Direct Electrochemistry and Electrocatalysis of Horseradish Peroxidase Immobilized in a DNA/Chitosan-Fe3O4 Magnetic Nanoparticle Bio-Complex Film

A DNA/chitosan-Fe₃O₄ magnetic nanoparticle bio-complex film was constructed for the immobilization of horseradish peroxidase (HRP) on a glassy carbon electrode. HRP was simply mixed with DNA, chitosan and Fe₃O₄ nanoparticles, and then applied to the electrode surface to form an enzyme-incorporated polyion complex film. Scanning electron microscopy (SEM) was used to study the surface features of DNA/chitosan/Fe₃O₄/HRP layer. The results of electrochemical impedance spectroscopy (EIS) show that Fe₃O₄ and enzyme were successfully immobilized on the electrode surface by the DNA/chitosan bio-polyion complex membrane. Direct electron transfer (DET) and bioelectrocatalysis of HRP in the DNA/chitosan/Fe₃O₄ film were investigated by cyclic voltammetry (CV) and constant potential amperometry. The HRP-immobilized electrode was found to undergo DET and exhibited a fast electron transfer rate constant of 3.7 s⁻¹. The CV results showed that the modified electrode gave rise to well-defined peaks in phosphate buffer, corresponding to the electrochemical redox reaction between HRP(Fe^(III)) and HRP(Fe^(II)). The obtained electrode also displayed an electrocatalytic reduction behavior towards H₂O₂. The resulting DNA/chitosan/Fe₃O₄/HRP/glassy carbon electrode (GCE) shows a high sensitivity (20.8 A·cm⁻²·M⁻¹) toward H₂O₂. A linear response to H₂O₂ measurement was obtained over the range from 2 μM to 100 μM (R² = 0.99) and an amperometric detection limit of 1 μM (S/N = 3). The apparent Michaelis-Menten constant of HRP immobilized on the electrode was 0.28 mM. Furthermore, the electrode exhibits both good operational stability and storage stability.     

Effect of Sintering Temperature on Adhesion Property and Electrochemical Activity of Pt/YSZ Electrode

The (Pt/YSZ)/YSZ sensor unit is the basic component of the NO_x sensor, which can detect the emission of nitrogen oxides in exhaust fumes and optimize the fuel combustion process. In this work, the effect of sintering temperature on adhesion property and electrochemical activity of Pt/YSZ electrode was investigated. Pt/YSZ electrodes were prepared at different sintering temperatures. The microstructure of the Pt/YSZ electrodes, as well as the interface between Pt/YSZ electrode and YSZ electrolyte, were observed by SEM. Chronoamperometry, linear scan voltammetry, and AC impedance were tested by the electrochemical workstation. The results show that increasing the sintering temperature (≤1500 °C) helped to improve adhesion property and electrochemical activity of the Pt/YSZ electrode, which benefited from the formation of the porous structure of the Pt/YSZ electrode. For the (Pt/YSZ) electrode/YSZ electrolyte system, O²⁻ in YSZ is converted into chemisorbed O₂ on Pt/YSZ, which is desorbed into the gas phase in the form of molecular oxygen; this process could be the rate-controlling step of the anodic reaction. Increasing the sintering temperature (≤1500 °C) could reduce the reaction activation energy of the Pt/YSZ electrode. The activation energy reaches the minimum value (1.02 eV) when the sintering temperature is 1500 °C.     

The antioxidant role of thiocyanate in the pathogenesis of cystic fibrosis and other inflammation-related diseases

Cystic fibrosis (CF) is a pleiotropic disease, originating from mutations in the CF transmembrane conductance regulator (CFTR). Lung injuries inflicted by recurring infection and excessive inflammation cause ≈90% of the morbidity and mortality of CF patients. It remains unclear how CFTR mutations lead to lung illness. Although commonly known as a Cl⁻ channel, CFTR also conducts thiocyanate (SCN⁻) ions, important because, in several ways, they can limit potentially harmful accumulations of hydrogen peroxide (H₂O₂) and hypochlorite (OCl⁻). First, lactoperoxidase (LPO) in the airways catalyzes oxidation of SCN⁻ to tissue-innocuous hypothiocyanite (OSCN⁻), while consuming H₂O₂. Second, SCN⁻ even at low concentrations competes effectively with Cl⁻ for myeloperoxidase (MPO) (which is released by white blood cells), thus limiting OCl⁻ production by the enzyme. Third, SCN⁻ can rapidly reduce OCl⁻ without catalysis. Here, we show that SCN⁻ and LPO protect a lung cell line from injuries caused by H₂O₂; and that SCN⁻ protects from OCl⁻ made by MPO. Of relevance to inflammation in other diseases, we find that in three other tested cell types (arterial endothelial cells, a neuronal cell line, and a pancreatic β cell line) SCN⁻ at concentrations of ≥100 μM greatly attenuates the cytotoxicity of MPO. Humans naturally derive SCN⁻ from edible plants, and plasma SCN⁻ levels of the general population vary from 10 to 140 μM. Our findings raise the possibility that insufficient levels of antioxidant SCN⁻ provide inadequate protection from OCl⁻, thus worsening inflammatory diseases, and predisposing humans to diseases linked to MPO activity, including atherosclerosis, neurodegeneration, and certain cancers.     

