Optimization of the tandem enzyme activity of V-MOF and its derivatives for highly sensitive nonenzymatic detection of cholesterol in living cells.

It remains a great challenge to properly design and synthesize single-component artificial tandem enzymes for specific substrates with high selectivity. Herein, V-MOF is synthesized by solvothermal method and its derivatives are constructed via pyrolyzing V-MOF in nitrogen atmosphere at different temperatures, which are denoted as V-MOF-y (y = 300, 400, 500, 700 and 800). V-MOF and V-MOF-y possess tandem enzyme-like activity, i.e. cholesterol oxidase-like and peroxidase-like activity. Among them, V-MOF-700 shows the strongest tandem enzyme activity for V-N bonds. Based on the cascade enzyme activity of V-MOF-700, the nonenzymatic detection platform for cholesterol by fluorescent assay can be established in the presence of o-phenylenediamine (OPD) for the first time. The detection mechanism is that V-MOF-700 catalyzes cholesterol to generate hydrogen peroxide and further form hydroxyl radical (•OH), which can oxidize OPD to obtain oxidized OPD (oxOPD) with yellow fluorescence. The linear detection of cholesterol ranges of 2-70 µM and 70-160 µM with a lower detection limit of 0.38 µM (S/N = 3) are obtained. This method is used to detect cholesterol in human serum successfully. Especially, it can be applied to the rough quantification of membrane cholesterol in living tumor cells, indicating that it has the potential for clinical application.

Fe-Ni metal-organic frameworks with prominent peroxidase-like activity for the colorimetric detection of Sn2+ ions.

Fe-Ni-MOFs with different amounts of Fe are synthesized through a two-step template etching method. Kinetic analysis indicates that Fe-Ni-MOF exhibits prominent intrinsic peroxidase-like activity, which could catalytically oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to produce oxidized TMB (oxTMB) with a blue color. As a peroxidase-mimicking MOF, Fe-Ni-MOF with its efficient stable catalysis properties is demonstrated to allow a sensitive colorimetric assay for Sn2+ ions. The mechanism is explored, whereby Sn2+ ions could reduce the peroxidase-like activity of Fe-Ni-MOF based on a redox interaction, making the oxTMB color lighter and decreasing the absorbance intensity at 652 nm. The linear determination of the Sn2+ ion concentration using a UV-vis spectrometer ranges from 0.01 mM to 1.0 mM and from 1.0 mM to 4.0 mM. The presented Fe-Ni-MOF-based assay of Sn2+ ions was successfully applied to real water samples.

Highly active Ce, Y, La-modified Cu/SiO2 catalysts for hydrogenation of methyl acetate to ethanol.

Rare earth element (Ce, Y, and La) modified Cu/SiO2 catalysts via hydrolysis precipitation and impregnation method were fabricated for the vapor-phase hydrogenation of methyl acetate to ethanol. LaO x showed the most pronounced promotion in the catalytic tests. After detailed characterizations, via N2 adsorption-desorption, XRD, N2O chemisorption, FTIR, H2-TPR, H2-TPD, TEM, XPS, and TG/DTA, we found that the addition of promoter LaO x can decrease the particle size while in turn, it can increase the dispersion of copper species. The strong interactions between copper and lanthanum atoms alter the surface chemical states of the copper species. This results in the generation of more Cu+ species and high S Cu + values, which are responsible for the excellent activity and stability during hydrogenation. In addition, the content of additive LaO x and reaction conditions (reaction temperature and LHSV) were optimized. Then, the long-term stability performance was evaluated over the selected catalyst in contrast with Cu/SiO2.

Trapping of Polysulfides with Sulfur-Rich Poly Ionic Liquid Cathode Materials for Ultralong-Life Lithium-Sulfur Batteries.

