Single Microelectrode Research Articles

New Long-Term Use Solid Bismuth Microelectrode Arrays for Rapid and Sensitive Determination of Sunset Yellow in Isotonic Beverages and Water Samples by Adsorptive Stripping Voltammetry.

This article reports on the long-term use, solid bismuth microelectrode arrays for the first time. The presented working microelectrode is characterized by particular advantages compared to bismuth film electrodes and solid single bismuth microelectrodes; these advantages include environmentally friendly properties and the amplification of recorded currents, which are subsequently more resistant to interference. The proposed solid bismuth microelectrode array was applied to develop an adsorptive stripping voltammetric procedure for Sunset Yellow determination. The main experimental parameters were optimized. The calibration graph was linear from 5 × 10-9 to 1 × 10-7 mol L-1 (time of accumulation, 60 s). The detection limit was equal to 1.7 × 10-9 mol L-1. The relative standard deviation for a concentration of Sunset Yellow of 2 × 10-8 mol L-1 was 4.1% (n = 7). Potential interference effects were examined. The presented analytical procedure was applied for the determination of Sunset Yellow in isotonic beverages and the results were confirmed by HPLC as a comparative method. The correctness of the presented procedure was also confirmed by satisfactory recovery values obtained during the analysis of spiked environmental water samples.

Engineering an in vitro retinothalamic nerve model.

Understanding the retinogeniculate pathway in vitro can offer insights into its development and potential for future therapeutic applications. This study presents a Polydimethylsiloxane-based two-chamber system with axon guidance channels, designed to replicate unidirectional retinogeniculate signal transmission in vitro. Using embryonic rat retinas, we developed a model where retinal spheroids innervate thalamic targets through up to 6 mm long microfluidic channels. Using a combination of electrical stimulation and functional calcium imaging we assessed how channel length and electrical stimulation frequency affects thalamic target response. In the presented model we integrated up to 20 identical functional retinothalamic neural networks aligned on a single transparent microelectrode array, enhancing the robustness and quality of recorded functional data. We found that network integrity depends on channel length, with 0.5-2 mm channels maintaining over 90% morphological and 50% functional integrity. A reduced network integrity was recorded in longer channels. The results indicate a notable reduction in forward spike propagation in channels longer than 4 mm. Additionally, spike conduction fidelity decreased with increasing channel length. Yet, stimulation-induced thalamic target activity remained unaffected by channel length. Finally, the study found that a sustained thalamic calcium response could be elicited with stimulation frequencies up to 31 Hz, with higher frequencies leading to transient responses. In conclusion, this study presents a high-throughput platform that demonstrates how channel length affects retina to brain network formation and signal transmission in vitro.

Improved circuitry and post-processing for interleaved fast-scan cyclic voltammetry and electrophysiology measurements.

The combination of electrophysiology and electrochemistry acquisition methods using a single carbon fiber microelectrode (CFM) in the brain has enabled more extensive analysis of neurochemical release, neural activity, and animal behavior. Predominantly, analog CMOS (Complementary Metal Oxide Semiconductor) switches are used for these interleaved applications to alternate the CFM output between electrophysiology and electrochemistry acquisition circuitry. However, one underlying issue with analog CMOS switches is the introduction of transient voltage artifacts in recorded electrophysiology signals resulting from CMOS charge injection. These injected artifacts attenuate electrophysiology data and delay reliable signal observation after every switch actuation from electrochemistry acquisition. Previously published attempts at interleaved electrophysiology and electrochemistry were able to recover reliable electrophysiology data within approximately 10-50 ms after switch actuation by employing various high-pass filtering methods to mitigate the observed voltage artifacts. However, high-pass filtering of this nature also attenuates valuable portions of the local-field potential (LFP) frequency range, thus limiting the extent of network-level insights that can be derived from in vivo measurements. This paper proposes a solution to overcome the limitation of charge injection artifacts that affect electrophysiological data while preserving important lower-frequency LFP bands. A voltage follower operational amplifier was integrated before the CMOS switch to increase current flow to the switch and dissipate any injected charge. This hardware addition resulted in a 16.98% decrease in electrophysiology acquisition delay compared to circuitry without a voltage follower. Additionally, single-term exponential modeling was implemented in post-processing to characterize and subtract remaining transient voltage artifacts in recorded electrophysiology data. As a result, electrophysiology data was reliably recovered 3.26 ± 0.22 ms after the beginning of the acquisition period (a 60% decrease from previous studies), while also minimizing LFP attenuation. Through these advancements, coupled electrophysiology and electrochemistry measurements can be conducted at higher scan rates while retaining data integrity for a more comprehensive analysis of neural activity and neurochemical release.

