Side Effect of Good's Buffers on Optical Properties of Gold Nanoparticle Solutions

In search of fluorescent nanoclusters (NCs) for bioimaging, several methods of synthesis have been attempted. Particularly, formation of gold NCs (AuNCs) during synthesis of gold nanoparticles (AuNPs) using Good's buffers was reported based on the optical properties of the reactions mixtures. Here we chose the Good's buffers 2-(N-morpholino)ethanesulfonic acid (MES), 3-(N-morpholino)propanesulfonic acid (MOPS) and 4-(N-morpholino)butanesulfonic acid (MOBS) as [AuCl4]- reducing agents. Resulting AuNP solutions were subjected to electrochemical investigations along with UV-vis and fluorescence spectroscopy. Distinct absorption features at ca. 290 and 360 nm and fluorescence emission in the 408-484 nm range are observed in filtered AuNP-free solutions. Electrochemical oxidation of these buffers generates similar optical properties, suggesting that the degradation products of the buffers contribute to the optical properties of AuNP solutions. This work indicates deeper evaluation of fluorescence signals based on metal NPs or NCs is needed.