Stanford researcher Zhenan Bao has developed a new stretchable, solar-powered “super skin” sensor that is so sensitive it can feel a fly touch down. The flexible electronic material harnesses polymer solar cells to generate electricity and can detect chemicals and sense various kinds of biological molecules. The technology holds potential for an incredible array of applications ranging from clothing, to robots, prosthetic limbs and beyond.
Chemical engineering Professor Zhenan Bao
The foundation for the artificial skin is a flexible organic transistor made with flexible polymers and carbon-based materials that can be stretched up to almost one-third of its size without compromising any of the mechanisms or losing power. The cells maintain a wavy microstructure that extends like an accordion when stretched, and a liquid metal electrode conforms to the surface of the device in both its relaxed and stretched states.
To allow for touch sensitivity, the transistor features a thin, highly elastic rubber layer, molded into a grid of tiny inverted pyramids. When pressed, this layer changes thickness, which changes the current flow through the transistor. The sensors can have anywhere from several hundred thousand to 25 million pyramids per square centimeter, corresponding to the desired level of sensitivity. The surface of the transistor can also be coated with a nanometer-thick layer of molecules that bind to and detect the presence of particular biological compounds.
So far Bao’s team has successfully demonstrated the concept by detecting certain strains of DNA, and the researchers are now working on extending the technique to detect proteins, which could prove useful in diagnosing medical conditions in ailing patients. “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 said. By simply adjusting the transistor structure the super skin can also detect chemical substances in either gaseous or liquid environments, and it can transmit electronic signals to a computer or even the human brain.
Using solar power to keep the sensors running actually simplifies their design – using batteries or hooking up to the electrical grid can prove problematic for frequent use, but solar cells give way to a lighter skin, more mobility and a wider range of applications including fabrics, machines, cars, lenses, architectural elements, and even our bodies. But don’t worry about a power outage – the solar cells continue to generate electricity while they are stretched out.
Bao refers to the technology as a “super skin”, saying “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.'”
Bao has also found a way to build the transistor with biodegradable materials, making the skin not just a technological and medical feat, but an eco-friendly one.