Fig. 1. Quantification of ratio of full cell membrane coating.

a Schematic illustration of the preparation procedure of the cell membrane-coated mesoporous SiO₂ nanoparticles (CM-SiO₂ NPs). Membrane materials including fragments and vesicles were derived from source cells through extraction and extrusion processes. Then, the membrane materials were further fused with SiO₂ NPs to obtain CM-SiO₂ NPs by extrusion or sonication. The resulting mixture contained uncoated SiO₂ NPs, partially coated SiO₂ NPs and fully coated SiO₂ NPs. b Reduction of the fluorescent nitro-2,1,3-benzoxadiazol-4-yl (NBD) to the nonfluorescent 7-amino-2,1,3-benzoxadiazol (ABD) with dithionite (DT). c Schematic representation of probing the integrity of the cell membrane coating by the fluorescence quenching assay. In the presence of DT, which is a membrane-impermeant fluorescence quencher, the fluorescence of uncoated SiO₂ NPs (labeled with NBD) and partly coated SiO₂ NPs disappeared while only that of fully coated SiO₂ NPs was retained. d, e TEM images of bare SiO₂ NPs (d) and CM-SiO₂ NPs (e). Insets are magnified images of the areas highlighted with the respective yellow dashed box. Scale bars, 200 nm (top); 50 nm (bottom). f Schematic representation of symmetrically distributed NBD-labeled giant unilamellar vesicles (GUVs). g Typical confocal laser scanning microscopy (CLSM) image of symmetrical GUVs. Scale bar, 20 μm. h Schematic showing that SiO₂ NPs were endocytosed into CT26 cells after incubation 24 h, then localized within endosomes. i TEM images of CT26 cell endocytosed SiO₂ (E-SiO₂) NPs. Inset shows a magnified image of the area highlighted with a yellow dashed box. Scale bars, 2 μm (top); 200 nm (bottom). j Representative fluorescence traces corresponding to DT treatment of SiO₂ NPs, CM-SiO₂ NPs, GUVs and E-SiO₂ NPs. DT was first added at t = 120 s to bleach the fluorescence of NPs with a defective cell membrane coating. After a stable baseline was obtained, 1% Triton X-100 (TX-100) was added at 420 s to disrupt the integrated cell membrane and bleach the remaining fluorescence of fully coated NPs. k CLSM images of CM-SiO₂ NPs, GUVs and E-SiO₂ NPs before (top) and after (bottom) addition of DT. Scale bars, 20 μm. l Quantification of the relative fluorescence intensity of CM-SiO₂ NPs as well as the blank control (bare SiO₂ NPs) and positive control (GUVs and E-SiO₂ NPs). Data represents mean ± SD (n = 3). One-way ANOVA followed by post hoc Tukey test was used to determine the significance of data. ns: not significant.