Heterogeneous Electron Transfer Rate Constant Research Articles

Microbiologically influenced corrosion can cause a dental implant rejection

In the present study, we apply electrochemical and molecular biology approaches to establish whether microbiologically influenced corrosion (MIC) may be the reason for dental implant rejection. Titanium-based implants have been incubated in vitro in Ringer/glucose solution in the presence and absence of a salivary microbiota and the change in their corrosion potential and current density was monitored over time by potentiodynamic polarization. The charge transfers processes occurring on the Ti-based implant surface during the initial bacterial adhesion and after biofilm formation were analyzed by electrochemical impedance spectroscopy. The components of the equivalent electrical circuit as well as the heterogeneous electron transfer rate constants were estimated. In parallel, bacterial species from the salivary microbiota have been identified by sequencing of the 16S ribosomal amplicon method, and their contribution to the corrosion processes of dental implants was verified and compared to that of native saliva in vitro. The scanning electron microscopy observation and energy dispersive spectroscopy analysis of the implant surface after long-term exposure to a bacterial-containing environment revealed more detailed features of the occurring corrosion processes.

Reviving the absorbent chemistry of electrochemically mediated amine regeneration for improved point source carbon capture

Electrochemically mediated amine regeneration (EMAR) is emerging as a promising electrochemical approach for carbon capture from point sources. In this study, for the first time, the absorbent chemistry of the EMAR process was revived by considering criteria beyond metal-amine complexation. The systematic investigation focused on using second amines, which were previously overlooked in EMAR due to limited metal-amine interaction, despite their proven effectiveness in conventional carbon capture processes. The integration of second amines— monoethanolamine (MEA), aminomethyl propanol (AMP), and methyldiethanolamine (MDEA)—with the benchmark ethylenediamine (EDA) was thoroughly studied, evaluating their impact on absorption and desorption kinetics and capacities, and electrochemical performance. Among the blends, EDA + MDEA emerged as the top performer, particularly excelling in electrochemical aspects. The charge transfer resistance (RCT) of the deposition reaction, as the rate-limiting step, for the EDA + MDEA blend was reduced by 40 % compared to pure EDA, and the heterogeneous electron transfer rate constant (k0) improved threefold. In the bench-scale assessments, the EDA + MDEA blend showed a notable decrease in desorption energetics to 37 kJ/molCO2, marking a 34 % reduction compared to the 56 kJ/molCO2 required for pure EDA. This marks the lowest reported energetics for an EMAR process targeting point source carbon capture. This research paves the way for future systematic investigations of a wider range of amine blends for EMAR and eventually the process implementation at larger scales.

Comparison of Different Electrochemical Methodologies for Electrode Reactions: A Case Study of Paracetamol

Understanding electrochemical reactions at the surface of electrodes requires the accurate calculation of key parameters—the transfer coefficient (α), diffusion coefficient (D0), and heterogeneous electron transfer rate constant (k0). The choice of method to calculate these parameters requires careful consideration based on the nature of the electrochemical reaction. In this study, we conducted the cyclic voltammetry of paracetamol to calculate the values of these parameters using different methods and present a comparative analysis. Our results demonstrate that the Ep − Ep/2 equation for α and the modified Randles–Ševčík equation for D0 is particularly effective for the calculations of these two parameters. The Kochi and Gileadi methods are reliable alternatives for the calculation of k0. Nicholson and Shain’s method using the equation k0 = Ψ(πnD0Fν/RT)1/2 gives the overestimated values of k0. However, the value of k0 calculated using the plot of ν−1/2 versus Ψ (from the Nicholson and Shain equation, where ν is scan rate) agrees well with the values calculated from the Kochi and Gilaedi methods. This study not only identifies optimal methodologies for quasi-reversible reactions but also contributes to a deeper understanding of electrochemical reactions involving complex electron transfer and coupled chemical reactions, which can be broadly applicable in various electrochemical studies.

An on-site and portable electrochemical sensing platform based on spinel zinc ferrite nanoparticles for the quality control of paracetamol in pharmaceutical samples.

