Plasmonic structures offer exciting possibilities for biosensors applications, such as neuro-endoscopy. However, the interaction of plasmonic structures with brain cells in an endoscopic fashion requires precise control of the excitation light achievable only through a microscopy-based sensing scheme, where it is possible to finely tune the distribution of intensity and phase of the excitation field. Here we describe the available technological strategies to incorporate plasmonic structures at the tip of multimode optical fibers, tackling both the fabrication and photonic coupling challenges.
Raman spectroscopy is a powerful technique used across the life sciences to measure the molecular composition of a sample. There has been growing interest to miniaturize Raman imaging devices for endoscopic applications, however typically these probes are based on fiber bundles which increase the overall footprint of the probe. Recent works have shown that by applying a wavefront shaping technique, a single fiber may be transformed into a sub-cellular resolution Raman endoscope. However, a single probe both exciting and collecting the signal leads to an unavoidable large background signal from the fiber itself, masking large portions of the Raman signal from the sample. Here, we adopt a data-driven approach to de-convolve the background signal from the sample. In particular, we demonstrate that by applying PCA and machine learning techniques, sub-cellular resolution Raman images of pharmaceutical clusters can be made with supervision-free analysis.
The ability to fabricate plasmonic structures on the distal facet of an optical fiber has led to a diverse range of minimally invasive sensors. However these applications have been hindered by the inherent turbidity of the fiber and complex transmission properties of the nanostructures. We propose to use a wavefront shaping technique to pre-shape light prior to transmission through the nanostructed fiber to control the coupling between the guided modes of the fiber and the plasmonic nanostructures. We show that the sensing resolution of a plasmonic fiber optic can achieve a sub-cellular spatial resolution in biological applications. In this work, a broad range of plasmonic structures are explored as candidates for spatially resolved plasmonic sensing including periodic nanostructures for extraordinary optical transmission and sub-diffraction beam formation as well as nanoislands fabricated by a solid-state dewetting procedure for surface enhanced Raman spectroscopy.
Recent advancements in optogenetics and brain interfacing technologies have significantly improved neuroscience research. However, developing user-friendly and efficient probes with high spatial and temporal resolution and specificity remains a challenge. Tapered Optical Fibers (TOFs) have emerged as an intriguing solution due to their unique properties. This work reviews the strategies developed to enable precise definitions of light delivery and collection sites along the TOF axis, incorporating additional functionalities such as electrical recording sites or exploiting alternative light-matter interactions for label-free applications. The latest progresses in TOF micro and nanostructuring are categorized based on these objectives, highlighting the benefits and limitations of each approach. This manuscript aims at providing a comprehensive overview of recent advancements in TOF micro and nanostructuring.
Neurophotonics was launched in 2014 coinciding with the launch of the BRAIN Initiative focused on development of technologies for advancement of neuroscience. For the last seven years, Neurophotonics’ agenda has been well aligned with this focus on neurotechnologies featuring new optical methods and tools applicable to brain studies. While the BRAIN Initiative 2.0 is pivoting towards applications of these novel tools in the quest to understand the brain, in this article we review an extensive and diverse toolkit of novel methods to explore brain function that have emerged from the BRAIN Initiative and related large-scale efforts for measurement and manipulation of brain structure and function. Here, we focus on neurophotonic tools mostly applicable to animal studies. A companion article, scheduled to appear later this year, will cover diffuse optical imaging methods applicable to noninvasive human studies. For each domain, we outline the current state-of-the-art of the respective technologies, identify the areas where innovation is needed and provide an outlook for the future directions.
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