Hunan University develops a wearable microfluidic chip for "temporal sampling" to achieve dynamic monitoring of sweat cortisol
9月 22, 2026
During the process of exercise, stress, and other physiological changes, biomarkers in human sweat undergo dynamic changes over time. Compared with traditional samples such as blood, sweat has the characteristics of non-invasive, easy to obtain, and suitable for continuous collection, so wearable sweat sensors have received widespread attention in recent years. However, existing wearable sweat sensing technologies often focus on detecting single time points or continuous average signals. For biomarkers such as cortisol with obvious temporal dynamic characteristics, relying solely on single point sampling is difficult to fully record their changes.
According to Mims Consulting, a research team from Hunan University recently proposed a wearable microfluidic chips with integrated "timing sampling" function. The system utilizes soluble polymer valves to control sweat to enter different detection chambers at different times, and combines an adapter based fluorescence detection strategy to achieve dynamic monitoring of sweat cortisol during exercise.
The relevant research results have been published in the journal Analytical Chemistry under the title "Wearable Microfluidic Chip Integrated with Chrono Sampling for Cortisol Detection in Sweat".
Figure 1 Wearable microfluidic chip with integrated timing sampling function
Moving from "continuous detection" to "temporal sampling"
At present, implementing sweat timing sampling typically requires the introduction of multiple storage areas and programmable fluid control units in microfluidic systems, but external drivers, complex valves, and power supply requirements may increase the size and complexity of wearable systems.
Figure 2 Feasibility Study of Polymer Valve
In response to this issue, the research team combined soluble polymer valves with paper-based materials to construct a "time valve" that does not require external energy drive. The core idea is to drop polymer solution onto filter paper and dry it to form a polymer film that can block liquid pathways. When sweat comes into contact with the valve, the polymer gradually dissolves, and the previously blocked capillary channels reopen, allowing sweat to enter the corresponding detection area at the predetermined time.
This design directly converts "time control" into the dissolution kinetics of materials, thereby avoiding the complex driving structure required by traditional active valves.
Material selection and structural design of wearable microfluidic chips
The researchers first compared the valve performance of water-soluble polymers such as polyvinyl alcohol (PVA), polyethylene glycol (PEG), polystyrene sulfonic acid (PSS), and hyaluronic acid (HA).
Experiments have shown that different polymer concentrations can significantly affect valve opening time. Among them, PSS showed good liquid isolation capability and more continuous and adjustable opening time. As the PSS concentration increases from 10% to 20%, the valve opening time can be adjusted within a range of approximately 10-60 minutes.
Figure 3 Optical images of polymer valves opened at different time points
The research team further developed wearable microfluidic chips. The chip is composed of 5 layers of PET structure and assembled with double-sided tape. The overall structure includes sweat inlet, central channel, multiple branch channels, detection chamber, air hole layer, and sweat outlet.
Figure 4: Structure and Dimensions of Microfluidic Chips
Among them, the central channel is responsible for guiding sweat to flow forward preferentially, while the five branch channels are connected to different detection chambers. Each branch channel is equipped with a PSS polymer valve, which adjusts the PSS concentration to open different valves at different times.
The researchers ultimately set 5 sampling time points to enable the chip to collect sweat samples in a predetermined time sequence. Experiments have shown that valves prepared with different concentrations of PSS can be opened sequentially in a predetermined order, and sweat from corresponding time periods can be introduced into different detection chambers.
Combining smartphone imaging to achieve cortisol detection
The research team pre stored fluorescent probes for cortisol recognition in the detection chamber. The basic detection mechanism is based on the specific binding between the adapter and cortisol, and detectable fluorescence changes are generated through DNA hybridization chain reaction design.
The chip does not need to be connected to large instruments. Researchers use smartphones to capture fluorescence images of the detection area, and then calculate the fluorescence brightness based on the RGB information in the images, thereby achieving cortisol concentration analysis.
The artificial sweat experiment showed that as the concentration of cortisol increased, the green fluorescence in the detection area increased. The detection limit of the system for cortisol reaches 6 nM, while the physiological concentration of cortisol in sweat is about 20-400 nM, indicating that its detection range can cover the relevant concentration range in human sweat.
Dynamic detection capability verified through sports experiments
To verify the actual application performance, researchers fixed the chip on the exercise headband of volunteers' foreheads and collected sweat at set time points during the exercise.
Figure 5 Utilizing the developed wearable microfluidic chip to capture the dynamic sweat cortisol profile during motion
The results showed that in some volunteers, the overall level of cortisol in sweat showed an increasing trend with prolonged exercise time; At some final time points, cortisol levels decreased, which the research team believes may be related to the dilution of biomarkers caused by increased sweating. This result also reflects the value of time-series sweat sampling: compared to single time point detection, multi time point data can present a more complete physiological change process.
In addition, the researchers further collected sweat from three volunteers at different exercise time points and simultaneously used the microfluidic chips;and commercial ELISA kit for detection. There was no statistically significant difference observed between the results obtained by the two methods, indicating that the wearable chip has good detection consistency.
Conclusion and Prospects
The core value of this study lies not only in detecting cortisol, but also in integrating "time control sample collection biochemical detection" into the same wearable microfluidic platform. By using the dissolution kinetics of the material itself to achieve time programming, the chip can complete sweat sampling at multiple time points without complex electronic control and external energy.
At present, the chip is mainly aimed at single step reaction detection, and in the future, multi-step reactions can be achieved by adding more functional units; Meanwhile, by simply replacing the corresponding recognition probes and pre stored detection reagents, theoretically it can be extended to other sweat biomarkers.
This microfluidic architecture based on soluble materials for "passive time programming" is expected to further promote the transformation of sweat detection from "measurement at a certain moment" to "how the entire physiological process changes", providing a new technological path for sports physiology monitoring, personalized health management, and dynamic biomarker analysis.
