Transverse Electrode Research Articles

A General Method To Measure the Hall Effect in Nanowires: Examples of FeS2 and MnSi

We present a general methodology for measuring the Hall effect on nanostructures with one-dimensional (1D) nanowire morphology. Relying only on typical e-beam lithography, the methodology developed herein utilizes an angled electrode evaporation technique so that the nanowire itself is a shadow mask and an intimate sidewall contact can be formed for the Hall electrodes. A six-contact electrode scheme with offset transverse contacts is utilized that allows monitoring of both the longitudinal resistivity and the Hall resistivity which is extracted from the raw voltage from the transverse electrodes using an antisymmetrization procedure. Our method does not require the use of a highly engineered lithographic process to produce directly opposing Hall electrodes with a very small gap. Hall effect measurements on semiconducting iron pyrite (FeS2) nanowire devices are validated by comparing to Hall effect measurements in the conventional Hall geometry using FeS2 plate devices. This Hall effect measurement is further extended to MnSi nanowires, and the distinct anomalous Hall effect signature is identified for the first time in chiral magnetic MnSi nanowires, a significant step toward identifying the topological Hall effect due to skyrmions in chiral magnetic nanowires.

Spatial distribution of surface action potentials generated by individual motor units in the human biceps brachii muscle

This study analyses the spatial distribution of individual motor unit potentials (MUPs) over the skin surface and the influence of motor unit depth and recording configuration on this distribution. Multichannel surface (13×5 electrode grid) and intramuscular (wire electrodes inserted with needles of lengths 15 and 25mm) electromyographic (EMG) signals were concurrently recorded with monopolar derivations from the biceps brachii muscle of 10 healthy subjects during 60-s isometric contractions at 20% of the maximum torque. Multichannel monopolar MUPs of the target motor unit were obtained by spike-triggered averaging of the surface EMG. Amplitude and frequency characteristics of monopolar and bipolar MUPs were calculated for locations along the fibers’ direction (longitudinal), and along the direction perpendicular (transverse) to the fibers. In the longitudinal direction, monopolar and bipolar MUPs exhibited marked amplitude changes that extended for 16–32mm and 16–24mm over the innervation and tendon zones, respectively. The variation of monopolar and bipolar MUP characteristics was not symmetrical about the innervation zone. Motor unit depth had a considerable influence on the relative longitudinal variation of amplitude for monopolar MUPs, but not for bipolar MUPs. The transverse extension of bipolar MUPs ranged between 24 and 32mm, whereas that of monopolar MUPs ranged between 72 and 96mm. The mean power spectral frequency of surface MUPs was highly dependent on the transverse electrode location but not on depth. This study provides a basis for the interpretation of the contribution of individual motor units to the interference surface EMG signal.

Enhancement of electro-optic stability in the vertical configuration of a deformed-helix ferroelectric liquid crystal

We propose a reliable vertical configuration of a deformed-helix ferroelectric liquid crystal (DHFLC) mode in a transverse electrode structure by introducing reactive mesogens (RMs) into the DHFLC material. Polymerized RMs remember the direction of the DHFLC molecules in the absence of an applied voltage and suppress the bending and breaking of the smectic layer under a strong electric field. In this DHFLC mode with polymerized RMs, reliable switching characteristics are obtained in the vertical configuration.

Transverse Interdigitated Electrode Actuation of Homogeneous Bulk PZT

A new method for achieving transverse bending-mode actuation of piezoelectric devices microfabricated from homogeneous layers of bulk lead zirconate titanate (PZT) is presented. The technique, which employs a set of interdigitated electrodes patterned on a single side of the piezoelectric substrate, takes advantage of an engineered electric field gradient within the PZT that can be optimized by selecting an appropriate electrode gap. Bulk PZT cantilevers have been fabricated by micropowder blasting, allowing the actuation technique to be evaluated experimentally and compared against analytical and finite-element-model results. Optimal poling conditions for the microfabricated cantilevers are reported, together with both quasi-static and resonant behaviors of the devices. The transverse interdigitated electrode topology provides a simple method for realizing high-performance bending-mode piezoelectric microactuators from a single homogeneous layer of bulk PZT using a simple two-mask process.

