Fig. 1

Characterization and biocompatibility of PDA NPs. (A) The schematic diagram illustrates the synthesis of PDA nanoparticles (PDA NPs). PDA NPs were prepared via oxidized and self-polymerized dopamine hydrochloride in an alkaline water-ethanol solution. (B) Transmission electron microscopy (TEM) images of PDA NPs. (C) Quantitative analysis of particle size distribution of PDA NPs (n = 100). (D, E) Elemental mapping and energy dispersive spectra of PDA NPs. Scale bar = 500 nm. (F) DPPH free-radical scavenging ability of different concentrations of PDA NPs (0, 220, 260, 300, 340, and 380 μg/mL). (G) UV-absorbance spectra of 0.1 wt% PDA and PBS solution. (H) HaCaT cells (an immortal cell line of human keratinocytes) were incubated with different concentrations of PDA NPs (0, 20, 40, 60, 80, 100, and 200 μg/mL) for 2 h. The cell viability of HaCaT cells was detected by CCK-8 assay. Scale bar = 10 μm. (I) Confocal laser scanning microscopy images of PDA NPs intake by HaCaT cells and colocalized with lysosomes (UVR-/+). Lysosomes were stained with LysoTracker Red DND-99 (red). Nuclei were stained with Hoechst 33,258 (blue); PDA NPs were black in HaCaT cells under a bright field. Data represent the mean ± SD. *p < 0.05.