Water as a biomarker: unveiling dynamic properties through dielectric and NMR spectroscopy

Water is an active participant of biochemical and physiological processes in living systems. This review explores the emerging recognition of water as structural biomarker, which gives knowledge about its biological environment studying water mobility by means of dielectric and nuclear magnetic resonance (NMR) techniques. Recent advances in the broadband dielectric spectroscopy (BDS) and NMR technique have deepened our understanding of water's behavior under confinement, hydration, and interactions with biomacromolecules and biological interfaces. These methods reveal pronounced deviations of water dynamic structure in biosystems from its bulk state, indicating manyfold specific interaction of water with its local environment. Microwave dielectric spectroscopy, particularly through analysis of γ-dispersion, captures disruptions in water hydrogen-bond network caused by interactions with ions, macromolecules, and cellular structures. Complementary NMR diffusion and relaxation studies enable precise characterization of water mobility and confinement effects. Evidence from biological tissues, cells, and model systems, including red blood cells, protein and polysaccharide hydrogels demonstrates how water's dielectric and NMR signatures can serve as indicators of biological systems stability and functionality. This review revisits a hypothesis proposed nearly 50 years ago, that water dynamical structure in biological systems is intimately connected with chemical composition and architecture of supramolecular and cellular structures in norm and pathology. Ultimately, dielectric and NMR assessments of water represent a powerful, yet underutilized, approach to non-invasive diagnostics and real-time biomonitoring. Recognizing water as a responsive probe of biological status opens new frontiers in the understanding of fundamental phenomena in living systems and their rational use in modern health and technological applications.