Light-driven formation of gold/tryptophan nanoparticles

The direct photoactivation of the red-ox process between tryptophan (Trp) and Au 3+ through indole moiety of amino acid is the perspective and effective way to obtain tailored gold nanoparticles (Au NPs) in colloids. We systematically varied experimental parameters (concentration and ratio of reagents, pH of the solution) and adjusted UV illumination parameters to influence the kinetics of the process and optical properties of obtained Au NPs. Products of reaction in Au/Trp system were studied using absorption and fluorescence spectroscopies, and mass spectrometry. The complementary analysis evidenced the transformation of tryptophan via the kynurenine pathway, which can improve the biocompatibility of Au NPs. We found that the photoactivated formation of Au NPs proceeded through two stages: reduction of Au 3+ ions by an amino acid that leads to the formation of metal “primary clusters” and their further accumulation and growth of Au NPs. The use of UV light for the photochemical activation of reaction promotes up to three times faster formation of more homogeneous and uniform in size Au NPs compare to only chemical reaction pathway.