Ultrasensitive electrochemical immunosensor for the detection of C-reactive protein antigen.

Cardiovascular disease is one of the leading causes of premature death worldwide, and the determination of C-reactive protein (CRP) from human serum is of vital importance for the diagnosis of the disease. For this study, we have developed an electrochemical immunosensor based on onion-like carbon@polyacrylonitrile (OLC-PAN) for the detection of CRP antigens. This was accomplished by immobilizing CRP antibodies on a modified glassy carbon electrode (GCE). Several electrochemical techniques such as cyclic voltammetry (CV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS) were employed to evaluate the electrochemical detection of the CRP antigen. This ultrasensitive method for CRP antigen detection exhibited a very good logarithmic plot from -4.52 to -12.05 g mL-1 and a limit of detection (LOD) of 0.9 fg mL-1. The high selectivity, sensitivity, and stability of the developed electrochemical immunosensor would facilitate miniaturization for point-of-care applications and the efficient diagnosis of cardiovascular diseases.

Nanostructured cobalt/copper catalysts for efficient electrochemical carbon dioxide reduction.

The search for an efficient and stable catalyst for the electrochemical reduction of CO2 to value-added chemicals is especially critical for lowering the atmospheric CO2 concentration. In this study, self-supported cobalt/copper nanostructured catalysts were designed, where the influences of the elemental composition and acid-etching on their efficiency towards the CO2 reduction reaction were studied. The developed Co/Cu catalysts showed superb catalytic activity with a low onset potential at -0.2 V vs. RHE. Gas and liquid product analysis revealed that formate and CO were the main products. It was observed that lower reductive potentials were favourable for formate production, while higher reductive potentials were more favourable for CO formation. In situ electrochemical FTIR studies were further conducted to gain insight into the CO2 reduction mechanism. The novel synthetic procedure reported in this study leads to promising electrocatalysts with high efficiencies for the conversion of CO2 into valuable products.

In Situ Spectroelectrochemical Study of Acetate Formation by CO2 Reduction Using Bi Catalyst in Amine-Based Capture Solution.

Carbon capture and utilization (CCU) are technologies sought to reduce the level of CO2 in the atmosphere. Industrial carbon capture is associated with energetic penalty, thus there is an opportunity to research alternatives. In this work, spectroelectrochemistry was used to analyze the electrochemical CO2 reduction (eCO2R) in CO2 saturated monoethanolamine (MEA)-based capture solutions, in a novel CCU process. The in situ Fourier transform infrared (FTIR) spectroscopy experiments show that at the Bi catalyst, the active species involved in the eCO2R is the dissolved CO2 in solution, and not carbamate. In addition, the products of eCO2R were evaluated under flow, using commercial Bi2O3 NP as catalyst. Formate and acetate were detected, with normalized FE for acetate up to 14.5 %, a remarkable result, considering the catalyst used. Acetate is formed either in the presence of cetrimonium bromide (CTAB) as surfactant or at higher current density (>-100 mA cm-2) and the results enabled the proposition of a pathway for its production. This work sheds light on the complex reaction environment of a capture medium electrolyte and is thus relevant for an improved understanding of the conversion of CO2 into value-added products and to evaluate the feasibility of a combined CCU approach.

Growth and Electrochemical Study of Bismuth Nanodendrites as an Efficient Catalyst for CO2 Reduction.

There is a growing interest in creating cost-effective catalysts for efficient electrochemical CO2 reduction to address pressing environmental issues and produce valuable products. A bimetallic ZnBi catalyst that enhances catalytic activity and stability toward the electrochemical reduction of CO2 is designed. It is based on bismuth nanodendrites grown using a facile, scalable, and low-cost method. The results have shown that the incorporation of bismuth can decrease the charge transfer resistance and facilitate CO2 reduction toward the formation of CO and formate. It was revealed that the ZnBi catalyst exhibited higher catalytic activity compared with that of the pure Zn catalyst for CO2 reduction, with a lower onset potential [-0.75 V vs a reversible hydrogen electrode (RHE) compared with -0.85 V vs RHE for Zn]. In situ electrochemical attenuated total internal reflection Fourier transform infrared spectroscopy was employed to study the reaction mechanism, showing the formation of CO and formate through the adsorbed *COO- intermediates. This study has demonstrated a new approach for the feasible synthesis of high-performance catalysts for large-scale electrochemical CO2 reduction.

