Abstract: Clinically useful diagnostic devices are prepared from commercially available metal sheet stock by a sequence of steps. The metal is one of a type on the surface of which a tenacious oxide layer can be produced. Steps in the preparation include roughening surface area of the bulk metal with pits on a fine scale to render that surface area of the metal non-specularly reflecting, chemically etching the surface area to produce some first preselected measure of reflectivity, anodizing the surface area to produce a dull, non-specularly reflecting oxide surface having a second preselected degree of reflectivity and applying a layer of protein over this dull surface area. The preferred metal is titanium and the reflectivity of the modified surface area is selected dependent on the immunological reaction being detected.