Noninvasive and Continuous Monitoring of On-Chip Stem Cell Osteogenesis Using a Reusable Electrochemical Immunobiosensor

Noninvasive monitoring of biofabricated tissues during the biomanufacturing process is needed to obtain reproducible, healthy, and functional tissues. Measuring the levels of biomarkers secreted from tissues is a promising strategy to understand the status of tissues during biofabrication. Continuous and real-time information from cultivated tissues enables users to achieve scalable manufacturing. Label-free biosensors are promising candidates for detecting cell secretomes since they can be noninvasive and do not require labor-intensive processes such as cell lysing. Moreover, most conventional monitoring techniques are single-use, conducted at the end of the fabrication process, and, challengingly, are not permissive to in-line and continual detection. To address these challenges, we developed a noninvasive and continual monitoring platform to evaluate the status of cells during the biofabrication process, with a particular focus on monitoring the transient processes that stem cells go through during in vitro differentiation over extended periods. We designed and evaluated a reusable electrochemical immunosensor with the capacity for detecting trace amounts of secreted osteogenic markers, such as osteopontin (OPN). The sensor has a low limit of detection (LOD), high sensitivity, and outstanding selectivity in complex biological media. We used this OPN immunosensor to continuously monitor on-chip osteogenesis of human mesenchymal stem cells (hMSCs) cultured 2D and 3D hydrogel constructs inside a microfluidic bioreactor for more than a month and were able to observe changing levels of OPN secretion during culture. The proposed platform can potentially be adopted for monitoring a variety of biological applications and further developed into a fully automated system for applications in advanced cellular biomanufacturing.

Elucidating the Role of Electrochemically Formed LiF in Discharge and Aging of Li-CFx Batteries

Fifty years after its introduction, the lithium-carbon monofluoride (Li-CFx) battery still has the highest cell-level specific energy demonstrated in a practical cell format. However, few studies have analyzed how the main electrochemical discharge product, LiF, evolves during the discharge and cell rest periods. To fill this gap in understanding, we investigated molecular-level and interfacial changes in CFx electrodes upon the discharge and aging of Li-CFx cells, revealing the role of LiF beyond that of a simple discharge product. We reveal that electrochemically formed LiF deposits on the surface of the CFx electrode and subsequently partially disperses into the electrolyte to form a colloidal suspension during cell aging, as determined from galvanostatic electrochemical impedance spectroscopy (EIS), solid-state 19F nuclear magnetic resonance (NMR), dynamic light scattering (DLS), and operando optical light microscopy measurements. Electrochemical LiF formation and LiF dispersion into the electrolyte are distinct competing rate processes that each affect the cell impedance differently. Using knowledge of LiF dispersion and saturation, an in-line EIS method was developed to compute the depth of discharge of CFx cells beyond coulomb counting. Solid-state 19F NMR measurements quantitatively revealed how LiF and CF moieties evolved with discharge. Covalent CF bonds react first, followed by a combination of covalent and ionic CF bonds. Quantitively correlating NMR and electrochemical measurements reveals not only how LiF formation affects cell impedance but also that CF bonds with the most ionic character remain unreacted, which limits realization of the full theoretical specific capacity of the CFx electrode. The results reveal new insights into the electrochemical discharge mechanism of Li-CFx cells and the unique role of LiF in cell discharge and aging, which suggest pretreatment strategies and methods to improve and measure the performance of Li-CFx batteries.

Understanding the Behavior of Supercapacitor Materials via Electrochemical Impedance Spectroscopy: A Review

Energy harvesting and energy storage are two critical aspects of supporting the energy transition and sustainability. Many studies have been conducted to achieve excellent performance devices for these two purposes. As energy-storing devices, supercapacitors (SCs) have tremendous potential to be applied in several sectors. Some electrochemical characterizations define the performance of SCs. Electrochemical impedance spectroscopy (EIS) is one of the most powerful analyses to determine the performance of SCs. Some parameters obtained from this analysis include bulk resistance, charge-transfer resistance, total resistance, specific capacitance, response frequency, and response time. This work provides a holistic and comprehensive review of utilizing EIS for SC characterization. Overall, researchers can benefit from this review by gaining a comprehensive understanding of the utilization of electrochemical impedance spectroscopy (EIS) for characterizing supercapacitors (SCs), enabling them to enhance SC performance and contribute to the advancement of energy harvesting and storage technologies.

The Influence of Cathode Degradation Products on the Anode Interface in Lithium-Ion Batteries

Degradation of cathode materials in lithium-ion batteries results in the presence of transition metal ions in the electrolyte, and these ions are known to play a major role in capacity fade and cell failure. Yet, while it is known that transition metal ions migrate from the metal oxide cathode and deposit on the graphite anode, their specific influence on anode reactions and structures, such as the solid electrolyte interphase (SEI), is still quite poorly understood due to the complexity in studying this interface in operational cells. In this work we combine operando electrochemical atomic force microscopy (EC-AFM), electrochemical quartz crystal microbalance (EQCM), and electrochemical impedance spectroscopy (EIS) measurements to probe the influence of a range of transition metal ions on the morphological, mechanical, chemical, and electrical properties of the SEI. By adding representative concentrations of Ni2+, Mn2+, and Co2+ ions into a commercially relevant battery electrolyte, the impacts of each on the formation and stability of the anode interface layer is revealed; all are shown to pose a threat to battery performance and stability. Mn2+, in particular, is shown to induce a thick, soft, and unstable SEI layer, which is known to cause severe degradation of batteries, while Co2+ and Ni2+ significantly impact interfacial conductivity. When transition metal ions are mixed, SEI degradation is amplified, suggesting a synergistic effect on the cell stability. Hence, by uncovering the roles these cathode degradation products play in operational batteries, we have provided a foundation upon which strategies to mitigate or eliminate these degradation products can be developed.

Exploring the Living Cell: Applications and Advances of Scanning Electrochemical Microscopy

A living cell is a complex network of molecular, biochemical and physiological processes. Cellular activities, such as ion transport, metabolic processes, and cell-cell interactions can be determined electrochemically by detecting the electrons or ions exchanged in these processes. Electrochemical methods often are noninvasive, and they can enable the real-time monitoring of cellular processes. Scanning electrochemical microscopy (SECM) is an advanced scanning probe electroanalysis technique that can map the surface topography and local reactivity of a substrate with high precision at the micro- or nanoscale. By measuring electrochemical signals, such as redox reactions, ion fluxes, and pH changes, SECM can provide valuable insights into cellular activity. As a result of its compatibility with liquid medium measurements and its nondestructive nature, SECM has gained popularity in living cell research. This review aims to furnish an overview of SECM, elucidating its principles, applications, and its potential to contribute significantly to advancements in cell biology, electroporation, and biosensors. As a multidisciplinary tool, SECM is distinguished by its ability to unravel the intricacies of living cells and offers promising avenues for breakthroughs in our understanding of cellular complexity.

Inhibition of corrosion on API 5L X52 pipeline steel in acid media by Tradescantia spathacea

The concentration effect of Tradescantia spathacea (T. spathacea) as corrosion inhibitor of API 5L X52 steel in 0.5 M of H2SO4 was studied here through electrochemical and gravimetric techniques. To achieve it, samples of the material were prepared to be submitted to each of the tests. Results from electrochemical impedance spectroscopy (EIS) showed that there was an optimum concentration of the inhibitor in which is reached the maximum inhibition efficiency, displaying the best inhibition characteristics for this system with a maximum inhibition of 89% by using 400 ppm. However, the efficiency decreased until 40% when the temperature was increased to 60°C. Potentiodynamic polarization curves (PDP) revealed that some of the present compounds of T. spathacea may affect anodic and cathodic process, so it can be classified as a mix-type corrosion inhibitor for API 5L X52 in sulfuric acid. Also, this compound followed an adsorption mechanism; this can be described through a Frumkin isotherm with an adsorption standard free energy difference (ΔG°) of -56.59 kJmol-1. Metal surface was studied through scanning electron microscope, results revealed that by adding inhibitor, the metal surface is protected; also, they evidenced low damages compared with the surface with no inhibitor. Finally, Tradescantia spathacea inhibited the corrosion process with 82% efficiency.

