PEN AND INK: To draw the sensors, scientists used a normal ballpoint pen filled with special, electronic ink.

Scientists at the University of Houston in Texas have developed a new way to monitor vital signs—by drawing sensors directly onto patients’ skin. Researchers created a pen filled with electronic inks that contain flakes of silver. The pen is used to trace a circuit, or path through which electricity flows, on a person’s body. “It’s just like you would write on a piece of paper,” says Cunjiang Yu, an engineer whose team built the pen. After the ink dries, a wire can connect the circuit to a computer. Yu says the drawn-on sensor can measure things like heart rate and temperature more accurately than traditional sensors because it molds perfectly to the skin’s surface.