Sulfur-rich polymers synthesized by inverse vulcanization are promising cathodes for Li-S batteries and can suppress the shuttle effect to improve the cycling properties of Li-S batteries. However, developing a sulfur-rich copolymer with new chemical functionality to enhance performance of Li-S batteries remains a huge challenge. In this report, a sulfur-rich polymer cathode containing ionic liquid segments named poly(sulfur-co-1-vinyl-3-allylimidazolium bromide) [poly(S-co-DVIMBr)] was obtained by the inverse vulcanization of S8 with DVIMBr and used as cathode for the first time. This sulfur-rich poly ionic liquid cathode showed effective suppression of the shuttle effect through joint effects of the stable chemical bonding of C-S and strong cation absorption for lithium polysulfides, which was confirmed by DFT calculations. In particular, the Li-S cell with poly(S-co-DVIMBr) cathode delivered high capacity retention of 90.22 % even over 900 cycles. Developing sulfur-rich poly ionic liquids may provide a new strategy of introducing the functional groups with cations into the cathode materials for suppressing the shuttle effect and improving the performance of Li-S batteries.

Confining Hyperbranched Star Poly(ethylene oxide)-Based Polymer into a 3D Interpenetrating Network for a High-Performance All-Solid-State Polymer Electrolyte.

The original poly(ethylene oxide)-based polymer electrolytes normally show low ionic conductivity and inferior mechanical property, which greatly restrict their practical application in all-solid-state lithium-ion batteries (LIBs). In this work, a hyperbranched star polymer with poly(ethylene glycol) methyl ether methacrylate flexible chain segments is embedded into a three-dimensional (3D) interpenetrating cross-linking network created by the rapid one-step UV-derived photopolymerization of the cross-linker (ethoxylated trimethylolpropane triacrylate) in the presence of lithium salt. The rigid 3D network framework provides the polymer electrolyte with not only enhanced mechanical behavior, including film-forming and dendrite-inhibiting capabilities, but also nanoconfinement effects, which can speed up polymer chain segmental dynamics and reduce the crystallinity of the polymer. Depending on this unique rigid-flexible coupling network, the prepared solid polymer electrolyte shows enhanced ionic conductivity (6.8 × 10-5 S cm-1 at 50 °C), widened electrochemical stability window (5.1 V vs Li/Li+), and enough mechanical stability to suppress the growth of uneven Li dendrite (the Li symmetrical cells can operate steadily at both current densities of 0.05 and 0.1 mA cm-2 for 1000 h). Moreover, the assembled LiFePO4//Li cell also exhibited good cycle performance at 50 °C, making the hyperbranched star polymer electrolyte with a nanoconfined cross-linking structure to have potential application in high-safety and high-performance LIBs.

Nitrogen-doped carbon dots-V2O5 nanobelts sensing platform for sensitive detection of ascorbic acid and alkaline phosphatase activity.

In this work, the as-prepared V2O5 nanobelts can sensitively quench the fluorescence of nitrogen-doped carbon dots (N-CDs) based on the inner filter effect (IFE). In the presence of ascorbic acid (AA), the fluorescence of N-CDs can recover through the redox reaction between V2O5 nanobelts and AA. Meanwhile, in the presence of both alkaline phosphatase (ALP) and ascorbyl-2-phosphate (AAP), the fluorescence of N-CDs can also restore since AAP can be hydrolyzed into AA by ALP. Under optimum conditions, the linear range for AA is from 0.01 to 2.5 µM with a detection limit of 3 nM and that for ALP is from 0.1 to 30 U/L with a detection limit of 0.04 U/L (S/N = 3). Particularly, the proposed probe could be successfully used to detect AA and ALP in human serum samples. Furthermore, N-CDs can be applied in fluorescence imaging of Human breast cancer cells with satisfactory results.

A novel anodic electrochemiluminescence behavior of sulfur-doped carbon nitride nanosheets in the presence of nitrogen-doped carbon dots and its application for detecting folic acid.

The application of carbon dots as a coreactant for Ru(bpy)32+ (where bpy is 2,2'-bipyridine) electrochemiluminescence (ECL) has been widely studied. However, the high cost of Ru(bpy)32+ and its derivatives has prohibited its widespread use in ECL biosensors. Herein, a novel anodic ECL system based on sulfur-doped graphitic carbon nitride nanosheets (S-g-C3N4 NSs) and nitrogen-doped carbon dots (N-CDs) is presented. In this ECL system, N-CDs serve as a new ECL coreactant that can significantly enhance the anodic ECL signal of S-g-C3N4 NSs (approximately 83 times) under optimal conditions. The possible ECL response mechanism of the S-g-C3N4 NSs/N-CDs system is proposed in detail on the basis of cyclic voltammograms, ECL-time curves, and ECL spectra. Furthermore, the ECL signal of the S-g-C3N4 NSs/N-CDs system was quenched by folic acid (FA), which was chosen as a model analyte to study the potential application of the new ECL system. The ECL intensity decreased linearly with the concentration of FA in the range from 0.05 to 200 µM. The detection limit for FA measurement is 16 nM (signal-to-noise ratio of 3). The proposed new ECL system has many advantages over traditional approaches, such as low toxicity and excellent biocompatibility. Especially, the proposed approach can detect FA in diluted human serum samples with satisfactory recoveries, indicating promising application for bioanalysis. Graphical abstract.

