Conventional Cyclic Voltammetry Research Articles

Disruption Dynamics and Charge Transfer of a Single Attoliter Emulsion Droplet Revealed by Combined Fast-Scan Sinusoidal Voltammetry and Short Time Fourier Transform Analysis.

Single-entity electrochemistry has gained significant attention for the analysis of individual cells, nanoparticles, and droplets, which is leveraged by robust electrochemical techniques such as chronoamperometry and cyclic voltammetry (CV) to extract information about single entities, including size, kinetics, mass transport, etc. For an in-depth understanding such as dynamic interaction between the electrode and a single entity, the unconventional fast electrochemical technique is essential for time-resolved analysis. This fast experimental technique is unfortunately hindered by a substantial nonfaradaic response. In this work, we introduce fast-scan sinusoidal voltammetry (FSSV) combined with a short-time Fourier transform (STFT) for analyzing single emulsion droplets. Utilizing ultramicroelectrode and fast potential sweeps up to apparent 200 V/s, we achieved high temporal resolution (8 ms per voltammogram) to capture the current signals during droplet collisions. STFT analysis reveals the amplitude and phase changes, allowing for the accurate detection of collision events even in the absence of redox species. By adopting an algorithm of drift-free baseline subtraction, a conventional CV shape was obtained in FSSV. The reacted charge from the single-entity voltammogram at every 8 ms was also plotted. This method effectively addresses limitations in traditional techniques, providing insights into emulsion dynamics such as droplet contact and droplet breakdown.

Efficient nitrite determination by electrochemical approach in liquid phase with ultrasonically prepared gold-nanoparticle-conjugated conducting polymer nanocomposites.

An electrochemical nitrite sensor probe is introduced herein using a modified flat glassy carbon electrode (GCE) and SrTiO3 material doped with spherical-shaped gold nanoparticles (Au-NPs) and polypyrrole carbon (PPyC) at a pH of 7.0 in a phosphate buffer solution. The nanocomposites (NCs) containing Au-NPs, PPyC, and SrTiO3 were synthesized by ultrasonication, and their properties were thoroughly characterized through structural, elemental, optical, and morphological analyses with various conventional spectroscopic methods, such as field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller method. The peak currents due to nitrite oxidation were characterized in detail and analyzed using conventional cyclic voltammetry (CV) as well as differential pulse voltammetry (DPV) under ambient conditions. The sensor response increased significantly from 0.15 to 1.5mM of nitrite ions, and the sensor was fabricated by coating a conducting agent (PEDOT:PSS) on the GCE to obtain the Au-NPs/PPyC/SrTiO3 NCs/PEDOT:PSS/GCE probe. The sensor's sensitivity was determined as 0.5μA/μM∙cm2 from the ratio of the slope of the linear detection range by considering the active surface area (0.0316cm2) of the flat GCE. In addition, the limit of detection was determined as 20.00 ± 1.00 µM, which was found to be satisfactory. The sensor's stability, pH optimization, and reliability were also evaluated in these analyses. Overall, the sensor results were found to be satisfactory. Real environmental samples were then analyzed to evaluate the sensor's reliability through DPV, and the results showed that the proposed novel electrochemical sensor holds great promise for mitigating water contamination in the real samples with the lab-made Au-NPs/PPyC/SrTiO3 NC. Thus, this study provides valuable insights for improving sensors for broad environmental monitoring applications using the electrochemical approach.

Rapid and Direct Detection of Trimethylamine N-oxide Using an Off-Chip Capacitance Biosensor with Readout SoC for Early-Stage Thrombosis and Cardiovascular Disease.