Endothelial nitric oxide synthase negatively regulates hydrogen peroxide-stimulated AMP-activated protein kinase in endothelial cells

Hydrogen peroxide and other reactive oxygen species are intimately involved in endothelial cell signaling. In many cell types, the AMP-activated protein kinase (AMPK) has been implicated in the control of metabolic responses, but the role of endothelial cell redox signaling in the modulation of AMPK remains to be completely defined. We used RNA interference and pharmacological methods to establish that H₂O₂ is a critical activator of AMPK in cultured bovine aortic endothelial cells (BAECs). H₂O₂ treatment of BAECs rapidly and significantly increases the phosphorylation of AMPK. The EC₅₀ for H₂O₂-promoted phosphorylation of AMPK is 65 ± 15 μM, within the physiological range of cellular H₂O₂ concentrations. The Ca²⁺/calmodulin-dependent protein kinase kinase-β (CaMKKβ) inhibitor STO-609 abolishes H₂O₂-dependent AMPK activation, whereas eNOS inhibitors enhance AMPK activation. Similarly, siRNA-mediated knockdown of CaMKKβ abrogates AMPK activation, whereas siRNA-mediated knockdown of eNOS leads to a striking increase in AMPK phosphorylation. Cellular imaging studies using the H₂O₂ biosensor HyPer show that siRNA-mediated eNOS knockdown leads to a marked increase in intracellular H₂O₂ generation, which is blocked by PEG-catalase. eNOS^−/− mice show a marked increase in AMPK phosphorylation in liver and lung compared to wild-type mice. Lung endothelial cells from eNOS^−/− mice also show a significant increase in AMPK phosphorylation. Taken together, these results establish that CaMKKβ is critically involved in mediating the phosphorylation of AMPK promoted by H₂O₂ in endothelial cells, and document that eNOS is an important negative regulator of AMPK phosphorylation and intracellular H₂O₂ generation in endothelial cells.     

Phosphatidylinositol 4,5-bisphosphate (PIP2) stimulates the electrogenic Na/HCO3 cotransporter NBCe1-A expressed in Xenopus oocytes

Bicarbonate transporters are regulated by signaling molecules/ions such as protein kinases, ATP, and Ca²⁺. While phospholipids such as PIP₂ can stimulate Na-H exchanger activity, little is known about phospholipid regulation of bicarbonate transporters. We used the patch-clamp technique to study the function and regulation of heterologously expressed rat NBCe1-A in excised macropatches from Xenopus laevis oocytes. Exposing the cytosolic side of inside-out macropatches to a 5% CO₂/33 mM HCO₃⁻ solution elicited a mean inward current of 14 pA in 74% of macropatches attached to pipettes (−V_p = −60 mV) containing a low-Na⁺, nominally HCO₃⁻-free solution. The current was 80–90% smaller in the absence of Na⁺, approximately 75% smaller in the presence of 200 μM DIDS, and absent in macropatches from H₂O-injected oocytes. NBCe1-A currents exhibited time-dependent rundown that was inhibited by removing Mg²⁺ in the presence or absence of vanadate and F⁻ to reduce general phosphatase activity. Applying 5 or 10 μM PIP₂ (diC8) in the presence of HCO₃⁻ induced an inward current in 54% of macropatches from NBC-expressing, but not H₂O-injected oocytes. PIP₂-induced currents were HCO₃⁻-dependent and somewhat larger following more NBCe1-A rundown, 62% smaller in the absence of Na⁺, and 90% smaller in the presence of 200 μM DIDS. The polycation neomycin (250–500 μM) reduced the PIP₂-induced inward current by 69%; spermine (100 μM) reduced the current by 97%. Spermine, poly-D-lysine, and neomycin all reduced the baseline HCO₃⁻-induced inward currents by as much as 85%. In summary, PIP₂ stimulates NBCe1-A activity, and phosphoinositides are regulators of bicarbonate transporters.     

