If you’ve ever had blood drawn, whether to check cholesterol, kidney function, hormone levels, blood sugar or as part of a general checkup, you may have – ask questions at Why isn’t there an easier and less painful way. The answer is New wearable sensor detects even more compounds in human sweat.
Now, maybe. A team of researchers from Caltech’s Cherng Department of Medical Engineering has revealed a new wearable sensor that can detect even minute-by-minute levels of many common nutrients and biological compounds in human sweat. can be used as an indicator of human health.
The sensor technology was developed in the lab of Wei Gao, assistant professor of medical engineering, researcher at the Heritage Medical Research Institute, and Ronald and JoAnne Willens Fellow. For many years, Gao’s research has focused on wearable sensors with medical applications, and this latest work represents the most sensitive and accurate iteration to date.
“We’ve done wearable sweat sensors before,” he says. “There are a lot of biomarkers that we wanted to detect, but we couldn’t before. There was no good way.”
Gao says previous versions of its sweat sensor relied on built-in enzymes to detect a limited number of related compounds. While antibodies can be used in sensors to detect more compounds at low concentrations, this technique has one major weakness: the antibodies in the sensor can only be used once, means the sensor will use.
The new sensor technology includes what Gao calls molecularly imprinted polymers, like reusable artificial antibodies. To visualize how they work, imagine a hypothetical object shaped like a plus sign. If you take this and pour silicone rubber over it, let the rubber harden, and then separate the molecules from the rubber, you will now have a piece of rubber with a plus-shaped indentation. Only objects of the same size and shape fit in the void.
Molecularly imprinted polymers work in a similar way, but on a much smaller scale. If you want to make a sensor that can detect, for example, the amino acid glutamine, you prepare polymers with glutamine molecules inside. Then, by a chemical process, remove the glutamine and you get a polymer with holes in the exact shape of glutamine.
Gao’s innovation is to combine this specially formed polymer with a material that can oxidize or reduce under applied voltage when exposed to human sweat. As long as these glutamine-like holes are open, the sweat comes into contact with the inner layer of the sensor and an electrical signal is generated. But when the glutamine molecules come into contact with the polymer, they get through the holes made for them.
When these holes are plugged with glutamine molecules, less sweat can reach the inner layer and the electrical signal is weaker. By monitoring this electrical signal, the researchers were then able to deduce the amount of glutamine present in sweat. More glutamine means a weaker signal. Less glutamine for a stronger signal.
“This unique strategy allowed us to detect all nine essential amino acids and several vitamins,” explains Gao. “We can do all of them continuously.”
And unlike antibodies, polymers can easily be “cleaned up” for reuse through the application of a weak electrical signal to destroy the target molecule or empty the hole in which it resides.
The second innovation in Gao’s research is the use of microfluidics, a technology that uses microscopic channels less than a quarter of a millimeter wide to manipulate small amounts of liquid. Microfluidics allows the sensor to work even with a small amount of sweat.
Human skin can be artificially stimulated to sweat drug molecules delivered by an electric current, but previous sensors required more sweat and therefore more current, which could make it difficult to bear for the user, Gao said. Thanks to microfluids and the use of a different drug, the sensor now requires less sweat, and the current required to produce sweat can be very low.
“This microfluidic design allows us to use very small currents,” he said. “We can stimulate sweat for four to five hours from a few minutes of stimulation with tens of micrometers.”
So far, sensor technology has been shown to work on human subjects in the laboratory. Gao hopes to test it in larger-scale human trials.
“This approach allowed us to detect a wide range of new important nutrients and metabolites. “We can track when we eat and keep track of how nutritional levels change,” he said. “It not only tracks nutrients, but also hormones and medications. It can provide ongoing monitoring for many health problems.
