Electrocatalytic Current Research Articles

Photo- and Electrocatalytic Hydrogen Evolution by Heteroleptic Dirhodium(II,II) Complexes: Role of the Bridging and Diimine Ligands.

A series of heteroleptic Rh2(II,II) complexes, cis-[Rh2(μ-DPhF)2(μ-bncn)2]2+ (1; bncn = benzo[c]cinnoline), cis-[Rh2(μ-DPhF)(μ-OAc)(μ-bncn)2]2+ (2), and cis-[Rh2(μ-OAc)2(μ-bncn)2]2+ (3), is presented, and the excited state and redox properties of each complex was characterized for the photo- and electrocatalytic production of H2. The oxidation potentials shift anodically from 1 to 3, consistent with a highest occupied molecular orbital (HOMO) with significant metal-ligand mixing, Rh2(δ*)/DPhF(π/nb). In contrast, modest differences in the first two bncn-localized reversible reduction potentials were observed in 1 - 3. The lowest energy metal/ligand-to-ligand charge transfer (1ML-LCT) transition, Rh2(δ*)/DPhF(π/nb) → bncn(π*), shifts from 633 nm in 1 to 553 nm in 2, and the metal-to-ligand charge transfer (1MLCT) Rh2(π*) → bncn(π*) absorption in 3 appears at 462 nm in CH3CN. Although the 3ML-LCT excited state of 2 is shorter lived than that of 1, 2.7 ns as compared to 19 ns, respectively, photocatalytic hydrogen generation is observed for the former upon 595 nm irradiation in the presence of 0.1 M TsOH (p-tolylsulfonic acid) and 0.1 M BNAH (1-benzyl-1,4-dihydronicotinamide). The temperature dependence of the 3ML-LCT lifetimes of 1 and 2 shows the presence of a thermally accessible deactivating state. In addition, the singly reduced intermediate, [2]-, is photoactive and able to generate hydrogen in the presence of TsOH. Importantly, the electrocatalytic currents generated by equimolar concentrations of 1 - 3 in CH3CN are nearly identical, consistent with a mechanism of catalysis that is localized on the bncn ligand and does not require a Rh-H hydride intermediate. This finding can be used to develop earth-abundant first-row transition metal complexes for photo- and electrocatalytic H2 production.

Superior Single-Entity Electrochemistry Performance of Capping Agent-Free Gold Nanoparticles Compared to Citrate-Capped Gold Nanoparticles.

In observing the electrocatalytic current of nanoparticles (NPs) using single-entity electrochemistry (SEE), the surface state of the NPs significantly influences the SEE signal. This study investigates the influence of capping agents on the electrocatalytic properties of gold (Au) NPs using SEE. Two inner-sphere reactions, hydrazine oxidation and glucose oxidation, were chosen to explore the SEE characteristics of Au NPs based on the capping agent presence. The results revealed that "capping agent-free" Au NPs exhibited signal magnitudes and frequencies consistent with theoretical expectations, indicating superior stability and catalytic performance in electrolyte solutions. In contrast, citrate-capped Au NPs showed signals varying depending on the applied potential, with larger magnitudes and lower frequencies than expected, likely due to an aggregation of NPs. This study suggests that capping agents play a crucial role in the catalytic performance and stability of Au NPs in SEE. By demonstrating that minimizing capping agent presence can enhance effectiveness in SEE, it provides insights into the future applications of NPs, particularly highlighting their potential as nanocatalysts in energy conversion reactions and environmental applications.

Influence of Particle Size on Mass Transport during the Oxygen Reduction Reaction at Single Silver Particles Using Scanning Electrochemical Cell Microscopy.

Single entity electrochemical measurements enable insight into the electrocatalytic activity of individual particles based on composition, shape, and crystallographic orientation. In addition to structural effects, particle size can further influence electrocatalytic activity and reaction mechanisms through mass transport effects. In this work, electrodeposition was used to grow well-separated silver particles of varying sizes from 100 to 500 nm in radius. Using a multimicroscopy approach of scanning electrochemical cell microscopy combined with scanning electron microscopy, the electrocatalytic current of individual silver particles toward the oxygen reduction reaction was evaluated as a function of their size. It was found that the current density increased with decreasing particle radius, which was correlated to the mass transport of oxygen to the silver particle, demonstrating the importance of size dependent mass transport effects that can occur at the single particle level using scanning electrochemical cell microscopy and opening new opportunities for quantitative electrocatalysis measurements.

