High performance liquid chromatography coupled to an optical fiber detector coated with laccase for screening catecholamines in plasma and urine

An analytical method based on separation by high performance liquid chromatography (HPLC) and detection by optical fiber (OF) coated with an enzyme (laccase), has been developed for separation and quantification of catecholamines, namely epinephrine, dopamine and norepinephrine. The application of OF as a detector in this analytical system relies on the variation of the reflected optical power detected when the catecholamines eluted from the HPLC column act as the substrate of the laccase immobilized on a tip of a single-mode OF. The developed method shows a high linearity in a range between 5 and 125 pg/mL and detection limits of 3.5, 2.9 and 3.3 pg/mL for epinephrine, dopamine and norepinephrine, respectively. The analytical performance of the proposed method was compared with a classical analytical method, namely high performance liquid chromatography-electrochemical detector (HPLC-ED) regarding catecholamines detection, showing great analytical advantages such as low cost of equipment. Additionally, the proposed method was applied to catecholamines determination in actual samples of plasma and human urine.     

High-performance,synergistically catalytic luminescent nanozyme for the degradation and detection of endocrine-disrupting chemical diethylstilbestrol

A synergistically catalytic luminescent nanozyme was designed and synthesized for the degradation and enzymatic fluorescence detection of diethylstilbestrol, an endocrine-disrupting environmental pollutant. Because of the integration of cocatalytic Cu²⁺ ion and CeO₂ particle, luminescent Tb³⁺ ion, and functional ligand dipicolinic acid through flexible metal-organic framework structure, this nanozyme has not only the dual functions of luminescence and multienzyme such as laccase and horseradish peroxidase but also synergistically catalytic effect via a regeneration of Cu²⁺ oxidized by CeO₂. The synergistically catalytic effect of nanozyme greatly enhances the degradation of diethylstilbestrol. The resultants sensitized the luminescence of Tb³⁺ ions, which was used to sense the pM level of diethylstilbestrol in environmental samples. Such a high-performance catalytic luminescent nanozyme can be used to replace natural enzymes for the enzyme-based degradations and ultrasensitive assays. The strategy of constructing artificial enzymes directly from functional units provides a new way for developing fit-for-purpose multifunctional artificial enzymes.     

Graphene Quantum Dots‐based Electrochemical Biosensor for Catecholamine Neurotransmitters Detection

An useful electrochemical sensing approach was developed for epinephrine (EP) detection based on graphene quantum dots (GQDs) and laccase modified glassy carbon electrodes (GC). The miniature GC biosensor was designed and constructed via the immobilization of laccase in an electroactive layer of the electrode coated with carbon nanoparticles. This sensing arrangement utilized the catalytic oxidation of EP to epinephrine quinone. The detection process was based on the oxidation of catecholamine in the presence of the enzyme – laccase. With the optimized conditions, the analytical performance demonstrated a high degree of sensitivity −2.9 μA mM⁻¹ cm⁻², selectivity in a broad linear range (1–120×10⁻⁶ M) with detection limit of 83 nM. Moreover, the method was successfully applied for EP determination in labeled pharmacological samples.     

Dual-active-site Fe/Cu single-atom nanozymes with multifunctional specific peroxidase-like properties for S2− detection and dye degradation

Designing single-atom nanozymes with densely exposed metal atom active sites and enhancing catalytic activity to detect pollutants remain a serious challenge. Herein, we reported a single-atom nanozyme with layered stacked Fe/Cu dual active sites (Fe/Cu-NC SAzyme) synthesized via hydrothermal and high-temperature pyrolysis using folic acid as a template. Compared with Fe-NC and Cu-NC SAzyme, Fe/Cu-NC SAzyme has higher peroxidase-like activity, which indicates that the doping of synthesized Fe/Cu bimetals can improve the catalytic activity and that the atomic loading of Fe and Cu in Fe/Cu-NC is 5.5 wt% and 2.27 wt%, respectively. When S²⁻ is added to the Fe/Cu-NC catalytic system, a high-sensitivity and high-selectivity S²⁻ colorimetric sensing platform can be established, with a wide linear range (0.09–6 µmol/L) and a low detection limit (30 nmol/L), which can be used to detect S²⁻ in environmental water samples. What's more, the Fe/Cu-NC SAzyme can activate peroxymonosulfate (PMS) to degrade 99.9% of rhodamine B (RhB) within 10 min with a degradation kinetics of 0.5943 min⁻¹. This work details attractive applications in Fe/Cu-NC SAzyme colorimetric sensing and dye degradation.     