Corrosion of Stainless Steel in Simulated Nuclear Reactor Primary Coolant-Experiments and Modeling

In the present paper, the effect of the evolution of primary water chemistry during power operation on the corrosion rate and conduction mechanism of oxide films on stainless steel is studied by in situ impedance spectroscopy at 300 °C/9 MPa during 1-week exposure periods in an autoclave connected to a recirculation loop. At the end of the exposure period, the samples were anodically polarized in a wide range of potentials to evaluate the stability of the passive oxide. Separate samples of the same steel were simultaneously exposed to the coolant and subsequently analyzed by glow discharge optical emission spectroscopy (GDOES) in order to estimate the thickness and the in-depth composition of the formed oxides. Impedance data were quantitatively interpreted using the mixed-conduction model for oxide films (MCM) to estimate the rates of metal oxidation at the alloy/oxide interface, oxide dissolution and restructuring at the film/coolant interface, and ion transport in the protective corrosion layer.

Machine learning assisted analysis of equivalent circuit usage in electrochemical impedance spectroscopy applications

Electrical equivalent circuits are a widely applied tool with which electrical processes can be rationalized. There is a wide-ranging selection of fields from bioelectrochemistry to batteries to fuel cells making use of this tool. Enabling meta-analysis on the similarities and differences in the used circuits will help to identify commonly used circuits and aid in evaluating the underlying physics. We present a method and an implementation that enables the conversion of circuits included in scientific publications into a machine-readable form for generating machine learning datasets or circuit simulations.

Recording Quality Is Systematically Related to Electrode Impedance

Extracellular recordings with planar microelectrodes are the gold standard technique for recording the fast action potentials of neurons in the intact brain. The introduction of microfabrication techniques has revolutionized the in vivo recording of neuronal activity and introduced high-density, multi-electrode arrays that increase the spatial resolution of recordings and the number of neurons that can be simultaneously recorded. Despite these innovations, there is still debate about the ideal electrical transfer characteristics of extracellular electrodes. This uncertainty is partly due to the lack of systematic studies comparing electrodes with different characteristics, particularly for chronically implanted arrays over extended time periods. Here a high-density, flexible, and thin-film array is fabricated and tested, containing four distinct electrode types differing in surface material and surface topology and, thus, impedance. It is found that recording quality is strongly related to electrode impedance with signal amplitude and unit yield negatively correlated to impedance. Electrode impedances are stable for the duration of the experiment (up to 12 weeks) and recording quality does not deteriorate. The findings support the expectation from the theory that recording quality will increase as impedance decreases.

Phage Display's Prospects for Early Diagnosis of Prostate Cancer

Prostate cancer (PC) is the second most diagnosed cancer among men. It was observed that early diagnosis of disease is highly beneficial for the survival of cancer patients. Therefore, the extension and increasing quality of life of PC patients can be achieved by broadening the cancer screening programs that are aimed at the identification of cancer manifestation in patients at earlier stages, before they demonstrate well-understood signs of the disease. Therefore, there is an urgent need for standard, sensitive, robust, and commonly available screening and diagnosis tools for the identification of early signs of cancer pathologies. In this respect, the "Holy Grail" of cancer researchers and bioengineers for decades has been molecular sensing probes that would allow for the diagnosis, prognosis, and monitoring of cancer diseases via their interaction with cell-secreted and cell-associated PC biomarkers, e.g., PSA and PSMA, respectively. At present, most PSA tests are performed at centralized laboratories using high-throughput total PSA immune analyzers, which are suitable for dedicated laboratories and are not readily available for broad health screenings. Therefore, the current trend in the detection of PC is the development of portable biosensors for mobile laboratories and individual use. Phage display, since its conception by George Smith in 1985, has emerged as a premier tool in molecular biology with widespread application. This review describes the role of the molecular evolution and phage display paradigm in revolutionizing the methods for the early diagnosis and monitoring of PC.

Multiphysics Modeling of Electrochemical Impedance Spectroscopy Responses of SAM-Modified Screen-Printed Electrodes

In this work, we present a multiphysics modeling approach capable of simulating electrochemical impedance spectroscopy (EIS) responses of screen-printed electrodes (SPEs) modified with self-assembled monolayers of 11-Mercaptoundecanoic acid (MUA). Commercially available gold SPEs are electrochemically characterized through experimental cyclic voltammetry and EIS measurements with 10 mM [Fe(CN)6]3-/4- redox couple in phosphate buffered saline before and after the surface immobilization of MUA at different concentrations. We design the multiphysics model through COMSOL Multiphysics® based on the 3D geometry of the devices under test. The model includes four different physics considering the metal/solution interface electrochemical phenomena, the ion and electron potentials and currents, and the measurement set-up. The model is calibrated through a set of experimental measurements, allowing the tuning of the parameters used by the model. We use the calibrated model to simulate the EIS response of MUA-modified SPEs, comparing the results with experimental data. The simulations fit the experimental curves well, following the variation of MUA concentration on the surface from 1 µM to 100 µM. The EIS parameters, retrieved through a CPE-modified Randles' circuit, confirm the consistency with the experimental data. Notably, the simulated surface coverage estimates and the variation of charge transfer resistance due to MUA-immobilization are well matched with their experimental counterparts, reporting only a 2% difference and being consistent with the experimental electrochemical behavior of the SPEs.

Hybrid Impedimetric Biosensors for Express Protein Markers Detection

Impedimetric biosensors represent a powerful and promising tool for studying and monitoring biological processes associated with proteins and can contribute to the development of new approaches in the diagnosis and treatment of diseases. The basic principles, analytical methods, and applications of hybrid impedimetric biosensors for express protein detection in biological fluids are described. The advantages of this type of biosensors, such as simplicity and speed of operation, sensitivity and selectivity of analysis, cost-effectiveness, and an ability to be integrated into hybrid microfluidic systems, are demonstrated. Current challenges and development prospects in this area are analyzed. They include (a) the selection of materials for electrodes and formation of nanostructures on their surface; (b) the development of efficient methods for biorecognition elements' deposition on the electrodes' surface, providing the specificity and sensitivity of biosensing; (c) the reducing of nonspecific binding and interference, which could affect specificity; (d) adapting biosensors to real samples and conditions of operation; (e) expanding the range of detected proteins; and, finally, (f) the development of biosensor integration into large microanalytical system technologies. This review could be useful for researchers working in the field of impedimetric biosensors for protein detection, as well as for those interested in the application of this type of biosensor in biomedical diagnostics.

Construction and Curing Behavior of Underwater In Situ Repairing Coatings for Offshore Structures

The development of polymeric materials for the repair and reinforcement of damaged sites in water has many practical applications, especially in ocean engineering. However, it is difficult to construct an anticorrosion coating in water. In addition, curing kinetics, which are the key to enhance the performance of coatings, seem to hardly be observed and regulated in an underwater condition. Herein, a novel underwater in situ repairing coating was prepared. Meanwhile, electrochemical impedance spectroscopy (EIS) was applied to observe its curing behavior underwater. Adhesion tests showed that the coatings cured underwater had good adhesion to different substrate surfaces and the ideal ratio of curing agent to epoxy resin was 0.6. Long-term anticorrosive tests demonstrated that the coatings had an excellent anti-corrosion performance. The viscosity changes in different curing stages were well reflected by frequency response characteristics from Bode and Nyquist curves by EIS. Two equivalent electrical circuits were selected to simulate the impedance date at the initial and final curing stage. A formula was put forward to evaluate the curing degree during the curing process. Finally, the effects of temperature and the ingredient ratio on the reaction rate and curing degree were also investigated here. This underwater in situ repairing coating may find applications in many offshore engineering structures in marine environments, and the EIS technique has attractive development and application prospects when observing the curing information of thermosetting resin systems under special circumstances.

