Complementary Homogeneous Electrochemical and Photothermal Dual-Modal Sensor for Highly Sensitive Detection of Organophosphorus Pesticides via Stimuli-Responsive COF/Methylene Blue@MnO2 Composite.

Credible and on-site detection of organophosphorus pesticides (OPs) in complex matrixes is significant for food security and environmental monitoring. Herein, a novel COF/methylene blue@MnO2 (COF/MB@MnO2) composite featured abundant signal loading, a specific recognition unit, and robust oxidase-like activity was successfully prepared through facile assembly processes. The multifunctional composite acted as a homogeneous electrochemical and photothermal dual-mode sensing platform for OPs detection through stimuli-responsive regulation. Without the presence of OPs, the surface MnO2 coating could recognize thiocholine (TCh), originating from acetylcholinesterase (AChE)-catalyzed hydrolysis of acetylthiocholine (ATCh), and exhibited a distinctly amplified diffusion current due to the release of plentiful MB; while the residual MnO2 nanosheets could only catalyze less TMB into oxidized TMB (oxTMB) with a typical near-infrared (NIR) absorption, enabling NIR-driven photothermal assay with a low temperature using a portable thermometer. Based on the inhibitory effect of OPs on AChE activity and OP-regulated generation of TCh, chlorpyrifos as a model target can be accurately detected with a low limit of detection of 0.0632 and 0.108 ng/mL by complementary electrochemical and photothermal measurements, respectively. The present dual-mode sensor was demonstrated to be excellent for application to the reliable detection of OPs in complex environmental and food samples. This work can not only provide a complementary dual-mode method for convenient and on-site detection of OPs in different scenarios but also expand the application scope of the COF-based multifunctional composite in multimodal sensors.

NiO-NiMoO4 Nanocomposites on Multi-Walled Carbon Nanotubes as Efficient Bifunctional Electrocatalysts for Total Water Splitting.

Multicomponent synergistic regulation and defect design have been effective strategies to enhance the electrocatalytic activity of transition-metal oxides. In this work, NiO and NiMoO4 nanocomposites on multi-walled carbon nanotubes (termed NiO-NiMoO4/mCNTs) are synthesized through a two-step method. Physical characterizations show NiO-NiMoO4/mCNTs have a well-defined NiO-NiMoO4 structure, large specific surface area, and abundant oxygen vacancies. For oxygen evolution reaction (OER), NiO-NiMoO4/mCNTs deliver lower overpotential (277 mV) than NiO/mCNTs, NiO, and commercial RuO2 nanocrystals at 10 mA cm-2. For hydrogen evolution reaction (HER), NiO-NiMoO4/mCNTs still show the best HER activity, manifested by the smallest onset potential and the lowest Tafel. Density functional theory calculations show that the adsorption energies of hydrogen- and oxygen-containing intermediates on the NiO-NiMoO4/mCNTs surface have changed, which can lower the energy barriers required for HER and OER. The excellent electrocatalytic activity of bifunctional NiO-NiMoO4/mCNTs for OER and HER can be attributed to the synergy effect between NiO, NiMoO4, and mCNTs. A symmetrical two-electrode water electrolyzer with NiO-NiMoO4/mCNTs as both the cathode and anode are constructed, which can reach a current density of 10 mA cm-2 and only requires 1.57 V.

A separable nanodevice enables multilayer imaging of diverse biomarkers for precise diagnosis.

An acid-driven separable nanodevice was designed for multilayer imaging of diverse biomarkers with different spatial distributions in living cells. The proposed nanodevice can simultaneously perform in situ imaging of the intracellular microRNAs and extracellular pH, affording a new approach to develop a precise imaging system for disease diagnosis.

A self-circulating electro-fenton-like process over Fe3O4-CaO2 cathode for highly efficient degradation of levofloxacin.

