For centuries, animals have been our first line of defense against toxins. A canary in a coalmine served as a living monitor for poisonous gases. Scientists used fish to test for contaminants in our water. Even with modern advances, though, it can take days to detect a fatal chemical or organism. Until now. Working in the miniaturized world of nanotechnology, researchers have made an enormous — and humane — leap forward in the detection of pollutants.