Wearable capillary microfluidics for continuous perspiration sensing.

Perspiration contains valuable information indicating physiological health. For most wearable perspiration sensors, the sensing element contacts with skin directly. Yet lack of precise fluidic manipulation unit limits accurate and continuous analysis considering perspiration aggregation, evaporation loss and electrolyte reabsorption by sweat glands. The potential skin irritation caused by the chemicals in the sensor is also a safety concern. In this work, we report a wearable microfluidic device with fluidic manipulation unit based on capillary force to address these issues. Inspired by wicking materials for wiping perspiration in our daily life, herein, we use biocompatible threads to collect perspiration by capillary absorption. Then the collected perspiration was spontaneously delivered to a hydrophilic microfluidic channel, forming a continuous flow. Electrodes were embedded in the microfluidic channel for continuous electrochemical analysis and to avoid the direct skin contact. On-body tests demonstrated that continuous perspiration collection, transportation and analysis of Na+ as a proof-of-concept analyte can be achieved using the pump-free epidermal microfluidic device.