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

Abstract

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. The functionalization of PPy changes both the wettability and the chemical composition of the interface, what is of fundamental importance for the sensor’s operation. The PPy structure has excellent mechanical stability, enduring at least 600 bending cycles, what is of relevance on flexible electronics. The electrical resistance correlates with the local relative humidity (RH) inside of the sealed microfluidic system, and the sensor response is fully reversible. The integrated system capable of locally monitoring the RH allowed us to verify that inside the microfluidic channel, water molecules can diffuse across the wax barriersa possibility disregarded so far. Our results attest that RH variations of 5–10% can affect the flow of extended channels (>5 cm) even when they are fully enclosed.

Multilayered Microfluidic Paper-Based Devices: Characterization, Modeling, and Perspectives

“…The final variable we assess is the humidity, which has previously been shown to affect the flow rate and sample loss through evaporation of the solvent (water). , Elevated humidity levels are particularly problematic for paper devices as it can slow flow rates, and unexpectedly change assay times for unsealed devices (i.e., paper open to air) . For the multilayered μPAD design described in this study, the devices are sealed in tape, with only the sample addition edge open to air.…”

Paper-based sensors for diagnostics, human activity monitoring, food safety and environmental detection

“…Recently research has focused on developing new classes of paper-based sensors with improved performance. Some of these recent sensors include all-paper piezoresistive sensors for human movement detection, 11 hydrophobic paper sensor with gas permeability for gas detection, 12 nano-cellulose paper sensors for multi-channel biological detection, 13 temperature 14 and humidity sensors 15,16 . In addition to sensors, paper has also been used for creating microfluidic batteries, 17,18 self-powered devices, [19][20][21][22] supercapacitors, [23][24][25] wet generator 26 and other types of paper-based devices.…”

Ultrasensitive Microfluidic Paper-Based Electrochemical/Visual Analytical Device via Signal Amplification of Pd@Hollow Zn/Co Core–Shell ZIF67/ZIF8 Nanoparticles for Prostate-Specific Antigen Detection

“…A microfluidic paper-based analytical device (μPAD), as a novel analysis tool using paper-based working electrodes, possesses the characteristics of easy functionalization, satisfactory flexibility, and perfect biocompatibility, giving it enormous potential in the fields of biomedicine, environment, and manufacturing − and has been widely used in the detection of various biomarkers. − However, the nonconductivity of the paper itself greatly limits the realization of its excellent performance . Recently, inkjet printing, screen printing, and other technologies have been used to improve the conductivity of paper and further to grow different conductive materials on the surface of paper.…”