Fabricated Microelectrode Arrays Research Articles

Aerosol Jet-Printed High-Aspect Ratio Micro-Needle Electrode Arrays Applied for Human Cerebral Organoids and 3D Neurospheroid Networks.

The human brain is a complex and poorly accessible organ. Thus, new tools are required for studying the neural function in a controllable environment that preserves multicellular interaction and neuronal wiring. In particular, high-throughput methods that alleviate the need for animal experiments are essential for future studies. Recent developments of induced pluripotent stem cell technologies have enabled in vitro modeling of the human brain by creating three-dimensional brain tissue mimic structures. To leverage these new technologies, a systematic and versatile approach for evaluating neuronal activity at larger tissue depths within the regime of tens to hundreds of micrometers is required. Here, we present an aerosol-jet- and inkjet-printing-based method to fabricate microelectrode arrays, equipped with high-aspect ratio μ-needle electrodes that penetrate 3D neural network assemblies. The arrays have been successfully applied for electrophysiological recordings on interconnected neurospheroids formed on an engineered substrate and on cerebral organoids, both derived from human induced pluripotent stem cells.

A flexible implantable microelectrode array for recording electrocorticography signals from rodents.

Electrocorticography signals, the intracranial recording of electrical signatures of the brain, are recorded by non-penetrating planar electrode arrays placed on the cortical surface. Flexible electrode arrays minimize the tissue damage upon implantation. This work shows the design and development of a 32-channel flexible microelectrode array to record electrocorticography signals from the rat's brain. The array was fabricated on a biocompatible flexible polyimide substrate. A titanium/gold layer was patterned as electrodes, and a thin polyimide layer was used for insulation. The fabricated microelectrode array was mounted on the exposed somatosensory cortex of the right hemisphere of a rat after craniotomy and incision of the dura. The signals were recorded using OpenBCI Cyton Daisy Biosensing Boards. The array faithfully recorded the baseline electrocorticography signals, the induced epileptic activities after applying a convulsant, and the recovered baseline signals after applying an antiepileptic drug. The signals recorded by such fabricated microelectrode array from anesthetized rats demonstrate its potential to monitor electrical signatures corresponding to epilepsy. Finally, the time-frequency analyses highlight the difference in spatiotemporal features of baseline and evoked epileptic discharges.

PtNPs/PEDOT:PSS-Modified Microelectrode Arrays Reveal Electrophysiological Activities of Different Neurons in Medial Amygdala of Mice Under Innate Fear.

The medial amygdala (MA) plays an important role in the innate fear circuit. However, the electrophysiological mechanism of MA for processing innate fear needs to be further explored. In this study, we fabricated microelectrode arrays (MEAs) with detecting sites arranged to match the location and shape of MA in mice and detected the electrophysiology in freely behaving mice under 2-methyl-2-thiazoline (2MT)-induced fear. The detection performance of MEA is improved by modifying metal nanoparticles and conductive polymers (PtNPs/PEDOT:PSS). After modification, the impedance magnitude and phase of electrodes were decreased to 27.0 ± 2.3 kΩ and −12.30 ± 0.52°, respectively, leading to a signal-to-noise ratio of 10. Its electrochemical stability and mechanical stability were also verified by cyclic voltammetry (CV) sweeping and ultrasonic vibration. MEAs were then implanted into the MA of mice, and the electrophysiology and behavioral characteristics were synchronously recorded and analyzed. The results showed that 2MT induced strong defensive behaviors in mice, accompanied by increases in the average spike firing rate and local field potential (LFP) power of MA neurons. According to principles commonly applied to cortical extracellular recordings, the recorded neurons are divided into two classes based on waveforms. Statistics showed that about 37% of type 1 neurons (putative GABAergic neurons) and 87% of type 2 neurons (putative glutamatergic neurons) were significantly activated under innate fear. At the same time, the firing rate of some activated neurons had a good linear correlation with the freezing rate.