Structure simulation into a lamellar supramolecular network and calculation of the metal ions/ligands ratio

Background

Biosensors have attracted increasing attention as reliable analytical instruments in in situ monitoring of public health and environmental pollution. For enzyme-based biosensors, the stabilization of enzymatic activity on the biological recognition element is of great importance. It is generally acknowledged that an effective immobilization technique is a key step to achieve the construction quality of biosensors.

Results

A novel disposable biosensor was constructed by immobilizing laccase (Lac) with silica spheres on the surface of multi-walled carbon nanotubes (MWCNTs)-doped screen-printed electrode (SPE). Then, it was characterized in morphology and electrochemical properties by scanning electron microscopy (SEM) and cyclic voltammetry (CV). The characterization results indicated that a high loading of Lac and a good electrocatalytic activity could be obtained, attributing to the porous structure, large specific area and good biocompatibility of silica spheres and MWCNTs. Furthermore, the electrochemical sensing properties of the constructed biosensor were investigated by choosing dopamine (DA) as the typical model of phenolic compounds. It was shown that the biosensor displays a good linearity in the range from 1.3 to 85.5 ??M with a detection limit of 0.42 ??M (S/N = 3), and the Michaelis-Menten constant (K_m ^app) was calculated to be 3.78 ??M.

Conclusion

The immobilization of Lac was successfully achieved with silica spheres to construct a disposable biosensor on the MWCNTs-doped SPE (MWCNTs/SPE). This biosensor could determine DA based on a non-oxidative mechanism in a rapid, selective and sensitive way. Besides, the developed biosensor could retain high enzymatic activity and possess good stability without cross-linking reagents. The proposed immobilization approach and the constructed biosensor offer a great potential for the fabrication of the enzyme-based biosensors and the analysis of phenolic compounds.     

Dual-signal immuno-competitive determination of brain natriuretic peptide based on magnetic nanozyme

Brain natriuretic peptide (BNP) has been a disease marker in the diagnosis of heart failure. In this study, gold nanoparticles modified with Hemin (H-AuNPs) as nanozymes were used to oxidize ABST and MB to amplified colorimetric and electrochemical redox signals respectively. BNP was combined with H-AuNPs (BNP-H-AuNPs) through electrostatic adsorption to construct competitive nanozyme probes. Target BNP in the sample compete with BNP-H-AuNPs to bind the antibody-modified magnetic nanoparticles (AntiBNP-MNPs). Due to the excellent catalytic performance of the nanozyme, BNP can be observed well by colorimetric and electrochemical assays. Electrochemical method ensured more accurate detection of BNP with a wide detection range (1–200 pg/mL) and a low detection of limit (0.03 pg/mL). Meanwhile, the results of the experiment can be easily observed with the naked eye by simple colorimetric method with a range from 5 ng/mL to 25 ng/mL and a limit of detection down to 80.3 pg/mL. Thus, based on the important role of H-AuNPs, this assay has exhibited potential value of detection the other small proteins through this competitive nanozyme method.     

锰-铜双金属层状硅酸盐纳米酶的构筑及类酶活性

采用一步溶胶凝胶法, 在室温下合成了一种含有锰、 铜的双金属层状硅酸盐(AMCP), 并探究了其类漆酶和类过氧化物酶活性. 结果表明, AMCP具有与天然黏土类似的层状结构, 且结构中多价态的锰和铜使其具有优异的类漆酶和类过氧化物酶活性. 此外, 与天然酶相比, AMCP在极端温度和pH值下具有更强的耐受性, 当温度高于70 ℃后, 天然酶完全失活, 而AMCP仍保留了80%以上的活性, 而在pH=3~9条件下AMCP依然保持90%左右的催化活性. 随后, 进一步探究了其类酶活性机理, 证实了锰、 铜之间的电子传导可加速活性位点中铜电对的循环, 从而促进活性氧的产生, 提高其类酶催化活性. 本研究为高效多酶活性纳米酶的构筑提供了参考, 也可为双金属层状硅酸盐在生物传感、 疾病诊疗及环境修复等领域的应用奠定了基础.     

