Highly sensitive benzothiazole-based chemosensors for detection and bioimaging of peroxynitrite in living cells.

It is well accepted that peroxynitrite (ONOO-) plays a crucial role in various physiological and pathological processes. Thus, the detection and imaging of ONOO- in vitro and in vivo with high selectivity and sensitivity is of great significance. Here we report two simple benzothiazole-based fluorescent chemosensors, BS1 and BS2. Under physiological pH, both probes could quickly sense ONOO- with a remarkable "turn-on" fluorescence signal at 430 nm. The limit of detection (LOD) of BS1 and BS2 toward ONOO- was 12.8 nM and 25.2 nM, respectively, much lower than the reported values. Experimental results indicated that BS1 with a diphenyl phosphonate unit presented higher selectivity for ONOO- than BS2. Furthermore, based on the advantages of lower cytotoxicity and pH-stabilities of BS1, probe BS1 was successfully employed to detect and image ONOO- in HepG2 cells. More importantly, we used BS1 to successfully showcase drug-induced hepatotoxicity via imaging ONOO- upregulated by acetaminophen (APAP), and also evaluated the remediation effect of GSH. All the results illustrated that the fluorescent probe BS1 has great potential for the detection of ONOO- and to further uncover the roles of ONOO- during the drug-induced liver injury (DILI) process.

Enhanced Mechanical Stability and Proton Conductivity Performance from the Dense Mn(II)-Metal-Organic Framework to Porous Mn(II)-Fe(III)-Metal-Organic Framework.

Postsynthetic modification (PSM) of the metal-organic framework (MOF) has been demonstrated to be an effective strategy to enhance performance. In this particular work, the anion framework Mn-MOF {[Mn3O(H2O)3(HTC)]2-} (HTC6- = (5'-(3,5-dicarboxyphenyl)-[1,1':3',1″-terphenyl]-3,3″,5,5″-tetracarboxylate] was obtained, and NH2(CH3)2+ ions were filled within the pores to balance the charge. In order to release the internal pores of Mn-MOF, the trivalent Fe(III) was introduced instead of Mn(II) nodes, resulting in the porous Mn1-xFex-MOF, and the NH2(CH3)2+ ions were simultaneously deported from the pores. The content of Fe(III) in Mn1-xFex-MOF was highly dependent on the concentration of Fe(III) solution, and the maximum could be up to Mn0.05Fe0.95-MOF with a BET surface area of 1209.457 m2 g-1. Compared to the amorphization of dense Mn-MOF at 0.8 GPa in a diamond anvil cell, the mechanical stability of porous Mn0.05Fe0.95-MOF has been dramatically enhanced, and the framework integrity could be maintained up to 16.5 GPa. The proton conductivity for the Mn1-xFex-MOF series was also investigated, where Mn0.93Fe0.07-MOF showed the best performance of 1.47 × 10-2 S cm-1 under 70 °C and 98% RH due to the onset of reversed charge from the anionic framework to cationic framework and the formation of the most compact hydrogen bonding net. This work has not only provided an example for the PSM strategy but also illustrated that the versatile functionalities of MOF materials were mainly ascribed to the tunable porosity.

Ultrathin 2D Eu3+@Zn-MOF Nanosheets: A Functional Nanoplatform for Highly Selective, Sensitive, and Visualized Detection of Organochlorine Pesticides in a Water Environment.

Facile and rapid detection of residual organic pesticides on the fruits and vegetables has recently drawn increased attention in the food safety field. Herein, a surfactant-assisted solvothermal route with subsequent post-modification was designed for the preparation of Eu3+-functionated Zn-BDC ultrathin nanosheets (labeled as Eu3+@Zn-MOF-NS, BDC: 1,4-benzenedicarboxylate) with the thickness of 5 nm. The as-obtained Eu3+@Zn-MOF-NS could be homogeneously dispersed in aqueous systems to form a highly-stable collosol. Under the UV excitation of 325 nm, the as-obtained Eu3+@Zn-MOF-NS displayed red photoluminescence emission of Eu3+ ions, which could be notably quenched by an organochlorine pesticide, 2,6-dichloro-4-nitroaniline (DCNA), without interferences from ions, organic small molecules, and other pesticides. The detection limit and Ksv were 0.17 µM (35 ppb) and 3.2 × 105 M-1 in the water system, respectively. Moreover, the present 2D Eu3+@Zn-MOF sensor was also employed for the detection of DCNA in Chaohu Lake water and tap water and in apple, cabbage, and pakchoi samples with the relative standard deviation (RSD) ranging from 4.74 to 9.77%. Further investigations revealed that the competitive absorption between DCNA and the as-obtained Eu3+@Zn-MOF-NS resulted in the fluorescence quenching of the probe.

