Biogenic gold nanoparticles synthesized using Hibiscus sabdariffa enhance antioxidant activity and induce apoptosis in breast and colorectal cancer cells

Gold nanoparticles (AuNPs) have attracted significant attention in biomedical applications due to their unique physicochemical and diverse biological activities. The present study investigated the in vitro antioxidant and cytotoxic effects of biogenic AuNPs synthesised using Hibiscus sabdariffa (HS). The nanoparticles were characterised by ultraviolet-visible spectroscopy, dynamic light scattering, high-resolution transmission electron microscopy (HRTEM), and Fourier transform-infrared spectroscopy. Quantitative phytochemical analysis and the antioxidant activities, including 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, total antioxidant capacity, and ferric reducing antioxidant power activities were evaluated for HS extract and its synthesised AuNPs. Cytotoxic effects were assessed using cell viability, apoptosis, and oxidative stress assays. The HRTEM analysis revealed predominantly spherical nanoparticles with an average size of 10.0 ± 2.00 nm. Hibiscus sabdariffa -AuNPs (HS-AuNPs) demonstrated significant antioxidant ability, indicating retained bioactivity of the extract. Cytotoxicity assessment revealed dose- and cell type-dependent inhibition of breast and colorectal cancer cells. Apoptosis was confirmed by Hoechst 33,342 staining and annexin V/propidium iodide (PI) assays, indicating both early and late apoptotic events. In addition, HS-AuNPs increased intracellular reactive oxygen species and malondialdehyde levels (lipid peroxidation). These findings suggest that HS-AuNPs are a promising biocompatible and eco-friendly nanotherapeutic candidate for oxidative stress-mediated cancer therapy and targeted drug delivery.