High Electrochemical Performance Silicon Thin-Film Free-Standing Electrodes Based on Buckypaper for Flexible Lithium-Ion Batteries

Recently, applications for lithium-ion batteries (LIBs) have expanded to include electric vehicles and electric energy storage systems, extending beyond power sources for portable electronic devices. The power sources of these flexible electronic devices require the creation of thin, light, and flexible power supply devices such as flexile electrolytes/insulators, electrode materials, current collectors, and batteries that play an important role in packaging. Demand will require the progress of modern electrode materials with high capacity, rate capability, cycle stability, electrical conductivity, and mechanical flexibility for the time to come. The integration of high electrical conductivity and flexible buckypaper (oxidized Multi-walled carbon nanotubes (MWCNTs) film) and high theoretical capacity silicon materials are effective for obtaining superior high-energy-density and flexible electrode materials. Therefore, this study focuses on improving the high-capacity, capability-cycling stability of the thin-film Si buckypaper free-standing electrodes for lightweight and flexible energy-supply devices. First, buckypaper (oxidized MWCNTs) was prepared by assembling a free stand-alone electrode, and electrical conductivity tests confirmed that the buckypaper has sufficient electrical conductivity (10⁻⁴(S m⁻¹) in LIBs) to operate simultaneously with a current collector. Subsequently, silicon was deposited on the buckypaper via magnetron sputtering. Next, the thin-film Si buckypaper freestanding electrodes were heat-treated at 600 °C in a vacuum, which improved their electrochemical performance significantly. Electrochemical results demonstrated that the electrode capacity can be increased by 27/26 and 95/93 μAh in unheated and heated buckypaper current collectors, respectively. The measured discharge/charge capacities of the USi_HBP electrode were 108/106 μAh after 100 cycles, corresponding to a Coulombic efficiency of 98.1%, whereas the HSi_HBP electrode indicated a discharge/charge capacity of 193/192 μAh at the 100th cycle, corresponding to a capacity retention of 99.5%. In particular, the HSi_HBP electrode can decrease the capacity by less than 1.5% compared with the value of the first cycle after 100 cycles, demonstrating excellent electrochemical stability.     

Redox Response of Reduced Graphene Oxide-Modified Glassy Carbon Electrodes to Hydrogen Peroxide and Hydrazine

The surface of a glassy carbon (GC) electrode was modified with reduced graphene oxide (rGO) to evaluate the electrochemical response of the modified GC electrodes to hydrogen peroxide (H₂O₂) and hydrazine. The electrode potential of the GC electrode was repeatedly scanned from −1.5 to 0.6 V in an aqueous dispersion of graphene oxide (GO) to deposit rGO on the surface of the GC electrode. The surface morphology of the modified GC electrode was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). SEM and AFM observations revealed that aggregated rGO was deposited on the GC electrode, forming a rather rough surface. The rGO-modified electrodes exhibited significantly higher responses in redox reactions of H₂O₂ as compared with the response of an unmodified GC electrode. In addition, the electrocatalytic activity of the rGO-modified electrode to hydrazine oxidation was also higher than that of the unmodified GC electrode. The response of the rGO-modified electrode was rationalized based on the higher catalytic activity of rGO to the redox reactions of H₂O₂ and hydrazine. The results suggest that rGO-modified electrodes are useful for constructing electrochemical sensors.     

Carbon Felt-Based Bioelectrocatalytic Flow-Through Detectors: 2,6-Dichlorophenol Indophenol and Peroxidase Coadsorbed Carbon-Felt for Flow-Amperometric Determination of Hydrogen Peroxide

2,6-dichlorophenol indophenol (DCIP) and horseradish peroxidase (HRP) were coadsorbed on a porous carbon felt (CF) from their mixed aqueous solution under ultrasound irradiation for 5 min. The resulting DCIP and HRP-coadsorbed CF (DCIP/HRP-CF) showed an excellent bioelectrocatalytic activity for the reduction of H₂O₂. The coadsorption of DCIP together with HRP was essential to obtain larger bioelectrocatalytic current to H₂O₂. The DCIP/HRP-CF was successfully used as a working electrode unit of a bioelectrocatalytic flow-through detector for highly sensitive and continuous amperometric determination of H₂O₂. Under the optimized operational conditions (i.e., applied potential, +0.2 V versus Ag/AgCl; carrier pH 5.0, and carrier flow rate, 1.9 mL/min), the cathodic peak current of H₂O₂ linearly increased over the concentration range from 0.1 to 30 μM (the sensitivity, 0.88 μA/μM (slope of linear part); the limit of detection, 0.1 μM (S/N = 3) current noise level, 30 nA) with a sample through-put of ca. 40–90 samples/h.     

Tribological Behavior of Reduced Graphene Oxide–Al2O3 Nanofluid: Interaction among Testing Force,Rotational Speed and Nanoparticle Concentration

The tribological properties of nanofluids are influenced by multiple factors, and the interrelationships among the factors are deserving of further attention. In this paper, response surface methodology (RSM) was used to study the tribological behavior of reduced graphene oxide–Al₂O₃ (rGO-Al₂O₃) nanofluid. The interaction effects of testing force, rotational speed and nanoparticle concentration on the friction coefficient (μ), wear rate (W_r) and surface roughness (R_a) of steel disks were investigated via the analysis of variance. It was confirmed that all the three input variables were significant for μ and W_r values, while testing force, nanoparticle concentration and its interaction with testing force and rotational speed were identified as significant parameters for R_a value. According to regression quadratic models, the optimized response values were 0.088, 2.35 × 10⁻⁷ mm³·N⁻¹·m⁻¹ and 0.832 μm for μ, W_r and R_a, which were in good agreement with the actual validation experiment values. The tribological results show that 0.20% was the optimum mass concentration which exhibited excellent lubrication performance. Compared to the base fluid, μ, W_r and R_a values had a reduction of approximately 45.6%, 90.3% and 56.0%. Tribochemical reactions occurred during the friction process, and a tribofilm with a thickness of approximately 20 nm was generated on the worn surface, consisting of nanoparticle fragments (rGO and Al₂O₃) and metal oxides (Fe₂O₃ and FeO) with self-lubrication properties.     

