On March 17, 2009, the U.S. Food and Drug Administration (FDA) announced that it has completed a “proof-of-concept” study of a test that “quickly and accurately detects the presence of even the smallest amount of the deadly anthrax toxin.” According to FDA, the proof-of-concept study relies on a nanotechnology-based test platform built from tiny molecular-sized particles. The europium nanoparticle-based immunoassay (ENIA) was able to detect the presence of a protein made by the anthrax bacteria known as protective antigen (PA). PA combines with another protein, lethal factor, to form anthrax lethal factor toxin, the protein that enters cells and causes toxic effects. FDA states that its researchers showed that ENIA is capable of detecting PA in quantities that are 100 times lower than current tests, such as the enzyme-linked immunosorbent assay (ELISA). The ENIA uses nanospheres covered with thousands of light-emitting atoms of europium that emit light, which acts as a signal that PA is present. The ENIA detected PA in 100 percent of samples of mouse plasma compared to 36.4 percent through ELISA. A report on the results of this study appears in the March issue of Clinical and Vaccine Immunology.