Direct measurements of colloidal behavior of polystyrene nanoparticles into budding yeast cells using atomic force microscopy and confocal microscopy

Abstract

The colloidal behavior of positively charged polystyrene latex (PSL) nanoparticles (NPs) toward yeast cells (Saccharomyces cerevisiae) was investigated using atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM). AFM imaging revealed that the conically-shaped pits connected with endocytosis were observed in 154 mM NaCl, and the surface was completely covered with NPs within 60 s in 5 mM NaCl. AFM force measurements revealed that the adhesion rate of NPs in 5 mM NaCl was faster than that in 154 mM NaCl. This strongly suggested that in 5 mM NaCl, the NPs accumulated on the cell surface over a short time followed by cell death. Furthermore, the accumulation of NPs on the cell surface in 5 mM NaCl could be suppressed by adding polyethylene glycol to the medium, resulting in an increase in the number of living cells. This suggests that the adhesion rate of NPs primarily depended on the interaction forces between the surfaces, and the viscosity of the medium. Thus, the colloidal behavior of the positively charged PSL NPs toward yeast cells was controlled by the balance between the adhesion rate of NPs on the cells and the uptake rate of NPs into the cells. Additionally, the uptake of the PSL NPs and an endocytosis marker into the cells was inhibited by Latrunculin B and NaN3. However, their locations without inhibitor treatment were obviously different, indicating that NPs were not transported to the vacuole and accumulated in the vesicles.