Abstract: An article and a method for monitoring the concentration of an analyte, e. g., glucose, in blood. In one aspect, the invention involves an article comprising a multiple-layer element. In one embodiment, the article comprises: a multiple-layer element comprising: (a) a base layer (b) a cover layer, the cover layer having a first opening for venting the multiple-layer element and a second opening for receiving a biological sample; and (c) a core layer having a first major surface and a second major surface, the core layer disposed between the base layer and the cover layer, the core layer comprising a sample introduction chamber and a optical reading chamber, the first major surface of the core layer in face-to-face contact with the base layer, the second major surface of the core layer in face-to-face contact with the cover layer.