Microwire Electrodes Research Articles

Real-time monitoring of cellular superoxide anion release in THP-1 cells using a catalytically amplified superoxide dismutase-based microbiosensor.

Reactive oxygen species (ROS) including the superoxide anion (O2•-) are typically studied in cell cultures using fluorescent dyes, which provide only discrete single-point measurements. These methods lack the capabilities for assessing O2•- kinetics and release in a quantitative manner over long monitoring times. Herein, we present the fabrication and application of an electrochemical biosensor that enables real-time continuous monitoring of O2•- release in cell cultures for extended periods (> 8h) using an O2•- specific microelectrode. To achieve the sensitivity and selectivity requirements for cellular sensing, we developed a biohybrid system consisting of superoxide dismutase (SOD) and Ti3C2Tx MXenes, deposited on a gold microwire electrode (AuME) as O2•- specific materials with catalytic amplification through the synergistic action of the enzyme and the biomimetic MXenes-based structure. The biosensor demonstrated a sensitivity of 18.35 nA/μM with a linear range from 147 to 930nM in a cell culture medium. To demonstrate its robustness and practicality, we applied the biosensor to monitor O2•- levels in human leukemia monocytic THP-1 cells upon stimulation with lipopolysaccharide (LPS). Using this strategy, we successfully monitored LPS-induced O2•- in THP-1 cells, as well as the quenching effect induced by the ROS scavenger N-acetyl-L-cysteine (NAC). The biosensor is generally useful for exploring the role of oxidative stress and longitudinally monitoring O2•- release in cell cultures, enabling studies of biochemical processes and associated oxidative stress mechanisms in cellular and other biological environments.

The Surgical Method of Craniectomy Differentially Affects Acute Seizures, Brain Deformation and Behavior in a TBI Animal Model.

Traumatic brain injury (TBI) is the leading cause of morbidity and mortality worldwide. Multiple injury models have been developed to study this neurological disorder. One such model is the lateral fluid-percussion injury (LFPI) rodent model. The LFPI model can be generated with different surgical procedures that could affect the injury and be reflected in neurobehavioral dysfunction and acute EEG changes. A craniectomy was performed either with a trephine hand drill or with a trephine electric drill that was centered over the left hemisphere of adult, male Sprague Dawley rats. Sham craniectomy groups were assessed by hand-drilled (ShamHMRI) and electric-drilled (ShamEMRI) to evaluate by MRI. Then, TBI was induced in separate groups (TBIH) and (TBIE) using a fluid-percussion device. Sham-injured rats (ShamH/ShamE) underwent the same surgical procedures as the TBI rats. During the same surgery session, rats were implanted with screw and microwire electrodes positioned in the neocortex and hippocampus and the EEG activity was recorded 24 hours for the first 7 days after TBI for assessing the acute EEG seizure and Gamma Event Coupling (GEC). The electric drilling craniectomy induced greater tissue damage and sensorimotor deficits compared to the hand drill. Analysis of the EEG revealed acute seizures in at least one animal from each group after the procedure. Both TBI and Sham rats from the electric drill groups had a significant greater total number of seizures than the animals that were craniectomized manually (p<0.05). Similarly, EEG functional connectivity was lower in ShamE compared to ShamH rats. These results suggest that electrical versus hand drilling craniectomies produce cortical injury in addition to the LFPI which increases the likelihood for acute post-traumatic seizures. Differences in the surgical approach could be one reason for the variability in the injury that makes it difficult to replicate results between preclinical TBI studies.

