Overcoming diffraction limit: From microscopy to nanoscopy

The advancement of super-resolution imaging technologies has significantly extended microscopy to nanoscopy, making it possible for the study of physical, chemical, and biological processes at the length scale that is much smaller than the wavelength of light. However, challenges still remain, including the development of high-resolution devices for real-time imaging of living cells in cost effective ways. In this review, a small number of super-resolution microscopic techniques, which we call “nanoscopy,” are classified by their working principles. Not only is fluorescence microscopy such as stochastic optical reconstruction microscopy (STORM) or photo-activated localized microscopy (PALM), stimulated emission depletion (STED), and structured illumination microscopy (SIM) reviewed in detail, but also label-free microscopy whose functions are originated from nanostructures such as micro-curvilinear lens, disordered media, super-oscillation, and metamaterials. Comprehensive discussion including the advantages and disadvantages of each nanoscopy is followed.