Optical Spectroscopy for Noninvasive Monitoring of Stem Cell Differentiation

Figure 6

CARS microscopy image of fixed MCF-7 breast cancer cells, of size 100 × 100 𝜇m. The green channel is specific to the O−P−O stretch frequency (1095 cm⁻¹) and originates from the DNA backbone, so highlights the nucleus (whose shape may have been distorted in some cells, by the fixation process). The red channel is specific to the CH₂ deformation (1448 cm⁻¹) and is dominated by lipids and the cytoskeleton. The image plane is restricted to a 1 𝜇m slice, acquired several micrometres above the glass substrate, and the lateral resolution is around 350 nm. Images of both channels were acquired in 1 second, and averaged 5 times; both channels were acquired sequentially after retuning one laser source. Pulse widths of 6 ps correspond to a spectral resolution of ∼3 cm⁻¹.