Micro-Electrode Arrays

Over the last 30 years, non-invasive extracellular recording from multiple electrodes has developed into a widely-used standard method.
Systems and methods have been greatly improved, leading to more features, lower costs, and higher throughput. Almost all excitable or electrogenic cells and tissues can be used for extracellular recording in vitro, for example central or peripheral neurons, heart cells, retina, or muscle cells.

Micro-Electrode Arrays

Over the last 30 years, non-invasive extracellular recording from multiple electrodes has developed into a widely-used standard method.
Systems and methods have been greatly improved, leading to more features, lower costs, and higher throughput. Almost all excitable or electrogenic cells and tissues can be used for extracellular recording in vitro, for example central or peripheral neurons, heart cells, retina, or muscle cells.

Background

Learn more about the basics of multi-site extracellular recording from microelectrode arrays (MEAs), the many advantages of the system, and compare it with other methods.

Extracellular Recording

A microelectrode array (MEA) is an arrangement of several (typically 60) electrodes allowing the targeting of several sites for stimulation and extracellular recording at once. The following components are important for an extracellular recording system:

• Signal source (cells/tissue)
• Cell/sensor interface
• Biosensor (MEA)
• Filter amplifier (MEA1060)
• Recording hardware (MC_Card) and software (MC_Rack)

 

Advantages of MEAs

• Examine the activities of whole cells and tissues rather than single receptors as in patch clamp experiments
• Study the interaction of several cells in a culture or in their natural environment, for example in organotypic slices, or even in whole organs (for example, whole heart from chicken embryo)
• The MEA system is easy to set up and operate resulting in a greatly increased throughput
• Cultivation of cell cultures or slices for several weeks or even months (long-term studies) possible
• Record single unit activities from several cells in parallel, increasing your throughput and allowing a better comparison of activities under similar experimental conditions
• Analyze not only single unit activities, but also compound action potentials of several cells and tissues, that is, field potentials
• Study the spatio-temporal pattern of responses in a neuronal network or slice by using a new class of information, not only about time and amplitude, but also about space, in a two-dimensional setup
• Create spatial maps of drug effects at separate sites in the tissue that will provide you deeper insights into the specificity of a drug

Single Unit Activities

Usually several cells are plated onto an MEA. The waveform of a single unit spike depends on the signal source, the geometry of the extracellular space, and the distance of the signal source to the electrode.
The property of a waveform derived from a single neuron is reproducible over time and therefore specific for that neuron. Therefore, the differences of waveforms from separate signal sources can be used to distinguish the activities and to sort spikes into single unit spikes. Thus, you can acquire single unit data from multiple cells in parallel by recording from a single MEA.
You have to discriminate between independent activities and network responses. Responses of cells on an MEA triggered by a chemical or electrical stimulus can be either statistically independent or show a specific pattern. The latter is quite interesting for studying the role of cells and different tissues in a pathway.
MEA recording allows such studies under controlled experimental settings and is much easier and less labor intensive than an in vivo experiment.

Local Field Potentials

If the dendrite-soma axes of the active cells are aligned, the waveforms from multiple units on an MEA overlay and form a compound potential, or local field potential (LFP).
The higher the activity, that is, the spike rate, the higher is the amplitude of the LFP. A modulation of the stimulus results in a higher frequency of action potentials that will result in a graded multi-unit response.
LFPs often show a high signal-to-noise ratio, which is very beneficial for the analysis.
If dendrites are arranged in a nonparallel or radial fashion forming a closed field, the waveforms may cancel each other out, when the neurons fire in synchrony.

for technical specifications on the Multi Electrode Arrayys (MEA) view the pdf file below:

datasheet : MEA

Technical Details

Introduction
Learn more about the MEA product line in general. MCS does not only provide MEAs for all kind of applications, but also complete systems for signal amplification and filtering, stimulation, data acquisition and analysis.

Production

The NMI in Reutlingen, Germany produces MEA sensors from very pure fine quality and highly biocompatible materials. The NMI is a research institute, with which Multi Channel Systems has collaborated in many projects and over many years. Quality controls and production processes have been improved over the last years so that MEAs are always of a fine consistent quality.

