Broadband coherent anti-Stokes Raman scattering (B-CARS) has typically been considered unusable for bioimaging. But researchers at National Institute of Standards and Technology (NIST) have shown that with improvements in both hardware and signal processing, the label-free spectroscopic technique can quickly produce detailed molecular maps of the contents of cells without damaging them.1
Raman spectroscopy measures frequencies associated with the vibration of atoms and their bonds, and thus can detect how stem cells differentiate into new forms, and distinguish between subtly different cell and tissue types-for instance, precancerous and cancerous cells. But the usual method, spontaneous Raman scattering, is far too time-consuming for practical use. CARS advanced the Raman technique by using lasers to pump up vibrational states and increase the signal, and now NIST's discovery adds power.
While many argue that the lasers used in CARS must run at power levels above the damage threshold for living cells to get the necessary data, the NIST team describes a combination of improved hardware to gather spectra over a very broad range of wavelengths, and a mathematical technique that effectively amplifies the useable signal by examining a portion normally ignored as background interference. The result pushes minimum power levels below the damage threshold while retaining the speed of CARS. "We have all the information that you have in a Raman spectrum, but we get it 5 to 100 times faster," says NIST chemist Marcus Cicerone, adding that some obvious modifications should enable still further improvements.
1. S.H. Parekh et al., Biophys. J. 99 (2010)