TIANJIN -- A Chinese research team has developed a novel system to enable non-invasive and dynamic monitoring of blood sodium levels, which addresses critical needs in managing dehydration, kidney diseases and neuroendocrine disorders.

Findings of the study, conducted by Tianjin University, were recently published in the international journal Optica.

Terahertz radiation — positioned between microwave and mid-infrared bands — offers unique advantages for biomedical sensing: low energy usage, minimal tissue damage and high sensitivity to molecular changes. However, its strong absorption by water and limited penetration capabilities of biological tissues have hindered practical applications.

The team's breakthrough terahertz optoacoustic systems overcome the two challenges by emitting terahertz waves at frequencies resonant with sodium ions but screening out water absorption signals, according to the paper.

This selectively excites sodium vibrations, generating ultrasound that are captured by transducers for analysis. The conversion to acoustic waves reduces scattering and attenuation, enabling deeper penetration through muscle and bone, as well as successful capture by ultrasound transducers.

Led by Tian Zhen, a professor at Tianjin University, the team achieved label-free, continuous sodium monitoring with validated accuracy in live mice and human volunteers. Their approach promises a painless alternative to needle-based tests, with potential for clinical adoption.

"The system holds promise beyond sodium monitoring," said Li Jiao, a researcher on the team. "By leveraging terahertz characteristic absorption spectra, it could potentially detect other ions like potassium and calcium, as well as biomolecules such as sugars, proteins and enzymes — significantly expanding its clinical utility."