Nanostructured Fiber Optics for High Sensitivity, Minimally Invasive, Spatially-Resolved, Plasmonic Diagnosis and Therapeutics

Plasmonic fiber optics have attracted considerable research interest from perspectives ranging from fundamental physics to biomedical optics. However, across all fields, researchers face two distinct but strongly connected challenges. First, a nanofabrication challenge: integrating nanostructures on a substrate fiber; second, a photonic problem: engineer the interaction between the plasmonic structures and the modal patterns of light propagation. In this work we aim to show how both state-of-the-art fabrication approaches and optical techniques may be used to resolve these issues for plasmonic endoscopy in both deep and shallow brain regions. By applying wavefront shaping, we show that either a sub-region or entire plasmonic structure on a flat fiber facet can be holographically activated. We have applied this method to a wide range of plasmonic structures including periodic nanostructures for EOT and sub-diffraction beam formation and nanoislands for Surface Enhanced Raman Spectroscopy (SERS), resulting in a multifunctional plasmonic endoscope targeted at shallow brain regions. Alternatively, we show how a tapered optical fiber can also be used as a substrate of plasmonic structures targeted at detection of neurotransmitters in deep brain regions.