Tokyo, Japan | Japanese researchers have developed a micro-thin thermal sensor that can be attached directly to the skin, potentially useful in monitoring the health of infants or even making sportswear more comfortable.

The group said that the device, embedded in an ultra-fine film, can measure target temperatures between 25 and 50 degrees Celsius (77-122 F), a range that includes that of the human body.

The finding, made in collaboration with the University of Texas, was published in the journal Proceedings of the National Academy of Sciences of the United States of America this week.

Professor Takao Someya, who heads a research team at the University of Tokyo working on such flexible devices, said that the electronic circuit composed of graphite and a semicrystalline acrylate polymer is just 15 micrometres in thickness, or about one fourth that of a human hair.

He said that the sensors can be printed onto adhesive plasters that can used to monitor body temperature.

"For example, a plaster applied directly to a wound or after surgery could provide warning of infection by detecting local changes in temperature due to inflammation," he told reporters on Monday.

"By putting it on the skin of a baby you can easily check the infant's body temperature... or the measuring of changes in body temperature over a large area could help develop comfortable (clothing)."

He added that the materials are cheap and widely used in manufacturing and envisions the device could be commercialised for practical use in as soon as three years.

The team tested the sensor by placing it directly on the lung of a rat to measure the organ's temperature.

"The device successfully measured cyclic changes in lung temperature of just 0.1 degree centigrade as the animal breathed, demonstrating its utility as a sensor for monitoring body vital signs in physicological settings," research associate Tomoyuki Yokota said.