From microscopy to nanoscopy via visible light

Abstract

The resolution of conventional optical equipment is always restricted by the diffraction limit, and improving on this was previously considered improbable. Optical super-resolution imaging, which has recently experienced rapid growth and attracted increasing global interest, will result in applications in many domains, benefiting fields such as biology, medicine and material research. This review discusses the contributions of different researchers who identified the diffractive barrier and attempted to realize optical super-resolution. This is followed by a personal viewpoint of the development of optical nanoscopy in recent decades and the road towards the next generation of optical nanoscopy. Researchers in China have reviewed techniques for imaging at resolutions beyond the diffraction limit of light. Xiang Hao and co-workers from Zhejiang University in China describe how superlenses made from thin silver films and hyperlenses incorporating meta-materials can capture near-field evanescent waves that provide fine and rich spatial information about an object. Alternative approaches include placing transparent microspheres onto the object or scanning a microscale optical fiber across it. The role of popular fluorophore-based schemes such as STED, STORM and PALM, which achieve super-resolution imaging by employing the controlled switching of fluorescence in space and time, is also described. Finally, the authors comment on the emergence of approaches such as the HIRES lens, which uses light scattering to achieve enhanced resolution.