A demonstration of an off-chip capacitance array sensor with a limit of detection of 1 μM trimethylamine N-oxide (TMAO) to diagnose a chronic metabolism disease in urine is presented. The improved Cole-Cole model is employed to determine the parameters of R_catalyzed, C_catalyzed, and Rp_catalyzed, enabling the prediction of the catalytic resistance of enzyme, reduction effects of the analyte, and characterize the small signal alternating current properties of ionic strength caused by catalysis. Based on the standard solutions, we investigate the effects of pixel geometry parameters, driving electrode width, and sensing electrode width on the electrical field change of the off-chip capacitance sensor; the proposed off-chip sensor with readout system-on-chip exhibits a high sensitivity of 21 analog-to-digital converter counts/μM TMAO (or 2.5 mV/μM TMAO), response time of 1 s, repetition of 98.9%, and drift over time of 0.5 mV. The proposed off-chip sensor effectively discriminates TMAO in a phosphate-buffered saline solution based on minute changes in capacitance induced by the TorA enzyme, resulting in a discernible 2.15% distinction. These measurements have been successfully corroborated using the conventional cyclic voltammetry method, demonstrating a mere 0.024% variance. The off-chip sensor is crafted with a specific focus on detecting TMAO, achieved by excluding any reduction reactions between the TMAO-specific enzyme TorA and the compounds creatine and creatinine present in urine. This deliberate omission ensures that the sensor's attention remains solely on TMAO, thereby enhancing its precision in achieving accurate and reliable TMAO detection.

Investigation of electrocatalysis for tiered-tower micro-electro-mechanical-system-based biosensors: application in the early detection of the thrombosis factor trimethylamine N-oxide.

Trimethylamine N-oxide (TMAO) has been recognized as a biomarker for the early detection of thrombosis. However, testing for TMAO typically requires expensive laboratory equipment and skilled technicians, making it unsuitable for home care pre-screening. To enable its widespread use in home applications, it is crucial to develop a scalable and sensitive device capable of catalyzing TMAO metabolism with a specific enzyme that is tailored for point-of-care use. This study presents an investigation of a MEMS-based two-tiered-tower biosensor array with a detection limit of 0.1 μM for TMAO, aiming to diagnose chronic metabolic diseases using urine or serum samples. Based on the augmented Cole-Cole model, the proposed parameters R_catalyzed, C_catalyzed, and Rp_catalyzed can predict the catalytic impedance of enzymatic activities such as the redox effects of analytes and characterize the small-signal current caused by catalysis. The proposed MEMS biosensor, integrated with a readout circuitry, demonstrates a high sensitivity of 41 ADC counts per μM TMAO (or 4.5 mV μM-1 TMAO), a response time of 1 second, a repetition rate of 98.9%, and a drift over time of 0.5 mV. The sensor effectively distinguishes TMAO based on minute capacitance changes induced by the TorA enzyme, resulting in a discernible distinction of 10.6%. These measurements were successfully compared to conventional cyclic voltammetry (CV) results, showing a variance of only 0.024%. The proposed biosensor is well-suited for pre-screening thrombosis factors for the early detection and prevention of thrombosis in point-of-care applications. The device is cost-effective, lightweight, and demonstrates excellent performance, with a conversion rate of 88% of TMAO and a selectivity rate of 97% for the by-product TMA, allowing for the prediction of cardiovascular risks.

Understanding the electrochemical features of ZnFe2O4, anode for LIBs, by deepening its physico-chemical properties

ZnFe2O4 (ZFO) has emerged as anode material for lithium ion batteries (LIBs) thanks to its intercalation mechanism combining conversion and alloying reactions. The understanding of electrochemical behaviour is related to the knowledge of the physico-chemical properties of electrode materials. In this paper, ZFO was prepared by co-precipitation and template syntheses, obtaining samples with different morphologies and crystallite sizes. The sample purity was verified by combining X-ray powder diffraction with spectroscopic techniques such as Micro-Raman, EPR and Mössbauer. The electrochemical features, measured by using conventional cyclic voltammetry, impedance spectroscopy, charge-discharge measurements and in situ X-ray diffraction experiments, were then interpreted on the basis of the physico-chemical features. The higher electrode area of the template ZFO, with smaller particles, is responsible for better reactivity in the first cycles, but, in the long term, a lower crystallinity of active material, leading to nano-crystalline reaction products, could determine a better reversibility.

