Abstract: ［Abstract］ Objective〖HTSS〗To compare and analyze the staining effect and select the best negative dyeing solution for exosomes after negatively staining the exosomes with four kinds of dyes, such as osmium tetroxide, phosphotungstic acid, ammonium molybdate and uranyl acetate.
〖HTH〗〖WTHZ〗Methods〖HTSS〗After exosomes were extracted by differential centrifugation, the exosomes were negatively stained with four different dyeing solutions of osmium tetroxide, phosphotungstic acid, ammonium molybdate and uranyl acetate by means of floating method, and observed by transmission electron microscopy. The clarity of the cupshaped or discshaped structure of the exosomes, the sharpness of the film edge, the cleanness of the staining background, and the contrast effect werecompared according the effects of the four dyeing solutions.
〖HTH〗〖WTHZ〗Results〖HTSS〗Osmium tetroxide staining background appeared a large number of vesicles, exosome structurewas not obvious. The dyeing effect of phosphotungstic acid on exosomes was not as good as that of uranium dioxide acetate and ammonium molybdate. The cell membrane edge of exosomes was not clear and the dyeing background was impurities. Ammonium molybdate had a better staining effect on exosomes. The membrane structure of the vesicles was clear, and the cupsupporting structure of the exosomes can be clearly seen, but the contrast was weak. Under uranium acetate hydrogen peroxide staining, the typical cupshaped or discoid structure of exosome were clearly visible, the edge of membrane was sharp, the dyeing background was clean, and the contrast effect were good.
〖HTH〗〖WTHZ〗Conclusion〖HTSS〗The uranyl acetate has the best staining effect on exosomes, and it is the most suitable negative dyeing solution.

Key words: exosomes, negative staining； transmission electron microscopy