Single and Multisite Graphene‐Based Electroretinography Recording Electrodes: A Benchmarking Study

AbstractElectroretinography (ERG) is a clinical test employed to understand and diagnose many retinopathies. ERG is usually performed by placing a macroscopic ring gold wire electrode on the cornea while flashing light onto the eye to measure changes in the transretinal potential. However, macroscopic gold electrodes are severely limiting since they do not provide a flexible interface to contact the sensitive corneal tissue, making this technique highly uncomfortable for the patient. Another major drawback is the opacity of gold electrodes, which only allows them to record the ERG signal on the corneal periphery, preventing central ERG recordings. To overcome the limitations of metal‐based macroscopic ERG electrodes, flexible electrodes are fabricated using graphene as a transparent, flexible, and sensitive material. The transparency of the graphene is exploited to fabricate microelectrode arrays (MEAs) that are able to perform multisite recording on the cornea. The graphene‐based ERG electrodes are benchmarked against the widely used gold electrodes in a P23H rat model with photoreceptor degeneration. This study shows that the graphene‐based ERG electrodes can faithfully record ERGs under a wide range of conditions (light intensity, stage of photoreceptor degeneration, etc.) while offering additional benefits for ERG recordings such as transparency and flexibility.

Carbon 3D microelectrode arrays for neuron and brain slice measurements

Carbon 3D microelectrode arrays for neuron and brain slice measurements

Design, Fabrication, Simulation and Characterization of a Novel Dual-Sided Microelectrode Array for Deep Brain Recording and Stimulation.

In this paper, a novel dual-sided microelectrode array is specially designed and fabricated for a rat Parkinson’s disease (PD) model to study the mechanisms of deep brain stimulation (DBS). The fabricated microelectrode array can stimulate the subthalamic nucleus and simultaneously record electrophysiological information from multiple nuclei of the basal ganglia system. The fabricated microelectrode array has a long shaft of 9 mm and each planar surface is equipped with three stimulating sites (diameter of 100 μm), seven electrophysiological recording sites (diameter of 20 μm) and four sites with diameter of 50 μm used for neurotransmitter measurements in future work. The performances of the fabricated microelectrode array were characterized by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. In addition, the stimulating effects of the fabricated microelectrode were evaluated by finite element modeling (FEM). Preliminary animal experiments demonstrated that the designed microelectrode arrays can record spontaneous discharge signals from the striatum, the subthalamic nucleus and the globus pallidus interna. The designed and fabricated microelectrode arrays provide a powerful research tool for studying the mechanisms of DBS in rat PD models.

A wafer-scale etching technique for high aspect ratio implantable MEMS structures

Microsystem technology is well suited to batch fabricate microelectrode arrays, such as the Utah electrode array (UEA), intended for recording and stimulating neural tissue. Fabrication of the UEA is primarily based on the use of dicing and wet etching to achieve high aspect ratio (15:1) penetrating electrodes. An important step in the array fabrication is the etching of electrodes to produce needle-shape electrodes with sharp tips. Traditional etching processes are performed on a single array, and the etching conditions are not optimized. As a result, the process leads to variable geometries of electrodes within an array. Furthermore, the process is not only time consuming but also labor-intensive. This report presents a wafer-scale etching method for the UEA. The method offers several advantages, such as substantial reduction in the processing time, higher throughput and lower cost. More importantly, the method increases the geometrical uniformity from electrode to electrode within an array (1.5 ± 0.5% non-uniformity), and from array to array within a wafer (2 ± 0.3% non-uniformity). Also, the etching rate of silicon columns, produced by dicing, are studied as a function of temperature, etching time and stirring rate in a nitric acid rich HF–HNO 3 solution. These parameters were found to be related to the etching rates over the ranges studied and more importantly affect the uniformity of the etched silicon columns. An optimum etching condition was established to achieve uniform shape electrode arrays on wafer-scale.

Sonochemically Fabricated Microelectrode Arrays for Use as Sensing Platforms

The development, manufacture, modification and subsequent utilisation of sonochemically-formed microelectrode arrays is described for a range of applications. Initial fabrication of the sensing platform utilises ultrasonic ablation of electrochemically insulating polymers deposited upon conductive carbon substrates, forming an array of up to 70,000 microelectrode pores cm−2. Electrochemical and optical analyses using these arrays, their enhanced signal response and stir-independence area are all discussed. The growth of conducting polymeric “mushroom” protrusion arrays with entrapped biological entities, thereby forming biosensors is detailed. The simplicity and inexpensiveness of this approach, lending itself ideally to mass fabrication coupled with unrivalled sensitivity and stir independence makes commercial viability of this process a reality. Application of microelectrode arrays as functional components within sensors include devices for detection of chlorine, glucose, ethanol and pesticides. Immunosensors based on microelectrode arrays are described within this monograph for antigens associated with prostate cancer and transient ischemic attacks (strokes).

