Nanophotonic sensing and label-free imaging of extracellular vesicles.

This review examines imaging-based nanophotonic biosensing and interferometric label-free imaging, with a particular focus on vesicle detection. It specifically compares dielectric and plasmonic metasurfaces for label-free protein and extracellular vesicle detection, highlighting their respective advantages and limitations. Key topics include: (i) refractometric sensing principles using resonant dielectric and plasmonic surfaces; (ii) state-of-the-art developments in both plasmonic and dielectric nanostructured resonant surfaces; (iii) a detailed comparison of resonance characteristics, including amplitude, quality factor, and evanescent field enhancement; and (iv) the relationship between sensitivity, near-field enhancement, and analyte overlap in different sensing platforms. The review provides insights into the fundamental differences between plasmonic and dielectric platforms, discussing their fabrication, integration potential, and suitability for various analyte sizes. It aims to offer a unified, application-oriented perspective on the potential of these resonant surfaces for biosensing and imaging, aiming at addressing topics of interest for both photonics experts and potential users of these technologies.