Luminous tattoo designed for the first time

Scientists from UCL and IIT – Istituto Italiano di Tecnologia (Italian Institute of Technology) have created a temporary tattoo with luminescent technology used in TV and smartphone screens, paving the way for a new type of ‘smart tattoo’ with a range of possible applications.

The technology, which uses organic light-emitting diodes (OLEDs), is applied in the same way as water transfer tattoos. That is, the OLEDs are fabricated on temporary tattoo paper and transferred to a new surface by pressing and dabbing with water.

The researchers described the process in a new article in the journal Advanced electronic materials, suppose it can be combined with other tattoo electronics to emit light, for example, 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 indicate when a product has passed its expiration date or will soon become inedible, or used for fashion in the form of glowing tattoos.

Professor Franco Cacialli (UCL Physics & Astronomy), senior author of the paper, said: “The tattooable OLEDs that we first demonstrated can be made to scale and very cheaply. They can be combined with other forms of tattoo electronics for a very wide range of possible applications, for example for fashion, such as providing glowing tattoos and luminous fingernails, and in sports they can be combined with a sweat sensor to signal dehydration.

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

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

The OLED device the researchers developed is a total of 2.3 micrometers thick (less than one 400th of a millimeter) – about one 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 electrodes. An insulating layer is placed between the electrodes and the commercially available tattoo paper.

The luminescent polymer is 76 nanometers thick (one nanometer is one millionth of a millimeter) and is made using a technique called spin coating, where the polymer is applied to a substrate that is spun at high speed, creating an extremely thin and even surface. low.

After building the technology, the team applied the tattooable OLEDs, which emitted green light, to a window pane, a plastic bottle, an orange, and a paper package.

Senior author Professor Virgilio Mattoli, researcher at the Italian Institute of Technology said: “Tattoo electronics is a fast-growing field of research. At the Italian Institute of Technology, we have previously developed electrodes that we have tattooed on people’s skin that can be used to 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 off with soap and water. “

OLEDs were first used in a flat screen TV 20 years ago. One of the advantages of the technology is that they can be used on flexible, pliable surfaces and that they can be made from liquid solvents. This means they are printable, which is an inexpensive way to create custom new OLED designs.