A device for determining the presence of an antigen in a sample uses a substrate shaped to define a plurality of lateral flow channels and a detection region. Each lateral flow channel is associated with a load spot. The substrate includes, for each of the lateral flow channels, a fluid conducting medium, and, for the detection region, a fluid retaining medium. A first load spot receives a sample from the subject. Each of the other load spots uses a dried mixture of silk fibroin with a reagent. The detection region includes an antibody. A second load spot includes a secondary detection antibody. A third load spot includes a color reagent. The device implements an ELISA reaction when activated by sequentially placed aliquots of an aqueous solution.