A novel copper ion enhanced electrochemical DNA biosensor for the determination of epinephrine

A novel electrochemical biosensor was developed for the detection of epinephrine (EP) by immobilizing double-strand DNA (dsDNA) bound with copper ions on a gold electrode (Cu2+/dsDNA/MCH/AuE). The electrochemical behavior of EP at Cu2+/dsDNA/MCH/AuE was examined, and the results demonstrated a significant enhancement in the electrocatalytic oxidation peak current of EP due to the formation of a stable G-Cu(II)-G sandwich structure between Cu2+ and guanine at the modified electrode. The modification process of the electrode was characterized by scanning electron microscopy, infrared spectroscopy, electrochemical impedance spectroscopy, and differential pulse voltammetry. A study on the effect of pH in phosphate buffer solution on the electrochemical oxidation of EP indicated that the catalytic oxidation process was pH-dependent. A plot of catalytic current versus EP concentration exhibited a dual-linear relationship within two ranges: 1.0–12.5 μM and 12.5–1000.0 μM, with correlation coefficients of 0.995 and 0.997, respectively. The limit of detection was determined to be 47 nM (S/N = 3). According to the calculated Hill coefficient (0.99), it can be concluded that the electrocatalytic process followed the Michaelis-Menten kinetic mechanism. The maximum catalytic current Im was 25 μA, while the apparent Michaelis-Menten constant Km was 1.425 mM. These findings indicated excellent electrocatalytic activity of the modified electrode towards oxidation of EP. The developed biosensor successfully detected EP in spiked mouse serum as well as epinephrine hydrochloride injection with high selectivity, sensitivity, stability, and accuracy.

Development of electrode by using gold-platinum alloy nanopar¬ticles for electrochemical detection of serum amyloid A protein

Gold-platinum alloy nanoparticles (AuPtNP) were electrochemically deposited on the surface of indium-tin-oxide (ITO) modified with (3-aminopropyl)triethoxysilane (APTES), after optimizing deposition conditions for the electroplating solution and number of deposition cycles. Different part ratios of Au/Pt used were 4/0, 3/1, 2/2, 1/3 and 0/4 (AuNP, Au3Pt1, Au2Pt2, Au1Pt3 and PtNP, respectively) in preparation of 1 mM solutions. FE-SEM, EDAX and XRD surface characterization techniques were used to confirm the presence of deposited AuPt alloy nanoparticles on the modified ITO surface. Electrochemical methods (CV, DPV and EIS) were used to investigate the electrochemical properties of prepared electrodes in the presence of ferri/ferrocyanide redox couple, which indicated the following increasing order of electrocatalytic peak current: Au < Au2Pt2 < Pt < Au1Pt3 < Au3Pt1. The most active electrode, Au3Pt1NP/APTES/ITO (with Au/Pt part ratio 3:1), was further used to fabricate the immunoelectrode SAA-Ab/Au3Pt1NP/APTES/ITO. The prepared immunoelec­trode was tested for detection of serum amyloid A protein biomarker (APO-SAA) by immobilising SAA-specific antibodies (SAA ½ Ab) on its surface. Sensing studies on this immunoelectrode, performed by DPV technique, revealed the SAA biomarker detection in the linear range of 10 to 106 fg ml-1. The limit of detection was calculated as 7.0 fg ml-1.

Biomass-derived porous carbon with single-atomic cobalt toward high-performance aqueous zinc-sulfur batteries at room temperature

Aqueous zinc-sulfur batteries at room temperature hold great potential for next-generation energy storage technology due to their low cost, safety and high energy density. However, slow reaction kinetics and high activation energy at the sulfur cathode pose great challenges for the practical applications. Herein, biomass-derived carbon with single-atomic cobalt sites (MMPC-Co) is synthesized as the cathode in Zn-S batteries. The catalysis of single-atom Co sites greatly promotes the transform of cathode electrolyte interface (CEI) on the cathode surface, while offering accelerated charge transfer rate for high conversion reversibility and large electrochemical surface area (ECSA) for high electrocatalytic current. Furthermore, the rich pore structure not only physically limits sulfur loss, but also accelerates the transport of zinc ions. In addition, the large pore volume of MMPC-Co is able to relieve the stress effect caused by the volume expansion of ZnS during charge/discharge cycles, thereby maintaining the stability of electrode structure. Consequently, the sulfur cathode maintains a high specific capacity of 729.96 mA h g−1 after 500 cycles at 4 A g−1, which is much better than most cathode materials reported in the literature. This work provides new insights into the design and development of room-temperature aqueous Zn-S batteries.