In this study, crystalline spinel zinc ferrite nanoparticles (ZnFe2O4 NPs) were successfully prepared and proposed as a high-performance electrode material for the construction of an electrochemical sensing platform for the detection of paracetamol (PCM). By modifying a screen-printed carbon electrode (SPE) with ZnFe2O4 NPs, the electrochemical characteristics of the ZnFe2O4/SPE and the electrochemical oxidation of PCM were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), and differential pulse voltammetry (DPV) methods. The calculated electrochemical kinetic parameters from these techniques including electrochemically active surface area (ECSA), peak-to-peak separation (ΔEp), charge transfer resistance (Rct), standard heterogeneous electron-transfer rate constants (k0), electron transfer coefficient (α), catalytic rate constant (kcat), adsorption capacity (Γ), and diffusion coefficient (D) proved that the as-synthesized ZnFe2O4 NPs have rapid electron/mass transfer characteristics, intrinsic electrocatalytic activity, and facilitate the adsorption-diffusion of PCM molecules towards the modified electrode surface. As expected, the ZnFe2O4/SPE offered excellent analytical performance towards sensing of PCM with a detection limit of 0.29 μM, a wide linear range of 0.5-400 μM, and high electrochemical sensitivity of 1.1 μA μM-1 cm-2. Moreover, the proposed ZnFe2O4-based electrochemical nanosensor also exhibited good repeatability, high anti-interference ability, and practical feasibility toward PCM sensing in a pharmaceutical tablet. Based on these observations, the designed electrochemical platform not only provides a high-performance nanosensor for the rapid and highly efficient detection of PCM but also opens a new avenue for routine quality control analysis of pharmaceutical formulations.

The effect of gold nanostructure morphology on label-free electrochemical immunosensor design

In this research, various electrodeposition techniques were used to form gold nanostructures (AuNSs) on the surface of graphite rod electrode (GE). Three distinct AuNS morphologies on GE have been achieved based on the composition of electrodeposition solution. The use of H2SO4 as a supporting electrolyte resulted in the formation of smaller but more numerous AuNSI with a modified electrode’s electroactive surface area (EASA) of 0.213 cm2. Exchanging the supporting electrolyte to KNO3 and increasing HAuCl4 concentration facilitated the formation of bigger AuNSII particles with electrode EASA of 0.116 cm2. Finally, a partial coverage of GE by branched gold nanostructures (AuNSIII) was achieved with an estimated EASA of 0.110 cm2, when the HAuCl4 and KNO3 concentrations were increased. Estimated values of heterogeneous electron transfer rate constant did not depend on AuNS morphology. Electrode modified with AuNSI exhibited the highest bovine serum albumin (BSA) immobilization efficiency and the highest relative response for the detection of specific polyclonal antibodies against BSA (p-anti-BSA) compared to other modified electrodes. The limit of p-anti-BSA detection in PBS buffer was calculated as 0.63 nM, while in blood serum it was 0.71 nM. Linear ranges were from 1 to 7 nM and from 1 to 5 nM, respectively.

(Invited) The Effect of Surfactants on Vanadium Electrochemistry in Porous Carbon Electrodes

We present a study of vanadium electrochemistry in porous electrodes with and without sodium dodecyl sulfate (SDS) additives present. Carbon paper and felt electrodes are compared. Carbon felt electrodes are the de facto standard in flow batteries. There are significant differences in the electronic conductivity of these media. The carbon paper has a much higher conductivity than the felt, which has an electronic conductivity similar to the ionic conductivity of the electrolytes used. The latter fact motivates an extension of available theory for polarization curve fitting to explicitly include both electronic and ionic contributions in the porous electrode. We demonstrate agreement between our model and an existing model evaluated at the limit where electrode conductivity is significantly greater than electrolyte conductivity. Our model uses the product of the electrode surface area per volume ratio and the heterogeneous electron transfer rate constant, and the Damköhler number as fitting parameters for carbon paper and felt electrodes. We discuss the effect of SDS additives on kinetics in the context of the cation hydration shell for the vanadium ions. To this point, we apply Marcus-Hush-Chidsey formalism to our porous electrode model to quantify reorganization energies obtained through polarization curve fitting. This work was supported as part of the Breakthrough Electrolytes for Energy Storage (BEES2), an Energy Frontier Research Center funded by the United States. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0019409.