Evaluation of Poly(o‐phenylenediamine) Films for Application as Insulating Layers upon Carbon Substrates for Use within Sonochemically Fabricated Microelectrode Arrays

AbstractThe formation of insulating layers of poly(o‐phenylenediamine) via electropolymerization was performed on single carbon screen‐printed electrodes. The effects of experimental parameters on the properties of the film were investigated, allowing for technique optimization. These conditions were then used to deposit films upon surfaces of 100 interconnected electrodes, with cyclic voltammetry used to study the electroactivity of the resulting electrodes. The insulating property of the film, for use in the formation of microelectrode array amperometric sensors, was evaluated. Finally, the insulated sensors were exposed to ultrasonic ablation to form microelectrode arrays, and these were subsequently assessed using optical and electrochemical techniques.

Screen printed recessed microelectrode arrays

The construction and characterisation of screen printed recessed microelectrode arrays are reported. This screen printing approach results in the fabrication of shallow recessed microelectrode arrays which are characterised by microscopy and cyclic voltammetry. The analytical utility of the shallow recessed microelectrode arrays is demonstrated with the cathodic stripping of manganese (II) allowing nano-molar levels to be readily detected exhibiting a superior performance over conventional carbon based electrodes. The limitations of using screen printing technology to fabricate microelectrode arrays are also discussed.

Investigations into the use of screen-printed carbon electrodes as templates for electrochemical sensors and sonochemically fabricated microelectrode arrays

The paper critically evaluates the suitability of carbon inks as hosts for the fabrication and subsequent mass production of sonochemically produced microelectrode arrays. Two commercially available carbon inks (GEM and Dupont) were compared in terms of electroactivity towards standard redox couples, and their electroanalytical response was investigated in terms of reversibility, operational potential range, background currents and steady-state response characteristics. Following on from these findings, the inks were then subjected to simple activation and modification procedures (comprising of electrochemical, chemical and physical treatments), with a view to maximising the electrode response, in terms of how modifications to the carbon surface translate into changes in the performance characteristics of the electrodes. The results from these investigations are discussed in the context of the use of pre-treated carbon surfaces for the enhanced production of sonochemically fabricated microelectrode array sensors, for use as electrochemical sensors and biosensors.

A cobalt-coated needle-type microelectrode array sensor for in situ monitoring of phosphate

In this paper, a new cobalt-coated needle-type microelectrode array sensor for in situ measurements of phosphate has successfully been designed, fabricated and characterized. MEMS technologies were used to fabricate microelectrode arrays with a small tip size. An HF-based etching technique was used to taper and sharpen three-dimensional glass probes. A cobalt thin film was electroplated on a gold conductive layer using a cobalt sulfate electrolyte and then was oxidized to form CoO on the surface. The microelectrode array (MEA) was packaged on a designed printed circuit board (PCB) for electrical connections. The MEA sensors were fully characterized with potassium sulfate solution in the concentration range of 1 × 10−5.1−1 × 10−3 M at pH 7.5. The repeatable phosphate-selective potentials with a sensitivity of ∼96 mV per decade were exhibited with less than 30 s response times and good signal stability. This sensitivity is the highest value among the reported cobalt-based phosphate sensors to date. Ultimately, in the long term, we envision extension of this MEA sensor to include additional sensors for multi-analyte, rapid, accurate and reliable in situ sensing in biological applications.

Genomic detection using an indicator-free DNA on a DNA chip microarray

Abstract This research aims to develop DNA chip array without an indicator. We fabricated microelectrode array by photolithography technology. Several DNA probes were immobilized on an electrode. Then, target DNA was hybridized and measured electrochemically. Cyclic-voltammograms (CVs) showed a difference between DNA probe and mismatched DNA in an anodic peak. This indicator-free DNA chip resulted in a sequence-specific detection of the target DNA.

Hybridization by an Electrical Force and Electrochemical Genome Detection Using an Indicator-free DNA on a Microelectrode-array DNA Chip

This research aims to develop DNA chip array without an indicator. We fabricated microelectrode array by photolithography technology. Several DNA probes were immobilized on an electrode. Then, indicator-free target DNA was hybridized by an electrical force and measured electrochemically. Cyclic-voltammograms (CVs) showed a difference between DNA probe and mismatched DNA in an anodic peak. Immobilization of probe DNA and hybridization of target DNA could be confirmed by fluorescent. This indicator-free DNA chip microarray resulted in the sequence-specific detection of the target DNA quantitatively ranging from M in the buffer solution. This indicator-free DNA chip resulted in a sequence-specific detection of the target DNA.

