Microfluidic paper-based wearable electrochemical biosensor for reliable cortisol detection in sweat

Herein, we report the first paper-based microfluidic device encompassing the filter paper to manage the flow and to load the reagents for a reagent-free competitive magnetic-bead-based immunosensor for cortisol analysis in sweat. The paper-based microfluidic pattern was made using wax printing and laser-cutter techniques, for the delivery of capillary-driven microfluidics. The presence of magnetic beads functionalized with monoclonal antibodies for the recognition of the cortisol in the reaction zone allows for the specific measurement of the target analyte. The competitive reaction between the target cortisol and the labeled cortisol with acetylcholinesterase enzyme gives a response inversely proportional to the target cortisol in the range of 10 and 140 ng/mL, by simply folding the pad loaded with the enzymatic substrate. The paper-based microfluidic device was successively combined with a Near-Field Communication wireless module to develop a flexible integrated wearable analytical tool for cortisol detection in sweat. The paper-based integrated device was successfully applied to determine the level of cortisol in sweat in one volunteer during cycling activities at two different times, demonstrating the reliability of this sustainable paper-based device.