Electrocatalytic Reduction of Benzyl Bromide during Single Ag Nanoparticle Collisions.

Previous reports of the electrocatalytic activity of Ag nanoparticles (AgNPs) toward the reduction of organic halides have been limited to measurements of immobilized nanoparticle ensembles. Here, we have investigated the electrochemical reduction of benzyl bromide (PhCH2Br) occurring at single AgNPs (4.2 to 37 nm radius) in methanol, where the effects of nanoparticle size on catalytic behavior can be more thoroughly examined and rigorously quantified. AgNP collisions at a 6.3 μm radius Au ultramicroelectrode (UME) result in measurable electrocatalytic amplification currents from the reduction of PhCH2Br, where collision events are indicated by a sudden step increase in the reduction current recorded in the current-time trace. The dependence of the height of these steps on the applied potential allowed for an analysis of reaction kinetics based on the Butler-Volmer model, resulting in an estimation of the standard rate constant (k0) as a function of AgNP size. Measured values of k0 range from 4.0 × 10-4 to 8.0 × 10-4 cm/s on AgNPs with radii of 14, 29, and 37 nm, whereas k0 was found to be 6.2 × 10-4 cm/s at a 12.3 μm radius Ag disk UME. The results indicate that the kinetics of PhCH2Br reduction are independent of AgNP size and are similar to the reaction kinetics observed at a Ag UME. The frequency of observed particle collisions was found to be dependent on particle size, where 14 nm radius AgNPs resulted in the highest-frequency collisions. The potential- and size-dependent interactions of AgNPs with the Au UME are discussed in terms of the DLVO theory.

Mechanistic Basis of Conductivity in Carbon Dioxide-Expanded Electrolytes: A Joint Experimental-Theoretical Study.

Electrolyte conductivity contributes to the efficiency of devices for electrochemical conversion of carbon dioxide (CO2) into useful chemicals, but the effect of the dissolution of CO2 gas on conductivity has received little attention. Here, we report a joint experimental-theoretical study of the properties of acetonitrile-based CO2-expanded electrolytes (CXEs) that contain high concentrations of CO2 (up to 12 M), achieved by CO2 pressurization. Cyclic voltammetry data and paired simulations show that high concentrations of dissolved CO2 do not impede the kinetics of outer-sphere electron transfer but decrease the solution conductivity at higher pressures. In contrast with conventional behaviors, Jones reactor-based measurements of conductivity show a nonmonotonic dependence on CO2 pressure: a plateau region of constant conductivity up to ca. 4 M CO2 and a region showing reduced conductivity at higher [CO2]. Molecular dynamics simulations reveal that while the intrinsic ionic strength decreases as [CO2] increases, there is a concomitant increase in ionic mobility upon CO2 addition that contributes to stable solution conductivities up to 4 M CO2. Taken together, these results shed light on the mechanisms underpinning electrolyte conductivity in the presence of CO2 and reveal that the dissolution of CO2, although nonpolar by nature, can be leveraged to improve mass transport rates, a result of fundamental and practical significance that could impact the design of next-generation systems for CO2 conversion. Additionally, these results show that conditions in which ample CO2 is available at the electrode surface are achievable without sacrificing the conductivity needed to reach high electrocatalytic currents.

