A new sensor material has been developed that can be attached to the skin to precisely detect not only body temperature changes but also extremely subtle physical movements such as swallowing or coughing.
The Ulsan National Institute of Science and Technology (UNIST) announced Tuesday that a research team led by professors Kim Su-hyun and Kwon Soon-yong of the Graduate School of Semiconductor Materials and Devices Engineering has successfully developed an ultra-high-sensitivity "titanium carbonitride-based MXene" that simultaneously recognizes temperature and pressure stimuli.
MXene, a two-dimensional nanomaterial, has an accordion-like structure in which carbon or nitrogen is layered between metal atomic layers. Thin and flexible with excellent electrical conductivity, it has been spotlighted as a core material for next-generation wearable healthcare devices and smart clothing.
The new MXene (Ti₃CNTz) unveiled by the research team offers temperature and pressure sensitivities more than three and four times higher, respectively, compared to the existing nitrogen-free material (Ti₃C₂Tx). Electrical resistance values react significantly even to minute external stimuli, allowing machines to read the body's subtle biosignals more clearly.
The researchers achieved this performance improvement by optimizing the nitrogen concentration within the material. Nitrogen atoms increase the electron density at specific sites and amplify lattice vibrations, maximizing responsiveness to external stimuli. The team also confirmed that MXene's distinctive layered structure enhances physical durability. The team scientifically elucidated the operating principle through density functional theory (DFT) calculations and synchrotron X-ray absorption fine structure (XAFS) analysis.
When applied to a sensor attached to the neck, the material accurately distinguished subtle differences in vocal cord vibrations such as swallowing, vocalization, and coughing. Attached near the eyes, it tracked blinking, and on the wrist, it read pulse waves in real time. When attached to shoe soles, it even analyzed the user's walking habits.
The sensor also features non-contact detection capable of measuring body temperature without physical contact. It can recognize body temperature simply by placing a finger 1 to 2 millimeters away from the sensor and can even detect the faint infrared heat emitted from a smartphone flash.
"Precisely measuring pressure and temperature simultaneously while effectively suppressing the interference between the two signals will serve as an important milestone for the advancement of electronic skin for intelligent robots and human-machine interface (HMI) technology," Professor Kim said. He added, "We have expanded the scope of MXene research, which has been centered on carbides, to nitrogen-containing carbonitrides, securing diversity in nanomaterials," and predicted, "Its utility will be high across advanced industries, including energy storage devices, catalysts, and electromagnetic wave shielding materials, beyond wearable healthcare devices."
The research was supported by the Ministry of Science and ICT, the National Research Foundation of Korea (NRF), and the InnoCORE program. The findings were published in the online edition of the international journal Advanced Functional Materials on April 12.
