LAUSR

Abstract Blue- and green-emitting gold nanostructures have been synthesized by spontaneous interactions of the tetrachloroaurate anions (AuCl4−) with L-histidine (His) and L-tryptophan (Trp) at 37 °C in aqueous medium. The dominant role of AuCl4−/amino acid molar ratios as well as the pH in the formation of gold nanoparticles (Au NPs) or nanoclusters (Au NCs) was confirmed by numerous spectroscopic techniques. We demonstrate that without additional reducing agents the His and Trp show different reduction behaviour with AuCl4− which supports the fact that the unique optical features originate from diverse structures. Because of the pH-dependent complexation and reduction capability of the studied amino acids the dominant presence of polynuclear fluorescent gold(I) complexes (quantum yield (QY%) ∼4%) with a well-ordered structure is presumable for His-directed Au system confirmed by mass spectrometry, X-ray diffraction and infrared experiments. The existence of d = 8 nm-sized Au NPs or subnanometer-sized (d