A Novel Voltametric Measurements of Beta Blocker Drug Propranolol on Glassy Carbon Electrode Modified with Carbon Black Nanoparticles

A new voltametric method for highly sensitive propranolol (PROP) determination was developed. A glassy carbon electrode modified with a hybrid material made of carbon black (CB) and Nafion was used as the working electrode. The preconcentration potential and time were optimized (550 mV and 15 s), as well as the supporting electrolyte (0.1 mol L⁻¹ H₂SO₄). For 15 s preconcentration time, linearity was achieved in the range 0.5–3.5 μmol L⁻¹ and for 120 s in 0.02–0.14 μmol L⁻¹. Based on the conducted calibration (120 s preconcentration time) limit of detection (LOD) was calculated and was equal to 7 nmol L⁻¹. To verify the usefulness of the developed method, propranolol determination was carried out in real samples (tablets and freeze-dried urine). Recoveries were calculated and were in the range 92–102%, suggesting that the method might be considered as accurate. The repeatability of the signal expressed as relative standard deviation (RSD) was equal to 1.5% (n = 9, PROP concentration 2.5 µmol L⁻¹). The obtained results proved that the developed method for propranolol determination might be successfully applied in routine laboratory practice.     

Insights into the P-to-Q conversion in the catalytic cycle of methane monooxygenase from a synthetic model system

For the catalytic cycle of soluble methane monooxygenase (sMMO), it has been proposed that cleavage of the O–O bond in the (μ-peroxo)diiron(III) intermediate P gives rise to the diiron(IV) intermediate Q with an Fe₂(μ–O)₂ diamond core, which oxidizes methane to methanol. As a model for this conversion, (μ–oxo) diiron(III) complex 1 ([Fe^III₂(μ–O)(μ–O₂H₃)(L)₂]³⁺, L = tris(3,5-dimethyl-4-methoxypyridyl-2-methyl)amine) has been treated consecutively with one eq of H₂O₂ and one eq of HClO₄ to form 3 ([Fe^IV₂(μ–O)₂(L)₂]⁴⁺). In the course of this reaction a new species, 2, can be observed before the protonation step; 2 gives rise to a cationic peak cluster by ESI-MS at m/z 1,399, corresponding to the {[Fe₂O₃L₂H](OTf)₂}⁺ ion in which 1 oxygen atom derives from 1 and the other two originate from H₂O₂. Mössbauer studies of 2 reveal the presence of two distinct, exchange coupled iron(IV) centers, and EXAFS fits indicate a short Fe–O bond at 1.66 Å and an Fe–Fe distance of 3.32 Å. Taken together, the spectroscopic data point to an HO-Fe^IV-O-Fe^IV = O core for 2. Protonation of 2 results in the loss of H₂O and the formation of 3. Isotope labeling experiments show that the [Fe^IV₂(μ–O)₂] core of 3 can incorporate both oxygen atoms from H₂O₂. The reactions described here serve as the only biomimetic precedent for the conversion of intermediates P to Q in the sMMO reaction cycle and shed light on how a peroxodiiron(III) unit can transform into an [Fe^IV₂(μ–O)₂] core.     

Hierarchical Nanocomposites Electrospun Carbon NanoFibers/Carbon Nanotubes as a Structural Element of Potentiometric Sensors

This work proposes new carbon materials for intermediate layers in solid-contact electrodes sensitive for potassium ions. The group of tested materials includes electrospun carbon nanofibers, electrospun carbon nanofibers with incorporated cobalt nanoparticles and hierarchical nanocomposites composed of carbon nanotubes deposited on nanofibers with different metal nanoparticles (cobalt or nickel) and nanotube density (high or low). Materials were characterized using scanning electron microscopy and contact angle microscopy. Electrical parameters of ready-to-use electrodes were characterized using chronopotentiometry and electrochemical impedance spectroscopy. The best results were obtained for potassium electrodes with carbon nanofibers with nickel-cobalt nanoparticles and high density of nanotubes layer: the highest capacity value (330 µF), the lowest detection limit (10^−6.3 M), the widest linear range (10⁻⁶–10⁻¹) and the best reproducibility of normal potential (0.9 mV). On the other hand the best potential reversibility, the lowest potential drift (20 μV·h⁻¹) in the long-term test and the best hydrophobicity (contact angle 168°) were obtained for electrode with carbon nanofibers with cobalt nanoparticles and high density of carbon nanotubes. The proposed electrodes can be used successfully in potassium analysis of real samples as shown in the example of tomato juices.     

