Nanoporous Ag-Au Bimetallic Triangular Nanoprisms Synthesized by Galvanic Replacement for Plasmonic Applications

Galvanic replacement is a versatile method of converting simple noble metallic nanoparticles into structurally more complex porous multimetallic nanostructures. In this work, roughened nanoporous Ag-Au bimetallic triangular nanoprisms (TNPs) are synthesized by galvanic replacement between smooth Ag triangular plates and AuCl4− ions. Transmission electron microscope and the elementary mapping measurements show that numerous protrusions and pores are formed on the {111} facets, and Ag and Au atoms are homogeneously distributed on the triangular plates. Due to the additional “hot spots” generated by the surface plasmon coupling of the newly formed protrusions and pores, the roughened nanoporous Ag-Au TNP aggregates demonstrate a higher surface-enhanced Raman scattering enhancement factor (seven times larger) and better reproducibility than that of smooth Ag triangular particle aggregates. These synthesized roughened nanoporous Ag-Au bimetallic TNPs are a promising candidate for the applications in analytical chemistry, biological diagnostics, and photothermal therapy due to their excellent plasmonic performances and good biocompatibility.

Present and Future Observations of the Earthshine from Antarctica

It is likely that images of Earth-like planets will be obtained in the next years. The first images will actually come down to single dots, in which biomarkers can be searched. Taking the Earth as a example of planet providing life, Earthshine observations showed that the spectral signature of photosynthetic pigments and atmospheric biogenic molecules was detectable, suggesting that, in principle, life on other planets could be detected on a global scale, if it is widely spread and distinguishable from known abiotic spectral signatures. As for the Earth, we already showed that the Vegetation Red Edge which is related to chlorophyll absorption features was larger when continents, versus oceans, were facing the Moon. It proved that an elementary mapping of a planet was even possible. In the frame of the LUCAS (LUmière Cendrée en Antarctique par Spectroscopie) project, the Earthshine has been measured in the Concordia Research Station (Dome C, Antarctica) long enough to observe variations corresponding to different parts of the Earth facing the Moon. An extension of this project, called LUCAS II, would allow long-term observations to detect seasonal variations in the vegetation signal. These data, together with precise measurements of the Earth's albedo, will help to validate a model of global and spectral albedo of our planet.