Researchers at Tomsk Polytechnic University, together with their colleagues from China, have developed a new material for wearable medical sensors and a device based on it to detect glucose levels in sweat. The development quickly and accurately shows glucose content and can independently provide itself with energy. Test results showed that the system retains its functions even after 15,000 charge-discharge cycles and bends.

The results of the study have been published in the journal Chemical Engineering Journal (Q1, IF: 12,5).

In modern personalized medicine, wearable sensors are becoming increasingly demanded. They help to monitor health in real time without blood sampling or complicated procedures. Sweat analysis is one of the promising approaches to data collection. It contains elements that can be used to track physiological changes in the body, including glucose metabolism. However, such devices usually consist of two separate modules (the sensor itself and the power supply). This makes the device bulky and uncomfortable to wear, as well as complicates its use.

TPU researchers, together with their colleagues from China, have developed a sensor material based on highly sensitive carbon nanotubes and a conductive mesh of a two-dimensional nickel metal-organic framework. It is able to quickly and accurately monitor the glucose level in sweat and at the same time not "stray" to other substances in the composition of the biological fluid — urea, salt, lactate, uric acid and ascorbic acid.

"The sensor material has hybrid structure. Thin nickel nanosheets therein act as active sites where all electrochemical reactions take place, and carbon nanotubes work as "wires", accelerating these reactions and the interaction of the entire system with glucose molecules," — notes Raul Rodriguez, one of the authors of the study, Professor of the TPU Research School of Chemical and Biomedical Technologies.

The researchers studied the developed material using the methods of Raman spectroscopy and X-ray diffraction. The analysis results showed that the material has a high sensitivity — at the level of 1896.7 µA/(mM·cm2) — and noise immunity. The average response time of the material to glucose in sweat samples is five seconds.

Based on the developed material, the researchers have created a compact, flexible supercapacitor that can act as an energy storage device and power a monitoring system. According to the developers, compared with similar materials based on nickel, iron and cobalt, the proposed structure showed higher performance. The new accumulator has an energy capacity of 61.1 Wh/kg with a power density of 746.7 W/kg.

The researchers combined the proposed solutions into a single electrochemical sensor system. It consists of a glucose-sensitive patch with an energy storage device, a power control module, and wireless data transmission.

“The device retained about 80% of its initial capacity after 15,000 charge-discharge cycles and with multiple bends, which is especially important for flexible wearable devices,” — adds the professor.

The system was tested on a volunteer. The module was fixed on his skin. The man did physical exercises for 40 minutes. Data on the glucose level in sweat was monitored in real time and transmitted from the module to the smartphone via Bluetooth. In parallel, measurements were also carried out using a commercial kit to assess the reliability of the system. The results were in good agreement with the data obtained using the commercial sensor.

In the future, such sensors can be used in personalized medicine and sports diagnostics.

The research involved researchers from the TERS-Team research group of the TPU Research School of Chemical and Biomedical Technologies and the University of Electronic Science and Technology of China.