The use of paper-based biosensors for low-cost diagnostics has been hindered by a lack of sensitive detection methods that can be easily implemented on paper substrates. However, SWNT-based chemiresistive biosensors are gaining popularity as label-free, highly sensitive biosensors. The challenge is to make these sensors more affordable for use in resource-limited settings. In this study, Shen et al. report on the fabrication, optimization, and analytical characterization of a chemiresistive biosensor on paper for label-free immunosensing. The authors used a waterbased ink made from pyrene carboxylic acid (PCA) and SWNTs to create a well-defined ink deposition on paper, which was achieved through a combination of wax printing and vacuum filtration. The resulting biosensor was found to be easy to fabricate, and was designed for rapid, sensitive, and selective detection of human serum albumin (HSA). The biosensor achieved a limit of detection (LOD) of 1 pM, thanks in part to the porous structure of the paper surface, which can accommodate more SWNTs. This study provides a potential platform for future automated, disposable paper-based biosensors with multiplexed detection capability and self-driven microfluidic controls, meeting the "ASSURED" criteria sought for diagnostics technologies in resource-limited environments.