Multi-electrode arrays technology for the non-invasive recording of neural signals: a review article

The recording of electrophysiological activities of brain neurons in the last half-century has been considered as one of the effective tools for the development of neuroscience. One of the techniques for recording the activity of nerve cells is the multi-electrode arrays (MEAs). Microelectrode arrays (MEAs) are usually employed to record electrical signals from electrogenic cells like neurons or cardiomyocytes. MEAs consist of an array of planar or three-dimensional electrodes that act as electrical interfaces and record cellular signals or stimulate cells. These platforms can be used in different applications including neuroscience studies, prostheses and rehabilitation, deep brain stimulation (DBS), cardiac pacemakers, retinal and cochlear implants, or for brain-computer interfaces (BCI) in general. Multi-electrode arrays are known as long-term recording and non-invasive devices. The MEA structure includes arrays of electrodes with micrometer and nanometer dimensions which are designed to stimulate and record the electrical activity of cells, and are fabricated using micromachining technologies. MEAs should be biocompatible to serve as a substrate for cell growth. On the other hand, they must have low impedance to be able to provide a high signal-to-noise ratio, and small size to offer a suitable spatial resolution for recording. MEAs are usually fabricated on glass substrates patterned with high-conductivity metals such as gold, iridium or platinum, which are insulated with a biocompatible layer. Despite fast progress, current multi-electrode arrays for neural applications still face limitations such as low signal-to-noise ratio and spatial resolution. To achieve better spatial resolution and lower noise levels and therefore more accurate signal, it is necessary to develop arrays with smaller sizes and lower impedance. Meanwhile, many nanostructures such as graphene, carbon nanotubes, gold nanoparticles, and also conductive polymers have become attractive candidates for this application due to their interesting properties. In this paper, the technology of multi-electrode arrays, how it works and its various parts are introduced, and finally, the challenges and developments in this field are investigated. Multi-electrode array technology is used for neuroscience research, neural network analysis, drug effects screening, and neural prosthesis studies.