Metabolic glycan labeling of living U2OS cells with modified neuraminic acids. A. Fluorescence microscope images of U2OS cells cultured with Neu5Ac, Neu9NAz (8), Neu5SydCl (4) and Neu9NSydCl (7), treated with BCN-biotin and stained with Streptavidin-AlexaFluor568 (Red) and DAPI (Blue), Scale bar: 10 μm. B. Flow cytometry analysis of U2OS cells cultured respectively with No Sugar, Neu5Ac, Neu9NAz (8), Neu5SydCl (4) and Neu9NSydCl (7). All cells were treated with BCN-biotin and Streptavidin-AlexaFluor568.