Reference Electrode Research Articles

Electrochemical Analysis of Metal Stability in Candidate Reference Electrode Fluoride Salts (FLiNaK + 1 wt% AgF, MnF2, or NiF2)

This paper investigates the long-term stability of Ag/AgF, Mn/MnF2, and Ni/NiF2 redox couples for use in reference electrodes (REs) for molten fluoride salt systems such as molten salt reactors. A quasi-RE system was used with FLiNaK + 1 wt% AgF, MnF2, or NiF2, to evaluate the stability of various metals that may be used as the reference electrode body, reference internal element, or membrane for a molten fluoride salt RE design. Cyclic voltammetry was used to measure changes in the electrochemical response of different metal wires in the melts tested. Salt samples were analyzed for dissolved metal concentrations and oxide concentrations via inductively coupled plasma mass spectroscopy and combustion analysis, respectively. To observe the surface morphology of the electrodes used in the Ag/AgF test, cross-sectional imaging of the electrodes was provided via scanning electron microscopy (SEM). The resulting electrochemical measurements show that a RE constructed using a Mn/MnF2 or Ni/NiF2 redox couple should perform with greater potential stability compared to a Ag/AgF redox couple. The instability of the Ag/AgF redox couple is due to the strong oxidizing property of the AgF salt with metals compared to the MnF2 and NiF2 salts. The SEM results from the Ag/AgF test indicate that Ag metal is corrosion resistant, but having AgF in the salt causes it to be corrosive towards other metals (Ni and W) that are considered relatively corrosion resistant in molten salts.

Exploration of the influence of the quantification method and reference scheme on feedback-related negativity and standardized measurement error of feedback-related negativity amplitudes in a trust game

Various approaches have been taken over the years to quantify event-related potential (ERP) responses and these approaches may vary in their utility connecting empirical research and scientific claims. In this work we compared different quantification methods as well as the influence of three reference methods (linked mastoids, average reference, and current source density) on the resulting ERP amplitude. We use the experimental effects and effect sizes (Cohen's d) to evaluate the different methodological variants and we calculate intraclass correlation coefficients (ICC). In addition, the bootstrapped standard error of the means (SME, Luck et al., 2021), which was recently suggested as a quality criterion for ERP research, is used for this purpose. Our example for an ERP is the feedback-related negativity (FRN) to feedback about trustee behavior in a trust game with participants in the trustor position. We found that the quantification methods concerning the FRN influenced the absolute value of condition effects in the experimental paradigm. Yet, the patterns of effects were detected by all chosen methods, except for the ‘individual difference wave’-based peak window approach. In addition, our findings stress the importance of checking the reference electrodes concerning effects of the experimental conditions. Furthermore, interactions of topographical distribution and reference choice should be considered. Finally, we were able to show that the SME is lower for more datapoints that are given in the quantification period of the FRN, and higher for more negative FRN amplitudes. These biases may lead to divergence of SME and effect size detection. Therefore, if the SME was used to compare different processing choices one should consider controlling for these important aspects of the data and possibly include other quality criteria like effect sizes.

Fabrication of a polishable and reusable triple electrode as a new generation of three-electrode systems for the electrochemical analysis applications through both immersion and drop casting-procedures

An innovative three-electrode system was developed for electrochemical analysis, aiming to overcome the limitations of conventional approaches. The system incorporates a glassy carbon rod as the working electrode, platinum wire as the counter electrode, and silver wire as the quasi-reference electrode that are positioned within an epoxy resin substrate. The advantages of this type of three-electrode system include the possibility of sample analysis in both drop mode and when immersed in the solution, low manufacturing cost, reduction of chemical consumption, no need for special maintenance protocols, no requirement for stand, absence of liquid junction potential (due to the direct contact of the reference electrode with the solution), usability for on-site analysis, and usability for non-aqueous solutions.To check the efficiency of this electrode, cyclic voltammetry technique was used. Also, for direct comparison of PTE with conventional three-electrode system and screen-printed electrode (SPE), current density was used instead of peak current. According to the results, PTE system shows more peak current for the same surface area of the working electrode compared to other systems, which shows the high efficiency of the proposed system for electrochemical analysis. Acetaminophen (ACT) was chosen in order to investigate the ability to measure an analyte with PTE using differential pulse voltammetry (DPV). The linear range was obtained from 29.12 μM to 609.37 μM with a detection limit (LOD) 20.22 μM. Also, PTE was used to measure ACT in tablet as real sample.

