Water is the Main Target of Terahertz Biophotonics: A Review

The terahertz range has long been difficult to access for spectral studies. About 20 years ago, technologies for high-sensitivity spectroscopy in the THz range appeared. The most advanced method is the THz time-domain spectroscopy (THz-TDS). The application of THz spectroscopy in biology has proved to be extremely productive. This is due to the fact that water is an integral component of any biological object, and the THz range has the greatest sensitivity to the intermolecular structure and dynamics of water. It turned out to be possible to study the molecular objects contacting water by analyzing this water. All research in this field can be divided into two areas. The first, to which main attention has been paid, is devoted to the development of THz methods for medical diagnostics. Much has been done in this area, but so far these technologies have not been introduced into widespread medical practice. The second (fundamental) direction is the study of hydrate shells of biomolecules. Fundamentally new data have been obtained in this field, which showed a much greater extent and greater importance of hydrate shells for biological processes than was previously suggested. Both areas logically fit into a new scientific field: THz biophotonics. This review summarizes the main achievements in this line of research. Attention is drawn to the fact that the main target of THz biophotonics is water. It is the spectral manifestations of water in various biological objects that are the main material for analysis in both applied and fundamental research.