Photocatalytic Degradation, Anticancer, and Antibacterial Studies of Lysinibacillus sphaericus Biosynthesized Hybrid Metal/Semiconductor Nanocomposites

The biological synthesis of nanocomposites has become cost-effective and environmentally friendly and can achieve sustainability with high efficiency. Recently, the biological synthesis of semiconductor and metal-doped semiconductor nanocomposites with enhanced photocatalytic degradation efficiency, anticancer, and antibacterial properties has attracted considerable attention. To this end, for the first time, we biosynthesized zinc oxide (ZnO) and silver/ZnO nanocomposites (Ag/ZnO NCs) as semiconductor and metal-doped semiconductor nanocomposites, respectively, using the cell-free filtrate (CFF) of the bacterium Lysinibacillus sphaericus. The biosynthesized ZnO and Ag/ZnO NCs were characterized by various techniques, such as ultraviolet-visible spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy. The photocatalytic degradation potential of these semiconductor NPs and metal-semiconductor NCs was evaluated against thiazine dye, methylene blue (MB) degradation, under simulated solar irradiation. Ag/ZnO showed 90.4 +/- 0.46% photocatalytic degradation of MB, compared to 38.18 +/- 0.15% by ZnO in 120 min. The cytotoxicity of ZnO and Ag/ZnO on human cervical HeLa cancer cells was determined using an MTT assay. Both nanomaterials exhibited cytotoxicity in a concentration- and time-dependent manner on HeLa cells. The antibacterial activity was also determined against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus). Compared to ZnO, Ag/ZnO NCs showed higher antibacterial activity. Hence, the biosynthesis of semiconductor nanoparticles could be a promising strategy for developing hybrid metal/semiconductor nanomaterials for different biomedical and environmental applications.

Automated summary

The biological synthesis of nanocomposites provides a cost-effective and environmentally friendly way to produce materials with enhanced properties. In this study, zinc oxide and silver/zinc oxide nanocomposites were biosynthesized using the cell-free filtrate of Lysinibacillus sphaericus, and their properties were characterized using various techniques. The nanocomposites showed improved photocatalytic efficiency, cytotoxicity against cancer cells, and antibacterial activity, making them promising materials for biomedical and environmental applications.