Silicon Carbide Waveguides for Optogenetic Neural Stimulation
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Silicon Carbide Waveguides for Optogenetic Neural Stimulation Joseph Register1, Andreas Muller,2 Justin King1, Edwin Weeber,3 Christopher L. Frewin3 and Stephen E. Saddow1,3 1 Department of Electrical Engineering, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620 2 Department of Physics, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620 3 Department of Molecular Pharmacology and Physiology, USF, 4202 East Fowler Avenue, Tampa, Florida 33620 ABSTRACT In this paper we present a microfabricated SiC based alternative to glass-fiber optogenetic stimulation. The glass fiber system currently used for stimulation has numerous drawbacks. First, the very presence of glass can evoke an immune response in cortical tissue that can impede the light-to-neuron optical interface. This glial scarring of brain tissue effectively lowers the spatial resolution and power output of the system. Second, the fragility of an implanted glass fiber is a problem that has yet to be fully addressed. Using SiC the proposed optical structure will address these problems by significantly lowering the amount glial scarring and astrocytic activity expressed as a result of the implant. In addition, single crystal SiC allows for a flexible device that can move with the surrounding tissue without fracturing. Finally, the current glass fibers tend be single channel devices with a single ended emitter. The proposed microfabricated device will allow for multiple channels, multiple wavelengths of stimulation, and electrical feedback on each channel improving upon the current standard. INTRODUCTION Optogenetics was first pioneered in 2005 by a team of researchers led by Dr. Karl Deisseroth at Stanford University1. Deisseroth and his team genetically isolated a photosensitive ion channel called Channelrhodopsin-2(ChR2) that responds to blue light (centered at 473 nm in wavelength). Once illuminated, the ChR2 channel opens, allowing Na+ cations to flow inward and thereby increasing the depolarization of the membrane past threshold level and instigating an action potential. Just as blue light can activate ChR2, yellow light (centered at 580 nm in wavelength) can be used to activate another light driven Na+ ion pump called Halorhodopsin (NpHR ). In contrast to ChR2, NpHR can effectively assist in repolarizing the neuron’s membrane to essentially “turn off” the action potential. Total bipolar state control (i.e. ON and OFF states) can be realized using these two ion-channel structures in conjunction with blue and yellow light stimulation. Cell-type-specific promoters for genetic modification can add ChR2 and/or NpHr ion channels and their variants to specific types of neurons. This differential targeting provides a great advantage over traditional electrical stimulation which has very low levels of neuronal selectivity. Moreover, this high level of selectivity allows diseased brain circuitry to be traced leading to development of new models for neuropsychiatric diseases2. Other variants of these two ion pumps have be
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