Fig. 4

Cell metabolic activity; MTT assay (a) and cell viability; dual staining assay (b) of mouse fibroblasts (NIH3T3) and human osteosarcoma (U2OS) after exposure to melanin-based gold nanoparticles. For MTT assay, cells were incubated for 24 h with different amounts of AuNPs. Results are presented as a percentage of metabolically active cells after AuNPs melanin treatment (three replicates with ± SD) compare to control (without AuNPs). Statistical analysis was performed using one-way ANOVA and Dunett’s a posteriori. *p < 0.05, no asterisk indication—no statistical significance. For dual staining, cells after AuNPs treatment were stained with acridine orange and ethidium bromide. Cells were imaged with inverted fluorescence microscope, objective ×20. Dead cells were scored per 100 total cells analyzed and expressed as %