Electro-Fenton reaction was limited by the generation of H2O2 and the circulation of Fe(Ⅱ)/Fe(Ⅲ). Herein, an efficient electro-Fenton-like process was constructed based on Fe3O4-CaO2 cathode promoted by peroxymonosulfate (PMS). Levofloxacin (LEV) could be efficiently degraded (92.1%) and mineralized with the TOC removal of 74.5% in this self-circulating process. More importantly, the Fe3O4-CaO2 exhibited good stability in the recycles due that CaO2 was covered by Fe3O4, which inhibited the rapid release of H2O2. Mechanism analysis indicated that CaO2 could not only replace H2O2 to accelerate the oxidation of Fe(Ⅱ) to Fe(Ⅲ), but also could form complexes with Fe(Ⅲ) and PMS to transfer electrons from ligands to metals, thereby enhancing the reduction of Fe(Ⅲ) to Fe(Ⅱ). As a result, the electrical consumption was significantly reduced, which was only 5.0% of the Fe3O4 in electro-Fenton reaction. Meanwhile, the hydrolyzed product of Ca(OH)2 reacted with Fe(Ⅲ) in the presence of H2O2 and converted into CaO2. Thus, the self-circulation of CaO2/Ca(OH)2 and Fe(Ⅲ)/Fe(Ⅱ) was realized, which accelerated the generation of active species, such as, ·OH, O2·- and 1O2. This work first proposed a self-circulating electro-Fenton-like system and demonstrated the potential application of Fe3O4-CaO2 in the treatment of wastewater.

An Ultrasensitive Electrochemical Biosensor Integrated by Nicking Endonuclease-Assisted Primer Exchange Reaction Cascade Amplification and DNA Nanosphere-Mediated Electrochemical Signal-Enhanced System for MicroRNA Detection.

Specific and sensitive microRNAs (miRNAs) detection is essential to early cancer diagnosis. The development of these technologies including functional nuclease-mediated target amplification and DNA nanotechnology possesses tremendous potential for the high-performance detection of miRNAs in the accurate diagnosis of disease. In this study, we have established an ultrasensitive electrochemical biosensor by combining nicking endonuclease-assisted primer exchange reaction (PER) cascade amplification with a DNA nanosphere (DNS)-mediated electrochemical signal-enhanced system for the detection of miRNA-21 (miR-21). The cascade amplification is initiated by a nicking endonuclease that can cleave specific DNA substrates and highly amplify translation of the target to single-stranded DNA fragments (sDNA). Then, the PER cascade is powered by strand-displacing polymerase and generates a large amount of nascent single-stranded connector DNA (cDNA) via sDNA triggering of the dumbbell probe (DP), thus achieving the cascade amplification of the target. Finally, the DNS loaded with plenty of electroactive substances can be captured on the electrode via cDNA for further enhancing the electrochemical signal and highly sensitive detection of miR-21. The proposed electrochemical biosensor exhibits a wide detection range of 1 aM to 0.1 nM and a low detection limit of 0.58 aM. The excellent selectivity allows the biosensor to discriminate miR-21 from other miRNAs, even the one base-mismatched sequence. Moreover, the practicability of the biosensor is investigated by analyzing miR-21 in human serum and cancer cell lysate. Therefore, our proposed nicking endonuclease-assisted PER cascade amplification strategy provides a powerful platform for the early detection of miRNA-related disease and molecular diagnosis.

A carbon dots-enhanced laccase-based electrochemical sensor for highly sensitive detection of dopamine in human serum.

Enzyme-based electrochemical sensor possesses a significant advantage in the highly efficient detection of small molecules, however, the poor electron transport efficiency limits their wide application. In this study, taking advantage of the distinct biocatalytic activity of laccase and the excellent electroconductibility of carbon dots, a carbon dots-enhanced laccase-based electrochemical sensor for the detection of dopamine (DA) is established. Thereinto, laccase can specifically recognize DA and promote its electrocatalytic oxidation on the electrode, while, the carbon dots can be used as the immobilization substrate of laccase and enhance its electron transfer efficiency, thus achieving the highly sensitive detection of dopamine. The electrochemical performance of the modified electrode interface is studied by electrochemical impedance spectroscopy and differential pulse voltammetry. As demonstrated, the electrocatalytic activity of the proposed electrochemical sensor for DA is significantly improved and exhibits a low detection limit (0.08 µM) and a wide linear range (0.25 µM-76.81 µM). The excellent selectivity allows the sensor has the capacity for specific discrimination the DA from other interferents. Furthermore, by analyzing the DA in human serum verifies the practicability of this assay in real sample analysis.