Bactericidal Effect and Cytotoxicity of Graphene Oxide/Silver Nanocomposites.

To tackle the proliferation of pathogenic microorganisms without relying on antibiotics, innovative materials boasting antimicrobial properties have been engineered. This study focuses on the development of graphene oxide/silver (GO/Ag) nanocomposites, derived from partially reduced graphene oxide adorned with silver nanoparticles. Various nanocomposites with different amounts of silver (GO/Ag-1, GO/Ag-2, GO/Ag-3, and GO/Ag-4) were synthesized, and their antibacterial efficacy was systematically studied. The silver nanoparticles were uniformly deposited on the partially reduced graphene oxide surface, exhibiting spherical morphologies with an average size of 25 nm. The nanocomposites displayed potent antibacterial properties against both gram-positive bacteria (S. aureus and B. subtilis) and gram-negative bacteria (E. coli and S. enterica) as confirmed by minimum inhibition concentration (MIC) studies and time-dependent experiments. The optimal MIC for Gram-positive bacteria was 62.5 µg/mL and for Gram-negative bacteria was 125 µg/mL for the GO/Ag nanocomposites. Bacterial cells that encountered the nanocomposite films exhibited significantly greater inhibitory effects compared to those exposed to conventional antibacterial materials. Furthermore, the cytotoxicity of these nanocomposites was assessed using human epithelial cells (HEC), revealing that GO/Ag-1 and GO/Ag-2 exhibited lower toxicity levels toward HEC and remained compatible even at higher dilution rates. This study underscores the potential of GO/Ag-based nanocomposites as versatile materials for antibacterial applications, particularly as biocompatible wound dressings, offering promising prospects for wound healing and infection control.

Electrochemical and Infrared Studies of a Model Bilayer of the Outer Membrane of Gram-Negative Bacteria and its Interaction with polymyxin─the Last-Resort Antibiotic.

A model bilayer of the outer membrane (OM) of Gram-negative bacteria, composed of lipid A and 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE), was assembled on the ß-Tg modified gold (111) single crystal surface using a combination of Langmuir-Blodgett and Langmuir-Schaefer transfer. Electrochemical and spectroscopic methods were employed to study the properties of the model bilayer and its interaction with polymyxin. The model bilayer is stable on the gold surface in the transmembrane potential region between 0.0 and -0.7 V. The presence of Mg2+ coordinates with the phosphate and carboxylate groups in the leaflet of lipid A and stabilizes the structure of the model bilayer. Polymyxin causes the model bilayer leakage and damage in the transmembrane potential region between 0.2 and -0.4 V. At transmembrane potentials lower than -0.5 V, polymyxin does not affect the membrane integrity. Polymyxin binds to the phosphate and carboxylate groups in lipid A molecules and causes the increase of the tilt angle of acyl chains and the decrease of the tilt of the C═O bond. The results in this paper indicate that the antimicrobial activity of polymyxin depends on the transmembrane potential at the model bilayer and provides useful information for the development of new antibiotics.

Modulating paired Ir-O-Ir via electronic perturbations of correlated Ir single atoms to overcome catalytic selectivity.

Single-atom catalysts have been extensively utilized for electrocatalysis, in which electronic metal-support interactions are typically employed to stabilize single atoms. However, this neglects the metal-metal interactions of adjacent atoms, which are essential for the fine-tuning of selective sites. Herein, the high-loading of Ir single atoms (Ir SAs) (8.9 wt%) were adjacently accommodated into oxygen vacancy-rich Co3O4 nanosheets (Ir SAs/Co3O4). Electronic perturbations for both Ir single atoms and Co3O4 supports were observed under electronic metal-support and metal-metal interactions, thus generating Ir-O-Co/Ir units. Electrons were transferred from Co and Ir to O atoms, inducing the depletion of 3d/5d states in Co/Ir and the occupation of 2p states in O atoms to stabilize the Ir SAs. Moreover, the O atoms of Ir-O-Ir functioned as the main active sites for the electrocatalysis of As(iii), which reduced the energy barrier for the rate-determining step. This was due to the stronger electronic affinities for intermediates from reduction of As(iii), which were completely distinct from other coordinated O atoms of Co3O4 or IrO2. Consequently, the resultant Ir SAs/Co3O4 exhibited far more robust electrocatalytic activities than IrO2/Co3O4 and Co3O4 in the electrocatalysis of As(iii). Moreover, there was a strong orbital coupling effect between the coordinated O atoms of Ir SAs and the -OH of H3AsO3, thus exhibiting superior selectivity for As(iii) in contrast to other common heavy metal cations. This work offers useful insights into the rational design of intriguing SACs with high selectivity and stability for the electrocatalysis and electrochemical analysis of pollutants on an electronic level.

