Non-destructive and accurate quantification of water content enabled by terahertz thermal absorption analysis

Water is an essential component of all life, and its accurate quantification is critical for both fundamental research and interdisciplinary applications. The hydrogen-bonding network of water interacts strongly with terahertz (THz) radiation, making THz waves a sensitive probe for evaluating water content. However, THz measurements of water concentration rely on effective medium theories that treat the sample as a binary mixture of water and non-aqueous components. This approach requires precise knowledge of the dielectric properties of the non-aqueous phase, often necessitating destructive sample preparation or oversimplified assumptions, which limit the accuracy and applicability. In this work, we present a non-destructive method for highly accurate water-content quantification. The method exploits the distinct temperature dependencies of THz absorption in water and non-aqueous substances. Theoretical analysis reveals a simple correlation between the THz absorption-temperature slope and the water volume fraction. By measuring samples at down to two temperatures within a narrow range of less than 10°C, water concentration can be determined with high precision in vitro . We validated the method across various materials, including liquid solutions, hydrated solids, and biological tissues from plants and animals. The extracted water contents show excellent agreement with theoretical or reference values, demonstrating broad applicability across samples with diverse compositions and hydration levels.