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Microstructure and properties of alloyed silver-gold nanoparticles

Prymak O., Ristig S., Meyer-Zaika W., Raabe D., Epple M.

Engineering of Biomaterials

2014

Vol. 17, no. 128-129

Alloyed silver-gold nanoparticles recently raised an interest in biomedicine as potential antibacterial and surface-functionalized agents for imaging, drugdelivery, and tumor thermo-therapy [1,2]. The here synthesized alloyed AgAu nanoparticles with different compositions of silver and gold, as determined by atomic absorption spectroscopy (AAS), were prepared by reduction with citrate and tannic acid in aqueous media and subsequently functionalized by the addition of polyvinylpyrrolidone (PVP) [3]. UV spectroscopy confirmed that the particles consisted of alloyed Ag:Au and are not of a separate core-shell structure. The resulting nanoparticles were monodisperse and had a uniform size of ~6 nm, except pure Ag and Ag:Au-90:10, as shown by differential centrifugal sedimentation (DCS) and transmission electron microscopy (TEM). By means of X-ray powder diffraction (XRD) and use of Rietveld refinement [4], the precise lattice parameters, crystallite size and microstrain were determined. Based on the results by XRD, DCS and TEM it was shown, that the nanoparticles were not twinned, except pure Ag and Ag:Au-90:10. Additionally, a distinct deviation from Vegard’s linear rule of alloy mixtures for the lattice parameter was found for the nanoparticles. This effect was also found for AgAu bulk materials, but was much more pronounced in the nanostate. Further investigations of the crystal structure of the alloyed nanoparticles by means of synchrotron radiation might be helpful to gain more information about the interactions of silver and gold atoms.

Correlation of composition and structure of shark teeth

Prymak O., Enax J., Fabritius H., Raabe D., Epple M.

Engineering of Biomaterials

2013

Vol. 16, no. 122-123 spec. iss.

In contrast to mammalian teeth with the biomineral phase hydroxyapatite, the shark teeth contain harder mineral phase fluoroapatite with partial substitutions of phosphate by carbonate and of fluoride by hydroxide [1]. Their excellent mechanical properties are due to a special hierarchical structure of the constituting fluoroapatite crystals and organic matrix [2]. The two main structural elements of teeth, i.e. hard and mineral-rich enameloid on the outside and softer and less mineralized dentin on the inside, were structurally, chemically and mechanically characterized [3]. The teeth of two different shark species mako shark (Isurus oxyrinchus) and tiger shark (Galeocerdo cuvier) were investigated and their hierarchical structure by high-resolution scanning electron microscopy presented (Fig.1). X-ray diffraction showed that the inorganic matrix of both enameloid and dentin consisted of fluoroapatite, with a high crystalline phase in enameloid and nanocrystalline phase in dentin. FTIR-spectra of the shark teeth showed the characteristic bands of biological apatite. It was found by thermogravimetry that dentin had a higher content of water, organic matrix and carbonate than enameloid. To investigate the mechanical properties of the teeth in longitudinal and cross sections, nanoindentation and Vickers microhardness were carried out. Both methods gave comparable results: the enameloid of both shark teeth was approximately six times harder than the dentin with an isotropic hardness (longitudinal or cross section).