Nanoengineers at the University of California, San Diego have designed a flexible sensor that can be printed on temporary tattoo paper and applied to the skin to test blood sugar levels. It's inexpensive, easy-to-use, and best of all, painless.

The tattoo is a series of carefully placed electrodes that measure glucose molecules in the fluid of the skin. It gives off a very mild electrical current that forces sodium ions in the fluid towards the tattoo's electrodes, carrying glucose molecules with them along the way. The sensor built into the tattoo uses this information to measure overall glucose levels. 

With the current prototype, the tattoo must be removed so that glucose levels can be analyzed, but researchers are hoping that this early design will lead to a model that can display numeric glucose levels right on the tattoo. Researchers are also working on embedding Bluetooth capabilities into the tattoo, meaning blood sugar data could be sent directly to a patient's doctor or smartphone. They also envision other uses for the design, such as monitoring prescription drug levels, proteins, or even illegal drugs or alcohol levels.