Sustainable fabrication of Fe₂O₃ and ZnO nanoparticles using Curcuma caesia peel extract: structural characterization and anticancer performance against HepG2 and HT29 cell lines

The aqueous peel extract of Curcuma caesia (black turmeric) was used in the eco-friendly production of iron & zinc oxide (Fe₂O₃/ZnO) nanoparticles (NPs). The particles appeared spherical, polydisperse, polycrystalline and size for Fe₂O₃ NPs is observed as 36.84 nm, whereas for ZnO NPs is 37.93 nm. Black turmeric aqueous peel extract (TOSE)-mediated ZnO NPs demonstrated better antioxidant activity, achieving 74.27% scavenging at a concentration of 150 µg/mL, and exhibited convincing cytotoxicity in the brine shrimp lethality assay (LC₅₀ = 2.62 µg/mL), outpacing Fe₂O₃ NPs and the crude extract comparatively. Furthermore, ZnO NPs showed less hemolytic activity, indicating moderate biocompatibility with human RBCs. Zeta potential values of − 11.4 mV for Fe₂O₃ NPs and − 19.2 mV for ZnO NPs generally indicate limited electrostatic stabilization, significant heterogeneity and a higher likelihood of aggregation. In anticancer studies, ZnO NPs exhibited prominent cytotoxicity than Fe₂O₃ NPs, with an IC₅₀ of 84.81 µg/mL against HepG2 cells and 130.20 µg/mL against HT-29 cells. In conclusion, ZnO NPs synthesized via TOSE revealed significant pharmacological potential, which lend scientific credibility to the traditional use of black turmeric in herbal medicine and highlight its potential in therapeutics.