Two step electrochemical redox mechanism of cu2+ through kinetic parameters and digital simulation technique

Cycle voltammetric behaviour of Cu(II)SO4 in aqueous NaCl (supporting electrolyte) has been explored in comprehensive manner. 5 mM Cu2+, 1.0 M NaCl and glass carbon (GC) reveals the optimum response. Two stage electromechanical redox EE mechanism [(Cu2+/Cu+) and (Cu+/ Cu0)] has been explored by using different theoretical and experimental methods. The mass transfer co-efficient, dimensionless parameters and heterogeneous electron transfer rate constant ( confirmed the quasi-reversible response of (Cu2+/Cu+) redox couple. The experimental Gileadi ( and simulated Digi Sim ( values found as 0.052 cm/s and 0.0012 cm/s respectively. The diffusion co-efficient (D) of (Cu2+/Cu+) redox couple computed from 9.96 X 10-6 to 4.43 X 10-6 cm2/s through different methods. The novelty of the present work is to confirm the quasi-reversible response of (Cu2+/Cu+) through obtained electrochemical and kinetic parameters by using simple, fast, and cost-effective technique.

Amperometric flow injection analysis of hydroquinone in dermatological creams using a porous diamond-like carbon electrode

A porous diamond-like carbon film deposited on vertically aligned multi-walled carbon nanotubes (DLC:VAMWCNT) was evaluated as an electrode material in flow injection analysis (FIA) with amperometric detection. The redox behavior of hydroquinone (H2Q) was carried out as proof of concept. From cyclic voltammetry tests, H2Q gave a heterogeneous electron transfer rate constant (k0) of 4.9 × 10−3 cm s−1, which is comparable or better than those obtained with conventional electrodes. For the H2Q determination with the FIA-amperometry system, optimizations were performed regarding the supporting electrolyte, applied potential and FIA parameters (flow rate and sample injection volume). Under optimal conditions, the amperometric response of the DLC:VAMWCNT electrode was linear in the H2Q concentration range from 1.0 × 10−6 to 1.0 × 10−4 mol L−1, with a limit of detection (LOD) of 7.7 × 10−7 mol L−1. Interestingly, the DLC:VAMWCNT electrode displayed a very stable response under hydrodynamic conditions, with no memory effect while retaining accuracy towards the analysis of commercial H2Q-based dermatological creams. From these findings, DLC:VAMWCNT appears to be an outstanding candidate for flow injection analysis systems coupled to electrochemical detection.

Use of Inner/Outer Sphere Terminology in Electrochemistry—A Hexacyanoferrate II/III Case Study

Salts of hexacyanoferrate II/III anions have been widely used as redox couple probe molecules to determine the characteristics of electrode surfaces. Examples include the assessment of electrocatalysts for energy applications and electrocatalysts for the detection of biological or chemical species, as well as the determination of electrochemically active surface areas. An examination of the electrochemical literature, based largely on cyclic voltammetric investigations, reveals a wide range of peak separation and/or heterogeneous electron transfer rate constants, classified sometimes as inner or outer sphere electron transfer processes. Originally developed for the mechanistic interpretation of inorganic transition metal compounds in solution, this terminology has since been extended to account for heterogeneous electron transfer occurring at electrodes. In the case of the hexacyanoferrate II/III anions, there can be a number of reasons why it sometimes behaves as an outer sphere probe and at other times displays inner sphere electron transfer characteristics. After examining some of the structural and chemical properties of the hexacyanoferrate II/III species, the methods used to determine such classifications are described. The most common method involves measuring peak-to-peak separation in a cyclic voltammogram to ascertain a heterogeneous rate constant, but it has inherent flaws. This paper reviews the reasons for the classification disparity, including the effects of various oxygen surface species, the influence of organic surface films, the nature of the cation counter-ion, surface adsorption and surface hydrophilicity/hydrophobicity. Other surface interactions may also take place, such as those occurring with Au corrosion or pH effects. These can impact the electrical double layer and thus may affect the electron transfer process. Consequently, it is recommended that hexacyanoferrate II/III should be considered a multi-sphere or alternatively a surface-sensitive electron transfer species.

