In this work, in order to increase the biocompatibility of the nanoscale system, the synthesis of gold nanoparticles was performed in the presence of Trp. The reaction between HAuCl₄ and Trp proceeded in aqueous medium with neutral pH at different temperatures. Spectral characteristics of products formed in Au/Trp systems and were studied.

In the absorption spectra the main band of Trp at 280 nm was shifted to 250 nm during the reaction; for all studied systems upon excitation of fluorescence with the wavelength of λ_ex = 340 nm the maximum of the emission bands were observed at λ_em = 450 nm, while for initial tryptophan (λ_ex = 280 nm) it was located at λ_ex = 375nm.

Mass spectra of Trp solution in positive mode contained the signal at 131 Da, that was characteristic for ionized indole moiety of amino acid. For supernatants of studied Au/Trp systems in positive mode signals of ionized fragments with masses of 118, 146 and 174 Da were observed. Based on the data it was revealed that amino acid oxidation proceeded through the formation of kynurenine or through the "kynurenine pathway", that corresponds to the metabolic conversion of amino acid in human organism and proves the biocompatibility of formed products.