There is an old adage that says “To see is to believe,” and it still seems to be true in many fields of biology. For an experimental validation of hypotheses, modern biology takes advantage of various fluorescence-based techniques (fluorescence microscopy, digital image analysis) for visualization and quantification. Fluorescence Recovery after Photobleaching (FRAP), a widely used fluorescence-based technique to visualize and quantify the diffusion of fluorescently tagged proteins, is one good example. The first observation of fluorescence was made by Sir John Frederick William Herschel (1845) from a quinine solution, and the concept of fluorescence was first named after fluorite by Sir George G. Stokes (1857). On a microscopic scale, fluorescence was first observed by August K?ler (1904), who discovered that a biological tissue could autofluoresce under ultraviolet light irradiation. Later, it became popular in the biological field after M. Haitinger (1933) succeeded in staining histological specimens with fluorescent dyes for the first time, which is called the technique of secondary fluorescence, distinguishing it from autofluorescent tissue previously observed by M. Haitinger. Haitinger and others extended the application of the technique of secondary fluorescence to stain not only specific tissues but also bacteria, or other pathogens that are not autofluorescent 1. Although the technique of secondary fluorescence demonstrated that nonfluorescent cells can be made fluorescent, it was a nonspecific staining technique. The breakthrough in a specific immunofluorescence staining technique was provided by Albert Coons in 1941 by attaching a fluorescent dye to an antibody 2. Later, Coons and N.H. Kaplan developed the fluorescein isothiocyanate (FITC) immunofluorescence technique 3.