In vivo live cell imaging for the quantitative monitoring of lipids by using Raman microspectroscopy.

A straightforward in vivo monitoring technique for biomolecules would be an advantageous approach for understanding their spatiotemporal dynamics in living cells. However, the lack of adequate probes has hampered the quantitative determination of the chemical composition and metabolomics of cellular lipids at single-cell resolution. Here, we describe a method for the rapid, direct, and quantitative determination of lipid molecules from living cells using single-cell Raman imaging. In vivo localization of lipids in the form of triacylglycerol (TAG) within oleaginous microalga and their molecular compositions are monitored with high spatial resolution in a nondestructive and label-free manner. This method can provide quantitative and real-time information on compositions, chain lengths, and degree of unsaturation of fatty acids in living cells for improving the cultivating parameters or for determining the harvest timing during large-scale cultivations for microalgal lipid accumulation toward biodiesel production. Therefore, this technique is a potential tool for in vivo lipidomics for understanding the dynamics of lipid metabolisms in various organisms.