Abstract
In this paper, a polyimide-based flexible device that integrates 16 micro-LEDs and 16 IrOx-modified microelectrodes for synchronous photostimulation and neural signal recording is presented. The 4 × 4 micro-LEDs (dimensions of 220 × 270 × 50 μm3, 700 μm pitch) are fixed in the SU-8 fence structure on a polyimide substrate and connected to the leads via a wire-bonding method. The recording electrodes share a similar fabrication process on the polyimide with 16 microelectrode sites (200 μm in diameter and 700 μm in pitch) modified by iridium oxide (IrOx). These two subparts can be aligned with alignment holes and glued back-to-back by epoxy, which ensures that the light from the LEDs passes through the corresponding holes that are evenly distributed around the recording sites. The long-term electrical and optical stabilities of the device are verified using a soaking test for 3 months, and the thermal property is specifically studied with different duty cycles, voltages, and frequencies. Additionally, the electrochemical results prove the reliability of the IrOx-modified microelectrodes after repeated pressing or friction. To evaluate the tradeoff between flexibility and strength, two microelectrode arrays with thicknesses of 5 and 10 μm are evaluated through simulation and experiment. The proposed device can be a useful mapping optogenetics tool for neuroscience studies in small (rats and mice) and large animal subjects and ultimately in nonhuman primates.
Highlights
Considerable progress has been made in the last decade in optogenetics to manipulate specific circuits by excitation or inhibition of a specific neuron type with the expression of light-sensitive ion channels or ion pumps
Four circular holes are evenly distributed in the middle of the micro-lightemitting diode (LED) array footprint, in which the two middle holes are used for dispensing the adhesive and the two side holes are used for the alignment with the same two holes on the microelectrode array
To verify the performance of the device, we studied the electrical, optical, and thermal properties of the microLED array, as well as the electrochemical, flexible, and mechanical properties of the microelectrode array
Summary
Considerable progress has been made in the last decade in optogenetics to manipulate specific circuits by excitation or inhibition of a specific neuron type with the expression of light-sensitive ion channels or ion pumps. This method is critically important in neuroscience research because of its capabilities in sophisticated functional studies in neural systems[1,2]. The light sources have low spatial resolution due to the limited number of beams and the relatively imprecise positioning of the sources. Because optical fibers can restrict the movement of the animal or even lead to entanglement, the ultra-miniaturized wirelesspowered LED array is a superior choice[8,9]
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