-Amino Acids as Reducing and Capping Agents in Gold Nanoparticles Synthesis Using the Turkevich Method

Amino acid-capped gold nanoparticles (AuNPs) are a promisingtoolfor various applications, including therapeutics and diagnostics.Most often, amino acids are used to cap AuNPs synthesized with otherreducing agents. However, only a few studies have been dedicated tousing alpha-amino acids as reducing and capping agents in AuNPssynthesis. Hence, there are still several gaps in understanding theirrole in reducing gold salts. Here, we used 20 proteinogenic alpha-aminoacids and one non-proteinogenic alpha-amino acid in analogy to sodiumcitrate as reducing and capping agents in synthesizing AuNPs usingthe Turkevich method. Only four of the twenty-one investigated aminoacids have not yielded gold nanoparticles. The shape, size distribution,stability, and optical properties of synthesized nanoparticles werecharacterized by scanning electron microscopy, differential centrifugalsedimentation, the phase analysis light scattering technique, andUV-vis spectroscopy. The physicochemical characteristics ofsynthesized AuNPs varied with the amino acid used for the reduction.We proposed that in the initial stage of gold salts reduction mostof the used alpha-amino acids behave similarly to citrate in theTurkevich method. However, their different physicochemical propertiesresulting from differences in their chemical structures significantlyinfluence the outcomes of reactions.