Analysis of Performance Losses and Degradation Mechanism in Porous La2−X NiTiO6−δ:YSZ Electrodes

The electrode performance and degradation of 1:1 La_2−xNiTiO_6−δ:YSZ composites (x = 0, 0.2) has been investigated to evaluate their potential use as SOFC cathode materials by combining electrochemical impedance spectroscopy in symmetrical cell configuration under ambient air at 1173 K, XRD, electron microscopy and image processing studies. The polarisation resistance values increase notably, i.e., 0.035 and 0.058 Ωcm² h⁻¹ for x = 0 and 0.2 samples, respectively, after 300 h under these demanding conditions. Comparing the XRD patterns of the initial samples and after long-term exposure to high temperature, the perovskite structure is retained, although La₂Zr₂O₇ and NiO appear as secondary phases accompanied by peak broadening, suggesting amorphization or reduction of the crystalline domains. SEM and TEM studies confirm the ex-solution of NiO with time in both phases and also prove these phases are prone to disorder. From these results, degradation in La_2−xNiTiO_6−δ:YSZ electrodes is due to the formation of La₂Zr₂O₇ at the electrode–electrolyte interface and the ex-solution of NiO, which in turn results in the progressive structural amorphization of La₁₈NiTiO_6−δ phases. Both secondary phases constitute a non-conductive physical barrier that would hinder the ionic diffusion at the La_2−xNiTiO_6−δ:YSZ interface and oxygen access to surface active area.     

One-Pot Self-Assembly of Dinuclear,Tetranuclear, and H-Bonding-Directed Polynuclear Cobalt(II), Cobalt(III), and Mixed-Valence Co(II)/Co(III) Complexes of Schiff Base Ligands with Incomplete Double Cubane Core

The reaction of 2,6-diformyl-4-methylphenol (DFMF) with 1-amino-2-propanol (AP) and tris(hydroxymethyl)aminomethane (THMAM) was investigated in the presence of Cobalt(II) salts, (X = ClO₄⁻, CH₃CO₂⁻, Cl⁻, NO₃⁻), sodium azide (NaN₃), and triethylamine (TEA). In one pot, the variation in Cobalt(II) salt results in the self-assembly of dinuclear, tetranuclear, and H-bonding-directed polynuclear coordination complexes of Cobalt(III), Cobalt(II), and mixed-valence Co^IICo^III: [Co₂^III(H₂L⁻¹)₂(AP⁻¹)(N₃)](ClO₄)₂ (1), [Co₄(H₂L⁻¹)₂(µ₃-1,1,1-N₃)₂(µ-1,1-N₃)₂Cl₂(CH₃OH)₂]·4CH₃OH (2), [Co₂^IICo₂^III(HL⁻²)₂(µ-CH₃CO₂)₂(µ₃-OH)₂](NO₃)₂·2CH₃CH₂OH (3), and [Co₂^IICo₂^III (H₂L1²⁻)₂(THMAM⁻¹)₂](NO₃)₄ (4). In 1, two cobalt(III) ions are connected via three single atom bridges; two from deprotonated ethanolic oxygen atoms in the side arms of the ligands and one from the1-amino-2-propanol moiety forming a dinuclear unit with a very short (2.5430(11) Å) Co-Co intermetallic separation with a coordination number of 7, a rare feature for cobalt(III). In 2, two cobalt(II) ions in a dinuclear unit are bridged through phenoxide O and μ₃-1,1,1-N₃ azido bridges, and the two dinuclear units are interconnected by two μ-1,1-N₃ and two μ₃-1,1,1-N₃ azido bridges generating tetranuclear cationic [Co₄(H₂L⁻¹)₂(µ₃-1,1,1-N₃)₂(µ-1,1-N₃)₂Cl₂(CH₃OH)₂]²⁺ units with an incomplete double cubane core, which grow into polynuclear 1D-single chains along the a-axis through H-bonding. In 3, HL²⁻ holds mixed-valent Co(II)/Co(III) ions in a dinuclear unit bridged via phenoxide O, μ-1,3-CH₃CO₂⁻, and μ₃-OH⁻ bridges, and the dinuclear units are interconnected through two deprotonated ethanolic O in the side arms of the ligands and two μ₃-OH⁻ bridges generating cationic tetranuclear [Co₂^IICo₂^III(HL⁻²)₂(µ-CH₃CO₂)₂(µ_3-OH)₂]²⁺ units with an incomplete double cubane core. In 4, H₂L1⁻² holds mixed-valent Co(II)/Co(III) ions in dinuclear units which dimerize through two ethanolic O (μ-RO⁻) in the side arms of the ligands and two ethanolic O (μ₃-RO⁻) of THMAM bridges producing centrosymmetric cationic tetranuclear [Co₂^IICo₂^III (H₂L1⁻²)₂(THMAM⁻¹)₂]⁴⁺ units which grow into 2D-sheets along the bc-axis through a network of H-bonding. Bulk magnetization measurements on 2 demonstrate that the magnetic interactions are completely dominated by an overall ferromagnetic coupling occurring between Co(II) ions.     

