When things get small–like millionths-of-an-inch small–they get very interesting. The ordinary rules of physics we’re used to fade back as the oddness of quantum physics looms large. Engineers have taken advantage of this fact by fashioning tiny bits of matter, known as quantum dots, that behave in all sorts of useful ways. For example, quantum dots made from cadmium telluride will respond to ultraviolet light by giving off a flash of visible light–the color depending on their size. If you attach certain molecules to cadmium telluride quantum dots, they will latch onto certain targets, making it possible to detect trace amounts of substances ranging from pesticides to cancer cells.

As versatile as cadmium telluride quantum dots are, however, they’re