Magnetic nanoparticles exhibit many interesting properties that can be exploited in a variety of applications such as biomedicine. In this study, superparamagnetic iron oxide nanoparticles (SPIONs) were prepared using a rapid and green method by reduction of ferric chloride solution with Rosmarinus officinalis water extract as the reducing and stabilizing agent. Further the antibacterial effect of iron oxide nanoparticles was evaluated against four pathogenic bacteria. Rosemary plant (Rosmarinus officinalis) were collected from Ferdowsi University of Mashhad Farm, washed thoroughly with distilled water, and dried overnight in 40 °C. The extract was prepared by mixing 20 g of the rosemary fine powder with 100 mL distilled water and heated at 60 °C for 30 min[1]. The crude extract was filtered with filter Whatman 42 for future use. SPIONs were prepared by mixing 25 mL of FeCl 3.6H2O solution (50 mM) with 50 mL of rosemary extract at 80 °C for 1 h under constant stirring at 1800 rpm. Changing color of solution from yellow to dark brown was an indication for NPs biosynthesis. The biosynthesized SPIONs were purified and further characterized by UV-vis spectrophotometry, X-ray Diffraction (XRD) analysis, Fourier Transform Infrared Spectroscopy (FTIR) and vibrating sample magnetometer (VSM). Antibacterial properties were evaluated against Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis and Staphylococcus aureus by standard broth microdilution method [2]. The results showed that the SPIONs had a cubic structure with the crystallite size of about 17.51 nm, and the maximum absorbance at 270 nm. The FTIR spectra of prepared iron oxide NPs under different conditions exhibited peak at 570 cm -1 assigned to Fe-O stretching vibration mode. Also, the prepared iron oxide NPs had superparamagnetic property with saturation magnetization of 39.64 emu g -1 . The results showed that prepared nanoparticles have moderate antibacterial activity against both Gram positive and Gram negative pathogenic bacterial strains. References 1. Xin Lee, K., et al., Journal of Nanomaterials, 2016. 2. Wypij, M., et al., World Journal of Microbiology and Biotechnology, 2018. 34(2): p. 23.

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