Electrical Properties of Thin-Film Capacitors Fabricated Using High Temperature Sputtered Modified Barium Titanate

Simple thin-film capacitor stacks were fabricated from sputter-deposited doped barium titanate dielectric films with sputtered Pt and/or Ni electrodes and characterized electrically. Here, we report small signal, low frequency capacitance and parallel resistance data measured as a function of applied DC bias, polarization versus applied electric field strength and DC load/unload experiments. These capacitors exhibited significant leakage (in the range 8–210 μA/cm²) and dielectric loss. Measured breakdown strength for the sputtered doped barium titanate films was in the range 200 kV/cm −2 MV/cm. For all devices tested, we observed clear evidence for dielectric saturation at applied electric field strengths above 100 kV/cm: saturated polarization was in the range 8–15 μC/cm². When cycled under DC conditions, the maximum energy density measured for any of the capacitors tested here was ~4.7 × 10⁻² W-h/liter based on the volume of the dielectric material only. This corresponds to a specific energy of ~8 × 10⁻³ W-h/kg, again calculated on a dielectric-only basis. These results are compared to those reported by other authors and a simple theoretical treatment provided that quantifies the maximum energy that can be stored in these and similar devices as a function of dielectric strength and saturation polarization. Finally, a predictive model is developed to provide guidance on how to tailor the relative permittivities of high-k dielectrics in order to optimize their energy storage capacities.     

Bismuth/Porous Graphene Heterostructures for Ultrasensitive Detection of Cd (II)

Heavy metals pollution is one of the key problems of environment protection. Electrochemical methods, particularly anodic stripping voltammetry, have been proven a powerful tool for rapid detection of heavy metal ions. In the present work, a bismuth modified porous graphene (Bi@PG) electrode as an electrochemical sensor was adopted for the detection of heavy metal Cd²⁺ in an aqueous solution. Combining excellent electronic properties in sensitivity, peak resolution, and high hydrogen over-potential of bi-continuous porous Bi with the large surface-area and high conductivity on PG, the Bi@PG electrode exhibited excellent sensing ability. The square wave anodic stripping voltammetry response showed a perfect liner range of 10⁻⁹–10⁻⁸ M with a correlation coefficient of 0.9969. The limit of detection (LOD) and the limit of quantitation (LOQ) are calculated to be 0.1 and 0.34 nM with a sensitivity of 19.05 μA·nM⁻¹, which is relatively excellent compared to other carbon-based electrodes. Meanwhile, the Bi@PG electrode showed tremendous potential in composite detection of multifold heavy metals (such as Pb²⁺ and Cd²⁺) and wider linear range.     

Machine learning–based inverse design for electrochemically controlled microscopic gradients of O2 and H2O2

A fundamental understanding of extracellular microenvironments of O₂ and reactive oxygen species (ROS) such as H₂O₂, ubiquitous in microbiology, demands high-throughput methods of mimicking, controlling, and perturbing gradients of O₂ and H₂O₂ at microscopic scale with high spatiotemporal precision. However, there is a paucity of high-throughput strategies of microenvironment design, and it remains challenging to achieve O₂ and H₂O₂ heterogeneities with microbiologically desirable spatiotemporal resolutions. Here, we report the inverse design, based on machine learning (ML), of electrochemically generated microscopic O₂ and H₂O₂ profiles relevant for microbiology. Microwire arrays with suitably designed electrochemical catalysts enable the independent control of O₂ and H₂O₂ profiles with spatial resolution of ∼10¹ μm and temporal resolution of ∼10° s. Neural networks aided by data augmentation inversely design the experimental conditions needed for targeted O₂ and H₂O₂ microenvironments while being two orders of magnitude faster than experimental explorations. Interfacing ML-based inverse design with electrochemically controlled concentration heterogeneity creates a viable fast-response platform toward better understanding the extracellular space with desirable spatiotemporal control.