Shedding light on the calculation of electrode electroactive area and heterogeneous electron transfer rate constants at graphite screen-printed electrodes

We present in detail the most known and commonly used methods for the calculation of electrode electroactive area (A) and heterogeneous electron transfer rate constants ({k}^{0}). The correct procedure for the calculation of these parameters is often disregarded due to either lack of a minimum theoretical background or oversimplification of each method’s limitations and prerequisites. The aim of this work is to provide the theoretical background as well as a detailed guide for the implementation of these measurements by impressing upon the electrochemists the parameters that need to be considered so that the obtained results are safe and useful. Using graphite screen-printed electrodes, A, and {k}^{0} were calculated with different methods and techniques. Data are compared and discussed.Graphical

Disposable Pencil Lead as an Electrochemical Transducer for Monitoring Catechol in River and Tap Water

A cheap and disposable pencil graphite electrode (PGE) was developed by the incorporation of amine groups (Am-PGE-1). A further improvement in the performance was observed when the aminated electrode (Am-PGE-1) was activated by applying a negative potential scan (Am-PGE-2). The electrochemical transport properties were evaluated through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The Nyquist plot showed a reduced charge transfer resistance value of 24.3 Ω for Am-PGE-2, while it was 95.1 Ω for bare PGE. Thus, Am-PGE-2 was used as a sensing platform for the detection of catechol. It was found that the electrochemical response of catechol oxidation at Am-PGE-2 was twice than the current obtained for bare PGE. Additionally, the effect of pH of the supporting electrolyte and reaction kinetic were studied. The heterogeneous electron transfer rate constant was calculated to be 0.01 s−1. Moreover, CV study revealed that the redox reaction of catechol was a quasi-reversible and diffusion-controlled process. The square wave voltammetry (SWV) technique was applied for the quantitative determination of catechol. The peak current showed a linear dependency on the concentration of catechol from 3 to 150 µM. Furthermore, the analyte could be detected as low as 3.86 µM. Likewise, the sensor demonstrates a good selectivity towards the target analyte than the other possible interfering molecules or ions. Aiming to examine practical applicability, real samples, such as river and household tap water, were tested by using the proposed transducer, and the satisfactory recoveries demonstrate the effectiveness of Am-PGE-2 in real life applications.

Room-Temperature Ionic Liquid Cation Effects on the Structure and Stability of Anionic Lanthanide Complexes.

Room-temperature ionic liquids (RTILs) are a subset of molten salts that are liquids at room temperature and may offer an elegant, low-temperature route to predicting the properties of solvated metal complexes in their high-temperature analogues. This work studied the chemistry of chloride anion-containing RTILs to determine their similarity to inorganic molten chloride salts. The behaviors of complexes of Mn, Nd, and Eu were evaluated in a variety of chloride RTILs by absorption spectrophotometry and electrochemistry to elucidate trends in cation effects on the coordination geometry and redox properties of the solvated species. Spectrophotometric data indicated the metals are present as anionic complex (e.g., MnCl42- and NdCl63-) analogous to those observed in molten chloride salts. Strongly polarizing, charge-dense RTIL cations induced distortions to the symmetry of these complexes, resulting in lower oscillator strengths and red-shifted energies for the observed transitions. Cyclic voltammetry experiments were used to characterize the Eu(III/II) redox couple producing diffusion coefficients on the order of 10-8 cm2 s-1 and heterogeneous electron transfer rate constants ranging between 6 × 10-5 and 2 × 10-4 cm s-1. The E1/2 potentials for Eu(III/II) were also found to shift positively with increasing cation polarization power, stabilizing the Eu(II) oxidation state by removing electron density from the metal center over chloride bond networks. Both the optical spectrophotometry and electrochemistry results suggest that the polarization strength of an RTIL cation plays a major role in the geometry and stability of a metal complex.

Voltammetric Evidence of Proton Transport through the Sidewalls of Single-Walled Carbon Nanotubes.