Laccase-Catalyzed Oxidative Polymerization of Phenolic Compounds

Enzymatic polymerization of phenolic compounds (catechol, resorcinol, and hydroquinone) was carried out using laccase. The mechanism of polymerization and the structures of the polymers were evaluated in terms of UV–Vis and Fourier transform infrared spectroscopy. The molecular weights of the produced polyphenols were determined with GPC. The results showed that the phenolic monomers firstly turned into quinone intermediates by laccase catalysis. Through further oxidation, the intermediates formed covalent bonds. Finally, catechol units were linked together with ether bonds, and both resorcinol and hydroquinone units were linked together with C-C bonds. The number-average molecular weights of the polyphenols ranged from 1,000 to 1,400 Da (corresponding to the degree of polymerization that varied from 10 to 12) with a lower polydispersity value of about 1.10, showing selective polymerization of phenolic compounds catalyzed by laccase.     

Self-assembled nanozyme complexes with enhanced cascade activity and high stability for colorimetric detection of glucose

In this work, a hybrid multi-enzyme system, CeO₂/glucose oxidase (GOx) nanocomplex was developed via self-assembly and exhibited excellent catalytic activity toward cascade reactions, offering a simple and efficient example to build spatially confined multi-enzyme systems to potentiate their applications in energy conversion, detoxification and bioanalysis.     

3DRGO-NiFe2O4/NiO nanoparticles for fast and simple detection of organophosphorus pesticides

The residues of organophosphorus pesticide(OPs)on fruits and vegetables pose a threat to human health,so it is very meaningful to explore simple and fast detect methods for OPs residual.In this work,nickel ferrite/nickel oxide nanoparticles co-loaded three-dimensional reduced graphene oxide(3DRGONiFe2O4/NiO NPs),as a new low cost nanocomposite,was prepared.Based on its high performance mimetic peroxidase activity,a colorimetric method for the detection of OPs has been developed.Dichlorvos was chosen as model compounds to evaluate the detection performance.The detection linear range for dichlorvos is from 50μg/mL to 2.5×10^4μg/mL with a detection limit of 10μg/mL.Furthermore,a test paper can be developed based on the 3 DRGO-NiFe2O4/NiO NPs for visual detection of dichlorvos,and the image information of the paper sensor can be converted into digital signal and quantitative detection by a smartphone.Notably,this method can also be used to detect dichlorvos in real samples,including vegetables and fruits.Thus,the developed naked assay holds great potential in simple,inexpensive and rapid detection of OPs in fruit and vegetable samples.     

蛋黄-壳结构Fe3O4@SiO2@PMO磁性微球的制备及对漆酶的固定化

以蛋黄-壳结构的Fe₃O₄@SiO₂@PMO磁性微球作为载体, 采用交联法对漆酶进行固定, 考察了戊二醛浓度等对固定效果的影响, 并对固定后漆酶的活性进行了研究. 结果表明, 蛋黄-壳结构的磁性微球负载漆酶仅需6 h, 磁性微球对漆酶的固载量高达475 mg/g. 固定后漆酶的稳定性显著提高, 在pH=2.5~4.5的强酸性条件下, 固定后漆酶酶活仍可保持70%以上, 即使温度升高至60 ℃, 固定后漆酶的相对酶活仍保持65%以上. 这说明漆酶经所合成的材料固定后, 其耐酸和耐热能力都明显优于游离漆酶. 包覆的Fe₃O₄粒子使得材料很容易经磁铁分离法回收, 固定后漆酶经磁分离循环使用10次后仍然能保留85%的酶活, 具有良好的可操作性和稳定性, 有效降低了漆酶的使用成本.     