Ubiquitous spatiotemporal heterogeneity of natural environments fosters the diverse and fascinating biology that our world embraces, and motivates researchers to mimic natural environments with high spatiotemporal resolution (1–5). Given their close relevance in biochemical metabolisms, dioxygen (O₂) and hydrogen peroxide (H₂O₂) as a surrogate of reactive oxygen species (ROS) are two ubiquitous biologically relevant species in extracellular medium (1, 6). Their extracellular spatial and temporal distributions, particularly at the microscopic scale ranging from 1 μm to 100 μm (7–11), are critical for signal transduction, protein expression, biochemical redox balance, and regulation for cellular metabolism with extensive ecological, environmental, and biomedical implications (Fig. 1A) (1, 3, 8–13). A programmable creation of the spatiotemporal concentration profiles of O₂ and H₂O₂ offers the freedom to mimic, control, and perturb the microenvironments of O₂ and H₂O₂ and hence advance our understanding in microbiology.Open in a separate windowFig. 1.AI-based inverse design of electrochemically generated O₂ and H₂O₂ heterogeneities. (A) The ubiquitous spatiotemporal heterogeneities of O₂ and H₂O₂ in microbiology and the challenges posed in this research topic. (B) The combination of electrochemistry and ML-based inverse design offers a viable approach to mimicking and controlling the heterogeneities of O₂ and H₂O₂ in microbiology. O, oxidant; R, reductant; E_appl (t), the time-dependent electrochemical voltages applied on electrodes. (C) The design of the electrochemically active microwire array electrodes for the generation of O₂ and H₂O₂ gradients; 4e⁻ ORR & 2e⁻ ORR, four-electron and two-electron oxygen reduction reaction into H₂O and H₂O₂, respectively. (D and E) The 45°-tilting images of SEM for the representative microwire arrays used for the training of the ML model (D) and the ones inversely designed for targeted O₂ and H₂O₂ gradients (E); k = (P, D, L), the morphological vector that includes the P, D, and L of the synthesized wire arrays in units of micrometers. (Scale bars, 20 μm.)Despite recent progress (14–18), there remain major technical challenges, particularly in the achievable spatiotemporal resolution and high-throughput design of concentration profiles to suit a plethora of scenarios in microbiology. Approaches based on microfluidics and hydrogels have been able to achieve concentration gradients of O₂ and H₂O₂ through the provision of either O₂/H₂O₂ source (14, 19–21), O₂/H₂O₂ scavenging agents (15, 22, 23), or a combination of both (24) across liquid-impermeable barriers such as agar layers or polymeric thin films (25, 26). Yet such approaches, dependent on passive mass transport and diffusion across more than 10² μm, are inherently incapable of achieving spatial features of less than 100 μm and temporal resolution smaller than ∼10¹ s, the prerequisites to investigate microbiology at cluster or single-cell levels (10–12). Moreover, the large variations of extracellular O₂ and H₂O₂ gradients in different microbial systems demand an inverse design strategy, which, with minimal expenditure, quickly programs a desired concentration profile catering to a specific biological scenario (2–5). The current lack of inverse design protocol impedes the adoption of controllable extracellular heterogeneity to mimic and investigate microbial systems that are of environmental, biomedical, and sustainability-related significance.We envision that the integration of electrochemically generated concentration gradients with inverse design based on machine learning (ML) will address the aforementioned challenges (Fig. 1B). Electrochemistry offers a venue for transducing electric signals into microscopic concentration profiles within ∼10⁰ μm to ∼10² μm away from electrodes’ surface, following the specific electrode reaction kinetics and the mass transport governing equations in the liquid phase (27). Proper designs of electrodes’ microscopic spatial arrangement and electrochemical kinetics lead to concentration gradients that are spatiotemporally programmable by time-dependent electric signals of varying voltages (28). Such benefits of electrochemically generated concentration gradients lead us to employ electrochemistry as a tool to spatiotemporally control the concentration profiles in the extracellular medium. In one example, we found that wire arrays electrochemically active toward O₂ reduction create anoxic microenvironment about 20 μm away from the aerobic external bulk environments, modulate the size and extent of O₂ depletion in the anoxic microenvironment by the wire array’s morphology and applied electrochemical potential (E_appl), and hence enable O₂-sensitive rhizobial N₂ fixation in ambient air powered by renewable electricity (29). Moreover, while not reported before as far as we know, electrochemically generated concentration heterogeneity is commensurate with ML-based inverse design (30, 31), thanks to the mathematically well-defined electrochemical processes that can be numerically simulated (32, 33). We recently reported neural networks, trained by numerically simulated data, that explore the influence of electrode geometry on electrochemical N₂ fixation and achieve optimized morphologies of wire array electrodes untenable without such an ML-based strategy (34). An inverse design for the electrochemically generated gradients will quickly program desirable microenvironments of O₂ and ROS with high spatiotemporal resolutions, thanks to the well-reported electrochemical transformation related to O₂ and H₂O₂ with high electrochemical selectivity (35, 36).In this work, we report an inverse design based on neural networks for independent electrochemical creation of O₂ and ROS microscopic gradients that are relevant, and mimic their extracellular heterogeneities in microbial systems. We hypothesize that careful design of electrocatalysis of O₂ reduction reaction (ORR) can either facilitate four-electron ORR on Pt electrocatalyst for a controllable O₂ spatiotemporal profile or promote two-electron ORR on Au electrocatalyst for a programmable generation of H₂O₂ gradient without significantly perturbing the O₂ one, thanks to their concentration differences in biological mediums (∼10⁻¹ μM to ∼10¹ μM for H₂O₂ and ∼10¹ μM to ∼10² μM for O₂) (2, 7–11). Electrochemically active microwire array electrodes as exemplary model systems (Fig. 1C) are experimentally shown to achieve tunable heterogeneities of O₂ and H₂O₂ independently, with spatial resolution of ∼10¹ μm and temporal resolution of ∼10° s, and are suitable as a platform for independently perturbing biologically relevant O₂ and H₂O₂ profiles in microbial systems. We further established and experimentally validated two neural networks that inversely design the wire array electrodes’ morphologies toward targeted microenvironments of O₂ and H₂O₂, respectively, which is at least one order of magnitude faster than trial-and-error numerical simulation and two orders of magnitude faster than experimental explorations. The demonstrated inverse design of electrochemically generated controlled gradients not only demonstrates a full electrochemical control of concentration profiles in an electrode’s proximity but also establishes an approach of spatiotemporally mimicking and perturbing extracellular space guided by artificial intelligence.     

