Detection of raffinose hydration state at different temperatures using terahertz metamaterials

D(+)-Raffinose pentahydrate (Rf·5H₂O, C₁₈H₃₂O₁₆·5H₂O), a three-dimensional network hydrate composed of five water molecules connected by hydrogen bonds, is widely used in the proliferation of bifidobacterium, inhibition of germ cell cancer, and regulation of intestinal flora. Its bioavailability and stability are closely related to its hydration status. Nevertheless, the storage temperature is crucial to accurately monitor its hydration status. The inherent limitations of traditional characterization methods, such as X-ray diffractometers, Raman spectroscopy, etc., pose major challenges for their further development in practical applications with high stability, accuracy, and non-invasions. Consequently, this study utilized terahertz absorption spectroscopy to monitor the vibration of hydrogen bonds in Rf·5H₂O at drying temperatures of 50℃ and 100℃, aiming to achieve hydration state monitoring of the hydrate. To further improve the detection sensitivity, we designed a metamaterial sensor with a sensitivity of 338.75 GHz/RIU to achieve a detection and identification of the hydration state of Rf·5H₂O with high sensitivity, providing a new perspective for monitoring the temperature-dependent hydration state of hydrates.