Stanford researcher Zhenan Bao has created ‘super skin’ – so sensitive to pressure it can feel a fly touch down, and powered by flexible, stretchable solar cells.
It’s based on a flexible organic transistor, made of polymers and carbon-based materials. This contains a thin, highly elastic rubber layer, molded into a grid of tiny inverted pyramids, which changes thickness when pressed to alter the current flow through the transistor.
To sense a particular biological molecule, the surface of the transistor has to be coated with another molecule to which the first one will bind when it comes into contact. 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 sense chemicals or biological material,” says Bao.
“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, ‘Oh, this person has that disease. Or the robot might touch the sweat from somebody and be able to say, ‘Oh, this person is drunk.'”
Her team’s successfully demonstrated the concept by detecting a certain type of DNA, and is now working on extending the technique to detect proteins – useful in medical diagnostics.
“For any particular disease, there are usually one or more specific proteins associated with it – called biomarkers – that are akin to a ‘smoking gun’, and detecting those protein biomarkers will allow us to diagnose the disease,” Bao says.
The same approach would allow the sensors to detect chemicals, she says.
The solar cells which power the artificial skin have a microstructure that extends like an accordion when stretched. A liquid metal electrode conforms to the surface of the device in both its relaxed and stretched states.
“One of the applications where stretchable solar cells would be useful is in fabrics for uniforms and other clothes,” says graduate student Darren Lipomi.
“There are parts of the body, at the elbow for example, where movement stretches the skin and clothes. A device that was only flexible, not stretchable, would crack if bonded to parts of machines or of the body that extend when moved.”