Detection of ultra-low oxygen concentration based on the fluorescence blinking dynamics of single molecules

Aqueous solutions of tetrachloroauric acid of high purity and stability were synthesised using the known reaction of gold metal with chlorine gas. The straightforward procedure developed here allows the resulting solution to be used directly for gold nanoparticle synthesis. The procedure involves bubbling chlorine gas through pure water containing a pellet of gold. The reaction is quantitative and progressed at a satisfactory rate at 50 °C. The gold(III) chloride solutions produced by this method show no evidence of returning to metallic gold over at least twelve months. This procedure also provides a straightforward method to determine the concentration of the resulting solution using the initial mass of gold and volume of water.

Knowledge concerning the sintering behavior of gold nanoparticles (AuNPs) allows for improved nanomaterials for applications such as printed electronics, catalysis and sensing. In this study, we examined the ability of a range of compounds to stabilize AuNPs against thermal sintering and compared compounds with and without functional groups that anchor the molecules to the nanoparticle surface. Thermal stability was characterized in terms of the temperature of the sintering event (TSE) as well as thermogravimetric analysis and scanning electron microscopy. We show that anchored stabilizing compounds with high thermal stability are effective at preventing the sintering of AuNPs until the decomposition of the compound. A TSE of 390 °C was achieved using 1pyrenebutanethiol as stabilizer. Of the unanchored stabilizers, which were combined with butanethiol-capped AuNPs, two were found to be particularly effective: oleylamine (TSE ≈ 300 °C) and a perylenedicarboximide derivative (TSE ≈ 540 °C), the latter conferring an unprecedented level of thermal stability on ligand-stabilized AuNPs. When selecting stabilizers without anchoring groups, our results demonstrate the importance of choosing those that have an affinity with the capping ligands on the AuNPs to ensure a uniform mixture of AuNPs and stabilizer within a film.

A gold nanoparticle (AuNP) ruthenium phthalocyanine (RuPc) nanocomposite has been synthesised that exhibits high thermal stability. Electrical resistance measurements revealed that the nanocomposite is stable up to ∼320 °C. Examination of the nanocomposite and the RuPc stabiliser complex using thermogravimetric analysis and differential scanning calorimetry show that the remarkable thermal stability is due to the RuPc molecules, which provide an effective barrier to sintering of the AuNPs.

The changes in optical properties that occur as gold nanoparticles (AuNPs) are thermally converted to a continuous thin film were studied with the purpose of determining the roles of particle coarsening and temperature. In situ reflectance spectroscopy, electron microscopy and synchrotron X-ray diffraction were applied to provide complementary information on the changes in particle size and shape. The AuNPs studied were stabilized with 1-butanethiol, 1-octanethiol, oleylamine or 4-(pyren-1-yl)butane-1-thiol. Initially the films were dark brown or purple in color, due to the plasmon resonance of the AuNPs. As the temperature was increased the AuNPs started to coalesce and percolate, thereby changing the color of the films to that of bulk gold. Films of AuNPs stabilized with alkanethiols sintered very rapidly, measured as a rapid change in the reflectance spectrum. In contrast, films of AuNPs stabilized with oleylamine or 4-(pyren-1-yl)butane-1-thiol sintered more gradually and at a higher temperature. This permitted the transition to be studied in greater detail than for the alkanethiols. Red-shifted plasmon peaks and increased intensity in the reflectance data, and XRD and electron microscopy measurements, revealed that a prolonged process of nanoparticle coarsening occurred prior to sintering. The effect of temperature on the optical properties was isolated by monitoring samples as they cooled. The insulator-to-metal transition in these types of composites offers a very flexible platform for controlling spectral properties in the near-infrared region.Supporting Information. UV-visible spectra, SEM and TEM micrographs, histogram of particle sizes for OA@AuNPs, photographs showing decomposition of PyBuOH. This material is available free of charge via the Internet at http://pubs.acs.org.