Electrochemical Impedance Microscopy Research Articles

Deep Learning Enhanced Label-Free Action Potential Detection Using Plasmonic-Based Electrochemical Impedance Microscopy.

Measuring neuronal electrical activity, such as action potential propagation in cells, requires the sensitive detection of the weak electrical signal with high spatial and temporal resolution. None of the existing tools can fulfill this need. Recently, plasmonic-based electrochemical impedance microscopy (P-EIM) was demonstrated for the label-free mapping of the ignition and propagation of action potentials in neuron cells with subcellular resolution. However, limited by the signal-to-noise ratio in the high-speed P-EIM video, action potential mapping was achieved by averaging 90 cycles of signals. Such extensive averaging is not desired and may not always be feasible due to factors such as neuronal desensitization. In this study, we utilized advanced signal processing techniques to detect action potentials in P-EIM extracted signals with fewer averaged cycles. Matched filtering successfully detected action potential signals with as few as averaging five cycles of signals. Long short-term memory (LSTM) recurrent neural network achieved the best performance and was able to detect single-cycle stimulated action potential successfully [satisfactory area under the receiver operating characteristic curve (AUC) equal to 0.855]. Therefore, we show that deep learning-based signal processing can dramatically improve the usability of P-EIM mapping of neuronal electrical signals.

Ultrasensitive CCL2 Detection in Urine for Diabetic Nephropathy Diagnosis Using a WS2-Based Plasmonic Biosensor.

The accurate diagnosis of diabetic nephropathy relies on achieving ultrasensitive biosensing for biomarker detection. However, existing biosensors face challenges such as poor sensitivity, complexity, time-consuming procedures, and high assay costs. To address these limitations, we report a WS2-based plasmonic biosensor for the ultrasensitive detection of biomarker candidates in clinical human urine samples associated with diabetic nephropathy. Leveraging plasmonic-based electrochemical impedance microscopy (P-EIM) imaging, we observed a remarkable charge sensitivity in monolayer WS2 single crystals. Our biosensor exhibits an exceptionally low detection limit (0.201 ag/mL) and remarkable selectivity in detecting CC chemokine ligand 2 (CCL2) protein biomarkers, outperforming conventional techniques such as ELISA. This work represents a breakthrough in traditional protein sensors, providing a direction and materials foundation for developing ultrasensitive sensors tailored to clinical applications for biomarker sensing.

Localised Electrochemical Impedance Spectroscopy of Gold Nanoparticles Labelled Antibodies Probed by Platinum Microstructured Ultramicroelectrode.

This research is focused on enhancing the capabilities of scanning electrochemical impedance microscopy (SEIM) for detecting gold nanoparticle-labelled antibodies using electrochemically modified platinum ultramicroelectrode. The primary objective was to address the high resistance issue encountered in previous measurements with SEIM via the utilization of SEIM probes based on micro-electrodes modified by platinum microstructures, which improved the sensitivity and precision of the detection of targeted biomolecules. The modified probe resulted in a lowered charge transfer resistance by over ten times and a decrease in detection to around 100 fg/mL. We suggest potential applications in various biotechnological and biomedical fields, with future research expected to further refine this technique.

The impact of environmentally friendly supramolecular coordination polymers as carbon steel corrosion inhibitors in HCl solution: synthesis and characterization

Two 3D-supramolecular coordination polymers (SCP1 & SCP2) have been synthesized and characterized by physicochemical and spectroscopic methods. In a solution of 1.0 M HCl, SCPs were used to prevent corrosion of carbon steel (CS). The inhibition productivity (%η) rises as the synthetic inhibitor dose rises, and the opposite is true as the temperature rises. The study was carried out using chemical (mass loss, ML) and electrochemical ( potentiodynamic polarization, PDP and electrochemical impedance microscopy, EIS) techniques, which showed %η reached to 93.1% and 92.5% for SCP1 & SCP2, respectively at 21 × 10−6 M, 25 °C. For the polarization results, SCPs behave as mixed-type inhibitors. With increasing doses of SCPs, the charge transfer resistance grew and the double layer's capacitance lowered. The creation of a monolayer on the surface of CS was demonstrated by the finding that the adsorption of SCPs on its surface followed the Henry adsorption isotherm. The parameters of thermodynamics were computed and explained. The physical adsorption of SCPs on the surface of CS is shown by the lowering values of free energy (∆Goads < − 20 kJ mol−1) and increasing the activation energy (E*a) values in presence of SCP1 & SCP2 than in their absence. Atomic force microscope (AFM) and scanning electron microscopy (SEM) demonstrated the development of a protective thin film of SCPs precipitated on the surface of CS. There is a strong matching between results obtained from experimental and theoretical studies. Results from each approach that was used were consistent.

