Simple synthesis of peanut shell-like MoCoFe-HO@CoMo-LDH for efficient alkaline oxygen evolution reaction.

Due to the depletion of fossil energy on earth, it is crucial to develop resource rich and efficient non-precious metal electrocatalysts for oxygen evolution reaction (OER). Herein, we synthesized an efficient and economical electrocatalyst using a simple self-assembly strategy. Firstly, rod-shaped MIL-88A was synthesized by hydrothermal method. Then, the surface of MIL-88A was functionalized and encapsulated in zeolitic imidazolate framework-67 (ZIF-67) by hydrothermal method. The combination of MIL-88A and ZIF-67 resulted in a slight ion-exchange reaction between Co2+ and the surface of MIL-88A to generate CoFe-LDH@ZIF-67 core-shell structure. Afterwards, in the presence of Mo6+, ZIF-67 was converted into CoMo-nanocages through ion-exchange reactions, forming a core-shell structure of MoCoFe hydr (oxy) oxide@CoMo-LDH (MoCoFe-HO@CoMo-LDH). Due to the advantages of core-shell structure and composition, this material exhibits excellent OER characteristics, with a small Tafel slope (45.11 mV dec-1) and low overpotential (324 mV) at 10 mA cm-2. It exhibits good stability in alkaline media. This research work provides a novel approach for the development of efficient and economical non-precious metal electrocatalysts.

Electrocatalytically active cuprous oxide nanocubes anchored onto macroporous carbon composite for hydrazine detection.

Cuprous oxide (Cu2O) is a p-type semiconductor with excellent catalytic activity and stability that has gained much attention because it is non-toxic, abundant, and inexpensive. Porous carbon materials have large specific surface areas, which offer abundant electroactive sites, enhance the electrical conductivity of materials, and prevent the aggregation of Cu2O nanocubes. In this study, a composite with high electrocatalytic activity was prepared based on Cu2O nanocubes anchored onto three-dimensional macroporous carbon (MPC) by a simple, eco-friendly, and cheap method for hydrazine detection. Due to the synergistic effect of MPC and Cu2O, the sensor exhibited high electrocatalytic activity, sensitivity, better selectivity, and low limit of detection. The resulting sensor could be a sensitive and effective platform for detecting hydrazine and promising practical applications.

Deciphering Competitive Routes for Nickel-Based Nanoparticle Electrodeposition by an Operando Optical Monitoring.

Electrodeposition of earth-abundant iron group metals such as nickel is difficult to characterize by simple electrochemical analyses since the reduction of their metal salts often competes with inhibiting reactions. This makes the mechanistic interpretation sometimes contradictory, preventing unambiguous predictions about the nature and structure of the electrodeposited material. Herein, the complexity of Ni nanoparticles (NPs) electrodeposition on indium tin oxide (ITO) is unraveled operando and at a single entity NP level by optical microscopy correlated to ex situ SEM imaging. Our correlative approach allows differentiating the dynamics of formation of two different NP populations, metallic Ni and Ni(OH)2 with a <25 nm limit of detection, their formation being ruled by the competition between Ni2+ and water reduction. At the single NP level this results in a self-terminated growth, an information which is most often hidden in ensemble averaged measurements.

Epoxy-functionalized macroporous carbon with embedded platinum nanoparticles for electrochemical detection of telomerase activity via telomerase-triggered catalytic hairpin assembly.