Electrochemical high sensitive detection of hydrogen peroxide based on platinum-palladium nano-enzyme modified microelectrode

Hydrogen peroxide (H2O2) is widely distributed in living organisms and the environment, and its concentration is closely associated with human health. Therefore, the development of an efficient and sensitive detection method for H2O2 is imperative. In this study, a PtPd nano-enzyme composite was electrodeposited onto a platinum wire microelectrode (ME) using a one-step electrochemical deposition method to fabricate an H2O2 electrochemical sensor (PtPd/ME) with exceptional performance. The successful modification of PtPd on the electrode surface was confirmed by scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). Chronoamperometry (i-t) was employed to investigate various technical parameters including sensitivity, detection limit, detection range, reproducibility, and anti-interference capability. The results demonstrate that the sensor exhibits a sensitivity of 11.94 mA M-1 cm-2 with a detection limit of 0.034 μM and a wide linear range from 31.25 μM to 4.15 mM while also demonstrating excellent anti-interference properties. These superior performances can be attributed to the strong catalytic activity towards H2O2 provided by PtPd nanoparticles as well as the fast electron transfer rate facilitated by microelectrodes. Furthermore, this sensor effectively enables real-time monitoring of H2O2 released by ascorbic acid-stimulated vascular endothelial cells and demonstrates its potential for detecting H2O2 in contact lens care solutions. These findings provide valuable insights for food and drug testing, and demonstrate great potential for monitoring key pathological processes within living cells.

The Surgical Method of Craniectomy Differentially Affects Acute Seizures, Brain Deformation, and Behavior in a Traumatic Brain Injury Animal Model.

Traumatic brain injury (TBI) is the leading cause of morbidity and mortality worldwide. Multiple injury models have been developed to study this neurological disorder. One such model is the lateral fluid percussion injury (LFPI) rodent model. The LFPI model can be generated with different surgical procedures that could affect the injury and be reflected in neurobehavioral dysfunction and acute electroencephalograph (EEG) changes. A craniectomy was performed either with a trephine hand drill or with a trephine electric drill that was centered over the left hemisphere of adult, male Sprague Dawley rats. Sham craniectomy groups were assessed by hand-drilled (ShamHMRI) and electric-drilled (ShamEMRI) to evaluate by magnetic resonance imaging (MRI). Then, TBI was induced in separate groups, (TBIH) and (TBIE), using a fluid-percussion device. Sham-injured rats (ShamH/ShamE) underwent the same surgical procedures as the TBI rats. During the same surgery session, rats were implanted with screw and microwire electrodes positioned in the neocortex and hippocampus and the EEG activity was recorded 24 h for the first 7 days after TBI for assessing the acute EEG seizure and gamma event coupling. The electric drilling craniectomy induced greater tissue damage and sensorimotor deficits compared with the hand drill. Analysis of the EEG revealed acute seizures in at least one animal from each group after the procedure. Both TBI and Sham rats from the electric drill groups had a significant greater total number of seizures than the animals that were craniectomized manually (p < 0.05). Similarly, EEG functional connectivity was lower in ShamE compared with ShamH rats. These results suggest that electrical versus hand-drilling craniectomies produce cortical injury in addition to the LFPI which increases the likelihood for acute post-traumatic seizures. Differences in the surgical approach could be one reason for the variability in the injury that makes it difficult to replicate results between preclinical TBI studies.

Use of 3D printing to integrate microchip electrophoresis with amperometric detection.

This paper describes the use of PolyJet 3D printing to fabricate microchip electrophoresis devices with integrated microwire electrodes for amperometric detection. The fabrication process involves 3D printing of two separate pieces, a channel layer and an electrode layer. The channel layer is created by 3D printing on a pre-fabricated mold with a T-intersection. For the electrode layer, a stencil design is printed directly on the printing tray and covered with a piece of transparent glass. Microwire electrodes are adhered over the glass piece (guided by underlaying stencil) and a CAD design of the electrode layer is then printed on top of the microwire electrode. After delamination from the glass after printing, the microwire is embedded in the printed piece, with the stencil design ensuring that alignment and positioning of the electrode is reproducible for each print. After a thermal bonding step between the channel layer and electrode layer, a complete electrophoresis device with integrated microelectrodes for amperometric detection results. It is shown that this approach enables different microwire electrodes (gold or platinum) and sizes (100 or 50µm) to be integrated in an end-channel configuration with no gap between the electrode and the separation channel. These devices were used to separate a mixture of catecholamines and the effect of separation voltage on the potential voltage applied on the working electrode was also investigated. In addition, the effect of electrode size on the number of theoretical plates and limit of detection was studied. Finally, a device that contains different channel heights and a detection electrode was 3D-printed to integrate continuous flow sampling with microchip electrophoresis and amperometric detection.