Experimental Validation of a Hybrid Computational Model for Selective Stimulation Using Transverse Intrafascicular Multichannel Electrodes

Recently a hybrid model based on the finite element method and on a compartmental biophysical representation of peripheral nerve fibers and intraneural electrodes was developed founded on experimental physiological and histological data. The model appeared to be robust when dealing with uncertainties in parameter selection. However, an experimental validation of the findings provided by the model is required to fully characterize the potential of this approach. The recruitment properties of selective nerve stimulation using transverse intrafascicular multichannel electrodes (TIME) were investigated in this work in experiments with rats and were compared to model predictions. Animal experiments were performed using the same stimulation protocol as in the computer simulations in order to rigorously validate the model predictions and understand its limitations. Two different selectivity indexes were used, and new indexes for measuring electrode performance are proposed. The model predictions are in decent agreement with experimental results both in terms of recruitment curves and selectivity values. Results show that these models can be used for extensive studies targeting electrode shape design, active sites shape, and multipolar stimulation paradigms. From a neurophysiological point of view, the topographic organization of the rat sciatic nerve, on which the model was based, has been confirmed.

Fabrication and characterization of a solid-state nanopore with self-aligned carbon nanoelectrodes for molecular detection

Stochastic molecular sensors based on resistive pulse nanopore modalities are envisioned as facile DNA sequencers. However, recent advances in nanotechnology fabrication have highlighted promising alternative detection mechanisms with higher sensitivity and potential single-base resolution. In this paper we present the novel self-aligned fabrication of a solid-state nanopore device with integrated transverse graphene-like carbon nanoelectrodes for polyelectrolyte molecular detection. The electrochemical transduction mechanism is characterized and found to result primarily from thermionic emission between the two transverse electrodes. Response of the nanopore to Lambda dsDNA and short (16-mer) ssDNA is demonstrated and distinguished.

Nanopore‐Based DNA Analysis via Graphene Electrodes

We propose an improvement for nanopore‐based DNA analysis via transverse transport using graphene as transverse electrodes. Our simulation results show conspicuous distinction of tunneling current during translocation of different nucleotides through nanopore. Applying the single‐atom thickness property of graphene, our findings demonstrate the feasibility of using graphene as transverse electrodes in future rapid and low‐cost genome sequencing.

New Technique of DNA Sensing: Nanoribbon Transverse Electrodes

The technique of DNA sensing by electrophoretically driving it through solid-state nanopores is promising to reach the goal of rapid sequencing of individual human genomes. This approach can allow for the label-free, amplification-free analysis of nucleic acids as either single stranded DNA or double stranded DNA. Molecules ranging in length from single nucleotides to kilobase-pair can potentially be analyzed with nanometerresolution.However, the standard 2-terminal nanopore sensing method also possesses disadvantages, as the measurement resolution does not allow sensing of individual nucleobases. In order to eliminate this disadvantage, modification of the nanopore sensing technique has been proposed theoretically [1, 2]. We are pursuing the structure of a graphene nanoribbon with an embedded nanopore as a transverse electrode. A unique change of the transverse current for each nucleobase could allow discrimination between different types of nucleotides.The graphene nanoribbons are fabricated on a suspended stacked graphene/dielectric nanocomposite membrane. The stacked membrane was implemented according to the method described recently [3]. The top graphene layer was patterned by e-beam lithography in a 2 μm long x 30 nm wide nanoribbon. We will report on the transport measurements in air and in buffer solution with and without the embedded nanopore within the graphene nanoribbon.[1] T. Nelson, B. Zhang, and O.V. Prezhdo, Nano Lett. 10, 3237 (2010).[2] K.K. Saha, M. Drndic, B.K. Nikolic, arXiv:1108.3801v1 (2011).[3] B. M. Venkatesan, D. Estrada, S. Banerjee, X. Jin, V. E. Dorgan, M.-H. Bae, N. Aluru, E. Pop, and R. Bashir, submitted, (2011).

Development of a neurotechnological system for relieving phantom limb pain using transverse intrafascicular electrodes (TIME)

Phantom limb pain (PLP) is a chronic condition that develops in the majority of amputees. The underlying mechanisms are not completely understood, and thus, no treatment is fully effective. Based on recent studies, we hypothesize that electrical stimulation of afferent nerves might alleviate PLP by giving sensory input to the patient if nerve fibers can be activated selectively. The critical component in this scheme is the implantable electrode structure. We present a review of a novel electrode concept to distribute highly selective electrode contacts over the complete cross section of a peripheral nerve to create a distributed activation of small nerve fiber ensembles at the fascicular level, the transverse intrafascicular multichannel nerve electrode (TIME). The acute and chronic implantations in a small animal model exhibited a good surface and structural biocompatibility as well as excellent selectivity. Implantation studies on large animal models that are closer to human nerve size and anatomical complexity have also been conducted. They proved implant stability and the ability to selectively activate nerve fascicles in a limited proximity to the implant. These encouraging results have opened the way forward for human clinical trials in amputees to investigate the effect of selective electrical stimulation on PLP.

