CAR-CACP projects

Scattering from biological particles

(Gledhill, Hesse, Hough, Kaye, Martin, Ulanowski)

A unique characteristic of life is its macroscopic homochirality. Chiral (handed) molecules are ubiquitous throughout all known life-forms, and amino acids - the basic building blocks of proteins, are all chiral (bar glycine). As chiral molecules interact differently with left and right-handed circularly polarized light, this offers the potential of a remote sensing diagnostic since a chiral signature can be revealed with circular polarization observations.

L-amino acid (left) and D-amino acid (right)

Establishing biomarkers that can be used for the remote detection of living organisms has importance in areas ranging from protection against bacteriological contamination to the search for life elsewhere in the Universe. The former has been given impetus with the increased awareness of biological agent threats and the latter, inter alia, by the realization that life can exist and thrive in extreme environments hitherto considered so hostile that they must be sterile. This proposal aims to establish biomarkers that can be widely used and are not overly specific to any organism.

In 2007, staff from CAR and CAIR (now CACP) commissioned a SRIF-funded Polarimetry Research Laboratory (PRL) dedicated to studying the scattering from biological organisms, with a Leverhulme award providing support for a two-year Fellowship. A parallel programme, led by Visiting Professor Bill Sparks, is being undertaken between STScI, COMB and NIST.

The capabilities of the PRL are centred on the Newport Spectra Physics Mai Tai HP laser and ancillary diagnostic equipment. In addition, a comprehensive suite of optics and active polarimetric devices and sensors allows the configuration of very high sensitivity linear and chiral polarimeters to analyse the transmitted and scattered light from a wide variety of specimens including liquids, solids, organic materials and biological samples. The tuneable femtosecond laser with its single pulse picker and second harmonic converter allows measurements at 690-1020nm and 345-510nm in both quasi-continuous wave and very high peak power modes. The former is used for linear spectropolarimetry while the latter allows multiphoton chiral polarimetry on biological materials without thermal destruction. The PRL has completed commissioning of the laser and diagnostics and is engaged in the first programme of measurements on inorganic and organic material relevant to biomarker research.

Papers to date include:

Martin et al. 2010, JWSRT, 111, 2444

Sparks et al. 2009, JQSRT, 110, 1771

Sparks et al. 2009, PNAS, 106, 7816