A nanoporous diamond particle microelectrode and its surface modification

Boron doped diamond electrode (BDDE) with dimensions of tens of or hundreds of μm has received widespread attention for electrochemical and biological applications because of exceptional features such as wide potential window for water stability, excellent electrochemical/chemical stability, and superior antifouling properties. This work reported a feasible way to fabricate a single nanoporous BDD particle microelectrode (sDPME) using a commercial single-crystal BDD particle (cBDD) as the substrate. The nanoporous surface of cBDD (pcBDD) was formed via thermal catalytic treatment with nickel as the catalyst, followed by further electrodeposition of gold nanoparticles (Au NPs) to fill the nanopores, increasing its electrocatalytic performance. As a comparison, the heavily-doped polycrystalline BDD film was deposited on cBDD via hot-filament chemical vapor deposition, increasing its electrical surface conductivity, followed by the similar thermal etching to form the nanoporous surface (prBDD) as well as Au NPs modification. We gradually characterized surface modification of cBDD using scanning electron microscopy, Raman, energy dispersive spectroscopy and various electrochemical techniques. The results demonstrated that among six sDPMEs, the Au NPs-modified nanoporous sDPMEs (Au/prBDD) have one order of magnitude higher heterogeneous electron transfer kinetic constant than the cBDD. This difference was attributed to synergistic effects of the improved electrical conductivity (with a higher doping level of few 1020 cm−3 versus 1018 cm−3), the improved capability for electron transfer (with lower charge transfer resistance of 1.3 kΩ versus 8.6 kΩ) as well as the increased electrochemically active surface area (1.12 mm2 versus 0.34 mm2).

Dual-Channel Electrochemical Measurements Reveal Rapid Adenosine is Localized in Brain Slices.

Rapid adenosine signaling has been detected spontaneously or after mechanical stimulation in the brain, providing rapid neuromodulation in a local area. To measure rapid adenosine signaling, a single carbon-fiber microelectrode has traditionally been used, which limits spatial resolution and an understanding of regional coordination. In this study, we utilized dual-channel fast-scan cyclic voltammetry to measure the spontaneous or mechanically stimulated adenosine release at two electrodes placed at different spacings in hippocampal CA1 mouse brain slices. For mechanically stimulated adenosine release, adenosine can be detected up to 150 μm away from where it was stimulated, although the signal is smaller and delayed. While spontaneous adenosine transients were detected at both electrodes, only 10 percent of the events were detected concurrently, and that number was similar at 50 and 200 μm electrode spacings. Thus, most adenosine transients were not caused by the widespread coordination of release. There was no evidence of diffusion of spontaneous transients to a second electrode 50-200 μm away. This study shows that spontaneous adenosine events are very localized and thus provide only local neuromodulation. Injury, such as mechanical stimulation, allows adenosine to diffuse farther, but the neuroprotective effects are still regional. These results provide a better understanding of the spatial and temporal profiles of adenosine available to act at receptors, which is crucial for future studies that design neuroprotective treatments based on rapid adenosine signaling.

Effects of tACS-Like Electrical Stimulation on Off- and On-Off Center Retinal Ganglion Cells: Part II.