Understanding ion transport in solid materials is crucial in the design of electrochemical devices. Of particular interest in recent years is the study of ion transport across 2-dimensional, atomically thin crystals. In this contribution, we describe the use of a host-guest hybrid redox material based on polyoxometalates (POMs) encapsulated within the internal cavities of single-walled carbon nanotubes (SWNTs) as a model system for exploring ion transport across atomically thin structures. The nanotube sidewall creates a barrier between the redox-active molecules and bulk electrolytes, which can be probed by addressing the redox states of the POMs electrochemically. The electrochemical properties of the {POM}@SWNT system are strongly linked to the nature of the cation in the supporting electrolyte. While acidic electrolytes facilitate rapid, exhaustive, reversible electron transfer and stability during redox cycling, alkaline-salt electrolytes significantly limit redox switching of the encapsulated species. By "plugging" the {POM}@SWNT material with C60-fullerenes, we demonstrate that the primary mode of charge balancing is proton transport through the graphenic lattice of the SWNT sidewalls. Kinetic analysis reveals little kinetic isotope effect on the standard heterogeneous electron transfer rate constant, suggesting that ion transport through the sidewalls is not rate-limiting in our system. The unique capacity of protons and deuterons to travel through graphenic layers unlocks the redox chemistry of nanoconfined redox materials, with significant implications for the use of carbon-coated materials in applications ranging from electrocatalysis to energy storage and beyond.

Electrochemistry at Back-Gated, Ultrathin ZnO Electrodes: Field-Effect Modulation of Heterogeneous Electron Transfer Rate Constants by 30× with Enhanced Gate Capacitance.

We report steady-state voltammetry of outer-sphere redox species at back-gated ultrathin ZnO working electrodes in order to determine electron transfer rate constants kET as a function of independently controlled gate bias, VG. We demonstrate that kET can be modulated as much as 30-fold by application of VG ≤ 8 V. The key to this demonstration was integrating the ultrathin (5 nm) ZnO on a high dielectric constant (k) insulator, HfO2 (30 nm), which was grown on a Pd metal gate. The high-k HfO2 dramatically decreased the required VG values and increased the gate-induced charge in ZnO compared to previous studies. Importantly, the enhanced gating power of the Pd/HfO2/ZnO stack meant it was possible to observe a nonmonotonic dependence of kET on VG, which reflects the inherent density of redox acceptor states in solution. This work adds to the growing body of literature demonstrating that electrochemical kinetics (i.e., rate constants and overpotentials) at ultrathin working electrodes can be tuned by VG, independent of the conventional electrochemical working electrode potential.

Effect of adsorption of pyocyanin on the electron transfer rate at the interface of a glassy carbon electrode

Redox mediators (RM) are an alternative to improve the performance of microbial electrochemical systems (MES) as they help significantly to develop the indirect electron transfer. However, their use is limited when the redox processes between the RM and the electrode surface are not thoroughly understood. The adsorption, the intermolecular interactions with the electrode, and the effects on charge transfer kinetics are important issues in MES such as microbial sensors, microbial electrosynthesis or microbial fuel cells, but are rarely analyzed. Pyocyanin, considered an RM, may present these features due to its chemical structure. Today, the electrochemical studies indicate that pyocyanin can presents adsorption processes on glassy carbon electrodes. However, the effects of adsorption on electron transfer rate and changes as a function of pyocyanin concentration have not yet been studied. Therefore, this work presents an electrochemical study of pyocyanin to determine the effect of concentration and adsorption on the electron transfer rate at a glassy carbon electrode. Analysis of the electrochemical profiles obtained by cyclic voltamperometry (CV) indicates that there is an effect of concentration (C*) on the heterogeneous electron transfer rate constant (k0) since the criterion ΔEp varies as a function of C*. In addition, the peak proportionality parameter Ipa/Ipc and the voltamperometric function Ip/v½ help deduct the adsorption to the electrode. Experimental data obtained by chronocoulometry (CC) and CV, indicate that k0 = 5.7 × 1011 m/s and Rct = 3.40 × 10−16 Ω under the C* = 0.14 mM condition, while k0 = 1.10 × 103 m/s and Rct = 1.60 × 10−7 Ω under the C* = 0.49 mM condition. The differences in k0 and Rct values at different values of C* are due to an accumulation of pyocyanin on the electrode surface in the inner Helmholtz plane (IHP), preventing the electron transfer of bulk-dissolved pyocyanin molecules present in the outer Helmholtz plane (OHP) region. The varying values of α, indicate that a part of the energy of the redox reaction could be employed for the adsorption processes. As for the interactions at the electrode, the values of the Laviron parameter (ν'gθT) indicate that attraction interactions between the pyocyanin molecules and the electrode dominate, since the values of ν'gθT are higher than 0. The results of this study will provide a comprehensive understanding of the redox cycle of pyocyanin. The information will be useful for the future development of electrochemical-microbial systems since that the interactions mediator-electrode may be an operational variable to facilitate their practical applications in environmental, sensing and electrosynthesis areas.

