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News & Views: Ag136 and Ag374 Plasmonic Nanoparticles with Atomically Precise Composition

September 19, 2016

On September 9, a collaborative study led by Professors Nanfeng Zheng at Xiamen University, Hannu Hakkinen at University of Jyvaskyla, and Alison Edwards at Australian Centre for Neutron Scattering entitled “Plasmonic Twinned Silver Nanoparticles with Molecular Precision“1 was published on Nature Communications (DOI: 10.1038/ncomms12809).

In this work, a new type of Ag136 and Ag374 species protected by 4-tert-butylbenzenethiolate were chemically synthesized and structurally resolved by X-ray crystallography. It is noteworthy that, although these silver nanoparticles (Ag NPs) were identified with atomically precise composition, these species showed plasmonic optical characteristics (Figure 1).1 Atomically precise silver species, taking Ag44 as an example, typically possess characteristic optical absorption peaks and thus were initially described as intensely and broadly absorbing nanoparticles (IBANs)2 before structurally ressolved.3 The ultraviolet–visible absorption (UV-vis) of Ag136 and Ag374 reported in this work was nowhere close to molecular species and showed clear metallic features.

uv-vis_of_ag136_and_ag374_nps

Figure 1. UV-vis spectra of experimental and computed Ag136 (a) and experimental Ag374 (b) NPs.1 The figure is used under a Creative Commons CC-BY license and the corresponding authors were fully acknowledged. Copyright 2016, Nature Publishing Group.

These Ag NPs were observed to have diameters around 2-3 nm which did not come from the irradiation of electron beam as the case of many Ag or Au nanoclusters. It is known that electron microscopy images are not representative for cluster size characterization due to metal growth and agglomeration under electron beam. However, the scanning transmission electron microscope (STEM) and high-resolution TEM (HRTEM) images (Figure 2) showed that the lattices of these particles were nicely ordered into fivefold twinning, which was indicative for nanoparticles of face-centered cubic (fcc) structures.4

tem_of_ag136_and_ag374_nps

Figure 2. STEM and HRTEM (inset) images of small (a) and large (b) 4-tert-butylbenzenethiolate-protected Ag NPs. Scale bars, 2 nm.1 The figure is used under a Creative Commons CC-BY license and the corresponding authors were fully acknowledged. Copyright 2016, Nature Publishing Group.

On the other hand, these particles were distinctive from conventional nanoparticles in the sense that they only contained one size rather than mixture of a broad range of particles. The uniformity of the particle size and composition made them unique and interesting to further investigate.

This study opened a door to a more vaguely defined area between nanoparticles and nanoclusters. It showed that atomically precise silver could be prepared with larger size that turned their properties from molecular into metallic type. It could lead to new insights that are helpful for mechanistic investigations and better understanding of the particle formation process.

For more background and details, see Opinion paper: Yangwei Liu, Plasmonic Silver Nanoparticles with Atomically Precise Composition. Journal of Nanomedicine Research, 2016 4(2): 00083. DOI: 10.15406/jnmr.2016.04.00083 http://medcraveonline.com/JNMR/JNMR-04-00083.php

References
1. Yang, H., et al., Plasmonic Twinned Silver Nanoparticles with Molecular Precision. Nat Commun 2016, 7:12809.
2. Bakr, O. M., et al., Silver Nanoparticles with Broad Multiband Linear Optical Absorption. Angew Chem Int Ed 2009, 48, 5921-5926.
3. Harkness, K. M., et al., Ag-44(Sr)(30)(4-): A Silver-Thiolate Superatom Complex. Nanoscale 2012, 4, 4269-4274.
4. Xia, Y., et al., Shape-Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics? Angew Chem Int Ed 2009, 48, 60-103.
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