower detection limit: 1.3 nM) and ultrafast (<5 s) response toward FA. The detection limit is lower than those of known MOF sensors for FA. The fluorescence quenching efficiency of the probe by FA was around 95%, whereas for other competitive analytes, the quenching was only 2–5%. The Stern–Volmer constant was found to be 9.2 × 10⁵ M⁻¹. UiO@Dansyl was also used to detect FA in food samples, human blood serum and urine. To be applicable for real-field purposes, a paper-strip device was fabricated for the on-site detection of FA. The mechanisms for quenching of fluorescence intensity by FA were investigated in a systematic way with the help of TRPL, UV-Vis spectroscopy, pH titration and theoretical calculations. The above experimental findings indicated the superiority of UiO@Dansyl for the detection and quantification of FA in a bio-friendly medium.