Fig. 2. Microscopic results of tagging sialoglycoproteins on the HEK293T cell surface by using click chemistry. (a, d and g) Images of cells (scale bar is 20 μm). (b, e and h) Fluorescence signals of labeled cells reacted with DBCO-Fluor545 via copper-free click chemistry. (c) Fluorescence signals of labeled cells bound to DBCO-sulfo-biotin, followed by incubation with streptavidin–FITC. (f) Cells without the biotin tag treated by streptavidin–FITC show no green signal. (i) After cell surface sialoglycoproteins with the azido group are tagged by the click chemistry reaction with DBCO-Fluor545, cells were further treated with DBCO-sulfo-biotin, followed by streptavidin–FITC. No green signal demonstrated that the click reaction was efficient and complete.