Characterization of thiolate-protected gold nanoparticles by mass spectrometry

Abstract

Thiolate-protected gold nanoparticles (AuNPs) are a highly versatile nanomaterial, with wide-ranging physical properties dependent upon the protecting thiolate ligands and gold core size. These nanoparticles serve as a scaffold for a diverse and rapidly increasing number of applications, extending from molecular electronics to vaccine development. Key to the development of such applications is the ability to quickly and precisely characterize synthesized AuNPs. While a unique set of challenges have inhibited the potential of mass spectrometry in this area, recent improvements have made mass spectrometry a dominant technique in the characterization of small AuNPs, specifically those with discrete sizes and structures referred to as monolayer-protected gold clusters (MPCs). The unique ability of mass spectrometry to analyze the protecting monolayer of the AuNP may cause it to become a major technique in the characterization of larger AuNPs. The development of mass spectrometry techniques for AuNP characterization has begun to reveal interesting new areas of research. This report is a discussion of the historical challenges in this field, the emerging techniques which aim to meet those challenges, and the future role of mass spectrometry in the growing field of thiolate-protected AuNPs.

Quantum‐Sized Gold Nanoclusters: Bridging the Gap between Organometallics and Nanocrystals

“…[74] Electron shell closing has also been found in some ligandprotected nanoclusters, for example, 8e in [Au 25 (SR) 18 ] À , [76] 58e in [Au 102 (SR) 44 ], and 34e in [Au 68 (SR) 34 ] [77] (identified in MALDI-MS). But there are many nanoclusters that do not conform to the electron shell closing numbers, include neutral [Au 25 (SR) 18 ] (7e), [78] [Au 38 (SR) 24 ] (14e), [59] [Au 144 (SR) 60 ] (84e), [65] [Au 20 (SR) 16 ] (4e), [79] [Au 24 (SR) 20 ] (4e), [80] [Au 40 (SR) 24 ] (16e), [81] etc. Thus far, it is not yet completely clear, to what extent the electronic or atomic shell-closing can interpret the observed stability numbers of [Au n L m ] nanoclusters.…”

“…From the cases of [Au 25 (SR) 18 ], [Au 38 (SR) 24 ], and other nanoclusters such as Au/Ag bimetal ones, it seems that the icosahedral motif is quite prevalent in the relatively small nanoclusters (say, n < 100). The M 13 icosahedron is thought to be the end of the atom-by-atom growth pattern [68] (from Au 2 to Au 13 clusters), but it serves as a new start for larger clusters (n > 13).…”

“…[56,57] Interestingly, a structurally related M 17 cluster was previously reported by Dahl et al, [1] in which a Pt 13 icosahedron is capped by two Ph 3 PAuÀAuPPh 3 dimers (resembling the partial structure shown in Figure 4 B). The charge state of [Au 25 (SR) 18 ] q (q = À1,0) does nota later the atom packing structure of the Au 25 cluster. [58] The next size is the 38-atom Au 38 (SR) 24 .…”

“…Here we briefly discuss some recent breakthroughs with a focus on the crystal structures of three [55][56][57][58][59] We start with [Au 25 (SR) 18 ] q since it is the smallest one. The structure of Au 25 is based on a centered icosahedron (Au 13 ) (Figure 4 A).…”

“…poor solubility 4 species is often identified in electrospray ionization (ESI) mass spectrometry analysis of gold clusters. [18,19] Note that a tetrameric cycle is an eight-membered cycle since the coordinate atom (S) of thiolate ligand bridges two Au atoms. Several types of structures of [Au I -SR] n complexes [6,20] have been proposed or identified, such as zigzag chains and rings.…”