Single-Entity Bioelectrochemistry

Interfacing biological catalytic entities, such as whole cells or enzymes, with electrodes, has a wide range of applications, ranging from fundamental studies of the entities themselves to power generation, bioremediation, chemical synthesis, and biosensing. In all cases, the operation of these bioelectrocatalytic systems is based on electron transfer phenomena within protein molecules, whether isolated or residing inside cells or parts of cells, as well as between proteins and electronics. Typically, the electron transfer and catalytic properties of proteins are studied using ensemble averaging methods, which obscure any heterogeneity and dynamics of individual molecules. This information, however, is especially important for understanding electron transfer and catalytic processes within a living cell where only one or a few protein molecules are present. While single-entity electrochemical measurements are particularly useful for studying electron transfer reactions at the nanoscale level, they have limited applications for investigating biological entities due to the experimental challenges associated with direct measurements of small electrical currents. 1,2 Here we will discuss our recent progress in investigating biological electron transfer reactions at the single-entity level, from bacterial cells to single redox proteins, using nano-impact (collision) single-entity electrochemistry. 3 We demonstrate how advances in electrode fabrication methods and detection setups enable current detection in the fA range. When combined with the developed data processing algorithm based on unsupervised learning and template matching techniques, this enabled unprecedented insight into electron transfer processes at the nanoscale. We will talk about insights provided by the method in the study of several important bioelectrocatalytic systems: single E.coli cells with overexpressed Fe-Fe hydrogenases, single bilirubin oxidase molecules, and single catalase molecules. In addition, we will discuss models that we developed for understanding the single bioentity electrode interactions for diffusion-controlled enzymes when the product of the catalytic reaction is detected on the electrode, as well as systems based on direct electron transfer between the bioentity and the electrode. Overall, we show how single-entity bioelectrochemistry can shed light on biological electron transfer and catalysis processes and discuss the challenges it currently faces. Zhang, J.-H.; Zhou, Y.-G. Nano-Impact Electrochemistry: Analysis of Single Bioentities. TrAC Trends Anal. Chem. 2019, 115768.Davis, C.; Wang, S. X.; Sepunaru, L. What Can Electrochemistry Tell Us About Individual Enzymes? Curr. Opin. Electrochem. 2020, 100643.Sekretaryova, A. N.; Vagin, M. Yu.; Turner, A. P. F.; Eriksson, M. Electrocatalytic Currents from Single Enzyme Molecules. J. Am. Chem. Soc. 2016, 138 (8), 2504–250

(Invited) Nickel Nanoparticles Modified Carbon Film Electrodes for Detection of Sugars

Metal nanoparticles such as Pt, Au, Ni and Cu have been employed to detect various analytes including hydrogen peroxide, alcohol and sugar. Among these metal nanoparticles, Ni and Cu nanoparticles show excellent electrocatalytic activity for oxidizing sugars in alkaline solution. We employed co-sputtering and plating technique to fabricate nanostructured electrodes for enhancing electrocatalytic activity for oxidation of sugars. First example is a metal hererodimer modified carbon film electrodes. The metal nanoparticles embedded carbon film electrodes was fabricated by unbalanced magnetron (UBM) sputtering and then plated different metal nanoparticles selectively only on the embedded metal nanoparticles by utilizing overpotential difference between carbon and metal nanoparticles surfaces. Using this technique, various combinations of metals are available to fabricate vertically oriented heterodimers embedded in the carbon films. In fact, we succeeded to fabricated Ni(upper)@Pd(lower), Pt@Pd, Au@Pd, Ni@Au, Pt@Au and Pd@Au heterodimers partially embedded in the carbon film. Among these heterodimers, Ni@Pd heterodimer embedded carbon film electrode shows much higher redox reaction of Ni(OH)2 covered on the Ni nanoparticles surface compared with that on the Ni nanoparticles without Pd. The NiOOH formed by electrochemical oxidation shows much higher electrocatalytic activity for glucose compared with that formed on Ni nanoparticles modified carbon film electrode. Also, the Ni@Pd heterodimers are mechanically very stable and most of the heterodimers remained on the surface after ultrasonication treatment because surface Ni nanoparticles attached strongly to Pd nanoparticles embedded in the carbon film. In contrast, almost all Ni nanoparticles deposited on pure carbon film were detached from carbon surface after ultrasonication. The second example is a nitrogen terminated carbon film modified with Ni nanoparticles by plating. Carbon films were fabricated by UBM or RF sputtering methods and then introduced nitrogen containing functional groups. Then Ni nanoparticles were deposited by plating. The supporting effect of a N-doped carbon film induced superior crystallinity in plated Ni@Ni(OH)2 nanoparticles, which was confirmed by HAADF-STEM-EDS. This realized a much higher regeneration rate of catalytic sites (NiOOH) , leading to higher oxidation current for maltopentaose, which is well known oligosaccharide. Also, the overpotential of maltopentaose oxidation decreased significantly due to the effect of the electrostatic interaction between Ni nanoparticles and maltopentaose in the alkaline solution at pH 12.7. We also studied dependence of nitrogen concentration in the carbon film on regeneration rate of NiOOH and glucose oxidation. Both regeneration rate and electrocatalytic current of glucose oxidation increased with increasing nitrogen concentration from 0 to 3.1 %. With optimized nitrogen concentration, we could measure glucose from 25 µM to 400 µM. The enhanced activity of Ni nanoparticles could be advantageous to develop enzyme free biosensor or fuel cells using organic compounds such as sugars and oligosaccharides.[1]S. Shiba, A. Koike, S. Takahashi, D. Kato, T. Kamata and O. Niwa, ACS Nano, 16, 10589-10599 (2022).[2] S. Shiba, S. Ohta, K. Ohtani, S. Takahashi, D. Kato and O. Niwa, RSC Advances, 11, 13311-13315 (2021).