Ce-doped MgO films on AZ31 alloy substrate for biomedical applications: preparation, characterization and testing

Magnesium ions, MgO nanoparticles and thin films, magnesium alloys and cerium compounds are materials intensively studied due to their corrosion protection, antibacterial and pharmacological properties. In this work, we have designed, prepared and investigated, novel thin films of MgO doped with cerium, deposited on Mg alloy (AZ31) for temporary implants, in order to enhance their life time. More precisely, we report on microstructure and corrosion behavior of MgO pure and doped with 0.1 at % Ce films, fabricated by sol-gel route coupled with spin-coating technique, on AZ31 alloy substrate. A modified sol-gel method that start from magnesium acetylacetonate, cerium nitrate and 2-methoxyethanol (as a stabilizer for the sol) was been used successfully for cerium doped MgO sol precursor preparation. The structure and morphology of the surface of the coatings, before and after immersion for 7-30 d in Hank's solution at 37 °C, were characterized by x-ray diffraction (XRD), scanning electron microscopy, high-resolution transmission electron microscope, x-ray photoelectron spectroscopy and Fourier infrared transmittance spectrum (FT-IR). A comparison between the corrosion protection of undoped MgO and MgO doped with 0.1 at % Ce coatings on the AZ31 alloy substrate is performed by electrochemical tests and immersion tests using open circuit potential and electrochemical impedance spectroscopy in Hank's solution, at 37 °C. The electrochemical results showed that the protection of the AZ31 alloy substrate against corrosion was better with the doped with 0.1 at % Ce MgO film deposited than with pure MgO coting. The investigations of the films after immersion in Hank's solution, at 37 °C, for 7, 21 and 30 d indicated that the grown layer on the film is bone like apatite that suggests a good bioactivity of 0.1 at % Ce-doped MgO coating. Our work demonstrates that the performance corrosion protection of the biodegradable magnesium alloys used for orthopedic applications, in simulated physiological environments (Hank and Ringer) can be enhanced through coating with Ce3+doped MgO sol-gel thin film.

Selective Perchlorate Sensing Using Electrochemical Impedance Spectroscopy with Self-Assembled Monolayers of semiaza-Bambusurils

In the last two decades, perchlorate salts have been identified as environmental pollutants and recognized as potential substances affecting human health. We describe self-assembled monolayers (SAMs) of novel semiaza-bambus[6]urils (semiaza-BUs) equipped with thioethers or disulfide (dithiolane) functionalities as surface-anchoring groups on gold electrodes. Cyclic voltammetry (CV) with Fe(CN)6 3-/4- as a redox probe, together with X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and ellipsometry, were employed to characterize the interactions at the interface between the anchoring groups and the metal substrate. Data showed that the anion receptors' packing on the gold strongly depends on the anchoring group. As a result, SAMs of BUs with lipoic amide side chains show a concentration-dependent layer thickness. The BU SAMs are extremely stable on repeated electrochemical potential scans and can selectively recognize perchlorate anions. Our electrochemical impedance spectroscopy (EIS) studies indicated that semiaza-BU equipped with the lipoic amide side chains binds perchlorate (2-100 mM) preferentially over other anions such as F- , Cl- , I- , AcO- , H2 PO4 - , HPO4 2- , SO4 2- , NO2 - , NO3 - , or CO3 2- . The resistance performance is 10 to 100 times more efficient than SAMs containing all other tested anions.

Naloxone-AuNPs@ZIF-8-Based Impedimetric Sensor Platform for Ultrasensitive Detection of Fentanyl and Fabrication of Fen-Track Prototype for Real-Field Analysis

Opioids are considered to be a global threat, and we are facing the worst opioid crisis of the decade. Synthetic opioids like fentanyl are highly potent and deadly toward human body, and hence its detection is an inevitable requirement globally. Naloxone is known for its antagonist property toward fentanyl, and we performed computational simulations to find their interactions and use this principle to build the first of a kind impedimetric sensor device, transduced by 3D-ZIF-8 with in situ encapsulated naloxone-gold nanoparticles. The probe is synthesized using a unique encapsulation strategy, thoroughly characterized by various physicochemical and microscopic tools. The sensor is highly selective toward fentanyl and can detect fentanyl up to 100 ppm in a synthetic sample. A prototype device is also built based on the synthetic calibration and applied to the spiked urine sample, and the performance is evaluated using statistical and machine learning tools.

Membrane-Disruptive Effects of Fatty Acid and Monoglyceride Mitigants on E. coli Bacteria-Derived Tethered Lipid Bilayers

We report electrochemical impedance spectroscopy measurements to characterize the membrane-disruptive properties of medium-chain fatty acid and monoglyceride mitigants interacting with tethered bilayer lipid membrane (tBLM) platforms composed of E. coli bacterial lipid extracts. The tested mitigants included capric acid (CA) and monocaprin (MC) with 10-carbon long hydrocarbon chains, and lauric acid (LA) and glycerol monolaurate (GML) with 12-carbon long hydrocarbon chains. All four mitigants disrupted E. coli tBLM platforms above their respective critical micelle concentration (CMC) values; however, there were marked differences in the extent of membrane disruption. In general, CA and MC caused larger changes in ionic permeability and structural damage, whereas the membrane-disruptive effects of LA and GML were appreciably smaller. Importantly, the distinct magnitudes of permeability changes agreed well with the known antibacterial activity levels of the different mitigants against E. coli, whereby CA and MC are inhibitory and LA and GML are non-inhibitory. Mechanistic insights obtained from the EIS data help to rationalize why CA and MC are more effective than LA and GML at disrupting E. coli membranes, and these measurement capabilities support the potential of utilizing bacterial lipid-derived tethered lipid bilayers for predictive assessment of antibacterial drug candidates and mitigants.

Machine learning-directed electrical impedance tomography to predict metabolically vulnerable plaques

The characterization of atherosclerotic plaques to predict their vulnerability to rupture remains a diagnostic challenge. Despite existing imaging modalities, none have proven their abilities to identify metabolically active oxidized low-density lipoprotein (oxLDL), a marker of plaque vulnerability. To this end, we developed a machine learning-directed electrochemical impedance spectroscopy (EIS) platform to analyze oxLDL-rich plaques, with immunohistology serving as the ground truth. We fabricated the EIS sensor by affixing a six-point microelectrode configuration onto a silicone balloon catheter and electroplating the surface with platinum black (PtB) to improve the charge transfer efficiency at the electrochemical interface. To demonstrate clinical translation, we deployed the EIS sensor to the coronary arteries of an explanted human heart from a patient undergoing heart transplant and interrogated the atherosclerotic lesions to reconstruct the 3D EIS profiles of oxLDL-rich atherosclerotic plaques in both right coronary and left descending coronary arteries. To establish effective generalization of our methods, we repeated the reconstruction and training process on the common carotid arteries of an unembalmed human cadaver specimen. Our findings indicated that our DenseNet model achieves the most reliable predictions for metabolically vulnerable plaque, yielding an accuracy of 92.59% after 100 epochs of training.

The Role of APTES as a Primer for Polystyrene Coated AA2024-T3

(3-Aminopropyl)triethoxysilane (APTES) silane possesses one terminal amine group and three ethoxy groups extending from each silicon atom, acting as a crucial interface between organic and inorganic materials. In this study, after APTES was deposited on the aluminum alloy AA2024-T3 as a primer for an optional top coating with polystyrene (PS), its role with regard to stability as a protection layer and interaction with the topcoat were studied via combinatorial experimentation. The aluminum alloy samples primed with APTES under various durations of concentrated vapor deposition (20, 40, or 60 min) with an optional post heat treatment and/or PS topcoat were comparatively characterized via electrochemical impedance spectroscopy (EIS) and surface energy. The samples top-coated with PS on an APTES layer primed for 40 min with a post heat treatment revealed excellent performance regarding corrosion impedance. A primed APTES surface with higher surface energy accounted for this higher corrosion impedance. Based on the SEM images and the surface energy calculated from the measured contact angles on the APTES-primed surfaces, four mechanisms are suggested to explain that the good protection performance of the APTES/PS coating system can be attributed to the enhanced wettability of PS on the cured APTES primer with higher surface energy. The results also suggest that, in the early stages of exposure to the corrosion solution, a thinner APTES primer (deposited for 20 min) enhances protection against corrosion, which can be attributed to the hydrolytic stability and hydrolyzation/condensation of the soaked APTES and the dissolution of the naturally formed aluminum oxide pre-existing in the bare samples. An APTES primer subjected to additional heat treatment will increase the impedance of the coating system significantly. APTES, and silanes, in general, used as adherent agents or surface modifiers, have a wide range of potential applications in micro devices, as projected in the Discussion section.