Nitrogen doped carbon dots for turn-off fluorescent detection of alkaline phosphatase activity based on inner filter effect.

The abnormal expression level of alkaline phosphatase (ALP) will lead to serious diseases. Therefore, a sensitive and rapid assay for ALP activity monitoring is of vital importance. In this work, a fluorescence turn-off approach for the detection of ALP is designed on the basis of nitrogen doped carbon dots (N-CDs), which were synthesized by one-step hydrothermal method and applied as signal readout. p-Nitrophenylphosphate (PNPP) can be hydrolyzed into p-nitrophenol (PNP) by ALP and their absorption peaks are different under alkaline conditions, so it was chosen as the ALP substrate. The absorption spectrum of PNP has good overlap with the excitation and emission spectra of N-CDs, thus the fluorescence of N-CDs can be effectively quenched by PNP via the inner filter effect (IFE). Consequently, quantitative detection of ALP is realized because the relative fluorescence intensity is linearly with the ALP activity in a wide range from 0.05 to 40 U L-1. The detection limit is 0.02 U L-1 (S/N = 3), which is much lower than the normal level of serum ALP in adults (about 40-190 U L-1). Moreover, the assay was successfully applied to evaluate ALP inhibitor efficiency and screen ALP inhibitors in drug discovery. It is also demonstrated that N-CDs possesses low cytotoxicity, excellent biocompatibility and photostability, and can be successfully applied in vivo fluorescence imaging, showing great potential in clinical applications.

Nitrogen-doped-carbon-coated hexagonal cobalt oxyhydroxide/reduced graphene oxide nanocomposite for sensitive and selective detection of nitrite in human hepatoma cells.

Selective and sensitive determination of nitrite is of great importance in practical application. In the present work, a novel nitrite sensing platform was built based on the fabrication of nitrogen-doped-carbon-coated hexagonal cobalt oxyhydroxide (CN@CoOOH) on reduced graphene oxide (RGO) using zeolitic imidazolate framework (ZIF)-67 as a precursor. The CN@CoOOH/RGO nanocomposite was confirmed by UV-visible spectroscopy, Fourier transform infrared spectroscopy, x-ray photoelectron spectrum, transmission electron microscopy, scanning electron microscopy, and x-ray diffraction. We applied the nanocomposite to detect nitrite selectively and sensitively through amperometry for the first time. The anodic current values increased with the addition of nitrite. Therefore, the concentrations of nitrite were quantitatively detected using a CN@CoOOH/RGO based sensor. A wider linear range of 0.1 to 7000 µM was obtained with a lower detection limit of 10 nM (S/N = 3). The proposed method was also applied to detect nitrite released from normal liver cells and human hepatoma cells.

In situ sulfur-doped graphitic carbon nitride nanosheets with enhanced electrogenerated chemiluminescence used for sensitive and selective sensing of l-cysteine.

In this study, in situ sulfur-doped carbon nitride nanosheets (S-g-C3N4 NSs) are used as the signal readout for the sensitive and selective sensing of l-cysteine (l-Cys) in human serum samples based on the competitive coordination chemistry of Cu2+ between l-Cys and S-g-C3N4 NSs. S-g-C3N4 NSs are prepared by using trithiocyanuric acid as a precursor for the first time, which exhibits stronger electrogenerated chemiluminescence (ECL) intensity compared with pristine graphitic carbon nitride nanosheets (g-C3N4 NSs). The ECL signals of the S-g-C3N4 NSs can be quenched by Cu2+ and the subsequent presence of l-Cys can recover the ECL signals of the S-g-C3N4 NSs. These changes are ascribed to the higher coordination ability between Cu2+ and l-Cys than that between Cu2+ and the S-g-C3N4 NSs. On the basis of this, the concentration of l-Cys can be quantitatively determined. Under optimized conditions, the ECL intensity recovery shows a linear relationship with the l-Cys concentration range from 30 nM to 0.2 mM with a lower detection limit of 5 nM (S/N = 3). The proposed method is highly sensitive and selective and is thus particularly useful for fast and simple clinical diagnosis of diseases, such as Alzheimer's disease and cardiovascular disease.

