Figure 5.

(a) Photograph showing a flexible toy pencil. (b) SEM image of the flexible pencil lead. (c) Schematic diagram showing a bilayer chemiresistor. The first rectangular-shaped layer was drawn with a flexible pencil, acting as the active sensing layer, on top of which a set of interdigitated electrode were drawn with an HB pencil to improve electrical contact during measurements. (d) Photograph of the pencil-drawn chemiresistor, showing the flexibility of the device. (e) Schematic diagram showing how VOC vapor swells the polymer matrix in the active sensing layer of the device and push the graphite particles apart, where the black dots represent graphite particles.