Sensors made from graphene and silly putty

Scientists have used the wonder material graphene to make the novelty children's toy silly putty conduct electricity, creating extremely sensitive sensors.
The research, led by Jonathan Coleman from Trinity College Dublin and Robert Young of the University of Manchester in the UK, potentially offers exciting possibilities for applications in new, inexpensive devices and diagnostics in medicine and other sectors.
Coleman, along with postdoctoral researcher Conor Boland, discovered that the electrical resistance of putty infused with graphene ("G-putty") was extremely sensitive to the slightest deformation or impact.
They mounted the G-putty onto the chest and neck of human subjects and used it to measure breathing, pulse and even blood pressure.

It showed unprecedented sensitivity as a sensor for strain and pressure, hundreds of times more sensitive than normal sensors.
The G-putty also works as a very sensitive impact sensor, able to detect the footsteps of small spiders. It is believed that this material will find applications in a range of medical devices.

"What we are excited about is the unexpected behaviour we found when we added graphene to the polymer, a cross-linked polysilicone. This material as well known as the children's toy silly putty," Coleman said.
When the researchers added the graphene to the silly putty, it caused it to conduct electricity, but in a very unusual way.

The electrical resistance of the G-putty was very sensitive to deformation with the resistance increasing sharply on even the slightest strain or impact.
Unusually, the resistance slowly returned close to its original value as the putty self-healed over time.
"While a common application has been to add graphene to plastics in order to improve the electrical, mechanical, thermal or barrier properties, the resultant composites have generally performed as expected without any great surprises," Coleman said.
The behaviour we found with G-putty has not been found in any other composite material. This unique discovery will open up major possibilities in sensor manufacturing worldwide, researchers said.

The findings were published in the journal Science.