Determination of the optimum potential window for super- and pseudocapacitance electrodes via in-depth electrochemical impedance spectroscopy analysis

Electrochemical analysis of energy storage materials in aqueous electrolytes requires an accurate determination of a working potential window. Applying potentials outside this window causes detrimental reactions, reducing the electrode's durability. Therefore, there is a need for rapid and accurate determination of the most desired potential window in the assembly of energy storage materials. The present work reports a novel single equivalent circuit model based on electrochemical impedance spectroscopy (EIS), Nyquist plots, and Bode plots that is capable of predicting the optimal operating potential of both electric double-layer capacitors (EDLCs) and pseudocapacitors. The model was evaluated on four electrodes, two EDLCs made of activated carbon derived from coffee residue and waste textile, and two MnOx and Mn1−x−y(CexLay)O2−δ pseudocapacitors. A ratio of Capacitance of diffusionCapacitance of double layer was defined and calculated at different DC potential windows. Results indicated that the optimum potential window is obtained at a ratio below 3 % for supercapacitors. The larger potential windows resulted in a significant increase in the ratio as a result of the emergence of unfavourable Faradic reactions. To address this issue, a mathematical factor (i.e., χ2) was defined and plotted vs. applied potential, verifying the accuracy of the optimum potential window for pseudocapacitors. Additionally, analysis of Bode plots indicated the presence of unfavourable Faradic reactions at voltages that exceeded the optimum potential window. Therefore, results of our proposed method have proven to be more reliable, rapid, sensitive, and accurate than those obtained using conventional cyclic voltammetry.

A novel cyclic voltammetric determination of free chlorine generated by ozone disinfection in seawater aquariums

The amount of free chlorine generated by disinfection is one of core parameters that should be monitored for the seawater aquarium. This article proposes a novel analytical method in which the amount of free chlorine in ozonized seawater can be determined by the conventional cyclic voltammetry (CV) with a bare platinum disk electrode without developing any new sensing material. The amounts of both free chlorine and ozone in ozonized seawater samples were determined by spectrophotometry, which showed that most of ozone was converted to free chlorine. CV experiments with a bare platinum electrode were carried out for the samples and our attention was paid to that the peak current of hydrogen oxidation generated by water electrolysis, which was ignored in the previous studies, depends on the amount of free chlorine in the sample. The CVs exhibited the well–defined oxidation peak for hydrogen molecules and the linear range of free chlorine amounts in the ozonized seawater samples spanned from 0.02 to 0.4 mg L–1 with a correlation coefficient of 0.9982 (n=5), a detection limit of 1.2 × 10–2 mg L–1 at 3σ and a high sensitivity of 4063 μA cm–2 mg–1 L. The repeatability of this technique had a relative standard deviation of 4.41% (n=10).

Potentiodynamic Electrochemical Impedance Spectroscopy of Polyaniline-Modified Pencil Graphite Electrodes for Selective Detection of Biochemical Trace Elements.

In this study, we analyzed the application of potentiodynamic electrochemical impedance spectroscopy (PDEIS) for a selective in situ recognition of biological trace elements, i.e., Cr (III), Cu (II), and Fe (III). The electrochemical sensor was developed using the electropolymerization of aniline (Ani) on the surface of the homemade pencil graphite electrodes (PGE) using cyclic voltammetry (CV). The film was overoxidized to diminish the background current. A wide range of potential (V = −0.2 V to 1.0 V) was investigated to study the impedimetric and capacitive behaviour of the PAni/modified PGE. The impedance behaviors of the films were recorded at optimum potentials through electrochemical impedance spectroscopy (EIS) and scrutinized by means of an appropriate equivalent circuit at different voltages and at their corresponding oxidative potentials. The values of the equivalent circuit were used to identify features (charge transfer-resistant and double layer capacitance) that can selectivity distinguish different trace elements with the concentration of 10 μM. The PDEIS spectra represented the highest electron transfer for Cu (II) and Cr (III) in a broad potential range between +0.1 and +0.4 V while the potential V = +0.2 V showed the lowest charge transfer resistance for Fe (III). The results of this paper showed the capability of PDEIS as a complementary tool for conventional CV and EIS measurement for metallic ion sensing.

