A newly developed smart ring can measure up to four different chemical biomarkers at the same time using sweat gathered from the finger - and it can do so without needing exercise-driven perspiration.
According to the engineers behind it, this is the first fully integrated smart ring designed for continuous, day-to-day biochemical monitoring, with the ability to track glucose, ketones, vitamin C, uric acid, lactate and alcohol.
The work was carried out by engineers at the University of California, San Diego, in the laboratory led by Joseph Wang.
They have named the device CHARM - short for Continuous Health Analyzing Ring Module. The ring weighs 5.1 grams (0.18 ounces) and measures roughly 3 centimetres (1.2 inches) in outer diameter.
More than a fitness tracker
“Commercial rings only provide biophysical information, but they lack molecular information about biochemical markers that offer deeper insights about an individual’s health status,” said lead author Tamoghna Saha, a postdoctoral researcher in Wang’s lab.
Most smart rings currently available focus on signals such as heart rate, temperature and movement. By contrast, this ring adds a molecular layer by collecting biochemical markers that indicate what is happening inside the body.
To achieve this, the engineers built the device as two joined halves. One half houses the sweat-extraction mechanism, the sensor array and the microfluidic channels.
The second half contains the flexible battery and the electronics, and the two sides are joined via a connector pad.
Monitoring without breaking a sweat with the CHARM smart ring
Many sweat-sensing wearables rely on exercise or exertion to produce enough fluid for analysis. This ring is designed to avoid that requirement entirely.
Instead, it draws sweat passively through the skin using osmosis - an approach that Saha developed specifically for this application.
Because the collection is passive, the device can gather biochemical information throughout the day whether the wearer is moving around or resting.
In tests, the osmotic extraction method produced sweat at a relatively consistent rate across different fingers and different individuals.
The approach delivered around five to six times more fluid than the skin would otherwise provide at that location, without causing visible sweating or discomfort.
“A ring capturing dynamic molecular information in real time would be extremely useful for making informed decisions regarding health, diet, and lifestyle,” Wang said.
Tested against medical devices
To evaluate how well the ring performs, the team ran studies involving healthy volunteers as well as participants living with type 1 diabetes.
Glucose values from the ring closely followed readings from commercial continuous glucose monitors.
Ketone measurements also aligned with results from commercial blood ketone meters - an important comparison given how established those tools are for clinical and personal monitoring.
In one set of experiments, a participant with type 1 diabetes wore the ring while eating meals, taking a ketone supplement, drinking alcohol, exercising and eating sweets to address a drop in blood sugar.
During that session, the ring registered glucose rises after meals, higher ketones following the ketone drink, increased lactate after moderate exercise, and an increase followed by a gradual decrease in blood alcohol after a glass of wine.
These patterns corresponded reasonably well with standard blood test results collected alongside the ring’s data.
Among healthy volunteers, the system also detected smaller post-meal glucose shifts and changes in ketones after a supplement drink.
It further identified uric acid changes after participants ate sardines - a purine-rich food known to raise uric acid levels.
Packed with tiny technology
The researchers produced the biomarker smart ring as a fully integrated prototype, combining biomarker sensing, low-power electronics and a flexible battery within the ring itself.
Biomarker readings are sent wirelessly to a companion smartphone app.
For sweat capture, the ring uses an osmotic hydrogel: a soft polymer that creates a pressure gradient capable of drawing fluid through the skin without pain.
The process is analogous to the way water moves from soil into a plant’s roots and up to its leaves.
After the sweat is collected, it is evaluated by an electrochemical sensor array built into the ring.
Using repeated sampling over time, the system derives subject-specific calibration factors that translate raw electrical current signals into concentration values.
This enables more tailored insight into how an individual’s biomarker levels change over time.
The team notes that these personalised calibration settings remained reliable for about two months before needing an update. As a result, wearers would not have to perform a daily finger-prick comparison blood reading to keep the ring calibrated.
Packing everything into a ring
Energy is supplied by a flexible, rechargeable zinc–silver oxide battery that can provide up to 12 hours of continuous use between charges.
The circuit board is smaller than a US quarter coin, a notably compact size given the number of functions it supports.
A 3D-printed polymer shell forms the ring’s outer casing and final structure.
In durability tests, the battery continued to hold a steady charge after being bent and folded repeatedly, including being flexed into tight loops thousands of times.
“Such integration onto the small footprint of a ring form factor is amazing,” Wang said.
The technology still needs work
The researchers emphasise that the current prototype is not yet ready for everyday consumer use.
For example, the ring is not fully waterproof at present, although the team expects that a more completely sealed design could address this in later iterations.
They also point out that the device has not yet been assessed in a large and diverse population of people with diabetes.
In addition, the team has not yet tested performance across the full range of blood glucose extremes - including severe hypoglycaemia - that a commercial system would need to measure dependably.
Using the ring over multiple days (rather than a single day of wear) will likely depend on improvements to the hydrogel and on components that are simpler to replace.
Before it can be practical for long-term daily use in diabetes management, developers will need to incorporate replaceable sensor cartridges or rechargeable battery modules.
Image Credit: David Baillot/UC San Diego Jacobs School of Engineering
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