A Bi-Directional Detection and Stimulation Optrode System With Charge Balancing for Neural Applications

Abstract

The design of a bi-directional optical-electrode or ‘optrode’ for peripheral nerve and brain-machine interfacing is proposed and its principle of operation detailed, which is able to provide biphasic stimulus and charge balancing functionalities. The prototype chip is fabricated, characterised on the bench, and assessed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vivo</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ex vivo</i> . Results show that it can simultaneously stimulate and record from the rabbit sciatic nerve, and entrainment of the sino-atrial node is achieved and observed by the prototype. Then, a discrete component circuit is tested for validation of this charge-balancing effect. Experimental results from <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vivo</i> testing on rabbit sciatic nerves demonstrate that the voltage generated by photodiodes at around 0.5 to 0.6V is able to evoke compound action potentials, and the activated light-dependent resistor removed more than 80% of the post-stimulus charge stored at the interface.