Control of colloidal behavior of polystyrene latex nanoparticles and their cytotoxicity toward yeast cells using water-soluble polymers

Positively charged polystyrene latex (PSL) nanoparticles (NPs) dispersed in physiological saline (154?mM NaCl solution) are taken up by yeast cells. However, in low ionic strength solutions, the yeast cells are covered with the NPs, leading to cell death. The environmental conditions under which NPs are taken up are therefore limited. In this study, we attempted to control the uptake of positively charged PSL NPs by Saccharomyces cerevisiae in 5?mM NaCl solution using a water-soluble polymer. Addition of a small amount of anionic sodium carboxymethylcellulose (CMC), which has a carboxyl group, to 5?mM NaCl solution allowed the uptake of PSL NPs by living yeast cells. In contrast, non-ionic methylcellulose did not affect the NP behavior. This is because the negatively charged CMC adhered to the positively charged PSL NP surfaces and the surface charge changed from positive to negative. Atomic force microscopy using a single-NP probe consisting of one NP immobilized on the flattened end of the silicon nitride tip showed that CMC significantly reduced the interaction force between a negatively charged living yeast cell and a positively charged PSL NP.