Effects of Intraoperative Cochlear Implant Electrode Conditioning on Impedances and Electrically Evoked Compound Action Potentials.

The current study investigates whether, during a Cochlear Implant (CI) surgery, conditioning (i.e. applying short bursts of electrical stimulation) within a saline solution can have positive effects on subsequent intra-operative measurements. We hypothesize that, based on previous research, the impedance values will be reduced, and that the reproducibility of Electrically Evoked Compound Action Potentials (ECAPs) is improved as a result of conditioning. We conditioned half of the electrode contacts, within a saline solution, before CI insertion, using 23 MED-EL implants. Impedance was measured for both the conditioned and non-conditioned groups at five time points. Repeated ECAP recordings were measured and compared between the conditioned and non-conditioned groups. Impedance of the electrode contacts were reduced by 31% after conditioning in saline solution; however, there were no clinically relevant differences after the implantation of the electrode array. The hypothesis that measurement reproducibility would be increased after conditioning could not be confirmed with our data. Within the saline solution, we observed that 44% of the electrode contacts were covered with air bubbles, which most disappeared after implantation. However, these air bubbles limited the effectiveness of the conditioning within the saline solution. Lastly, the effect of conditioning on the reference electrode stimulation was approximately 16% of the total reduction in impedance. Our data does not suggest that intraoperative conditioning is clinically required for cochlear implantation with MED-EL implants. Additionally, an in-vivo ECAP recording can be considered as a method of conditioning the electrode contacts. We confirm that the common clinical practice does not need to be changed.

Screen-printed wearable skin surface pH sensor for real-time monitoring of the buffering capacity of human skin.

This study demonstrated for the first time that skin surface pH can be monitored in real-time, using a screen-printed wearable pH sensor, to evaluate the buffering capacity of the human skin. The screen-printed pH sensor was composed of a polyaniline-based pH-sensitive electrode and a nitrocellulose membrane-based liquid junction type of Ag/AgCl reference electrode. This sensor showed a reliable and reversible potentiometric response to pH with long-term potential stability. Intermittent monitoring of the buffering capacity of skin surface pH demonstrated the reliability of the proposed wearable pH sensor, which was comparable to that of a commercially available flat-tip pH sensor. We found that contact of the wearable pH sensor with the subject's skin via aqueous electrolyte solutions was necessary for the sensor to continuously monitor the skin surface pH while sustaining the natural buffer capacity of the human skin surface.

Nonenzymatic Sensor Based on Polythiophene/Titanium Dioxide (PTh/TiO2) Composite for the Determination of Malathion in Water

This study presents a novel nonenzymatic pesticide sensor utilizing a polythiophene/TiO2 (PTh/TiO2) film deposited on a glassy carbon (GC) electrode as the working electrode. The thiophene monomer was polymerized onto TiO2 by cyclic voltammetric method in the range of 0.0-2.5 V with 15 cycles at room temperature. The prepared electrode was used for the sensitive and selective detection of malathion thus providing the basis for facile electrochemical quantification. The surface morphology and crystal structure of the (PTh/TiO2) film were studied by SEM and XRD. FTIR was used for the structural analysis of (PTh/TiO2) film. FTIR results indicated that the PTh/TiO2composite structure was formed. The smooth surface morphology of PTh/TiO2 was supported by SEM results. XRD analysis verified that PTh is covered on TiO2 particles. The crystal phase of TiO2 was changed to amorph state after PTh modification. Additionally, the electrochemical characterization of polymer film and its response to malathion was examined by the CV method. Under optimized operational conditions, the response of the pesticide sensor was measured by CV in the range of -1 to 2.3 V versus the Ag/AgCl reference electrode due to the electrooxidation of malathion. The analysis focused on current values at -0.73 V, where the reduction of the PTh/TiO2 system occurred upon the addition of known amounts of malathion. The PTh/TiO2 composite film was sensitive to malathion in a linear range from 9.9 ppm to 436 ppm. The sensitivity was calculated as 57.5 μA/ µM cm2 whereas the detection limit was calculated as 7.45 µM. The maximum reaction rate was estimated as 767 μA. The developed sensor also showed good selectivity and reproducibility. The nonenzymatic pesticide sensor was successfully applied to detect malathion in tap water with at least 90% recovery.

