Influence of the Surface Material and Illumination upon the Performance of a Microelectrode/Electrolyte Interface in Optogenetics

Abstract

Integrated optrodes for optogenetics have been becoming a significant tool in neuroscience through the combination of offering accurate stimulation to target cells and recording biological signals simultaneously. This makes it not just be widely used in neuroscience researches, but also have a great potential to be employed in future treatments in clinical neurological diseases. To optimize the integrated optrodes, this paper aimed to investigate the influence of surface material and illumination upon the performance of the microelectrode/electrolyte interface and build a corresponding evaluation system. In this work, an integrated planar optrode with a blue LED and microelectrodes was designed and fabricated. The charge transfer mechanism on the interface was theoretically modeled and experimentally verified. An evaluation system for assessing microelectrodes was also built up. Using this system, the proposed model of various biocompatible surface materials on microelectrodes was further investigated under different illumination conditions. The influence of illumination on the microelectrode/electrolyte interface was the cause of optical artifacts, which interfere the biological signal recording. It was found that surface materials had a great effect on the charge transfer capacity, electrical stability and recoverability, photostability, and especially optical artifacts. The metal with better charge transfer capacity and electrical stability is highly possible to have a better performance on the optical artifacts, regardless of its electrical recoverability and photostability under the illumination conditions of optogenetics. Among the five metals used in our investigation, iridium served as the best surface material for the proposed integrated optrodes . Thus, optimizing the surface material for optrodes could reduce optical interference, enhance the quality of the neural signal recording for optogenetics, and thus help to advance the research in neuroscience.

A 4-Channel Optogenetic Stimulation, 16-Channel Recording Neuromodulation System with Real-Time Micro-LED Detection Function

“…The optogenetic power density of a micro-LED is directly propotional to the driving current. At a current of 5 mA, the optogenetic power density can reach 1 mW/mm 2 [17,18], which meets the threshold requirement for the strong optical neurostimulation mentioned earlier. These microelectrodes are comparable in size to the neurons.…”

“…The customized planar optrode for the neuromodulation system was designed (see Figure 2), which was based on a sapphire substrate and processes the characteristics of high stiffness, high transparency, and high optogenetic density [17,18]. The optrode has a total length of L = 13 mm, with an 8 mm segment specifically reserved for the insertion into rodent brain tissue.…”

“…The micro-LED Driver Module is designed to provide a current output for driving micro-LEDs in an optrode for effective optogenetic stimulation. It has been observed that the luminance of a micro-LED has an explicit linear relationship to the current intensity [18], and the integral value of the irradiant density received by neurons within a short period of time will affect the response of neurons significantly [19,20]. Therefore, this variablecurrent-output Integrated Circuit (IC) is designed to precisely adjust the luminance of the micro-LED, thus enabling precise optogenetic neuromodulation stimulation.…”

An Integrated Neural Optrode with Modification of Polymer-Carbon Composite Films for Suppression of the Photoelectric Artifacts

“…In general, the conductive material of most recording electrodes is predominantly metal, such as gold, iridium, etc. , They have strong corrosion resistance and good biocompatibility. However, the elastic modulus of these materials is higher than that of brain tissue, which makes the interface between the microelectrode and brain tissue produce stress mismatch.…”