Second harmonic generation as a noninvasive method to study molecular processes on the surface of lipid membranes (brief review)

The development and implementation of modern experimental methods in interdisciplinary projects promote the solution of fundamental problems in molecular biology and medicine. One of these problems is the understanding of the physics of molecular interactions in a narrow (<1 nm) surface layer of cellular lipid membranes (hydration layer of the membrane), where most of the important electrochemical interactions with ions and proteins, transmembrane transport of molecules, and endocytosis occur. The solution of this problem requires noninvasive methods sensitive to changes in the molecular structure of the surface layer of membranes. The aims of this work are to describe advantages of nonlinear optical microscopy and spectroscopy for the study of structural and electrostatic features of lipid membranes, to present the developed method for the visualization of the hydration of lipid membranes, and to discuss the limits of applicability of this method.