Is the electrochemical or the “green chemistry” method the optimal method for the synthesis of ZnO nanoparticles for applications to biological material? Characterization and SERS on ZnO

Abstract

This work developed ecological procedures for the synthesis of stable, uniform, and pure ZnO nanoparticles for biological and medical applications. Nanoparticles were synthesized on two synthesis pathways: (i.) electrochemical zinc dissolution in a solution free of surfactants (ZnONPs) and (ii.) from banana skin (ZnONPs-GS) by a green synthesis – a cheap method that allows efficient use of waste from plant products. ATR-FTIR, Raman, and UV-Vis confirmed the formation of ZnO nanoparticles. XRD showed a high crystalline hexagonal structure, whereas TEM and DLS confirmed that nanoparticles are pure, well dispersed, and have a rather uniform size and spherical shape. ZnO nanoparticles were evaluated for their ability to adsorb selected amino acids and to promote the SERS effect. SERS spectra on the surface of ZnO nanoparticles were compared with SERS spectra on the surface of Zn. The obtained data show that (i.) with the use of specific marker bands SERS allows us to distinguish between amino acids and to determine the state of zinc surfaces (distinguish between Zn and ZnONPS and ZnONPs-GS), (ii.) ZnONPs-GS obtained from “green chemistry” are more friendly to biological material than those obtained using the electrochemical method because their surface is free from hydroxyl groups, which easily form reactive oxygen species, and (iii.) considering the view in the literature that metal surface type and metal roughness/nanoparticle size influence adsorption, the obtained results supplement the current understanding of amino acid adsorption on various metal surfaces.