Functionalized carbon nanotubes possess promising electronic properties, but their poor solubility often hampers their use in practical devices. Timothy M. Swager and colleagues at MIT have found a way around this problem: a solvent-free method to process nanostructured carbon materials. And they have used it to create gas and vapor sensors on paper (Proc. Natl. Acad. Sci. USA 2013, DOI: 10.1073/pnas.1307251110). The sensors can detect various gases and volatile organic compounds (VOCs). Creating them from commercially available materials takes just 15 minutes. The researchers start by taking one of three forms of nanostructured carbon: single-walled carbon nanotubes, multiwalled carbon nanotubes, or graphite. They mechanically mix the material in a ball-milling device containing a small-molecule selector that interacts with specific classes of gaseous analytes. Then they compress the resulting mixed solid into a pencil lead compatible with a mechanical pencil. Finally, they draw the material on weighing paper patterned with gold electrodes. The resulting sensor arrays on paper can sense and differentiate gases and VOCs at parts-per-million concentrations. Furthermore, the method allows the researchers to quickly identify the best combination of nanostructured carbon and small-molecule selector to discriminate among various analytes.