Water-stable Ag (Ⅰ) coordination polymer sensors to selectively and sensitively detect the chlortetracycline via fluorescence red-shift and turn-on effect

The antibiotic residue resulting from the abuse and overuse of antibiotics has threatened food safety and the environment. Establishing new detection strategies for antibiotic residues in food and the environment is necessary. A "turn-on" fluorescence sensor-[Ag(BIX)]n⋅ n(HBA) (Ag-CP)(BIX = 1,4-bis(imidazole-1-ylmethyl) benzene, BA = benzoic acid) was constructed herein using a convenient one-pot strategy. The ample benzene ring, imidazole ring, and free BA of Ag-CP provide the specific interaction sites for the interaction between the fluorescence sensor and the target. Due to its excellent chemical and fluorescent properties, it has been used to detect Chlortetracycline (CTC) sensitively. To our knowledge, Ag coordination polymer has not been previously reported for the detection of CTC. It is worth mentioning that the fluorescent intensity of Ag-CP remarkably enhances and the wavelength of the emission peak is red-shifted under the synergistic effect between the CTC and Ag-CP. Selectivity and sensitivity for detecting the CTC have been achieved over the concentration from 0.05 μM to 100 μM, along with the good linear fitting (R2 ≥ 0.9690) and the low limit of detection (34 nm). The recovery percentage in spiked food samples was assessed to be 84.12-96.82 %, and the RSD is less than 4.75 %. These results manifested that the Ag-CP-based fluorescence sensor, validated by the HPLC, represented good sensitivity and high precision. Therefore, our work reveals the advantages of coordination polymer-based fluorescence sensors and puts forward a novel strategy for the detection of antibiotic residues in food safety.

Multifunctional Cd-CP for fluorescence sensing of Cr(VI), MnO4-, acetylacetone and ascorbic acid in aqueous solutions

The development of multifunctional fluorescent chemosensors for the detection of multiple targets remains challenging but of great importance. In this paper, one novel coordination polymer (CP), denoted as [Cd₂(edda)(phen)₂]∙H₂O (compound 1, H₄edda = 5,5' (ethane-1,2-diylbis(oxy)) diisophthalic acid, phen = 1,10-phenanthroline) is successfully designed and prepared under hydrothermal conditions. Structural analysis indicates that compound 1 possesses a one-dimensional (1D) double chain structure, then self-assembles into a three-dimensional (3D) supramolecular framework via π…π interactions between phen molecules. Interestingly, compound 1 is found to be tolerant in wide range of acidic to alkaline aqueous solutions (pH = 2-13). Fluorescent spectral investigations reveal that compound 1 exhibits highly selective and sensitive fluorescence responses toward MnO₄^-, Cr(VI) ions, acetylacetone (acac) and ascorbic acid (AA) by fluorescence quenching in the aqueous phase. The detection limits are in the very low range, reaching μM level for the detection of MnO₄^-, Cr(VI) ions, nM for AA and ppm for acac detection. The distinguished multi-responsive performance suggests compound 1 to be a potential multifunctional probe. Furthermore, the possible quenching mechanisms have also been systematically investigated in this work.

A water-stable dual-responsive Cd-CP for fluorometric recognition of hypochlorite and acetylacetone in aqueous media

One novel cadmium(II)-coordination polymer [Cd₃L₂(datrz)(H₂O)₃] (CP 1) is controllably synthesized by surmising the astute combination of semi-rigid tricarboxylate acid 4-(2',3'-dicarboxylphenoxy) benzoic acid (H₃L) and auxiliary ligand 3,5-diamino-1,2,4-triazole (datrz). Structure analysis shows that CP 1 has a two-dimensional (2D) layer structure with a 5-nodal (4³) (4⁴·6²) (4⁵·6⁴·8) (4⁵·6) (4⁷·6⁶·8²) topology. Further investigations reveal that CP 1 shows superordinary water stability and good thermal stability. The fluorescent explorations suggest that the as-synthesized CP 1 could emit blue light centered at 485 nm, attributing to ligand-based emission. In terms of sensing investigations, CP 1 could act as a fluorescent sensor for detecting hypochlorite (ClO^-) and acetylacetone (acac) through fluorescence turn-off process in aqueous solution, and the detection limit could reach 0.18 μM and 0.056 μM, respectively. Further research reveals that it is more likely the N-H···O-Cl hydrogen bonds between -NH₂ groups of the triazole ligands and O atoms of ClO^- plays the key role in the system, which may serve as a bridge for the energy transfer, leading to fluorescence quenching of the chemosensor. While the photoinduced electron transfer (PET) combined with inner filter effect (IFT) should be responsible for the turn-off fluorescence of CP 1 triggered by acac.