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

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