Capsicum spp. Fruit Extract-based Gold Nanoparticles: Biogenic Synthesis, Physicochemical characterization, Antioxidant Properties and Cytotoxic Activities

Green synthesis of gold nanoparticles (AuNPs) using plant extracts offers an eco-friendly alternative to conventional chemical approaches. Yet, the influence of capsaicinoid content in Capsaicin spp. extract on the physicochemical and biological properties of AuNPs has not been systematically evaluated. This study, AuNPs were synthesized using three different Capsicum spp. i.e., Capsicum annuum (PM), Capsium chinense (KT), and Capsicum frutescens (CH). Capsaicinoid profiles in all extracts were determined using LC-MS/MS, the physicochemical characteristic of synthesized AuNPs were analyzed using UV-Vis spectroscopy, PSA, FT-IR, XRD, and TEM. The AuNPs were designated as PM-AuNPs, KT-AuNPs, and CH-AuNPs. The AuNPs then were assessed for their antioxidant activity by DPPH assay, and cytotoxic effects against HEK 293 kidney embryonic and MCF-7 breast cancer cells were evaluated using MTT. The potential anticancer activity was continued using live-dead staining and apoptosis assays. LC-MS/MS confirmed variations in capsaicin levels across the three extracts. UV-Vis spectra exhibited SPR peaks at 548 to 562 nm for AuNPs. The AuNPs had particle sizes ranged from 9.77 to 78.22 nm with a stars shape in KT and CH AuNPs and a spherical shape in PM-AuNPs, with zeta potentials below − 30 mV, indicating stable colloids of AuNPs. The FT-IR analysis suggested the involvement of phenolic and amide groups in nanoparticle capping and stabilization. Among the AuNPs produced, CH-AuNPs demonstrated the highest antioxidant activity (37.19 ± 3.79%), while PM-AuNPs exhibited the strongest cytotoxicity properties against MCF-7 cells (IC₅₀ = 131.43 µg/mL), without harming to normal HEK 293 cells. Overall, this study highlights that capsaicinoid content modulates the physicochemical and biological properties of green-synthesized AuNPs, identifying C. annuum is promising candidates for antioxidant and anticancer nanotherapeutics.