Thin films composed of a matrix of titanium and nickel oxides, doped with gold nanoparticles have been prepared with the sol–gel method and annealed at different time/temperature combinations. Structural characterizations demonstrate the crystallization of nickel titanate and of TiO₂-rutile due to nickel capability to promote rutile crystallization over anatase. Optical characterizations show a tunable refractive index of the samples according to the Ti/Ni ratio, and a high amount of residual porosity even after high temperature annealing. Sensor functionality measurements were performed with H2, CO and H₂S: high sensitivity for hydrogen sulfide detection has been proved, and the cross sensitivity to the other two gases can be tuned by controlling the nickel amount. For high Ni concentrations, the matrix is composed of NiTiO₃ and TiO₂-rutile, and no cross sensitivity is experienced. For lower Ni amounts, TiO₂-anatase starts to crystallize and the films become sensitive to H₂ and CO. ; peer reviewed: no ; NRC Pub: yes