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This paper compares materials potentially suitable for preparing solid reference electrodes, which could be used in miniaturized flow electrochemical cells. The tested electrodes are based on Sb, Bi, Pd, Pt, and Ag. The stable potential of the reference electrodes was maintained by the pH of the electrolyte, except for the AgCl electrode, whose potential was given by the concentration of chlorides. The performance of the reference electrodes was evaluated through a series of experiments focusing on potential dependences, long‐term and short‐term stability, cyclic voltammetry, and flow injection analysis with amperometric detection. Potentiometric experiments showed that Sb‐based electrodes had the closest slope to theoretical values with minor changes over five weeks. Theory‐consistent results of potential dependence were also observed for AgCl electrodes. The results of the voltammetric and flow amperometric experiment suggest that Sb‐based reference electrodes are the most suitable tools for electrochemical measurement. AgCl electrodes are limited by the necessity of maintaining a high chloride concentration. Bi‐based and PdH electrodes provide unstable results, the latter particularly due to hydrogen desorption. Although able to provide the stable potential to some extent, Pt electrodes are not suitable as the reference electrodes due to the deformation of mainly hydrodynamic voltammograms. [ABSTRACT FROM AUTHOR]

Excellent conductivity makes silver (Ag) an attractive electrode and current collector material for a variety of devices, also promising faster soft actuators. However, high reactivity challenges the use of Ag in electrochemical systems, as dendritic growth can create undesired conduction pathways and short‐circuit the oppositely polarized electrodes. The challenge of rapid Ag electrochemical migration is addressed using a mixed mixed‐room temperature ionic liquid (RTIL) system (l‐ethyl‐3‐methylimidazolium bis‐(trifluoromethylsulfonyl)‐imide and trihexyl(tetradecyl)phosphonium chloride) that prevents short‐circuiting by engaging the produced Ag+ ions with Cl− anions. The stability of the system is demonstrated on an ionic actuator using Ag–silver chloride (AgCl) electrodes and a mixed‐RTIL electrolyte. The work demonstrates fast (in 5 s) transfer of a large (0.2 C cm−2) charge to high‐specific‐surface‐area carbon without observable dendritic growth in cycling and good electromechanical performance: 4° s−1 deflection rate at 0.8 V s−1 scan rate. Simple spray‐deposition of the Ag–AgCl electrodes promises scalable and cost‐effective fabrication. The combination of high stability and vast charge capacity encourages the engagement of Ag‐based electrodes for many electrochemical applications involving organic electrolytes also beyond robotics. [ABSTRACT FROM AUTHOR]

The use of reference electrodes (REs) in lithium‐ion batteries allows enhanced electrochemical analysis of individual electrodes via potential monitoring or electrochemical impedance spectroscopy (EIS). The previous publication presents a concept for a laser‐perforated RE (PRE). Herein, this PRE is applied in ≈60 mAh graphite/NMC811 pouch cells. Despite more than 17% of the electrode surface being covered by the PRE, only negligible capacity differences are observed for charge rates up to 2C compared to cells without PRE. At higher rates up to 5C, the blocking effect is present but stable. Reproducible and plausible anode voltage curves are obtained and the beginning of Li plating is detected. Cell EIS spectra are in good agreement with comparison cells without RE. The impedance spectra of the individual electrodes recorded by the PRE are confirmative and, with one exception, artifact‐free. The results demonstrate that our PRE can be reliably applied for investigating lab‐scale electrode coatings in small pouch cell formats. [ABSTRACT FROM AUTHOR]

In this study, a range of miniaturized Ag/AgCl reference electrodes with various layouts were successfully fabricated on wafer-level silicon-based substrates with metallic intermediate layers by precisely controlling the electrochemical deposition of Ag, followed by electrochemical chlorination of the deposited Ag layer. The structure, as well as the chemical composition of the electrode, were characterized with SEM & EDS. The results showed that the chlorination is very sensitive to the applied electric field and background solution. Potentiostatic chlorination, in combination with an adjusted mushroom-shaped Ag sealing deposition, enabled the formation of electrochemical usable Ag/AgCl layers. The stability of the electrodes was tested using open circuit potential (OCP) measurement. The results showed that the reference electrodes stayed stable for 300 s under 3 M KCl solution. The first stage study showed that the stability of the Ag/AgCl reference electrode in a chip highly depends on chip size design, chlorination conditions, and a further protection layer. [ABSTRACT FROM AUTHOR]

Thermo‐electrochemical monitoring of state‐of‐the‐art rechargeable Li‐ion batteries during operation is critical for safety and reliability, yet it remains quite limited, relying on conventional full cell measurements with in situ techniques lagging behind. Here, the feasibility of incorporating Au, LiFePO4, and TiO2 electrochemical sensors into commercially available pouch cells, in conjunction with thermocouples to track the cell behavior during galvanostatic cycling at varying operating temperatures is demonstrated. It is found that Au provides the best in operando based electrochemical diagnostics for stable thermo‐electrochemical performance via long‐term cyclability (>1000 h), differential capacity curves, and at 25, 40, and 60 °C, followed by TiO2, and LiFePO4. Furthermore, cell temperature changes are analyzed alongside reference electrode readings, demonstrating the advantages of the complementary nature of these techniques for cell thermodynamics. Collectively, these findings offer deep insight into an improved battery management approach for next‐generation lithium‐ion energy storage systems. [ABSTRACT FROM AUTHOR]

