The first atomic structure of a gold nanoparticle (AuNP) was determined by X-ray crystallography (1). The atomic structure that identified the Au102NP as a molecule led to the idea of the gold cluster as a “super-atom”, and revealed a layer of alternating gold and ligand molecules at the interface (2). Subsequent X-ray structures of smaller organo-soluble AuNPs have supported the super-atom idea, and have shown a similar gold-thiol surface layer (3). Nevertheless, using X-ray crystallography as a general method for solving AuNP structures has been limited by the capability of forming well-ordered crystals. The structure determination of AuNPs at atomic resolution by aberration corrected electron microscopy (EM) was demonstrated (4,5). The successful structural determination was due to the implementation of a low dose strategy combined with a homogeneous sample that could be subjected to single particle reconstruction. Last but not least, the new structures do not respond to the super-atom model. Yet, they are well-defined particles of remarkable stability and reactivity. Such reactivity makes possible to form bio-conjugates that can be used to monitor traffic of small proteins inside human cells by cryo-electron tomography.
(1)Jadzinsky et al. Science (2007).
(2) Walter, et al. Proc. Natl. Acad. Sci. (2008)
(3)Häkkinen. Nature Chemistry (2012).
(4) Azubel et al. Science (2014).
(5) Azubel et al. ACSNano (2017)