Mechanical Exfoliation of Expanded Graphite to Graphene-Based Materials and Modification with Palladium Nanoparticles for Hydrogen Storage.

Hydrogen is a promising green fuel carrier that can replace fossil fuels; however, its storage is still a challenge. Carbon-based materials with metal catalysts have recently been the focus of research for solid-state hydrogen storage due to their efficacy and low cost. Here, we report on the exfoliation of expanded graphite (EG) through high shear mixing and probe tip sonication methods to form graphene-based nanomaterial ShEG and sEG, respectively. The exfoliation processes were optimized based on electrochemical capacitance measurements. The exfoliated EG was further functionalized with palladium nanoparticles (Pd-NP) for solid-state hydrogen storage. The prepared graphene-based nanomaterials (ShEG and sEG) and the nanocomposites (Pd-ShEG and Pd-sEG) were characterized with various traditional techniques (e.g., SEM, TEM, EDX, XPS, Raman, XRD) and the advanced high-resolution pair distribution function (HRPDF) analysis. Electrochemical hydrogen uptake and release (QH) were measured, showing that the sEG decorated with Pd-NP (Pd-sEG, 31.05 mC cm-2) and ShEG with Pd-NP (Pd-ShEG, 24.54 mC cm-2) had a notable improvement over Pd-NP (9.87 mC cm-2) and the composite of Pd-EG (14.7 mC cm-2). QH showed a strong linear relationship with an effective surface area to volume ratio, indicating nanoparticle size as a determining factor for hydrogen uptake and release. This work is a promising step toward the design of the high-performance solid-state hydrogen storage devices through mechanical exfoliation of the substrate EG to control nanoparticle size and dispersion.

Cobalt-Ceria Binary Oxide Nanojunctions for Aqueous-Phase Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid: The Role of Interfaces.

Cobalt-ceria binary oxide nanojunctions were prepared by a sol-gel method with various chelating agents. The formed interfaces among CeO2 and Co3O4 can promote the generation of nucleophilic •O2- from O2 and then tune the catalytic oxidizability of the as-prepared CoCe nanojunctions. Given the results of HMF oxidations, malic acid as a complexing agent during the preparation process of the cobalt-ceria binary oxide nanojunctions can lead to a good catalytic performance on HMF oxidations to FDCA, and a remarkable FDCA selectivity of 92.3% and almost 100% HMF conversion were obtained at 110 °C under O2 and alkali conditions. By comparing the catalytic performance of the nanojunctions and physical mixing of cobalt-ceria binary oxide on oxidations of HMF, 5-hydroxymethyl-2-furancarboxylic acid (HFCA), and 5-formyl-2-furancarboxylic acid (FFCA), the interfaces intrinsically enhanced the FDCA yield dominantly via boosting the HMF oxidation to HFCA with •O2- during the stepwise oxidation of HMF to FDCA. It can be enlightening that the introduction of the active sites for transforming O2 to •O2- to promote the transformation of HMF into HFCA is the key to boosting the selective aerobic oxidation of HMF to FDCA.

Spatially Resolved Optical Spectroscopic Measurements with Simultaneous Photoelectrochemical Mapping Using Scanning Electrochemical Probe Microscopy.

