Label-free cellular imaging by broadband coherent anti-Stokes Raman scattering microscopy
Sapun Parekh, Young J. Lee, Khaled A. Aamer, Marcus T. Cicerone
Raman micro-spectroscopy can provide chemical contrast needed to characterize the complex intracellular environment and macromolecular organization within cells without exogenous labels. It has shown remarkable ability to detect chemical changes underlying cell differentiation and pathology-related chemical changes in tissues but has not been widely adopted for imaging largely due to low signal levels. Broadband coherent anti-Stokes Raman scattering (B-CARS) offers the same inherent chemical contrast as spontaneous Raman, but with increased acquisition rates and reduced phototoxicity. To date, however, only spectrally resolved signals from the strong CH-related vibrations have been used for CARS imaging. Here, we obtain Raman spectral images of single cells with a spectral range of 600 cm-1 to 3200 cm-1, including signatures from weakly scattering modes as well as CH vibrations. We also show that B-CARS imaging can be used to measure spectral signatures of individual cells at least 10 to100-fold faster than spontaneous Raman micro-spectroscopy and can be used to generate maps of biochemical species in cells. This improved spectral range and signal intensity opens the door for more widespread use of vibrational spectroscopic imaging in biology and clinical diagnostics.