TiO2 and Au nanoparticles are synthesized by the colloidal technique and used for nanocomposite thin film preparation. The effect of thermal treatment and organic template presence is analyzed in order to tailor film microstructure. The Au-TiO2 interfaces as well as the overall porosity of the films are analyzed combining structural and morphological characterization along with spectroscopic ellipsometry and surface plasmon spectroscopy analyses. An efficient surrounding of TiO2 nanoparticles around Au colloids is obtained, leading to an extensive noble metal?metal oxide interface, improving functional properties of the films, while keeping a porous structure. Gas sensing tests are performed on these nanocomposites films: reversible sensing dynamics for CO detection are observed with high sensitivity and a correlation between response and recovery times and microstructure is reported. ; peer reviewed: no ; NRC Pub: yes