Label-free super-resolution imaging below 90-nm using photon-reassignment

Background: Achieving resolutions below 100 nm is key for many fields, including biology and nanomaterial characterization. Although nearfield and electron microscopy are the gold standards for studying the nanoscale, optical microscopy has seen its resolution drastically improve in the last decades. So-called super-resolution microscopy is generally based on fluorescence photophysics and requires modification of the sample at least by adding fluorescent tags, an inevitably invasive step. Therefore, it remains very challenging and rewarding to achieve optical resolutions beyond the diffraction limit in label-free samples. Methods: Here, we present a breakthrough to unlock label-free 3D super-resolution imaging of any object including living biological samples. It is based on optical photon-reassignment in confocal reflectance imaging mode. Results: We demonstrate that we surpass the resolution of all fluorescence-based confocal systems by a factor ~1.5. We have obtained images with a 3D (x,y,z) optical resolution of (86x86x248) nm 3 using a visible wavelength (445 nm) and a regular microscope objective (NA=1.3). The results are presented on nanoparticles as well as on (living) biological samples. Conclusions: This cost-effective approach double the resolution of reflectance confocal microscope with minimal modifications. It is therefore compatible with any microscope and sample, works in real-time, and does not require any signal processing.