On-Chip Micro-Supercapacitor with High Areal Energy Density Based on Dielectrophoretic Assembly of Nanoporous Metal Microwire Electrodes.

Advances in the Internet of Things (IoT) technology have driven the demand for miniaturized electronic devices, prompting research on small-scale energy-storage systems. Micro-supercapacitors (MSCs) stand out in this regard because of their compact size, high power density, high charge-discharge rate, and extended cycle life. However, their limited energy density impedes commercialization. To resolve this issue, a simple and innovative approach is reported herein for fabricating highly efficient on-chip MSCs integrated with nanoporous metal microwires formed by dielectrophoresis (DEP)-driven gold nanoparticle (AuNP) assembly. Placing a water-based AuNP suspension onto interdigitated electrodes and applying an alternating voltage induces in-plane porous microwire formation in the electrode gap. The DEP-induced AuNP assembly and the gold microwire (AuMW) growth rate can be adjusted by controlling the applied alternating voltage and frequency. The microwire-integrated MSC (AuMW-MSC) electrically outperforms its unmodified counterpart and exhibits a 30% larger electrode area, along with 72% and 78% higher specific and areal capacitances, respectively, than a microwire-free MSC. Additionally, AuMW-MSC achieves maximum energy and power densities of 3.33 µWh cm-2 and 2629 µW cm-2, respectively, with a gel electrolyte. These findings can help upgrade MSCs to function as potent energy-storage devices for small electronics.

Improving Fast Ripples Recording with Model-Guided Design of Microelectrodes.

Microelectrodes allow for the recording of neural activities with a high spatial resolution. However, their small sizes result in high impedance causing high thermal noise and poor signal-to-noise ratio. In drug-resistant epilepsy, the accurate detection of Fast Ripples (FRs; 250-600 Hz) can help in the identification of epileptogenic networks and Seizure Onset Zone (SOZ). Consequently, good-quality recordings are instrumental to improve surgical outcome. In this work, we propose a novel model-based approach for the design of microelectrodes optimized for FRs recording. A 3D microscale computational model was developed to simulate FRs generated in the hippocampus (CA1 subfield). It was coupled with a model of the Electrode-Tissue Interface (ETI) that accounts for the biophysical properties of the intracortical microelectrode. This hybrid model was used to analyze the microelectrode geometrical (diameter, position, and direction) and physical (materials, coating) characteristics and their impact on recorded FRs. For model validation, experimental signals (local field potentials, LFPs) were recorded from CA1 using different electrode materials: stainless steel (SS), gold (Au) and Au coated with poly(3,4-ethylene dioxythiophene) /Poly(styrene sulfonate) (Au:PEDOT/PSS). results indicated that a radius between 65 and 120 μm for a wire microelectrode is the most optimal for recording FRs. In addition, in silico and in vivo quantified results showed a possible improvement in FRs observability using PEDOT/PSS coated microelectrodes. the optimization of the design of microelectrodes for FRs recording can improve the observability and detectability of FRs which are a recognized marker of epileptogenicity. This model-based approach can assist in the design of hybrid electrodes (micro, macro) that can be used in the presurgical evaluation of epileptic patients with drug-resistant epilepsy.

Design of adhesive conducting PEDOT-MeOH:PSS/PDA neural interface via electropolymerization for ultrasmall implantable neural microelectrodes