Anion Exchange Membrane Water Electrolysis (AEMWE) stands out as one of the promising ways of producing green hydrogen. However, significant strides in performance and durability are necessary for commercial competitiveness. Shunt currents and reverse currents are common problems associated with electrolyzers using conductive liquid electrolytes during start/stop conditions and can enhance electrode degradation. This study incorporates a dual Pt-wire reference electrode within the flow cell consisting of a NiFe-layered double hydroxide anode and different cathode materials to decouple individual electrode kinetics under steady state and intermittent operating conditions. The performance of bimetallic cathode catalysts like PtRu/C and NiMo/C was assessed in comparison with traditional Pt/C catalysts in the context of the hydrogen evolution reaction. The initial observed catalyst activity displayed an evident trend in the order of PtRu/C > Pt/C > NiMo/C. When subjected to reverse currents, all three systems showed degradation in performance. The use of reference electrodes illustrated that all cathode coatings degraded as a result of the reverse currents while the anode remained relatively stable. The degradation followed the trend of NiMo/C > PtRu/C > Pt/C. This work thus shows that reverse currents are a real issue for AEMWE and demonstrates the importance of investigating electrodes under intermittent conditions. [Display omitted] • Reverse currents during shutdown conditions can enhance electrode degradation. • A reference electrode is employed to decouple individual electrode kinetics. • Cathode catalysts showed higher susceptibility to degradation. [ABSTRACT FROM AUTHOR]

In this study, a range of miniaturized Ag/AgCl reference electrodes with various layouts were successfully fabricated on wafer-level silicon-based substrates with metallic intermediate layers by precisely controlling the electrochemical deposition of Ag, followed by electrochemical chlorination of the deposited Ag layer. The structure, as well as the chemical composition of the electrode, were characterized with SEM & EDS. The results showed that the chlorination is very sensitive to the applied electric field and background solution. Potentiostatic chlorination, in combination with an adjusted mushroom-shaped Ag sealing deposition, enabled the formation of electrochemical usable Ag/AgCl layers. The stability of the electrodes was tested using open circuit potential (OCP) measurement. The results showed that the reference electrodes stayed stable for 300 s under 3 M KCl solution. The first stage study showed that the stability of the Ag/AgCl reference electrode in a chip highly depends on chip size design, chlorination conditions, and a further protection layer.

The advancement in triboelectric nanogenerator technology leads to numerous advantages in various fields, especially in biomedical and healthcare applications. Theoretical modeling and simulation of sensors is the initial step for an optimized cost‐effective real‐time sensor fabrication which reduces the wastage of materials and rapid prototyping, giving an expected sensor performance. Herein, a theoretical model of single‐electrode triboelectric nanogenerator is presented which finds its application in healthcare monitoring as a wearable flexible pulse sensor to measure the wrist pulse for disease diagnosis. The device optimization in terms of structure, material and output performance is done based on the said application. A brief study of the operating principle of the sensor along with the factors affecting the output is discussed in this work. The design is conceptually investigated considering the electrostatic shield effect from the contact electrode. The output performance variation concerning the plain and micro‐structured triboelectric surface is also determined in terms of open‐circuit voltage of ≈16.95 and ≈21.63 V, respectively, and also a short‐circuit charge of ≈181.81 and ≈196.57 pC, respectively. The superior output performance even for smaller wrist pulse displacement range can serve as a significant assistance for the rational plan of the device structure. [ABSTRACT FROM AUTHOR]

The integration of electronic sensors into single-use systems for bioprocessing is challenged by their sensitivity to sterilizing γ-irradiation. This challenge also applies to reference electrodes (REs), whose potentials may be destabilized upon ionization and drift over time. Here we evaluate the performance of thin-film Ag/AgCl REs over a two-month window following γ-ray sterilization using a 60Co source. γ-REs display a characteristic voltage decay during the first few weeks of operation ascribed to dissipation of radiation-induced charge defects, followed by long-term potentiometric stability when stored in phosphate-buffered saline with a 95 % confidence interval of 4 mV over 60 days. γ-REs have a mean insensitivity (inertness) of 0.6 mV/decade in pH buffers (4.5–9.0) and <1 mV/decade in the presence of organic solutes and ions at physiological ionic strength. γ-REs paired with thin-film working electrodes (WE) form sensors with near-Nernstian sensitivity, and irradiation of a thin-film pH sensor (γ-pH/WE plus γ-RE) produces a logarithmic voltage decay that is readily corrected by a single-point calibration function. The γ-irradiated sensor can monitor pH changes in sterile cell culture media over a 3-week period and produces readouts with a mean deviation below 0.04 pH units relative to a commercial meter (ground truth). [Display omitted] • γ-sterilized thin-film pH sensors perform reliably with low materials cost. • γ-irradiated sensors only need single-point calibration after conditioning. • γ-irradiated thin-film sensors can be used for 3 weeks in sterile culture media. • γ-irradiated thin-film sensors produce values within 0.04 units of ground-truth pH. • Irradiated reference electrodes show same inertness as controls over 60 days. [ABSTRACT FROM AUTHOR]

Reference electrodes (REs) based on moderately lipophilic ionic liquids (ILs) are an attractive approach to realize integrated potentiometric sensing systems that do not require a traditional liquid junction. However, it is not sufficiently understood how lipophilic sample ions can result in interference. Less lipophilic ILs should partition more easily into the aqueous phase where they can compete with sample ions and suppress ion-exchange, but since a decreased IL lipophilicity favors ion-exchange interference the overall effect is not immediately clear. We use here the established phase boundary potential model to describe failure of IL-based REs upon exposure to lipophilic solution ions. The traditional definition of the detection limit is employed to find the intersection of the separate Nernstian responses to IL and solution interference, which is mathematically simpler to process. The approach focuses on cation interference and considers ion pairing in the polymeric phase together with appropriate ion-exchange and coextraction equilibria. The range of RE potential stability is shown to depend on 1) the concentration of the IL in the membrane; 2) the lipophilicity of the IL expressed through its partition constant; 3) the relative lipophilicity of the lipophilic interference and the IL ion of the same charge expressed through the corresponding ion-exchange constant; 4) the stability constant of ion pairs between the interfering ion and the counterion from the IL. For the experimental evaluation of the model, two commercially available ionic liquids were selected: [C 8 mim+][C 1 C 1 N-] (IL1) and [TBMOEP+][C 1 C 1 N-] (IL2). Partition constants between water and a polymeric phase based on poly(vinyl chloride) (PVC) and dodecyl 2-nitrophenyl ether (NPDE) were determined for the first time for both IL1 (3.55 ± 0.05) and IL2 (4.68 ± 0.22) using so-called sandwich membrane experiments. Based on these values, the expected reference electrode lifetime is discussed. Tetramethylammonium, tetraethylammonium and tetrabutylammonium cations were selected as model interfering ions and the corresponding exchange constants were obtained experimentally. The model provides excellent RE failure prediction in which calculated critical activities for the tetrabutylammonium cation closely match the experimental values for both ILs. [Display omitted] • The influence of lipophilic ions on the potential of ionic liquid reference electrodes has not been fully understood before. • A model is proposed to describe the failure of reference electrodes based on ionic liquids in presence of lipophilic cations. • Partition constants in a PVC-NPDE/water system are determined for two moderately lipophilic ionic liquids. • The model provides excellent reference electrode failure prediction in terms of critical interfering ion activity. • The expected poor electrode lifetime is addressed and requirements for new ionic liquids are discussed. [ABSTRACT FROM AUTHOR]