Catalyzing Battery Materials Research via Lab‐Made, Sub‐Ampere‐Hour‐Scale Pouch Cells, and Long‐Term Electrochemical Monitoring by a Reparable Reference Electrode

AbstractBattery materials research is of crucial importance to the development of next‐generation batteries. However, the transition from lab‐scale studies, typically in gram quantities, to industrially relevant ones (i.e., kilogram scale) has been holding back by challenges in scale‐up synthesis and a lack of reliable approaches to verify the electrochemical performance of the lab‐made materials. Here the design and assembly procedures of sub‐Ah‐scale pouch cells that provide validations of several lab‐made Li‐ion and Na‐ion cathode materials available in a limited quantity (<5 g) are reported. These lab‐made pouch cells show superior cycle stability and consistency over the widely used coin cells, exemplified by multiple Ni‐rich layered oxide‐graphite full batteries retaining 84.29 ± 0.16% of the initial capacities over 1000 cycles. A four‐electrode pouch cell with a reparable reference electrode is further designed to monitor impedance growth and Li plating during long‐term electrochemical tests. It can be further integrated with in situ ultrasonic imaging to enable multi‐modal studies. This work provides a powerful platform to evaluate and boost the technology readiness levels of laboratory‐discovered battery materials.

Microporous Ag/AgCl on a Titanium Scaffold for Use in Capillary Reference Electrodes.

AgCl-coated silver fabricated with the thermal-electrolytic method can be used to prepare more reproducible reference electrodes than Ag/AgCl prepared with alternative methods such as electrolytic and chemical AgCl deposition or thermal fabrication. However, thermal-electrolytic fabrication requires a scaffold material upon which to build the layers upon. Platinum and rhodium have been used for this purpose as they are mechanically strong and chemically inert, but their cost is prohibitive for wider application. Herein, we report the stability of Ag/AgCl reference electrodes built atop a titanium scaffold using the thermal-electrolytic method and the use of these Ti/Ag/AgCl constructs in capillary-based reference electrodes. Electrochemical characterization shows that the probable presence of small amounts of oxygen at the Ti/Ag interface does not affect the reference electrode performance; in particular, over a wide pH range, the half-cell potential is pH independent. The electrical resistance of the Ti/Ag/AgCl/KCl system is dominated by the charge transfer resistance at the interface of the AgCl to KCl solution but is kept very small by the large AgCl surface area and a high solution concentration of chloride. The resulting high exchange current minimizes the effect of system impurities on the reference half-cell potential. Capillary-based reference electrodes comprising Ti/Ag/AgCl show exceptionally low potential drifts (as low as 0.03 ± 2.01 μV/h) and standard deviations of the potential at or below ±0.5 mV over a 60 h period. These capillary-based reference electrodes are suitable for very small sample volumes while still providing a free-flowing liquid junction that prevents reference electrode contamination.

Investigation of the Effects of Different H2SO4, HCI, HNO3 and HCIO4 Liquid Acid Media on the Synthesis of CdTe Semiconductor Thin Films for Solar Cells

The main target of the present paper is to investigate the effect of different acidic aqueous media(DAAM) on the synthesis of cadmium telluride thin films(CdTeTFm). The synthesis of CdTeTFm was carried out by the electrochemical deposition method(EDM) in DAAM. The chronoamperometry method of electrodeposition(ED) was used for the production of CdTeTFm. Furthermore, the electrochemical behaviors of the solutions were studied using cyclic voltammetry. The experiments were carried out with 3 electrodes (a working electrode (WE), a reference electrode(CE), and a counter electrode(RE)) using the electrochemical cell potentiostatic method. The experimental conditions of the acidic aqueous CdTe solution have been determined to be pH 3.56-3.57, the temperature of the solution is 85°C, the concentration of CdTe 2.45x10-1 M, and the reaction time is 25 minutes. The physical properties of CdTeTFm were determined by XRD, SEM/EDX, FT-IR, and UV-VIS analysis methods. According to the results of the analysis, it was observed that acidic aqueous media have an important role in the synthesis of CdTeTFm. The bandgap ranges and Cd/Te ratios of the synthesized thin films were obtained as 1.42, 1.48, 1.50, 1.58 eV, 0.65, 0.587, 0.79 and 0.738, respectively.

