Fig. 4. Confocal fluorescence images of HeLa cells incubated with BSA–SqNP hybrids in the ratio of 6 : 1, 12 : 1 and 1 : 1 at pH 6.5, 7.0 and 7.5 for 30 min at 37 °C. Green and red images were obtained by exciting at 405 and 640 nm respectively. The corresponding ratio images are also shown.