Investigation of electrocatalytic activity of palladium nanoparticle for ammonia borane oxidation via single‐entity electrochemistry

AbstractAmmonia borane (AB) has garnered significant attention as a high‐efficiency energy source, prompting extensive investigations into its electrochemical oxidation. One prominent avenue of research focuses on the development of electrocatalysts to enhance the oxidation of AB. Employing the novel approach of single‐entity electrochemistry (SEE), the electrocatalytic properties of gold (Au), silver (Ag), and palladium (Pd) nanoparticles (NPs) for AB oxidation were explored. In the case of Au and Ag NPs, SEE experiments yielded no discernible current signal, in contrast to the electrocatalytic currents observed with bulk electrodes. However, when Pd NPs were utilized, characteristic staircase signals in the SEE measurements were observed. The variation of the SEE current signal for Pd NPs under different applied potentials, AB concentrations, and NP concentrations was further investigated. An analysis of the SEE signal elucidated the conditions under which Pd NPs can effectively catalyze AB oxidation at the single NP level.

Dual amplified electrochemical sensing coupling of ternary hybridization-based exosomal microRNA recognition and perchlorate-assisted electrocatalytic cycle

Exosomal microRNA (miRNA) are important biomarkers for liquid biopsy, and display clinical molecular signatures for cancer diagnosis. Although advanced detection methods have been established to detect exosomal miRNAs, they are faced with certain challenges. Therefore, we aimed to establish a dual amplification-based electrochemical method for detecting exosomal miRNA. This method combined a two-hairpins-based ternary hybridization structure (thTHS)-initiated single-stranded DNA (ssDNA) amplification reaction (ssDAR) and sodium perchlorate (NaClO4)-assisted electrocatalytic cycle. Two DNA hairpins were designed to hybridize with target miRNA, forming thTHS. Next, ssDAR was triggered by thTHS to produce long ssDNA on magnetic beads. The long ssDNA, complementary to the signal probes, was subsequently released onto a methylene blue (MB)-labeled double-stranded DNA-modified electrode for strand displacement reaction. This led to a quantitative change in MB and a change in electrocatalytic reduction current from the electrocatalytic cycle of MB-ferricyanide. An amplified electrocatalytic reduction current was produced by adding NaClO4 to the electrocatalytic system, which substantially improved the signal response range and detection sensitivity. Ultimately, exosomal miRNA detection was achieved by recording changes in the electrocatalytic reduction current before and after miRNA addition. This electrochemical method exhibited a sensitive concentration response with a detection limit of 45 aM and selective miRNA recognition, and successfully used to detect exosomal miRNA derived from cells and serum. Additionally, this method exhibited better discrimination ability between patients with breast cancer (BC) and those people without BC (patients with benign breast disease and healthy people), providing a promising strategy for detecting and monitoring cancer biomarkers.