A deep understanding of the properties of semiconductor films at the micro-/nanoscale level is fundamental toward designing effective photoelectrocatalysts. Here, we integrated spatially resolved optical spectroscopy (SR-OS) with scanning photoelectrochemical microscopy (SPECM) to collect UV/vis spectra and quantify photocurrents of localized sites on a nanostructured BiVO4 thin film. Direct measurement of absorbance allowed for the determination of band gap energy at each location. Absorbance and photocurrent maps were obtained and used to investigate heterogeneities on the films. Scanning electrochemical cell microscopy (SECCM) was also coupled with SR-OS to acquire quantitative photoelectrochemical data at the FTO/BiVO4 film interface, revealing higher photocurrents at the boundary regions. As a droplet-based technique, SECCM was employed to estimate the wetted area by measuring the maximum height of droplet stretch at each point, allowing for the calculation of photocurrent density. This novel approach provides an advantageous mean to correlate localized photocatalytic activities and band gap energies.

Synthesis of 3D Porous Cu Nanostructures on Ag Thin Film Using Dynamic Hydrogen Bubble Template for Electrochemical Conversion of CO2 to Ethanol.

Cu-based nanomaterials have been widely considered to be promising electrocatalysts for the direct conversion of CO2 to high-value hydrocarbons. However, poor selectivity and slow kinetics have hindered the use of Cu-based catalysts for large-scale industrial applications. In this work, we report on a tunable Cu-based synthesis strategy using a dynamic hydrogen bubble template (DHBT) coupled with a sputtered Ag thin film for the electrochemical reduction of CO2 to ethanol. Remarkably, the introduction of Ag into the base of the three-dimensional (3D) Cu nanostructure induced changes in the CO2 reduction reaction (CO2RR) pathway, which resulted in the generation of ethanol with high Faradaic Efficiency (FE). This observation was further investigated through Tafel and electrochemical impedance spectroscopic analyses. The rational design of the electrocatalyst was shown to promote the spillover of formed CO intermediates from the Ag sites to the 3D porous Cu nanostructure for further reduction to C2 products. Finally, challenges toward the development of multi-metallic electrocatalysts for the direct catalysis of CO2 to hydrocarbons were elucidated, and future perspectives were highlighted.

Experimental and computational studies of photoelectrochemical degradation of atrazine by modified nanoporous titanium dioxide.

The presence of herbicides like Atrazine (ATZ) in groundwater from non-target runoff of the agriculture industry becomes a big concern due to its potential negative impacts on the environment and human health. The use of advanced oxidative processes (AOP) to remove harmful contaminants has been shown to be effective for wastewater treatment. Herein, we report on an advanced photoelectrochemical (PEC) approach based on electrochemically modified nanoporous TiO2 electrode for efficient degradation of ATZ. The electrochemical treated TiO2 electrodes were shown to have a six-fold increase in the photo-current density over the untreated ones. This increase in PEC activity was attributed to the increase in Ti3+ sites after the electrochemical modification, which was corroborated by low-temperature electron paramagnetic resonance (EPR) studies. The removal of ATZ by the PEC process resulted in a rate constant of 1.91 × 10-3 s-1, compared to 3.12 × 10-4 s-1 obtained by a strictly photocatalytic process. Liquid-Chromatography Mass-Spectrometric measurements showed the modified TiO2 electrodes highly effective at removing ATZ, with 96.1% removed after 10 h. Monitoring of the common degradation products desethyl atrazine (DEA), desisopropyl atrazine (DIA) and desethyl desisopropyl atrazine (DDA) revealed very low concentrations throughout the degradation process, indicating that further degradation was achieved. Quantum mechanical-based test for overall free radical scavenging activity (QM-ORSA) computational studies were performed and a mechanism for the N-dealkylation processes of ATZ has been proposed.

Electrochemical Exfoliation of Graphite to Graphene-Based Nanomaterials.

Here, we report on a new automated electrochemical process for the production of graphene oxide (GO) from graphite though electrochemical exfoliation. The effects of the electrolyte and applied voltage were investigated and optimized. The morphology, structure and composition of the electrochemically exfoliated GO (EGO) were probed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), FTIR spectroscopy and Raman spectroscopy. Important metrics such as the oxygen content (25.3 at.%), defect density (ID/IG = 0.85) and number of layers of the formed EGO were determined. The EGO was also compared with the GO prepared using the traditional chemical method, demonstrating the effectiveness of the automated electrochemical process. The electrochemical properties of the EGO, CGO and other carbon-based materials were further investigated and compared. The automated electrochemical exfoliation of natural graphite powder demonstrated in the present study does not require any binders; it is facile, cost-effective and easy to scale up for a large-scale production of graphene-based nanomaterials for various applications.