To achieve a transition from conventional liquid-junction reference electrodes (LJF REs) to their all-solid-state alternatives, organic electrolytes are often introduced into the polymeric electrode membranes. In this article, we implement a theoretical approach to the explanation and quantification of the boundary potential stabilization phenomenon for the electrodes modified with organic electrolytes (Q+B−). For the first time, stabilization of the phase boundary potential due to the partition of lipophilic ions of the Q+B− electrolyte between the polymeric and aqueous phases is numerically simulated to predict the LJF electrodes behavior. The impact of the hydrophilic electrolyte on the potential stabilization is demonstrated both numerically and experimentally. The developed model predicted that the small additions of a traditional ion-exchanger enhance performance of the Q+B−-based reference electrodes. For some specific cases, the optimal concentrations of Q+B− and ion-exchanger in the polymeric phase are suggested to provide stable electrode potential in a broad range of aqueous electrolyte concentrations. In addition, the efficiency of the stabilization was shown to be dependent on the overall Q+B− load in the polymeric membrane rather than on the closeness of the partition coefficients of the Q+ and B− ions; and on the volume of the aqueous phase. The model results are verified experimentally with poly(vinyl chloride) membranes containing ion-exchanger or hydrophilic electrolyte and Q+B− in various proportions. A good agreement between the measured electrode response and the theoretical results is observed in a broad range of solution concentrations. In particular, the cationic function of membranes containing KTpClPB is suppressed, and the electrodes begin to behave as REs starting from 50–60 mol. % of ETH500 electrolyte added to the membrane, relative to the total amount of salt.

Electrochemical energy storage systems play an increasingly important role in our daily lives. The detection/estimation of the state of electrochemical cells is therefore a prerequisite for the development of safe, high‐performance batteries. Reference electrodes (REs) are an effective tool for monitoring the status of batteries and are of critical significance in this field. However, the practical construction of a durable RE for long‐term research and industrial applications is still challenging. In this article, the fundamental principles of a three‐electrode system featuring the presence of REs are elucidated. The design parameters of REs in lithium batteries, including active materials, manufacturing, geometry, and placement, are comprehensively summarized, and the typical applications of REs in practical lithium‐ion batteries to facilitate working/failure mechanism analysis and methods to monitor Li plating are analyzed. Finally, the challenges and future trends of the exploitation and deployment of REs in lithium batteries are presented. [ABSTRACT FROM AUTHOR]

Lithiated gold wires can be used to build reference electrodes with outstanding potential stabilities over several days and even over the course of one year. These electrodes are well suited for investigations in the context of lithium-ion batteries (LIBs). In this work, a detailed procedure for the preparation of such electrodes with tailored mechanical properties, which can be fitted gastight into electrochemical cells using commercially available fittings, is given. The electrochemical lithiation process is studied using the electrochemical quartz crystal microbalance (EQCM) technique, and the differences in lithiation of wire type and thin film type gold electrodes are discussed. All experiments were carried out with two different electrolytes, namely, a LiPF6 and a lithium bis(trifluoromethane sulfonyl) imide (LiTFSI)-based electrolyte, and we conclude that for a higher lithiation rate and long-term stability, the use of LiTFSI-based electrolyte in the preparation phase is beneficial. The EQCM data provides a better insight in the analysis of film formation processes, like the buildup of the solid electrolyte interphase (SEI) during the lithiation, the rate of deposition of metallic lithium, or additional information on the kinetics of Li-Au alloy formation. [ABSTRACT FROM AUTHOR]

In vivo electrochemistry is a vital tool of neuroscience that allows for the detection, identification, and quantification of neurotransmitters, their metabolites, and other important analytes. One important goal of in vivo electrochemistry is a better understanding of progressive neurological disorders (e.g., Parkinson's disease). A complete understanding of such disorders can only be achieved through a combination of acute (i.e., minutes to hours) and chronic (i.e., days or longer) experimentation. Chronic studies are more challenging because they require prolonged implantation of electrodes, which elicits an immune response, leading to glial encapsulation of the electrodes and altered electrode performance (i.e., biofouling). Biofouling leads to increased electrode impedance and reference electrode polarization, both of which diminish the selectivity and sensitivity of in vivo electrochemical measurements. The increased impedance factor has been successfully mitigated previously with the use of a counter electrode, but the challenge of reference electrode polarization remains. The commonly used Ag/AgCl reference electrode lacks the long-term potential stability in vivo required for chronic measurements. In addition, the cytotoxicity of Ag/AgCl adversely affects animal experimentation and prohibits implantation in humans, hindering translational research progress. Thus, a move toward biocompatible reference electrodes with superior chronic potential stability is necessary. Two qualifying materials, iridium oxide and boron-doped diamond, are introduced and discussed in terms of their electrochemical properties, biocompatibilities, fabrication methods, and applications. In vivo electrochemistry continues to advance toward more chronic experimentation in both animal models and humans, necessitating the utilization of biocompatible reference electrodes that should provide superior potential stability and allow for unprecedented chronic signal fidelity when used with a counter electrode for impedance mitigation. [ABSTRACT FROM AUTHOR]

