Mapping Solvation Heterogeneity in Live Cells by Hyperspectral Stimulated Raman Scattering Microscopy

Water provides a dynamic matrix in which all biochemical processes occur in living organisms. The structure and dynamics of intracellular water constitute the cornerstone for understanding all aspects of cellular function. Fundamentally, direct visualization of subcellular solvation heterogeneity is essential but remains challenging with commonly used NMR methods due to poor spatial resolution. To explore this question, we demonstrate a vibrational-shift imaging approach by combining the spectral-focusing hyperspectral stimulated Raman scattering (hsSRS) technique with an environmentally-sensitive nitrile probe. The sensing ability of a near-infrared nitrile-containing molecule is validated in the solution phase, microscopic droplets and cellular environments. Finally, we quantitatively measure the subcellular solvation variance in the degree of free water content between the cytoplasm (29.7%, S.E. 1.1%) and the nucleus (56.4%, S.E. 1.3%), which is in good agreement with previous studies. This work sheds light on mapping the heterogenous solvation in live systems using coherent Raman microscopy and opens up new avenues to explore environmental variance in complex systems with high spatiotemporal resolution.