Mesoporous CuZnAl-layered double hydroxide/graphene oxide nanohybrid as an energy storage electrode for supercapacitor application

With the purpose of the enhancement of supercapacitor behaviour, a CuZnAl-layered double hydroxide/graphene (CuZnAl-LDH/GO) nanohybrid was synthesized via facile method. The layered structures of GO and CuZnAl-LDH lead to create favourable conditions for energy storage capacity. The prepared CuZnAl/GO nanohybrid was characterized by X-ray diffraction, inductively coupled plasma optical emission spectrometry analysis, field-emission scanning electron microscopy and energy dispersive X-ray spectroscopy, N2 adsorption/desorption analysis measurements. The electrochemical behaviour of prepared nanohybrid was evaluated by conventional cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy techniques. As a supercapacitor, the prepared CuZnAl/GO nanohybrid electrode revealed higher specific capacitance (3.87 F cm−2) than CuZnAl-LDHs (1.37 F cm−2). The CuZnAl/GO nanohybrid exhibited good stability, with high specific capacitance for over 1000 charge–discharge cycles. The obtained results can be justified by enhancing electrochemically active areas provided by layered structures of LDH and preventing effect of GO in the aggregation of LDH sheets. Moreover, the GO increase the electrical conductivity in nanohybrid. The facile synthesis and high electrochemical performance of CuZnAl/GO nanohybrid showed that this hybrid material can be suitable as an electrode material for energy storage and supercapacitor devices.

The electron transfer kinetics of adsorbed species derived by sampled current voltammetry

In sampled current voltammetry, a sampled current voltammogram (SCV) is constructed by performing a number of potential steps and plotting the currents taken at a specific sampling time against the corresponding step potentials. For diffusion-controlled processes, the technique produces sigmoidal current-potential curves that are easily analysed to obtain kinetic information. Here, we extend this approach to study the electron transfer kinetics of adsorbed species (Oads+ne−⇌kbkfRads) and show that the SCVs have a characteristic peak whose shape, potential and current depend on the sampling time. We also discuss the results in terms of chronocoulograms and show that the sampled charge voltacoulograms (SQVs) are also affected by kinetics. Analysis of the SCVs and SQVs is particularly useful to unravel the dependence of the electrode response on potential and time. We investigate different data treatments and show that a logarithmic SCV, a plot of ln(j) against E, is highly sensitive to the electron transfer rate constant and to the sampling time. The time dependence of the current yields ΓO0 (initial surface coverage) and E0, while the potential dependence of the current extrapolated to very short sampling times yields α and ks. This extrapolation bypasses the double layer charging distortion, provided the sampling times are selected where the current transients are free from capacitive distortion. From the analysis of the SCVs, we propose a simple protocol to derive ΓO0, E0, α and ks, from only two current transients, the only constraint being that one of the chronoamperograms must be recorded with a large overpotential, circa ±120 mV. We also propose a simpler alternative involving non-linear regression of the current transients to a single expression. The chronoamperometric approach offers advantages compared to the voltammetric methodology proposed by Laviron. 1) Capacitive distortions only affect the current transients at short times but affect the whole potential window in voltammetry. 2) The current transients can be extrapolated to very short sampling times where the backward reaction has no influence. 3) The extrapolation to very short sampling times bypasses the double layer distortion. 4) Whereas a chronoamperogram holds a wide range of timescales, the voltammetric approach requires a wide range of scan rates to distinguish the kinetic regimes. 5) The voltammetric method only yields the values of ks and α, while the chronoamperometric method also yields ΓO0 and E0. 6) Since electrochemical workstations allow shorter time scales by chronoamperometry than voltammetry, the method can assess faster electron transfer kinetics than conventional cyclic voltammetry.

Exonuclease I-Assisted General Strategy to Convert Aptamer-Based Electrochemical Biosensors from "Signal-Off" to "Signal-On".