As the most hazardous side reaction, Li plating poses high risks of undermining electrochemical performance of Li-ion batteries by accelerating degradation. Under some extreme abuse conditions, Li plating can even jeopardize safety performance and induce catastrophic results like thermal runaway. Therefore, multiscale observation of Li plating is of great significance for understanding the internal mechanisms and early detection of Li plating. In this mini-review, the recent progress of formation mechanisms of plated metallic lithium was introduced. Then, the in situ and ex situ observation methods of macroscopic, microscopic and atomic level were summarized. Reference electrode provides a promising tool for real-time monitoring of anode potential, which is the critical factor of Li plating, showing great potentials in cloud-based battery management systems. Finally, some perspectives for future researches on Li plating observation and corresponding utilizations in developing Li plating free control strategies were proposed. [ABSTRACT FROM AUTHOR]

Despite growing demand for Li‐ion batteries in the portable, industrial, and electric vehicle markets, the performance and safety monitoring of these state‐of‐the‐art rechargeable cells is quite limited, relying on conventional full‐cell measurements with in situ reference electrode technologies lagging behind in application. Herein, for the first time a long‐term (>2000 h) stable Ti‐based reference electrode is reported, and a new design enabling impact‐free implementation into pouch. The methodology can also be used with other reference electrode materials. Various electrochemical characterization techniques are used to verify the usability and stability of the developed reference electrode, in turn enabling monitoring of individual electrode cycling performance and open circuit potential (OCP) via the galavanostatic intermittent titration technique (GITT) and differential capacity analysis. The findings offer a potential way of incorporating stable in situ reference electrodes into current and future generations of lithium‐ion batteries. [ABSTRACT FROM AUTHOR]

In this paper we report on the novel polymeric membranes for the liquid junction‐free reference electrodes. The membranes contain the ionic liquids (ILs) based on the amino acid anions, namely valine‐, leucine‐, lysine‐ and histidine‐anions, and 1‐butyl‐3‐methylimidazolium cation. Addition of the ILs, and especially of the valine‐based one, to the polymeric plasticized membranes allows significant stabilization of the electrode potential and makes it insensitive to the solution composition. A simple criterion based on the calculated lipophilicities of the cation and anion of the IL is proposed for a priori estimation of its applicability for potential stabilization. The addition of the IL as a microcomponent is found to be advantageous over plasticizing the membrane with the IL due to better potential stability, higher dissociation degree and mobility of the species. The resistance of the novel reference membranes can be tuned by addition of the lipophilic membrane electrolytes, e. g. ETH500. The applicability of the developed reference electrodes is verified in the potentiometric calibration of the indicator K+‐ and Ca2+‐selective electrodes. Implementation of the amino acid‐based ionic liquids with low environmental toxicity can make a significant contribution to the development of nature‐friendly potentiometry. [ABSTRACT FROM AUTHOR]

Successful antibiotic treatment of infections relies on accurate and rapid identification of the infectious agents. Pseudomonas aeruginosa is implicated in a wide range of human infections that mostly become complicated and life threating, especially in immunocompromised and critically ill patients. Conventional microbiological methods take more than three days to obtain accurate results. Pyocyanin is a distinctive electroactive biomarker for Pseudomonas aeruginosa. Here, we have prepared polyaniline/gold nanoparticles decorated ITO electrode and tested it to establish a rapid, diagnostic and highly sensitive pyocyanin sensor in a culture of Pseudomonas aeruginosa clinical isolates with high selectivity for traces of pyocyanin when measured in the existence of different interferences like vitamin C, uric acid, and glucose. The scanning electron microscopy and cyclic voltammetry techniques were used to characterize the morphology and electrical conductivity of the constructed electrode. The determined linear range for pyocyanin detection was from 238 μM to 1.9 μM with a detection limit of 500 nM. Compared to the screen-printed electrode used before, the constructed electrode showed a 4-fold enhanced performance. Furthermore, PANI/Au NPs/ITO modified electrodes have demonstrated the ability to detect pyocyanin directly in Pseudomonas aeruginosa culture without any potential interference with other species. [ABSTRACT FROM AUTHOR]

Fe(III)-rich deposits referred to as “iron mounds” develop when Fe(II)-rich acid mine drainage (AMD) emerges at the terrestrial surface, and aeration of the fluids induces oxidation of Fe(II), with subsequent precipitation of Fe(III) phases. As Fe(III) phases accumulate in these systems, O2 gradients may develop in the sediments and influence the distributions and extents of aerobic and anaerobic microbiological Fe metabolism, and in turn the solubility of Fe. To determine how intrusion of O2 into iron mound sediments influences microbial community composition and Fe metabolism, we incubated samples of these sediments in a column format. O2 was only supplied through the top of the columns, and microbiological, geochemical, and electrochemical changes at discrete depths were determined with time. Despite the development of dramatic gradients in dissolved Fe(II) concentrations, indicating Fe(II) oxidation in shallower portions and Fe(III) reduction in the deeper portions, microbial communities varied little with depth, suggesting the metabolic versatility of organisms in the sediments with respect to Fe metabolism. Additionally, the availability of O2 in shallow portions of the sediments influenced Fe metabolism in deeper, O2-free sediments. Total potential (EH + self-potential) measurements at discrete depths in the columns indicated that Fe transformations and electron transfer processes were occurring through the sediments and could explain the impact of O2 on Fe metabolism past where it penetrates into the sediments. This work shows that O2 availability (or lack of it) minimally influences microbial communities, but influences microbial activities beyond its penetration depth in AMD-derived Fe(III) rich sediments. Our results indicate that O2 can modulate Fe redox state and solubility in larger volumes of iron mound sediments than only those directly exposed to O2. [ABSTRACT FROM AUTHOR]

