A hydrated leaf is a healthy leaf. That’s true for the leaves of crop plants in a farmer’s field, and for the leaves of trees in an area vulnerable to forest fires. But the traditional techniques to monitor leaf hydration require cutting them from their plants, which is time-consuming and cannot give live measurements. That’s why many researchers are building sensors that measure a plant’s health in real time. Now, researchers in Texas have developed a graphene “tattoo” that can be stuck directly onto a leaf to provide real-time moisture readings. The researchers also believe it could one day be the building block for a new kind of plant monitoring, by turning the patches into a neural network that computes on the plants themselves.

“Not only are we just sensing the moisture level, but we can have that sensor act as this artificial synapse, which then we can put into a neural network,” says Jean Anne Incorvia, an associate professor of electrical and computer engineering at the University of Texas at Austin. Incorvia and colleagues (including her graduate student Utkarsh Misra) published their work in Nano Letters in February. A forest of the future, Incorvia and colleagues…