Nanochannel system fabricated by MEMS microfabrication and atomic force microscopy

A silicon nanochannel system with integrated transverse electrodes was designed and fabricated by combining micro-electro-mechanical systems (MEMS) micromachining and atomic force microscopy (AFM)-based nanolithography. The fabrication process began with the patterning of microscale reservoirs and electrodes on an oxidised silicon chip using conventional MEMS techniques. A nanochannel, approximately 30 [micro sign]m long with a small semi-circular cross-sectional area of 20 nm × 200 nm, was then mechanically machined on the oxide surface between the micro reservoirs by applying AFM nanolithography with an all-diamond probe. Anodic bonding was used to seal off the nanochannel with a matching Pyrex cover. Continuous flow in the nanochannel was verified by pressurising a solution of fluorescein isothiocyanate in ethanol through the nanochannel in a vacuum chamber. It was further demonstrated by translocating negatively charged nanobeads (diameter approximately 20 nm) through the nanochannel by using an external DC electric field. The passage of the nanobeads caused a sharp increase in the transverse electrical conductivity of the nanochannel.

Gated electronic currents modulation and designs of logic gates with single molecular field effect transistors

The electronic transport properties of a gated single 1,3-benzenedithiol molecular device are studied by using nonequilibrium Green's function in combination with density functional theory, which is hoped to complement the experiments. The results show that the external transverse gate electrodes can effectively tune the electronic transport properties of the molecular devices. Negative differential resistance behaviors are observed almost at the same source-drain bias when applied different gate voltages. Mechanisms are proposed for these phenomena. Designs of using one gated molecular device to realize five basic logic gates are also put forward.

Giant magnetoresistance in zigzag graphene nanoribbon

Based on the mean-field Hubbard model (J. Guo et al., Appl. Phys. Lett. 92, 163109 (2008)), ballistic spin transport in zigzag graphene nanoribbons is investigated theoretically. A giant magnetoresistance effect is found with 100% change in resistance as the two transverse electrodes switch from the parallel to antiparallel magnetic configuration. Such change is shown to arise from different coupling between the subbands near the Fermi level, which is dependent of the orbital symmetry. In addition, the operating energy window of giant magnetoresistance exists in a wide range of ribbon widths, easing the way for experimental validation of the proposed device.

A Computational Model for the Stimulation of Rat Sciatic Nerve Using a Transverse Intrafascicular Multichannel Electrode

Neuroprostheses based on electrical stimulation could potentially help disabled persons. They are based on neural interface that aim at creating an intimate contact with neural cells. The efficacy of neuroprostheses can be improved by increasing the selectivity of the neural interfaces used to stimulate specific subsets of cells. Selectivity is strongly influenced by interface design. Computer models can be useful for exploring the high dimensional space of design parameters with the aim to provide guidelines for the development of more efficient electrodes, with minimal animal use and optimization of manufacturing processes. The purpose of this study was to implement a realistic model of the performance of a transverse intrafascicular multichannel electrode (TIME) implanted into the rat sciatic nerve. A realistic finite element method (FEM) model was developed taking into account the anatomical and physiological features of the rat sciatic nerve. Electric potentials were calculated and interpolated voltages were applied to the model of a rat sciatic nerve axon, based on experimental biophysical data. Results indicate that high intra-fascicular and inter-fascicular selectivity values with low current levels can be achieved with TIMEs. The selectivity of TIMEs was also compared to an extraneural electrode, showing that higher selectivity with less current can be obtained. Using this model, the robustness of electrode performances for translational and rotational displacements were evaluated.