Conducting polymers are emerging as promising neural interfaces towards diverse applications such as deep brain stimulation due to their superior biocompatibility, electrical, and mechanical properties. However, existing conducting polymer-based neural interfaces still suffer from several challenges and limitations such as complex preparation procedures, weak interfacial adhesion, poor long-term fidelity and stability, and expensive microfabrication, significantly hindering their broad practical applications and marketization. Herein, we develop an adhesive and long-term stable conducting polymer neural interface by a simple two-step electropolymerization methodology, namely, the pre-polymerization of polydopamine (PDA) as an adhesive thin layer followed by electropolymerization of hydroxymethylated 3,4-ethylenedioxythiophene (EDOT-MeOH) with polystyrene sulfonate (PSS) to form stable interpenetrating PEDOT-MeOH:PSS/PDA networks. As-prepared PEDOT-MeOH:PSS/PDA interface exhibits remarkably improved interfacial adhesion against metallic electrodes, showing 93% area retention against vigorous sonication for 20 min, which is one of the best tenacious conducting polymer interfaces so far. Enabled by the simple methodology, we can facilely fabricate the PEDOT-MeOH:PSS/PDA interface onto ultrasmall Pt-Ir wire microelectrodes (diameter: 10 μm). The modified microelectrodes display two orders of magnitude lower impedance than commercial products, and also superior long-term stability to previous reports with high charge injection capacity retention up to 99.5% upon 10,000,000 biphasic input pulse cycles. With these findings, such a simple methodology, together with the fabricated high-performance and stable neural interface, can potentially provide a powerful tool for both advanced neuroscience researches and cutting-edge clinical applications like brain-controlled intelligence.

Laser-Microfabricated Polymer Multielectrodes for Intraspinal Microstimulation.

The overall goal of this study was to design, fabricate, and characterize a new polymer-based multielectrode for the spinal cord for the application of intraspinal microstimulation (ISMS). Three-channel multielectrodes were fabricated from modified poly(dimethylsiloxane) (PDMS) and platinum-iridium (Pt-Ir) foil using nanosecond laser microfabrication techniques. These devices were compared against traditional 50 μm diameter Pt-Ir microwire electrodes mechanically and electrochemically in bench environments, and were assessed electrochemically and functionally in vivo in a domestic pig model. Polymer-based multielectrodes were significantly more flexible than microwire electrodes (p < 0.05) and had greater charge storage capacities in phosphate buffered saline (p < 0.05). In a domestic pig model, multielectrodes had significantly greater charge injection limits than microwire electrodes (p < 0.05). When stimulating within the quadriceps motor pool in the spinal cord, multielectrodes generated strong knee extensor joint torques of up to 4.4 ± 0.3 Nm and were able to extend the knee by up to 26 ± 1°. However, histological analyses showed that polymer-based multielectrodes, implanted with half-needle insertion aids, produced greater acute tissue damage compared to microwire electrodes (p < 0.05). Alternative insertion methods for these flexible electrodes should be explored to reduce acute tissue damage. The PDMS-based three-channel multielectrodes demonstrated improved flexibility and charge injection capabilities over traditional microwire electrodes, and were able to produce functional responses in vivo. Polymer-based multielectrodes demonstrate improved functionality over microwire electrodes while remaining more flexible than silicon multielectrode designs. These features may in the future permit polymer-based multielectrodes to implement ISMS with greater efficacy and biocompatibility compared to traditional technologies.

Oscillations support short latency co-firing of neurons during human episodic memory formation.

Theta and gamma oscillations in the medial temporal lobe are suggested to play a critical role for human memory formation via establishing synchrony in neural assemblies. Arguably, such synchrony facilitates efficient information transfer between neurons and enhances synaptic plasticity, both of which benefit episodic memory formation. However, to date little evidence exists from humans that would provide direct evidence for such a specific role of theta and gamma oscillations for episodic memory formation. Here, we investigate how oscillations shape the temporal structure of neural firing during memory formation in the medial temporal lobe. We measured neural firing and local field potentials in human epilepsy patients via micro-wire electrode recordings to analyze whether brain oscillations are related to co-incidences of firing between neurons during successful and unsuccessful encoding of episodic memories. The results show that phase-coupling of neurons to faster theta and gamma oscillations correlates with co-firing at short latencies (~20-30 ms) and occurs during successful memory formation. Phase-coupling at slower oscillations in these same frequency bands, in contrast, correlates with longer co-firing latencies and occurs during memory failure. Thus, our findings suggest that neural oscillations play a role for the synchronization of neural firing in the medial temporal lobe during the encoding of episodic memories.

