Comprehensive study upon physicochemical properties of (bio)ZnO NPs

Abstract

Abstract In this study, for the first time, the comparison of commercially available chemical ZnO NPs and bio-ZnO NPs produced extracellularly by two different probiotic strains (Latilactobacillus curvatus MEVP1 [OM736187] and Limosilactobacillus fermentum MEVP2 [OM736188]) isolated from milk were performed. All types of ZnO NPs were characterized by comprehensive interdisciplinary approach including various instrumental techniques in order to obtain nanoparticles with suitable properties for further applications, i.e. biomedical. Based on the X- ray diffraction analysis results, all tested NPs exhibited the wurtzite structure with an average crystalline size distribution of 21.1 nm (CHEM_ZnO NPs), 13.2 nm (1C_ZnO NPs) and 12.9 nm (4a_ZnO NPs). The microscopy approach with use of broad range of detectors (SE, BF, HAADF) revealed the core-shell structure of bio-ZnO NPs, compared to the chemical one. The metallic core of 1C and 4a_ZnO NPs are coated by the specific organic deposit coming from the metabolites produced by two probiotic strains, L. fermentum and L. curvatus. Vibrational infrared spectroscopy, photoluminescence (PL) and mass spectrometry (LDI-TOF-MS) have been used to monitor the ZnO NPs surface chemistry and allowed for better description of bio-NPs organic coating composition (amino acids residues). The characterized ZnO NPs were then assessed for their photocatalytic properties against methylene blue (MB). Both types of bio-ZnO NPs exhibited goof photocatalytic activity, however, the effect of CHEM_ZnO NPs was more potent than 1C and 4a_ ZnO NPs. Finally, the colloidal stability of the tested nanoparticles were investigated based on the zeta potential (ZP) and hydrodynamic diameter measurements in dependence of the NPs concentration and investigation time. Overall results in present study suggest that used accessible source such us probiotic strains, L. fermentum and L. curvatus, for extracellular bio-ZnO NPs synthesis are of high interest. What is important, no significant differences between organic deposit (e.g. metabolites) produced by tested strains were noticed –both of them allowed to form the nanoparticles with natural origin coating. In comparison to chemical ZnO NPs, those synthetized via microbiological route are promising material with further biological potential once have shown high stability during 7 days.