Sonochemically fabricated microelectrode arrays for biosensors—part II: Modification with a polysiloxane coating

A polymer-modified sonochemically fabricated glucose oxidase microelectrode array with microelectrode population densities of up to 2.5×10 5 microelectrodes per square centimetres is reported. These microelectrode sensors were formed by first depositing an insulating film on commercial screen printed electrodes which was subsequently sonicated to form cavities of regular sizes in the film. Electropolymerisation of aniline at the microelectrode cavities formed polyaniline protrusions containing entrapped glucose oxidase. Chemical deposition of polysiloxane from dichlorodimethysilane was used to deposit a thin protective and diffusion mass transport controlling coating over the electrodes. The physical and electrochemical properties of these films were studied. The performance of the final glucose oxidase based microelectrode sensor array is reported.

Sonochemically fabricated microelectrode arrays for biosensors offering widespread applicability: Part I

A novel and patented procedure is described for the sonochemical fabrication of a new class of microelectrode array based sensor with electrode element populations of up to 2×10 5 cm −2. For some years it has been accepted that microelectrode arrays offer an attractive route for lowering minimum limits of detection and imparting stir (convectional mass transport) independence to sensor responses; despite this no commercial biosensors, to date, have employed microelectrode arrays, largely due to the cost of conventional fabrication routes that have not proved commercially viable for disposable devices. Biosensors formed by our sonochemical approach offer unrivalled sensitivity and impart stir independence to sensor responses. This format lends itself for mass fabrication due to the simplicity and inexpensiveness of the approach; in the first instance impedimetric and amperometric sensors are reported for glucose as model systems. Sensors already developed for ethanol, oxalate and a number of pesticide determinations will be reported in subsequent publications.

Micromachined, Polyimide-Based Devices for Flexible Neural Interfaces

Micromachining technologies were established to fabricate microelectrode arrays and devices for interfacing parts of the central or peripheral nervous system in case of neuronal disorders. The devices were part of a neural prosthesis that allows simultaneous multichannel recording and multisite stimulation of neurons. Overcoming the brittle mechanics of silicon, we established a process technology to fabricate light-weighted and highly flexible polyimide based devices. Concerning the challenging housing demands close to the nerve to prevent mechanical induced nerve traumatization, we integrated interconnects to decouple the nerve interface from plugs and signal processing electronics. Hybrid integration with a new assembling technique—the MicroFlex interconnection (MFI)—has been applied for the connection of the flexible microsystems to silicon microelectronics. In this paper, we present different shapes and applications of the flexible electrodes: sieve electrodes for regeneration studies, cuff electrodes for interfacing peripheral nerves, and a retina implant for ganglion cell stimulation. The discussion is focused on electrode and material properties and the hybrid assembly of a fully implantable neural prosthesis.

Characterization of rat spinal cord neurons cultured in defined media on microelectrode arrays

Previous efforts to utilize mammalian spinal cord neurons as biosensor elements have relied on neuronal: glial co-cultures maintained in serum-containing media. We have examined the feasibility of culturing primary spinal cord neurons in serum-free medium, modified for neuronal longevity, on fabricated microelectrode arrays. Embryonic day 15 rat spinal cord cells were plated on trimethoxysilyl-propyldiethylenetriamine coated microelectrode arrays comprised of gold recording sites passivated with silicon nitride. Immunocytochemistry was performed to verify the presence of neurons and quantitatively assess astrocytes using antibodies against glial fibrillary acidic protein on the silicon nitride substrates. Modifications to culture media enabled viable neuronal culture to extend from approximately 14 days in vitro (DIV) to 40 DIV on the arrays containing only 1.1±0.5% (mean±SEM) astrocytes. Extracellular recording revealed tetrodotoxin-sensitive spontaneous electrical activity from the enriched neuronal culture. Threshold detection of extracellular potentials showed an increase in spike rate as a function of glutamate concentration with neurotoxicity at elevated levels. This approach suggests that functional measures related to biosensor applications, pharmacological screening, or the evaluation of neurological disease models can be implemented in a defined culture system.

Silicon Substrate Microelectrode Array for Surface-Enhanced Raman Spectroscopy

Electrode sites of a photolithographically fabricated microelectrode array have been demonstrated to function as surface-enhanced Raman Spectroscopy (SERS) microelectrodes. The 5 × 15 μm iridium electrodes on the substrate are electroplated with silver and activated by standard procedures. Working and counter-electrode functions are integrated onto the same assembly. The electrode is shown to yield adenosine and pyridine spectra at low concentrations and submilliwatt laser power.

Amperometric response of microlithographically fabricated microelectrode array flow sensors in a thin-layer channel

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