Physical processes of the action of laser radiation on biological systems

Introduction. Low-intensity laser radiation is widely used in therapy. In the infrared region, the photon energy is only sufficient to increase the vibrational energy of biological molecules, resulting in an increase in temperature. Visible light induces physico-chemical processes, which are divided into primary (light) and secondary (dark). The primary processes are excitation of the electronic state of molecules, ionisation (photoelectric effect) and decomposition into ions or radicals. The Grotkus-Dreiner rule, the Bunsen-Rosko rule, the Stark-Einstein law and the phenomenon of intermolecular energy migration are valid for these processes. In addition, it is the optical range of radiation whose quantum energy is sufficient for the transition of oxygen molecules from the triplet state to the excited singlet state. The occurrence of singlet oxygen promotes the formation of reactive oxygen species, which induces free-radical processes. Purpose: To carry out a comparative analysis of the contribution of various physical processes in the formation of the action of laser radiation of the optical range in the methods of therapy. To analyse the role of changes in water properties when exposed to laser radiation in the development of biological effects. Materials and methods. Water is known to be present in large quantities in biological tissues. There is a developed system of hydrogen bonds of water, which arise spontaneously under certain conditions. Under the action of electromagnetic fields this system of bonds changes, which leads to changes in the structure and properties of water itself. The effect of low-intensity laser radiation on the properties of water and substances dissolved in it has been investigated by spectral methods. Results. 1. analysis of changes in water absorption spectra shows that laser irradiation affects the hydrogen bonding system of water; 2. changes in the properties of water under low-intensity laser radiation enhances the effects of tryptophan fluorescence quenching; 3. changes in the spectral properties of whey albumin aromatic amino acid residues when dissolved in pre-irradiated water can be estimated as being related to a change in the macromolecule and to the transition from the native state to the molten globule state; 4. pre-irradiation of water affects the interaction of human serum albumin with a fluorescent probe. Conclusion. The interaction of laser radiation with biosystems is complex, multidimensional, and multifaceted, which can manifest itself because of changes in the structure and properties of water. (author)