Micro-Sized pH Sensors Based on Scanning Electrochemical Probe Microscopy.

Monitoring pH changes at the micro/nano scale is essential to gain a fundamental understanding of surface processes. Detection of local pH changes at the electrode/electrolyte interface can be achieved through the use of micro-/nano-sized pH sensors. When combined with scanning electrochemical microscopy (SECM), these sensors can provide measurements with high spatial resolution. This article reviews the state-of-the-art design and fabrication of micro-/nano-sized pH sensors, as well as their applications based on SECM. Considerations for selecting sensing probes for use in biological studies, corrosion science, in energy applications, and for environmental research are examined. Different types of pH sensitive probes are summarized and compared. Finally, future trends and emerging applications of micro-/nano-sized pH sensors are discussed.

Electrochemical Reduction of Carbon Dioxide at TiO2/Au Nanocomposites.

Herein, we report on the facile synthesis of nanocomposite consisting of TiO2 and Au nanoparticles (NPs) via a tailored galvanic replacement reaction (GRR). The electrocatalytic activity of the synthesized TiO2/Au nanocomposites for CO2 reduction was investigated in an aqueous solution using various electrochemical methods. Our results demonstrated that the TiO2/Au nanocomposites formed through the GRR process exhibited improved catalytic activities for CO2 reduction, while generating more hydrocarbon molecules than the typical formation of CO in contrast to polycrystalline Au. GC analysis and NMR spectroscopy revealed that CO and CH4 were the gas products, whereas HCOO-, CH3COO-, CH3OH, and CH3CH2OH were the liquid products from the CO2 reduction at different cathodic potentials. This remarkable change was further studied using the density functional theory (DFT) calculations, showing that the TiO2/Au nanocomposites may increase the binding energy of the formed ·CO intermediate and reduce the free energy compared to Au, thus favoring the downstream generation of multicarbon products. The TiO2/Au nanocomposites have high catalytic activity and excellent stability and are easy to fabricate, indicating that the developed catalyst has potential application in the electrochemical reduction of CO2 to value-added products.

Sensitive electrochemical detection of metabisulphite in gastrointestinal fluids.

Deoxynivalenol (DON) is a mycotoxin that is produced by the Fusarium genus and is widely found in cereal grains such as wheat and corn. Sodium metabisulphite (SMBS) is a promising feed additive in swine farming to mitigate the negative impact caused by DON on animal growth. Here we report on an advanced electrochemical sensor based on fluorinated reduced graphene oxide modified with gold nanoparticles (Au/F-rGO) for the rapid detection and monitoring of SMBS. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to characterize the morphology and composition of the prepared Au/F-rGO nanocomposites. Cyclic voltammetry, linear sweep voltammetry, and differential pulse voltammetry were utilized to investigate the electrochemical performance of the Au/F-rGO sensor. Our study showed that the optimized Au/F-rGO nanocomposite exhibited a wide linear range of responses, a low detection limit, high sensitivity, and high stability for the detection of SMBS. When tested in simulated digestive fluids (e.g., salivary fluid and gastric fluid), high selectivity of the sensor for SMBS detection was demonstrated, showing promise for practical applications.

Direct growth of three-dimensional nanoflower-like structures from flat metal surfaces.

Here we report on a facile top-down approach for the direct growth of Co3O4 hierarchical nanoflowers from a bulk Co surface via chemical etching and thermal annealing. The effect of the annealing temperature was investigated, showing that amorphous Co3O4 was formed at 250 °C, while crystalline Co3O4 with notable oxygen vacancies was created at 550 °C. The formed 3D nanostructures exhibited excellent oxygen evolution reaction (OER) activities with a low overpotential of 0.34 V at 10 mA cm-2 and high durability. The proposed novel approach was further demonstrated by the direct growth of 3D NiO and CuO nanostructures on Ni and Cu substrates.