Telomerase is regarded as a crucial biomarker for the early diagnosis of malignant tumors and a valuable therapeutic target. In this work, a telomerase-triggered amplification strategy was designed on the basis of a catalyzed hairpin assembly (CHA) for bridging a signal probe of platinum nanoparticles (Pt NPs) anchored on three-dimensional (3D) epoxy-functionalized macroporous carbon (Pt/MPC-COOH) in an ultrasensitive electrochemical biosensor. Pt/MPC-COOH nanomaterials with interconnected macroporous structure not only immobilized hairpin DNA probe 2 (H2) via an amide reaction (Pt/MPC-COOH-H2), but they also generated an obvious electrochemical signal in response to acetaminophen (AP) oxidation. After the introduction of telomerase, telomerase primer (TP) was extended to a telomerase extension product (TEP) with several hexamer repeats (TTAGGG)n to initiate the CHA cycle, leading to signal amplification. Subsequently, with the TEP-triggered CHA cycle amplification strategy, a large amount of Pt/MPC-COOH-H2 was introduced on the electrode surface for the construction of the electrochemical platform, which realized the sensitive detection of telomerase activity from 102 to107 cells mL-1 with a limit of detection (LOD) of 9.02 cells mL-1. This strategy provides a sensitive method for the detection of biomolecules that could be useful for bioanalysis and early clinical diagnoses of diseases.

An enzyme-free electrochemical biosensor based on target-catalytic hairpin assembly and Pd@UiO-66 for the ultrasensitive detection of microRNA-21.

MicroRNA-21 (miR-21) has been widely investigated as important biomarkers for cancer diagnosis and treatment. Herein, a highly sensitive nonenzymatic electrochemical biosensor based on Pd@metal-organic frameworks (Pd@UiO-66) and target-catalytic hairpin assembly (CHA) with target recycling approach has been proposed for the detection of miR-21. The proposed biosensor integrates the efficient CHA strategy and excellent electrocatalytic performance of Pd@UiO-66 nanocomposites. The concentration of miRNA-21 is related to the amount of the adsorbed electrocatalyst, leading to the different electrochemical signals for readout towards paracetamol (AP). This biosensor shows a low limit of detection of 0.713 fM with the dynamic range of 20 fM -600 pM under the optimal experimental conditions, providing a powerful platform for detecting miR-21. Furthermore, the designed biochemical self-assembly strategy of this electrochemical biosensor is promising candidate for potential applications in the analysis of other important genetic biomarkers for early diagnosis of cancers.

A novel cobalt and nitrogen co-doped mesoporous hollow carbon hemisphere as high-efficient electrocatalysts for oxygen reduction reaction.

Exploring a cheap catalyst with effective activity for oxygen reduction reaction (ORR) to replace precious metal electrocatalysts has gained tremendous attention for several decades. In this study, we designed and synthesized cobalt and nitrogen supported on mesoporous hollow carbon hemisphere (Co/N/HCHs) nanocomposites by a facile and economical approach. Semisphere-shaped mesoporous hollow carbon is self-generated using silica particles as template, followed by a pyrolysis-etching process; and exhibits high electrical conductivity and high specific surface. The unique porous structure of carbon provides significant number of the abundant defective sites and shortens the mass transfer pathway, leading to a greatly enhanced electrocatalytic activity with mainly 4e- reduction. Moreover, the synergistic effects of large electrochemically active areas and good electrical conductivity, resulting from the introduction of Co and N heteroatom, are the main reason for displaying outstanding ORR activity with a high half-wave potential of 0.8 V and the electron transfer numbers of 3.89. Furthermore, an excellent long-term stability (the current density retention of 87.0%) and superb methanol tolerance in alkaline medium are achieved. Undoubtedly, this demonstrates a potential way to strategically design the non-precious metal doped carbon catalysts for wider practical applications.

Preparation of Pt anchored on cerium oxide and ordered mesoporous carbon tri-component composite for electrocatalytic oxidation of adrenaline.

The preparation of Pt/cerium oxide and highly ordered mesoporous carbon (Pt/CeO2/OMC) nanohybrids is reported. CeO2 can be used as an active material that enhances the electrocatalytic properties of Pt nanoparticles. OMC exhibits excellent electrical conductivity and large specific surface area, which makes it a highly promising electrocatalyst support. Benefiting from the synergistic effects of the catalytic performance of Pt/CeO2 and excellent conductivity of OMC supports, the new nanocomposite of Pt/CeO2/OMC are able to create novel features of electrocatalytic activities. Pt/CeO2/OMC tri-component composite was used as an excellent sensing platform for the determination of adrenaline. The developed sensor exhibited excellent activity and convincing analytical performance towards adrenaline, such as wide linear range, high sensitivity, low limit of detection, and low limit of quantification. In addition, the recoveries ranging from 93.4 to 103.6% were obtained in human serum samples. The successful preparation of Pt/CeO2/OMC tri-component composite may promote the development of novel electrocatalyst and facilitate the design of new electrochemical sensors.

