Implantable nanophotonic neural probes for integrated patterned photostimulation and electrophysiology recording

Optogenetics has transformed neuroscience by allowing precise manipulation of neural circuits with light. However, a central difficulty has been to deliver spatially shaped light and record deep within the brain without causing damage or significant heating. Current approaches form the light beam in free space and record the neural activity using fluorescence imaging or separately inserted electrodes, but attenuation limits optical penetration to around 1 mm of the brain surface. Here, we overcome this challenge with foundry-fabricated implantable silicon neural probes that combine microelectrodes for electrophysiology recordings with nanophotonic circuits that emit light with engineered beam profiles and minimal thermal impact. Our experiments reveal that planar light sheets, emitted by our neural probes, excited more neurons and induced greater firing rate fatigue in layers V and VI of the motor and somatosensory cortex of Thy1-ChR2 mice at lower output intensities than low divergence beams. In the hippocampus of an epilepsy mouse model, we induced seizures, a network-wide response, with light sheets without exceeding the ∼ 1◦C limit for thermally induced electrophysiological responses. These findings show that optical spatial profiles can be tailored for optogenetic stimulation paradigms and that the probes can photostimulate and record neural activity at single or population levels while minimizing thermal damage to brain tissue. The neural probes, made in a commercial silicon photonics foundry on 200-mm silicon wafers, demonstrate the manufacturability of the technology. The prospect of monolithically integrating additional well-established silicon photonics devices, such as wavelength and polarization multiplexers, temperature sensors, and optical power monitors, into the probes holds the potential of realizing more versatile, implantable tools for multimodal brain activity mapping. ### Competing Interest Statement The authors have declared no competing interest.