Green synthesis of Rhodobryum roseum-mediated ZnO nanoparticles: a multifunctional evaluation of biomedical activities and agricultural applications.

Nanotechnology is a fast-growing field with diverse applications in various disciplines. Based on the applications in diverse fields and the medicinal significance, R. roseum was phytochemically investigated and was used for the synthesis of zinc oxide nanoparticles (ZnO-NPs). Biosynthesized NPs were characterized using UV spectrophotometry (UV), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscope (SEM), and used in antioxidant, antibacterial, and seed nano priming activities. Antibacterial activity was observed against Klebsiella pneumoniae, Bacillus subtilis, Enterococcus faecalis, and Staphylococcus aureus, with the maximum zone of inhibition recorded against S. aureus (23 mm ± 0.57) at 1000 µg/ml. ZnO-NPs exhibited the highest antioxidant activity (75.2%) at 100 µg/mL in comparison with the standard (ascorbic acid), which showed 79% activity at the same concentration. The IC50 value of R. roseum-mediated ZnO-NPs obtained was 35.79 at a 20 µg/mL ZnO-NP concentration. Seed priming with R. roseum-mediated ZnO NPs markedly enhanced maize growth, with the highest performance recorded at 200 ppm, yielding 3.33 ± 0.40 g fresh weight, 3.20 ± 0.1 g dry weight, and 6 ± 1 leaves. At this concentration, seedlings also exhibited increased root (13.5 ± 0.57 mm) and shoot length (12.6 ± 0.57 cm) along with elevated chlorophyll content (34.9 ± 4.57), indicating significant improvement in physiological attributes. Compared to the control, nanoparticle treatment at 50 µg/mL increased peroxidase activity from 18.4 to 31.3 U mg⁻1 protein, superoxide dismutase from 22.6 to 36.9 U mg⁻1 protein, and catalase from 15.2 to 27.8 U mg⁻1 protein. In conclusion, green-synthesized ZnO-NPs are effective and can be utilized in agriculture, biomedical, and other fields.