Light-emitting tattoo engineered for the first time
Scientists at UCL and the IIT –Istituto Italiano di Tecnologia (Italian Institute of Technology) have created a temporary tattoo with light-emitting technology used in TV and smartphone screens, paving the way for a new type of “smart tattoo” with a range of potential uses. 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 to temporary tattoo paper and transferred to a new surface by being pressed on to it and dabbed with water.
The researchers, who described the process in a new paper in the journal Advanced Electronic Materials, say it could be combined with other tattoo electronics to, for instance emit light when an athlete is dehydrated, or when we need to get out of the sun to avoid sunburn. OLEDs could be tattooed on packaging or fruit to signal when a product has passed its expiry date or will soon become inedible, or used for fashion in the form of glowing tattoos.
The OLED device the researchers developed is 2.3 micrometres thick in total (less than one 400th of a millimetre) – 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) in between electrodes. An insulating layer is placed in between the electrodes and the commercial tattoo paper.
The light-emitting polymer is 76 nanometres thick (a nanometre is a millionth of a millimetre) and was created using a technique called spin coating, where the polymer is applied to a substrate which is spun at high speed, producing an extremely thin and even layer.
Once they had built the technology, the team applied the tattooable OLEDs, which emitted green light, on to a pane of glass, a plastic bottle, an orange, and paper packaging.
OLEDs were first used in a flatscreen TV 20 years ago. Among the advantages of the technology are that they can be used on flexible, bendy surfaces, and that they can be made from liquid solvents. This means they are printable, providing a cheap way to create bespoke new OLED designs.