In terms of how the signal varies in response to increased concentration of an analyte, sensors can be classified as either "signal-on" or "signal-off" format. While both types hold potentials to be sensitive, selective, and reusable, in many situations "signal-on" sensors are preferred for their low background signal and better selectivity. In this study, with the detection of lysozyme using its DNA aptamer as a trial system, for the first time we demonstrated that such an aptamer-based electrochemical biosensor can be converted from intrinsically "signal-off" to "signal-on" with the aid of a DNA exonuclease. The fact that the stepwise cleavage of antilysozyme aptamer catalyzed by Exonuclease I (Exo I) is entirely inhibited upon binding lysozyme leads to the selective removal of unbound DNA probes (thiolate anti-lysozyme DNA aptamer strands immobilized on gold electrode) upon the introduction of Exo I to the sensor. With the aid of electrostatically bound redox cations ([Ru(NH3)6]3+), we were able to quantitate the number of aptamer strands that are bound with lysozymes via conventional cyclic voltammetry (CV) measurements. We demonstrated that Exo I-assisted signal-on conversion protocol not only improves the sensing performance (10 times better limit of detection) but also promises a versatile strategy for DNA-based biosensor design, i.e., it can be readily adapted to other aptamer-protein binding systems (thrombin, as another example).

Individual Modified Carbon Nanotube Collision for Electrocatalytic Oxidation of Hydrazine in Aqueous Solution

Collision at a single molecule level was achieved based on the nanoimpact of an individual pyrroloquinoline quinone (PQQ) modified multiwalled carbon nanotube (MWCNT) at the carbon fiber ultramicroelectrode (C UME). Electrocatalytic amplification of the current responses was observed when the PQQ-modified MWCNT collided with C UME in the presence of hydrazine (N2H4) in a Tris-HCl buffer solution, which was also supported by the conventional cyclic voltammetry and chronoamperometry techniques. The enhanced catalytic oxidation of N2H4 was due to the “addition-elimination” redox cycling mechanism of PQQ/PQQH2, where the oxidation of N2H4 occurred together with the reduction of PQQ under an external bias, and the formed PQQH2 intermediate would be reoxidized back to PQQ simultaneously. The average collision current, duration, and charge for PQQ-modified MWCNT at 1.0 V vs Ag/AgCl were 105 pA, 0.45 ms, and 49 fC, respectively. As a result, the turnover frequency of electrocatalytic oxidation of N2H4 by PQQ was ...

Localized-Plasmon Voltammetry to Detect pH Dependent Gold Oxidation

Localized-plasmon voltammetry (LPV) bears great potential for electrochemical sensing applications beyond conventional cyclic voltammetry. In order to determine the limitations of this method, it is of utmost necessity to investigate the response toward chemical instability of the plasmonic electrode. We therefore investigated electrooxidation of a gold nanowire array with LPV in acidic electrolytes with different pH values. LPV shows excellent agreement with simultaneously recorded cyclic voltammograms up to the onset of oxygen evolution. Beyond that point, LPV still appears to provide meaningful signals. Further, with LPV the pH dependent reduction potentials of electrochemically grown gold oxides were determined and show a linear characteristic over the investigated pH range according to Nernst’s equation.

Investigation of Charge Transfer Kinetics at Carbon/Hydroquinone Interfaces for Redox-Active-Electrolyte Supercapacitors

The redox-active electrolyte supercapacitor (RAES) is a relatively new type of energy storage device. Simple addition of selected redox species in the electrolyte can greatly enhance the energy density of supercapacitors relative to traditional electric double layer capacitors (EDLCs) owing to redox reactions. Studies on the kinetics at the interface of the electrode and redox mediator are important when developing RAESs. In this work, we employ highly accurate scanning electrochemical microscopy (SECM) to extract the kinetic constants at carbon/hydroquinone interfaces. The charge transfer rate constants are 1.2 × 10-2 and 1.3 × 10-2 cm s-1 for the carbon nanotube/hydroquinone and reduced graphene oxide/hydroquinone interfaces, respectively. These values are higher than those obtained by the conventional cyclic voltammetry method, approximately by an order of magnitude. The evaluation of heterogeneous rate constants with SECM would be the cornerstone for understanding and developing high performance RAESs.

