Terahertz spectra of electrolyte solutions under applied electric and magnetic fields

Most biomolecules require an aqueous environment to fully exert their biological activity. However, the rotation mode, vibration mode, and energy associated with the hydrogen bonding network of water are in the terahertz band, resulting in strong absorption. Therefore, it is difficult to detect liquid biological samples using the terahertz technology. Here, a high-transmittance double-layer microfluidic chip was prepared using a cycloolefin copolymer material with high transmittance of terahertz waves. Combined with terahertz time-domain spectroscopy, the terahertz spectral characteristics of deionized water, NaCl, NaCO3, and CH3COONa solutions were studied. The changes in the terahertz transmission intensity of these electrolyte solutions under constant electric and magnetic fields were measured. The results show that the terahertz spectra of different sodium salt solutions with the same concentration of 0.9 mol/l are different. Furthermore, the terahertz absorption coefficients of the different electrolyte solutions gradually decrease with the increase of their residence time under the electric field, which is contrary to the results obtained under the external magnetic field. This study provides a new idea for the detection of sodium salt solution and lays a foundation for the development of THz technology.