Cloth-based microfluidic devices integrated onto the patch as wearable colorimetric sensors for simultaneous sweat analysis

In this work, a flexible, and wearable point-of-care (POC) device integrated on a pain relief patch as wearable colorimetric sensors have been developed for sweat analysis, such as lactic acid, sodium ions, and pH simultaneously. Herein, the patch has still functioned as pain relief, while it allows for sweat monitoring during exercise, and in daily activities.

It was constructed on cotton cloth using wax printing technology (batik stamp) as cloth-based microfluidic devices (CMDs). Here, it uses micro volumes of samples to perform the reaction in the sensing zones, where the sensitive reagents are immobilized so that it can collect and analyze the sweat (lactic acid, sodium ions, and pH) as the model for sweat analytes. The colorimetric analysis was conducted via a smartphone camera by using a free app (Color Grab) for a color image analysis that uses for quantitative analysis or naked eye for semi-qualitative analysis.

The ΔRGB value of the CMDS shows the excellent linear correlation vs analytes concentration, where the coefficient of correlations was found for lactic acid (R2 = 0.994), sodium ion (R2 = 0.998), and pH (R2 = 0.994). The ΔRGB value shows the appropriate color value for the linear correlation of the analyte target concentrations in the sweat samples. Here, the limit of detection (LOD) was found at 45.73 μg/mL for lactic acid and 56.46 μg/mL for sodium ions. The reproducibility was found at 0.79% and 0.89%, for lactic acid and sodium ions respectively.

It was applied for sweat analysis during exercise, and the results show in agreement with the standard methods used in a clinical laboratory.