Recent advances in STED and RESOLFT super-resolution imaging techniques

Stimulated emission depletion (STED) and reversible saturable optical fluorescence transition (RESOLFI) microscopy are the super-resolution imaging techniques that can acquire nanoscale spatial resolution. The spatial resolution of the other far-field optical microscopic techniques is bound by diffraction limit, however, STED/RESOLFF techniques eliminate the diffraction barrier. These microscopic techniques have taken the limits of optical image resolution down to the nanometer scale and opened new paths for biomedical and nanophosphor research. In this paper, we review the recent advancements of these techniques in the field of nanoscopy using continuous wave (CW) laser sources. Further, we discuss the main limitation of the STED microscopy in terms of essential requirements of higher depletion beam power and photobleaching issues. The RESOLFT microscopic technique can be considered as an alternate technique to overcome limitations of existing STED microscopy. Moreover, the Bessel and Gaussian-Bessel beam STED microscopic techniques are also reviewed to produce deep images with faster scanning of the samples. The organic molecules as well as the fluorescent doped nanoparticles like ZnSe:Mn having characteristics of excited state absorption can be investigated using RESOLFT microscopy. (C) 2019 Elsevier B.V. All rights reserved.