Electrochemical Properties of PEDOT:PSS/Graphene Conductive Layers in Artificial Sweat

Electrodes based on PEDOT:PSS are gaining increasing importance as conductive electrodes and functional layers in various sensors and biosensors due to their easy processing and biocompatibility. This study investigates PEDOT:PSS/graphene layers deposited via spray coating on flexible PET substrates. The layers are characterized in terms of their morphology, roughness (via AFM and SEM), and electrochemical properties in artificial sweat using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The layers exhibit dominant capacitive behavior at low frequencies, with cut-off frequencies determined for thicker layers at 1 kHz. The equivalent circuit used to fit the EIS data reveals a resistance of about three orders of magnitude higher inside the layer compared to the charge transfer resistance at the solid/liquid interface. The capacitance values determined from the CV curves range from 54.3 to 122.0 mF m-2. After 500 CV cycles in a potential window of 1 V (from -0.3 to 0.7 V), capacitance retention for most layers is around 94%, with minimal surface changes being observed in the layers. The results suggest practical applications for PEDOT:PSS/graphene layers, both for high-frequency impedance measurements related to the functioning of individual organs and systems, such as impedance electrocardiography, impedance plethysmography, and respiratory monitoring, and as capacitive electrodes in the low-frequency range, realized as layered PEDOT:PSS/graphene conductive structures for biosignal recording.

Label-Free Detection of CA19-9 Using a BSA/Graphene-Based Antifouling Electrochemical Immunosensor

Evaluating the levels of the biomarker carbohydrate antigen 19-9 (CA19-9) is crucial in early cancer diagnosis and prognosis assessment. In this study, an antifouling electrochemical immunosensor was developed for the label-free detection of CA19-9, in which bovine serum albumin (BSA) and graphene were cross-linked with the aid of glutaraldehyde to form a 3D conductive porous network on the surface of an electrode. The electrochemical immunosensor was characterized through the use of transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscope (AFM), UV spectroscopy, and electrochemical methods. The level of CA19-9 was determined through the use of label-free electrochemical impedance spectroscopy (EIS) measurements. The electron transfer at the interface of the electrode was well preserved in human serum samples, demonstrating that this electrochemical immunosensor has excellent antifouling performance. CA19-9 could be detected in a wide range from 13.5 U/mL to 1000 U/mL, with a detection limit of 13.5 U/mL in human serum samples. This immunosensor also exhibited good selectivity and stability. The detection results of this immunosensor were further validated and compared using an enzyme-linked immunosorbent assay (ELISA). All the results confirmed that this immunosensor has a good sensing performance in terms of CA19-9, suggesting its promising application prospects in clinical applications.

Mobile Point-of-Care Device Using Molecularly Imprinted Polymer-Based Chemosensors Targeting Interleukin-1β Biomarker

Molecularly imprinted polymers (MIPs) have garnered significant attention as a promising material for engineering specific biological receptors with superior chemical complementarity to target molecules. In this study, we present an electrochemical biosensing platform incorporating MIP films for the selective detection of the interleukin-1β (IL-1β) biomarker, particularly suitable for mobile point-of-care testing (POCT) applications. The IL-1β-imprinted biosensors were composed of poly(eriochrome black T (EBT)), including an interlayer of poly(3,4-ethylene dioxythiophene) and a 4-aminothiophenol monolayer, which were electrochemically polymerized simultaneously with template proteins (i.e., IL-1β) on custom flexible screen-printed carbon electrodes (SPCEs). The architecture of the MIP films was designed to enhance the sensor sensitivity and signal stability. This approach involved a straightforward sequential-electropolymerization process and extraction for leaving behind cavities (i.e., rebinding sites), resulting in the efficient production of MIP-based biosensors capable of molecular recognition for selective IL-1β detection. The electrochemical behaviors were comprehensively investigated using cyclic voltammograms and electrochemical impedance spectroscopy responses to assess the imprinting effect on the MIP films formed on the SPCEs. In line with the current trend in in vitro diagnostic medical devices, our simple and effective MIP-based analytical system integrated with mobile POCT devices offers a promising route to the rapid detection of biomarkers, with particular potential for periodontitis screening.

Surface and Conductivity Characterization of Layered Organic Ionic Plastic Crystal (OIPC)-Polymer Films

Organic ionic plastic crystals (OIPCs) are attractive solid electrolyte materials for advanced energy storage systems owing to their inherent advantages (e.g., high plasticity, thermal stability, and moderate ionic conductivity), which can be further improved/deteriorated by the addition of polymer or metal oxide nanoparticles. The role of the nanoparticle/OIPC combinations on the resultant interphase structure and transport properties, however, is still unclear due to the complexity within the composite structures. Herein, we demonstrate a systematic approach to specifically interrogating the interphase region by fabricating layered OIPC/polymer thin films via spin coating and correlating variation in the ionic conductivity of the OIPC with their microscopic structures. In-plane interdigitated electrodes have been employed to obtain electrochemical impedance spectroscopy (EIS) spectra on both OIPC and layered OIPC/polymer thin films. The thin-film EIS measurements were evaluated with conventional bulk EIS measurements on the OIPC pressed pellets and compared with EIS obtained from the OIPC-polymer composites. Interactions between the OIPC and polymer films as well as the morphology of the film surfaces have been characterized through multiple microscopic analysis tools, including scanning electron microscopy, energy-dispersive X-ray spectroscopy, atomic force microscopy, and optical profilometry. The combination of EIS analysis with the microscopic visualization of these unique layered OIPC/polymer thin films has confirmed the impact of the OIPC-polymer interphase region on the overall ionic conductivity of bulk OIPC-polymer composites. By changing the chemistry of the polymer substrate (i.e., PMMA, PVDF, and PVDF-HFP), the importance of compatibility between the components in the interphase region is clearly observed. The methods developed here can be used to screen and further understand the interactions among composite components for enhanced compatibility and conductivity.

Anodic Oxidation of Tungsten under Illumination-Multi-Method Characterization and Modeling at the Molecular Level

Tungsten oxide has received considerable attention as photo-anode in photo-assisted water splitting due to its considerable advantages such as significant light absorption in the visible region, good catalytic properties, and stability in acidic and oxidative conditions. The present paper is a first step in a detailed study of the mechanism of porous WO3 growth via anodic oxidation. In-situ electrochemical impedance spectroscopy (EIS) and intensity modulated photocurrent spectroscopy (IMPS) during oxidation of W illuminated with UV and visible light are employed to study the ionic and electronic processes in slightly acidic sulfate-fluoride electrolytes and a range of potentials 4-10 V. The respective responses are discussed in terms of the influence of fluoride addition on ionic and electronic process rates. A kinetic model is proposed and parameterized via regression of experimental data to the EIS and IMPS transfer functions.

E-SCAN: Electrochemical Scanning of Carbonates, an In Situ Approach for Screening and Quantifying Inorganic Carbon in Soil

A modified three-electrode system was utilized with a correlated ion-capture film that is functional to changes in soil carbonate moieties to determine an understudied pool of soil carbon that is vital toward holistic carbon sequestration─carbonous soil minerals (CSM). This composite sensor was tested on soils with varying carbonate contents using cyclic voltammetry, chromatocoulometry (DC-based), and electrochemical impedance spectroscopy to determine signal output as a function of increasing dose. To determine the in-field capability, a portable potentiostat device was integrated into a probe head setup that could be inserted into soil for testing. The results from these experiments showed a linearity of R2 > 0.97 and a measurable sensing range from 0.01% (100 ppm) to 1% (10 000 ppm). Therefore, a first-of-a-kind in-soil sensor system was developed for determining carbonate content in real soil samples using electrochemistry that can be tested in-field to survey the field-deployable and point-of-use capability of the system.

