Novel nanoparticles with unique physicochemical characteristics are being developed with increasing frequency, leading to higher probability of nanoparticle release and environmental accumulation. Therefore, it is important to assess the potential environmental and biological adverse effects of nanoparticles. In this study, we investigated the toxicity and behavior of surface-functionalized nanoparticles toward yeast (Saccharomyces cerevisiae). The colony count method and confocal microscopy were used to examine the cytotoxicity of manufactured polystyrene latex (PSL) nanoparticles with various functional groups (amine, carboxyl, sulfate, and nonmodified). S. cerevisiae were exposed to PSL nanoparticles (40 mg/L) dispersed in 5-154 mM NaCl solutions for 1 h. Negatively charged nanoparticles had little or no toxic effect. Interestingly, nanoparticles with positively charged amine groups (p-Amine) were not toxic in 154 mM NaCl, but highly toxic in 5 mM NaCl. Confocal microscopy indicated that in 154 mM NaCl, the p-Amine nanoparticles were internalized by endocytosis, whereas in 5 mM NaCl they covered the dead cell surfaces. This demonstrates that nanoparticle-induced cell death might to be related to their adhesion to cells rather than their internalization. Together, these findings identify important factors in determining nanoparticle toxicity that might affect their impact on the environment and human health.

a b s t r a c tThe toxicity and the internalization, adhesion, and dispersion behavior of manufactured polystyrene latex (PSL) nanoparticles (nominal diameter: 50 nm) with various functional groups toward the yeast Saccharomyces cerevisiae (which was applied as a model eukaryote) were examined using the colony count method, and microscopic observations. The colony count tests suggested that PSL nanoparticles with a negative surface charge showed little or no toxicity toward the yeast. In contrast, PSL nanoparticles with an amine functional group and a positive surface charge (p-Amine) displayed a high toxicity in 5 mM NaCl. However, the yeast cells were mostly unharmed by the p-Amine in 154 mM NaCl, results that were quite different from the toxicological effects observed when Escherichia coli was used as a model prokaryote. Confocal and atomic force microscopies indicated that in 5 mM NaCl, the p-Amine nanoparticles entirely covered the surface of the yeast, and cell death occurred; in contrast, in 154 mM NaCl, the pAmine nanoparticles were internalized via endocytosis, and cell death did not occur.

Nanotechnology has the potential to produce a variety of new materials in the coming years, as a result of the design of novel nanoparticles with new physicochemical characteristics. However, their potential to adversely affect the environment and human health must be addressed. The toxicity of polystyrene latex (PSL) nanoparticles with various functional groups toward Escherichia coli KP7600 strain was investigated using the colony count method, and confocal microscopy observations. It was found that the positively charged PSL nanoparticles led to the death of the bacterial cells. Confocal observations of the bacterial cells after 1 h of exposure to the amine-modified, positively-charged PSL nanoparticles in an aqueous NaCl solution showed that the surfaces of the dead cells were almost entirely covered with the nanoparticles. No uptake of the nanoparticles into the bacterial cells was observed, regardless of the cell viability. It is likely that the adhesion of the positively charged nanoparticles onto the surface of the bacterial cells (due to the electrostatic attractive force) caused a decrease in the fluidity of the cell membrane, and the inhibition of metabolism through the cell membrane led to the death of the bacterial cells.

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