The development of new signal systems for electrical biosensors could provide exciting new opportunities for biomedical analysis, pollutant monitoring, and explosive detection. The signal systems for commercial portable sensors involve the integration of a battery and a circuit conditioning system to power an amperometric biosensor. However, this increases the size and complexity of the entire system. In this study, we develop a simple amperometric biosensor that is directly powered by a button cell battery for the detection of lactate. A two-electrode sensing transducer was printed on cardboard or integrated on a ring. It was directly powered by a button cell battery, and connected to a multimeter for current measurement. This sensor showed a sensitive detection range of 0.04762–9.21429 mM and short measuring time of 2 min. These results show that this system can achieve an excellent sensing performance, and the construction of this new sensing system directly powered by a button cell battery offers a new method for further developing a wide range of miniaturized, flexible, portable, or wearable sensing systems, and these could be used in detecting various analytes that are important in medical diagnosis and environmental monitoring. [ABSTRACT FROM AUTHOR]

Electrocorticography (ECoG) is becoming more prevalent due to improvements in fabrication and recording technology as well as its ease of implantation compared to intracortical electrophysiology, larger cortical coverage, and potential advantages for use in long term chronic implantation. Given the flexibility in the design of ECoG grids, which is only increasing, it remains an open question what geometry of the electrodes is optimal for an application. Conductive polymer, PEDOT:PSS, coated microelectrodes have an advantage that they can be made very small without losing low impedance. This makes them suitable for evaluating the required granularity of ECoG recording in humans and experimental animals. We used two-dimensional (2D) micro-ECoG grids to record intra-operatively in humans and during acute implantations in mouse with separation distance between neighboring electrodes (i.e., pitch) of 0.4 mm and 0.2/0.25 mm respectively. To assess the spatial properties of the signals, we used the average correlation between electrodes as a function of the pitch. In agreement with prior studies, we find a strong frequency dependence in the spatial scale of correlation. By applying independent component analysis (ICA), we find that the spatial pattern of correlation is largely due to contributions from multiple spatially extended, time-locked sources present at any given time. Our analysis indicates the presence of spatially structured activity down to the sub-millimeter spatial scale in ECoG despite the effects of volume conduction, justifying the use of dense micro-ECoG grids. [ABSTRACT FROM AUTHOR]

Despite sleep’s recognized biological importance, it has been remarkably difficult to demonstrate changes in brain physiology with reduced sleep durations. In a study of adolescents, we varied sleep durations by restricting time in bed for four nights of either 10, 8.5 or 7 h. Shorter sleep durations significantly decreased waking electroencephalogram (EEG) power in a wide range of frequencies with both eyes closed and eyes open in central and occipital leads. These findings suggest new research directions and raise the possibility that waking EEG power density could provide a non-invasive test for biologically sufficient sleep. [ABSTRACT FROM AUTHOR]

Insurmountable detection challenges will impede the development of many of the next-generation of lab-on-a-chip devices (e.g., point-of-care and real-time health monitors). Here we present the first membrane-based, microfluidic sample preconcentration method that is continuous, quantifiable, simple, and capable of working with any analyte. Forward osmosis rapidly concentrates analytes by removing water from a stream of sample fluid. 10-100X preconcentration is possible in mere minutes. This requires careful selection of the semi-permeable membrane and draw molecule; therefore, the osmosis performance of several classes of membranes and draw molecules were systematically optimized. Proof-of-concept preconcentration devices were characterized based on their concentration ability and fouling resistance. In-silico theoretical modeling predicts the experimental findings and provides an engineering toolkit for future designs. With this toolkit, inexpensive ready-for-manufacturing prototypes were also developed. These devices provide broad-spectrum detection improvements across many analytes and sensing modalities, enabling next-generation lab-on-a-chip devices. [ABSTRACT FROM AUTHOR]

Transcranial electrical stimulation (tES) is rapidly becoming an indispensable clinical tool with its different forms. Animal data are crucially needed for better understanding of the underlying mechanisms of tES. For reproducibility of results in animal experiments, the electric fields (E-Fields) inside the brain parenchyma induced by the injected currents need to be predicted accurately. In this study, we measured the electrical fields in the rat brain perpendicular to the brain surface, i.e. vertical electric field (VE-field), when the stimulation electrode was placed over the skin, skull, or dura mater through a craniotomy hole. The E-field attenuation through the skin was a few times larger than that of the skull and the presence of skin substantially reduced the VE-field peak at the cortical surface near the electrode. The VE-field declined much quicker in the gray matter underneath the pial surface than it did in the white matter, and thus the large VE-fields were contained mostly in the gray matter. The transition at the gray/white matter border caused a significant peak in the VE-field, as well as at other local inhomogeneties. A conductivity value of 0.57 S/m is predicted as a global value for the whole brain by matching our VE-field measurements to the field profile given by analytical equations for volume conductors. Finally, insertion of the current return electrode into the shoulder, submandibular, and hind leg muscles had virtually no effects on the measured E-field amplitudes in the cortex underneath the epidural electrodes. [ABSTRACT FROM AUTHOR]

Local field potential (LFP) recording is a very useful electrophysiological method to study brain processes. However, this method is criticized for recording low frequency activity in a large area of extracellular space potentially contaminated by distal activity. Here, we theoretically and experimentally compare ground-referenced (RR) with differential recordings (DR). We analyze electrical activity in the rat cortex with these two methods. Compared with RR, DR reveals the importance of local phasic oscillatory activities and their coherence between cortical areas. Finally, we show that DR provides a more faithful assessment of functional connectivity caused by an increase in the signal to noise ratio, and of the delay in the propagation of information between two cortical structures. [ABSTRACT FROM AUTHOR]

