Colloidal solutions of Au and TiO2 nanoparticles are prepared and deposited as nanocrystal inks for the fabrication of porous thin films to be used as optical gas sensor. The introduction of Au nanoparticles within the anatase matrix affects the reactions mechanism improving the sensing process; moreover the Au surface plasmon resonance peak can be used for the realization of a gas sensor with tunable sensitivity. Different thermal treatments, Au dimensions and concentrations are investigated and optimized in order to tailor films microstructure and their sensing properties. The nanocomposites show reversible change in optical absorption/reflection when exposed to reducing gasses (H2, CO) at 300 ◦C operative temperature or when exposed to volatile organic compounds (alcohols) at room temperature.