Efficient assembly of multi-color fiberless optoelectrodes with on-board light sources for neural stimulation and recording

Fiberless optoelectrodes are an emerging tool to enable brain circuit mapping by providing precise optical modulation and electrical monitoring of many neurons. While optoelectrodes having an on-board light source offer compact and optically efficient device solutions, many of them fail to provide robust thermal and electrical design to fully exploit the recording capabilities of the device. In this work, we present a novel fiberless multicolor optoelectrode solution, which meets the optical and thermal design requirements of an in vivo neural optoelectrode and offers potential for low-noise neural recording. The total optical loss measured for 405 nm and 635 nm wavelengths through the waveguide is 11.7±1.1 dB and 9.9±0.7 dB, corresponding to respective irradiances of 1928 mW/mm² and 2905 mW/mm² at the waveguide tip from 6 mW laser diode chips. The efficient thermal packaging enables continuous device operation for up to 190 seconds at 10% duty cycle. We validated the fully packaged device in the intact brain of anesthetized mice co-expressing Channelrhodopsin-2 and Archaerhodopsin in the hippocampal CA1 region and achieved activation and silencing of the same neurons. We discuss improvements made to reduce the stimulation artifact induced by applying currents to the laser diode chips.