Phytogenic Synthesis, Structural Elucidation and Antiplasmodial Activity of <i>Ocimum Gratissimum</i>-Mediated Silver Nanoparticles Against <i>Plasmodium Falciparum </i>Clinical Isolate

The growing resistance of Plasmodium falciparum to artemisinin-based combination therapies urgently calls for new antimalarial drugs. Silver nanoparticles (AgNPs) synthesized through green methods offer a promising therapeutic approach; however, research evaluating their efficacy against clinical parasite isolates and their direct comparison with standard antimalarial drugs remains limited. This study sought to biosynthesize and characterize AgNPs using Ocimum gratissimum L. leaf extract and to assess their antiplasmodial activity against clinical isolates of P. falciparum. AgNPs were synthesized by reacting a 1 mM silver nitrate (AgNO₃) solution with a 10% (v/v) aqueous leaf extract. The nanoparticles were characterized by UV-Vis spectroscopy, SEM, TEM, EDX, XRD, FTIR, DLS, and zeta potential analysis. Their in vitro antiplasmodial efficacy was evaluated against clinical P. falciparum strains using a 48-hour schizont inhibition assay. The half-maximal inhibitory concentration (IC₅₀) was calculated via probit regression and directly compared to that of quinine. The optimized protocol produced spherical, crystalline AgNPs with a core size of 42.5 ± 5.2 nm (by TEM), a hydrodynamic diameter of 58.3 ± 8.1 nm, and a zeta potential of -28.7 ± 2.1 mV, confirming excellent colloidal stability. FTIR analysis verified the role of plant phytochemicals in reducing and capping the nanoparticles. The O. gratissimum-AgNPs demonstrated significant, dose-dependent antiplasmodial activity, reaching 76.68 ± 1.44% inhibition at 100 µg/mL. The IC₅₀ value was determined to be 13.70 ± 0.99 µg/mL, indicating moderate potency relative to quinine (IC₅₀ = 3.14 ± 0.74 µg/mL). This work successfully establishes O. gratissimum as a viable source for producing stable AgNPs with substantial efficacy against drug-resistant clinical malaria parasites. The direct, quantitative comparison with quinine and the comprehensive analysis linking physicochemical properties to biological activity provide a solid foundation for future antimalarial nanotherapeutic development. Significance Statement: These findings validate a green nanotechnology strategy that utilizes local medicinal plants, presenting a potent, stable, and sustainable candidate for use as an adjunct in combination therapy against drug-resistant malaria.