Research

In this project, we investigate potential utility of sweat as a diagnostic biofluid for monitoring personal fitness level. Human subject studies reveal that 1) sweat pH collected from regions aligned with activated muscle tissue correlates strongly to blood lactate levels, 2) fit subjects maintain sweat pH homeostasis better than unfit subjects, as the basis for personal fitness evaluation, and 3) temporal variations of sweat pH and lactate relate to different modes of exercise and post-exercise muscle recovery processes. 

Detailed physiological studies are enabled by development of a microfluidic system in the geometry of a thin, elastic band for temporal monitoring of personal fitness through sweat dynamics and sweat chemistry. The band elastically seals to the surface of the skin without the use of adhesive, with unique capabilities for purely colorimetric determination of the timing of sweat collection into a series of analysis reservoirs. 

Coupled with nanoplasmonic lactate assays and dye-conjugated SiOx pH sensors, this platform provides a simple, non-electronic tool for investigating changes in sweat chemistry with time during exercise. These advances in wearable sensing technologies and physiology studies suggest possibilities for routine use of sweat in the area of personal fitness, with future potential for use in medical contexts.

We present a fully integrated, skin-interfaced platform for time-resolved monitoring of cortisol in eccrine sweat, combining plasmonic gold nanoflower-based lateral flow assays (LFA) with time-sequenced iontophoresis, paper-based delay valves, and self-powered electrochromic timers. 

This fully integrated paper-based platform offers an all-in-one solution enabling sequential sweat stimulation, collection, and cortisol detection with picomolar-level limit of detection over several hours or more. 

The device supports two modes of operation: 1) time-programmed iontophoretic sweat stimulation through an electrical timing circuit, and 2) fully passive fluidic routing via paper-based delay valves with self-powered electrochromic timers. 

A series of physiological studies examine cortisol dynamics in sweat in the context of circadian rhythms, cold pressors, and jet lag responses. The results, with strong correlation to serum and saliva cortisol, demonstrate the potential of the wearable LFA platform for time-resolved monitoring of cortisol, offering valuable opportunities for personalized management of stress and circadian misalignment.