Copyright © 2017 American Scientific Publishers All rights reserved Printed in the United States of America Article Journal of Nanoscience and Nanotechnology Vol. 17, 2582–2584, 2017 www.aspbs.com/jnn Design and Fabrication of Implantable Neural Probes with Monolithically Integrated Light-Emitting Diodes for Optogenetic Applications Ho-Kun Sung 1 2 , Hee-Kwan Lee 2 , Cong Wang 1 , and Nam-Young Kim 1 ∗ 1 Radio Frequency Integrated Circuit Center, Kwangwoon University, Seoul 139-701, Korea 2 Korea Advanced Nano Fab Center (KANC), Gyeonggi-do 443-270, South Korea We report an implantable neural probe with monolithically integrated light-emitting diodes (LEDs) and recording site for optogenetic applications. The device were designed and fabricated with 2- inch gallium nitride on silicon epitaxial wafer. The neural probe consisted of three LEDs (a mesa size of 310 × 41 mm 2  and four electrical recording sites, which had a total length of 6.72 mm (PCB bonding region + implanting region). The designed implantable neural probe was successfully processed by the conventional LED fabrication and Si microfabrcation. These methods can offer relatively rapid and easy fabrication. For fabricated LEDs, the optical and electrical properties were measured and characterized. At 1 mA, the emission wavelength was around 460 nm and it was slightly blue-shifted with the increase of injection current. Also, the optical power density was about 1 mW/mm 2 at an electrical input power of 3.5 mW, and it was increased to 6.3 mW/mm 2 at 24 mW. Keywords: Implantable Neural Probes, Monolithically Integrated LED, LEDs, Optogenetic Applications. 1. INTRODUCTION Optogenetics is an effective neuromodulation technology, which uses light-sensitive proteins (e.g., channel- rhodopsins (ChR2) and halorhodopsins (NpHR)) to con- trol neural activity. Commonly, the ChR2 and NpHR can be activated by the blue light (∼470 nm) and yellow light (∼590 nm), respectively. 1 2 There have been many research reports for the development of advanced optogenetic devices using various light sources and structure designs, such as optical waveguide and fiber-based devices, millimeter-sized light-emitting diodes (LEDs) within a glass pipette, and probe systems inte- grated micrometer-sized LEDs. 3–12 However, these devices involve complex designs, expensive and bulky optics, and complex fabrication processes. Moreover, the optical fibers are not suitable for long-term implantation due to their weak mechanical properties. In recent work, the neural probe with monolithically integrated LEDs was devel- oped and characterized, which was based on gallium nitride (GaN) epitaxial layers grown on sapphire wafer. ∗ Author to whom correspondence should be addressed. The monolithic integration system can offer the reduction of device size and well-controlled spatiotemporal resolu- tion. However, the sapphire material is still difficult to pro- cess because of its hardness. On the other hand, the GaN epitaxial layer grown on silicon (Si) wafer can be easily processed by conventional LED and Si microfabrication processes. In addition, the silicon material has relatively excellent thermal and mechanical properties. In this Letter, a new approach is introduced, an implantable neural probe with monolithically integrated GaN-based LEDs on Si, emitting at  ∼ 450 nm. The neural probes are designed and fabricated with 2-inch GaN epitaxial layer grown on Si wafer, which have LED light sources directly integrated onto Si probe. The fabrications are optimized by conven- tional LED fabrication and Si microfabrication processes. For fabricated probe, the electrical and optical properties are measured and characterized. 2. EXPERIMENTAL DETAILS The implantable neural probe with monolithically inte- grated LEDs was designed and fabricated with 2-inch GaN-on-Si epitaxial wafer. Figure 1 shows the schematic 2582 J. Nanosci. Nanotechnol. 2017, Vol. 17, No. 4 1533-4880/2017/17/2582/003 doi:10.1166/jnn.2017.13071