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.
