Scientists have created a temporary tattoo using light-emitting technology used in TV and smartphone screens, paving the way for a new type of smart tattoos with a range of potential uses.
The technology, which uses organic light-emitting diodes (OLED), is applied in the same way as temporary tattoos, which are translated with water. That is, OLED LEDs are made on temporary tattoo paper and transferred to a new surface by pressing on it and soaking it with water.
Researchers say it can 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. OLED LEDs can be tattooed on packaging or fruit to signal that a product has expired or is about to become inedible, or used as a trendy glowing tattoo.
“The tattooed OLED LEDs that we have demonstrated for the first time can be manufactured on a large scale and, above all, very cheaply. They can be combined with other forms of tattoo electronics for a very wide range of possible uses. This could be fashion, such as creating luminous tattoos and light-emitting nails. In sports, they can be combined with a sweat sensor to signal dehydration. In healthcare, they can emit light when the patient’s condition changes or, if the tattoo was turned into the skin the other way, they could potentially be combined with photosensitive therapy, for example, to target cancer cells.”Professor Franco Cachalli, UCL Physics & Astronomy
This pilot study is the first step. Future challenges will include encapsulating OLEDs as much as possible to prevent their rapid destruction due to exposure to air, as well as integrating the device with a battery or supercapacitor.
The OLED device developed by the researchers has a total thickness of 2.3 micrometers (less than 1/400 millimeter) – about a third of 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 commercial tattoo paper.
The light-emitting polymer is 76 nanometers thick (a nanometer is 1 / 1,000,000 of a millimeter) and was created using a technique called centrifugation, where a polymer is applied to a substrate that spins at high speed, resulting in an extremely thin and even layer.
After creating the technology, the team applied tattooed OLEDs that emitted green light to window glass, plastic bottle, orange and paper packaging.
“Tattoo electronics is a fast-growing area of research. At the Italian Institute of Technology, we first developed electrodes that we tattooed on people’s skin, which can be used to perform diagnostic tests such as electrocardiograms. The advantage of this technology is that it is low in cost, easy to apply and use, and can be easily washed off with soap and water.”Professor Virgilio Mattoli, Research Fellow at the Italian Institute of Technology
OLEDs were first used in flat-screen TVs 20 years ago. The advantages of this technology include the fact that they can be used on flexible, bendable surfaces and that they can be made from liquid solvents. This means they are printable, providing a cheap way to create custom OLED designs.