Graphene based sensors are made from an insulating layer coated with a graphene sheet. A worldwide research team led by the University of Illinois discovered that one can improve the sensitivity of graphene bases sensors by manipulating the chemical properties of the insulating layer used in those sensors.
It is known that a perfect graphene sheet is insensitive to other gas molecules, and it has to have "defects" to make it work. If the insulating layer is also perfect, the device is still not sensitive. But it turns out that a perfect graphene sheet on a insulating layer that has defects is also sensitive. This opens up a new "design space" for sensors - one can control the sensitivity by adding defects either to the graphene layer or the insulating layer.