Refining microbial potentiometric sensor performance with unique cathodic catalytic properties for targeted application scenarios

Traditional microbial electrochemical sensors encounter challenges due to their inherent complexity. In response to these challenges, the microbial potentiometric sensor (MPS) technology was introduced, featuring a straightforward high-impedance measurement circuit tailored for environmental monitoring. Nonetheless, the practical implementation of conventional MPS is constrained by issues such as the exposure of the reference electrode to the monitored water and the absence of methodologies to stimulate microbial metabolism. In this study, our objective was to enhance MPS performance by imbuing it with unique cathodic catalytic properties, specifically tailored for distinct application scenarios. Notably, the anodic region served as the sensing element, with both the cathodic region and reference electrode physically isolated from the analyzed water sample. In the realm of organic monitoring, the sensor without Pt/C coated in the cathodic region exhibited a faster response time (1 h) and lower detection limits (1 mg L−1 BOD, 1 mM acetic acid). Conversely, when monitoring toxic substances, the sensor with Pt/C showcased a lower detection limit (0.004% formaldehyde), while the Pt/C-free sensor demonstrated superior reusability. The sensor with Pt/C displayed a heightened anode biofilm thickness and coverage, predominantly composed of Rhodococcus. In conclusion, this study introduces simple, cost-effective, and tailorable biosensors holding substantial promise for water quality monitoring.

Electrode Montage for Bilateral Cervical Vestibular Evoked Myogenic Potential (cVEMP) Testing.

Cervical vestibular evoked myogenic potentials (cVEMPs) are predominantly ipsilateral, myogenic responses originating from saccular activation. Some individuals have contralateral-crossed cVEMP responses with monaural air-conducted stimulation (ACS) which can contaminate cVEMP responses with bilateral stimulation. While the origin of the contralateral-crossed response is under debate, its presence has implications for cVEMP testing with midline bone conduction vibration (BCV). The purpose of this study was to determine the origin of the contralateral-crossed cVEMP response. It was hypothesized that the crossed response is due to electrode contamination and would disappear with a modified electrode montage. Cross-sectional research study. Fifteen healthy participants (30 ears; mean age: 27.4 19-39; 10 females). Participants completed cVEMP testing using three stimulation methods (monoaural ACS, binaural ACS, and midline BCV) and two electrode montages (sternum reference and Fp reference). In the monoaural ACS with sternum reference condition, 53.3% ears had contralateral-crossed cVEMP responses that were in-phase with the ipsilateral response for all but 3 ears. Whereas in the monoaural ACS with Fp reference condition, 3% had a contralateral-crossed cVEMP response. ACS and BCV cVEMP corrected amplitudes were significantly larger in the sternum reference conditions, which is attributed to artificial enhancement from the in-phase contralateral-crossed responses. The significant reduction of contralateral-crossed responses in the Fp reference condition suggests that the contralateral-crossed cVEMP response is due to reference electrode contamination and may be a more appropriate reference placement when completing cVEMPs with midline BCV. The purpose of this study was to determine the origin of the contralateral-crossed cVEMP response. It was hypothesized that the crossed response is due to electrode contamination and would disappear with a modified electrode montage. Cross-sectional research study. Fifteen healthy participants (30 ears; mean age: 27.4 19-39; 10 females). Participants completed cVEMP testing using three stimulation methods (monoaural ACS, binaural ACS, and midline BCV) and three electrode montages (sternum reference, Fp reference, and active on Fp). In the monoaural ACS with sternum reference condition, 53.3% ears had contralateral-crossed cVEMP responses that were in-phase with the ipsilateral response for all but 3 ears. Whereas in the monoaural ACS with Fp reference condition, 3% had a contralateral-crossed cVEMP response. No participants demonstrated responses using Fp for the active electrode suggesting this is a neutral site. ACS and BCV cVEMP corrected amplitudes were significantly larger in the sternum reference conditions, which is attributed to artificial enhancement from the in-phase contralateral-crossed responses. The significant reduction of contralateral-crossed responses in the Fp reference condition suggests that the contralateral-crossed cVEMP response is due to reference electrode contamination and may be a more appropriate reference placement when completing cVEMPs with midline BCV.

