Plasmonics on a Neural Implant: Engineering Light–Matter Interactions on the Nonplanar Surface of Tapered Optical Fibers

Optical methods are driving a revolution in neuroscience. Ignited by optoge-netic techniques, a set of strategies has emerged to control and monitorneural activity in deep brain regions using implantable photonic probes. Ayet unexplored technological leap is exploiting nanoscale light-matter inter-actions for enhanced bio-sensing, beam-manipulation and opto-thermal heatdelivery in the brain. To bridge this gap, we got inspired by the brain cells’scale to propose a nano-patterned tapered-fiber neural implant featuringhighly-curved plasmonic structures (30 μm radius of curvature, sub-50 nmgaps). We describe the nanofabrication process of the probes and charac-terize their optical properties. We suggest a theoretical framework using theinteraction between the guided modes and plasmonic structures to engi-neer the electric field enhancement at arbitrary depths along the implant,in the visible/near-infrared range. We show that our probes can control thespectral and angular patterns of optical transmission, enhancing the angularemission and collection range beyond the reach of existing optical neuralinterfaces. Finally, we evaluate the application as fluorescence and Ramanprobes, with wave-vector selectivity, for multimodal neural applications.We believe our work represents a first step towards a new class of versatilenano-optical neural implants for brain research in health and disease