The combination of photolithography-patterning and embossing of a Parafilm® can fabricate microfluidic paper-based analytical devices (μPADs) without the use of a wax printer, cutter plotter and wet-chemical processing of paper.

Wearable devices have received tremendous interests in human sweat analysis in the past few years. However, the widely used polymeric substrates and the layer-by-layer stacking structures greatly influence the cost-efficiency, conformability and breathability of the devices, further hindering their practical applications. Herein, we report a facile and low-cost strategy for the fabrication of a skin-friendly thread/paper-based wearable system consisting of a sweat reservoir and a multi-sensing component for simultaneous in situ analysis of sweat pH and lactate. In the system, hydrophilic silk thread serves as the micro-channel to guide the liquid flow. Filter papers were functionalized to prepare colorimetric sensors for lactate and pH. The smartphone-based quantitative analysis shows that the sensors are sensitive and reliable. Although pH may interfere the lactate detection, the pH detected simultaneously could be employed to correct the measured data for the achievement of a precise lactate level. After being integrated with a hydrophobic arm guard, the system was successfully used for the on-body measurement of pH and lactate in the sweats secreted from the volunteers. This low-cost, easy-to-fabricate, light-weight and flexible thread/paper-based microfluidic sensing device may hold great potentials as a wearable system in human sweat analysis and point-of-care diagnostics.