Iron oxide nanoparticles: biosynthesis, peroxidase-like activity, and biosafety.

The rising threat of antibiotic-resistant bacterial infections has amplified the demand for alternative therapeutic strategies and efficient catalytic systems. While natural enzymes like horseradish peroxidase offer catalytic potential, their clinical use is limited by instability, high production costs, and environmental sensitivity. Iron oxide nanoparticles (FeO NPs) have emerged as promising alternatives, exhibiting unique physicochemical properties, magnetic responsiveness, biocompatibility, and intrinsic catalytic activity. A key advancement in this field is the adoption of green nanotechnology, which supports the eco-friendly biosynthesis of FeO NPs via biological systems. However, several limitations reduced catalytic activity under certain conditions. This review highlights progress in green synthesis, focusing on iron-resistant and probiotic bacteria as sustainable and scalable biogenic platforms. Compared to chemical methods, these biological routes reduce environmental impact, lower costs, and enhance nanoparticle stability and functionality. This review also addresses the factors influencing the peroxidase-like (POD) activity of NPs. The biomedical relevance of FeO NPs spans diverse applications, including antibacterial therapy, cancer treatment, biosensing, food safety, and enzyme-mimicking catalysis. However, despite their therapeutic promise, significant gaps remain in the biosafety and toxicity assessments of the catalytic activity of FeO. Hence, current advancement underscores the underutilized role of bacterial strains in nanoparticle synthesis and identifies critical knowledge gaps that need to be consolidated. It calls for standardized evaluation protocols to support the safe and effective translation of FeO into various applications. KEY POINTS: • The green synthesis approach of FeONPs offers an eco-friendly route over other methods • Probiotic-mediated synthesis of FeO NPs offers a sustainable and biocompatible approach • FeO NPs mimic POD-like activity for catalytic biomedical and environmental applications • POD-like activity of FeONPs boosts its antibacterial effects via ROS generation.