Hexagonal cobalt oxyhydroxide nanoflakes/reduced graphene oxide for hydrogen peroxide detection in biological samples.

Abnormal concentration of hydrogen peroxide (H2O2) in blood plasma and cells may lead to several diseases. Thus, it is important to develop a selective and sensitive method to monitor H2O2. In the present work, a novel nonenzymatic H2O2-sensing platform based on cobalt oxyhydroxide (CoOOH)/reduced graphene oxide (RGO) nanocomposite was fabricated. CoOOH nanoflakes were firstly synthesized via soft chemistry routes and then assembled on the surface of RGO. A series of characterizations by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy demonstrated that hexagonal CoOOH nanoflakes were well distributed on the surface of RGO. The nanocomposite exhibited excellent electrochemical performance for H2O2 detection. Two linear ranges of 6-200 µM and 200-1500 µM were obtained, and the detection limit was 0.01 µM (signal-to-noise ratio was 3). The good performance was attributed to more exposed catalytic active sites of CoOOH nanoflakes compared with zero-dimensional nanoparticles and outstanding conductivity of RGO as well as their synergistic effect. Moreover, the nanocomposite was used to detect H2O2 from human serum and HeLa cells with satisfactory results. Graphical abstract ᅟ.

A highly sensitive and selective detection of Cr(VI) and ascorbic acid based on nitrogen-doped carbon dots.

A highly sensitive and selective detection of hexavalent chromium (Cr(VI)) and ascorbic acid (AA) was proposed using nitrogen-doped carbon dots (N-CDs). In the absence of AA, the quantitative detection of Cr(VI) was realized through Cr(VI) acting as a quencher to quench the fluorescence of N-CDs by inner filter effect (IFE) and static quenching effect. Under the optimal conditions, the linear range for Cr(VI) detection was from 0.01 to 250µM with a detection limit of 5nM (S/N = 3). In the presence of AA, the fluorescence intensity could be rapidly enhanced compared with the fluorescence of N-CDs/Cr(VI) system since Cr(VI) can be reduced into trivalent chromium (Cr(III)) by AA. And a wide linear range for AA detection was obtained from 1 to 750µM. The detection limit was 0.3µM (S/N = 3). More importantly, this method can be successfully applied to the detection of Cr(VI) in real water samples, and AA in vitamins C tablets and human serum sample.

Polymer dots grafted TiO2 nanohybrids as high performance visible light photocatalysts.

As a new member of carbon dots (CDs), Polymer dots (PDs) prepared by hydrothermal treatment of polymers, usually consist of the carbon core and the connected partially degraded polymer chains. This type of CDs might possess aqueous solubility, non-toxicity, excellent stability against photo-bleaching and high visible light activity. In this research, PDs were prepared by a moderate hydrothermal treatment of polyvinyl alcohol, and PDs grafted TiO2 (PDs-TiO2) nanohybrids with TiOC bonds were prepared by a facile in-situ hydrothermal treatment of PDs and Ti (SO4)2. Under visible light irradiation, the PDs-TiO2 demonstrate excellent photocatalytic activity for methyl orange degradation, and the photocatalytic rate constant of PDs-TiO2 is 3.6 and 9.5 times higher than that of pure TiO2 and commercial P25, respectively. In addition, the PDs-TiO2 exhibit good recycle stability under UV-Vis light irradiation. The interfacial TiOC bonds and the π-conjugated structures in PDs-TiO2 can act as the pathways to quickly transfer the excited electrons between PDs and TiO2, therefore contribute to the excellent photocatalytic activity.

Dual signal amplification strategy of Au nanopaticles/ZnO nanorods hybridized reduced graphene nanosheet and multienzyme functionalized Au@ZnO composites for ultrasensitive electrochemical detection of tumor biomarker.