Spatial Transcriptomics as a Novel Approach to Redefine Electrical Stimulation Safety.

Current standards for safe delivery of electrical stimulation to the central nervous system are based on foundational studies which examined post-mortem tissue for histological signs of damage. This set of observations and the subsequently proposed limits to safe stimulation, termed the “Shannon limits,” allow for a simple calculation (using charge per phase and charge density) to determine the intensity of electrical stimulation that can be delivered safely to brain tissue. In the three decades since the Shannon limits were reported, advances in molecular biology have allowed for more nuanced and detailed approaches to be used to expand current understanding of the physiological effects of stimulation. Here, we demonstrate the use of spatial transcriptomics (ST) in an exploratory investigation to assess the biological response to electrical stimulation in the brain. Electrical stimulation was delivered to the rat visual cortex with either acute or chronic electrode implantation procedures. To explore the influence of device type and stimulation parameters, we used carbon fiber ultramicroelectrode arrays (7 μm diameter) and microwire electrode arrays (50 μm diameter) delivering charge and charge density levels selected above and below reported tissue damage thresholds (range: 2–20 nC, 0.1–1 mC/cm2). Spatial transcriptomics was performed using Visium Spatial Gene Expression Slides (10x Genomics, Pleasanton, CA, United States), which enabled simultaneous immunohistochemistry and ST to directly compare traditional histological metrics to transcriptional profiles within each tissue sample. Our data give a first look at unique spatial patterns of gene expression that are related to cellular processes including inflammation, cell cycle progression, and neuronal plasticity. At the acute timepoint, an increase in inflammatory and plasticity related genes was observed surrounding a stimulating electrode compared to a craniotomy control. At the chronic timepoint, an increase in inflammatory and cell cycle progression related genes was observed both in the stimulating vs. non-stimulating microwire electrode comparison and in the stimulating microwire vs. carbon fiber comparison. Using the spatial aspect of this method as well as the within-sample link to traditional metrics of tissue damage, we demonstrate how these data may be analyzed and used to generate new hypotheses and inform safety standards for stimulation in cortex.

Numerical Simulation and Modeling of Hydrogen Gas Evolution on Planar and Microwire Array Electrodes

The impact of gas evolution on the electrochemical characteristics of planar electrodes and microwire array electrodes has been analyzed using modeling and simulation. The impacts can mainly be broken into three phenomena: a) a shift in the local reversible hydrogen electrode potential; b) hyperpolarization; and c) an increase in the solution resistance of the electrolyte. The local reversible hydrogen electrode potential shift was found to play the most important role, constituting >40% of the total potential drop between the cathode and reference electrode, following correction for cell resistance. Compared to planar electrodes, a microwire array structure reduces the impact of bubbles on the solution conductance, but the shift in the local reversible hydrogen electrode potential varies with distance from the actual electrode surface.

Functional Interactions Between the Parafascicular Thalamic Nucleus and Motor Cortex Are Altered in Hemiparkinsonian Rat.

Parkinson’s disease (PD) is characterized by aberrant discharge patterns and exaggerated oscillatory activity within basal ganglia-thalamocortical circuits. We have previously observed substantial alterations in spike and local field potential (LFP) activities recorded in the thalamic parafascicular nucleus (PF) and motor cortex (M1), respectively, of hemiparkinsonian rats during rest or catching movements. This study explored whether the mutual effects of the PF and M1 depended on the amplitude and phase relationship in their identified neuron spikes or group rhythmic activities. Microwire electrode arrays were paired and implanted in the PF and M1 of rats with unilateral dopaminergic cell lesions. The results showed that the identified PF neurons exhibited aberrant cell type-selective firing rates and preferential and excessive phase-locked firing to cortical LFP oscillations mainly at 12–35 Hz (beta frequencies), consistent with the observation of identified M1 neurons with ongoing PF LFP oscillations. Experimental evidence also showed a decrease in phase-locking at 0.7–12 Hz and 35–70 Hz in the PF and M1 circuits in the hemiparkinsonian rats. Furthermore, anatomical evidence was provided for the existence of afferent and efferent bidirectional reciprocal connectivity pathways between the PF and M1 using an anterograde and retrograde neuroanatomical tracing virus. Collectively, our results suggested that multiple alterations may be present in regional anatomical and functional modes with which the PF and M1 interact, and that parkinsonism-associated changes in PF integrate M1 activity in a manner that varies with frequency, behavioral state, and integrity of the dopaminergic system.

