Au nanoparticle-functionalized (TiO2)1−x(ZnO:MgO)x nanocomposite thin films (0≤x≤0.3) were effectively produced by chemical spray pyrolysis and annealed at 600 °C. The effects of ZnO incorporation and Au nanoparticle modification on the films' structural, optical, and antibacterial properties were studied using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV–Vis spectroscopy, and field-emission scanning electron microscopy (FESEM). XRD analysis confirms the formation of polycrystalline anatase TiO2 and shows a composition-dependent structural development with increasing ZnO concentration. The optical experiments revealed increased transmittance and a progressive widening of the optical band gap from 3.5 eV to 4.0 eV in the undoped films, whereas Au incorporation modified the optical response via plasmonic effects. FESEM results revealed considerable morphological refinement and improved surface uniformity following ZnO addition and Au nanoparticle functionalization. Antibacterial studies demonstrated increased inhibition against both Gram-negative and Gram-positive bacteria, with the maximum activity seen for compositions comprising greater ZnO concentrations and Au nanoparticles. The higher performance is due to the combined effects of mixed-oxide engineering, plasmonic enhancement, and increased reactive oxygen species formation. The results obtained highlight the potential of Au-functionalized TiO2-ZnO:MgO nanocomposites for optical, environmental, and biomedical applications.