PurposeTranscranial alternating current stimulation (tACS) is used as a brain stimulation mechanism to enhance learning, ameliorate some psychiatric disorders, and modify behavior. This study assessed the effects of near threshold tACS-like currents on Off-center and On-Off retinal ganglion cell responsiveness in the rabbit retina eyecup preparation as a model for central nervous system effects.Materials and MethodsWe made extracellular recordings in the isolated rabbit eyecup preparation using single electrodes and microelectrode arrays to measure light-evoked spike responses in different classes of Off-center and On-Off retinal ganglion cells before, during, and after brief applications of alternating currents of 1–2 microamperes, at frequencies of 10, 20, 30, and 40 Hz.ResultstACS application sculpted the light-evoked response profiles without directly driving spiking activity of the 20 Off-center and On-Off ganglion cells we recorded from. During tACS application, Off responses were significantly enhanced for 6 cells and significantly suppressed for 14 cells, but after tACS application, Off responses were significantly enhanced for 7 cells and suppressed for 12 cells. The Off responses of the remaining two cells returned to baseline. On responses were less affected during and after tACS.ConclusiontACS sculpts Off-center and On-Off retinal ganglion cell responsiveness. The dissimilarity of effects in different cells within the same class and the differential effects on the On and Off components of the light response within the same cell are consistent with the hypothesis that tACS acts at threshold on amacrine cells in the inner plexiform layer.

Solvent dielectric effect on electrochemical properties of 3,4-propylenedioxythiophene

The present study is focused on the electrochemical properties of poly(3,4-propylene­dioxy­thiophene) (Poly(ProDOT)), electrocoated on the single carbon-fiber microelectrode (SCFME) in different electrolytic media, with different solvent dielectric constants (35.9, 41.7, 47.5, 53.3, 59.1 and 64.9). The highest deposition charge density of 24.49 mC cm-2 and the highest specific capacitance of 23.17 mF cm-2 were obtained for Poly(ProDOT) synthesized in a medium with the lowest solvent dielectric constant (e = 35.9). Electrochemical impedance spectroscopy (EIS) results of Poly(ProDOT) coated SCFME measured at open circuit potential showed continuously increased impedance magnitudes as ε was increased from 35.9 to 59.1. For all films, almost capacitive impedance responses at lower frequencies at least were obtained. The highest capacitance was observed for the polymer film synthesized in the medium of e = 35.9. The impedance of this film was also measured in different solvent mixtures with different dielectric constants at open circuit potential.

The role of oxygen-permeable ionomer for polymer electrolyte fuel cells

In recent years, considerable research and development efforts are devoted to improving the performance of polymer electrolyte fuel cells. However, the power density and catalytic activities of these energy conversion devices are still far from being satisfactory for large-scale operation. Here we report performance enhancement via incorporation, in the cathode catalyst layers, of a ring-structured backbone matrix into ionomers. Electrochemical characterizations of single cells and microelectrodes reveal that high power density is obtained using an ionomer with high oxygen solubility. The high solubility allows oxygen to permeate the ionomer/catalyst interface and react with protons and electrons on the catalyst surfaces. Furthermore, characterizations of single cells and single-crystal surfaces reveal that the oxygen reduction reaction activity is enhanced owing to the mitigation of catalyst poisoning by sulfonate anion groups. Molecular dynamics simulations indicate that both the high permeation and poisoning mitigation are due to the suppression of densely layered folding of polymer backbones near the catalyst surfaces by the incorporated ring-structured matrix. These experimental and theoretical observations demonstrate that ionomer’s tailored molecular design promotes local oxygen transport and catalytic reactions.

Effects of tACS-Like Electrical Stimulation on On-Center Retinal Ganglion Cells: Part I.

PurposeElectrical stimulation of the human central nervous system via surface electrodes has been used for both learning enhancement and the amelioration of neurodegenerative or psychiatric disorders. However, data are sparse on how such electrical stimulation affects neural circuits at the cellular level. This study assessed the effects of tACS-like currents at 10 Hz on On-center retinal ganglion cell responsiveness, using the rabbit retina eyecup preparation as a model for central nervous system effects.MethodsWe made extracellular recordings of light-evoked spike responses in different classes of On-center retinal ganglion cells before, during and after brief applications of 1 microampere alternating currents using single electrodes and microelectrode arrays.ResultstACS-like currents (tACS) of 1 microampere produced effects on On-center ganglion cell response profiles immediately after initiation or cessation of tACS, without driving phase-locked firing in the absence of light stimuli. tACS affected the initial transient responses to light stimulation for all cells, sustained response components (if any) more strongly for sustained cells, and the center-surround balance more strongly for transient cells.ConclusiontACS sculpted light-evoked responses that lasted for one or more hours after cessation of current without, itself, directly inducing significant firing changes. Functionally, tACS effects could result in effects on contrast thresholds for both broad classes of cells, but because tACs differentially affects the center-surround balance of transient On-center cells, there may be greater effects on the spatial resolution and gain. The isolated retina appears to be a useful model to understand tACS actions at the neuronal level.