A high-density theta burst paradigm enhances the aftereffects of transcranial magnetic stimulation: Evidence from focal stimulation of rat motor cortex

BackgroundTheta burst stimulation (TBS) is an efficient noninvasive neuromodulation paradigm that has been widely adopted, clinically. However, the efficacy of TBS treatment remains similarly modest as conventional 10 Hz repetitive transcranial magnetic stimulation (rTMS). Objective/hypothesisTo develop a new TBS paradigm that enhances the effects of TMS administration while maintaining high time-efficiency. MethodsWe describe here a new TMS paradigm, named High-Density Theta Burst Stimulation (hdTBS). This paradigm delivers up to 6 pulses per burst, as opposed to only 3 in conventional TBS, while maintaining the inter-burst interval of 200 ms (or 5 Hz) – a critical parameter in inducing long-term potentiation. This paradigm was implemented on a TMS stimulator developed in-house; its physiological effects were assessed in the motor cortex of awake rats using a rodent specific focal TMS coil. Microwire electrodes were implanted into each rat's limb muscles to longitudinally record motor-evoked potential (MEP). Four different TBS paradigms (3, 4, 5 or 6 pulses per burst, 200 s per session) were tested; MEP signals were recorded immediately before (baseline) and up to 35 min post each TBS session. ResultsWe developed a stimulator based on a printed-circuit board strategy. The stimulator was able to deliver stable outputs of up to 6 pulses per burst. Animal experiments (n = 15) revealed significantly different aftereffects induced by the four TBS paradigms (Friedman test, p = 0.018). Post hoc analysis further revealed that, in comparison to conventional 3-pulse TBS, 5- and 6-pulse TBS enhanced the aftereffects of MEP signals by 56% and 92%, respectively, while maintaining identical time efficiency. Conclusion(s)A new stimulation paradigm is proposed, implemented and tested in the motor cortex of awake rats using a focal TMS coil developed in the lab. We observed enhanced aftereffects as assessed by MEP, with no obvious adverse effects, suggesting the translational potentials of this paradigm.

Low-cost and easy-fabrication lightweight drivable electrode array for multiple-regions electrophysiological recording in free-moving mice

Objective. Extracellular electrophysiology has been widely applied to neural circuit dissections. However, long-term multiregional recording in free-moving mice remains a challenge. Low-cost and easy-fabrication of elaborate drivable electrodes is required for their prevalence. Approach. A three-layer nested construct (outside diameter, OD ∼ 1.80 mm, length ∼10 mm, <0.1 g) was recruited as a drivable component, which consisted of an ethylene-vinyl acetate copolymer heat-shrinkable tube, non-closed loop ceramic bushing, and stainless ferrule with a bulge twining silver wire. The supporting and working components were equipped with drivable components to be assembled into a drivable microwire electrode array with a nested structure (drivable MEANS). Two drivable microwire electrode arrays were independently implanted for chronic recording in different brain areas at respective angles. An optic fiber was easily loaded into the drivable MEANS to achieve optogenetic modulation and electrophysiological recording simultaneously. Main results. The drivable MEANS had lightweight (∼0.37 g), small (∼15 mm × 15 mm × 4 mm), and low cost (⩽$64.62). Two drivable MEANS were simultaneously implanted in mice, and high-quality electrophysiological recordings could be applied ⩾5 months after implantation in freely behaving animals. Electrophysiological recordings and analysis of the lateral septum (LS) and lateral hypothalamus in food-seeking behavior demonstrated that our drivable MEANS can be used to dissect the function of neural circuits. An optical fiber-integrated drivable MEANS (∼0.47 g) was used to stimulate and record LS neurons, which suggested that changes in working components can achieve more functions than electrophysiological recordings, such as optical stimulation, drug release, and calcium imaging. Significance. Drivable MEANS is an easily fabricated, lightweight drivable microwire electrode array for multiple-region electrophysiological recording in free-moving mice. Our design is likely to be a valuable platform for both current and prospective users, as well as for developers of multifunctional electrodes for free-moving mice.