Artesunate-luminol chemiluminescence system for the detection of hemin.

Fabricating simple, accurate and user-friendly diagnostic device for "point of care testing" (POCT) applications is one of the most challenging objectives in the analytical field. Hemin detection is important for drugs monitoring, diagnosis, and forensic latent bloodstain imaging. Herein is developed, luminol chemiluminescence biosensor for hemin detection using artesunate as coreactant. A possible mechanism to account for the chemiluminescence reaction is discussed. Hemin was detected using both photomultiplier tube (PMT) and smartphone as detector. The detection limit for hemin using smartphone as detector is 20 nM, enabling the visual detection of hemin in blood sample with a dilution factor of blood up to 120,000. While PMT detector is used, the system is able to detect hemin down to 0.22 nM. In addition to high sensitivity, this sensing system exhibit high selectivity. It can successfully distinguish bloodstain from other stains while applying the system for point of care testing using smart phone as detector. Moreover, the system can detect artesunate with a linear range from 0.1 nM to 1.0 µM with a limit of detection of 0.078 nM.

Stainless steel electrode for simultaneous stripping analysis of Cd(II), Pb(II), Cu(II) and Hg(II).

Traditional electrodes for stripping analysis generally have narrow electrochemical window, require the modification of electrode or the addition of additional ions. To solve these problems, stainless steel has been used as the electrode for electrochemical stripping analysis for the first time. Square wave anodic stripping voltammetry (SWASV) has been used for the detection of Cd2+, Pb2+, Cu2+, and Hg2+. Type 304 stainless steel electrode gives well-defined, sharp, and separated stripping peaks for these metal ions. The electrode, best operated at + 0.3 V (Hg2+), - 0.05 V (Cu2+), - 0.41 V (Pb2+), and - 0.7 V (Cd2+) and after a 300 s deposition at - 1.0 V, has linear responses in the concentration ranges of 0.075-5 µM for Pb2+ and Cu2+, 0.5-5 µM for Cd2+, and 0.1-5 µM for Hg2+. The limits of detection (at S/N = 3) are 0.033 µM for Pb2+, 0.0073 µM for Cu2+, 0.23 µM for Cd2+, and 0.028 µM for Hg2+. The reproducibility, expressed as relative standard deviation, is 3.2% for Pb2+, 2.6% for Cu2+, 5.1% for Cd2+, and 2.5% for Hg2+ (each 1 µM levels; for n = 6). The electrode was successfully applied to the determination of the ions in spiked groundwater samples. This study shows that stainless steel is a better alternative to mercury electrode for stripping analysis because of its well-defined and sharp stripping peaks, high sensitivity, low background, low toxicity, good reproducibility, and much wider electrochemical window.

Tris(2,2'-bipyridyl)ruthenium(II) electrochemiluminescent determination of ethyl formate.

Ethyl formate is extensively used as food flavor, fungicide, and larvicide. It naturally exists in coffee, fruits, honey, brandy, and rum as well as dust clouds in an interstellar space of the Milky Way galaxy. Herein, its electrochemiluminescence (ECL) property has been firstly investigated. It shows intense ECL in reaction with Ru(bpy)32+ as luminophore, and thus a rapid and sensitive detection method for ethyl formate is proposed. Effects of pH, working potential, scan rate, and concentration of Ru(bpy)32+ were studied. ECL spectrum analysis was used to reveal the reaction mechanism. At the optimized experimental conditions, a linear relationship between ECL intensities and concentrations of ethyl formate is observed from 3.0 µM to 1.0 mM (R2 = 0.997). The limit of detection for ethyl formate is 0.7 µM (S/N = 3). The relative standard deviation with 1.0 mM concentration of ethyl formate for nine analyses is 2.7%. A 101.20-102.10% recovery was obtained in a real samples analysis. Graphical Abstract ᅟ.