Flow-sensory contact electrification of graphene

All-electronic interrogation of biofluid flow velocity by electrical nanosensors incorporated in ultra-low-power or self-sustained systems offers the promise of enabling multifarious emerging research and applications. However, existing nano-based electrical flow sensing technologies remain lacking in precision and stability and are typically only applicable to simple aqueous solutions or liquid/gas dual-phase mixtures, making them unsuitable for monitoring low-flow (~micrometer/second) yet important characteristics of continuous biofluids (such as hemorheological behaviors in microcirculation). Here, we show that monolayer-graphene single microelectrodes harvesting charge from continuous aqueous flow provide an effective flow sensing strategy that delivers key performance metrics orders of magnitude higher than other electrical approaches. In particular, over six-months stability and sub-micrometer/second resolution in real-time quantification of whole-blood flows with multiscale amplitude-temporal characteristics are obtained in a microfluidic chip.

Fabrication of a Novel, Cost-Effective Double-Sided Indium Tin Oxide-Based Nanoribbon Electrode and Its Application of Acute Toxicity Detection in Water.

Microelectrode plays a crucial role in developing a rapid biosensor for detecting toxicity in water. In this study, a nanoribbon electrode (NRE) with amplified microelectrode signal was successfully prepared by electrodepositing 2-allylphenol on a double-sided indium tin oxide glass. The NRE provided a simple mean for obtaining large steady-state current response. Its advantages were discussed by contrasting the toxicity detection of 3,5-dichlorophenol (DCP) with single microelectrode, microelectrode array, and millimeter electrode as working electrodes in which potassium ferricyanide (K3[Fe(CN)6]) was adopted as a mediator, and Escherichia coli was selected as bioreceptor. At a constant potential of 450 mV, the current reached a steady state within 10 s. The biosensor was constructed using the NRE as working electrode, and its feasibility was verified by determining the toxicity of DCP. A 50% inhibitory concentration (IC50) of 3.01 mg/L was obtained by analyzing the current responses of different concentrations of DCP within 1 h. These results exhibited that the proposed method based on the as-prepared NRE was a rapid, sensitive, and cost-effective way for toxicity detection in water.

Fused deposition modeling (FDM) based 3D printing of microelectrodes and multi-electrode probes

Electrode fabrication is one of the basic practices for electrochemists. Especially, microelectrodes are generally known as “hand-made” and their fabrication is often like an art. In this work, we report a new protocol for fabricating microelectrodes and multi-electrode probes based on recently matured 3D Fused Deposition Modeling (FDM) printing technique. The general concept is to print half of the insulating body in PETG, insert the (etched) metal or carbon wire(s) in the channel(s), and resume printing to complete the whole electrode. The printed electrodes are then sealed by heating and mechanically polished before use. The process requires only low-cost non-specialized facilities that can be easily equipped even in teaching laboratories. Single microelectrodes of Pt, C, Au, Ag, W and Cu with diameter below 5 µm are fabricated and examined by cyclic voltammetry and scanning electron microscopy. Furthermore, a multi-electrode probe consisting of W, Cu, Ag (oxidized to Ag/AgCl) and Pt is also printed and demonstrated for pH (potentiometric) and H2O2 (amperometric) sensing applications.

Cover Feature: Determination of Rate Constants and Reaction Orders of Vanadium‐Ion Kinetics on Carbon Fiber Electrodes. (ChemElectroChem 21/2020)

The Cover Feature shows a 3D microscopic image of a single carbon fiber microelectrode. The fibers are obtained from carbon felt materials, which are commonly used as electrodes in vanadium redox flow batteries. As the porous structure makes detailed investigations of the vanadium ion kinetics difficult, studies on single fiber electrodes can contribute to a better understanding of the electrode processes. More information can be found in the Article by I. Kroner et al.

