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The structure of nanoparticles typically differs
from its bulk counterpart. Predominantly, the structures of
gold nanoparticles have been under exceedingly intense
discussion since the discovery of their high catalytic
activity. We found an increasing bond length contraction
with decreasing particle size for citrate-stabilized gold
nanoparticles in aqueous solution as determined by in situ
extended X-ray absorption fine structure (EXAFS) spectroscopy.
Particle sizes and size distributions were determined
by small-angle X-ray scattering. The analysis of the
obtained EXAFS spectra employing ab initio calculations
reveals that the Au–Au bond length undergoes a contraction
of 2 pm for nanoparticles with a radius of 2.9 nm. NIST
reference material RM 8011 gold nanoparticles with a
radius of 4.4 nm exhibit a smaller contraction of approximately
1 pm. Finally, gold atoms in RM 8013 particles
with a radius of 25.7 nm show distances of 288 pm—
identical to the distance in gold foil—and exhibits bulk-like
properties. The observed bond length contraction of gold
nanoparticles in solution is significantly smaller than
previously reported for gold nanoparticle deposited on
surfaces, which is up to 15 pm. This indicates that the
bond length contraction effect of 'free' and 'surfaceimmobilized'
nanoparticles differ fundamentally. Such
difference could be essential for the understanding of
nanoparticle-supported catalysis.
Recent results from a three-year multi-disciplinary project on Ancient Egyptian gold jewellery revealed that items of jewellery from the Middle Kingdom to the New Kingdom were manufactured using a variety of alluvial gold alloys. These alloys cover a wide range of colours and the majority contain Platinum Group Elements inclusions. However, in all the gold foils analysed, these inclusions were found to be absent. In this work a selection of gilded wood and leather items and gold foil fragments, all from the excavations by John Garstang at Abydos (primarily from Middle Kingdom graves), were examined using Scanning Electron Microscopy-Energy Disperse Spectroscopy (SEM-EDS), X-Ray Fluorescence (µXRF), Particle Induced X-Ray Emission (µPIXE) and Double Dispersive X-Ray Fluorescence (D²XRF). The work allowed us to characterise the composition of the base-alloys and also to reveal the presence of Pt at trace levels, confirming the use of alluvial gold deposits. Corrosion products were also investigated in the foils where surface tarnish was visually observed. Results showed that the differences in the colour of corrosion observed for the foils are related not only to the thickness of the corrosion layer but also to a multi-layer structure containing the various corrosion products.
Dose enhancement by gold nanoparticles (AuNP) was shown to increase the biological effectiveness of radiation damage in biomolecules and tissue. Most of the current studies focus on external beam therapy on combination with AuNP. Here we present a Monte-Carlo study (Geant4) to characterise radioactive AuNP. Radioactive 198 Au emits beta and gamma rays and is considered for applications with solid tumours. To effectively apply 198 AuNP their energy deposit characteristics have to be determined in terms of intrinsic and extrinsic properties e.g. AuNP diameter, AuNP density, and their clustering behaviour. After each decay process, the energy deposit, inelastic scattering events, kinetic energy spectrum of secondary particles within the AuNP themselves and in a spherical target volume of water up to 1 μm radius were determined. Simulations were performed for AuNP radii ranging from 2.5 nm to 20 nm radius, different cluster sizes and densities. The results show an increase of the energy deposit in the vicinity of the AuNP up to 150 nm. This effect nearly vanishes for distances up to one micron. For the case of AuNP clusters and the same activity, the enhancement of the energy deposit increases with the relative gold mass percentage and therefore can be adjusted by changing AuNP radius or clustering behaviour.