Silver-based crystalline nanoparticles, microbially fabricated

Abstract

One mechanism of silver resistance in microorganisms is accumulation of the metal ions in the cell. Here, we report on the phenomenon of biosynthesis of silver-based single crystals with well-defined compositions and shapes, such as equilateral triangles and hexagons, in Pseudomonas stutzeri AG259. The crystals were up to 200 nm in size and were often located at the cell poles. Transmission electron microscopy, quantitative energy-dispersive x-ray analysis, and electron diffraction established that the crystals comprise at least three different types, found both in whole cells and thin sections. These Ag-containing crystals are embedded in the organic matrix of the bacteria. Their possible potential as organic-metal composites in thin film and surface coating technology is discussed.

Figure 1

TEM of a thin section of P. stutzeri AG259 cells. Large crystalline Ag⁰ and Ag₂S particles are deposited between the cell wall and the plasma membrane.

Figure 2

A variety of crystal typologies; i.e., different morphologies, sizes, and chemical compositions can be produced by P. stutzeri AG259. (a) Whole, uncontrasted cell grown on Ag⁺-containing environment with large, triangular, Ag-containing particles at both poles; an accumulation of smaller Ag-containing particles can be found all over the cell. (b and c) Triangular, hexagonal, and spheroidal Ag-containing nanoparticles accumulated at different cellular binding sites.

Figure 3

Crystal structure analysis. (a) Regularly shaped nanocrystalline Ag particle taken from a thin, unstained section of a P. stutzeri AG259 cell, with a corresponding EDX spectrum (Right) and its electron diffraction pattern (Center) indicating elemental crystalline silver. (b) Second crystal type embedded in the periplasmic space of the cell. EDX spectrum and electron diffraction indicate monoclinic Ag₂S. (c) A third type of crystal taken from a whole cell. The crystal structure is not yet clear. The electron diffraction pattern is not consistent with the pattern of elemental silver, whereas the EDX spectrum shows only Ag in considerable amounts.