Metal-Based Aerogels Catalysts for Electrocatalytic CO2 Reduction.

General strategies for metal aerogel synthesis, including single-metal, transition-metal doped, multi-metal-doped, and nano-metal-doped carbon aerogel are described. In addition, the latest applications of several of the above-mentioned metal aerogels in electrocatalytic CO2 reduction are discussed. Finally, considering the possibility of future applications of electrocatalytic CO2 reduction technology, a vision for industrialization and directions that can be optimized are proposed.

2D Catalysts for CO2 Photoreduction: Discussing Structure Efficiency Strategies and Prospects for Scaled Production Based on Current Progress.

Currently, the excessive consumption of fossil fuels is accompanied by massive emissions of CO2 , leading to severe energy shortages and intensified global warming. It is of great significance to develop and use renewable clean energy while reducing the concentration of CO2 in the atmosphere. Photocatalytic technology is a promising strategy for carbon dioxide conversion. Clearly, the achievement of the above goals largely depends on the design and construction of catalysts. This review is mainly focused on the application of 2D materials for photocatalytic CO2 reduction. The contribution of synthetic strategies to their structure and performance is emphasized. Finally, the current challenges, and prospects of 2D materials for photoreduction of CO2 with high efficiency, even for practical applications are discussed. It is hoped that this review can provide some guidance for the rational design, controllable synthesis of 2D materials, and their application for efficient photocatalytic CO2 reduction.

A fluorogenic RNA aptamer nanodevice for the low background imaging of mRNA in living cells.

A fluorogenic RNA aptamer nanodevice integrating an entropy-driven RNA amplifier with near-infrared (NIR) light control was developed, affording high contrast and sensitivity for imaging low-abundance mRNA in living cells. The design principle offers a new approach for developing low-background imaging systems for live-cell studies and manipulation.

A novel electrochemically enhanced homogeneous PMS-heterogeneous CoFe2O4 synergistic catalysis for the efficient removal of levofloxacin.

A novel electrochemically enhanced homogeneous-heterogeneous catalytic system was constructed by placing the prepared heterogeneous catalyst (CoFe2O4/NF) in parallel between the anode and the cathode for peroxymonosulfate (PMS) activation to remove levofloxacin (LVF) in this work. Over 90% of LVF could be effectively removed by the constructed system after 40 min's degradation. And the electrical energy consumption was only 2.51 kWh/m3, which was lower than 54.5% of the traditional electrochemical advanced oxidation process. Besides, the system broadened the response range of pH and overcame the inhibitory effect of alkaline conditions on degradation. These activities were mainly due to the high generation ability of free radical (SO4·-, ·OH and O2·-) and non-radical (1O2). And the SO4·- was found to be the main radical for LVF degradation. The high SO4·- generation ability was demonstrated to be resulted from the dual effects of synergy of CoFe2O4/PMS and enhancement of electrochemistry in EC/CoFe2O4/PMS system. In detail, electrochemistry could effectively promote the continuous circulation of Co2+/Co3+ and Fe2+/Fe3+ redox cycles on the surface of CoFe2O4 to enhance the activation of PMS, thereby generating SO4·-. This work can provide a promising and cost-effective approach to construct highly efficient organic pollutant degradation system.

Tannic acid reinforced electro-Fenton system based on GO-Fe3O4/NF cathode for the efficient catalytic degradation of PNP.

