THz Spectroscopy of Bound Water in Glucose: Direct Measurements from Crystalline to Dissolved State

The main reason for the alternation of terahertz (THz) response in biological samples is the transition of a part of water from its free to bound state and back. To analyze such results, a precise spectrum of bound water within THz range should be known. The suggested wet powder spectroscopy method is optimal for this task. We measured the THz transmission of dry glucose pressed into pellets. Then, we added a small amount of water to these pellets and again measured the THz spectra. The contribution from the free water state starts to appear in resulting THz spectra after water concentration in glucose samples reaches 14–16%. Just below is the optimal point to extract the spectral contribution from bound water. We extracted the absorption and refraction spectra of bound water and confirmed that they are an order of magnitude weaker than those of free water within 0.07–1-THz range.