A Structural Mass Spectrometry Strategy for the Relative Quantitation of Ligands on Mixed Monolayer-Protected Gold Nanoparticles

Abstract

It is becoming increasingly common to use gold nanoparticles (AuNPs) protected by a heterogeneous mixture of thiolate ligands, but many ligand mixtures on AuNPs cannot be properly characterized due to the inherent limitations of commonly used spectroscopic techniques. Using ion mobility-mass spectrometry (IM-MS), we have developed a strategy which allows measurement of the relative quantity of ligands on AuNP surfaces. This strategy is used for the characterization of three samples of mixed-ligand AuNPs: tiopronin:glutathione (avg. diam. 2.5 nm), octanethiol:decanethiol (avg. diam. 3.6 nm), and tiopronin:11-mercaptoundecyl(poly ethylene glycol) (avg. diam. 2.5 nm). For validation purposes, the results obtained for tiopronin:glutathione AuNPs were compared to parallel measurements using nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS) without ion mobility separation. Relative quantitation measurements for NMR and IM-MS were in excellent agreement, with an average difference of less than 1% relative abundance. IM-MS and MS without ion mobility separation were not comparable, due to a lack of ion signals for MS. The other two mixed-ligand AuNPs provide examples of measurements which cannot be performed using NMR spectroscopy.

Short-Chain PEG Mixed Monolayer Protected Gold Clusters Increase Clearance and Red Blood Cell Counts

“…30 Also shown is a positive correlation between concentration of PEG in solution and percent coverage; however, no significant gain in percent coverage was noted until larger PEG feed ratios were used. At lower feed ratios, the loading percentage difference between 10:1 and 15:1 was minimal.…”

“…In keeping with our previous experiments, 30 1% relative abundance and 30 ppm mass accuracy cutoffs were used to reduce false positive identifications, and the monoisotopic ion abundances for the identified peaks were normalized to the expected monoisotopic abundance for each respective ion. The final set of identified peaks was used in quantitation calculations by the application of Eqn.…”

“…The intensity of the peak for tiopronin alone (1.6 ppm) decreases as the percentage of PEG 4 -acid applied to the monolayer increases. Quantification was performed as previously described 30 by integration of the PEG 4 -acid and tiopronin peaks. The result of the integration by NMR and the subsequent molecular formulas are shown in Figure S4 as well.…”

Mass spectrometry for the characterization and quantification of engineered inorganic nanoparticles

“…In this context, MALDI-Ion Mobility-MS [70] allowed to measure the relative quantity of ligands on a given AuNPs surface. The results were successfully validated by nuclear magnetic resonance (NMR) spectroscopy and by MS without ion mobility separation (in fact, average differences of less than 1% relative abundance were reported).…”

High-performance liquid chromatography coupled with mass spectrometry for analysis of ultrasmall palladium nanoparticles

“…Since then, MS has been widely adopted in almost all the structural analysis of metal NPs. So far various MS techniques such as MALDI-TOF MS [28,43,44,55,56], ESI-MS [57,58], LDI-MS [59], ion mobility MS [60,61] and fast atom bombardment MS [62] have been applied to explore the metal core mass of all kinds of metal NPs. Among them, MALDI-TOF MS is the most popular MS technique in determining the number of metal atom of NP fractions.…”