In order to overcome the sluggish kinetics of the redox conversion between Fe3+ and Fe2+ in Fenton process, we established a novel electro-Fenton system based on GO-Fe3O4 cathode and tannic acid (TA) for the efficient degradation of p-nitrophenol (PNP). Under the optimal degradation parameters (including the initial PNP concentration of 20 mg L-1, pH = 5, current density of 30 mA cm-2 and feeding ratio of PNP: TA = 1:2), the TA reinforced GO-Fe3O4 electro-Fenton system exhibited the removal rate of PNP over 90.1 ± 0.2%, the COD removal rate of 69.5 ± 0.84% and satisfactory reusability (with the removal rate of ∼80% after 5 recycles). The excellent degradation performance of the proposed TA reinforced GO-Fe3O4 electro-Fenton system was partly attributed to the optimized morphology (with the particle size of Fe3O4 reduced to tens of nanometers, pore size decreased by ∼80% and pore volume increased by 24.3 times) and larger specific surface area (increased by 72.7 times) after compositing GO with Fe3O4, which exposed more active sites. In return, the electron transfer process, the two-electron oxygen reduction reaction (ORR) and the degradation efficiency were promoted in the cooperation of GO and Fe3O4. Moreover, the incorporated TA would form a TA-Fe(III) complex to promote the reduction reaction from Fe3+ to Fe2+, which strengthened the self-circulation of Fe2+ and Fe3+ and indirectly enhanced the conversion of H2O2 to ROS to decompose PNP into smaller organic fragments or mineralize into CO2, H2O, NO2- or NO3-, etc. Obviously, the incorporation of TA provided a promising strategy to improve the electro-Fenton efficiency and realize the efficient removal of PNP in wastewater.

Prediction of cooling moisture content after cut tobacco drying process based on a particle swarm optimization-extreme learning machine algorithm.

The stability of the moisture content of the cigarette is an important index to evaluate the quality of the cigarette. The cooling moisture content after cut tobacco drying process is a key factor affecting the stability of the moisture content of the cigarette. In order to realize its accurate prediction and ensure the stability, in Honghe cigarette factory, a cooling moisture content prediction model is built based on a particle swarm optimization-extreme learning machine (PSO-ELM) algorithm via the historical production data. Besides, the proposed PSO-ELM algorithm is also compared with multiple linear regression (MLR), support vector machine (SVM) and the traditional extreme learning machine (ELM) algorithms in the same data set on the prediction. The prediction accuracy of PSO-ELM method is the highest and the average error of the prediction standard is the lowest. The results indicated the proposed method can achieve a better prediction performance over compared methods and it provides a new method to realize the prediction of the cooling moisture content after cut tobacco drying process.

Plasmon-Enhanced Electroactivity of AuRu Nanostructures for Electroanalysis Applications.

An electrochemical sensing interface is limited by poor reproducibility and inevitable interferences present in practical applications due to the weak electrochemical signals of nanotags. This motivates the need for effective strategies to enhance the electroactivity performances of nanotags. In this contribution, a plasmon-enhanced electroactivity mechanism is proposed for AuRu-based nanostructures under illumination and applied for accurate detection of human epidermal growth factor receptor-2 (HER2). AuRu nanoparticles (NPs) harvested light energy through plasmon excitation and generated holes to participate in the electrooxidation process. The production of holes resulted in the electrooxidation signal enhancement of AuRu NPs. AuRu NPs were assembled with Au NPs using HER2 aptamers as linkers, and the plasmonic coupling between AuRu NPs and Au NPs produced an intense electromagnetic field, which further enhanced the electrooxidation signals of AuRu NPs. An AuRu-Au NP assembly-dependent electrochemical aptasensor was established for the accurate detection of HER2, and the limit of detection (LOD) was as low as 1.7 pg/mL. The plasmon-enhanced electroactivity mechanism endowed AuRu-based nanostructures with strong and noninterfering electrochemical signals for sensitive and accurate detection. This insight opens new horizons for the construction of desired electroactive nanostructures for electroanalysis applications.

Oxygen reduction reaction electrocatalysis inducing Fenton-like processes with enhanced electrocatalytic performance based on mesoporous ZnO/CuO cathodes: Treatment of organic wastewater and catalytic principle.

To treat typical organic wastewater efficiently, a novel Fenton-like processes based on ZnO/CuO composite cathode induced by oxygen reduction reaction (ORR) electrocatalysis with enhanced electrocatalytic performance was established successfully. Electrochemical testing investigation indicated that the ZnO/CuO cathode possessed conspicuous redox peak and better conductivity than uncompounded electrodes. Additionally, the removal efficiency of methylene blue and its chemical oxygen demand (COD) reached 96.4% and 70.8% after 120 min, respectively. Next, the feasibility of the material in practical application was also discussed. Subsequently, electrocatalytic principle based on valence state changes of metal elements on the electrode surface were also studied by x-ray photoelectron spectroscopy (XPS). Redox reactions between the active species H2O2 and the species Cu+ promoting Fenton-like processes were deduced. Namely, the conversion of Cu(I) and Cu(II) on the electrode surface was accompanied by OH generation. The combination of ZnO and CuO improved the surface morphology, increasing the active site of ORR and the yield of H2O2, thus greatly enhanced the Fenton-like activity. Finally, the main intermediates were identified by Gas chromatography-mass spectrometer (GC-MS), and possible pathways for dye degradation were proposed. In short, the research of ZnO/CuO cathode provided great significance for heterogeneous Fenton-like degradation and also showed its application potential in water treatment and remediation.