Redox cycling-based immunoassay for detection of carcinogenic embryonic antigen

Redox cycling based on an interdigitated electrode (IDE) was used as a highly sensitive immunoassay for carcinogenic embryonic antigen (CEA) through the quantification of 3,3′,5,5′-tetramethylbenzidine (TMB). For the redox cycling process, one pair of interdigitated finger electrodes was used as the first working electrode (generator) for cyclic voltammetry of TMB, and another pair of interdigitated finger electrodes was used as the second working electrode (collector) for sequential application of potentials for reduction and oxidation of TMB. The reduction (and oxidation) products of TMB at the collector were supplied to the generator, and following sequential oxidization (and reduction) at the generator, again supplied to the collector. Such redox recycling processes between the generator and collector allowed signal amplification. In this work, the influences of the following factors on the redox cycling of TMB were analyzed: (1) the redox potential at the collector, (2) the gap between the interdigitated finger electrodes, and (3) the scan rate of the generator. The redox potential and electrode gap influences were simulated with COMSOL software and compared with empirical results. At the optimum redox potentials and electrode gap, redox cycling was estimated to be five-fold more sensitive for the quantification of TMB than conventional cyclic voltammetry using one pair of interdigitated finger electrodes as the working electrode. Finally, redox cycling was applied to a commercial immunoassay for CEA, and the sensitivity of redox cycling was three-fold higher than that of conventional cyclic voltammetry using a single set of interdigitated finger electrodes as the working electrode.

The role of correlations in the determination of the transport properties of LaCl3 in high temperature molten eutectic LiCl–KCl

Abstract It is important to develop an accurate assessment of fundamental data of lanthanides in high temperature molten salts to enable an efficient application of pyroprocessing. This requires a careful consideration of uncertainties in the reported results. In this study, cyclic voltammetry (CV) tests of LaCl3 in KCl–LiCl molten salt were conducted at low concentration levels in the molten salt at 723 K and at several scan rates. The CV signals were subsequently analyzed through the conventional CV analysis and using a BET-based model through a nonlinear least-squares fitting procedure. It was determined that the parameters of the model were strongly correlated and the support plane procedure was implemented to assign joint confidence intervals for the diffusivity of lanthanum. Accounting for the correlations led to a significant increase in the uncertainty of the reported diffusivity which led to better agreement with the literature. Accounting for the correlations may be important for higher concentration levels.

The thermodynamic and transport properties of GdCl3 in molten eutectic LiCl-KCl derived from the analysis of cyclic voltammetry signals

Pyroprocessing technology is a promising tool for recycling nuclear fuel and producing high purity gadolinium for industrial applications. An efficient implementation of pyroprocessing entails a careful characterization of the electrochemical and transport properties of lanthanides in high temperature molten salts. In this work, the cyclic voltammetry signals of Gd in molten LiCl-KCl salt were recorded for a combination of three temperatures (723 K, 773 K, and 823 K) and three concentration levels (3 wt. %, 6 wt. %, and 9 wt. %) including concentration levels higher than previously reported and relevant for a realistic application of pyroprocessing for molten salt recycle, and the concentration effects were investigated. Four scan rates (200 mV/s to 500 mV/s) were used for each condition, and the signals were examined using conventional Cyclic Voltammetry (CV) analysis equations and by utilizing a two-plate Brunauer, Emmett, and Teller (BET) model accounting for mass diffusion, kinetics, adsorption, and the evolution of electrode morphology via a nonlinear least squares procedure for fitting the model to the experimental signals. It was determined that the redox process is quasi-reversible for the scan rates being used. Furthermore, the applicability of the conventional equations for CV analysis was shown to be problematic for the conditions used, and this is thought to be due to the fact that these equations were derived under the assumption of reversible conditions. The model-derived values for diffusivity are consistent with the literature and are shown to decrease with increasing concentration. This may be due to increased interactions at higher concentration levels. It was also shown that the formal redox potential increased with a concentration and was slightly more positive on the covered electrode.