Rhodamine-based chemosensor for Sn2+ detection and its application in nanofibrous film and bioimaging.

A simple rhodamine-based compound CK was designed and synthesized as a fluorescent chemosensor for Sn2+ based on Sn2+-mediated cyclization. The optical investigation indicated that the probe could quantitatively detect Sn2+ in a concentration range of 10-30 µM, with a detection limit of 118 nM. Moreover, probe CK, with low cytotoxicity, was successfully applied for imaging of Sn2+ in HeLa cells and mice, exhibiting excellent biocompatibility and cell membrane permeability. For on-site monitoring, CK-hybridized polymethyl methacrylate (PMMA) nanofibers were prepared by electrospinning and successfully employed for the visual detection of Sn2+ in actual samples. All the results demonstrated that the chemosensor could be a promising tool for the detection of Sn2+ in vitro and in vivo.

Polyvinylpyrrolidone-assisted synthesis of highly water-stable cadmium-based metal-organic framework nanosheets for the detection of metronidazole.

Recently, much effort has been dedicated to ultra-thin two-dimensional metal-organic framework (2D MOF) nanosheets due to their outstanding properties, such as ultra-thin morphology, large specific surface area, abundant modifiable active sites, etc. However, the preparation of high-quality 2D MOF nanosheets in good yields still remains a huge challenge. Herein, we report 2D cadmium-based metal-organic framework (Cd-MOF) nanosheets prepared in a one-pot polyvinylpyrrolidone (PVP)-assisted synthesis method with high yield. The Cd-MOF nanosheets were characterized with good stability and dispersion in aqueous systems, and were highly selective and sensitive to the antibiotic metronidazole (MNZ) with low limit of detection (LOD: 0.10 µM), thus providing a new and promising fluorescent sensor for rapid detection of MNZ in aqueous solution.

Highly water-stable Cd-MOF/Tb3+ ultrathin fluorescence nanosheets for ultrasensitive and selective detection of Cefixime.

Two-dimensional Cd-MOF/Tb3+ (Cd-MOF = [Cd (µ-2,3-pdc) (H2O)3]n (2,3-pdc = 2,3-pyridine dicarboxylic acid)) fluorescent nanosheets with the thickness of 1.4 nm were successfully synthesized by a simple solution route with subsequent ultrasonic exfoliation at room temperature. It was found that as-obtained Cd-MOF/Tb3+ ultrathin nanosheets could be homogeneously dispersed in aqueous system to form a sol with excellent stability. Also, the fluorescence intensity of nanosheets remarkably increased to almost 12 times higher than that of Cd-MOF/Tb3+ microsheets before exfoliation. Further investigations uncovered that the above strong fluorescence of Cd-MOF/Tb3+ nanosheets could be highly sensitively quenched by Cefixime antibiotic in aqueous solution without interference from other antibiotics, amino acids and pesticides. Hence, the as-obtained ultrathin Cd-MOF/Tb3+ nanosheets could be prepared as a highly selective and sensitive fluorescence probe for the detection of Cefixime in aqueous system. Compared with the bulk Cd-MOF/Tb3+ sensor, the Cd-MOF/Tb3+ ultrathin nanosheets sensor exhibited a far lower detection limit down to 26.7 nM for CFX. Also, the as-obtained nanosheets sensor presented satisfactory recovery ranging from 98.07% to 103.01% and acceptable repeatability (RSD < 6.29%, n = 6) for the detection of CFX in domestic water. Furthermore, the sensing mechanism studies revealed that the high selection of the present fluorescent probe for detection of CFX should be attributed to the cooperation of the photoinduced electron transfer and the inner filter effect.

Fe-Doped Co-Mo-S microtube: a highly efficient bifunctional electrocatalyst for overall water splitting in alkaline solution.

