The preferential generation of anionic nanoparticles of mass around 30 kamufrom thiol-derivatized gold nanoparticles and its significance

Thiol-derivatized gold nanoparticles have been prepared by the reduction of gold cations in an ethanol solvent in the presence of alkanethiols such as dodecanethiol and nonanethiol. Negative ion laser ablation time-of-flight mass spectra (LA-TOF-MS) of the as-prepared samples indicate the presence of a single predominant peak at around 30 kamu even for samples prepared using widely different gold to thiol molar ratios in the reactant mix. The preponderant observation of such nanoparticles in the mass spectra is attributed to a region of especially high thermodynamic stability existing in this mass range for negative ions derived from nanoparticles prepared from the Au–RSH material combine. These studies also support the assertion that the thiol-derivatized gold nanoparticles prepared by the method of Murthy et al. are qualitatively different than that prepared by the method of Brust et al.