Versatile and Robust Integrated Sensors To Locally Assess Humidity Changes in Fully Enclosed Paper-Based Devices.

The synergic combination of materials and interfaces to create novel functional devices is a crucial approach for various applications, including low-cost paper-based point-of-care systems. In this work, we demonstrate the implementation of surface-modified polypyrrole (PPy) structures, monolithically integrated into a three-dimensional multilayered paper-based microfluidic device, to locally assess humidity changes. The fabrication and integration of the system include the deterministic incorporation of PPy into the paper-based structure by gas-phase polymerization and the modification of the polymer properties to allow local humidity monitoring.