Shungite (Mineralized Carbon) as a Promising Electrode Material for Electroanalysis.

In this study, two different types of amorphous carbonaceous Precambrian rock, classified as noble elite shungite and black raw shungite, were tested as possible electrode materials of natural origin. Both types were machined into cylindrical shapes to form the corresponding solid electrodes and their physicochemical and electrochemical properties were compared with the standard glassy carbon electrode (GCE). The raw stones were first subjected to microscopic imaging by using scanning electron microscopy and energy-dispersive X-ray spectroscopy, both of which indicated significant differences in their morphology and in the content of impurities. An electrode prototype manufactured from noble elite shungite (EShE) with a carbon content of about 94% (w/w) has offered a very satisfactory electrochemical performance with a nearly identical heterogeneous electron-transfer rate constant of 7.8 × 10-3 cm s-1 for ferro/ferricyanide redox couple, a slightly narrower potential range (~2.1 V) and a relatively low double-layer capacitance (of ca. 50 μF), resulting in low background currents comparable to those at the GCE. In contrast, the second electrode based on black raw shungite (BShE) with a carbon content of ca. 63% (w/w) exhibited markedly worse electrochemical properties and more than four times higher double-layer capacitance, both of which were probably due to the presence of poorly conductive impurities. The whole study has been completed with three different examples of electroanalytical applications, revealing that the first type, EShE, is a more suitable material for the preparation of electrodes and may represent a cheap alternative to commercially marketed products.

A disposable and low-cost laser-scribed graphene electrochemical sensor for simultaneous detection of hydroquinone, paracetamol and methylparaben

• A new disposable LSG sensor was fabricated using Polyetherimide substrate. • Sensor presented high reproducibility, sensitivity, and selectivity. • A LSG sensor was applied to simultaneous detection of emerging pollutants. • A porous graphene-like material with high electrochemical performance was developed. A novel and inexpensive laser-scribed graphene (LSG) sensor using polyetherimide (PEI) substrate was fabricated using CO 2 laser. The material was characterized by scanning electron microscopy (SEM), Raman spectroscopy, and electrochemical techniques, demonstrating a high porous carbonaceous material, which resulted in an electroactive area with 3.4-fold enhancement compared to geometric area and a high heterogeneous electron transfer rate constant (k°) of 3.20x10 -2 cm/s for ferricyanide redox probe. As a proof of applicability, the LSG-PEI sensor was applied for simultaneous detection of hydroquinone (HQ), paracetamol (PA), and methylparaben (MP) emerging pollutants (EP) in tap water and natural (lake) water samples, providing recoveries between 93.1% and 118% with limits of detection of 9.42x10 -8 , 3.23x10 -7 , and 2.95x10 -7 mol/L for HQ, PA, and MP, respectively.

A highly efficient and portable laser-scribed graphene-based electrochemical system for forensic-oriented determination of acepromazine.

