PB@UiO-67-CDC-(CH₃)₂ as an Ultrasensitive Ratiometric Fluorescence Sensor: Visible “Turn-On” Effect for Detecting Preservatives and Amino Acids

Abstract

Sensory material which can recognize preservatives and amino acids through different fluorescence changes has significant application value in many fields. Here, a pore-functionalized metal–organic framework (MOF) becomes a versatile platform for fluoro-sensing various preservatives and amino acids with higher emission and multicolorful scaffolds and allows for visible detection. The carbazole groups in a Zr-based MOF UiO-67-CDC (CDC = 9H-carbazole-2,7-dicarboxylic acid) are partially substituted into dimethylation through postsynthetic N-methylation to form a positively charged framework UiO-67-CDC-(CH3)2. Because of electrostatic induction, the postmodification skeleton can efficaciously encapsulate the anionic dye phloxine B (PB) in the cavity of the electron-deficient MOF, and a newfangled fluorescence “turn-on” behavior is ascribed due to the inhibition of photoinduced electron transfer (PET) (from the benzene rings to the quaternary ammonium group on the ligand) and the stunning synergistic effect of the confinement-induced emission (CIE) enhancement. PB@UiO-67-CDC-(CH3)2 shows a unique fluorescence response for preservatives and amino acids with variable colors and visual, quantitative discrimination effects, which could be applied for sensing, switching, and anticounterfeiting identification. Notably, the fluorescence emission peak of dye (PB) and MOF presents a ratiometric change, further improving the detection’s resolution and veracity. The sodium acetate and leucine detection limits are as low as 0.0157 μM and 0.1084 μM, respectively. In addition, a smartphone was used to visualize sodium acetate by identifying the RGB value of the fluorescent changes, and the LOD can be as low as 7.23 μM. These features make the dye-embedded MOF composite a simple, efficient, and instrument-free stratagem for the on-site and convenient detection of preservatives in various samples.

SCSC Transformation and Post-Synthesis Modification of MOFs with Proton Conduction and Ratiometric Fluorescence-Sensing Properties

“…The broad peak shifted to the left/right and the absorbance decreased significantly after the addition of Glu and Trp (Figure S42), indicating that Glu and Trp interact with Tb 3+ @ 1 . On the other hand, the enhanced fluorescence emission of the ligand can be explained by the interaction between the O atoms of the methoxy group in the MeO–H 2 ip ligand, and Trp and Glu through a photoinduced electron transfer (PET) mechanism. , When the electron-rich methoxy group interacts with amino acids, the lone pair of electrons of the methoxy group is more easily transferred to Trp and Glu rather than the ground state. Therefore, the excited state electrons of the fluorescent framework can easily transform to the ground state.…”

The construction of dual-emissive ratiometric fluorescent probes based on fluorescent nanoparticles for the detection of metal ions and small molecules

“…The small size of organic dyes allows them to easily encapsulated in the pores of MOFs and dispersed uniformly, thus avoiding ACQ. Many dye@MOF composites have been explored for the detection of metal ions, [121][122][123][124][125][126][127][128][129] antibiotics, [130][131][132] food additives, 133,134 explosives, [135][136][137] pesticides, [138][139][140] medicine, 141 and water in organic solvents. 142 In addition to dyes, CDs, QDs, and Ru (bpy) 3 2+ can also be encapsulated in LMOFs to avoid their agglomeration and improve their stability.…”

Luminescent Guests Encapsulated in Metal–Organic Frameworks for Portable Fluorescence Sensor and Visual Detection Applications: A Review

“…An electron-deficient MOF is used to encapsulate the anionic dye interhydrodiphenol B (PB), resulting in a novel fluorescence “on” behavior, by preventing light-induced electron transfer. For preservatives with different hues and visual (blue–red) quantitative discriminatory effects, PB@UiO-67-CDC-(CH 3 ) 2 exhibits a distinctive fluorescence response that could be used for sensing, switching, and anti-counterfeiting identification [ 159 ].…”