Visualizing intra-medulla lipids in human hair using ultra-multiplex CARS, SHG, and THG microscopy.

We performed label-free imaging of human-hair medulla using multi-modal nonlinear optical microscopy. Intra-medulla lipids (IMLs) were clearly visualized by ultra-multiplex coherent anti-Stokes Raman scattering (CARS) spectroscopic imaging. Two groups of IMLs were found: second harmonic generation (SHG) active and inactive. By combining SHG analysis with CARS, the two groups were identified as free fatty acids and wax esters, respectively.