Light-emitting tattoo designed for the first time

Scientists from UCL and IIT – Istituto Italiano di Tecnologia (Italian Institute of Technology) created a temporary tattoo with light-emitting technology used on TV screens and smartphones, paving the way for a new type of ‘smart tattoo’ with a range of uses potential.

The technology, which uses organic light-emitting diodes (OLEDs), is applied in the same way as water transfer tattoos. In other words, OLEDs are made from temporary tattoo paper and transferred to a new surface when pressed and rubbed with water.

The researchers, who described the process in a new article in the journal Advanced Electronic Materials, say it could be combined with other tattoo electronics to, for example, emit light when an athlete is dehydrated or when we need to get out of the sun to avoid sunburn. OLEDs can be tattooed on packaging or fruit to signal when a product has passed its expiration date or will soon become unpalatable, or used for fashion in the form of shiny tattoos.

Professor Franco Cacialli (UCL Physics & Astronomy), senior author of the article, said: “The tattooable OLEDs that we demonstrated for the first time can be made in scale and very inexpensively. They can be combined with other forms of electronic tattooing for a very wide range of possible uses. These can be for fashion – for example, providing shiny tattoos and nails that emit light. In sports, they can be combined with a sweat sensor to signal dehydration.

“In healthcare, they can emit light when there is a change in a patient’s condition – or, if the tattoo is turned to the other side of the skin, they can be combined with light-sensitive therapies for cancer cells, for example.

“Our proof-of-concept study is the first step. Future challenges will include encapsulating OLEDs as much as possible to prevent them from degrading rapidly through contact with air, as well as integrating the device with a battery or supercapacitor.”

The OLED device that the researchers developed is 2.3 micrometers thick in total (less than a 400th of a millimeter) – about a third the length of a single red blood cell. It consists of an electroluminescent polymer (a polymer that emits light when an electric field is applied) between the electrodes. An insulating layer is placed between the electrodes and the commercial tattoo paper.

The light-emitting polymer is 76 nanometers thick (one nanometer equals one millionth of a millimeter) and was created using a technique called spin coating, in which the polymer is applied to a substrate that is spun at high speed, producing a extremely thin and uniform layer.

After building the technology, the team applied the tattooable OLEDs, which emitted green light, on a glass panel, a plastic bottle, an orange and a paper packaging.

The senior author, Professor Virgilio Mattoli, a researcher at the Italian Institute of Technology, said: “Electronic tattooing is a rapidly growing field of research. At the Italian Institute of Technology, we have already created electrodes that we tattoo on people’s skin and that can be used To perform diagnostic tests, such as electrocardiograms. The advantage of this technology is that it is inexpensive, easy to apply and use and can be easily washed with soap and water. “

OLEDs were first used on a flat screen TV 20 years ago. Among the advantages of the technology are the fact that they can be used on flexible and foldable surfaces and are made of liquid solvents. This means that they can be printed, offering an inexpensive way to create new OLED designs to size.