Synthesis of ultra-small cysteine-capped gold nanoparticles by pH switching of the Au(I)–cysteine polymer

Abstract

We report a synthetic approach for the production of ultra-small (0.6nm) gold nanoparticles soluble in water with a precise control of the nanoparticle size. Our synthetic approach utilizes a pH-depending Au–cysteine polymer as a quencher for the AuNPs grown. The method extends the synthetic capabilities of nanoparticles with sizes down to 1nm. In addition to the strict pH control, the existence of free –SH groups present in the mixture of reaction has been observed as a key requirement for the synthesis of small nanoparticles in mild conditions. UV–Vis, SAXS, XANES, EXAFS and HR-TEM, has been used to determinate the particle size, characterization of the gold precursor and gold–cysteine interaction.