Patterned thin films of titanium dioxide (TiO2), with micrometer-sized features, were prepared on transparent, conductive indium-tin oxide glass platforms via microtransfer molding and electrochemical deposition. The grating pattern produces optical diffraction, where the efficiency of diffraction (g) depends on the degree of contrast in refractive index between the patterned material and the surrounding medium. The refractive index of a representative micropatterned TiO2 film (anatase) was estimated, via solvent index matching experiments, to be 2.72-a value sufficiently large to achieve good contrast with air or water. A new method, based on the measurement of changes in diffraction efficiency, is described for the detection and evaluation of organic chemical adsorption on various titanium dioxide surfaces. The strategy is illustrated for the vapor-phase adsorption of chloroform on high-area amorphous, anatase, and rutile forms of titanium dioxide. The uptake of 2,4,5-trichlorophenol from aqueous solutions by amorphous TiO2 was also examined by the modulated optical-diffraction-grating technique.