A comparative study of microwire electrode array with built-in and external reference electrodes

Objective: To compare the difference between the built-in and external reference electrode of microwire electrode array in the process of recording rat brain neuron firings, optimizing the production and embedding of the microwire electrode array, and providing a more affordable and excellent media tool for multi-channel electrophysiological real-time recording system. Methods: A 16 channel microwire electrode array was made by using nickel chromium alloy wires, circuit board, electrode pin and ground wires (silver wires). The reference electrode of the microwire electrode array was built-in (the reference electrode and electrode array were arranged in parallel) or external (the reference electrode and ground wire were welded at both ends of one side of the electrode), and the difference between the two electrodes was observed and compared in recording neuronal discharges in ACC brain area of rats. Experimental rats were divided into built-in group and external group, n=8-9. The test indicators included signal-to-noise ratio (n=8), discharge amplitude (n=380) and discharge frequency (n=54). Results: The microwire electrode array with both built-in and external reference electrodes successfully recorded the electrical signals of neurons in the ACC brain region of rats. Compared with the external group, the electrical signals of neurons in built-in group had the advantages of a higher signal-to-noise ratio (P＜0.05), a smaller amplitude of background signals and less noise interference, and a larger discharge amplitude(P＜0.05); there was no significant difference in spike discharge frequency recorded by these two types of electrodes (P＞0.05). Conclusion: When recording the electrical activity of neurons in the ACC brain region of rats, the microwire electrode array with built-in reference electrode recorded electrical signals with higher signal-to-noise ratio and larger discharge amplitude, providing a more reliable tool for multi-channel electrophysiology technology.

Electrochemical Study on MgO as an Additive in Molten Li2CO3-Na2CO3 for Molten Carbonate Fuel Cells

This study investigates the effect of MgO as an additive in molten Li2CO3-Na2CO3 electrolyte for molten carbonate fuel cells through electrochemical analyses. Addition of MgO (1∼5 mol%) increased the electrochemical response in cyclic voltammogram of peroxide in molten Li2CO3-Na2CO3. The diffusion coefficient of peroxide in molten Li2CO3-Na2CO3 containing MgO was determined via the comparison between the peak currents of cyclic voltammograms from microwire electrode and macrowire electrode. The addition of MgO did not impact the diffusion coefficient, indicating that the increase in the electrochemical response with the addition of MgO might be attributed to the increase in the peroxide concentration. The change in peroxide concentration was also confirmed by electrochemical impedance analyses, which exhibited a decrease in the charge transfer resistance. The increase in the concentration of peroxide with the addition of MgO might be associated with the high thermal decomposition constant of MgCO3, implying the high concentration of oxide ion in the molten Li2CO3-Na2CO3. This study suggests that MgO might be an effective additive for increasing the oxygen solubility in the molten Li2CO3-Na2CO3, and subsequently for enhancing the performance of molten carbonate fuel cells.

