pH dependent adsorption of GC-AuNPs on live HeLa cell membrane. Brightfield (A, C) and fluorescence (B, D) images of live HeLa cells incubated with 0.2 mg/mL GC-AuNPs at pH 7.4 (A, B) and 5.3 (C, D) in PBS at 25°C for 10 min respectively (scalar bar, 20 µm). (E) Co-localization of GC-AuNPs with DiR (a phospholipid bilayer membrane dye) on live cell membrane (scalar bar, 20 µm).