Cytotoxicity and behavior of polystyrene latex nanoparticles to budding yeast

• NPs adhered on the yeast cell surface showed high toxicity in low ionic strength.
• NPs entrapped in the yeast cells showed little toxicity in high ionic strength.
• The electrostatic attractive force between yeast and NP affected cell viability.
• The osmotic pressure inhibited the uptake of NPs.

The cytotoxicity and behavior of positively charged amine-modified polystyrene latex nanoparticles (NPs) toward budding yeast cells were examined in different environments. The yeast cells, dispersed in either 27.8 mM glucose or low-ionic strength aqueous electrolyte solution, were covered with NPs regardless of the ionic species or diameter of the NPs. The NPs that adhered to the cell surface showed high toxicity. The cell viability following NP exposure increased with the NaCl concentration independently of the glucose concentration in the dispersion medium. Therefore, the strong electrostatic attraction between the negatively charged yeast cells and positively charged NPs resulted in NP adhesion to the cell surface and subsequent cell death. However, the amount of endocytosis-like NPs inside the cell, dispersed in the hypertonic solution, was lower than that in the isotonic solution. These results indicate that the osmotic pressure affects the uptake of NPs rather than the cell viability. In contrast, NPs dispersed in a high-ionic strength electrolyte solution with a diameter of ∼100 nm or less were absorbed by the yeast cells. NPs incorporated in the living yeast cells showed little toxicity.

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