Accurate spatial co-registration of EEG electrode positions with individual head models is an important component for EEG source localization and imaging. Due to variations in head shape between individuals, this requires measurements of electrode locations in each individual. Existing hardware for digitization can be accurate, but also relatively expensive. With the goal of making digitization more accessible for a range of research laboratories, we have developed an open-source software tool that can make use of less expensive consumer virtual reality hardware for EEG electrode digitization. Here we describe our developed VRDigitizer system and compare it to existing digitization solutions. Experimental evaluations were performed in a phantom head model and in 12 human subjects. In our comparison experiments, VRDigitizer was able to measure electrode positions with a mean error of 3.74 mm, compared to 1.73 mm and 2.98 mm for the commercial systems tested. [ABSTRACT FROM AUTHOR]

In comparison to neutral faces, facial expressions of emotion are known to gain attentional prioritization, mainly demonstrated by means of event-related potentials (ERPs). Recent evidence indicated that such a preferential processing can also be elicited by neutral faces when associated with increased motivational salience via reward. It remains, however, an open question whether impacts of inherent emotional salience and associated motivational salience might be integrated. To this aim, expressions and monetary outcomes were orthogonally combined. Participants (N = 42) learned to explicitly categorize happy and neutral faces as either reward- or zero-outcome-related via an associative learning paradigm. ERP components (P1, N170, EPN, and LPC) were measured throughout the experiment, and separately analyzed before (learning phase) and after (consolidation phase) reaching a pre-defined learning criterion. Happy facial expressions boosted early processing stages, as reflected in enhanced amplitudes of the N170 and EPN, both during learning and consolidation. In contrast, effects of monetary reward became evident only after successful learning and in form of enlarged amplitudes of the LPC, a component linked to higher-order evaluations. Interactions between expressions and associated outcome were absent in all ERP components of interest. The present study provides novel evidence that acquired salience impacts stimulus processing but independent of the effects driven by happy facial expressions. [ABSTRACT FROM AUTHOR]

Abstract Solid-state fast-ion conductors are a core class of functional materials for solid-state electrochemical cells such as batteries, sensors and fuel cells. The Na 2 Si 2 O 5 glass has recently been reported as a potential intermediate-temperature Na+-conductor, but a direct evidence of its pure Na+ conduction is still lacking. We here show that the Na+ transport number of the Na 2 Si 2 O 5 glass can be determined by the ratio of the measured open-circuit voltage to the theoretical Nernst potential of a Na-concentration cell. The Na-concentration cell is consisted of a Na 2 Si 2 O 5 glass electrolyte and two two-phase reference electrodes of defined Na-chemical potentials, Na 2 ZrO 3 + ZrO 2 and NaAlO 2 + Al 2 O 3. The result explicitly suggests that the Na 2 Si 2 O 5 glass is a pure Na+ conductor at <400 °C. Highlights • Demonstrated a new Na-concentration cell configuration • Measured Na+ transport number • Concluded Na 2 Si 2 O 5 is a pure Na+ conductor at <400 °C. [ABSTRACT FROM AUTHOR]

Abstract Pseudo reference electrodes forms an essential part of electrochemical transducers, where they are used to maintain a reference potential for the system. Yet, little is known about their long-term stability, and any drift may cause undesired changes in the sensor signal. This paper investigates the stability of the reference potential of five material systems of screen-printed reference electrodes. Their potential was continuously monitored for a duration of 40 days in a phosphate buffered solution, and any signal changes were corroborated with EDX elemental analyses, SEM micrographs and cyclic voltammetry. The electrodes were considered to be stable as long as they remained within 30 mV of their initial potential throughout the study. It was found that Ag/AgCl electrodes with a 3:1 atomic ratio kept a stable reference potential (±2.2 mV), whereas Ag/AgCl electrodes with a 9:1 atomic ratio, despite showing good overall constancy of ±3.2 mV, seemed to statistically lose stability towards the end of the 40 day trial due to AgCl depletion through dissolution. The daily potential drift for the respective Ag/AgCl electrodes were −0.2 mV (3:1 ratio) and −0.1 mV (9:1 ratio), suggesting a proportionality between the amount of dissociated AgCl close to the electrode surface and the initial AgCl loading. Electrodes consisting of only Ag showed tendencies towards a mixed potential contribution, which reduced the long-term stability (±24.2 mV) as well as the longevity span (2 days). Ag/Pd electrodes proved to be more unstable (±29.7 mV), with an average lifetime of around 3.5 days. Pt had the greatest potential instability (±59.8 mV), rendering its average lifetime to less than a day. It was shown that electrodes which deviates from the Ag/AgCl equilibrium had the greatest potential variation with time. [ABSTRACT FROM AUTHOR]

Abstract Vanadium redox flow battery performance is actually hindered by increased overpotentials at high current, due to poor electrochemical activity of the most commonly used carbon electrodes and to electrolyte distribution, implying local mass transport limiting conditions. Moreover, vanadium cross-contamination leads to coulombic efficiency reduction and uncontrolled electrolytes imbalance. This work presents the application of through-plate reference electrodes at inlet and outlet of both positive and negative electrodes. The utility of the electrodes potential measurement is firstly demonstrated in the identification of a relation between electrolytes potential and the corresponding state of charge. Subsequently, local overpotentials and impedance spectra at both electrodes are evaluated, evidencing that the negative electrode is kinetically dominated and presents high overpotential even at low current, while the positive exhibits mass transport effects at high current, especially at cell outlet. Finally, during cycling operation with fixed capacity reference electrode measurements permit to monitor electrolytes imbalance induced by cross-contamination, that mainly affects negative electrolyte. Moreover, additional insights into electrodes potential loss during cycling are provided. Highlights • We applied through-plate reference electrodes at electrodes inlet and outlet of a VRFB. • Negative electrode is kinetically dominated and the positive is mass transport limited. • Electrodes OCP trends reveal electrolytes imbalance during cycling. • Cross-contamination mainly affects the negative electrolyte. [ABSTRACT FROM AUTHOR]