The Effects of Electrode Size and Orientation on the Sensitivity of Myoelectric Pattern Recognition Systems to Electrode Shift

Myoelectric pattern recognition systems for prosthesis control are often studied in controlled laboratory settings, but obstacles remain to be addressed before they are clinically viable. One important obstacle is the difficulty of maintaining system usability with socket misalignment. Misalignment inevitably occurs during prosthesis donning and doffing, producing a shift in electrode contact locations. We investigated how the size of the electrode detection surface and the placement of electrode poles (electrode orientation) affected system robustness with electrode shift. Electrodes oriented parallel to muscle fibers outperformed electrodes oriented perpendicular to muscle fibers in both shift and no-shift conditions (p < 0.01). Another finding was the significant difference (p < 0.01) in performance for the direction of electrode shift. Shifts perpendicular to the muscle fibers reduced classification accuracy and real-time controllability much more than shifts parallel to the muscle fibers. Increasing the size of the electrode detection surface was found to help reduce classification accuracy sensitivity to electrode shifts in a direction perpendicular to the muscle fibers but did not improve the real-time controllability of the pattern recognition system. One clinically important result was that a combination of longitudinal and transverse electrodes yielded high controllability with and without electrode shift using only four physical electrode pole locations.

Biocompatibility of Chronically Implanted Transverse Intrafascicular Multichannel Electrode (TIME) in the Rat Sciatic Nerve

The transverse intrafascicular multichannel electrode (TIME) is intended to be transversally implanted in the peripheral nerve and to selectively interface subsets of axons in different fascicles within the same nerve. Two versions of TIME (TIME-2, TIME-3) were designed and tested for biocompatibility and safety in the sciatic nerve of the rat. TIME-2 was implanted in two groups: one group had only an acute implant and the second group had chronic implantation for 2 months; a third group was also chronically implanted with the TIME-3 version, designed to avoid the mechanical traction produced by muscles motion. We evaluated the functional and morphological effects of either TIME-2 or TIME-3 implanted in the rat sciatic nerve for 2 months. The results of the study indicate that implantation of the TIME-2 and TIME-3 devices in the rat sciatic nerve did not cause significant axonal loss or demyelination, as evidenced by the functional and histological results. The results of this study indicate that the TIME-2 and TIME-3 designs are biocompatible and safe after chronic implantation in a small peripheral nerve, such as the rat sciatic nerve.

Comparative analysis of transverse intrafascicular multichannel, longitudinal intrafascicular and multipolar cuff electrodes for the selective stimulation of nerve fascicles

The selection of a suitable nerve electrode for neuroprosthetic applications implies a trade-off between invasiveness and selectivity, wherein the ultimate goal is achieving the highest selectivity for a high number of nerve fascicles by the least invasiveness and potential damage to the nerve. The transverse intrafascicular multichannel electrode (TIME) is intended to be transversally inserted into the peripheral nerve and to be useful to selectively activate subsets of axons in different fascicles within the same nerve. We present a comparative study of TIME, LIFE and multipolar cuff electrodes for the selective stimulation of small nerves. The electrodes were implanted on the rat sciatic nerve, and the activation of gastrocnemius, plantar and tibialis anterior muscles was recorded by EMG signals. Thus, the study allowed us to ascertain the selectivity of stimulation at the interfascicular and also at the intrafascicular level. The results of this study indicate that (1) intrafascicular electrodes (LIFE and TIME) provide excitation circumscribed to the implanted fascicle, whereas extraneural electrodes (cuffs) predominantly excite nerve fascicles located superficially; (2) the minimum threshold for muscle activation with TIME and LIFE was significantly lower than with cuff electrodes; (3) TIME allowed us to selectively activate the three tested muscles when stimulating through different active sites of one device, both at inter- and intrafascicular levels, whereas selective activation using multipolar cuff (with a longitudinal tripolar stimulation configuration) was only possible for two muscles, at the interfascicular level, and LIFE did not activate selectively more than one muscle in the implanted nerve fascicle.

Comparative gastric motility study of EnterraTM Therapy and neural gastric electrical stimulation in an acute canine model

Gastric electrical stimulation (GES) is an avenue for treating gastroparesis and obesity by controlling gastric motility using electrically mediated gastric contractions. Neural gastrointestinal electrical stimulation (NGES) is a GES modality capable of producing strong lumen-occluding local gastric contractions. Conversely, Enterra ™ Therapy, a commercial implantable gastric electrical stimulator, has been utilized to treat symptoms of gastroparesis, but its nominal electrical parameters are not capable of generating lumen-occluding contractions. However, comparative studies between these two stimulation modalities are lacking. Strain gauge transducers complemented by endoscopic monitoring have been utilized to register gastric contractions invoked with NGES and Enterra neurostimulators in four acute dogs. Mucosal and serosal electrode implantations, 'nominal' and 'maximum' electrical parameters, and longitudinal and transverse electrode placements have been tested with each neurostimulator type. Strong lumen-occluding, circumferential contractions were induced with a wide variety of NGES parameters utilizing both transverse and longitudinal electrode configurations from the serosal side of the stomach. Similarly, local gastric contractions were observed with the Enterra neurostimulator programmed at its 'maximum' electrical parameters but only when utilizing transverse serosal electrode implantation. Under 'maximum' electrical parameters Enterra was not capable of producing registerable gastric contractions with longitudinally implanted serosal electrodes. Mucosal electrode implantations did not result in GES-invoked gastric contractions in both stimulation modalities. Enterra Therapy is capable of producing gastric contractions under 'maximum' parameters and transverse electrode configuration. Neural gastrointestinal electrical stimulation produces stronger, lumen-occluding contractions under a wider range of electrode configurations and parameters.

