A combinatorial chemical formation and assay disc (1) having a base (20) and an upper surface (26) and a lower surface, one of the upper or lower surfaces being an assay surface and a data surface (40) spaced from the assay surface wherein the data surface is on or within the assay disc. The assay surface has a conductive layer (64) on the base, a dielectric or photo-conductive layer (66) on the conductive layer and a chemically functional layer (68, 69) on the dielectric or photo-conductive layer. The assay surface may be planar or include three dimensional features (100, 168).