An invisible patch placed on the skin much like a temporary tattoo can pick up and transmit physiological signals such as heart rate, brain waves and muscle activity.

This new advance in "wearable electronics" might one day replace the bulky wires and electrodes now used to assess body functions.

"Our goal was to develop an electronic technology that could integrate with the skin in a way that is invisible to the user,” John Rogers, professor in material science and engineering at the University of Illinois, told BBC News.

The epidermal electronic system improves on existing products and processes, many of them borrowed from Silicon Valley and the semiconductor industry.

The EES might also form the basis of a "smart" Band-Aid in the future, by using electrical stimulation to accelerate wound healing.

BBC News reports that there are also tiny solar cells which can generate power or get energy from electromagnetic radiation. The device is small, less than 50 micrometers thick - less than the diameter of a human hair.

The sensor is mounted on to a water-soluble sheet of plastic, so it is attached to the body by brushing with water, just like a temporary tattoo, the British news wire reported.

"I can't feel its presence," said John Rogers, senior author of a paper on the patch published in the Aug. 12 issue of Science, who demonstrated the two-inch-square device on his forearm during a Wednesday teleconference.

"The distinction between electronics and the skin is blurred. It's much like a temporary transfer tattoo, though this has high-quality electronics embedded," said Rogers.

The EES has an antenna, so it is functional. The researchers' next challenge is make all the different elements work as a coherent system, to add Wi-Fi and to figure out the best power sources, such as batteries, wireless coils and solar cells.

"This is not [yet] a fully integrated system with all the bells and whistles we hope to achieve. The story doesn't end here," Rogers said.