Subsurface Hydride Formation Leads to Slow Surface Adsorption Processes on a Pd(111) Single-Crystal Electrode in Acidic Electrolytes

Palladium is one of the most important catalysts due to its widespread use in heterogeneous catalysis and electrochemistry. However, an understanding of the electrochemical processes and interfacial phenomena at Pd single-crystal electrodes/electrolytes is still scarce. In this work, the electrochemical behavior of the Pd(111) electrode was studied by the combination of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in different acidic electrolytes, namely, sulfuric acid, perchlorate acid, methane sulfonic acid, and hydrofluoric acid. An analysis of CV profiles shows the strong adsorption of all anions at low electrode potential, partially overlapping with underpotential deposited hydrogen (UPD-H), leading to the appearance of a pair of sharp peaks in what would be considered the "hydrogen region". All anions studied (HSO4-, ClO4-, CH3SO3-, and F-) adsorb specifically and interact with (or effectively block) the surface-adsorbed hydroxyl phase formed on the Pd(111) terrace at higher potentials. Strikingly, the scan rate-dependent results show that the process of anion adsorption and desorption is a kinetically rather slow step. EIS measurements show that the exact mechanism of this slow anion ad/desorption process actually stems from (sub)surface phenomena: the direct hydrogen insertion into Pd lattice (hydrogen subsurface absorption) commences from ca. 0.40 V and leads to the formation of (subsurface) Pd hydrides (PdHx). We argue that the subsurface hydrogen phase significantly alters the work function and thereby the kinetics of the anion adsorption and desorption processes, leading to irreversible peaks in the voltammetry. This precise understanding is important in guiding further fundamental work on Pd single crystals and will be crucial to advancing the eventual design of optimized Pd electrocatalysts.

Effect of Artificial Saliva Modification on Pitting Corrosion and Mechanical Properties of the Remanium®-Type Orthodontic Archwire

The pitting corrosion of orthodontic apparatus elements in the oral environment is an interest of both clinicians and scientists dealing with the assessment of the biocompatibility of medical materials. This work presents a study on the effect of ready-to-use Listerine® and Meridol® mouthwashes and sodium fluoride on the resistance of the commercial Remanium®-type orthodontic archwire to pitting corrosion in artificial saliva at 37 °C. XRD, SEM, EDS, mechanical properties, and microhardness measurements were used to characterize the archwire. The in vitro corrosion resistance of the archwire was examined using the open-circuit potential method, electrochemical impedance spectroscopy, and anodic polarization curves. The physicochemical characteristics confirmed the presence of a bi-phase alloy with a mixed austenite/ferrite structure containing Fe 74.4(7) at.%, Cr 18.4(4) at.%, and Ni 7.2(4) at.%. The Fe-Cr-Ni alloy was characterized by high tensile strength and Vickers microhardness. EIS revealed the capacitive behavior with high corrosion resistance. It was found that the kinetics of pitting corrosion in the artificial saliva decreased in the presence of NaF and mouthwashes. The potentiodynamic characteristics confirmed the decrease in susceptibility to pitting corrosion after the modification of artificial saliva. The pitting corrosion mechanism of the self-passive oxide layer on the surface of the Fe-Cr-Ni electrode in the biological environment containing chloride ions was discussed in detail. Mechanical properties after corrosion tests were weakened.

Aminosilanized Interface Promotes Electrochemically Stable Carbon Nitride Films with Fewer Trap States on FTO for (Photo)electrochemical Systems

We have demonstrated the direct growth of a CNx layer on a plasma-cleaned and aminosilanized F-doped SnO2 (FTO) electrode to study the CNx|FTO interface that is critical for (photo)electrocatalytic systems. The (3-aminopropyl)triethoxysilane (APTES) was chosen as a bifunctional organosilane, with the amino end incorporating into CNx and the silane end connecting to the hydroxylated FTO surface. Plasma cleaning and aminosilanization resulted in a highly hydrophilic surface, which leads to better contact of melted thiourea to the aminosilanized FTO (p-FTONH2) during CNx polymer condensation, thus generating a thinner and more compact CNx layer. The modification at the interface was shown to influence the CNx growth on length scales of tens of micrometers. We grew CNx thin films on p-FTONH2 (CNx/p-FTONH2) and nonaminosilanized p-FTO (CNx/p-FTO). CNx/p-FTONH2 had a smaller density of trap states and passed 2.4 times the charges before failure compared to CNx/p-FTO. Additionally, a 40% decrease in interfacial charge transfer resistance at the CNx|electrolyte interface was measured for CNx/p-FTONH2 compared to CNx/p-FTO under -0.5 V vs RHE in 0.1 M Na2SO4. Furthermore, with the CNx surface coated with a Pt cocatalyst, Pt/CNx/p-FTONH2 exhibited faster hydrogen evolution rates and larger current densities than Pt/CNx/p-FTO. The highest Faraday efficiency toward electrochemical hydrogen evolution (FEH2) in 0.1 M Na2SO4 (pH = 7) was 46.1%, 37.3%, 57.7%, and 70.5% for Pt/CNx/p-FTONH2, Pt/CNx/p-FTO, CNx/p-FTONH2, and CNx/p-FTO, respectively. The increase in hydrogen evolution rate did not follow the magnitude of the current density change, indicating electrochemical processes other than proton reduction. Overall, we have carefully investigated the CNx|FTO interface and suggested potential solutions to make CNx films better (photo)electrodes for (photo)electrochemical systems.

Facile Synthesis of Mesoporous Nanohybrid Two-Dimensional Layered Ni-Cr-S and Reduced Graphene Oxide for High-Performance Hybrid Supercapacitors

This study describes the single-step synthesis of a mesoporous layered nickel-chromium-sulfide (NCS) and its hybridization with single-layered graphene oxide (GO) using a facile, inexpensive chemical method. The conductive GO plays a critical role in improving the physicochemical and electrochemical properties of hybridized NCS/reduced GO (NCSG) materials. The optimized mesoporous nanohybrid NCSG is obtained when hybridized with 20% GO, and this material exhibits a very high specific surface area of 685.84 m2/g compared to 149.37 m2/g for bare NCS, and the pore diameters are 15.81 and 13.85 nm, respectively. The three-fold superior specific capacity of this optimal NCSG (1932 C/g) is demonstrated over NCS (676 C/g) at a current density of 2 A/g. A fabricated hybrid supercapacitor (HSC) reveals a maximum specific capacity of 224 C/g at a 5 A/g current density. The HSC reached an outstanding energy density of 105 Wh/kg with a maximum power density of 11,250 W/kg. A 4% decrement was observed during the cyclic stability study of the HSC over 5000 successive charge-discharge cycles at a 10 A/g current density. These results suggest that the prepared nanohybrid NCSG is an excellent cathode material for gaining a high energy density in an HSC.

Influence of Residual Water Traces on the Electrochemical Performance of Hydrophobic Ionic Liquids for Magnesium-Containing Electrolytes

A trace amount of water is typically unavoidable as an impurity in ionic liquids, which is a huge challenge for their application in Mg-ion batteries. Here, we employed molecular sieves of different pore diameters (3, 4, and 5 Å), to effectively remove the trace amounts of water from 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide (MPPip-TFSI) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP-TFSI). Notably, after sieving (water content <1 mg ⋅ L-1 ), new anodic peaks arise that are attributed to the formation of different anion-cation structures induced by minimizing the influence of hydrogen bonds. Furthermore, electrochemical impedance spectroscopy (EIS) reveals that the electrolyte resistance decreases by ∼10 % for MPPip-TFSI and by ∼28 % for BMP-TFSI after sieving. The electrochemical Mg deposition/dissolution is investigated in MPPip-TFSI/tetraglyme (1 : 1)+100 mM Mg(TFSI)2 +10 mM Mg(BH4 )2 using Ag/AgCl and Mg reference electrodes. The presence of a trace amount of water leads to a considerable shift of 0.9 V vs. Mg2+/ Mg in the overpotential of Mg deposition. In contrast, drying of MPPip-TFSI enhances the reversibility of Mg deposition/dissolution and suppresses the passivation of the Mg electrode.

