Wirelessly Powered and Controlled, Implantable, Multi-channel, Multi-wavelength Optogenetic Stimulator Ranajay Mandal * , Sudip Nag † , Nitish V. Thakor ‡ * Department of Electrical and Engineering Indian Institute of Technology, Kharagpur, India 721-302 Email: ranajay_mandal.iitkgp@yahoo.com † National University of Singapore, Singapore Email: sudipnag1@nus.edu.sg ‡ National University of Singapore, Singapore Abstract — In recent years, major developments in RF based power transmission systems have made a great impact in the progress of wirelessly powered implantable biomedical devices. In this paper, we present a multichannel and multi-wavelength optogenetic stimulator, suitable for chronic and acute implantation in freely moving rodents. Optogenetic stimulators provide a pathway for complex spatiotemporal control of photosensitized neurons in the brain. The design consists of an 8×8 micro light emitting diode array of equally spaced amber and blue LED pairs at alternate positions. The closely packed illumination structure facilitates light delivery at a high spatial (0.5mm) and temporal (0.1 ms) resolution. Low Frequency RFID (Radio Frequency Identification) technique was used for both power delivery and communication with the onboard low power microcontroller via custom built Reader circuitry. Index Terms — Multi-channel, multi-wavelength, wireless, optogenetic, micro light emitting diode (LED) I. INTRODUCTION Improvement of our understandings of different neurological disorders is essentially dependent on the identification of the underlying neural circuits. Optogenetic stimulators open completely new opportunities for efficient and reliable mapping and tracking of interactions between neurons in different areas of the brain. Specific type of neurons and neural circuits can be genetically targeted to express ion channels of different chromatic sensitivity [1]. As, a result it is possible to not only excite particular set of neural cell, but inhibit them also. Optogenetic neural stimulation requires a high level of optical intensity for activation and inhibition of the neurons. Typical irradiance between 0.1 mW/ mm² and 1 mW/mm² is necessary [2] for optical stimulation. The main challenge is to generate such luminescence with high efficiency and spatial selectivity to optimize the electrical power consumption. We needed a separate illumination system, due to the requirement of much higher light intensity than that provided by most standard spatial light modulation technologies, such using liquid-crystal displays. For in vivo optogenetics including freely moving mammals, µLED arrays provide a good platform for stimulation [4, 5]. In this work, we demonstrate a miniature 8×8 µLED array consisting of LEDs of two wavelengths. Photosensitive ion channels determined the wavelengths of the LEDs at Approximately 470 nm (Blue) [6,7] and 592 nm (Amber) [8], corresponding to excitation and inhibition of the ion channels. Also the temporal resolution of the LEDs was much higher than ms temporal response [3] required for neural stimulation. The onboard low power microcontroller, in our design, can be effectively controlled wirelessly to generate optical patterns at high time precision. There is provision for commanding the microcontroller through a PC via the custom built GUI or through the custom built reader board. Fig.1 depicts the two layered implantable light delivery system. In this report, we present the concept, structure and design of the multichannel, multi-wavelength optogenetic stimulator. We also demonstrate the wireless data communication and power transmission through Low Frequency RFID technology. Fig.1Concept diagram of Wirelessly powered Multichannel Optogenetic Stimulator. Antenna Wireless data receiver Low power microcontroller Addressable micro-LED array Genetically Modified Neural Cells RF Power and Data Receiver 2013 IEEE MTT-S International Microwave Workshop Series on RF and Wireless Technologies for Biomedical and Healthcare Applications (IMWS-BIO) 978-1-4673-6096-8/13/$31.00 ©2013 IEEE