Generation of gold nanoparticles according to procedures described in the eighteenth century

Abstract

Gold nanoparticles have received much attention in recent years due to their unique size-dependent properties, as they find useful applications in materials science [Mayoral et al. (Nanoscale 2:335–342, 2010)], catalysis [Schwerdtfeger (Angew Chem Int Ed 42:1892–1895, 2003)] [Hashmi and Hutchings (Angew Chem Int Ed 45:7896–7936, 2006)] and biology [Sperling et al. (Chem Soc Rev 37:1896–1908, 2008)]. The preparation of such nanoparticles benefits from modern chemical knowledge, and a large variety of several procedures have been developed aiming at controlling the size and shape of these metal nanoparticles. Here, we show that two eighteenth-century recipes (Online Resource 1) used at that time to prepare drinkable solutions of gold, used as drugs, actually generate gold nanoparticles, clusters and even monoatomic species of gold. These simple methods involve the dissolution of gold in a solution of ammonium chloride in nitric acid (aqua regia) and the mixing of the resulting solution with rosemary or cinnamon essential oils. The complex mixture of compounds resulting from the fast reaction between aqua regia and the essential oils behave simultaneously as reductants and stabilisers of the nascent gold particles. These results not only prove that historical speculations on the presence of finely divided gold particles floating in these solutions were basically correct but they could also serve as a source of inspiration for new experimental approaches procuring the generation of stable sub-nanometer gold nanoparticles.