Carbon Nanotube Assemblies for Neuroscience Applications

Assembling carbon nanotubes (CNTs) into macroscopic materials allows multiple applications that takes advantage of their physical properties. Specifically, the synthesis, fiber assembly, polymer coating and application of CNTs as microelectrodes has allowed us explore physiological applications as well as sensor development. This talk will summarize our research in CNT microelectrode development, neural recording and stimulation, and neurotransmitter detection and quantification through voltammetric techniques. Recordings and stimulations of neuronal electrical activity is a topic of great interest in neuroscience. Current commercial electrodes for transferring charges from solid electrode materials to and from biological tissue still have some limitations. A microelectrode that is flexible, chemically inert, electrically conducting, and preferentially transfers electrons via capacitive charge-injection is needed to treat multiple neurological disorders. This talk will compare charge transport capabilities from carbon nanotube fibers, noble metals Au and Ag wire microelectrodes to biological tissue. The recording ability of microelectrodes is demonstrated through Electroretinography (ERG) on Sarcophaga bullata fly eyes, where light stimulation generates potential changes that were detected by our microelectrodes. Stimulation is demonstrated through Au wire and carbon nanotube fiber implants in Madagascar hissing cockroach (Gromphadorhina portentosa) antennas to control their locomotion directions. In addition, CNT microelectrodes has been found to detect neurotransmitters dopamine (DA), serotonin (5-HT), epinephrine (Epn) and nor-epinephrine (Nor-epn) using voltammetric techniques with excellent limits of detection in the range of ~10-11 M. For practical applicability, the electrodes can detect in real time DA release from culture rat pheochromocytoma (PC12) cells upon concentrate K+stimulation.

Determination of diffusion coefficient in high temperature molten salt using cyclic voltammetry on microwire electrode: Its validity and limitation

• A method for the determination of diffusion coefficient ( D ) is developed. • This method is based on cyclic voltammetry at microwire electrode. • This method is useful for D determination in high temperature molten salt. • D values of Eu 3+ in LiCl-KCl melt and O 2 2– in Li 2 CO 3 -Na 2 CO 3 melt are determined. • The validity and limitation of this method is examined by numerical simulations. In this study, we developed a method for the determination of the diffusion coefficient ( D ) of electroactive species in high temperature molten salt without the knowledge of its concentration, via cyclic voltammetry at a simple unshielded microwire electrode. This method is based on the assessment of the ratio of the peak current ( i p ) of the cyclic voltammogram for its electrochemically reversible reaction at the microwire electrode, with i p at the macrowire electrode. The scan rate ( ν )-dependent contribution of radial diffusion to i p at the microwire electrode provides a linear relationship between the i p ratio and ν −0.425 , where its slope includes information on D . The theoretical evaluation with numerical simulation on this method revealed that possible underestimation in D determination could occur because of the minor contribution of radial diffusion at the macrowire electrode used in this study. D determination in the molten salt was experimentally verified with Eu 3+ in 450 °C LiCl-KCl and O 2 2– in 580 °C Li 2 CO 3 -Na 2 CO 3 . For both cases, the determined D values were similar to the reported values, and they were further cross-validated by calculating their concentrations from the D values. However, the accurate determination is limited for electrochemically reversible reaction as D is overestimated for quasi-reversible and totally irreversible reactions.

Novel Composite Gold-Aluminum Electrode with Application to Neural Recording and Stimulation in Ultrahigh Field Magnetic Resonance Imaging Scanners.

Traditional electrodes used for neural recording and stimulation generate large regions of signal void (no functional MRI signal) when used in ultrahigh field (UHF) MRI scanners. This is a significant disadvantage when simultaneous neural recording/stimulation and fMRI signal acquisition is desired, for example in understanding the functional mechanisms of deep brain stimulation (DBS). In this work, a novel gold-aluminum microwire neural electrode is presented which overcomes this disadvantage. The gold-aluminum design greatly reduces the magnetic susceptibility difference between the electrode and brain tissue leading to significantly reduced regions of signal void. Gold-aluminum microwire samples are imaged at ultrahigh field 16.4 Tesla and compared with gold-only and aluminum-only microwire samples. First, B0 field mapping was used to quantify field distortions at 16.4T and compared with analytical computations in an agarose phantom. The gold-aluminum microwire samples generated substantially less field distortion and signal loss in comparison with gold-only and aluminum-only samples at 16.4T using gradient echo imaging and echo planar imaging sequences. Next, the proposed gold-aluminum electrode was used to successfully record local field potential signals from a rat cortex. The newly proposed gold-aluminum microwire electrode exhibits reduced field distortions and signal loss at 16.4T, a finding which translates to MRI scanners of lower magnetic field strengths as well. The design can be easily reproduced for widespread study of DBS using MRI in animal models. Additionally, the use of non-reactive gold and aluminum materials presents an avenue for translation to human implant applications in the future.