Sensitive electrochemical detection of sodium azide based on the electrocatalytic activity of the pasting liquid of a carbon paste electrode.

Sodium azide (NaN3) is highly toxic and widely used in, for example, automobile airbags and biochemical laboratories. The electrochemical detection of sodium azide on commonly used electrodes is challenging due to sluggish electron transfer, but it has been achieved using a boron-doped diamond thin-film electrode and a highly oriented pyrolytic graphite electrode. Utilizing the electrocatalytic activity of the pasting liquid of a carbon paste electrode, we developed an effective method for the electrochemical detection of sodium azide in which silicone oil was employed as the pasting liquid of the carbon paste electrode. This simple and cheap silicone-oil-based carbon paste electrode exhibited comparable sensitivity to the boron-doped diamond thin-film electrode and highly oriented pyrolytic graphite electrode. The limit of detection for sodium azide at the silicone-oil-based carbon paste electrode was found to be 0.1 µM. Recoveries from diluted human serum samples were between 97.2 and 101.3%. Graphical abstract ᅟ.

Determination of Concentrated Hydrogen Peroxide Free from Oxygen Interference at Stainless Steel Electrode.

H2O2 is frequently used at high concentrations in various applications. It is very challenging to detect high concentrations of H2O2 and to eliminate oxygen interference for H2O2 detection through electrochemical reduction. In the present investigation, the electrochemistry of H2O2 at stainless steel electrode has been carried out for the first time. A cathodic peak for H2O2 reduction was observed at about -0.40 V, and no cathodic peak for dissolved oxygen reduction was observed on type 304 stainless steel electrode. Amperometric determination of H2O2 on type 304 stainless steel electrode displayed a linear range from 0.05 up to 733 mM with a detection limit of 0.02 mM (S/N = 3) and a sensitivity of 16.7 µA mM-1 cm-2. The type 304 stainless steel electrode not only shows much higher upper limit than other reported electrodes for the detection of concentrated H2O2 but also is free from oxygen interference, which is of great importance for practical applications. This method could detect H2O2 in wound wash and lake water with excellent recoveries. Moreover, we successfully applied the stainless steel electrode to determine glucose using glucose oxidase to catalyze the oxidation of glucose to generate hydrogen peroxide. The linear range for glucose is between 0.5 and 25 mM, which covers clinically important blood glucose concentrations well.

Development of luminol-N-hydroxyphthalimide chemiluminescence system for highly selective and sensitive detection of superoxide dismutase, uric acid and Co2.

N-hydroxyphthalimide (NHPI), a well known reagent in organic synthesis and biochemical applications, has been developed as a stable and efficient chemiluminescence coreactant for the first time. It reacts with luminol much faster than N-hydroxysuccinimide, eliminating the need of a prereaction coil used in N-hydroxysuccinimide system. Without using prereaction coil, the chemiluminescence peak intensities of luminol-NHPI system are about 102 and 26 times greater than that of luminol-N-hydroxysuccinimide system and classical luminol-hydrogen peroxide system, respectively. The luminol-NHPI system achieves the highly sensitive detection of luminol (LOD = 70pM) and NHPI (LOD = 910nM). Based on their excellent quenching efficiencies, superoxide dismutase and uric acid are sensitively detected with LODs of 3ng/mL and 10pM, respectively. Co2+ is also detected a LOD of 30pM by its remarkable enhancing effect. Noteworthily, our method is at least 4 orders of magnitude more sensitive than previously reported uric acid detection methods, and can detect uric acid in human urine and Co2+ in tap and lake water real samples with excellent recoveries in the range of 96.35-102.70%. This luminol-NHPI system can be an important candidate for biochemical, clinical and environmental analysis.

