Novel transparent neurotool compatible with light

Optogenetics allows us to control neuronal activities using light with high spatial and temporal resolution. However, the light affects not only the neurons, but also the electrodes that are used to record the neural signals, generating noise signals called photoelectric artifacts. For accurate recording without photoelectric artifacts, a KAIST joint research team has developed a transparent microelectrodes array based on nano-network structures that evade these photoelectric artifacts.

Article | Spring 2021

A KAIST joint research team led by Prof. Hyunjoo Jenny Lee and Prof. Jung-Yong Lee has developed a transparent electrocorticography (ECoG) electrode array that allows us to measure brain signals without photoelectric artifacts. The conventional opaque electrode array not only blocks the transmission of light used for the optical stimulation but is also subject to noise signals created by the Becquerel effect. Thus, the research team proposed the use of transparent electrodes for ECoG recording using gold nano-network structures. The developed array offers great advantages for neuroscience applications: photoelectric artifact-free recording during optical stimulation, high conductivity through the use of gold, and recording with a high-spatial resolution by passing light directly through the electrodes.

 

Optogenetics, first introduced in 2009, allows us to control neuronal activities using light with high spatial and temporal resolution. Unlike conventional neuromodulation techniques, optogenetics can excite and inhibit neural activities at a cell-type-specific resolution through transfection of various opsins. Thus, this technique is widely used in many neuroscience studies in discovering new neuronal circuits and brain functionalities.

A typical method to measure in vivo reactions to the light stimulation is to record the electrophysiological signals. However, general metal-based electrodes for electrophysiological recording have the disadvantages of disrupting light transmission derived from the high reflectivity, as well as generating noise signals called photoelectric artifacts by the Becquerel effect.

To address this issue, the KAIST research team has proposed the idea of devising a transparent, yet highly-conductive electrode array for ECoG recording during optical stimulation. The key enabling technologies involved in the development was the MEMS technology and the polymer electrospinning technology.

 

By adjusting the electrospinning time, the research team proposed an optimal density of gold nano-network for ECoG recording. The electrospinning time was an interesting knob to adjust the characteristics of the electrodes, such as electrochemical impedance and electrical conductivity. Compared to other transparent microelectrode arrays, due to the use of nano-network of gold, the developed electrodes offer higher conductivity, higher transparency, and lower electrochemical impedance.

 

The proposed transparent electrodes showed photoelectric artifacts 10 times smaller than those measured by common metal film-based microelectrodes. When placed across various cortical regions of the mouse brain, the developed electrodes enabled recording of the propagation of ECoG signals induced by the optical stimulation without signal distortion during the stimulation.

Based on these results, the research team is going to develop a multifunctional microelectrodes array that integrates microelectrodes and light sources in the future. This multifunctional platform will be a great candidate for a new neuro tool for many interesting neuroscience studies that use optogenetics.