Graphene Electrode for Studying CO2 Electroreduction Nanocatalysts under Realistic Conditions in Microcells.

The ability to resolve the dynamic evolution of electrocatalytically induced processes with electrochemical liquid-phase electron microscopy (EM)is limited by the microcell configuration. Herein, a free-standing tri-layer graphene is integrated as a membrane and electrode material into the electrochemical chip and its suitability as a substrate electrode at the high cathodic potentials required for CO2 electroreduction (CO2ER) is evaluated. The three-layer stacked graphene is transferred onto an in-house fabricated single-working electrode chip for use with bulk-like reference and counter electrodes to facilitate evaluation of its effectiveness. Electrochemical measurements show that the graphene working electrode exhibits a wider inert cathodic potential range than the conventional glassy carbon electrode while achieving good charge transfer properties for nanocatalytic redox reactions. Operando scanning electron microscopy studies clearly demonstrate the improvement in spatial resolution but reveal a synergistic effect of the electron beam and the applied potential that limits the stability time window of the graphene-based electrochemical chip. By optimizing the operating conditions, in situ monitoring of Cu nanocube degradation is achieved at the CO2ER potential of -1.1V versus RHE. Thus, this improved microcell configuration allows EM observation of catalytic processes at potentials relevant to real systems.

Simultaneous detection of SARS-CoV-2 S1 protein by using flexible electrochemical and Raman enhancing biochip

Flexible laser-scribed graphene (LSG) substrates with gold nanoislands have been developed as biochips for in situ electrochemical (EC) and surface-enhanced Raman scattering (SERS) biodetection (biomolecules and viral proteins). A flexible biochip was fabricated using CO2 laser engraving polyimide (PI) films to form a 3D porous graphene-like nanostructure. Gold nanoislands were deposited on the LSG substrates to enhance the intensity of the Raman signals. Moreover, the addition of auxiliary and reference electrodes induced a dual-function EC-SERS biochip with significantly enhanced detection sensitivity. The biochip could selectively and easily capture SARS-CoV-2 S1 protein through the SARS-CoV-2 S1 antibody immobilized on EC-SERS substrates using 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The grafted antibody specifically bound to SARS-CoV-2, resulting in a significant increase in the SERS signal of the target analyte. The limit of detection (LOD) of the SARS-CoV-2 S1 protein was 5 and 100 ng/mL by using EC and SERS detection, respectively. Although the LOD of the SARS-CoV-2 S1 protein detected using SERS is only 100 ng/mL, it can provide fingerprint information for identification. To improve the LOD, EC detection was integrated with SERS detection. The three-electrode detection chip enables the simultaneous detection of SERS and EC signals, which provides complementary information for target identification. The dual-functional detection technology demonstrated in this study has great potential for biomedical applications, such as the rapid and sensitive detection of SARS-CoV-2.

Temperature-driven path dependence in Li-ion battery cyclic aging

Operation temperature is known to be one of the most impacting parameters for aging of Li-ion batteries under cycling conditions. While Li plating usually dominates aging at low temperatures, Solid-Electrolyte-Interphase (SEI) growth often dominates aging at elevated temperatures. The longest cycle life for Li-ion batteries is observed at the crossover temperature of both aging mechanisms at around 25 °C. We introduce aging color maps to show changes in the aging rate during battery aging. Reconstructed 3-electrode full cells with Li reference electrode show that the prolonged CV phase during charging at low temperatures counteracts Li plating by an increasing anode potential. Thirty-six temperature variations during cycling between 0 °C and 45 °C were studied to investigate the temperature path dependence of battery aging. The permutability of aging temperatures is analyzed by means of commutators. It turns out that aging at elevated temperatures is only slightly affected by previous aging processes and aging at lower temperatures with Li plating accelerates itself. Previous high temperature cycling decelerates Li plating and shifts its onset to lower temperatures, leading to a new and improved optimum cycling temperature of 20 °C. Differential voltage analysis and Post-Mortem analysis were performed to identify the underlying aging mechanisms.