Electrochemical microcalorimetry at single electrodes

The heat, which is reversibly exchanged at a single electrode, directly correlates with the entropy change during the electrochemical reaction. With recent experimental improvements also surface electrochemical reactions, i.e., reactions with only submonolayer conversion became accessible for heat measurements. Since the reaction entropy includes all side reactions, e.g., also charge–neutral coadsorption or ordering processes of the solvent, it provides complementary information to the current–potential relation, as for example measured by conventional cyclic voltammetry. Here, we will briefly review the theoretical background and recent developments and compare the method to other approaches for the measurement of the entropy of electrochemical systems.

Probing Redox Reactions at the Nanoscale with Electrochemical Tip-Enhanced Raman Spectroscopy.

A fundamental understanding of electrochemical processes at the nanoscale is crucial to solving problems in research areas as diverse as electrocatalysis, energy storage, biological electron transfer, and plasmon-driven chemistry. However, there is currently no technique capable of directly providing chemical information about molecules undergoing heterogeneous charge transfer at the nanoscale. Tip-enhanced Raman spectroscopy (TERS) uniquely offers subnanometer spatial resolution and single-molecule sensitivity, making it the ideal tool for studying nanoscale electrochemical processes with high chemical specificity. In this work, we demonstrate the first electrochemical TERS (EC-TERS) study of the nanoscale redox behavior of Nile Blue (NB), and compare these results with conventional cyclic voltammetry (CV). We successfully monitor the disappearance of the 591 cm(-1) band of NB upon reduction and its reversible reappearance upon oxidation during the CV. Interestingly, we observe a negative shift of more than 100 mV in the onset of the potential response of the TERS intensity of the 591 cm(-1) band, compared to the onset of faradaic current in the CV. We hypothesize that perturbation of the electrical double-layer by the TERS tip locally alters the effective potential experienced by NB molecules in the tip-sample junction. However, we demonstrate that the tip has no effect on the local charge transfer kinetics. Additionally, we observe step-like behavior in some TERS voltammograms corresponding to reduction and oxidation of single or few NB molecules. We also show that the coverage of NB is nonuniform across the ITO surface. We conclude with a discussion of methods to overcome the perturbation of the double-layer and general considerations for using TERS to study nanoscale electrochemical processes.

Variability, toxicity, and antioxidant activity of Eupatorium cannabinum (hemp agrimony) essential oils

Content: Eupatorium cannabinum L. (Asteraceae) is as a potential source of biologically active compounds. The plant is used in traditional medicine for the treatment of diarrhea and livers diseases.Objective: The present study provides investigation on pharmacological properties (antioxidant and toxic activities) of essential oils of E. cannabinum, collected from 11 wild populations in Lithuania.Materials and methods: Twenty-two hemp agrimony essential oil samples were prepared by hydrodistillation according to the European Pharmacopoeia, and their chemical composition was determined by GC–FID and GC–MS. Compositional data were subjected to principal components analysis (PCA). Instead of conventional spectrophotometric methods, cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques were applied to determine antioxidant activity of hemp agrimony essential oils. Meanwhile, toxicity of the oils was determined using brine shrimp (Artemia sp.) assay.Results: Chemical profiles of E. cannabinum oils were described according to the first predominant components: germacrene D (≤22.0%), neryl acetate (≤20.0%), spathulenol (≤27.2%), and α-terpinene (11.5%). For the first time, α-zingiberene (≤7.8%) was found to be among three major constituents (as the second one) for hemp agrimony oils. SWV measurements revealed that oxidation potentials of compounds present in the oils are lower (below 0.1 V) compared with that of well-known antioxidant quercetin (0.15 V). Toxicity tests evaluated that hemp agrimony oils containing predominant amounts of germacrene D and neryl acetate were notably toxic (LC50 value 16.3–22.0 μg/mL).Conclusion: The study provided some new data concerning chemical composition and pharmaceutical properties of E. cannabinum essential oils.