Preparation of an antibacterial chitosan-coated biochar-nanosilver composite for drinking water purification.

Microbial contamination has evolved as a life-threatening problem afflicting people due to various diseases caused by pathogenic bacteria in drinking water. Thus developing novel antibacterial materials is an urgent need. Herein, a chitosan (CTS)/ biochar-nanosilver (C-Ag) antibacterial composite was prepared by a method of CTS-coated on C-Ag obtained through a facile high-temperature carbonization process using corn straw as the carbon substrate. The results from FT-IR, XRD, SEM and TG-DSC revealed that the biochar loading spherical silver nanoparticles was coated with CTS in the composite. The antibacterial activity of the CTS/C-Ag composite was investigated using the plate counting method with Escherichia coli (E. coli), and the results suggest that the composite exhibited excellent antibacterial activity against E. coli. In this application study, it was proven that the CTS/C-Ag composite exhibits sustainable antibacterial activity and good reusability for drinking water. Therefore, the CTS/C-Ag composite has potential application in drinking water treatment.

C60 Mediated Ion Pair Interaction for Label-Free Electrochemical Immunosensing with Nanoporous Anodic Alumina Nanochannels.

Label-free biosensing based on the nanoporous anodic alumina (NAA) membrane emerged as a versatile biosensing platform in the recent decade. In the present work, we developed a new immunosensing strategy based on the nanochannels of NAA and the ion pair interaction mediated by electrochemistry of C60. The NAA served as the matrix for the immobilization of the capture antibodies. The incubation of target antigens resulted in the formation of the immunocomplexes and thus an increase of the steric hindrance of the nanochannels. Therefore, the concentration of the redox probe transported through the nanochannels decreases, which can be detected at the working electrode modified with C60. Herein, we initially found that the cathodic peak ascribed to the reduction of C60 to C60- was obviously enhanced by the presence of the redox probe K3[Fe(CN)6] and which was contributed to the formation of a ternary ion association complex among C60, tetraoctylammonium bromide, and K3[Fe(CN)6]. Therefore, the transportation of K3[Fe(CN)6] though the NAA-based bionanochannels can be detected by a C60 modified electrode with an amplified signal. Choosing human epididymis protein 4 (HE4) as the model target, a linear range of 1.0 ng mL-1 to 100 ng mL-1 can be established between the peak current obtained from the differential pulse voltammetric response of the platform and the concentration of HE4. The detection limit was 0.2 ng mL-1. This study not only provides a new avenue to develop the other nanochannel-based biosensing platform for a variety of other disease biomarkers but also contributes to the electrochemistry of fullerene.

Recycling of Cr (VI) from weak alkaline aqueous media using a chitosan/ triethanolamine/Cu (II) composite adsorbent.

A Chitosan/triethanolamine/Cu (Ⅱ) (CTS/TEA/Cu (Ⅱ)) composite adsorbent was prepared and applied to recycle Cr (Ⅵ) from aqueous media in alkaline conditions. To investigate the adsorption behavior, the influence of pH was evaluated via batch experiments, and the prepared adsorbent was characterized by FT-IR, SEM, XRD, and Zeta potential. This adsorbent exhibited high adsorption capacity for Cr (Ⅵ) in a wide pH range (especially above 7), suggesting a possible way to separate Cr (Ⅵ) from other metal cations by adjusting the pH value prior to adsorption. Adsorption kinetic and thermodynamic experiments were conducted to explore the adsorption mechanism. Regeneration studies showed that the adsorbent can be reused for five adsorption-desorption cycles without substantial loss of adsorption capacity. Overall, the CTS/TEA/Cu (Ⅱ) adsorbent exhibits high potential for recyclingCr (Ⅵ) from wastewater.