Investigating electrochemical corrosion at Mg alloy-steel joint interface using scanning electrochemical cell impedance microscopy (SECCIM)

Developing strategies to prevent corrosion at the interface of dissimilar metal alloys is challenging because of the presence of heterogenous distribution of galvanic couples and microstructural features that significantly change the corrosion rate. Devising strategies to mitigate this interfacial corrosion requires quantitative and correlative understanding of its surface electrochemical reaction. In this work, scanning electrochemical cell impedance microscopy (SECCIM) was employed to study location-specific corrosion in the interfacial region of dissimilar alloys, such as AZ31 (magnesium alloy) and DP590 (steel) welded using the Friction-stir Assisted Scribe Technique (FAST) processes. Herein, SECCM and SECCIM were used to perform correlative mapping of the local electrochemical impedance spectroscopic and potentiodynamic polarization to measure the effect of electronic and microstructural changes in the welded interfacial region on corrosion kinetics. Microstructural characterization including scanning electron microscopy and electron backscatter diffraction was performed to correlate changes in microstructural features and chemistry with the corresponding electronic properties that affect corrosion behavior. The variations in corrosion potential, corrosion current density, and electrochemical impedance spectroscopy behavior across the interface provide deeper insights on the interfacial region—which is chemically and microstructurally distinct from both bare AZ31 and DP590 that can help prevent corrosion in dissimilar metal structures.

Electrochemical behavior of in-situ electrosynthetized 3D metal-organic framework (MOF) as ultra-stable thin film on nickel foam

Metal-organic frameworks (MOFs) based materials have recently attracted a wide attention for developing of high-performing supercapacitors (SCs). In the present work, the Ni3(HITP)2 MOF was successfully electrosynthetized via a one-pot approach from and to the surface of nickel foam (NF) and served as ultra-stable thin film electrode. The presence of the active layer is evidenced by a wide range of technique ranging from morphological, spectroscopic to electrochemical ones. As the film was formed within the diffusion layer of the NF surface, the electrochemical accessible surface area was improved and the drawback of being low electrically conductive of MOF based materials could be minimized. Accordingly, it is confirmed by a significant charge accumulation over dissipation obtained by electrochemical impedance microscopy and a capacitance retention about 40% from 0.01 to 10 V.s−1. Besides, this approach allows the formed materials to be strongly attached to the surface of the current collector, thus significantly enhance the cycling stability around 100% capacitance retention over 0.9 V for 170,000 cycles

Electrochemical measurement of tamoxifen in the presence of acetaminophen and ascorbic acid using carbon paste electrode modified with novel nanoparticles

Tamoxifen (TMX) is a non-steroidal anti-estrogen used to treat human breast cancer, although the International Olympic Committee has banned this drug. Here, a sensor based on an electrochemical process was prepared by modifying the carbon paste electrode with alumina/carbon core–shell and vanadium oxide nanoparticles (Al2O3@C/V2O5/CPE) and used to analyze TMX in an aqueous medium. The modified electrode surface was studied using electrochemical impedance and scanning electron microscopy. The electrochemical behavior of TMX was studied using cyclic voltammetry, CV, and differential pulse, DP, techniques. The DP current response of the Al2O3@C/V2O5/CPE electrode was 2.3 times that of the CPE. In the measurement level of TMX using the DP technique at the Al2O3@C/V2O5/CPE electrode surface, the linear dependence of the anodic current with TMX concentration in the linear range of 0.1–200 μM and a detection limit of 0.025 μM was obtained. The modified electrode showed excellent selectivity in the presence of organic and inorganic species which is available in real examples. Then, after examining the effective parameters in the electrode response to TMX, measurement of TMX in the presence of acetaminophen (AC) and ascorbic acid (AA) was also evaluated by the DP method. The results showed that simultaneous measurement of three species by Al2O3@C/V2O5/CPE electrode is possible without disturbing each other. Finally, the proposed sensor was successfully used to measure TMX in drug samples.

