Tumbleweeds in the Bloodstream
If you have a tumor in your body, it would be nice if your body could tell you long before symptoms appear. Then the tumor still would be harmless and you could do some acting. Some NASA scientist will make this happen in the future.
The idea is to place "nanoparticles" inside the cells to function as molecule-size sensors. If they find sickness or certain signs of trouble they would begin to glow, signaling the outside world that something is wrong.
It would be a revolution to human health if that happens.