Implantable Optrodes Based On μLED For Optogenetics

The channel been used for information exchange between human or animal’s nervous system and the outside world is called neural interface(NI). The electrophysiological neural interface(ENI), as the main treatment for nervous system diseases or injury, was applied in clinical research widely. However, there are two unavoidable problems of the ENI: in the aspect of neural regulation, ENI cannot inhibit nerve; in the aspect of target, the stimulating area of ENI is large and the nervous type is non-optional. On the other hand, optogenetics neural interface(Optrode) is a good alternative technique. Optrode is able to regulate neurons(stimulation or inhibition) through light and photosensitive protein. Furthermore, the temporal resolution of the regulation can achieve to millisecond-timescale, which provides the precondition for the research of the neural regulation mechanism and the interreaction of the different neural circuits.Most traditional optrodes use laser as light source and are made of optical fibers. There are several drawbacks of laser system. Laser devices are expensive and fibers can be fragile. Besides, the effective illumination area of the optical fibers in the plane perpendicular to the axial is small. Moreover, the fiber connecting to the laser device can restrain the experimental animals. In the recent years, along with the development of high-power and microsize LEDs, more and more optrodes are designed with usage of LEDs as light source.This study orienting neural population in nuclei and neural circuits research aims to provide the optogenetics experiments, especially the behavioral research a more efficient、easier to operate、 easier to be bulk produced and brand new optogenetics tool. Two kinds of optrodes are developed in this study. One has function of neural stimulation, the other has function of both neural stimulation and electrical recording. The optrodes’ s properties are tested in the round relatively and the stimulation function of the optrodes is demonstrated.Firstly, the optrodes are designed in the aspects of light source, material and structural size. Main components of the optrodes include parylene coating layer, μLED chip and base layer. The width of the two optrodes is within 500μm and 600μm respectively. Manufacturing process of the optrodes combining FPC process and MEMS technology was proposed and applied. Single-layer substrate is used to form the base layer of the optrode with neural stimulation function and three-layer substrate is applied in the optrode with neural stimulation and electrical recording function., A “low temperature micro-welding platform” is set up to solder the μLED during the manufacturing process. Manually pasting simple mask is applied in the coating process, which keeps the cost down and reduces the production cycle.Secondly, the optrodes’ s properties are tested in terms of current-voltage characteristics, optical output power, impedance of the recording contacts, thermal property and operating life. The maximum optical output power is 3.9mW and the effective illumination area is a 0.98mm2 when the optrode is driven by the wireless stimulator developed by our group. Impedance of the recording contacts is about 1.14 kΩ at 1kHz. The maximum temperature rise of the μLED surface is below 1.4℃. The neural stimulation function is still available after 30 days in vivo and the electrical recording function’s validity period is about 20 days.Moreover, the optrode’s neural stimulation and recording function is demonstrated in vivo. An electrophysiological signal recording experiment was set up and robust spiking activities of the expressing Channelrhodopsin-2 neurons in the entire cortex of a dopey mice caused by optrode stimulation were recorded. Then a behavioral experiment was set up and obvious behavior change was observed when light stimulation was applied to the expressing of Channelrhodopsin-2 neurons in the secondary motor cortex of a freely-moving mice. At last, spontaneous local field potentials in the secondary motor cortex of a slightly dopey mice were recorded by the optrode.The advantages of the optrode demonstrated in this study include large effective illumination range, flexibility of implantation and long-term implantation at one time. The optrode and wireless stimulator together form a micro-based removable neural regulation system, which provide neural population in nuclei or neural circuits research a novel optogenetics tool.