An electroplated Ag/AgCl quasi-reference electrode based on CMOS top-metal for electrochemical sensing

The integration and mass-production of reference electrodes for CMOS-based electrochemical sensing systems pose a challenge for the accessibility and commercial-viability of such devices. In this paper, a method of electroplating an Ag/AgCl quasi-reference electrode using CMOS top-metal as a base is presented for the first time. The aluminium bond-pad of a CMOS microchip was zincated, an electroless nickel immersion gold layer applied, and a thick silver layer electroplated and chemically chlorinated. The resulting reference electrode was able to provide a stable potential with a drift rate of 0.3mV/h for up to 18h. This validates the approach of a fully electroplated bond-pad reference electrode, which offers simplified post-processing and greater scalability of production. Further work towards an entirely electroless process is envisaged.

Preparation of PVDF/PVP blend polymer nanofiber films and application on screen-printed flexible electrodes

The preparation of three electrodes (working electrode, counter electrode, reference electrode) on soft, deformable, and breathable film substrates with good adhesion is a novel approach for the development of wearable devices for plants. In this study, the adsorption energy of carbon paste, graphite, and a polymer was calculated via molecular dynamics simulations, and the optimal polymer ratio was selected for the preparation of nanofiber films. Electrospinning technology was used to prepare a breathable ultrathin polymer film, which was used as a flexible substrate for three electrodes, and a conductive carbon paste was patterned on the nanofiber film substrate by screen printing. The properties of the composite nanofiber membrane substrate and flexible screen-printing electrode were studied by scanning electron microscopy (SEM), infrared (IR) spectroscopy, X-ray diffraction (XRD), 3D profile scanning, and electrochemical experiments. The combination of electrospinning technology and screen-printing technology is a new path for the preparation of nondestructive and wearable detection devices.

Demonstrating the Analytical Potential of a Wearable Microneedle-Based Device for Intradermal CO2 Detection.

Monitoring of carbon dioxide (CO2) body levels is crucial under several clinical conditions (e.g., human intensive care and acid-base disorders). To date, painful and risky arterial blood punctures have been performed to obtain discrete CO2 measurements needed in clinical setups. Although noninvasive alternatives have been proposed to assess CO2, these are currently limited to benchtop devices, requiring trained personnel, being tedious, and providing punctual information, among other disadvantages. To the best of our knowledge, the literature and market lack a wearable device for real-time, on-body monitoring of CO2. Accordingly, we have developed a microneedle (MN)-based sensor array, labeled as CO2-MN, comprising a combination of potentiometric pH- and carbonate (CO32-)-selective electrodes together with the reference electrode. The CO2-MN is built on an epidermal patch that allows it to reach the stratum corneum of the skin, measuring pH and CO32- concentrations directly into the interstitial fluid (ISF). The levels for the pH-CO32- tandem are then used to estimate the PCO2 in the ISF. Assessing the response of each individual MN, we found adequate response time (t95 < 5s), sensitivity (50.4 and -24.6 mV dec-1 for pH and CO32-, respectively), and stability (1.6 mV h-1 for pH and 2.1 mV h-1 for CO32-). We validated the intradermal measurements of CO2 at the ex vivo level, using pieces of rat skin, and then, with in vivo assays in anesthetized rats, showing the suitability of the CO2-MN wearable device for on-body measurements. A good correlation between ISF and blood CO2 concentrations was observed, demonstrating the high potential of the developed MN sensing technology as an alternative to blood-based analysis in the near future. Moreover, these results open new horizons in the noninvasive, real-time monitoring of CO2 as well as other clinically relevant gases.

Understanding the different effects of fouling mechanisms on working and reference electrodes in fast-scan cyclic voltammetry for neurotransmitter detection.

