Effect of salt concentration and exposure temperature on adhesion and cytotoxicity of positively charged nanoparticles toward yeast cells

We have comprehensively scrutinized the effect of NaCl salt concentration (C_NaCl = 5–600 mM) and exposure temperature (T_exp = 4 and 25 °C) on the adhesion and cytotoxicity of positively charged nanoparticles (NPs) of 100-nm diameter toward two yeast strains (Saccharomyces cerevisiae and Schizosaccharomyces pombe) during exposure of t_exp = 0.5–24 h. On the short-time exposure toward S. cerevisiae at T_exp = 25 °C, the number of the NPs adhered to a yeast cell (N_adh) monotonically decreased with C_NaCl to become negligibly small at C_NaCl ≥ 150 mM. The greater value of N_adh resulted in the higher cell mortality. Similar results were obtained for S. pombe at C_NaCl = 5–100 mM. Interestingly, N_adh for S. pombe increased with C_NaCl (=100 to 600 mM), where the cells considerably covered with the NPs showed relatively low mortalities during the short-time exposure. The favorable NaCl concentration was found as C*_NaCl = 150 and 100 mM for S. cerevisiae and S. pombe, respectively, to survive in the aqueous suspensions of positively charged NPs during 24 h. The lower-temperature exposure (T_exp = 4 °C) for each exposure duration caused the significantly decreasing mortality of every yeast strain at the NaCl concentrations around C*_NaCl.