The 4T1 cells (mouse breast carcinoma cells) were purchased from the cell bank of the Chinese Academy of Sciences (Beijing, China) and maintained in RPMI 1640 (Gibco) medium containing 10% FBS (Gibco). The cells were seeded in six-well plates at 2.0×105/well, and cultured at 37°C and 5% CO2 for 24 h until they adhered to the bottom of the plate. The ICG, PHSA-ICG, and PHSA-ICG-TAT (10 μM) were added to the cells, respectively, and the cell suspension was collected after 0, 1, 4, and 8 h. The cell suspension was filtered with a 70 μM filter, and the cells were resuspended in 200 μL of PBS in a 1.5 mL Eppendorf tube. Monochromatic flow fluorescence analysis was carried out at 640 nm excitation and 780 nm emission to determine the cell uptake of materials. The above cells cultured for 24 h were stained with Hoechst staining solution for 15 min and observed using a fluorescence microscope (DP80; Olympus, Tokyo, Japan) for the colocalization of materials.