Biogenically synthesized copper oxide, titanium oxide, and silver oxide nanoparticles: characterization and biological effects

Foodborne and phytopathogenic bacteria pose notable threats to human health and agricultural productivity. Biologically produced metal oxide nanoparticles (MONPs) can act as potent antimicrobial alternatives. Using the cultural filtrate of Trichoderma virens, copper oxide (CuO), titanium oxide (TiO₂), and silver oxide (Ag₂O) NPs were mycofabricated. The pale yellowish filtrate gradually turned in color to greenish, white creamy, and brownish colloidal dispersions, implying initial confirmation for the synthesis of CuO NPs, TiO₂ NPs, and Ag₂O NPs, respectively. CuO NPs, TiO₂ NPs, and Ag₂O NPs exhibited distinct absorption peaks at 275 nm, 380 nm, and 422 nm as revealed by UV–Vis spectroscopy. X-ray diffraction depicted the crystallinity of monoclinic CuO, rutile TiO₂, and cubic Ag₂O NPs with respective average sizes of 31.2 nm, 75.6 nm, and 31 nm. Functional groups from fungal bioconstituents, as shown by FTIR, contributed to the chelation and stability of the MONPs. Zeta potential analysis demonstrated the stability of the CuO NPs, TiO₂ NPs, and Ag₂O NPs (+ 20.5 mV, − 32.7 mV, and − 18.0 mV, respectively). EDX spectroscopy verified the purity of the MONPs, showing no impurities. Raman analysis identified structural defects, while XPS confirmed the pure elemental composition, chemical oxidation states, and binding energies of the MONPs. FESEM revealed the mycosynthesis of flake-shaped and plate-like structures of CuO NPs with sharp edges. TiO₂ NPs had a monodispersed morphology, involving quasi-spherical, polygonal, and tetragonal structures, whereas Ag₂O NPs had sphere- and oval-shaped architectures. CuO NPs and Ag₂O NPs suppressed the growth of three foodborne pathogens, including Escherichia coli, Salmonella enterica, and Staphylococcus aureus, in addition to six phytopathogenic bacteria, involving Clavibacter michiganensis subsp. michiganensis, C. michiganensis subsp. capsici, and streptomycin-susceptible wild types and streptomycin-resistant mutants of Pectobacterium carotovorum and Xanthomonas citri subsp. citri. However, TiO₂ NPs had no antibacterial potential against the tested bacterial pathogens. FESEM revealed significant deformation of bacterial cells upon exposure to CuO NPs and Ag₂O NPs. The findings establish a framework for the role of T. virens as a nano-biofactory for synthesizing antibacterial MONPs.