Ultra-sensitive pressure sensor
Sensors made of graphene and plasticine can monitor blood pressure in real time for 24 hours.
Simply add a little graphene to turn the plasticine into a pressure sensor. This sensor is extremely sensitive, not only can monitor the body's pulse, but can even detect the footsteps of a small spider.
This graphene plasticine is called "G-putty," and developers hope to develop devices that continuously monitor blood pressure based on it. In addition, G-putty has demonstrated its ability to repair itself, indicating that it may become a smarter graphene composite.
Since graphene was first isolated in 2004, researchers have tried to add these thin layers of carbon atoms to various materials in hopes of creating composites that benefit from the high strength and excellent conductivity of graphene. Surprisingly, almost no one has attempted to mix graphene with a viscoelastic material such as plasticine. The plasticine also exhibits the characteristics of elastic solids and liquids, such as placing a piece of plasticine on a hole that slowly leaks past.
The researchers mixed about 20 layers of atomic-thick, 800-nm-long graphene sheets with a homemade plasticine (a silicone polymer) to give a conductive dark gray G-putty. A key feature of this material is that even if the researchers apply only a small amount of pressure, its resistance will change greatly. This plasticine is at least 10 times more sensitive than other nanocomposite sensors.
The researchers attached a G-putty to the wire and placed it on a student's neck, and his carotid pulse was clearly measured by a change in resistance. In fact, the pulse profile is very detailed and can be converted to accurate blood pressure readings. The sensor can also be placed on the student's chest to monitor breathing. In addition, it is a bit ridiculous that it can also record every step in which a spider weighing only 20 milligrams falls.
“They fully demonstrate the versatility of this material,” said Vincenzo Palermo, a materials scientist at the National Research Council of Italy. “I think this is a great job, very novel.” The study was published in Science.
Coleman's team found that graphene sheets form a conductive network in the plasticine, and plasticine deformation can damage the network, causing a rapid increase in resistance. Then, due to the lower viscosity of the G-putty, the graphene sheets can be moved back to their original positions and the network recombined. “This is a self-healing phenomenon,” Coleman explained.
Coleman is already in talks with medical device companies interested in continuous physiological monitoring with G-putty. For example, a patient usually needs to wear a heavy wristband to measure blood pressure and only get one instantaneous reading. But G-putty is a cheap and compact non-invasive sensor that allows patients to easily monitor blood pressure at home.
Sanna Arpiainen, a senior scientist who studies graphene, works at VTT, a large contract research organization near Helsinki. She says some companies, such as Nokia, are interested in the health of graphene sensors. But she warned that before commercializing G-putty, there are a number of obstacles to overcome – including proof that it can be mass-produced on a large scale, and testing its long-term performance. Palermo agrees: "For practical applications, you need it to run thousands of times in the same way."
When conducting the G-putty experiment, the researchers encountered an unexpected obstacle. Boland wanted to compare tests between the two spiders, but he found that he didn't notice that the slightly larger spider had swallowed its little partner into the belly. "He didn't expect to encounter this difficulty when working with animals," Coleman said.