石墨炔在电化学储能器件中的应用

当今社会,电化学储能器件在人类的社会活动中变得越来越重要。电极材料作为电化学储能器件的核心部分,一直是人们研究的焦点。石墨炔是一种新型的二维平面结构的全碳材料,它宽的层间距、大的比表面积、独特的三维孔隙结构和好的导电性使其在能源存储器件电极材料应用中具有巨大的潜力。基于石墨炔温和的制备方法与独特的结构特征,本文详细介绍了近年来石墨炔在储能方面的理论分析和实验进展。通过研究锂/钠在单层、多层石墨炔上的迁移率和存储,理论分析石墨炔基电池具有很好的储锂储钠性能。实验方面,石墨炔作为电极材料在储钠储锂方面的容量与理论值相近。此外石墨炔作为电极材料成功应用于超级电容器和金属-硫电池,并表现出了优异的容量存储性能。石墨炔纳米形貌的调控、石墨炔的热处理,以及异原子的掺杂等均可以有效地提高石墨炔在这些储能器件中的性能。     

MnO2 nanozyme induced the chromogenic reactions of ABTS and TMB to visual detection of Fe2+ and Pb2+ ions in water

In this study, we used a simple and rapid colourimetric reaction for visual sensing of Fe²⁺ and Pb²⁺ ions in water by employing nano-MnO₂ as a natural oxidase mimic to respectively catalyse ABTS and TMB in citrate-phosphate buffer solution (C-PBS) at 25°C and pH 3.8. It was found that nano-MnO₂ possessed highly oxidase-mimicking activity with the K_m values of 0.030 and 0.027 toward ABTS and TMB, respectively, indicating TMB had a stronger affinity on nano-MnO₂ than ABTS. Interestingly, the presence of 0.01 mmol·L^?1 Fe²⁺/Pb²⁺ ion was able to significantly down-regulate the activity of MnO₂ nanozyme in nano-MnO₂-mediated ABTS reaction processes (P < 0.01), which mainly due to the strong adsorption of metal ion toward nano-MnO₂ surface via the electrostatic attractions, thus leading to the passivation and inactivation of MnO₂ nanozyme catalytic activity. Thereinto, Fe²⁺ reacted with multivalent manganese by oxidation-reduction, while Pb²⁺ was specifically adsorbed onto the surface of MnO₂ nanozyme and formed complexes. Notably, only Fe²⁺ ion inhibited the activity of MnO₂ nanozyme-TMB with a detection limit as low as 1.0 μmol·L^?1. In MnO₂ nanozyme-ABTS sensing systems, Fe²⁺ and Pb²⁺ ions detection limit of 0.5 and 2.0 μmol·L^?1 were, respectively, achieved with a linear response range of 0–0.02 and 0–0.8 mmol·L^?1, implying the developed MnO₂ nanozyme-ABTS sensor was potentially applicable for the visual determination of Fe²⁺ and Pb²⁺ ions in water. In the real water samples, MnO₂ nanozyme-ABTS achieved high accuracy (relative errors: 3.4?10.5%) and recovery (96?110%) for respective detection of Fe²⁺ and Pb²⁺ ions. The simple and rapid MnO₂ nanozyme-ABTS sensing systems might provide a practical assay for visual detection of Fe²⁺ and Pb²⁺ ions in the environmental water samples.     

Antioxidant activity assay based on laccase-generated radicals

A novel antioxidant activity assay was developed using laccase-oxidized phenolics. In a three-step approach, phenolic compounds were first oxidized by laccase. Laccase was then inhibited using 80% (v/v) methanol which also stabilized the oxidized phenolics which were then used to measure antioxidant activities of ascorbic acid and Trolox. From a number of laccase-oxidized phenolics screened for potential use in the measurement of antioxidant activities, syringaldazine emerged the best, giving results comparable to the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical, which is currently used in conventional methods. Like DPPH radicals, two moles of stoichiometric oxidized syringaldazine were reduced by one mole of either ascorbic acid or Trolox. For the first time we show that antioxidant activity can be correlated to oxygen consumption by laccase. Reduction of one molecule of oxygen corresponded to oxidation of four molecules of syringaldazine which in turn is reduced by two molecules of Trolox or ascorbic acid. This study therefore demonstrates the great potential of using laccase-oxidized syringaldazine for the measurement of antioxidant activity.     

