Experimental Evaluation of the Density of Water in a Cell by Raman Microscopy

We report direct observation of a spatial distribution of water molecules inside of a living cell using Raman images of the O–H stretching band of water. The O–H Raman intensity of the nucleus was higher than that of the cytoplasm, indicating that the water density is higher in the nucleus than that in the cytoplasm. The shape of the O–H stretching band of the nucleus differed from that of the cytoplasm but was similar to that of the balanced salt solution surrounding cells, indicating less crowded environments in the nucleus. The concentration of biomolecules having C–H bonds was also estimated to be lower in the nucleus than that in the cytoplasm. These results indicate that the nucleus is less crowded with biomolecules than the cytoplasm.