An article which is sensitive to non-ionizing electromagnetic radiation in the radiofrequency radiation range, consisting essentially of a substrate, a layer of a binder material and a layer of activated diazoluminomelanin. This article is prepared by coating at least one surface of a substrate with a binder, immersing the binder-coated substrate into a solution comprising luminol, 3AT and a soluble nitrite for a period of about 2 to 12 days to provide a layer of diazoluminomelanin (DALM) on the binder layer, removing the DALM-coated film from the solution and rinsing the same, activating the DALM with sodium bicarbonate and hydrogen peroxide for a period of about 2 to 12 days.