Abstract: A thin film diagnostic device capable of detecting the presence of a specific organic material in a sample solution. The device comprises a layer of an anodizable color-generating metal (e.g. tantalum), a porous anodic film containing aluminum oxide overlying the color generating metal, and a reagent capable of binding with the specific organic material forming a coating on the anodic film. The porous anodic film and the coating have a combined thickness such that a color change is produced when the specific organic material binds to the reagent. The device can be used to test the biological or synthetic products in samples taken from patients or other sources.