Stainless Steel Electrode for Sensitive Luminol Electrochemiluminescent Detection of H2O2, Glucose, and Glucose Oxidase Activity.

Electrogenerated chemiluminescence (ECL) application of stainless steel, a robust and cost-effective material, has been developed for the first time. Type 304 stainless steel electrode shows appealing ECL performance in the luminol-H2O2 system. It enables the detection of H2O2 with a linear range from 1 to 1000 nM and a limit of detection of 0.456 nM [signal-to-noise ratio (S/N) = 3]. The ECL method based on type 304 stainless steel electrode is more sensitive, more cost-effective, and much simpler than other ECL methods reported before. Because the stainless steel electrode has excellent performance for H2O2 detection and H2O2 participates in many important enzymatic reactions, applications of stainless steel electrode-based ECL for detection of enzyme activities and enzyme substrates were further investigated by use of glucose oxidase (GODx) and glucose as representative enzyme and substrate. The concentrations of glucose and the activity of GODx were directly proportional to ECL intensities over a range of 0.1-1000 µM and 0.001-0.7 units/mL with limits of detection of 0.076 µM and 0.00087 unit/mL (S/N = 3), respectively. This method was successfully used for determining glucose in honey. Because of their remarkable performance and user-friendly features, stainless steel electrodes hold great promise in various electroanalytical applications, such as biosensing, disposable sensors, and wearable sensors.

Surfactant-free synthesis of three-dimensional nitrogen-doped hierarchically porous carbon and its application as an electrode modification material for simultaneous sensing of ascorbic acid, dopamine and uric acid.

Three-dimensional N-doped hierarchically porous carbon (3D NHPC) was synthesized successfully without using any surfactant or etching agent. This simple and effective synthesis method was accomplished by solvothermal synthesis followed by pyrolysis. The physical morphology and chemical composition of 3D NHPC were verified by scanning electron microscopy, nitrogen adsorption-desorption, and X-ray photoelectron spectroscopy. Its structural studies reveal that it exhibits a micro-mesoporous hierarchical structure and contains C, O and N atoms forming different functional groups. The characterization also reveals that 3D NHPC has a Brunauer-Emmett-Teller (BET) surface area of 594.774 m2 g-1 and the micropore volume was calculated to be 0.192 cm3 g-1 using the t-plot method. Its catalytic activity was investigated by studying its application for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) by cyclic voltammetry and square-wave voltammetry at physiological pH. A 3D NHPC-modified glassy carbon electrode exhibits linear ranges from 0.05 to 14.50 µM, 1.0 to 120.0 µM, and 2.0 to 30.0 µM for DA, AA and UA, respectively. It also exhibits low detection limits (0.02, 0.10, and 0.14 µM for DA, AA, and UA, respectively), good reproducibility and stability. The urine sample analysis results show good recoveries ranging between 96.30% and 105.40%.

Sensitive and selective electrochemical detection of artemisinin based on its reaction with p-aminophenylboronic acid.

The electrochemical detection of artemisinin generally requires high oxidation potential or the use of complex electrode modification. We find that artemisinin can react with p-aminophenylboronic acid to produce easily electrochemically detectable aminophenol for the first time. By making use of the new reaction, we report an alternative method to detect artemisinin through the determination of p-aminophenol. The calibration curve for the determination of artemisinin is linear in the range of 2 µmol L(-1) to 200 µmol L(-1) with the detection limit of 0.8 µmol L(-1), which is more sensitive than other reported electrochemical methods. The relative standard deviation is 4.83% for the determination of 10 µM artemisinin. Because the oxidation potential of p-aminophenol is around 0 V, the present method is high selective. When 40 µM, 90 µM and 140 µM of artemisinin were spiked to compound naphthoquine phosphate tablet samples, the recoveries are 107.6%, 105.4% and 101.7%, respectively. This detection strategy is attractive for the detection of artemisinin and its derivatives. The finding that artemisinin can react with aromatic boronic acid has the potential to be exploited for the development of other sensors, such as fluorescence artemisinin sensors.

