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Science  25 Jan 2008:
Vol. 319, Issue 5862, pp. 387b
DOI: 10.1126/science.319.5862.387b

Selective detection of airborne biohazards in a background environment filled with all manner of pollen, dust, and debris remains a serious challenge. Pestov et al. have pursued a promising approach based on coherent anti-Stokes Raman scattering (CARS) spectroscopy. In general, Raman-based techniques should offer high specificity based on molecular vibrational signatures, but they have been plagued by high background noise due to nonresonant scattering of the light by the molecules in the beam path. The authors' group previously addressed this shortcoming using a precisely timed series of broadband pump and Stokes excitation pulses followed by a delayed narrowband probe, a modification of the more conventional CARS protocol in which pump and probe pulses are closer in time and duration (see Pestov et al., Reports, 13 April 2007, p. 265). They now show that by shifting wavelengths from the visible to the lower-energy near-infrared regime, they can increase the signal strength by raising photon intensity while avoiding damage to the sample that would preclude identification. Further optimization of the pulse bandwidths and relative timings allowed detection of as few as 10,000 bacterial spores with a single laser shot. — JSY

Proc. Natl. Acad. Sci. U.S.A. 105, 422 (2008).

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