Impedimetric DNA Sensors for Epirubicin Detection Based on Polythionine Films Electropolymerized from Deep Eutectic Solvent

An electrochemically active polymer, polythionine (PTN), was synthesized in natural deep eutectic solvent (NADES) via multiple potential scans and characterized using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). NADES consists of citric acid monohydrate, glucose, and water mixed in the molar ratio of 1:1:6. Electrodeposited PTN film was then applied for the electrostatic accumulation of DNA from salmon sperm and used for the sensitive detection of the anticancer drug epirubicin. Its reaction with DNA resulted in regular changes in the EIS parameters that made it possible to determine 1.0-100 µM of epirubicin with the limit of detection (LOD) of 0.3 µM. The DNA sensor developed was successfully applied for the detection of epirubicin in spiked samples of artificial and natural urine and saliva, with recovery ranging from 90 to 109%. The protocol of the DNA sensor assembling utilized only one drop of reactants and was performed with a minimal number of steps. Together with a simple measurement protocol requiring 100 µL of the sample, this offers good opportunities for the further use of the DNA sensor in monitoring the drug level in biological samples, which is necessary in oncology treatment and for the pharmacokinetics studies of new antitumor drugs.

Electrochemical Impedance as an Assessment Tool for the Investigation of the Physical and Mechanical Properties of Graphene-Based Cementitious Nanocomposites

This investigation explores the potential of electrochemical impedance spectroscopy (EIS) in evaluating graphene-based cementitious nanocomposites, focusing on their physical and structural properties, i.e., electrical resistivity, porosity, and fracture toughness. EIS was employed to study cement mixtures with varying graphene nanoplatelet (xGnP) concentrations (0.05-0.40% per dry cement weight), whereas flexural tests assessed fracture toughness and porosimetry analyses investigated the structural characteristics. The research demonstrated that the electrical resistivity initially decreased with increasing xGnP content, leveling off at higher concentrations. The inclusion of xGnPs correlated with an increase in the total porosity of the cement mixtures, which was indicated by both EIS and porosimetry measurements. Finally, a linear correlation emerged between fracture toughness and electrical resistivity, contributing also to underscore the use of EIS as a potent non-destructive tool for evaluating the physical and mechanical properties of conductive nano-reinforced cementitious nanocomposites.

MEASURE: Multiplex Exhaled Breath Condensate - Scanning Using Rapid Electro-Analytics

Exhaled breath condensate is an emerging source of inflammatory biomarkers suitable for the noninvasive detection of respiratory disorders. Current gold standard methods are highly invasive and pose challenges in sample collection during airway inflammation monitoring. Cytokine biomarkers are detectable in EBC at increased or decreased concentrations. IL-6, IL-1β, IL-8, and hs-CRP are characteristic biomarkers identified in respiratory disorders. We have demonstrated the promising outcomes of a 16-plexed electrochemical platform - READ 2.0 for the multiplexed detection of characteristic biomarkers in EBC. The sensor demonstrates dynamic ranges of 1-243 pg/mL with a lower detection limit of 1 pg/mL for IL-6 and IL-1β, while the detection range and limit of detection for IL-8 and hs-CRP is 1-150 pg/mL and 3 pg/mL, respectively. The detection accuracies for the biomarkers are in the range of ∼85 ± 15% to ∼100 ± 10%. The sensor shows a nonspecific response to similar cross-reacting biomarkers. Analytical validation of the sensor with ELISA as the standard reference generated a correlation of R2 > 0.96 and mean biases of 10.9, 3.5, 17.4, and 3.9 pg/mL between the two methods for IL-6, IL-1β, IL-8, and hs-CRP, respectively. The precision of the sensor in detecting low biomarker concentrations yields a %CV of <7%. The variation in the sensor's response on repeat EBC sample measurements and within a 6 h duration is less than 10%. The READ 2.0 platform shows a promise that EBC-based biomarker detection can prove to be vital in predicting the severity and survival rates of respiratory disorders and serve as a reference point for monitoring EBC-based biomarkers.

Paper-Based All-in-One Origami Nanobiosensor for Point-of-Care Detection of Cardiac Protein Markers in Whole Blood

Rapid and accurate diagnosis of cardiovascular diseases (CVDs) at the earliest stage is of paramount importance to improve the treatment outcomes and avoid irreversible damage to a patient's cardiovascular system. Microfluidic paper-based devices (μPADs) represent a promising platform for rapid CVD diagnosis at the point of care (POC). This paper presents an electrochemical μPAD (E-μPAD) with an all-in-one origami design for rapid and POC testing of cardiac protein markers in whole blood. Based on the label-free, electrochemical impedance spectroscopy (EIS) immunoassay, the E-μPAD integrates all essential components on a single chip, including three electrochemical cells, a plasma separation membrane, and a buffer absorption pad, enabling easy and streamlined operations for multiplexed detection of three cardiac protein markers [cardiac troponin I (cTnI), brain natriuretic peptide (BNP)-32, and D-Dimer] on a finger-prick whole blood sample within 46 min. Superior analytical performance is achieved through sensitive EIS measurement on carbon electrodes decorated with semiconductor zinc oxide nanowires (ZnO NWs). Using spiked human plasma samples, ultralow limits of detection (LODs) of E-μPAD are achieved at 4.6 pg/mL (190 fM) for cTnI, 1.2 pg/mL (40 fM) for BNP-32, and 146 pg/mL (730 fM) for D-Dimer. Real human blood samples spiked with purified proteins are also tested, and the device's analytical performance was proven to be comparable to commercial ELISA kits. The all-in-one E-μPAD will allow rapid and sensitive testing of cardiac protein markers through easy operations, which holds great potential for on-site screening of acute CVDs in nonlaboratory settings such as emergency rooms, doctor's offices, or patient homes.

Nanomaterials and Their Recent Applications in Impedimetric Biosensing

Impedimetric biosensors measure changes in the electrical impedance due to a biochemical process, typically the binding of a biomolecule to a bioreceptor on the sensor surface. Nanomaterials can be employed to modify the biosensor's surface to increase the surface area available for biorecognition events, thereby improving the sensitivity and detection limits of the biosensor. Various nanomaterials, such as carbon nanotubes, carbon nanofibers, quantum dots, metal nanoparticles, and graphene oxide nanoparticles, have been investigated for impedimetric biosensors. These nanomaterials have yielded promising results in improving sensitivity, selectivity, and overall biosensor performance. Hence, they offer a wide range of possibilities for developing advanced biosensing platforms that can be employed in various fields, including healthcare, environmental monitoring, and food safety. This review focuses on the recent developments in nanoparticle-functionalized electrochemical-impedimetric biosensors.

Tissue-Engineered Cochlear Fibrosis Model Links Complex Impedance to Fibrosis Formation for Cochlear Implant Patients

Cochlear implants are a life-changing technology for those with severe sensorineural hearing loss, partially restoring hearing through direct electrical stimulation of the auditory nerve. However, they are known to elicit an immune response resulting in fibrotic tissue formation in the cochlea that is linked to residual hearing loss and suboptimal outcomes. Intracochlear fibrosis is difficult to track without postmortem histology, and no specific electrical marker for fibrosis exists. In this study, a tissue-engineered model of cochlear fibrosis is developed following implant placement to examine the electrical characteristics associated with fibrotic tissue formation around electrodes. The model is characterized using electrochemical impedance spectroscopy and an increase in the resistance and a decrease in capacitance of the tissue using a representative circuit are found. This result informs a new marker of fibrosis progression over time that is extractable from voltage waveform responses, which can be directly measured in cochlear implant patients. This marker is tested in a small sample size of recently implanted cochlear implant patients, showing a significant increase over two postoperative timepoints. Using this system, complex impedance is demonstrated as a marker of fibrosis progression that is directly measurable from cochlear implants to enable real-time tracking of fibrosis formation in patients, creating opportunities for earlier treatment intervention to improve cochlear implant efficacy.

Sensitive detection of SARS-CoV-2 spike protein based on electrochemical impedance spectroscopy of Fe3O4@SiO2–Au/GCE biosensor

Highly contagious COVID-19 disease is caused by a novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which poses a serious threat to global public health. Therefore, the development of a fast and reliable method for the detection of SARS-CoV-2 is an urgent research need. The Fe3O4@SiO2–Au is enriched with a variety of functional groups, which can be used to fabricate a sensitive electrochemical biosensor by biofunctionalization with angiotensin-converting enzyme 2 (ACE2). Accordingly, we developed a novel electrochemical sensor by chemically modifying a glassy carbon electrode (GCE) with Fe3O4@SiO2–Au nanocomposites (hereafter Fe3O4@SiO2–Au/GCE) for the rapid detection of S-protein spiked SARS-CoV-2 by electrochemical impedance spectroscopy (EIS). The new electrochemical sensor has a low limit detection (viz., 4.78 pg/mL) and a wide linear dynamic range (viz., 0.1 ng/mL to 10 μg/mL) for detecting the EIS response signal of S-protein. The robust Fe3O4@SiO2–Au/GCE biosensor has high selectivity, stability, and reproducibility for the detection of S-protein with good recovery of saliva samples.

