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A pill could soon radio signals from inside your gut to help doctors diagnose diseases from ulcers to cancer to inflammation, according to a new study. Scientists have developed a small, ingestible capsule that mixes synthetic biology and electronics to detect bleeding in the digestive tract. The system can be adapted for a range of medical, environmental and other uses, the researchers say. The biological part of the pill uses bacteria engineered to glow when exposed to heme, the iron-containing molecule in blood. The electronic side includes a tiny light detector, computer chip, battery and transmitter that sends data to a cellphone or computer. "A major challenge for sensing in the GI tract is, the space available for a device is very limited," said Massachusetts Institute of Technology electrical engineer Phillip Nadeau. Using very low-power electronics that Nadeau and his colleagues designed, they fit all the components into a capsule about 3 centimeters long by 1 centimeter wide. It's still a bit big to swallow, but Nadeau says it likely can be engineered to a third that size. The engineered bacteria are contained in chambers covered by a membrane that lets small molecules in, but does not let the organisms out. The researchers say the bacteria can be engineered to die if they accidentally leak from the capsule; or, future models may just use the key enzymes, rather than whole bacteria. In laboratory tests, the pill successfully distinguished pigs fed small amounts of blood from those not given blood. The capsule has not been tested on humans, but the team aims to do so in the next year or two. Since the components are all fairly inexpensive to manufacture, researchers speculate that the cost would be in the range of tens to hundreds of dollars. And they say the same platform could be used to detect markers of a range of illnesses, or to sense chemicals in the environment. "It's really exciting, and I think it's got a lot of legs," said Rice University bioengineer Jeff Tabor, who was not part of the research team. But Tabor notes that the sensors may need to be much more sensitive than what was used in the pig tests. He says there may be much less blood in the guts of actual patients than what the pigs were given. Other conditions may have the same limitations. "For many actual diseases, you might have far less of the molecule that you need to sense available to you," he added. The research was published in the journal Science.