Fluorescent AF dyes are fluorescent substances with sulfonated groups. AF dyes are negatively charged and are characterized by high hydrophilicity, high brightness, strong light stability, instrument compatibility, and insensitivity to pH. The excitation peak of the AF dye is suitable for the laser spectrum, the emission peak is relatively narrow, the quenching resistance is strong, and it is beneficial to a variety of fluorescent labels. It is very suitable for laser confocal and is often used in microscopy technology. For example, AF 488 NHS ester with a maximum excitation wavelength of 495nm can be excited by a standard 480nm laser.