This paper presents printed thick film Ag|AgCl|KCl reference electrodes (RE) for electrochemical sensors. The screen-printed REs with 10- $\mu \text{m}$ thick glass-KCl salt matrix layer exhibit a stable potential of 5 mV. Cyclic voltammetric analysis shows that the anodic and cathodic peak current of the RE increases with the scan rate in the range of 25–150 mVs−1. The analytical performance of the REs shows a stable open circuit potential for the NaCl concentrations in the range of 30–100 mM. Testing the presented REs for electrochemical pH sensor application (with RuO2-based sensitive electrode) the sensitivity of 55 mV/pH was noted in the pH range of 4.5–9. Evaluating the effect of temperature on the performance of REs, a potential variation of −3.8 mV/ °C was observed. Finally, a LabVIEW interface was developed to store, analyze, and calculate the sensitivity of the sensor under different temperature conditions. The LabVIEW interface can also be used to calculate the pH-value/temperature of unknown solutions under known temperature/pH conditions. [ABSTRACT FROM AUTHOR]

We examined the effect of hearing two types of self-relevant words, one’s own name and the name of others, on vigilant attention, arousal, and subjective sleepiness during performing the Psychomotor Vigilance Test (PVT). Participants performed the PVT under three experimental conditions, (a) hearing own full name (high self-relevant condition), (b) hearing other’s name (low self- relevant condition) and (c) the control condition with no stimuli. Participants heard the names every 20 sec. Self-relevance was assessed before the experiment using the self-relevance scale. The results of the behavioral effects are relatively small and not consistently supported by all of the performance indicators. A tentative conclusion, based on the overall pattern of results, is that (1) arousal increased by hearing a name, regardless of its self-relevance, and (2) hearing less self-relevant stimuli such as other’s name had a distractive effect on ongoing task performance, although it increased arousal, being aware that further experiments are urgently necessary. [ABSTRACT FROM AUTHOR]

Small-holding farmers in the developing world suffer from sub-optimal crop yields because they lack a soil diagnostic system that is affordable, usable, and actionable. This paper details the fabrication and characterization of an integrated point-of-use soil-testing system, comprised of disposable ion-selective electrode strips and a handheld electrochemical reader. Together, the strips and reader transduce soil ion concentrations into to an alphanumeric output that can be communicated via text message to a central service provider offering immediate, customized fertilizer advisory. The solid-state ion-selective electrode (SS-ISE) strips employ a two-electrode design with screen-printable carbon nanotube ink serving as the electrical contacts for the working and reference electrodes. The working electrode comprises a plasticizer-free butyl acrylate ion-selective membrane (ISM), doped with an ion-selective ionophore and lipophilic salt. Meanwhile, the reference electrode includes a screen-printed silver-silver chloride ink and a polyvinyl-butyral membrane, which is doped with sodium chloride for stable reference potentials. As a proof of concept, potassium-selective electrodes are studied, given potassium’s essential role in plant growth and reproduction. The ISE-based system is reproducibly manufactured to yield a Nernstian response with a sub-micromolar detection limit (pK+ of 5.18 ± 0.08) and near-Nernstian sensitivity (61 mV/decade) in the presence of a 0.02 M strontium chloride extraction solution. Analysis of soil samples using the printed electrodes and reader yielded a correlation coefficient of 푅2 = 0.89 with respect to values measured via inductively coupled plasma atomic emission spectroscopy (ICP-AES). The reliable performance of this system is encouraging toward its deployment for soil nutrient management in resource-limited environments. [ABSTRACT FROM AUTHOR]

Chemical disinfectants effectively kill pathogenic microorganisms, eliminating routes of transmission for infectious diseases. Accurate quantification of the active ingredients can help make a more effective use of disinfectants. In this study, the active ingredients in six different types of chemical disinfectants were systematically quantified with great precision and accuracy using potentiometric titration. The coefficient of variations fell in the range of 0.04%-0.46%. The recovery rates of samples were all above 95% and the extended uncertainty was 0.32g/L. This method can be broadly applied to the analysis of disinfectants in the future. [ABSTRACT FROM AUTHOR]

Previous language production studies targeting the inferior frontal and superior temporal gyrus using anodal tDCS have provided mixed results. Part of this heterogeneity may be explained by limited target region focality of conventionally used electrode montages. We examined the focality of conventionally and alternative electrode montages. Electrical field distributions of anodal tDCS targeting IFG and pSTG were simulated in conventional setups (anodal electrode over left IFG/pSTG, reference electrode over right supraorbital region) and an alternative electrode montage in four different brains. Conventional montages showed maximum field strengths outside of the target regions. Results from alternative electrode montages showed that focality of tDCS could be improved by adjustments in electrode placement. Heterogeneity of findings of language production studies deploying conventional montages may in part be explained by diffuse electrical field distributions. Alternative montages may improve focality and provide more unequivocal results. [ABSTRACT FROM AUTHOR]

In this paper we demonstrate a potentiostat built with a single commercially available integrated circuit (IC) that does not require any external electronic components to perform electrochemical experiments. This is done using the capabilities of the Programmable System on a Chip (PSoC®) by Cypress Semiconductor, which integrates all of the necessary electrical components. This is in contrast to other recent papers that have developed potentiostats but require technical skills or specialized equipment to produce. This eliminates the process of having to make a printed circuit board and soldering on electronic components. To control the device, a graphical user interface (GUI) was developed in the python programming language. Python is open source, with a style that makes it easy to read and write programs, making it an ideal choice for open source projects. As the developed device is open source and based on a PSoC, modification to implement other electrochemical techniques is straightforward and only requires modest programming skills, but no expensive equipment or difficult techniques. The potentiostat developed here adds to the growing amount of open source laboratory equipment. To demonstrate the PSoC potentiostat in a wide range of applications, we performed cyclic voltammetry (to measure vitamin C concentration in orange juice), amperometry (to measure glucose with a glucose strip), and stripping voltammetry experiments (to measure lead in water). The device was able to perform all experiments and could accurately measure Vitamin C, glucose, and lead. [ABSTRACT FROM AUTHOR]

