Shape Homogenization and Long-Range Arrangement of Gold Nanorods Using a pH-Responsive Multiamine Surfactant

A relatively new and efficient method is reported here for the purification and arrangement of high-aspect-ratio gold nanorods (AuNRs) using a multiamine surfactant, bis­[[(amidoethyl)­carbamoyl]­ethyl]­octadecylamine (C18N3), which strongly adsorbs to the surface of AuNRs. The adsorbed layers of the multiamine surfactant on AuNRs exhibit the ability to deaggregate gold nanoparticles at low pH in an aqueous medium and to promote their aggregation at high pH. Through regulation of the pH of the dispersion medium, a well-ordered arrangement of 99% monodisperse AuNRs was obtained, having dimensions of approximately 18 nm diameter and 353 nm length and an area of several dozens of square micrometers, which is much larger than what has been reported in the literature. A very strong optical absorption in the near-infrared region of as-prepared AuNRs was shown. This strategy of using pH-responsive multiamine surfactant to mediate both the homogenization in shape and the arrangement of nanoparticles provides a new methodology for the formation of nanoparticle assemblies

Isotopic Composition and Distribution of Plutonium in Northern South China Sea Sediments Revealed Continuous Release and Transport of Pu from the Marshall Islands

The ^239+240Pu activities and ²⁴⁰Pu/²³⁹Pu atom ratios in sediments of the northern South China Sea and its adjacent Pearl River Estuary were determined to examine the spatial and temporal variations of Pu inputs. We clarified that Pu in the study area is sourced from a combination of global fallout and close-in fallout from the Pacific Proving Grounds in the Marshall Islands where above-ground nuclear weapons testing was carried out during the period of 1952–1958. The latter source dominated the Pu input in the 1950s, as evidenced by elevated ²⁴⁰Pu/²³⁹Pu atom ratios (>0.30) in a dated sediment core. Even after the 1950s, the Pacific Proving Grounds was still a dominant Pu source due to continuous transport of remobilized Pu from the Marshall Islands, about 4500 km away, along the North Equatorial Current followed by the transport of the Kuroshio current and its extension into the South China Sea through the Luzon Strait. Using a simple two end-member mixing model, we have quantified the contributions of Pu from the Pacific Proving Grounds to the northern South China Sea shelf and the Pearl River Estuary are 68% ± 1% and 30% ± 5%, respectively. This study also confirmed that there were no clear signals of Pu from the Fukushima Daiichi Nuclear Power Plant accident impacting the South China Sea