Fig. 2

Characterization of ultrasmall PEI-GOS-PEG-FA and its tumor-targeting effect. a Photographs of GOS, carboxylated GOS and PEI-GO-PEG-FA in DI water show a visible color difference. b Representative diagram from Zetasizer Nano ZSP for the sizes of various GOS derivatives. c Zeta potential values of various GO derivatives. d XPS binding energy survey of the PEI-GO-PEG-FA conjugate (black), GOS (red) and carboxylated GOS (blue). e AFM images of small GOS, ultrasmall carboxylated GOS and PEI-GO-PEG-FA. f HeLa human cervical carcinoma cells largely express FR. FA and PEI-GOS-PEG-FA were labeled with rhodamine (FA-Rho and PEI-GOS-PEG-FA-Rho), a commonly used fluorescent dye. Cell-surface FR expression of the HeLa cells was determined by fluorescence-activated cell sorting analysis. g A total of 5 × 10⁶ HeLa cells/0.1 ml/mouse was subcutaneously injected into the left flanks of 5- to 6-week-old male Foxn1nu mut/mut mice; 10 days later, the tumors became visible. The mice were randomly divided into three groups. PEI-GOS-PEG or PEI-GOS-PEG-FA was labeled with rhodamine; then, nude mice bearing HeLa human cervical carcinoma tumors were intravenously injected with Rho, PEI-GOS-PEG-Rho or PEI-GOS-PEG-FA-Rho (200 μl of a 0.15 mg/ml solution for each mouse; a dose of 20 mg/kg) and then spectrally imaged by the IVIS Lumina XR system at 1 h and 24 h postinjection. The percentage of tumor enriched Rho was calculated by dividing the fluorence intensity in tumor by total (lower panel, n = 3). * p < 0.05, **p < 0.01