Yeast cells carrying metal nanoparticles

Abstract

Yeast cells can be used as carriers for hosting metal nanoparticles via in situ metal ion reduction methods. We synthesized Ag and Pd nanoparticles (NPs) located in different positions of yeast cells, either in yeast cell envelope or inside yeast cells. Ag NPs were able to grow at the cell wall and inside the cells depending on the preparation methods. Glucans at the cell wall functioned as reductive reagents in Tollens's reaction and Ag NPs with average size of about 9 nm (measured with Scherrer equation) were formed covering yeast cells. By UV illumination on yeast cells with AgNO3 solution imported in cytoplasm in advance, Ag nanoparticles with size of about 4 nm were produced inside yeast cells. UV illumination in the presence of Ag ions could carbonize the yeast cells as indicated by Raman spectroscopic analysis, which may be conducive to establishing new sterilization mechanism. Yeast cells carrying palladium nanoparticles were also synthesized by hydrazine hydrate reduction inside cells. It was found that Pd nanoparticles with size of about 11 nm were almost evenly distributed in every parts of yeast cells, in the envelope and inside cells. Ag NPs and Pd NPs on yeast cells were observed with optical microscopy, scanning electronic microscopy (SEM), and transmission electron microscopy (TEM). Crystal structures of Ag NPs and Pd NPs were confirmed by X-ray powder diffraction (XRD). The sizes of the NPs were calculated based on XRD results and Scherrer equation. The size distribution of NPs was obtained by counting the sizes of NPs on TEM images. Those results showed that easily affordable yeast cells are good bio-carriers for synthesis and stabilization of metal nanoparticles in aqueous environments, and no other chemical stabilizers were needed. The yeast carrying metal nanoparticles structures may find applications in medical or environmental treatment fields.