Novel Lanthanide-Based Metal–Organic Framework Isomer as a Double Ratiometric Fluorescent Probe for Vanillymandelic Acid

Abstract

The concentration of vanillymandelic acid (VMA) in urine is closely related with pheochromocytoma diagnosis. Thus, it is essential to develop more accurate and convenient fluorescence sensing strategies toward VMA. Until now, the design of double ratiometric detection methods for VMA was still in the unexplored stage. In this work, novel Ln3+-based metal–organic frameworks (QBA-Eu and QBA-Gd0.875Eu0.125) possessing dual emission peaks was fabricated successfully, which served as isomers of YNU-1 and exhibited more excellent water stability in fluorescence and structure than the ones of YNU-1. The formation of the complex between QBA ligands and VMA molecules via hydrogen bonds within QBA-Eu frameworks produced a new emission band centered at 450 nm and resulted in the decline of monomer emission intensity for QBA at 390 nm. Owing to the reduced energy gap [ΔE (S1 – T1)], the antenna effect was hampered and luminescence of Eu3+ ions also decreased. The developed double ratiometric (I 615nm/I 475nm, I 390nm/I 475nm) fluorescence sensors based on QBA-Eu and QBA-Gd0.875Eu0.125 possessed the advantages of fast response (4 min), low detection limits (0.58 and 0.51; 0.22 and 0.31 μM), and wide linear ranges (2–100 and 2–80 μM), which met the requirements of pheochromocytoma diagnosis. We also applied them to determine VMA in an artificial urine sample and diluted human urine sample and obtained satisfactory results. They will become prospective fluorescence sensing platforms for VMA.

Multifunctional Luminescent 3D Ln-MOFs with High Sensitivity for Trace Detection of Micronutrients

“…Metal–organic frameworks (MOFs) are novel porous crystalline compounds that are created by combining ligands that are organic in nature with many teeth to coordinate metal ions or clusters. MOFs materials have large surface area, porous properties and high crystallinity, with regular arrangement and dense adsorption active sites inside the pores. , The simultaneous luminescence of lanthanide ions (Ln 3+ ) and ligands produces double fluorescence emission, which reduces the interference of external conditions on detection, thus improving the detection sensitivity and reducing the detection limit, which makes the fluorescence MOFs get great development. − …”