Dual functional evaluation of biogenically synthesized noble metal-doped ZnO nanoparticles for gas sensing and biocompatibility

This study presents the Garcinia indica leaf extract-mediated biogenic synthesis and dual-functional assessment of zinc oxide nanoparticles (ZnO NPs) doped with biogenic gold (Au) and silver (Ag) nanoparticles (NPs). The synthesis of Au NPs and Ag NPs was optimized by varying reaction parameters. Au NPs were optimally synthesized using 2.5 mM HAuCl 4 at pH 7 and 80 °C for 55 min with a 1:1 extract-to-precursor ratio, while AgNPs were best synthesized with 4 mM AgNO 3 at pH 8 in 10 min. These yielded stable, well-dispersed NPs with surface plasmon resonance peaks at ∼545 nm (Au NPs) and ∼410 nm (Ag NPs). Using these conditions, Au@ZnO and Ag@ZnO NPs were synthesized. XRD confirmed the hexagonal wurtzite structure of ZnO and successful doping without lattice distortion. Crystallite sizes reduced from 25 nm (ZnO NPs) to 22 nm (Au@ZnO) and 20 nm (Ag@ZnO), suggesting dopant-induced lattice strain. TEM and HR-TEM analyses revealed quasi-spherical, well-dispersed particles with distinct lattice fringes, and SAED patterns confirmed the presence of both metal and ZnO phases. XPS further validated doping and indicated electronic interactions between dopants and the ZnO matrix. Gas sensing studies demonstrated enhanced NO 2 detection, with Au@ZnO NPs exhibiting the highest response (137.8), lowest recovery time (15 s), and detection limit of 1 ppm, compared to 5 ppm for undoped ZnO NPs. Biocompatibility assays using L929 fibroblast cells showed improved cell viability for doped variants, indicating their suitability for biomedical applications. This work highlights the potential of biogenic Au NPs and Ag NPs doped ZnO NPs as promising nanomaterials for environmental monitoring and biomedical use. • Garcinia indica employed for optimized biogenic synthesis of Au NPs and Ag NPs. • Biogenic ZnO NPs were doped with Au NPs and Ag NPs. • Doping enhanced NO 2 detection response, sensitivity, and selectivity. • Doping enhanced biocompatibility when tested against L929 fibroblast cells.