Role of UHPLC in evaluating as-synthesised ligand-protected gold nanoparticles products

Analytical separation of metal nanoparticles (NPs) remains a significant challenge as it is very useful in assessing the purity, particle size, protecting ligands and dispersity of the as-synthesised NPs products. In this paper, two liquid chromatographic methods have been developed and their efficiencies in separating samples of polydisperse gold nanoparticles protected with N-acetyl-l-cysteine ligand (NAC-AuNPs) and other ultrasmall water-soluble ligand-protected gold NPs are compared. The total elution time for analysing a NAC-AuNPs sample by ultra high-performance liquid chromatography (UHPLC) is ten times shorter than that of high-performance liquid chromatography. The major attributes of UHPLC are smaller sample volume (1-2 μL) and better separation efficiency. More importantly, our proposed UHPLC method has been successfully applied to evaluate and compare polydisperse NAC-AuNPs products synthesised with the one-phase and two-phase Brust-Schiffrin methods. The results indicate that the two-phase method would harvest AuNPs product with smaller core size and less dispersity.