Phytogenic Synthesis of Platinum Nanoparticles: Characterization and In Vitro Biological Evaluation of Antioxidant, Antimicrobial, and Anticancer Activities

ABSTRACT This study presents the eco‐friendly synthesis of platinum nanoparticles (PtNPs) utilizing Coleus barbatus leaf extract as both a reducing and stabilizing agent. Fourier transform infrared spectroscopy (FTIR) identified key biomolecules, including ascorbic acid, terpenoids, amino acids, and hydrocarbons, responsible for reducing platinum ions. X‐ray diffraction (XRD) analysis confirmed a face‐centered cubic (FCC) crystal structure with a crystallite size of 62 nm. Zeta potential measurements, ranging from 9.4 to 11.8 mV, indicated moderate colloidal stability. Morphological characterization via scanning electron microscopy (SEM) and high‐resolution transmission electron microscopy (HRTEM) revealed spherical PtNPs with diameters between 42 and 65 nm. The biological efficacy of the synthesized PtNPs was assessed through antimicrobial, antioxidant, and anticancer assays. The NPs demonstrated significant antibacterial activity against Escherichia coli (Gram‐negative) and Staphylococcus aureus (Gram‐positive), effectively inhibiting bacterial growth. Antioxidant evaluation showed strong free radical scavenging capabilities, particularly against superoxide ions and hydroxyl radicals. Furthermore, cytotoxicity tests on the MCF‐7 breast cancer cell line revealed potent anticancer properties, yielding an IC 50 value of 2.28. These findings underscore the potential of C. barbatus ‐mediated PtNPs as effective agents for antimicrobial treatments, antioxidant applications, and cancer therapy, highlighting the promise of green chemistry in nanomedicine.