Fabrication of nanopores with embedded annular electrodes and transverse carbonnanotube electrodes

Nanopores with one or two embedded nanoelectrodes can be fabricated by highresolution, milling-based methods. We first demonstrate how a focused ion beam,whose sputtering mechanism is well understood, can create a nanopore containingan annular electrode of an arbitrary metal, and with a regular perimeter. Theinner surface of the nanopore can be insulated, and its diameter can be reducedwith nanometer precision, by conformally coating a dielectric material by atomiclayer deposition. We then investigate the mechanism of pore formation using atransmission electron microscope (TEM) through studies of the milling rate, and itsdependence on the flux of electrons and on the atomic number of different targetmetals. Sputtering from the surface is identified as the dominant mechanism.Accordingly, light element conductors should be chosen to enhance the rate andresolution of TEM milling, which we demonstrate by articulating a nanoporewith transverse carbon nanotube electrodes. Finally, we electrochemically verifythat TEM milling preserves the quality of an annular gold electrode throughcyclic voltammetry measurements performed at various stages of the fabrication.

Dipolar cortico-muscular electrical stimulation: a novel method that enhances motor function in both - normal and spinal cord injured mice

BackgroundElectrical stimulation of the central and peripheral nervous systems is a common tool that is used to improve functional recovery after neuronal injury.MethodsHere we described a new configuration of electrical stimulation as it was tested in anesthetized control and spinal cord injury (SCI) mice. Constant voltage output was delivered through two electrodes. While the negative voltage output (ranging from -1.8 to -2.6 V) was delivered to the muscle via transverse wire electrodes (diameter, 500 μm) located at opposite ends of the muscle, the positive output (ranging from + 2.4 to +3.2 V) was delivered to the primary motor cortex (M1) (electrode tip, 100 μm). The configuration was named dipolar cortico-muscular stimulation (dCMS) and consisted of 100 pulses (1 ms pulse duration, 1 Hz frequency).ResultsIn SCI animals, after dCMS, cortically-elicited muscle contraction improved markedly at the contralateral (456%) and ipsilateral (457%) gastrocnemius muscles. The improvement persisted for the duration of the experiment (60 min). The enhancement of cortically-elicited muscle contraction was accompanied by the reduction of M1 maximal threshold and the potentiation of spinal motoneuronal evoked responses at the contralateral (313%) and ipsilateral (292%) sides of the spinal cord. Moreover, spontaneous activity recorded from single spinal motoneurons was substantially increased contralaterally (121%) and ipsilaterally (54%). Interestingly, spinal motoneuronal responses and muscle twitches evoked by the test stimulation of non-treated M1 (received no dCMS) were significantly enhanced as well. Similar results obtained from normal animals albeit the changes were relatively smaller.ConclusionThese findings demonstrated that dCMS could improve functionality of corticomotoneuronal pathway and thus it may have therapeutic potential.

A transverse intrafascicular multichannel electrode (TIME) to interface with the peripheral nerve

Many different concepts of peripheral nerve interfaces have been developed over the past few decades and transferred into neuroscientific or clinical applications with varying degrees of success. In this study, we present a novel electrode design that transversally penetrates the peripheral nerve and is intended to selectively activate subsets of axons in different fascicles within the nerve. The “transverse intrafascicular multichannel electrode” (TIME) has been designed and fabricated using the micromachining and patterning of a polyimide substrate and insulation material and platinum electrode sites. In vitro characterization of the electrodes were carried out to determine the electrochemical transfer characteristics during recording and stimulation. Acute implantations were performed in the sciatic nerves of rats and recruitment curves were determined. Results indicated selective stimulation of different fascicles with graded recruitment. Future studies will address chronic implantation to investigate the reactions on the material-tissue interface and the long-term behavior and recruitment properties of the TIMEs.