In Vitro Testing of Floating Light Activated Micro-Electrical Stimulators

Chronic tissue response to microelectrode implants stands in the way as a major challenge to development of many neural prosthetic applications. The long term tissue response is mostly due to the movement of interconnects and the resulting mechanical stress between the electrode and the surrounding neural tissue. Remotely activated floating micro-stimulators are one possible method of eliminating the interconnects. As a method of energy transfer to the micro-stimulator, we proposed to use a laser beam at near infrared (NIR) wavelengths. FLAMES of various sizes were fabricated with integrated silicon PIN photodiodes. Sizes varied from 120 (Width) times 300 (Length) times 100 (Height) mum to 200 times 500 times 100 mum. Devices were bench tested using 850 nm excitation from a Ti:Sapphire laser. To test this method, the voltage field of the FLAMES was experimentally tested in saline solution pulsed with a NIR laser beam. The voltage generated is around 196 mV in peak at the cathodic contact as a response to a single pulse. When a train of laser pulses was applied at 100 Hz, the peak voltage at the cathodic contact remained around 141 mV suggesting the feasibility of this approach for applications with pulse frequencies up to 100 Hz.