Caltech’s Wearable Sensor Detects Metabolites and Nutrients From Sweat

In many ways, continuous health monitoring is considered the gold standard of wearable technology. A challenge, however, is that most conventional health monitoring techniques require blood samples that are invasive and uncomfortable to obtain from the patient.

Alternatively, some have turned to sweat monitoring as a solution.

 

A version of the sweat sensor. Image used courtesy of Caltech

 

This week, researchers from the California Institute of Technology (Caltech) published a paper describing a new continuous and reusable wearable sweat monitoring system.

 

Why Monitor Sweat?

Today, most of the most reliable and detailed health monitoring reports come from blood analysis. Medical evaluation and metabolic testing rely on periodically drawing blood from a patient and sending that blood to a lab for testing and analysis. This method is uncomfortable or painful for the patient and labor intensive and slow for lab workers.

At the same time, there is an increased demand for continuous health monitoring via wearable technology, so users can have their health monitored passively. Since wearables cannot draw or analyze blood, researchers have turned their attention to other health monitoring techniques—namely, through sweat.

 

Locations of sweat glands and chemical traces. Image used courtesy of Sensors (Basel)

 

Sweat is a prime candidate for health monitoring because it is a readily available bodily fluid that contains a plethora of chemicals that are indicative of the body’s nutritional and metabolic conditions. By transitioning to sweat-based monitoring, some researchers—like those at Caltech—hope to develop a non-invasive, continuous health monitoring system that goes beyond the limited functionality of current wearables. 

 

Challenges with Traditional Sweat Monitors

Despite the potential benefits of sweat-monitoring wearables, researchers face several hurdles in designing these devices.

According to Caltech researchers, one of the largest challenges is that current sweat sensors are severely limited in the number of analytes they focus on. This is because most existing solutions focus on strategies that are based on ion-selective electrodes or electroactive molecules. Because of this shortcoming, most clinically-relevant nutrients and metabolites are rarely detected by existing technologies.

Beyond this, current sensors are not very sensitive and require large amounts of sweat to work properly. This requires the user to vigorously exercise to obtain any useful information from the sensor. Finally, many of the proposed solutions are not reusable, either losing adhesion or function after a single sample of sweat.

 

Caltech Creates a More Sensitive Sweat Sensor

In their new paper published in Nature, the researchers from Caltech proposed a new sweat-monitoring system that addresses the aforementioned issues.

 

Schematic of the layer assembly of the microfluidic sweat-sensing patch for sampling and biosensing. Image (modified) used courtesy of Nature and Wang et al

 

The team created an extra-sensitive sweat monitoring system using a technique called molecularly imprinted polymers. These molecularly imprinted polymers act as receptacles to receive specific analytes. Inside of these polymers is a material that is either oxidized or reduced under an electric voltage when exposed to human sweat. By tailor-fitting their sensor to be tuned for specific analytes, the system requires less sweat to sense the analytes than previous solutions. This technique also allows the system to be reusable.

Since the system required less sweat, the team also developed a microfluidic system that allows it to capture and analyze small samples. In this design, the patient is made to sweat through small, indetectable currents to the skin. The generated sweat is then collected through the microfluidic channels and fed to the analysis point, where the metabolites and nutrients can be assessed.

So far, the system has been successful in in-lab human patients, but the team states there is much more testing required before this technology can come to market.