Structure and Reactivity of Metal-Oxide-Supported Noble Metal Nanoparticles: Electrooxidation of Simple Organic Molecules

There has been growing interest in utilizing small (simple) organic molecules, as alternative fuels to hydrogen, in electrochemical energy conversion systems. In addition to ethanol (biofuel), that can be ideally oxidized to carbon dioxide thus delivering twelve electrons, recent important systems include dimethyl ether as well. But realistically the respective reaction is rather slow at ambient conditions. Obviously, there is a need to develop novel electrocatalytic materials.Platinum has been recognized as the most active catalytic metal towards oxidation of ethanol at low and moderate temperatures. But Pt anodes are readily poisoned by the strongly adsorbed intermediates, namely by CO-type species, requiring fairly high overpotentials for their removal. To enhance activity of Pt catalysts towards methanol and ethanol oxidation, additional metals including ruthenium, tin, molybdenum, tungsten or rhodium are usually introduced as the alloying component. More recently it has been demonstrated that catalytic activity of platinum-based nanoparticles towards electrooxidation of ethanol has been significantly enhanced through interfacial modification with ultra-thin monolayer-type films of metal oxo species of tungsten, titanium or zirconium.We pursue a concept of utilization of mixed metal (e.g. zirconium/tungsten or titanium/tungsten) oxide matrices for supporting and activating noble metal nanoparticles (e.g. PtRu) during electrooxidation of methanol, ethanol, formic acid and dimethyl ether. Among important issues is incorporation of Rh nanostructures capable of weakening, or even breaking, the C-C bond in the ethanol molecules. On the other hand, rhodium itself is not directly electrocatalytic toward oxidation of ethanol. The oxides and noble metal nanoparticles have been deposited in a controlled manner using the layer-by-layer method. Remarkable increases of electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. The most likely explanation takes into account possibility of specific interactions of noble metals with transition metal oxide species as well as existence of active hydroxyl groups in the vicinity of catalytic noble metal sites. In addition, formation of “nanoreactors” where ethanol is partitioned (at Rh) to methanolic residues further oxidized at PtRu cannot be excluded.

Facilitated Enzymatic Chain Reaction-Based Bioelectrocatalysis via Solid Binding Peptide-Guided Bienzyme Co-Immobilization Strategy

The multienzyme complex in biological systems are highly ordered so that intermediate molecules occurred during enzymatic sequential reaction are efficiently delivered to downstream enzymes without diffused to bulk phase. Recently, the cascadic multienzymes have been adopted to enzymatic electrocatalytic platform to be applied for enzyme-based bioelectronics such as enzyme fuel cell, biosensors, and electrosynthetic system. This cascadic enzyme-electrode, in which interfacial electron transfer (ET) occurs concurrently with inter-enzyme chain reaction, has been regarded promising for the advancement of enzyme-based bioelectronics performance. However, co-regulation of interfacial electrical connection and inter-enzyme chain reaction efficiency has been known to be highly challenging due to systematic complexity. In this context, the generalized enzyme immobilization tool is significantly needed to be developed to control inter-enzyme and enzyme-electrode interface concurrently.Herein, enzyme cascade-based direct bioelectrocatalytic system has been constructed by immobilizing enzymes using the solid binding peptide (SBP) linker that can control surface-orientation of enzymes on electrode. Here, invertase (INV) and FAD-dependent glucose dehydrogenase gamma-alpha complex (GDHγα) were utilized as upstream- and downstream enzyme so that the sucrose hydrolysis (at INV) and glucose oxidation (at GDHγα) is concomitantly occurred. Especially, the GDHγα that is direct electron transfer (DET)-capable oxidoreductase, has bi-function that are downstream catalysis and transport of produced electrons toward electrode that cause bioelectrocatalytic current signal. To immobilize enzymes and control relative orientation of coupling enzymes, the SBP linker was tethered various termini (C-, N-, or both termini) of INV when SBP fusion site of GDHγα was fixed to C-terminus of GDH α subunit to enable efficient interfacial DET, based on previous study. Therefore, the inter-enzyme relative orientation dependent chain reaction efficiency was evaluated with resulting DET-based electrocatalytic current. In the result, it was found that the interfacial DET at GDHγα-electrode could be affected by binding conformation of co-immobilized enzyme, fusion INV. Most importantly, the chain reaction efficiency between INV and GDHγα was revealed to be diverse depending on different relative orientation determined by SBP tethering sites in enzymes. The intermediate delivery route was changed by relative positioning of coupling active sites, affecting overall cascade reaction rate. Taking into account the factors related with interfacial DET and intermediate delivery, precise design of bienzymatic electrode is indeed necessary in order to introduce SBP-tethering technique to cascadic enzyme-derived direct electrocatalytic platform. Figure 1

