Scalable nanophotonic neural probes for multicolor and on-demand light delivery in brain tissue

Abstract

Neural probes are in vivo brain-invasive devices that record and manipulate neural circuits using electricity, light, or drugs. The capability to shine distinct wavelengths and control their respective output locations for activation or deactivation of specific groups of neurons is desirable but remains unachieved. Here, we discuss our probe’s capability to deliver two independently controllable wavelengths (450 and 655 nm) in the location(s) of interest using nanophotonic directional couplers and ring resonators. These nanophotonics are scalable to dozens of outputs without significantly increasing the device’s lateral dimensions. Furthermore, they are entirely passive and thus do not require electrical input that results in heat generation. Besides, we integrate a high number of electrodes for a simultaneous neural activity readout. Thus, we overcome the challenges associated with multicolor illumination for neural devices by exploiting the capability of miniaturizable, passive probes to deliver two different frequencies in several areas of interest. These devices open the path towards investigating the in vivo electrical signal propagation under the individual or simultaneous activation or inhibition of distinct brain regions.

Development of wafer-scale multifunctional nanophotonic neural probes for brain activity mapping

“…10(e)). Other designs have used ring-resonator filters to route red and blue light to specific grating coupler emitters 58 (Fig. 10(b)) or optical MZI switches to independently address red and blue light emitters.…”

“…Nanophotonic neural probes to date [45][46][47][48][49][50][51][52][57][58][59][60][61][62][63][64] use SiN and SiO 2 as the core and cladding of the waveguide, respectively, due to their optical transparency in the visible spectrum and compatibility with Si photonic foundries. 46,67 The waveguide propagation loss is typically dominated by scattering from the sidewall roughness, quantified by the root mean squared of the roughness profile.…”

“…Second, most probes suffer from high optical loss, ≳8 dB, at the fiber-to-chip coupling interface. 45,52,[57][58][59][62][63][64] The shrinkage of UV-epoxy during curing can further reduce the fiber-to-chip coupling efficiency. 125 The long-term stability and reliability of the optical package remain an area for further study and improvement.…”