Sodium Hexa-Titanate Nanowires Modified with Cobalt Hydroxide Quantum Dots as an Efficient and Cost-Effective Electrocatalyst for Hydrogen Evolution in Alkaline Media.

A novel electrocatalyst with high activity and enhanced durability toward the hydrogen evolution reaction (HER) in alkaline media has been designed and fabricated based on sodium hexa-titanate (Na2Ti6O13) nanowires synthesized by a hydrothermal process and modified with Co(OH)2 quantum dots (QDs) by a facile chemical bath deposition (CBD) method. The current response of the developed Ti/Na2Ti6O13/Co(OH)2 nanocomposite electrode attained 10 mA cm-2 at an overpotential of 159 mV. The nanocomposite electrode exhibited a high stability at an applied current of 100 mA cm-2. The remarkable catalytic behavior was achieved with a loading amount of ca. 0.06 mg cm-2 cobalt hydroxide. This is attributed to the high electrochemically active surface area (EASA) gained by the nanowire-structured substrate and considerable enhancement of electrochemical conductivity with the use of Co(OH)2 quantum dots as an active material. The superior catalytic activity and high stability show that the developed catalyst is a promising candidate for hydrogen production in alkaline media.

Unraveling the Chemosensing Mechanism by the 7-(Diethylamino)coumarin-hemicyanine Hybrid: A Ratiometric Fluorescent Probe for Hydrogen Peroxide.

The hemicyanine hybrid containing the 7-(diethylamino)coumarin (ACou) donor attached to the cationic indolenium (Ind) acceptor through a vinyl linkage (ACou-Ind) represents a classic ratiometric fluorescent probe for detecting nucleophilic analytes, such as cyanide and reactive sulfur species (RSS), through addition reactions that disrupt dye conjugation to turn off red internal charge transfer (ICT) fluorescence and turn on blue coumarin emission. The chemosensing mechanism for RSS detection by ACou-Ind suggested in the literature has now been revised. Our studies demonstrate that thiolates react with ACou-Ind through conjugate addition to afford C4-SR adducts that lack coumarin fluorescence due to photoinduced electron transfer quenching by the electron-rich enamine intermediate. Thus, ACou-Ind serves as a turn-off probe through loss of red ICT fluorescence upon RSS addition. The literature also suggests that blue coumarin emission of thiolate adducts is enhanced in the presence of reactive oxygen species (ROS) due to ROS-mediated cellular changes. Our studies predict that such a scenario is unlikely and that thiolate adducts undergo oxidative deconjugation in the presence of H2O2, the pervasive ROS. Under basic conditions, H2O2 also reacts directly with ACou-Ind to generate intense coumarin fluorescence through an epoxidation process. The relevance of our chemosensing mechanism for ACou-Ind was assessed within live zebrafish, and implications for the utility of ACou-Ind for unraveling the interplay between RSS and ROS are discussed.

Electrochemical Sensing of Vanillin Based on Fluorine-Doped Reduced Graphene Oxide Decorated with Gold Nanoparticles.

4-hydroxy-3-methoxybenzaldehyde (vanillin) is a biophenol compound that is relatively abundant in the world's most popular flavoring ingredient, natural vanilla. As a powerful antioxidant chemical with beneficial antimicrobial properties, vanillin is not only used as a flavoring agent in food, beverages, perfumery, and pharmaceutical products, it may also be employed as a food-preserving agent, and to fight against yeast and molds. The widespread use of vanilla in major industries warrants the need to develop simple and cost-effective strategies for the quantitative determination of its major component, vanillin. Herein, we explore the applications of a selective and sensitive electrochemical sensor (Au electrodeposited on a fluorine-doped reduced-graphene-oxide-modified glassy-carbon electrode (Au/F-rGO/GCE)) for the detection of vanillin. The electrochemical performance and analytical capabilities of this novel electrochemical sensor were investigated using electrochemical techniques including cyclic voltammetry and differential pulse voltammetry. The excellent sensitivity, selectivity, and reproducibility of the proposed electrochemical sensor may be attributed to the high conductivity and surface area of the formed nanocomposite. The high performance of the sensor developed in the present study was further demonstrated with real-sample analysis.