Stretchable solar cells power electronic 'super skin'

The foundation of the artificial skin is made up of a flexible organic transistor, made with flexible polymers and carbon based materials. To allow touch sensing, the transistor contains a thin, highly elastic rubber layer, moulded into a grid of tiny inverted pyramids. When pressed, this layer changes thickness, which changes the current flow through the transistor. The sensors have from several hundred thousand to 25million pyramids per cm², corresponding to the desired level of sensitivity. To sense a particular biological molecule, the surface of the transistor has to be coated with another molecule to which the first one binds when it comes into contact. According to Bao, the coating layer only needs to be a nanometer or two thick. "Depending on what kind of material we put on the sensors and how we modify the semiconducting material in the transistor, we can adjust the sensors to detect chemicals or biological material," she said. The researchers are now working on extending the technique to detect proteins, which could prove useful for medical diagnostics purposes. "For any particular disease, there are usually one or more specific proteins associated with it – called biomarkers – that are akin to a 'smoking gun'. Detecting these protein biomarkers will allow us to diagnose a host of diseases," said Bao. The professor believes the same approach would also allow the sensors to detect chemicals, as by adjusting aspects of the transistor structure, the 'super skin' can detect chemical substances in either vapour or liquid environments. Bao says by running the sensors from solar energy, generating power is simple and allows the sensors to be lighter and more mobile. "The solar cells continue to generate electricity while they are stretched out, producing a continuous flow of electricity for data transmission from the sensors. They have a wavy microstructure that extends like an accordion when stretched. A liquid metal electrode conforms to the wavy surface of the device in both its relaxed and stretched states." Beyond the detection of chemicals, Bao belives the artificial skin has the potential to do much more than mimic human skin and could even allow robots or other devices to perform functions beyond human capability. "You can imagine a robot hand that can be used to touch some liquid and detect certain markers or a certain protein that is associated with some kind of disease and the robot will be able to effectively say, 'this person has that disease'," she said.