CARS microscopy lights up lipids in living cells (original) (raw)

2004

Abstract

these techniques, imaging with chemical selectivity in unstained samples. CARS microscopy is a nonlinear imaging technique that produces images of chemical species based on their vibra-tional signatures. The past five years have seen advances in both the understanding of the method's contrast mechanism and the available instrumentation. 1 Conventional laser scanning microscopes can rou-B iologists desire imaging techniques that provide contrast with high sensitivity and selectivity but without altering the sample. Fluorescence mi-croscopy has high sensitivity, but dyes can alter the sample. Phase-contrast and differential-interference-contrast microscopes avoid this problem at the cost of chemical specificity. Coherent anti-Stokes Raman scattering (CARS) microscopy fits CARS Microscopy Lights Up Lipids in Living Cells tinely carry out these imaging experiments with benign excitation powers of 1 to 2 mW and image acquisition rates up to that of video. The technique is shedding light on many emerging and exciting biological applications. Among the chemical species that it has revealed in living cells, 2 lipids provide the best contrast, offering great potential to augment biomedical research in lipid-related diseases such as obesity and atherosclerosis. CARS microscopy relies on the Raman effect. In the spontaneous Raman process, molecules scatter photons, modifying the photon energy with energy quanta that corresponds to the molecules' vibrational modes. Hence, spontaneous Raman LIVE-CELL IMAGING Figure. 1. In Raman scattering processes, incoming light changes frequency according to a vibrational frequency (Ω) of the molecules. Red-and blue-shifted components are termed Stokes and anti-Stokes lines, respectively. In spontaneous Raman (A), thermally driven and random-phased molecular vibrations cause inefficient scattering in all directions. In coherent anti-Stokes Raman scattering (B), two excitation beams at frequencies ω p and ω s form a beating field with frequency ω p Ϫ ω s. When ω p Ϫ ω s matches Ω, the molecular vibrations occur in-phase and efficiently, resulting in a strong directional signal.

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