Adsorption of molybdate on molybdate-imprinted chitosan/triethanolamine gel beads.

Mo (VI)-imprinted chitosan (CTS)/triethanolamine (TEA) gel beads (Mo (VI)-ICTGBs) (ICTGBs=imprinted chitosan triethanolamine gel beads) were prepared by using ion-imprinted technology, in which TEA and molybdate solution were used in coagulation bath. The spectrum of FT-IR implies that bonding are formed between TEA and the primary hydroxyl of CTS, and ion gel reaction happen between CTS and molybdate; XRD patterns also prove the change among CTS, TEA and molybdate. SEM images and N2 adsorption show that the surface area increases obviously after eluting Mo (VI) ions. The adsorption isotherm of Mo (VI)-ICTGBs imply that the adsorption process is according with Freundlich model. Adsorption kinetics suggests that the pseudo-second order adsorption mechanism is predominant for this adsorbent system of Mo (VI)-ICTGBs. The Mo (VI)-ICTGBs show high adsorption capacity and good selectivity for Mo (VI) anions in the coexistence system at pH=6.0. The Mo (VI)-ICTGBs have a good application prospect, because it is with a simple and rapid technique and good durance.

Electrochemical characterization of poly-beryllon II modified carbon paste electrode and its application to selective determination of pyrocatechol and hydroquinone.

A poly-beryllon II film modified carbon paste electrode (PBL-II/CPE) has been constructed by electropolymerization method. Electrochemical characterization of the PBL-II/CPE was investigated by electrochemical impedance spectroscopy (EIS). The electrochemical behaviors of pyrocatechol (PC) and hydroquinone (HQ) were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at the PBL-II/CPE in pH 7.0 phosphate buffer solution (PBS). The anodic peak currents were dramatically enhanced about threefold for PC at PBL-II/CPE. In addition, the modified electrode exhibits good selectivity toward selective determination of PC and HQ. By using DPV method, low detection limits of 0.8µM for PC and 1.0µM for HQ were obtained, respectively. Many outstanding advantages, such as wide linear ranges, low detection limits, excellent sensitivity, selectivity and stability confirmed that the PBL-II/CPE has promising analytical performance. Meanwhile, the electrode was successfully used for the determination of PC and HQ in local tap water sample and the results are satisfactory.

Effects of ionic liquid and nanogold particles on high-performance liquid chromatography-electrochemical detection and their application in highly efficient separation and sensitive analysis of five phenolic acids in Xuebijing injection.

A novel high performance liquid chromatography-electrochemical detector (HPLC-ECD) analytical system was developed in this study by integratedly utilizing ionic liquid (IL) of 1-butyl-3-methylimidazolium bromide and an additive of gold nanoparticles. The resulted pilot study was first performed to assess the effects of 1-butyl-3-methylimidazolium bromide and gold nanoparticles on the chromatographic characteristics of five phenolic acids in Xuebijing injection, including danshensu (DSS), protocatechuic acid (PA), protocatechuic aldehyde (PAH), hydroxy safflower yellow A (HSYA) and ferulic acid (FA). It was notable to observe that retainability of the phenolic acids were markly lowered by IL addition. Compared with the cases without IL addition, the retention times of DSS, PA, PAH, HSYA and FA have decreased 2.851, 1.532, 1.53, 0.818 and 0.552 min, respectively when 0.6% IL in the mobile phase. In addition, the corresponding theoretical plate numbers and peak areas for these compounds were significantly increased. Area response for DSS, PA, PAH, HSYA and FA were enhanced by 772%, 628%, 584%, 703% and 600%, respectively. It was observed that nano-gold catalysis power enabled peak areas of DSS, PAH, FA and PA to enhance 5.7, 6.2, 8.5 and 66.5 times relative to the case with addition of IL. Altogether, the optimized HPLC-ECD system was successfully applied to the pharmacokinetics study of Xuebijing injection with underlying applicability to in vivo and in vitro analysis of a variety of natural product from Chinese medicine plants, TCM formulae and associated patent TCM preparation.