Label-free detection of mitochondrial distribution in cells by nonresonant Raman microspectroscopy

High spatial resolution Raman maps of fixed cells in an aqueous environment are reported. These maps were obtained by collecting individual Raman spectra via a Raman microspectrometer in a raster pattern on a 0.5-microm grid and assembling pseudocolor maps from the spectral hypercubes by multivariate methods. The Raman maps show the nucleus and the nucleoli of cells as well as subcellular organization in the cytoplasm. In particular, the distribution of mitochondria in the perinuclear region could be demonstrated by correlating distinct areas of the Raman maps with corresponding areas of fluorescence maps of the same cells after staining with mitochondria-specific labels. To the best of our knowledge, this is the first report of label-free detection of mitochondria inside a somatic mammalian cell using Raman microspectroscopy.