Amperometric Detection of Catecholamine Neurotransmitters Using Electrocatalytic Substrate Recycling at a Laccase Electrode

An enzyme electrode based on the coimmobilization of an osmium redox polymer and laccase on glassy carbon electrodes has been applied to ultra sensitive amperometric detection of the catecholamine neurotransmitters dopamine, epinephrine and norepinephrine, resulting in nanomolar detection limits, as low as 4 nM for dopamine. The sensitivity of the electrode is due to signal amplification via oxidation of the catecholamine by the immobilized laccase, which is regenerated by concomitant reduction of oxygen to water, coupled to the electrocatalytic re‐reduction of the oxidized catecholamine by the osmium redox complex: electrocatalytic substrate recycling. In addition because the sensor can be operated in reductive mode at ?0.2 V (vs. Ag/AgCl), noise and interferences are diminished. Combined with its high sensitivity this enzyme electrode also exhibited excellent selectivity allowing the detection of catecholamines in the presence of ascorbic acid. However, differentiation between the current responses achieved for the three catecholamines is not possible. The effective mode of constant recycling, resulting in amplification of the current response, of the laccase enzyme electrode sensor combined with the inherent advantages of using electrochemical techniques holds great promise for the future of catecholamine detection and monitoring.     

Simultaneous Determination of Epinephrine and Dopamine by Using Candida tropicalis Yeast Cells Immobilized in a Carbon Paste Electrode Modified with Single Wall Carbon Nanotube

A new electrochemical microbial biosensor system based on Candida tropicalis was developed for the fast detecting of dopamine and epinephrine. Candida tropicalis was immobilized in a carbon paste electrode (CPE) with single wall carbon nanotube (SWCNT). Immobilized cells were used as a origin of the polyphenol oxidase (PPO) to develop voltammetric epinephrine and dopamine biosensor. Voltammetric determination of phenolic compounds such as epinephrine and dopamine a simple technique which is available. Direct oxidation of phenols can be used, but the oxidation potentials of this compounds are similar and they can not be detected distinctively. Another possibility is the use of biosensors based on the polyphenol oxidase (tyrosinase) enzyme that oxidizes the phenolic compounds into their related quinones. By this way, phenolic compounds are epinephrine and dopamine which were used in this study as well detected at different potentials. In this study differential pulse voltammetry and amperometry techniques were used for the determination of dopamine and epinephrine. The effect of varying the amounts of SWCNT and the response of microorganism to epinephrine was investigated to find the optimum composition of the sensor. The effects of pH and temperature were also examined. Increases in biosensor responses obtained by amperometric measurements were linearly related to dopamine concentrations between 0.025 and 0.25 mM and epinephrine concentrations between 0.01 and 0.1 mM. Limits of detection of the biosensor for dopamine and epinephrine were calculated to be 0.008 and 0.0023 mM, respectively. Finally, proposed system was applied to epinephrine and dopamine analysis in pharmaceutical drugs and synthetic serum and the results were compared with LC MS MS method.     

Programmable and Reversible Regulation of Catalytic Hemin@MOFs Activities with DNA Structures

Metal-organic frameworks(MOFs)-based nanozyme plays an important role in biosensing,therapy and catalysis.In this study,the effects of single-stranded DNA(ssDNA)with programmable sequences and its complementary DNA(Tdna)on the intrinsic peroxidase-like activity of hemin loaded MOFs(UiO-66-NH2),denoted as he-min@UiO-66-NH2,were investigated.The hemin@UiO-66-NH2 exhibited improved catalytic activity compared with free hemin.However,the catalytic activity is inhibited in the presence of ssDNA,as ssDNA can be adsorbed by MOFs and therefore protected the active sites from contact with substrates.Upon the addition of the TDNA,double-stranded DNA(dsDNA)was formed and detached from the MOFs,resulting in the recovery of catalytic activity.Sequentially adding ssDNA or its complementary DNA strands can achieve the reversible regulation of the catalytic activity of MOFs nanozymes.Moreover,the DNA hybridization-based regulation was further applied to a cascaded catalytic system composed of the nanozyme,hemin@UiO-66-NH2,and glucose oxidase.These nanozyme based programmable and reversibly regulated catalytic systems may have potential applications in future smart biosensing and catalysis systems.     