HfAlOx/Al2O3 Bilayer Dielectrics for a Field Effect Transistor on a Hydrogen-Terminated Diamond

In this work, a hydrogen-terminated (H-terminated) diamond field effect transistor (FET) with HfAlO_x/Al₂O₃ bilayer dielectrics is fabricated and characterized. The HfAlO_x/Al₂O₃ bilayer dielectrics are deposited by the atomic layer deposition (ALD) technique, which can protect the H-terminated diamond two-dimensional hole gas (2DHG) channel. The device demonstrates normally-on characteristics, whose threshold voltage (V_TH) is 8.3 V. The maximum drain source current density (I_DSmax), transconductance (G_m), capacitance (C_OX) and carrier density (ρ) are −6.3 mA/mm, 0.73 mS/mm, 0.22 μF/cm² and 1.53 × 10¹³ cm⁻², respectively.     

Synthesis,Crystal Structure and Luminescent Property of Mg(II) Complex with N-Benzenesulphonyl-L-Leucine and 1,10-Phenanthroline

A new complex [Mg(L)₂(phen)(H₂O)₂](phen)(H₂O)₂ [L= N-benzenesulphonyl-L-leucine] was synthesized by the reaction of magnesium chloride hexahydrate with N-benzenesulphonyl-L-leucine and 1,10-phenanthroline in the CH₃CH₂OH/H₂O (v:v = 5:1). It was characterized by elemental analysis, IR and X-ray single crystal diffraction analysis. The crystal of the title complex [Mg(L)₂(phen)(H₂O)₂](phen)(H₂O)₂ belongs to triclinic, space group P-1 with a = 0.72772(15) nm, b = 1.4279(3) nm, c = 1.4418(3) nm, α = 63.53(3)°, β = 79.75(3)°, γ = 81.83(3)°, V = 1.3163(5) nm³, Z =1, D_c= 1.258 μg·m⁻³, μ = 0.177 mm⁻¹, F(000) = 526, and final R₁ = 0.0506, ωR₂ = 0.1328. The complex comprises a six-coordinated magnesium(II) center, with a N₂O₄ distorted octahedron coordination environment. The molecules are connected by hydrogen bonds and π-π stacking to form one dimensional chain structure. The luminescent property of the Mg(II) complex has been investigated in solid.     

Development of High-Performance Thermoelectric Materials by Microstructure Control of P-Type BiSbTe Based Alloys Fabricated by Water Atomization

Developing inexpensive and rapid fabrication methods for high efficiency thermoelectric alloys is a crucial challenge for the thermoelectric industry, especially for energy conversion applications. Here, we fabricated large amounts of p-type Cu_0.07Bi_0.5Sb_1.5Te₃ alloys, using water atomization to control its microstructure and improve thermoelectric performance by optimizing its initial powder size. All the water atomized powders were sieved with different aperture sizes, of 32–75 μm, 75–125 μm, 125–200 μm, and <200 μm, and subsequently consolidated using hot pressing at 490 °C. The grain sizes were found to increase with increasing powder particle size, which also increased carrier mobility due to improved carrier transport. The maximum electrical conductivity of 1457.33 Ω⁻¹ cm⁻¹ was obtained for the 125–200 μm samples due to their large grain sizes and subsequent high mobility. The Seebeck coefficient slightly increased with decreasing particle size due to scattering of carriers at fine grain boundaries. The higher power factor values of 4.20, 4.22 × 10⁻³ W/mk² were, respectively, obtained for large powder specimens, such as 125–200 μm and 75–125 μm, due to their higher electrical conductivity. In addition, thermal conductivity increased with increasing particle size due to the improvement in carriers and phonons transport. The 75–125 μm powder specimen exhibited a relatively high thermoelectric figure of merit, ZT of 1.257 due to this higher electric conductivity.