MEA design

A typical MEA biosensor has a square recording area of approximately 150 µm to 4500 µm length. In standard planar arrays, 60 flat TiN electrodes, with diameters of 10 µm or 30 µm, are arranged in a grid (typically 8 x 8), with interelectrode distances of 30,100, 200, or 500 µm (see d). In 3-D arrays, protruding three-dimensional Pt electrodes extend from a 40 micron base at the array surface to a tip that is elevated 50 µm to 70 µm above the surface. In the HEXarrays, flat TiN electrodes with diameters of 10, 20 and 30 µm are arranged in a hexagonal configuration.
Several MEA types and layouts are available for all kind of applications. Most of them are available with an internal reference electrode.
All electrodes can either be used for recording or for stimulation. The acute slice or the cells can be positioned directly on the recording site; the MEA can serve as a culture and perfusion chamber.
The cells or tissue can be cultivated directly on the MEA for up to several weeks.
A TC01/ TC02 temperature controller controls the MEA’s temperature. For cell cultures, MEAs have to be coated before use to improve the cell attachment and growth. Coating methods differ according to the properties of the cell culture. For more information on coating, please see unde "Support". Spike activity can be detected at distances of up to 100 µm from a neuron in an acute brain slice. Typically, signal sources are within a radius of 30 µm around the electrode center. The smaller the distance, the higher are the extracellular signals.
All standard designs and custom designs made by the NMI, please follow the corresponding link on the Links page.

Electrodes, tracks, and insulation

The impedance of a flat, round titanium nitride electrode ranges between 20 kOhm and 400 kOhm, depending on the diameter.
The smaller an electrode, the higher is the impedance. On one hand, lower impedance seems desirable, but on the other hand, a smaller electrode and interelectrode distance results in a higher spatial resolution.
Therefore, Multi Channel Systems provides different MEA layouts suitable for different kinds of applications. The electrodes are embedded in a carrier material, usually glass. Standard tracks made of titanium or indium tin oxide (ITO) are electrically isolated with silicon nitride (PEVCD).
The contact pads are of the same material as the tracks are. ITO contact pads and tracks are transparent, for a perfect view of the specimen under the microscope.

Handling and Properties

Due to very stable materials, all MEAs have a long life and can be reused several times if handled with care. If used for acute slices, MEAs can be used for approximately one year.
Long-time experiments with cell cultures and rigid cleaning methods shorten the MEA lifetime, but you can still reuse an MEA about 30 times, depending on the coating, cell culture, and cleaning procedure.
All MEAs (except FlexMEAs and 3-D MEAs) show excellent temperature compatibility and are stable from 0 °C to 125 °C, that is, they can be autoclaved.

Recording and Stimulation

The MEA sensor is placed directly into the small-sized MEA1060 amplifier. When the amplifier is closed, the contact pins in the lid of the amplifier are pressed onto the MEA contact pads. The very close location of the amplifier to the MEA sensor is very favorable concerning a high signal-to-noise ratio. The amplifier is connected with a single cable to the data acquisition computer.
You can then simply ground bad or unwanted electrodes by moving small switches on the amplifier. You can also connect a stimulus generator (STG) to any electrode(s) for stimulation. Stimulating electrodes are disconnected from the amplifier to prevent its saturation.
With the new advanced MEA1060BC amplifier, you can use the same MEA electrodes for both stimulation and recording. Stimulus artifacts and amplifier saturation are effectively prevented with a blanking circuit. Also, you will be able to ground electrodes by software controls from the data acquisition computer.

Signal Amplification and Filters

Different filter settings are used to enhance the signal-to-noise ratio. The pass band of the filter amplifier depends on the signal type.
For slow signals like field potentials, a bandwidth of 1-300 Hz is appropriate. If you like to record fast signals like spikes, a pass band of 300 Hz to 3 kHz is suitable.
Cardiac signals have fast and slow components; therefore, you usually need a wide bandwidth of 1 Hz to 3 kHz. Multi Channel Systems provides custom amplifiers with a bandwidth of your choice, from 0.1 Hz to 10 kHz. It is often wise to acquire the data with a broadband amplifier and use the digital filter of the free MC_Rack program to filter the raw data. This way, you are much more flexible in designing your experiments.
As a further advantage, you can see the original (not filtered) data as well. This is especially important because all filters are known to distort signals.
The gain of the amplifier can also be adjusted according to your setup. For example, for large signals (for example from heart), you need a lower gain to prevent a saturation of the amplifier. Gain settings from 100 to 5000 are possible.

Data Acquisition

MESystems and MEASystems feature a sampling rate of up to 50 kHz/channel. It is recommended to adjust the sampling rate according to your signals, because the higher the sampling rate, the bigger the file size will be. As a rule of thumb, the sampling rate should equal five times the highest signal rate. If the sampling rate is too low, you will miss signals and/or see artifacts.
With the high-performance data acquisition and analysis program MC_Rack, you can flexibly manage all data streams. For example, you can display the raw data of all channels while recording only the raw data of the channels of interest and the extracted parameters of all channels. This saves computer performance and hard disk space.
MC_Rack is not limited to special applications, but can be flexibly adapted to a wide range of applications. Unlimited software licenses and support come free with the system; and free software updates lower the costs as well.

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ALA MEA-MEM5
MEA-MEM Covers (QTY 5) & O-rings (QTY 5) & loading tool

ALA MEA-INSERT
f perfusion insert for all MEA-Parray planar type - polycarbonate