Recent advances in metallic nanoparticles: From characterization to toxicity and bioactivity

Over the past decade, the biomedical applications of monometallic (MNPs), bimetallic (BMNPs), and multimetallic nanoparticles (MMNPs) have expanded exponentially, with green synthesis emerging as a cornerstone due to its sustainability, and eco-friendliness. Driven by the global urgency for novel therapeutics against microbial epidemics and oncological diseases, multi-element nanoparticles have gained significant traction. This review comprehensively examines the classification, structural characterization, and distinct differences among MNPs, BMNPs, and MMNPs. A core focus is placed on the synergistic effects inherent to bi- and multi-metallization; the interaction of multiple metallic species induces structural, electrical, and mechanical alterations that yield unique optical, thermal, and magnetic properties unattainable by their monometallic counterparts. Furthermore, we highlight the economic and environmental sustainability of these systems, demonstrating how blending earth-abundant transitional metals (e.g., Fe, Cu) with precious metals (e.g., Au, Ag) creates cost-effective, high-efficiency frameworks. The role of Surface Plasmon Resonance (SPR) as a critical diagnostic tool is also evaluated, illustrating how SPR shifts serve as an internal blueprint to decipher complex internal configurations, such as mixed alloys versus core-shell structures. Finally, this paper addresses the toxicological profiles of these nanoparticles and outlines strategic pathways for their safe, efficient deployment in anticancer, antibacterial, and anti-inflammatory therapies.