Characterization of L-cysteine methyl ester hydrochloride–stabilized gold nanoparticles

The synthesis of gold nanoparticles (AuNPs) by bottom-up methods, such as redox reactions using amino acids and gold salts, has turned out to be a novel method for obtaining nanoparticles due to the reducing properties of these biomolecules and the ability to give the nanoparticle peculiar physicochemical characteristics for its biological application, thus derived from the known structure and amino acids functional groups. In this sense, this work shows the characterization using UV-Vis, DLS, FTIR, XPS, and HRTEM techniques of AuNPs synthesized using sodium borohydride (NaBH₄) as a reducing compound and L-cysteine methyl ester hydrochloride (cysteine precursor) (HSCH₂CH (NH₂) COOCH₃ • HCl) as a stabilizing agent. The above elucidates the reaction mechanisms for the formation of the nanoparticle through these reactions, as well as the stabilizing action and possible reducing potential of cysteine. Likewise, the resulting Cis@AuNP compounds were subjected to a preliminary biological evaluation using cell viability toxicity tests. The Cis@AuNPs showed high colloidal stability in a pH range of 3 to 11, where the L-cysteine methyl ester hydrochloride functional groups strongly influenced the hydrodynamic diameter and zeta potential behavior. Cytotoxicity assays in mouse leukocytes demonstrated the safety of these nanoparticles. These encouraging results open the way to explore the biological application potential of these systems with the perspective of their possible application in vaccinology.