Fast-scan cyclic voltammetry (FSCV) is a widely used technique for detecting neurotransmitters. However, electrode fouling can negatively impact its accuracy and sensitivity. Fouling refers to the accumulation of unwanted materials on the electrode surface, which can alter its electrochemical properties and reduce its sensitivity and selectivity. Fouling mechanisms can be broad and may include biofouling, the accumulation of biomolecules on the electrode surface, and chemical fouling, the deposition of unwanted chemical species. Despite individual studies discussing fouling effects on either the working electrode or the reference electrode, no comprehensive study has been conducted to compare the overall fouling effects on both electrodes in the context of FSCV. Here, we examined the effects of biofouling and chemical fouling on the carbon fiber micro-electrode (CFME) as the working electrode and the Ag/AgCl reference electrode with FSCV. Both fouling mechanisms significantly decreased the sensitivity and caused peak voltage shifts in the FSCV signal with the CFME, but not with the Ag/AgCl reference electrode. Interestingly, previous studies have reported peak voltage shifts in FSCV signals due to the fouling of Ag/AgCl electrodes after implantation in the brain. We noticed in a previous study that energy-dispersive spectroscopy (EDS) spectra showed increased sulfide ion concentration after implantation. We hypothesized that sulfide ions may be responsible for the peak voltage shift. To test this hypothesis, we added sulfide ions to the buffer solution, which decreased the open circuit potential of the Ag/AgCl electrode and caused a peak voltage shift in the FSCV voltammograms. Also, EDS analysis showed that sulfide ion concentration increased on the surface of the Ag/AgCl electrodes after 3 weeks of chronic implantation, necessitating consideration of sulfide ions as the fouling agent for the reference electrodes. Overall, our study provides important insights into the mechanisms of electrode fouling and its impact on FSCV measurements. These findings could inform the design of FSCV experiments, with the development of new strategies for improving the accuracy and reliability of FSCV measurements in vivo.

A Corundum Membrane Ni/Ni2+ Reference Electrode for High-Temperature Fluoride Molten Salt

Molten salts are widely employed as attractive electrolytes in electrolytic refining, extraction and separation of spent fuel, and electrochemical formation of metals and its alloys, etc. However, the high temperature and strong corrosiveness of fluorine molten salt make it difficult to select and establish a stable and reliable reference electrode. To meet this challenge, a new reference electrode for fluorine molten salt was conveniently fabricated by sealing the Ni/Ni2+(NiF2) couple in a commercial corundum tube whose closed end was ground into a membrane (ca. 0.1 mm in thickness) as ion membrane to facilitate ion conduction. The performances of Ni/NiF2 reference electrode were determined by various electrochemical techniques. The results showed that the Ni/NiF2 reference electrode had a good stability tested by CV for 50 h, and the deviation of the potential was 10 mV. The potential deviation of the Ni/NiF2 electrode prepared after different fabricated times and multiple cooling and melting could be controlled within 5 mV, which showed that Ni/NiF2 had a good reproducibility. Furthermore, Ni/NiF2 exhibited a good temperature reversibility and reusability. These findings indicated that the prepared Ni/NiF2 electrode could be a suitable reference electrode for fluoride molten salt.

Rapid and sensitive electrochemiluminescence detection using easily fabricated sensor with an integrated two-electrode system.

The electrochemiluminescence (ECL) behavior of a tri(2,2'-bipyridyl)ruthenium(ii) (Ru(bpy)32+)/tripropylamine (TPrA) system was investigated in sensor chips with two kinds of integrated two-electrode systems, which included screen-printed electrodes (SPE) and physical vapor deposition (PVD) electrodes. Firstly, under excitation with an optimal transient potential (TP) within 100 ms, the ECL assay could be carried out on the microchips using an Au & Au electrode system, emitting strong and stable light signal. Secondly, on the PVD chip, the ECL intensity initiated by optimal TP was eight times stronger than the peak light signal emitted by the linear sweep voltammetry model. Finally, the logarithmic ECL intensities exhibited a linear increase with the logarithmic concentrations of Ru(bpy)32+ in both the SPE and PVD chips without any reference electrode (RE). Typically, the integration of an interdigital two-electrode system in the microchip significantly enhanced the ECL sensitivity of Ru(bpy)32+ because the large relative area between the working electrode (WE) and counter electrode (CE) achieved a highly efficient mass transfer. This improvement enabled the establishment of a reliable linear relationship across a wide concentration range, spanning from 1 pM to 1 μM (R2 = 0.998). Therefore, the exceptional ECL response of the Ru(bpy)32+/TPrA system on microfluidic chips using a two-electrode system and the TP excitation model has been demonstrated. This suggests that ECL chips without a RE have broad potential for the rapid and sensitive detection of multiple targets.