A Systematic Study of the Role of Cathodic Polarization and New Findings on the Soft Sparking Phenomenon from Plasma Electrolytic Oxidation of an Al-Cu-Li Alloy

Understanding the role of cathodic polarization and soft sparking is critical for plasma electrolytic oxidation (PEO). In this study, PEO of an Al-Cu-Li alloy has been carried out under cathodic to anodic current density ratio (R) from 0 to 3.3. Controlled potential tests and electrochemical impedance microscopy are also adopted. The results show that increased cathodic polarization improves the long-term oxide growth efficiency until an optimum soft sparking regime is reached at R = 1.2, after that the efficiency decreases and damages to the coatings occur. Interestingly, anodic potential drop, which was considered one of the characteristics of soft sparking, is absent in some cases under R = 1.2, and the coatings under R = 1.2 is also featured by a white outer layer enriched with cations. Excessive cathodic polarization (R = ∼2.0–3.3) leads to the compact coatings with highest impedance values at the early PEO stage (300 s), but they deteriorated rapidly. The complex PEO behaviors with different cathodic polarization has been explained in terms of the intercalation of hydrogen species, mass transportation affected by H2 evolution, charge extraction and hydrogen induced stresses. Reciprocally, controlled potential tests indicate that anodic polarization also suppresses the subsequent cathodic hydrogen evolution.

Estimation of effective thickness of Cyclopore polycarbonate membrane by scanning electrochemical impedance microscopy

• O impedance related to radial diffusion and restricted planar diffusion; for tip closely to hole surface-Cyclopore membrane. • Equivalent circuits including Cole-Cole diffusion impedance (Z M ), Cole-Davidson type impedance (Z W ) and O impedance (Z O ) proposed for different separation distances. • Difference in diffusion impedance on hole and that on flat surface on Cyclopore membrane for estimating membrane thickness. A new, feasible, on-line method was proposed to determine Cyclopore polycarbonate membrane thickness by scanning electrochemical impedance microscopy (SEIM) technique. The thickness is 8.4 µm, which close to the report technical data. Three effective impedances for equivalent circuit model including Cole-Cole diffusion impedance, Cole-Davidson type impedance and O impedance were firstly proposed for radial diffusion and restricted planar diffusion mode when tip electrode on flat or hole surface in Cyclopore membrane. Data analysis results showed that restricted planar diffusion emerged when tip electrode approach tightly to hole surface. Additionally, SEIM responses on the flat and hole surface were compared and could be applied for topographic imaging in the future work.

Scanning Electrochemical Impedance Microscopy in Redox-Competition Mode for the Investigation of Antibodies Labelled with Horseradish Peroxidase.

Scanning electrochemical microscopy enhanced by electrochemical impedance spectroscopy (SEIM) was applied to detect immobilized antibodies labelled with horseradish peroxidase (Ab-HRP). The localized HRP activity was investigated by the SEIM redox competition (RC-SEIM) mode using hydrogen peroxide as a substrate and hexacyanoferrate as a redox mediator. Electrochemical impedance shows to be related to the consumption of hydrogen peroxide at the ultramicroelectrode. For the evaluation of impedimetric results, an equivalent electric circuit was applied with solution resistance, double-layer capacitance, and charge-transfer resistance. These equivalent circuit characteristics depend on the distance between the sample and ultramicroelectrode, and the concentration of substrate. From the gathered data, the charge-transfer resistance appeared to be the parameter describing the behavior of HRP catalyzed reaction as it showed a linear dependence on H2O2 concentration. The RC-SEIM mode suitability for the studying of HRP catalyzed reactions and for the evaluation of Ab-HRP bound to the surface was demonstrated. Additionally, the applicability of RC-SEIM mode for the determination of Ab-HRP affinity bound to the target analyte was discussed.

