  Neural probes are in vivo invasive devices that combine electrophysiology and
optogenetics to gain insight into how the brain operates, down to the single
neuron and its network activity. Their integration of stimulation sites and
sensors allows for recording and manipulating neurons` activity with a high
spatiotemporal resolution. State of the art probes are limited by tradeoffs
between their lateral dimension, the number of sensors, and the ability to
selectively access independent stimulation sites. Here, we realize a highly
scalable probe that features a three-dimensional integration of small footprint
arrays of sensors and nanophotonic circuits and scales the density of sensors
per cross-section by one order of magnitude with respect to state of the art
devices. For the first time, we overcome the spatial limit of the nanophotonic
circuit by coupling only one waveguide to numerous optical ring resonators as
passive nanophotonic switches. With our strategy, we achieve accurate on-demand
light localization while avoiding spatial demanding bundles of waveguides and
demonstrate the feasibility of a proof of concept device and its additional
scalability, towards high resolution and low damaging neural optoelectrodes.

Biological Physics;Applied Physics