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Super-Stable, Highly Monodisperse Plasmonic Faradaurate-500 Nanocrystals with 500 Gold Atoms: Au∼500(SR)∼120

Kumara, Chanaka, Zuo, Xiaobing, Ilavsky, Jan, Chapman, Karena W., Cullen, David A., Dass, Amala
Journal of the American Chemical Society 2014 v.136 no.20 pp. 7410-7417
X-radiation, gold, mass spectrometry, nanocrystals, nanogold, nanoparticles, transmission electron microscopy
Determining the composition of plasmonic nanoparticles is challenging due to a lack of tools to accurately quantify the number of atoms within the particle. Mass spectrometry plays a significant role in determining the nanoparticle composition at the atomic level. Significant progress has been made in understanding ultrasmall gold nanoparticles such as Au₂₅(SR)₁₈ and Au₃₈(SR)₂₄, which have Au core diameters of 0.97 and 1.3 nm, respectively. However, progress in 2–5 nm-diameter small plasmonic nanoparticles is currently impeded, partially because of the challenges in synthesizing monodisperse nanoparticles. Here, we report a plasmonic nanocrystal that is highly monodisperse, with unprecedentedly small size variability. The composition of the superstable plasmonic nanocrystals at 115 kDa was determined as Au₅₀₀±₁₀SR₁₂₀±₃. The Au∼₅₀₀ system, named Faradaurate-500, is the largest system to be characterized using high resolution electrospray (ESI) mass spectrometry. Atomic pair distribution function (PDF) data indicate that the local atomic structure is consistent with a face-centered cubic (fcc) or Marks decahedral arrangement. High resolution scanning transmission electron microscopy (STEM) images show that the diameter is 2.4 ± 0.1 nm. The size and the shape of the molecular envelope measured by small-angle X-ray scattering (SAXS) confirms the STEM and PDF analysis.