N-doped graphitic layer encased cobalt nanoparticles as efficient oxygen reduction catalysts in alkaline media.

Nitrogen doped graphitic layer encased cobalt (N-C@Co) nanoparticles, as novel non-precious-metal catalysts for the oxygen reduction reaction (ORR), were fabricated by a facile method using cyanamide and cobalt nitrate as precursors. The N-C@Co catalysts exhibited comparable catalytic performance, better stability and improved methanol tolerance towards the ORR than those of the commercial Pt/C catalyst.

Green and facile synthesis of an Au nanoparticles@polyoxometalate/ordered mesoporous carbon tri-component nanocomposite and its electrochemical applications.

The one-pot synthesis of a well-defined Au nanoparticles@polyoxometalates/ordered mesoporous carbon (Au@POMs/OMC) tri-component nanocomposite is reported, which is facile, green and rapid. The polyoxometalates were used as both reductant and bridging molecules. The formation of these composite materials was verified by a comprehensive characterization using X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectra, scanning electron microscopy, and transmission electron microscopy. The novel nanohybrids of Au@POMs/OMC can provide new features of electrocatalytic activities, because of the synergetic effects of Au nanoparticles and OMC materials. Most importantly, the amperometric measurements show that the Au@POMs/OMC nanohybrids have a high catalytic activity with a good sensitivity, long-term stability, wide linear range, low detection limit, and fast response towards acetaminophenol, H2O2, and NADH detection for application as an enzyme-free biosensor.

Metal organic frameworks/macroporous carbon composites with enhanced stability properties and good electrocatalytic ability for ascorbic acid and hemoglobin.

The thermal, water and electrochemical stability of Cu-based metal organic frameworks (Cu-MOFs) confined in macroporous carbon (MPC) hybrids has been investigated. Thermogravimetric analyses, X-Ray diffraction, scanning electron microscopy, and cyclic voltammetry were employed to confirm the stability of pure Cu-MOFs, MPC, and Cu-MOFs-MPC. As compared to pure Cu-MOFs, the porous composite materials of MPC and Cu-MOFs interact and seem to form new materials having homogenous structure and chemistry, which show structural stability in aqueous media and electrochemical stability in phosphate buffer solution (PBS pH 7.4). The detection of ascorbic acid and hemoglobin is performed as an electrochemical probe, indicating Cu-MOFs-MPC holds great promise for the design of electrochemical sensors.

Electrochemical properties of boron-doped ordered mesoporous carbon as electrocatalyst and Pt catalyst support.

The electrochemical properties of boron-doped ordered mesoporous carbon (BOMC) as an electrode material and Pt catalyst support were investigated. The BOMC was synthesized and its structure was examined by transmission electron microscopy (TEM), scanning electron microscopy, nitrogen adsorption-desorption, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). More defective sites were introduced into OMC by the doping of boron. Six electroactive compounds were employed to investigate their electrochemical responses on BOMC and OMC modified glassy carbon electrodes. The BOMC, with more defective sites, exhibited high activity toward the electroactive compounds. The property of BOMC of supporting platinum nanoparticle catalyst was examined. Pt nanoparticles were loaded onto BOMC and OMC, and this was confirmed by TEM, XPS and thermogravimetric analysis. Pt nanoparticles with an average diameter of 2.62 nm were deposited on BOMC. The doping of boron into OMC facilitates the dispersion of Pt nanoparticles. Pt nanoparticles supported on BOMC (Pt-BOMC) and Pt nanoparticles supported on OMC (Pt-OMC) were electrochemically characterized. The electrocatalytic activity of Pt-BOMC toward methanol oxidation reaction was compared with that of Pt-OMC and commercial Pt-C catalyst. The results show that the electrocatalytic activity of BOMC is significantly higher than that of other used catalysts.