Pencil-on-paper: electronic devices

Paper based electronics have been rapidly growing in recent years. Drawing with a pencil on paper is perhaps the simplest and easiest way of establishing graphitic circuitry in a solvent-free manner, which in the post-graphene years, has attracted an unusual interest. Here in this focus article, we highlight the recent efforts in the literature employing pencil drawings in various ways including sensors, microfluidics, energy storage and microanalytical devices. Even active devices such as piezo and chemiresistive devices as well as field effect transistors have been realised by utilizing pencil-traces. Pencil-on-paper may offer a viable route for developing lab-on-paper applications through suitable integration of the passive and active roles of the pencil-trace.