Fig. 1: Overview of reported sensing modalities that exploit all-optical detection of local refractive index contrast.

Approaches based on a, b optical microscopy of single plasmonic nanoparticles and metallic films, c, d optical transmission probing of nanometric apertures in a metal film, e, f optical spectroscopy of whispering gallery modes and Fabry Perot resonances in dielectric microcavities, g, h interferometric scattering microscopy, and i, j interferometric nanofluidic scattering microscopy. a Reproduced with permission from²⁷. Copyright 2015 American Chemical Society. b Adapted with permission from^28,165. Copyright 2024 American Chemical Society and 2018 National Academy of Sciences. e Adapted with permission from⁷⁵. Copyright 2021 The Authors. f Adapted withpermission from⁸⁰. Copyright 2024 Springer Nature. h Adapted with permission from^84,90,93. Copyright 2004 American Physical Society. Copyright 2014 Springer Nature. “This is an unofficial adaptation of an article that appeared in an ACS publication. ACS has not endorsed the content of this adaptation or the context of its use.” j, k Reproduced with permission from⁹⁶. Copyright 2022 Springer Nature.