Neural optoelectrodes merging semiconductor scalability with polymeric-like bendability for low damage acute in vivo neuron readout and stimulation

Neural optoelectrodes can read and manipulate large numbers of neurons in vivo. However, state-of-the-art devices rely on either standard microfabrication materials (i.e., silicon and silicon nitride), which result in high scalability and throughput but cause severe brain damage due to implant stiffness, or polymeric devices, which are more compliant but whose scalability and implantation in the brain are challenging. Here, we merge the gap between silicon-based fabrication scalability and low (polymeric-like) stiffness by fabricating a nitride and oxide-based optoelectrode with a high density of sensing microelectrodes, passive photonic circuits, and a very small tip thickness (5 μm). We achieve this by removing all the silicon supporting material underneath the probe's tip - while leaving only the nitride and glass optical ultrathin layers - through a single isotropic etch step. Our optoelectrode integrates 64 electrodes and multiple passive optical outputs, resulting in a cross-sectional area coefficient (the cross section divided by the number of sensors and light emitters) of 3.1 - smaller than other optoelectrodes. It also combines a low bending stiffness (∼4.4 × 10-11 N m2), comparable or approaching several state-of-the-art polymeric optoelectrodes. We tested several mechanical insertions of our devices in vivo in rats and demonstrated that we can pierce the pia without using additional temporary supports