Fabrication of the ZrC reinforced Ni[sbnd]W composite coating and exploration of its mechanical properties and corrosion resistance

Herein, zirconium carbide (ZrC) nanoparticles (NPs) dispersion strengthening NiW composite coatings were fabricated through pulse electrodeposition technology with an adoptive current density of 5 A·dm−2. The chemical composition, crystal properties, microstructure and micromorphology of coatings were analyzed by XRD, XPS, SEM and EDS in detail. Mechanical properties such as hardness, wear resistance, surface wettability, and apparent roughness were performed by Vickers hardness tester, reciprocating friction test, water contact angle test and AFM, respectively. Corrosion resistance was investigated by potentiometric polarization, electrochemical impedance and scanning electrochemical microscopy. The results showed that the addition of ZrC NPs significantly optimized the surface integrity and improved the mechanical properties of NiW coatings, the corrosion resistance of Ni-W/ZrC composite coating is far superior to the original coating. In addition, the addition of enhanced particles was discussed in detail. When the amount of ZrC NPS in the electroplating solution was 2 g/L, the fabricated composite coating had the best mechanical properties (the microhardness value was 723.36 HV and the average coefficient of friction was 0.235) and corrosion resistance properties (the corrosion potential was −0.200 V and the value of charge transfer resistance is 55.112 KΩ).

Study the variation of surface topography & corrosion resistance of Cr-GO nanocomposite coatings by addition of GO nanoparticles

The chromium-graphene oxide nanocomposite coating was synthesized successfully by the electroplating method in this investigation. The influence of the addition of GO on surface topography, microhardness and the corrosion behavior of chromium coatings was studied by polarization and electrochemical impedance microscopy methods. The maximum surface microhardness value was measured at a sample with 10 wt% of GO particle equals to 766 HV. The results of surface analysis (Atomic Force Microscopy and microhardness) reveals that the combination of two main factors of GO particle addition and coating thickness has more effect on the surface microhardness than the grain size of topographies. Corrosion results show the addition of the GO particles reduces the corrosion resistance of chromium coating but layer with 5 wt% of GO particles has better corrosion resistance than other composite coatings. Also, results show that corrosion resistance has a meaningful relationship with Sa/Sp ratio.

Nanogold modified glassy carbon sensor for the quantification of phytoestrogenchlorogenic acid

Nanogold modified glassy carbon electrode has been fabricated for electrochemical sensing of chlorogenic acid (CGA). The electrochemical properties and morphology of the prepared nanocomposite were studied by electrochemical impedance (EIS) and scanning electron microscopy (SEM). The response of the voltammetric sensor was found to be linear with concentration of CGA in the range of 0.4–3.6 µg mL−1 with detection limit of 0.0140 µg mL−1. The proposed method was also applied for the estimation of CGA in real samples.

Towards the application of fast Fourier transform - scanning electrochemical impedance microscopy (FFT-SEIM)

In this research we are proposing a combination of scanning electrochemical microscopy (SECM) and fast Fourier transform – electrochemical impedance spectroscopy (FFT-EIS) as a new tool, which we entitled ‘fast Fourier transform – scanning electrochemical impedance microscopy (FFT-SEIM)’ suitable for the evaluation and treatment of highly complicated electrochemical systems, in which the electrical signal is under limitations of very small surface area of the electrode and Faradaic process is controlled by slow diffusion of species in the solution. The identification and in situ treatment of unhealthy tissues at cellular level is futuristic direction of the biomedical research, which requires completely new tools and advanced techniques. In this manuscript we show that the combination of SECM and FFT-EIS systems can operate well in the absence of the additional redox probes, which are harmful for living cells and tissues. We are also addressing how some challenging electrochemical problems, which are arising during the application of FFT-SEIM in the absence of redox probe, can be solved. Particularly, in this research we have demonstrated how the quality of FFT-SEIM signal can be increased by the adjustment of FFT-SEIM parameters. Particularly, the reduction of preconditioning duration before the start of the FFT-EIS measurement and very short duration of FFT-EIS measurement, which takes just a little bit longer time than that required to register single period of sin-wave at lowest frequency of registered EIS spectra, significantly increased the quality of gathered EIS spectra.

