In this study, an implantable optrode was developed for optogenetics stimulation of neural population in nuclei or multi-sites in neural circuits. The optrode was composed of base layer, micro-light emitting diode (LED) and coating layer. The base layer was a 150 μm thick polyimide substrate on which copper wires and contacts were fabricated by flexible printed circuit board processes. The micro-LED was soldered on the contacts using SnBi. Parylene-C was deposited over the optrode as the coating layer using a vacuum vapor deposition system. The optical output power was tested by optical power meter and the insulating property was tested using saline in the experiment. The stimulation function of the optrode was demonstrated through animal experiment. The width of the optrode was 500 μm and the maximum thickness of the optrode was 310 μm at the LED position. The thickness of the parylene coating layer was about 1 μm. The maximum optical output power of optrode was 9.31 mW and the effective illumination area was a 3.03 mm2 spherical cap at 650 μm deep in brain tissue. The optrode was still functional after 14 days in physiological saline. Conventional copper electrodes were used to verify the efficacy of the optrode for stimulation and robust spiking activities of the expressing Channelrhodopsin-2 neurons in the entire cortex of a mouce were recorded. Obvious behavior change happened when light stimulation was applied to the expressing Channelrhodopsin-2 neurons in the secondary motor cortex of the mice. The optrode has the characteristics of large effective illumination range, flexible in implantation and long-term implantable, which provide neural population in nuclei research a new tool.
As an interface between external electronic devices and internal neural nuclei, microelectrodes play an important role in many fields, such as animal robots, deep brain stimulation and neural prostheses. Aiming at the problem of high price and complicated fabrication process of microelectrode, a microelectrode twisting machine based on open source electronic prototyping platform (Arduino) and three-dimensional printing technology was proposed, and its microelectrode fabrication performance and neural stimulation performance were verified. The results show that during the fabrication of microelectrodes, the number of positive twisting turns of the electrode wire should generally be set to about 1.8 times of its length, and the number of reverse twisting rings is independent of the length, generally about 5. Moreover, compared with the traditional instrument, the device is not only inexpensive and simple to manufacture, but also has good expandability. It has a positive significance for both the personalization and popularization of microelectrode fabrication and the reduction of experimental cost.