ZnO-NiO sol-gel thin films doped with Au nanoparticles have been prepared with NiO amounts ranging from 0 percent to 30 percent. X-ray diffraction, UV-visible spectroscopy and electron microscopy confirm the crystallization of Au, ZnO and NiO, and the high residual porosity of the nanocomposites. Optical sensor functionality towards CO detection has been presented, showing an increase in sensitivity with NiO amount when the wavelength of analysis is far from the Au surface plasmon resonance peak, while in the 500-750 nm range there is a strong wavelength dependence of the response with a decrease in sensitivity for a certain range of operative frequencies. This allows tuning of the sensor performance, and makes this material useful for multiple gases analysis. ; peer reviewed: yes ; NRC Pub: yes