Fe-Doped Co-Mo-S microtubes were successfully synthesized through a multistep synthetic route, employing MoO3 microrods as the sacrificial template, Co(NO3)2·6H2O and Fe(SO4)2·7H2O as the metal sources, 2-methylimidazole (2-MI) as the ligand and thioacetamide (TAA) as the S2- ion source. The as-prepared products were characterized by X-ray powder diffraction (XRD), energy dispersive spectrometry (EDS), inductively coupled plasma mass spectrometry (ICP-MS), X-ray photoelectron spectroscopy (XPS), (high-resolution) transmission electron microscopy (TEM/HRTEM) and HAADF-STEM-EDS elemental mapping. Experiments showed that the as-obtained Fe-doped Co-Mo-S microtube catalyst demanded overpotentials of ∼105 and 268 mV to afford the current density of -10 mA cm-2 for hydrogen evolution reaction (HER) and 10 mA cm-2 for oxygen evolution reaction (OER) with a durability of 60 h in 1.0 M KOH solution, respectively. In a two-electrode water-splitting device, the as-prepared Fe-doped Co-Mo-S microtubes acted as both anode and cathode simultaneously. To deliver a current density of 10 mA cm-2, a cell voltage of 1.605 V was required in 1.0 M KOH solution. After continuously catalyzing the overall water splitting for 60 h, the overpotential hardly changed, implying remarkable long-term stability. Obviously, the present Fe-doped Co-Mo-S microtubes have potential applications as bifunctional catalysts for electrochemical water splitting.

A novel Zn(II)-based metal-organic framework as a high selective and sensitive sensor for fluorescent detections of aromatic nitrophenols and antibiotic metronidazole.

A novel fluorescent Zn(II)-based metal-organic framework (Zn-MOF), [Zn2(oba)4(4,4'-bpy)2]n, was successfully synthesized through a simple solvothermal route at 130 °C for 48 h, employing Zn(NO3)2·6H2O, 4,4'-Oxybis(benzoic acid) (oba) and 4,4'-Bipyridine (4,4'-bpy) as the initial reactants, dimethylacetamide (DMA) as the reaction medium. The as-obtained Zn-MOF was characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectrum (FTIR), Thermogravimetric analysis (TGA) and elemental analysis. The fluorescence tests showed that the as-obtained Zn-MOF emit a strong violet light centered at 445 nm under the excitation of 323 nm UV light. Intriguingly, the above strong violet emission could be highly selectively quenched by aromatic nitrophenols or antibiotic metronidazole (MET) in aqueous systems with fairly low detection limits. Other substituted phenols and antibiotics, as well as some cations, anions, amino acids and small organic molecules hardly affected the violet emission of the as-obtained Zn-MOF, indicating that this novel Zn-MOF could be prepared as a selective fluorescent probe for detections of aromatic nitrophenols and MET antibiotic in water solutions.

Cobalt-Based MOF-on-MOF Two-Dimensional Heterojunction Nanostructures for Enhanced Oxygen Evolution Reaction Electrocatalytic Activity.

Two-dimensional (2D) Co-based MOF-on-MOF heterojunction nanostructures with improved electrocatalytic activity were successfully constructed via a mild two-step solution route, employing Co2+ ions as the center atoms, and 1,4-benzenedicarboxylate (BDC) and 4,4'-biphenyldicarboxylate (BPDC) as ligands. The as-obtained heterojunction nanostructures were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) technologies. Electrochemical measurements showed that as-prepared Co-BPDC/Co-BDC heterojunction nanostructures presented markedly enhanced OER electrocatalytic activity, compared with single Co-BPDC, Co-BDC, and/or their physical mixture. Also, the Co-BPDC/Co-BDC-3 heterojunction prepared after treatment for 3 h exhibited the strongest catalytic activity. To reach the current density jgeo = 10 mA cm-2, the Co-BPDC/Co-BDC-3 heterojunction-modified glassy carbon electrode required an overpotential of 335 mV in 1 M KOH, which was reduced by 57 and 93 mV, compared to the electrodes modified by Co-BDC and Co-BPDC, respectively. Simultaneously, the heterojunction catalyst also displayed better long-term stability. The improvement of the above performances should be attributed to the increased structure stability, BET surface area, ECSA, and electron transfer ability of the heterojunction.

Fixation of CO2 by electrocatalytic reduction and electropolymerization in ionic liquid-H2O solution.

The electrocatalytic synthesis of low-density polyethylene (LDPE) from carbon dioxide on a nanostructured (ns)TiO2 film electrode was investigated by controlled potential electrolysis in a solvent mixture of water and the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMI]BF4) at room temperature under ambient pressure. Under these conditions, the nsTiO2 film is remarkably efficient and selective for the electroreduction of CO2. The current efficiency for the formation of the electrolytic product is about 8-14% at -1.50 V (vs SCE). The electrocatalytic activity of the electrode in the electrochemical reduction of CO2 was investigated by cyclic voltammetry (CV), and the probable electrode reaction mechanism is discussed.