A biosensor disk includes a detection substrate with an upper side surface, a reflection substrate with a lower side surface facing oppositely toward the upper side surface, and fluidic channels reaching between the opposed side surfaces. The upper side surface has binding sites, and has non-binding sites adjoining the binding sites. The detection substrate is transparent at the non-binding sites. The lower side surface has non-reflective areas, and has reflective areas adjoining the non-reflective areas. The reflective areas are located opposite the non-binding sites and have discrete polygonal configurations of equal size and shape.