Introduction to Theories of Several Super-resolution Fluorescence Microscopy Methods and Recent Advance in The Field*

In life science research,it is often required to localize proteins in a live cell to a certain accuracy to study their localization-related function. However,due to the Abbe/Rayleigh criteria of light,the widely used wide-field/confocal microscopy can never resolve structures less than 200 nm in diameter. In recent year,different super-resolution microscopy techniques emerge as a result of new fluorescent probes and imaging theories. A full frame to the theories and recent advancements in this field is summarized. The concept of point-spread function of light source in the focal plane and the classical definition of resolution is explained in the first part. The fluorescence single-molecular imaging technique and the equation that defines the localization accuracy of a single molecule is introduced in the second part. Based on these knowledge,super-resolution microscopy methods based on single-molecular imaging technique,such as photoactivated localization microscopy (PALM) and stochastic optical reconstruction microscopy (STORM) is discussed further. On the other hand,by engineering the point spread function of the light source,super-resolution can also be achieved. Two typical methods,stimulated emission depletion (STED) and saturated structure illumination microscopy (SSIM) are explored thereafter. In the end,different methods to extract super-resolutional information along the z axis,and their combinations with the methods to increase xy plane resolution mentioned above are explained. In the end,the limitation to the current super-resolution methods and their future direction are also discussed.