Super-resolution optical microscope based on a water-immersion metalens

Owing to its non-invasive nature, high spatial resolution and user-friendly operation, optical microscopy has a wide range of applications. In past decades, tremendous breakthroughs have been made in breaking the diffraction limit in traditional optical imaging. Compared to commonly used fluorescence-based super-resolution microscopy, label-free super-resolution microscopy can extend to the applications unsuitable for fluorescencelabeling, especially for non-organic specimens. In addition, it can avoid the labeling-associated phototoxicity, which frequently occurs during live fluorescence microscopy. However, most reported label-free super-resolution microscopes employed dry lenses with short depth of focus, limiting resolution and complicating lens alignment. Here, we have developed a water-immersion transmission super-resolution optical microscope based on optical needle illumination. Compared to those working in air, the proposed water-immersion transmission superresolution optical microscope can achieve a lateral resolution of approximately 0.213 lambda. Such label-free optical super-resolution microscopy is promising for applications where florescence microscopy is not applicable.