Lac-based-biosynthesis of zinc–copper mixed metal oxide nanoparticles and evaluation of their antifungal activity against A.alternata and F. oxysporum

The use of animal-based sources for biosynthesis resonates with the growing market for sustainable and eco-friendly materials, but remains severely unexplored in comparison to plant-based and microbial sources. In this purview, shellac, a bioresin obtained from the Kerria lacca insect, is emerging as an ideal candidate for nanomaterial fabrication due to its abundant availability and anti-microbial properties. It is commonly available in the form of raw seed lac, (SL) and in the processed button lac (BL) form. Therefore, in the current study, the potential of shellac as a green agent for the synthesis of zinc-copper mixed metal oxide nanoparticles, and the anti-fungal activitiy of synthesized nanoparticles was investigated. Two types of zinc copper oxide nanoparticles were synthesized using button lac (ZnCu(BL)O) and seed lac (ZnCu(SL)O), and they were characterised using various techniques such as Powder X-Ray Diffraction (PXRD), Fourier Transform Infrared spectroscopy (FTIR) and Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX) spectroscopy. PXRD pattern confirmed the hexagonal wurtzite structure of crystalline ZnCuO NPs. FTIR analysis elucidated the presence of functional groups that were potentially involved in the synthesis of MMO nanoparticles, and the formation of Zn–O and Cu–O bonds was suggested by appearance of bands at 559 cm⁻¹ and 555 cm⁻¹. The morphology and elemental composition of the MMONPs were examined using SEM-EDX techniques that revealed the formation of biosynthesized ZnCuO NPs as spherical agglomerates having uniform distribution of Zn, Cu, C and O throughout the material. Further, the antifungal activity of synthesized NPs was evaluated against F. oxysporum and A. alternata fungal pathogens. It was found that the biosynthesized nanoparticles exhibited significant fungicidal potential against both F. oxysporum and A. alternata. Furthermore, the antifungal results indicated that ZnCuSL-(O) NPs exhibited higher antifungal activity against both fungal strains than ZnCuBL-(O) NPs and chemically synthesized ZnCu-O NPs. Thus, ZnCuSL-(O) NPs and ZnCuBL-(O) NPs prepared using shellac may be considered as cost-effective and eco-friendly substitutes over traditional fungicides.