Highly Sensitive Sensor for the Determination of Riboflavin Using Thionine Coated Cadmium Selenide Quantum Dots Modified Graphite Electrode

In this paper, the electrochemical non-enzymatic detection of Riboflavin (RF) was proposed based on its catalytic reduction in a Thionine-coated Cadmium Selenide Quantum dots (TH@CdSe QDs)-modified paraffin wax-impregnated graphite electrode (PIGE) that was prepared using a novel approach. The synthesized TH@CdSe QDs were confirmed by UV-Vis spectroscopy, Confocal Raman Microscopy and High Resolution Transmission Electron Microscopy (HRTEM) studies. The electrochemical response of the TH@CdSe QDs-modified PIGE was studied by cyclic voltammetry. The voltammetric response of RF at the TH@CdSe QDs-modified PIGE showed higher current than the bare PIGE. Under optimum conditions, the electrocatalytic reduction currents of RF was found to be linearly related to its concentration over the range of 1.6 × 10−7 M to 1.4 × 10−4 M with a detection limit of 53 × 10−9 M (S/N = 3). The TH@CdSe QDs-modified PIGE was utilized as an amperometric sensor for the detection of RF in flow systems was performed by carrying out hydrodynamic and chronoamperometric experiments. The TH@CdSe QDs-modified PIGE showed very good stability and a longer shelf life. The applicability of the fabricated electrode was justified by the quantification of RF in commercial tablets.

Enhancement of Electrocatalytic and Pseudocapacitive Properties as a Function of Structural Order in A2Fe2O5 (A = Sr, Ba).

Significant enhancements of electrocatalytic activities for both half-reactions of water-electrolysis, i.e., oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), as well as pseudocapacitive charge-storage properties are demonstrated upon changing the structural order in a perovskite-type system. The structural change is prompted by the increase in the ionic radius of the A-site ion in A2Fe2O5. The structure of Sr2Fe2O5 consists of alternating layers of FeO6 octahedra and FeO4 tetrahedra, whereas Ba2Fe2O5 comprises seven different coordination geometries for Fe. We note that the catalytically active metal, i.e., iron, and the oxygen stoichiometry are the same for both materials. Nevertheless, the change in the structural order results in significantly greater electrocatalytic activity of Ba2Fe2O5, manifested in smaller overpotentials, smaller charge-transfer resistance, greater electrocatalytic current, and faster reaction kinetics. In addition, this material shows significantly enhanced pseudocapacitive properties, with greater specific capacitance and energy density compared to Sr2Fe2O5. These findings indicate the important role of structural order in directing the electrochemical properties.

Direct electron transfer kinetics of histamine dehydrogenase at air plasma-treated graphite nanofibers

As histamine is one of the important mediators for allergic reactions, its efficient detection methods and real-time monitoring systems are required for food analyses and drug discoveries to suppress allergic reactions. Although histamine dehydrogenase (HmDH) is a promising candidate for developing enzyme-based electrochemical biosensors, some electron mediators are frequently employed to observe electrocatalytic currents for histamine oxidation. Here, direct electrochemistry of HmDH was studied at the surface of graphite nanofibers (GNFs), which provide active reaction sites for redox species. Air plasma-treated GNFs were used for constructing a three-dimensional network that works both as an electrical nanowire and an enzyme support. Even though the amount of oxygen-containing functional groups didn’t significantly increase at the GNF surface with increase in the air plasma treatment time, direct electron transfer from reduced HmDH by histamine to the GNFs was improved probably due to capped and curvature of the graphite edge sites with oxygen-containing functional groups, which were generated by the air plasma treatment. The air plasma-treated GNFs also allowed enhancement of the complex-formation reaction rate of HmDH with histamine, as the air plasma treatment time increased.