Decoding of Oxygen Network Distortion in a Layered High-Rate Anode by In Situ Investigation of a Single Microelectrode.

Sluggish conversion reactions severely impair the rate capability for lithium storage, which is the main disadvantage of the conversion-type anode materials. Here, the microplatform based on a single microelectrode is designed and utilized for the fundamental understanding of the conversion reaction. The kinetic-favorable layered structure of the anode material is on-site synthesized in the microplatform. The in situ characterization reveals that introducing an oxygen network distortion in the layered oxide anode effectively circumvents the severe passivation of the electrode material by lithium oxide, thus leading to highly reversible conversion reactions. As a result, the high-rate capability of the conversion-type anode materials is realized. The on-site synthesis strategy is further applied in the large-scale synthesis of nanomaterials for lithium-ion batteries. As such, oxide nanorods with the layered structure are synthesized by a facile chemical strategy, showing high rate performance (574 mAh g-1 at 10 A g-1). This work unveils the beneficial effect of oxygen network distortion in the layered anode for conversion reactions over cycling, thus providing an alternative strategy to enhance the rate capability of conversion-type anodes for lithium storage.

Focused Ion Beam Lithography to Etch Nano-architectures into Microelectrodes.

With advances in electronics and fabrication technology, intracortical microelectrodes have undergone substantial improvements enabling the production of sophisticated microelectrodes with greater resolution and expanded capabilities. The progress in fabrication technology has supported the development of biomimetic electrodes, which aim to seamlessly integrate into the brain parenchyma, reduce the neuroinflammatory response observed after electrode insertion and improve the quality and longevity of electrophysiological recordings. Here we describe a protocol to employ a biomimetic approach recently classified as nano-architecture. The use of focused ion beam lithography (FIB) was utilized in this protocol to etch specific nano-architecture features into the surface of non-functional and functional single shank intracortical microelectrodes. Etching nano-architectures into the electrode surface indicated possible improvements of biocompatibility and functionality of the implanted device. One of the benefits of using FIB is the ability to etch on manufactured devices, as opposed to during the fabrication of the device, facilitating boundless possibilities to modify numerous medical devices post-manufacturing. The protocol presented herein can be optimized for various material types, nano-architecture features, and types of devices. Augmenting the surface of implanted medical devices can improve the device performance and integration into the tissue.

Precise Targeting of Single Microelectrodes to Orientation Pinwheel Centers.

In the mammalian visual system, early stages of visual form perception begin with orientation selective neurons in primary visual cortex (V1). In many species (including humans, monkeys, tree shrews, cats, and ferrets), these neurons are organized in pinwheel-like orientation columns. To study the functional organization within orientation pinwheels, it is important to target pinwheel subdomains precisely. We therefore developed a technique to provide a quantitative determination of the location of pinwheel centers (PCs). Previous studies relied solely on blood vessel images of the cortical surface to guide electrode penetrations to PCs in orientation maps. However, considerable spatial error remained using this method. In the present study, we improved the accuracy of targeting PCs by ensuring perpendicularity of electrodes and by utilizing the orientation tuning of local field potentials (LFP) recorded at or near the optically determined positions.

Neuronal spiking in the pedunculopontine nucleus in progressive supranuclear palsy and in idiopathic Parkinson's disease.

The pedunculopontine nucleus (PPN) is engaged in posture and gait control, and neuronal degeneration in the PPN has been associated with Parkinsonian disorders. Clinical outcomes of deep brain stimulation of the PPN in idiopathic Parkinson's disease (IPD) and progressive supranuclear palsy (PSP) differ, and we investigated whether the PPN is differentially affected in these conditions. We had the rare opportunity to record continuous electrophysiological data intraoperatively in 30s blocks from single microelectrode contacts implanted in the PPN in six PSP patients and three IPD patients during rest, passive movement, and active movement. Neuronal spikes were sorted according to shape using a wavelet-based clustering approach to enable comparisons between individual neuronal firing rates in the two disease states. The action potential widths showed a bimodal distribution consistent with previous findings, suggesting spikes from noncholinergic (likely glutamatergic) and cholinergic neurons. A higher PPN spiking rate of narrow action potentials was observed in the PSP than in the IPD patients when pooled across all three conditions (Wilcoxon rank sum test: p = 0.0141). No correlation was found between firing rate and disease severity or duration. The firing rates were higher during passive movement than rest and active movement in both groups, but the differences between conditions were not significant. PSP and IPD are believed to represent distinct disease processes, and our findings that the neuronal firing rates differ according to disease state support the proposal that pathological processes directly involving the PPN may be more pronounced in PSP than IPD.