The combination of Transcranial Magnetic Stimulation (TMS) with Electroencephalography (EEG) exposes the brain’s global response to localized and abrupt stimulations. However, large electric artifacts are induced in the EEG by the TMS, obscuring crucial stages of the brain’s response. Artifact removal is commonly performed by data processing techniques. However, an experimentally verified physical model for the origin and structure of the TMS-induced discharge artifacts, by which these methods can be justified or evaluated, is still lacking. We re-examine the known contribution of the skin in creating the artifacts, and outline a detailed model for the relaxation of the charge accumulated at the electrode-gel-skin interface due to the TMS pulse. We then experimentally validate implications set forth by the model. We find that the artifacts decay like a power law in time rather than the commonly assumed exponential. In fact, the skin creates a power-law decay of order 1 at each electrode, which is turned into a power law of order 2 by the reference electrode. We suggest an artifact removal method based on the model which can be applied from times after the pulse as short as 2 milliseconds onwards to expose the full EEG from the brain. The method can separate the capacitive discharge artifacts from those resulting from cranial muscle activation, demonstrating that the capacitive effect dominates at short times. Overall, our insight into the physical process allows us to accurately access TMS-evoked EEG responses that directly follow the TMS pulse, possibly opening new opportunities in TMS-EEG research. [ABSTRACT FROM AUTHOR]

Poly(3-hydroxybutyrate) (PHB), a biodegradable polymer, can be produced by different microorganisms. The PHB belongs to the family of polyhydroxyalkanoate (PHA) that mostly accumulates as a granule in the cytoplasm of microorganisms to store carbon and energy. In this study, we established an integrated one-pot electromicrobial setup in which carbon dioxide is reduced to formate electrochemically, followed by sequential microbial conversion into PHB, using the two model strains, Methylobacterium extorquens AM1 and Cupriavidus necator H16. This setup allows to investigate the influence of different stress conditions, such as coexisting electrolysis, relatively high salinity, nutrient limitation, and starvation, on the production of PHB. The overall PHB production efficiency was analyzed in reasonably short reaction cycles typically as short as 8 h. As a result, the PHB formation was detected with C. necator H16 as a biocatalyst only when the electrolysis was operated in the same solution. The specificity of the source of PHB production is discussed, such as salinity, electricity, concurrent hydrogen production, and the possible involvement of reactive oxygen species (ROS). [ABSTRACT FROM AUTHOR]

The posterior auricular muscle (PAM) reflex to sounds has been used clinically to determine hearing threshold as an alternative to other audiological diagnostic measures such as the auditory brainstem response. We have shown that the PAM response is also sensitive to interaural timing differences in normally hearing adults. PAM responses were evoked by both ipsilateral/ contralateral monaural stimulation and by binaural stimulation. Introducing sound delays ipsilaterally or contralaterally decreased the PAM response amplitude and increased its latency. The PAM response in this study shows a qualitatively similar pattern to that seen by the binaural interaction component (BIC) of the auditory brainstem potential to binaural clicks described in previous studies, in that both: have their shortest latency and maximal amplitudes centred around zero interaural timing differences, have response latencies increase with increasing interaural delays up to 1.2 ms and have response amplitudes decrease with increasing interaural delays of up to 1.2 ms. Our data show that the PAM response may be useful in measuring binaural integration in humans non-invasively for diagnostic or research studies. [ABSTRACT FROM AUTHOR]

Pyocyanin is a toxin produced by Pseudomonas aeruginosa. Here we describe a novel paper-based electrochemical sensor for pyocyanin detection, manufactured with a simple and inexpensive approach based on electrode printing on paper. The resulting sensors constitute an effective electrochemical method to quantify pyocyanin in bacterial cultures without the conventional time consuming pretreatment of the samples. The electrochemical properties of the paper-based sensors were evaluated by ferri/ferrocyanide as a redox mediator, and showed reliable sensing performance. The paper-based sensors readily allow for the determination of pyocyanin in bacterial cultures with high reproducibility, achieving a limit of detection of 95 nM and a sensitivity of 4.30 μA/μM in standard culture media. Compared to the similar commercial ceramic based sensors, it is a 2.3-fold enhanced performance. The simple in-house fabrication of sensors for pyocyanin quantification allows researchers to understand in vitro adaptation of P. aeruginosa infections via rapid screenings of bacterial cultures that otherwise are expensive and time-consuming. [ABSTRACT FROM AUTHOR]

Visual experience during the critical period modulates visual development such that deprivation causes visual impairments while stimulation induces enhancements. This study aimed to determine whether visual stimulation in the form of daily optomotor response (OMR) testing during the mouse critical period (1) improves aspects of visual function, (2) involves retinal mechanisms and (3) is mediated by brain derived neurotrophic factor (BDNF) and dopamine (DA) signaling pathways. We tested spatial frequency thresholds in C57BL/6J mice daily from postnatal days 16 to 23 (P16 to P23) using OMR testing. Daily OMR-treated mice were compared to littermate controls that were placed in the OMR chamber without moving gratings. Contrast sensitivity thresholds, electroretinograms (ERGs), visual evoked potentials, and pattern ERGs were acquired at P21. To determine the role of BDNF signaling, a TrkB receptor antagonist (ANA-12) was systemically injected 2 hours prior to OMR testing in another cohort of mice. BDNF immunohistochemistry was performed on retina and brain sections. Retinal DA levels were measured using high-performance liquid chromatography. Daily OMR testing enhanced spatial frequency thresholds and contrast sensitivity compared to controls. OMR-treated mice also had improved rod-driven ERG oscillatory potential response times, greater BDNF immunoreactivity in the retinal ganglion cell layer, and increased retinal DA content compared to controls. VEPs and pattern ERGs were unchanged. Systemic delivery of ANA-12 attenuated OMR-induced visual enhancements. Daily OMR testing during the critical period leads to general visual function improvements accompanied by increased DA and BDNF in the retina, with this process being requisitely mediated by TrkB activation. These results suggest that novel combination therapies involving visual stimulation and using both behavioral and molecular approaches may benefit degenerative retinal diseases or amblyopia. [ABSTRACT FROM AUTHOR]