Lab-made flexible third-generation fructose biosensors based on 0D-nanostructured transducers

Herein, we report a scalable benchtop electrode fabrication method to produce highly sensitive and flexible third-generation fructose dehydrogenase amperometric biosensors based on water-dispersed 0D-nanomaterials.The electrochemical platform was fabricated via Stencil-Printing (StPE) and insulated via xurography. Carbon black (CB) and mesoporous carbon (MS) were employed as 0D-nanomaterials promoting an efficient direct electron transfer (DET) between fructose dehydrogenase (FDH) and the transducer. Both nanomaterials were prepared in water-phase via a sonochemical approach. The nano-StPE exhibited enhanced electrocatalytic currents compared to conventional commercial electrodes.The enzymatic sensors were exploited for the determination of D-fructose in model solutions and various food and biological samples. StPE-CB and StPE-MS integrated biosensors showed appreciable sensitivity (∼150 μA cm−2 mM−1) with μmolar limit of detection (0.35 and 0.16 μM, respectively) and extended linear range (2–500 and 1–250 μM, respectively); the selectivity of the biosensors, ensured by the low working overpotential (+0.15 V), has been also demonstrated. Good accuracy (recoveries between 95 and 116%) and reproducibility (RSD ≤8.6%) were achieved for food and urine samples.The proposed approach because of manufacturing versatility and the electro-catalytic features of the water-nanostructured 0D-NMs opens new paths for affordable and customizable FDH-based bioelectronics.

A flexible, transparent, and enzyme free sensor based on Ni@AgNW networks for glucose detection

Silver nanowires (AgNWs) are among the most promising materials for transparent conductive electrodes (TCE) owing to their stability and unique optoelectronic properties. However, the fact that they easily oxidize in chemical environments has limited their applications in devices such as electrochemical batteries, supercapacitors, and sensors. In this study, flexible Ni@AgNW/PET was prepared using the electrochemical deposition method. This electrode architecture prevented the delamination of the flexible electrodes during bending tests. Further, the Ni shell structure protected the AgNWs from oxidation and improved the stability of the conductive substrate. The Ni@AgNW/PET electrodes showed good electrochemical stability with a sheet resistance and optical transmittance of 6.8 Ω/sq and 64.1%, respectively. The electrocatalytic anodic currents correlated with the concentration of glucose, which had a detection limit of 40 μM (S/N = 3), a wide range of 0.01–5.0 mM (with a linear correlation coefficient of 0.998), and a high sensitivity of 915 μA mM−1 cm−2. The flexible Ni@AgNW/PET electrodes remained stable after 1000 bending cycles under different shapes. The excellent electrocatalytic performance for glucose showed that Ni@AgNWs/PET is a promising wearable electrode that can be used in glucose detection.

FeFe] Hydrogenase: 2‐Propanethiolato‐Bridged {FeFe} Systems as Electrocatalysts for Hydrogen Production in Acetonitrile‐Water

AbstractDiiron bis(monothiolato)‐bridged hydrogenase mimics [Fe2(μ‐SiPr)2(CO)6] A (iPr=isopropyl) and their phosphine derivatives [Fe2(μ‐SiPr)2(CO)5(L1/2)] and [Fe2(μ‐SiPr)2(CO)4(L3)] {tricyclohexylphosphine (L1, PCy3) 1, triphenylphosphine (L2, PPh3) 2 and cis‐1,2‐bis(diphenylphosphino)ethylene (L3, dppv) 3} have been synthesized and investigated for electrocatalytic proton reduction activity in CH3CN−H2O. Based on the FTIR data (red‐shift), the electron‐donating ability of the phosphines followed the order: dppv>PCy3>PPh3 (average shift value with respect to complex A was 61 (1), 51 (2) and 80 (3) cm−1). From CV measurements, it was seen that the catalytic reduction potential (acetic acid as proton source) shifted considerably towards positive potentials (anodic shift) on changing the solvent from pure CH3CN to CH3CN−H2O (4 : 1 v/v). An increase in the percentage of water in CH3CN led to the decomposition of complexes 1 and 3. Though complexes A and 2 were stable in CH3CN−H2O (3 : 2 v/v), no improvement in electrocatalytic currents was observed.