A model-based approach for targeted neurophysiology in the behaving non-human primate.

Acute neurophysiology in the behaving primate typically relies on traditional manufacturing approaches for the instrumentation necessary for recording. For example, our previous approach consisted of distributing single microelectrodes in a fixed plane situated over a circular patch of frontal cortex using conventionally-milled recording grids. With the advent of robust, multisite linear probes, and the introduction of commercially-available, high-resolution rapid prototyping systems, we have been able to improve upon traditional approaches. Here, we report our methodology for producing flexible, MR-informed recording platforms that allow us to precisely target brain structures of interest, including those that would be unreachable using previous methods. We have increased our single-session recording yields by an order of magnitude and recorded neural activity from widely-distributed regions using only a single recording chamber. This approach both speeds data collection, reduces the damage done to neural tissue over the course of a single experiment, and reduces the number of surgical procedures experienced by the animal.

Volitional control of single-electrode high gamma local field potentials by people with paralysis

Intracortical brain-computer interfaces (BCIs) can enable individuals to control effectors, such as a computer cursor, by directly decoding the user's movement intentions from action potentials and local field potentials (LFPs) recorded within the motor cortex. However, the accuracy and complexity of effector control achieved with such "biomimetic" BCIs will depend on the degree to which the intended movements used to elicit control modulate the neural activity. In particular, channels that do not record distinguishable action potentials and only record LFP modulations may be of limited use for BCI control. In contrast, a biofeedback approach may surpass these limitations by letting the participants generate new control signals and learn strategies that improve the volitional control of signals used for effector control. Here, we show that, by using a biofeedback paradigm, three individuals with tetraplegia achieved volitional control of gamma LFPs (40-400 Hz) recorded by a single microelectrode implanted in the precentral gyrus. Control was improved over a pair of consecutive sessions up to 3 days apart. In all but one session, the channel used to achieve control lacked distinguishable action potentials. Our results indicate that biofeedback LFP-based BCIs may potentially contribute to the neural modulation necessary to obtain reliable and useful control of effectors. NEW & NOTEWORTHY Our study demonstrates that people with tetraplegia can volitionally control individual high-gamma local-field potential (LFP) channels recorded from the motor cortex, and that this control can be improved using biofeedback. Motor cortical LFP signals are thought to be both informative and stable intracortical signals and, thus, of importance for future brain-computer interfaces.

Fabrication and evaluation of nanostructured microelectrodes for high-spatial resolution in retinal prostheses

To provide visual information to patients with retinal degenerative disease, retinal prosthetic devices based on multi-channel microelectrode arrays (MEAs) have shown some promising results. For high-quality information, the number of microelectrodes should be increased in the limited area of MEAs, which results in decreased dimensions of the single microelectrode and a limit of dynamic range of injection current. Previously, our research group has presented 3D microelectrodes to overcome the trade-off between high-spatial resolution and injection current range. However, the 3D microelectrode requires a complex fabrication process, including multiple steps in front-side and back-side microfabrication. In this paper, the nanostructured microelectrode with platinum-black is fabricated with a simple process, and its electrical characteristics are evaluated. The nanostructured microelectrode parameters are analyzed by a conventional three-element circuit model. The comprehensive electrical characteristics between planar 2D, 3D, and nanostructured microelectrodes with various base areas are compared by measuring electrode–electrolyte interface impedance and maximum allowable injection current limit. The experimental results show improved interface impedance in nanostructured microelectrodes compared to planar 2D and 3D microelectrodes with same base area. This implies that nanostructured microelectrodes have a large dynamic range for current stimulation, which can be more sufficient in retinal neuron stimulation. This research can be used to estimate the theoretical limit of injection current for high-resolution MEAs.