Detection of circular polarization in light scattered from photosynthetic microbes

The identification of a universal biosignature that could be sensed remotely is critical to the prospects for success in the search for life elsewhere in the universe. A candidate universal biosignature is homochirality, which is likely to be a generic property of all biochemical life. Because of th...

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Published in:	Proceedings of the National Academy of Sciences - PNAS Vol. 106; no. 19; pp. 7816 - 7821
Main Authors:	Sparks, William B, Hough, James, Germer, Thomas A, Chen, Feng, DasSarma, Shiladitya, DasSarma, Priya, Robb, Frank T, Manset, Nadine, Kolokolova, Ludmilla, Reid, Neill, Macchetto, F. Duccio, Martin, William
Format:	Journal Article
Language:	English
Published:	United States National Academy of Sciences 12-05-2009 National Acad Sciences
Subjects:	Absorption spectra Bacteria - metabolism Biochemistry Biological Sciences Chlorophyll - chemistry Chlorophylls Circular polarization Cyanobacteria Dichroism Equipment Design Exobiology - instrumentation Exobiology - methods Extraterrestrial Environment Light Linear polarization Microorganisms Molecules Optical reflection Optics Optics and Photonics Photosynthesis Physical Sciences Plant Leaves - metabolism Refractometry Remote sensing Scattering, Radiation Signatures Spectral reflectance Spectrum analysis Synechococcus - metabolism Visible spectrum
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Summary:	The identification of a universal biosignature that could be sensed remotely is critical to the prospects for success in the search for life elsewhere in the universe. A candidate universal biosignature is homochirality, which is likely to be a generic property of all biochemical life. Because of the optical activity of chiral molecules, it has been hypothesized that this unique characteristic may provide a suitable remote sensing probe using circular polarization spectroscopy. Here, we report the detection of circular polarization in light scattered by photosynthetic microbes. We show that the circular polarization appears to arise from circular dichroism of the strong electronic transitions of photosynthetic absorption bands. We conclude that circular polarization spectroscopy could provide a powerful remote sensing technique for generic life searches.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 Author contributions: W.B.S., J.H., T.A.G., and N.M. designed research; W.B.S., J.H., T.A.G., F.C., S.D., P.D., F.T.R., N.M., L.K., N.R., F.D.M., and W.M. performed research; F.C., S.D., P.D., and F.T.R. contributed new reagents/analytic tools; W.B.S., T.A.G., and N.M. analyzed data; and W.B.S., J.H., T.A.G., F.C., S.D., P.D., F.T.R., N.M., L.K., N.R., F.D.M., and W.M. wrote the paper. Edited by Rita R. Colwell, University of Maryland, College Park, MD, and approved March 24, 2009
ISSN:	0027-8424 1091-6490
DOI:	10.1073/pnas.0810215106