A novel multiemissive Ln/covalent-organic frameworks for ratiometric detection of 2,6-dipicolinic acid

Antenna effect-modulated luminescent lanthanide complexes for biological sensing

With the discovery and further exploitation of the antenna effect, the optical properties of luminescent lanthanide complexes (LLCs) have been greatly improved. Antenna effect-modulated LLCs exhibit long luminescence lifetimes, large Stokes shifts, narrow emission spectra, pure chromaticity, and high photostability. Meanwhile, LLCs have garnered considerable attention in recent years and are widely used as biosensors in the fields of food safety, environmental monitoring, clinical diagnosis, and drug analysis. In this review, we first systematically review the design of antenna effect-modulated LLC sensors, including the construction principle of antenna effect in LLCs and the selection of antenna ligands. Secondly, the classification of antenna ligands was discussed in detail. Thirdly, biological sensing applications of antenna effect-modulated LLCs in the past three years are described in terms of the role of LLCs in fluorescence sensors and electrochemiluminescence sensors. Finally, we also discussed the challenges and emerging opportunities of antenna effect-modulated LLCs in future sensing applications.

Ratiometric fluorescence sensor based on bimetallic organic frameworks for anthrax biomarker detection

It is of great significance to construct ratiometric fluorescence sensors with simple operation and desirable anti-interference ability. In this study, a bimetallic organic framework was prepared for the first time by a one-pot solvothermal method, using 4,4'-biphenyl dicarboxylic acid as ligand, lanthanide metal terbium ions (Tb3+) and transition metal zirconium ions (Zr4+) as central metal ions. This preparation method was easy to carry out. On this basis, a novel ratiometric fluorescence sensor Tb-Zr-MOF was constructed successfully for the detection of anthrax biomarker (2,6-pyridinedicarboxylic acid (DPA)). When DPA was added into the detection system, the fluorescence of Tb3+ was enhanced due to the energy transfer from DPA to Tb3+. Therefore, under the single excitation at 285 nm, the fluorescence emission intensity of Tb-Zr-MOF at 402 nm remained unchanged and the fluorescence emission intensity at 546 nm increased. As a ratiometric fluorescence sensor, Tb-Zr-MOF showed good linear response to DPA in the range of 5∼100 μM and the limit of detection was 1.72 μM. This sensor reduces the interference of environmental factors and achieves high sensitivity detection, which is superior to the traditional single emission peak fluorescence sensor. In addition, the developed Tb-Zr-MOF sensor was used to detect DPA in Bauhinia bark samples successfully. The recovery rate was 98.80%∼104.8%, which proved the practical application of Tb-Zr-MOF in complex environment. It is expected to provide a reliable method for the detection of biomarkers of Bacillus anthracis.

Qualitative and Quantitative Luminescence Detection of 2,6-Dipicolinic Acid and Levofloxacin Based on a High-Nuclearity Eu(III) Nanomolecular Sensor

Rapid and accurate testing of 2,6-dipicolinic acid (DPA) and levofloxacin (LFX) has been attracting much attention due to the fact that the former is an important biomarker of anthrax spores and the latter is a third-generation fluoroquinolone drug and has been recognized as an important environmental pollutant. Herein, we report the preparation of a 13-metal Eu(III) nanomolecular sensor (molecular sizes: 2.0 × 2.4 × 3.2 nm) bearing a new flexible Schiff base ligand for luminescence testing of DPA and LFX with high selectivity and sensitivity. The rapid enhancement of the Eu(III) luminescence of 1 caused by DPA and LFX is expressed by fitting equation I615nm = k × [C] + a, which can be used to quantitatively detect DPA and LFX concentrations in CH3CN, fetal calf serum (FCS), and a real drug. The response times of 1 to DPA and LFX are less than ten seconds, with detection limits as low as 3.78 × 10-2 to 2.71 nM. The test strips containing 1, as well as 1@SA films, can be used to qualitatively detect DPA and LFX by the color changes under the irradiation of UV light.

Double-emitting lanthanide metal-organic frameworks composed of Eu/Tb doping and ratiometric fluorescence detection of nitrofurazone

Lanthanide metal-organic frameworks (LnMOFs) have substantial potential in luminescence due to their unique antenna effect. Nevertheless, the single emission is susceptible to pseudo-signals caused by external environmental conditions, which significantly threaten the accurate measurement of the concentration. In this case, we prepared a dual-emission fluorescent probe {EuxTb1-x(NH2-BDC)3(DMF)4·2DMF}∞ (NH2-BDC = Diaminoterephthalic acid, DMF = N,N-dimethylformamide). The stable dual-emission signal provides a superior signal output for detecting nitrofurazone (NFZ), which is detected by the probe with excellent fluorescence for 0-10 μM NFZ. In the investigation of the detection mechanism, it is speculated that NFZ incorporates with probe to generate a novel complex. Furthermore, The UV absorption curves of the novel complexes and NFZ overlap extensively with those of the probe. The addition of NFZ attenuates the characteristic luminescence of Eu and Tb by competing for the absorption of the excitation light of the probe. The probe has exhibits rapid response, excellent sensitivity, visual detection and a meagre detection limit (LOD = 0.013 μM) for the detection of NFZ. This work not only broadens the application of LnMOFs in the field of ratiometric detection but also provides a favorable fluorescent probe for the quantitative detection of NFZ.

Highly efficient and stable catalysts-covalent organic framework-supported palladium particles for 4-nitrophenol catalytic hydrogenation

A covalent organic framework (COF) was used as the support of the catalyst in this work in order to obtain an environmentally friendly catalyst with high catalytic performance, selectivity and stability for 4-nitrophenol hydrogenation. Pd tiny particles are fixed in the cavity of COF to obtain Pd/COF catalysts, which has a quite narrow particle size distribution (5.09 ± 1.30 nm). As-prepared Pd/COF catalysts (Pd loading-2.11 wt%) shows excellent catalytic performance (conversion - 99.3%, selectivity >99.0% and turnover frequency (TOF)-989.4 h^-1) for 4-nitrophenol hydrogenation under relatively mild reaction conditions of reaction temperature-40 °C and reaction pressure-3.0 MPa H₂, and Pd/COF catalysts have high stability. Pd/COF catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope energy-dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscope (TEM), high resolution TEM (HRTEM), Brunauer-Emmett-Teller (BET), scanning TEM energy-dispersive X-ray spectroscopy (STEM-EDS) elemental analysis techniques to prove that the Pd nanoparticles are highly dispersed on the COF. Pd/COF catalysts have good stability and reusability hence with certain industrial application value.

Metalated covalent organic frameworks: from synthetic strategies to diverse applications

Covalent organic frameworks (COFs) are a class of organic crystalline porous materials discovered in the early 21st century that have become an attractive class of emerging materials due to their high crystallinity, intrinsic porosity, structural regularity, diverse functionality, design flexibility, and outstanding stability. However, many chemical and physical properties strongly depend on the presence of metal ions in materials for advanced applications, but metal-free COFs do not have these properties and are therefore excluded from such applications. Metalated COFs formed by combining COFs with metal ions, while retaining the advantages of COFs, have additional intriguing properties and applications, and have attracted considerable attention over the past decade. This review presents all aspects of metalated COFs, from synthetic strategies to various applications, in the hope of promoting the continued development of this young field.

The postsynthetic renaissance of luminescent lanthanide ions on crystalline porous organic framework materials

A series of crystalline porous organic framework materials (CPOFs), such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and hydrogen bonded organic frameworks (HOFs) have received extensive attentions due to...