Terahertz Transmission Characteristics of Water Induced by Electric Field

Many biomolecules' rotation, vibration or the whole vibration mode of the molecular group are located in the terahertz band, so we can use terahertz spectrum technology to detect biomolecules. At the same time, because the photon energy of the terahertz wave is only millivolts, it will not damage the internal structure of molecules, so terahertz time-domain spectroscopy technology has a good application prospect in biological detection. As we all know, most biomolecules can only play their biological activities in the liquid environment, so it is necessary to study the interaction between biomolecules in the liquid environment. However, the rotation mode, vibration mode and the energy related to hydrogen bond of water molecules are all in the terahertz band, so they have strong absorption; in addition, water molecules are polar molecules, and polar molecules have strong resonance absorption for terahertz wave, which makes it difficult to use terahertz technology to characterize the activity of biomolecules dynamically. Therefore, in the study of the interaction between biomolecules and terahertz wave in solution, it has become a research hotspot in recent years to minimize water molecules' absorption to terahertz wave. At present, the main methods to reduce the absorption of THz wave by water are : adding ions that inhibit hydrogen bond association in solution samples to reduce the absorption of THz wave by water; adjusting the absorption of THz wave by water by changing the temperature of the solution; reducing the absorption of THz wave by water by reducing the distance between the sample and THz wave by using microfluidic chip technology. In addition, the excitation of laser, the treatment of electric field or magnetic field can also change the absorption of THz wave by water. In this paper, a microfluidic chip containing deionized water is put into the electric field to study the influence of deionized water treated by electric field for different time on THz wave' s absorption intensity. The results show that THz wave's transmission intensity increases with the increase of the standing time of deionized water in the electric field. When standing in the electric field for 60 minutes, the spectrum intensity of the THz wave reaches the maximum, close to that of air. It can be concluded that the applied electric field changes the dipole moment of water molecules, which affects the vibration and rotation of water molecules as a whole, and changes the hydrogen bond structure in water, resulting in the enhancement of the THz transmission spectrum.