Acepromazine (ACP) is a phenothiazine derivative drug commonly used as a tranquilizer veterinary medication due to its sedative properties. Benefiting from sedative properties, ACP has emerged as a drug of abuse and has been associated with drug-facilitated sexual assaults. Herein, we report, for the first time, the electrochemical behavior of ACP using a miniaturized and environmentally friendly laser-scribed graphene-based (LSG) sensor fabricated on a polyetherimide (PEI) substrate. The LSG device presented high porosity, as demonstrated by scanning electron microscopy (SEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements of the PEI-LSG electrode confirmed the enhanced electroactive area (3.1-fold increase) caused by the rough surface and revealed a low charge transfer resistance of the electrode material, with a heterogeneous electron transfer rate constant (k0) of 8.66 × 10-3 cm s-1 for potassium ferricyanide redox probe. A simple and accurate method was applied to quantify ACP by using square wave voltammetry (SWV) under optimized experimental conditions, which exhibited high sensitivity (0.686 ± 0.008 A L mol-1 cm-2) and a low limit of detection (LOD) of 7.43 × 10-8 mol L-1, with a linear concentration ranging from 0.5 to 100 μmol L-1 ACP. Aiming for on-site analysis, the PEI-LSG sensor was integrated with a miniaturized potentiostat controlled by using a smartphone and applied as proof of applicability to ACP detection in commercial beverage and synthetic urine samples. These studies demonstrated adequate recoveries, ranging from 95.1% to 115.8%. The analytical parameters highlight the robustness and reliability of the proposed method for analyses of ACP directly at a potential crime scene.

Cyclic voltammetry, square wave voltammetry or electrochemical impedance spectroscopy? Interrogating electrochemical approaches for the determination of electron transfer rates of immobilized redox proteins

In this article, we cross-examine three well-established electrochemical approaches, namely cyclic voltammetry (CV), cyclic square-wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) to dissect the electron transfer (ET) rate of electrostatically immobilized cytochrome c on Ag electrodes. A detailed analysis supported by simulations of redox transition provided three distinct values for the heterogeneous electron transfer (HET) rate constant of cyt c interfaced on COOH-terminated C10-long alkanethiol, i.e., kHET= 47.8 (±2,91) s−1 in CV, kHET= 64.8 (±1,27) s−1 in SWV, and kHET= 26.5 s−1 in EIS. We discuss the obtained discrepancies obtained from electrochemical methods and compare them with the data from spectro-electrochemical experiments. A comprehensive selection list is created from which the most applicable approach can be chosen for studying proteins of interest. CV is most applicable to study the interfaced proteins exhibiting kHET of ca. 0.5 - 70 s−1, SWV is suitable for a broader range of kHET of 5 – 120 s−1 and EIS for kHET of 0.5 to 5 s−1 if alkanethiols are used as immobilization strategy.

An SECM-Based Spot Analysis for Redoxmer-Electrode Kinetics: Identifying Redox Asymmetries on Model Graphitic Carbon Interfaces.

The fundamental process in non-aqueous redox flow battery (NRFB) operation revolves around electron transfer (ET) between a current collector electrode and redox-active organic molecules (redoxmers) in solution. Here, we present an approach utilizing scanning electrochemical microscopy (SECM) to evaluate interfacial ET kinetics between redoxmers and various electrode materials of interest at desired locations. This spot-analysis method relies on the measurement of heterogeneous electron transfer rate constants (kf or kb ) as a function of applied potential (E-E0 '). As demonstrated by COMSOL simulations, this method enables the quantification of Butler-Volmer kinetic parameters, the standard heterogeneous rate constant, k0 , and the transfer coefficient, α. Our method enabled the identification of inherent asymmetries in the ET kinetics arising during the reduction of ferrocene-based redoxmers, compared to their oxidation which displayed faster rate constants. Similar behavior was observed on a wide variety of carbon electrodes such as multi-layer graphene, highly ordered pyrolytic graphite, glassy carbon, and chemical vapor deposition-grown graphite films. However, aqueous systems and Pt do not exhibit such kinetic effects. Our analysis suggests that differential adsorption of the redoxmers is insufficient to account for our observations. Displaying a greater versatility than conventional electroanalytical methods, we demonstrate the operation of our spot analysis at concentrations up to 100 mM of redoxmer over graphite films. Looking forward, our method can be used to assess non-idealities in a variety of redoxmer/electrode/solvent systems with quantitative evaluation of kinetics for applications in redox-flow battery research.