Investigation of Active and Inactivated Yeast Cells by Scanning Electrochemical Impedance Microscopy

AbstractScanning electrochemical microscopy (SECM), electrochemical impedance spectroscopy (EIS) and scanning electrochemical impedance microscopy (SEIM) were used to investigate electrochemical activity of active and inactivated yeast Saccharomyces cerevisiae cells. SEIM experiment was performed using a unique electrochemical impedance spectrometer with a fast Fourier transform (FFT‐EIS) function, which enabled simultaneously perturb/evaluate electrochemical system at 50 frequencies. This allowed very quick observing the differences between impedance spectra, which were taken every few seconds. Therefore, we were able to apply SEIM for relatively fast determination of electrochemical impedance dependence on the distance between ultramicroelectrode (UME) and surface modified by immobilized yeast cells. It was determined that electrochemical activity and ‘breathing’ (a consumption of dissolved oxygen) of yeast can be electrochemically observed when the distance between UME and surface of yeast cells is in the range from 0 μm to 25 μm. Therefore, 25 μm is the maximum distance suitable for efficient investigation of yeast cell activity when experiments are performed in FFT‐SEIM mode. Charge transfer resistance of active and inactivated yeast cells was determined using EIS. It was calculated that charge transfer resistance of active yeast cells is 1.5 times lower than that of inactivated yeast cells. Lipophilic vitamin K3 (Vit‐K3) and hydrophilic vitamin K1 (Vit‐K1) were mixtured and used as redox mediators for charge transfer from yeast cells.

Fabrication of binder-free electrode using reinforced resorcinol formaldehyde-based carbon aerogels

In this study, the electrochemical performance of the binder-free electrode based on the reinforced resorcinol formaldehyde (RF) carbon aerogels (CAs) was investigated for electric double layer capacitor (EDLC) application. Resorcinol formaldehyde aerogel (RF) was crosslinked using methylene diphenyl diisocyanate (MDI) and then pyrolyzed to produce carbon aerogel (CA). CA was subsequently activated using CO2 gas. The morphological changes due to the reinforcing and activation process were explored by SEM. The BET and BJH results showed an improvement in specific surface area and microporous volume. The CO2-activated CAs displayed up to twice more specific surface areas compared with the unactivated CAs. The compressive test verified an improvement of up to 5 times in the mechanical strength. In order to investigate the electrochemical performance, cyclic voltammetry (CV), charge/discharge (CD), and electrochemical impedance microscopy (EIS) were carried out. In an identical electrode weight, the specific capacity of binder-free electrodes increased about twice, in comparison with the common electrodes due to the removal of the binder and the collector. The highest specific capacitance among the fabricated samples was obtained for the reinforced and activated sample with resorcinol/catalyst (R/C) ratio of 700, which was equal to 55.5 F/g.

Progress in durability of metal-supported solid oxide fuel cells with infiltrated electrodes

High power density and longevity are required to commercialize solid oxide fuel cells for vehicular applications. In this work, electrochemical durability of high-performance metal-supported solid oxide fuel cells (MS-SOFCs) with infiltrated catalysts is investigated. Durability screening of various cathode and anode compositions is conducted. The Pr6O11 cathode and SDCN40 (40 vol% Ni-60 vol% SDC) anode are selected due to preferential tradeoff between performance and durability. X-ray diffraction indicates the catalyst phases are stable after prolonged thermal annealing. Electrochemical impedance and scanning electron microscopy analyses show that the evolution of SDCN40 is minimal, and coarsening and Cr poisoning of the Pr6O11 catalyst are the dominant degradation mechanisms. These degradation mechanisms are addressed by implementing three additional fabrication steps: (1) preoxidation of the metal support, (2) deposition of thin and protective atomic layer deposition (ALD) coatings throughout the cathode-side electrode and support, and (3) in situ pre-coarsening of the catalysts. A favorable tradeoff is achieved: the combination of the three fabrication steps reduces degradation rate at 0.7 V and 700 °C by two orders of magnitude to 2.3% kh−1, while sacrificing 35% of initial power density. The catalyst pre-coarsening step is primarily responsible for the loss of performance.