Antiradical and cytotoxic activity of different Helichrysum plicatum flower extracts

Flowers of Helichrysum plicatum were extracted under different experimental conditions, and their antioxidant activity was determined by DPPH radical scavenging assay. Extracts obtained with higher concentration of ethyl acetate (90% or 100%) were found to contain the greatest amount of total phenolics (> 250 mg gallic acid equivalents/g of dried extract), and high correlation between total phenolic content and antiradical activity was observed (r = -0.79). Based on the total phenolic content and antiradical activity, some extracts were selected for investigation of cytotoxic activity toward PC3, HeLa and K562 human cancer cell lines in vitro. All tested extracts exhibited moderate activity against HeLa cells (41.9-42.1 microg/mL), whereas the extract obtained with 100% ethyl acetate was the most active against K562 and PC3 cell lines (25.9 and 39.2 microg/mL, respectively). Statistical analysis revealed significant correlation between total phenolic content and cytotoxic activity against PC3 and K562 cells. HPLC identification of phenolic compounds from the extracts indicated the presence of apigenin, naringenin and kaempferol as free aglycones, and glycosides of apigenin, naringenin, quercetin and kaempferol. Among aglycones, kaempferol displayed moderate cytostatic activity against all cell lines (24.8-64.7 microM).     

新型(4-HBA)SbX5·H2O类钙钛矿单晶及其卤素结构对发光特性的调控(英文)

发光材料因其在照明、显示、成像等方面的广泛应用而备受关注。作为新兴发光材料之一,钙钛矿类材料的研究及报道较多。其中,铅基钙钛矿的研究取得了巨大进展,光致发光量子产率(PLQY)几乎达到了100%。然而,基于铅基钙钛矿化学毒性和低稳定性,在实际应用过程中需要特殊的封装,因而提高了生产成本并限制了其实际应用领域。被广泛关注的锡基钙钛矿的荧光量子产率几乎能达到90%,但Sn²⁺易氧化成Sn⁴⁺,在空气中极不稳定。相较于铅基钙钛矿和锡基钙钛矿,锑基钙钛矿的低化学毒性、高热稳定性等优点突出。此外,锑基钙钛矿的光学性能在过去几年中也取得了很大的进展,有望突破传统钙钛矿应用的局限。在此,我们报道了一系列新型单晶(4-HBA)SbX₅·H₂O (4-HBA为4-羟基苄胺缩写,X为Cl或Br)。利用溶剂热法可制备高质量的(4-HBA)SbBr₅·H₂O、(4-HBA)SbBr₃Cl₂·H₂O和(4-HBA)S...     

Screening of antioxidant phenolic compounds in Chinese Rhubarb combining fast counter‐current chromatography fractionation and liquid chromatography/mass spectrometry analysis

In this paper, an effective method combing fast elution‐extrusion counter‐current chromatography (CCC) and LC/MS for rapid screening of antioxidative phenolic compounds in Chinese Rhubarb is presented. An integrated three‐coil CCC column (40 mL each coil) was used to accomplish the optimization of biphasic liquid system. In a single run (approximately 40 min), the solvent system composed of n‐hexane/ethyl acetate/methanol/water (1:1:1:1, v/v) was selected as optimum CCC liquid system for fast fractionation of the crude ethanol extract. With a 140 mL‐capacity CCC instrument, 100 mg Chinese Rhubarb extract was separated under the optimized conditions, producing six fractions in only 100 min. The quantities of each fraction were ～15 mg. In addition, each fraction was subjected to antioxidant activity assay and characterized by LC/MS analysis. Fifty compounds, including phenolic acids, phenolic glucosides and hydroxyanthraquinones, were detected by LC/MS/MS analysis. As a result, gallic acid together with Fr I showed excellent antioxidant activity, which was well consistent with previous studies and exhibited great potential for natural drug discovery program of the present method.