Functional Enhancement and Characterization of an Electrophysiological Mapping Electrode Probe with Carbonic, Directional Macrocontacts

Electrophysiological mapping (EM) using acute electrode probes is a common procedure performed during functional neurosurgery. Due to their constructive specificities, the EM probes are lagging in innovative enhancements. This work addressed complementing a clinically employed EM probe with carbonic and circumferentially segmented macrocontacts that are operable both for neurophysiological sensing ("recording") of local field potentials (LFP) and for test stimulation. This paper illustrates in-depth the development that is based on the direct writing of functional materials. The unconventional fabrication processes were optimized on planar geometry and then transferred to the cylindrically thin probe body. We report and discuss the constructive concept and architecture of the probe, characteristics of the electrochemical interface deduced from voltammetry and chronopotentiometry, and the results of in vitro and in vivo recording and pulse stimulation tests. Two- and three-directional macrocontacts were added on probes having shanks of 550 and 770 μm diameters and 10-23 cm lengths. The graphitic material presents a ~2.7 V wide, almost symmetric water electrolysis window, and an ultra-capacitive charge transfer. When tested with clinically relevant 150 μs biphasic current pulses, the interfacial polarization stayed safely away from the water window for pulse amplitudes up to 9 mA (135 μC/cm2). The in vivo experiments on adult rat models confirmed the high-quality sensing of LFPs. Additionally, the in vivo-prevailing increase in the electrode impedance and overpotential are discussed and modeled by an ionic mobility-reducing spongiform structure; this restricted diffusion model gives new applicative insight into the in vivo-uprisen stimulation overpotential.

Understanding Transient Ionic Diode Currents and Impedance Responses for Aquivion-Coated Microholes

Ionic diode based devices or circuits can be applied, for example, in electroosmotic pumps or in desalination processes. Aquivion ionomer coated asymmetrically over a Teflon film (5 μm thickness) with a laser-drilled microhole (approximately 10 μm diameter) gives a cationic diode with a rectification ratio of typically 10-20 (measured in 0.01 M NaCl with ±0.3 V applied bias). Steady state voltammetry, chronoamperometry, and electrochemical impedance spectroscopy data are employed to characterize the ionic diode performance parameters. Next, a COMSOL 6.0 finite element model is employed to quantitatively assess/compare transient phenomena and to extract mechanistic information by comparison with experimental data. The experimental diode time constant and diode switching process associated with a distorted semicircle (with a typical diode switching frequency of 10 Hz) in the Nyquist plot are reproduced by computer simulation and rationalized in terms of microhole diffusion-migration times. Fundamental understanding and modeling of the ionic diode switching process can be exploited in the rational/optimized design of new improved devices.

Hybrid Mesoporous Carbon/Copper Ferrite Electrode for Asymmetric Supercapacitors

Asymmetric supercapacitors (ASCs) with two dissimilar electrodes are known to exhibit relatively moderate energy and power densities. If electrodes derived from earth-abundant materials or renewable resources such as lignocellulosic biomass (LCB) are used for fabrication, energy storage systems are expected to become less expensive and more sustainable. Hybrid electrode materials have advantages such as higher surface area, better chemical stability, and superior energy density. This study reports on the synthesis of a novel hybrid electrode material containing porous carbon (POC) and copper ferrite, which is designated as POC@Cu-ferrite, and its electrochemical performance in ASC configuration. Corn stover derived hydrochar is utilized for the sol-gel synthesis of POC@Cu-ferrite hybrid material using earth-abundant Cu and Fe-based precursors. This material is characterized using X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) surface area analyzer, and scanning and transmission electron microscopy (SEM/TEM). As-synthesized Cu-ferrite is found to contain 89.2% CuFe2O4 and 10.8% Fe2O3, whereas other phases such as Fe3O4, CuFeO2, and CuO are observed for the POC@Cu-ferrite. BET-specific surface area (SSA) and pore volume of POC@Cu-ferrite are observed as 1068 m2/g and 0.72 cm3/g, respectively. POC@Cu-ferrite hybrid electrode is used with POC opposite electrode to fabricate ASC, which is tested using Gamry G-300 potentiostat/galvanostat/ZRA to obtain cyclic voltammetry (CV) profiles and galvanostatic charge-discharge (GCD) plots. ASC is also prepared using Cu-ferrite and POC materials and its specific capacitance and stability are compared with ASCs prepared with POC@Cu-ferrite and POC or graphene nanoplatelets (GNPs) electrodes. POC@Cu-ferrite hybrid electrode is found to be superior with a 2-fold higher capacitance and significant electrochemical stability over 100 GCD cycles as compared to the Cu-ferrite electrode.

Classification-Based Evaluation of Multi-Ingredient Dish Using Graphene-Modified Interdigital Electrodes

A taste sensor with global selectivity can be used to discriminate taste of foods and provide evaluations. Interfaces that could interact with broad food ingredients are beneficial for data collection. Here, we prepared electrochemically reduced graphene oxide (ERGO)-modified interdigital electrodes. The interfaces of modified electrodes showed good sensitivity towards cooking condiments in mixed multi-ingredients solutions under electrochemical impedance spectroscopy (EIS). A database of EIS of cooking condiments was established. Based on the principal component analysis (PCA), subsets of three taste dimensions were classified, which could distinguish an unknown dish from a standard dish. Further, we demonstrated the effectiveness of the electrodes on a typical dish of scrambled eggs with tomato. Our kind of electronic tongue did not measure the quantitation of each ingredient, instead relying on the database and classification algorithm. This method is facile and offers a universal approach to simultaneously identifying multiple ingredients.

The Effect of Mechanical Pretreatment on the Electrochemical Characteristics of PEO Coatings Prepared on Magnesium Alloy AZ80

The main objective of this article is to provide new information on the effects of mechanical pretreatment of AZ80 magnesium alloy ground with SiC emery papers of different grain sizes on the plasma electrolytic oxidation (PEO) process and corrosion properties of AZ80 in 0.1 M NaCl solution. Then, the roughness of the coated samples was measured by confocal microscopy. The corrosion properties of the ground and coated surfaces were determined by potentiodynamic polarization (PDP) within 1 h of exposure, and electrochemical impedance spectroscopy (EIS) was performed during 168 h of exposure at laboratory temperature. Consequently, the obtained results of the PDP measurements were evaluated by the Tafel analysis and the EIS evaluation was performed by the equivalent circuit analysis through Nyquist diagrams. The morphology and structure of PEO coatings were observed by scanning electron microscopy (SEM) through the secondary imaging technology, and the presence of certain elements in PEO coatings was analyzed by EDS analysis.

Optimizing the Performance of Low-Loaded Electrodes for CO2-to-CO Conversion Directly from Capture Medium: A Comprehensive Parameter Analysis

Gas-fed reactors for CO2 reduction processes are a solid technology to mitigate CO2 accumulation in the atmosphere. However, since it is necessary to feed them with a pure CO2 stream, a highly energy-demanding process is required to separate CO2 from the flue gasses. Recently introduced bicarbonate zero-gap flow reactors are a valid solution to integrate carbon capture and valorization, with them being able to convert the CO2 capture medium (i.e., the bicarbonate solution) into added-value chemicals, such as CO, thus avoiding this expensive separation process. We report here a study on the influence of the electrode structure on the performance of a bicarbonate reactor in terms of Faradaic efficiency, activity, and CO2 utilization. In particular, the effect of catalyst mass loading and electrode permeability on bicarbonate electrolysis was investigated by exploiting three commercial carbon supports, and the results obtained were deepened via electrochemical impedance spectroscopy, which is introduced for the first time in the field of bicarbonate electrolyzers. As an outcome of the study, a novel low-loaded silver-based electrode fabricated via the sputtering deposition technique is proposed. The silver mass loading was optimized by increasing it from 116 μg/cm2 to 565 μg/cm2, thereby obtaining an important enhancement in selectivity (from 55% to 77%) and activity, while a further rise to 1.13 mg/cm2 did not provide significant improvements. The tremendous effect of the electrode permeability on activity and proficiency in releasing CO2 from the bicarbonate solution was shown. Hence, an increase in electrode permeability doubled the activity and boosted the production of in situ CO2 by 40%. The optimized Ag-electrode provided Faradaic efficiencies for CO close to 80% at a cell voltage of 3 V and under ambient conditions, with silver loading of 565 μg/cm2, the lowest value ever reported in the literature so far.

