Nanochemistry and biotechnology

The synthesis of irregularly shaped gold nanoparticles using natural polyphenols
Mariychuk R.1, Smolkova R.1, Eliašová A.1, 
Grishchenko L.M.2, Diyuk V. E.2, Lisnyak V.V.2
1 Department of Ecology, Faculty of Humanities and Natural Sciences, University of Prešov in Prešov, 17th November Str. 1, 08001, Prešov, Slovakia.
E-mail: ruslan.mariychuk@unipo.sk
2 Taras Shevchenko National University of Kyiv, Volodymyrska Str. 62a, 01601 Kyiv, Ukraine.

The synthesis of gold nanoparticles (AuNPs) using plant extracts has recently gained new importance due to its simplicity against the background of cost-effectiveness and environmental friendliness. Moreover, the biocompatibility of phytosynthesized AuNPs opens up opportunities for their biomedical applications. Biomolecules in the plant extract can reduce Au3+ cations to metallic gold (Au0). But they also have an influence on the morphology of the forming AuNPs, determining size and shape. Control over the morphology of nanogold makes it possible to control the optical properties. Currently, the researchers focus their interest on the bio-synthesis of irregularly shaped AuNPs. They can find applications in biomedicine due to their response in the near-infrared region.
Despite the simplicity, the complexity of the composition of plant extracts requires an understanding of what role different biomolecules play in the formation, growth, and stabilization of AuNPs. The known protocol for the synthesis of irregularly shaped AuNPs (nanorods, nanostars, nanohexagons, etc.) requires the use of toxic surfactants. Therefore, the presented study was aimed at finding alternative shape-forming biomolecules from plant extracts, such as polyphenols.
Several polyphenols are the major components of Melissa extracts. Typically, they are peppery acid, rosmarinic acid, caffeic acid, gallic acid, and several others. These components were used to synthesize irregular AuNPs. The obtained nanocolloidal solutions were examined by UV-Vis-NIR spectroscopy and transmission electron microscopy. Molecular and structural transformations of organic compounds were studied by NMR analysis. The results showed that the form of AuNPs depends on various factors, such as the concentration and ratio of reagents, temperature, and pH level. The interplay between factors was analyzed, and the respective dependences were proposed.