Expired Lorazepam Drug: A Medicinal Compound as Green Corrosion Inhibitor for Mild Steel in Hydrochloric Acid System

The present study explores the green corrosion inhibition property of expired Lorazepam tablet on the mild steel (MS) in 3M HCl solution using gravimetric (mass loss), atomic absorption, Tafel plot, electrochemical impedance, quantum chemical, and scanning electron microscopy (SEM) studies. It is found that; expired Lorazepam tablet shows the robust corrosion inhibition property (protection efficiency = 90%) on the MS at 0.4 g/L of expired Lorazepam drug (observed from the gravimetric studies) at 333 K with a contact time of 3 h. The significant enhancement in the protection performance of the expired Lorazepam tablet has been observed by atomic absorption spectroscopy technique. The results of Tafel plots show that, the presence of the expired Lorazepam tablet of different concentration decreases the both cathodic and anodic processes at MS in the 3M HCl solution by blocking the MS active sites and behave as a mixed mode corrosion inhibitor. Electrochemical impedance studies show that, increase in the amounts of expired Lorazepam tablet increases the charge transfer process at MS-HCl interface. The electron transfer nature of the expired Lorazepam tablet on the MS surface was confirmed from the Quantum chemical studies. The adsorbed invisible layer over the surface of MS was scrutinized by scanning electron microscopy technique.

Redox-probe-free scanning electrochemical microscopy combined with fast Fourier transform electrochemical impedance spectroscopy.

Scanning electrochemical microscopy (SECM) hybridized with fast Fourier transform-based electrochemical impedance spectroscopy (FFT-EIS) seems to be a powerful variation of scanning electrochemical impedance microscopy (SEIM), wherein both state-of-the-art techniques are combined (FFT-SEIM) and can be used for the investigation and treatment of tissues at single cell level. However, in most EIS-based experiments, harmful redox mediators are applied, which affect the functioning of living cells and tissues. Therefore, the development of a redox-probe-free FFT-SEIM is still a very important challenge in electrochemistry. For this reason, in this research, we have demonstrated a redox-probe-free evaluation of conducting and non-conducting surfaces by combining scanning electrochemical microscopy with FFT-EIS. It was demonstrated that using the fast Fourier transform-based FFT-EIS technique, EIS spectra could be registered much faster compared to experiments performed using the conventional EIS equipment. An ultramicroelectrode (UME) was used as a scanning electrode to ensure high spatial resolution. We have performed FFT-SEIM measurements in a redox-probe-free mode (without any additional redox probes) and have investigated several surfaces with different conductivities. The FFT-EIS equipment and the built-in software help to avoid the influence of possible formation of hydrogen bubbles on the UME. This research opens up a new avenue for the application of FFT-SEIM in the investigation of samples that are unstable and very sensitive towards redox mediators (e.g., tissues and/or living cells).

Tannic complexes coated nanocontainers for controlled release of corrosion inhibitors in self-healing coatings

Nanocontainers with controlled release properties have been used in self-healing coatings for many years. However, the spontaneous leakage of the small molecular weight inhibitors from the nanocontainers promoted the development of nanovalves or gatekeepers to control inhibitor release. Herein, we demonstrate a facile method to encapsulate corrosion inhibitor in mesoporous silica nanoparticles (MSNs) with the help of tannic acid complexes, which endow the inhibitor loaded MSNs with pH-controlled release function. Commercial water-borne alkyd coating impregnated with 2 wt% of benzotriazole-loaded nanocontainers presented significant self-healing effect after 20 days of immersion in 0.1 M NaCl solution from both released benzotriazole and tannic acid as confirmed by electrochemical impedance spectroscopy and microscopy. The impedance modulus of coating with nanocontainers increased from 4.7 × 104 Ω cm2 to 1.8 × 105 Ω cm2 after 15 days of immersion.