Early Warning for the Electrolyzer: Monitoring CO2 Reduction via In-Line Electrochemical Impedance Spectroscopy

The electrochemical CO2 reduction reaction (CO2 RR) to fuels and feedstocks presents an opportunity to decarbonize the chemical industry, and current electrolyzer performance levels approach commercial viability. However, stability remains below that required, in part because of the challenge of probing these electrolyzer systems in real time and the challenge of determining the root cause of failure. Failure can result from initial conditions (e. g., the over- or under-compression of the electrolyzer), gradual degradation of components (e. g., cathode or anode catalysts), the accumulation of products or by-products, or immediate changes such as the development of a hole in the membrane or a short circuit. Identifying and mitigating these assembly-related, gradual, and immediate failure modes would increase both electrolyzer lifetime and economic viability of CO2 RR. We demonstrate the continuous monitoring of CO2 RR electrolyzers during operation via non-disruptive, real-time electrochemical impedance spectroscopy (EIS) analysis. Using this technique, we characterise common failure modes - compression, salt formation, and membrane short circuits - and identify electrochemical parameter signatures for each. We further propose a framework to identify, predict, and prevent failures in CO2 RR electrolyzers. This framework allowed for the prediction of anode degradation ~11 hours before other indicators such as selectivity or voltage.

Electrochemical Behavior of Al/Mg Alloys Immobilized in a Magnesium Potassium Phosphate Cement-Based Mortar

Portland cement is extensively used for the conditioning of radioactive waste. However, its high alkalinity is a serious obstacle to the stabilization of waste containing aluminum metal since aluminum is oxidized by the pore solution with the production of dihydrogen. This work investigates the potential of an alternative binder, magnesium potassium phosphate (MKP) cement, for the stabilization of Al-Mg alloys comprising 2 to 4.5 wt% of Mg and other metallic impurities. The objective is to assess the influence of the alloy composition on its reactivity in the cementitious matrix at earlier ages, as well as at later ages, when the cement has reached a significant reaction degree. Two complementary techniques are used. Gas chromatography shows that the dihydrogen release, resulting from the corrosion process, is not influenced by the magnesium content in the alloy. Electrochemical impedance spectroscopy provides qualitative information about the corrosion but also makes it possible to assess the corrosion current using an equivalent electrical circuit linked to the kinetic parameters of the postulated corrosion mechanism. Over a one-year period, the corrosion current of the alloys, regardless of their Mg content, is reduced by almost three orders of magnitude in MKP mortar as compared to Portland-cement-based mortar.

Time-Resolved Electrochemical Impedance Spectroscopy of Stochastic Nanoparticle Collision: Short Time Fourier Transform versus Continuous Wavelet Transform

This work demonstrates the utilization of short-time Fourier transform (STFT), and continuous wavelet transform (CWT) electrochemical impedance spectroscopy (EIS) for time-resolved analysis of stochastic collision events of platinum nanoparticles (NPs) onto gold ultramicroelectrode (UME). The enhanced electrocatalytic activity is observed in both chronoamperometry (CA) and EIS. CA provides the impact moment and rough estimation of the size of NPs. The quantitative information such as charge transfer resistance (Rct ) relevant to the exchange current density of a single Pt NP is estimated from EIS. The CWT analysis of the phase angle parameter is better for NP collision detection in terms of time resolution compared to the STFT method.

Electrochemical Impedance Spectroscopy-Based Sensing of Biofilms: A Comprehensive Review

Biofilms are complex communities of microorganisms that can form on various surfaces, including medical devices, industrial equipment, and natural environments. The presence of biofilms can lead to a range of problems, including infections, reduced efficiency and failure of equipment, biofouling or spoilage, and environmental damage. As a result, there is a growing need for tools to measure and monitor levels of biofilms in various biomedical, pharmaceutical, and food processing settings. In recent years, electrochemical impedance sensing has emerged as a promising approach for real-time, non-destructive, and rapid monitoring of biofilms. This article sheds light on electrochemical sensing for measuring biofilms, including its high sensitivity, non-destructive nature, versatility, low cost, and real-time monitoring capabilities. We also discussed some electrochemical sensing applications for studying biofilms in medical, environmental, and industrial settings. This article also presents future perspectives for research that would lead to the creation of reliable, quick, easy-to-use biosensors mounted on unmanned aerial vehicles (UAVs), and unmanned ground vehicles (UGVs), utilizing artificial intelligence-based terminologies to detect biofilms.

Plant impedance spectroscopy: a review of modeling approaches and applications

Electrochemical impedance spectroscopy has emerged over the past decade as an efficient, non-destructive method to investigate various (eco-)physiological and morphological properties of plants. This work reviews the state-of-the-art of impedance spectra modeling for plant applications. In addition to covering the traditional, widely-used representations of electrochemical impedance spectra, we also consider the more recent machine-learning-based approaches.

Corrosion Behavior of CrFeCoNiV0.5 and CrFeCoNiV Alloys in 0.5 M and 1 M Sodium Chloride Solutions

The effects of the concentration of NaCl solutions on the corrosion resistance of granular CoCrFeNiV_0.5 and dendritic CrFeCoNiV high-entropy alloys were studied. The polarization behavior of CoCrFeNiV_0.5 and CrFeCoNiV alloys in deaerated 0.5 M and 1 M sodium chloride solution at different temperatures was measured by a constant galvanostatic/potentiometric. Electrochemical impedance spectroscopy (EIS) was used to examine CoCrFeNiV_0.5 CrFeCoNiV alloys in 0.5 M and 1 M NaCl solutions. The results indicated that the CoCrFeNiV_0.5 alloy showed a better corrosion resistance than that of CrFeCoNiV alloy because the dendritic structure of CrFeCoNiV had too many σ/FCC interfaces. The critical pitting temperatures (CPTs) of the alloys under different applied potentials were also analyzed. All of the results proved that CrFeCoNiV_0.5 alloy had better corrosion resistance in 0.5 M and 1 M NaCl solutions.

Magnesium Anode Protection by an Organic Artificial Solid Electrolyte Interphase for Magnesium-Sulfur Batteries

In the search for post-lithium battery systems, magnesium-sulfur batteries have attracted research attention in recent years due to their high potential energy density, raw material abundance, and low cost. Despite significant progress, the system still lacks cycling stability mainly associated with the ongoing parasitic reduction of sulfur at the anode surface, resulting in the loss of active materials and passivating surface layer formation on the anode. In addition to sulfur retention approaches on the cathode side, the protection of the reductive anode surface by an artificial solid electrolyte interphase (SEI) represents a promising approach, which contrarily does not impede the sulfur cathode kinetics. In this study, an organic coating approach based on ionomers and polymers is pursued to combine the desired properties of mechanical flexibility and high ionic conductivity while enabling a facile and energy-efficient preparation. Despite exhibiting higher polarization overpotentials in Mg-Mg cells, the charge overpotential in Mg-S cells was decreased by the coated anodes with the initial Coulombic efficiency being significantly increased. Consequently, the discharge capacity after 300 cycles applying an Aquivion/PVDF-coated Mg anode was twice that of a pristine Mg anode, indicating effective polysulfide repulsion from the Mg surface by the artificial SEI. This was backed by operando imaging during long-term OCV revealing a non-colored separator, i.e. mitigated self-discharge. While SEM, AFM, IR and XPS were applied to gain further insights into the surface morphology and composition, scalable coating techniques were investigated in addition to ensure practical relevance. Remarkably therein, the Mg anode preparation and all surface coatings were prepared under ambient conditions, which facilitates future electrode and cell assembly. Overall, this study highlights the important role of Mg anode coatings to improve the electrochemical performance of magnesium-sulfur batteries.