Computational and Experimental Investigation of Janus-like Monolayers on Ultrasmall Noble Metal Nanoparticles

Abstract

Detection of monolayer morphology on nanoparticles smaller than 10 nm has proven difficult with traditional visualization techniques. Here matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) is used in conjunction with atomistic simulations to detect the formation of Janus-like monolayers on noble metal nanoparticles. Silver metal nanoparticles were synthesized with a monolayer consisting of dodecanethiol (DDT) and mercaptoethanol (ME) at varying ratios. The nanoparticles were then analyzed using MALDI-MS, which gives information on the local ordering of ligands on the surface. The MALDI-MS analysis showed large deviations from random ordering, suggesting phase separation of the DDT/ME monolayers. Atomistic Monte Carlo (MC) calculations were then used to simulate the nanoscale morphology of the DDT/ME monolayers. In order to quantitatively compare the computational and experimental results, we developed a method for determining an expected MALDI-MS spectrum from the atomistic simulation. Experiments and simulations show quantitative agreement, and both indicate that the DDT/ME ligands undergo phase separation, resulting in Janus-like nanoparticle monolayers with large, patchy domains.

Defects in Self-Assembled Monolayers on Nanoparticles Prompt Phospholipid Extraction and Bilayer-Curvature-Dependent Deformations

“…This ligand-island morphology on AuNPs has previously been revealed via MD simulations by other groups − and is predicted to form among ligands with alkyl chain lengths exceeding four −CH 2 groups . Such ligand-island morphology has also been observed both experimentally and computationally in NPs of other metal chalcogenide and noble metal cores: CdSe, PbS, and silver …”

“…26 Such ligand-island morphology has also been observed both experimentally and computationally in NPs of other metal chalcogenide and noble metal cores: CdSe, 29 PbS, 30 and silver. 31 Here, we probed the association of AuNPs functionalized with either cationic MUTAB or anionic 11-mercaptoundecanoic acid (MUA) ligands (Figure S1 in the SI) with zwitterionic phospholipid bilayers computationally by dissipative particle dynamics (DPD) simulations using bottom-up coarse-grained NP models and experimentally by quartz crystal microbalance with dissipation monitoring (QCM-D). We modeled 4-nm MUA− and MUTAB−AuNPs in the simulations.…”

Nanoparticles in analytical laser and plasma spectroscopy – a review of recent developments in methodology and applications

“…450 Pioneering works in this eld were performed by Spengler et al and others. 453 More recently, LDI-MS was also used for the study of the relative quantity of ligands attached to Ag and Au NP surfaces 455,456 or the ligand shell morphology on such NPs. 457,458 These studies interpreted the detected noble metal-ligand clusters as being composed of surface noble metal atoms that had desorbed together with the ligands that were originally attached to them.…”

Quantification of surface composition and segregation on AuAg bimetallic nanoparticles by MALDI MS

“…phase segregation) of binary mixtures of ligand molecules on Au or Ag nanoparticles. [25][26][27][28][29][30][31][32][33] Initially, MALDI, coupled with ion mobility-MS, was used to analyze Au-thiolate complexes desorbed from the nanoparticles. These complexes were interpreted as being composed of surface Au atoms that had desorbed together with the thiolated ligands that were originally attached to them.…”

“…26 The same phenomenon was also reported on Ag nanoparticles. 29,31,34 Our group applied this technique to characterize the evolution of the ligand-shell's morphology during a ligand exchange reaction for Au nanoparticles. 32 We then further improved the characterization of the ligand shell by developing a Monte-Carlo-type simulation capable of reconstructing a model of the ligand shell morphology and provide a distribution of nearest neighbors.…”