Stevia-Capped Silver Nanoparticles with Tunable Optical Band Gap and Enhanced Cytotoxicity Toward MCF-7 Cells

This study reports the green synthesis, characterization, and anticancer evaluation of silver nanoparticles (S-AgNPs) may consuming aqueous stevia leaf extract (SE) as a reductant and stabilizer. UV-vis spectroscopy confirmed the formation of S-AgNPs by surface plasmon resonance at 438 nm, and Tauc plot analysis revealed a concentration-dependent decrease in optical band gap from 3.45 to 3.12 eV, indicating particle growth and surface modification with increasing SE. X-ray diffraction analysis demonstrated the S-AgNPs crystalline nature, while TEM and dynamic light scattering confirmed size evolution from 39.7–79.2 nm (24 h) to 55.5–128.5 nm (7 days) with higher SE concentrations. Cytotoxicity testing in vitro against MCF-7 breast cancer cells exposed that pure SE revealed minimal toxicity (IC50 3.27 µg/mL), whereas S-AgNPs displayed enhanced anticancer activity in an SE concentration-dependent manner, with IC50 decreasing to 0.351 µg/mL at 6 mg/mL SE. Cellular uptake studies demonstrated efficient internalization of S-AgNPs, with higher intracellular accumulation observed at increasing SE concentrations. Mechanistically, stevia glycosides acted as capping agents, improving nanoparticle stability, dispersion, and bioavailability. These findings highlight the synergistic potential of SE and AgNPs, providing a sustainable and effective approach for nanomedicine-based anticancer applications.