Herein, a dual signal amplification strategy was employed in fabricating ultrasensitive electrochemical immunosensor for alpha fetoprotein (AFP) detection, which was realized by utilizing of ZnO nanorods/Au nanopaticles hybridized reduced graphene nanosheet (Au/ZnO/RGO) and horseradish-peroxidase (HRP) bioconjugated detection antibody (Ab2) functionalized Au@ZnO (Ab2/HRP-Au@ZnO). During the fabrication of the immunosensor, a new kind of multiple-head surfactants CxN3 with different alkyl chain length played important roles such as acting as the surfactants of Au/ZnO/RGO and the reductant agents of Au@ZnO composite. Due to the good adsorption property and large surface area of Au/ZnO/RGO, plenty of the capture antibodies (Ab1) were immobilized on the electrode surface, and trace AFP was sensitively monitored. Furthermore, Ab2/HRP-Au@ZnO exhibited high affinity interaction with AFP through "sandwich" immunoreactions, along with the peroxidase-like catalytic activity of Au@ZnO, leading to a further enhancement in the sensitivity of the proposed immunosensor. The successful synthesis of the nanomaterials was characterized through a serious of techniques including Raman, XRD, FT-IR, SEM and UV-vis. Under the optimal conditions, two linear ranges of 0.02-10,000 and 10,000-100,000pgmL-1 AFP with a lower detection limit of 0.01pg mL-1 (S/N=3) was obtained. Especially, the proposed AFP immunosensor can be applied to detect human serum samples with satisfactory results, indicating a potential application in clinical monitoring of tumor biomarkers.

Coagulation of chitin and cellulose from 1-ethyl-3-methylimidazolium acetate ionic-liquid solutions using carbon dioxide.

Chemisorption of carbon dioxide by 1-ethyl-3-methylimidazolium acetate ([C2 mim][OAc]) provides a route to coagulate chitin and cellulose from [C2 mim][OAc] solutions without the use of high-boiling antisolvents (e.g., water or ethanol). The use of CO2 chemisorption as an alternative coagulating process has the potential to provide an economical and energy-efficient method for recycling the ionic liquid.

N-Nitro-1H-pyrrole-2-carboxamide.

In the title compound, C(5)H(5)N(3)O(3), the nitro group is twisted with respect to the amide group, with C-N-N-O torsion angles of 29.0 (2) and -153.66 (14)°. In the crystal, mol-ecules are linked through inter-molecular N-H⋯O and C-H⋯O hydrogen bonds, forming supra-molecular chains along the a axis. These chains stack in parallel and form distinct layer motifs in the (001) plane.

Design of efficient zeolite sensor materials for n-hexane.

The effectiveness of several zeolite catalysts was investigated using the cataluminescence (CTL) gas sensor system. Trace amounts of n-hexane in air samples were detected by this method. This research establishes that the specific pore size of the zeolite offers designable environment for selective CTL reaction, and "Lewis-type" basic sites appear to contribute to the catalytic nature of the zeolite surface. By incorporating either Cs+ or K+, the velocity and luminescence intensity of these catalytic reactions increase while going from Na to Cs, according to the basic nature of this group of cations in the following order: Cs > K > Na. The proposed sensor shows high sensitivity and selectivity to n-hexane at a mild reaction temperature of 225 degrees C. Quantitative analysis was performed at a selected wavelength of 460 nm. The linear range of CTL intensity versus concentration of n-hexane was 0.776-23.28 microg/mL (R = 0.997, n = 7) on CsNaY, and 0.776-23.28 microg/mL (R = 0.998, n = 7) on CsNaX, with a detection limit of 0.155 microg/mL (signal-to-noise ratio 3). Interferences from foreign substances such as methanol, ethanol, 2-propanol, acetone, acetonitrile, chloroform, or dichlormethane and other alkanes, aromatics, and alkyl aromatics such as methane, n-pentane, 3-methylpentane, 3,3-dimethylpentane, methylbenzene, ethylbenzene, and sec-butylbenzene were very low or not detectable. Results of a series of GC and GC/MS experiments suggest that the possible mechanism of the reaction is the formation of an unstable transition structure with a four-member ring, and this ring most probably consists of an oxygen atom and a carbonium ion localized on the zeolite suface.