Thermogravimetry and evolved gas analysis for the investigation of ligand-exchange reaction in thiol-functionalized gold nanoparticles

Abstract

The increasing use of gold nanoparticles (AuNPs), especially in biomedical applications, requires strict chemico-physical characteristics achievable by organic functionalization via ligand – exchange process. Nowadays, one of the most common synthetic procedures to obtain small and hydrophilic AuNPs consists on the synthesis of 1-Dodecanethiol (1–D) coated AuNPs, afterwards functionalized by a partial substitution of the previous alkyl hydrophobic moiety with carboxylic species, such as the 11-Mercaptoundecanoic acid (11 – MUA). It is evident that the characterization of the organic coating and the quantification of the ligand – exchange reaction become crucial for the nanoparticles real applicability. We report the use of thermogravimetry (TG) and evolved gas analysis, performed through gas chromatography – mass spectrometry (GC – MS), for the investigation of 1–D and mixed 1 – D/11–MUA functionalized AuNPs. The two samples present different thermal behaviours, discernible through the GC – MS use, thus allowing the quantification of the 1 – D/11 – MUA ratio. The insertion of GC before the MS analysis provides an accurate identification of the gaseous products and supplies additional information on the ligand − surface interaction. The results demonstrate that TG is a rapid and satisfactory method for the quantification of the ligands amount on the nanoparticles surface; moreover, the coupling with GC – MS provides additional information (more discernible respect to the only use of MS) on the decomposition products.