Field:
Chemistry/Biochemistry
Session Topic:
Revealing local molecular orders by nonlinear microscopy
Speaker:
Sophie Brasselet/LPQM,ENS Cachan
The structural symmetry of a molecular assembly is a determining factor for quadratic
nonlinear optical responses involved in two-photon microscopy imaging. Nonlinear
signals emitted by an ensemble of active molecules are intrinsically dependent on their
organization. In particular second harmonic generation (SHG), which is sensitive to noncentrosymmetry in a medium or at an interface, has been extensively used as a
structural probe in molecular interfaces such as in mono-layers. More recently this
process has been reduced to the sub-micrometric scale in a nonlinear imaging
configuration applied to cell membranes and intracellular auto-assembled structures.1,2
Further information can be gained from a deeper insight into the polarization
dependence of nonlinear signals. We present the monitoring of molecular orientational
orders down to the nanometric scale using a nonlinear microscopy imaging scheme
combined to a polarimetry detection.3 Second harmonic generation and two-photon
fluorescence are simultaneously used as complementary processes relative to their
dependence on the medium symmetry. In addition the sub-wavelength resolution scale,
this technique allows unique features to be identified such as structural disorder. Such
properties will be illustrated in molecular nanocrystals4,5 and molecular monolayers,6
and is now extended to the investigation of model bio-molecular assemblies such as
stretched DNA fibers and fixed chromosomes.7 The local polarization analysis of such
optical processes is shown to contain information that would be unreachable by averaged
measurements performed on large ensembles.
1. L. Moreaux, O. Sandre; J. Mertz, J. Opt. Soc. Am. B 17, 1685-1694 (2000).
2. W.R. Zipfel, R.W. Williams, R. Christie, A.Y. Nikitin, B.T. Hyman, W.W. Webb, PNAS,
100(12), 7075-7080 (2003)
3. V. Le Floc’h, S. Brasselet, J.F. Roch, J. Zyss, J. Phys. Chem. B, 107, 12403-12410
(2003)
4. S. Brasselet, V. Le Floc’h, F. Treussart, J.F. Roch, J. Zyss, E. Botzung-Appert,
A. Ibanez, Phys. Rev. Lett., 92(20), 207401 (2004)
5. K. Komorowska, S. Brasselet, J. Zyss, L. Pourlsen, M. Jazdzyk, H.J. Egelhaaf,
J. Gierschner, M. Hanack, Chem. Phys. 318 (1-2), 12-20 (2005)
6. C. Anceau, S. Brasselet, J. Zyss, Chem. Phys. Lett. 411(1-3), 98-102 (2005)
7. Collaboration Danièle Chassoux, Muséum National d’Histoire Naturelle, Paris, France
and J.F. Mouscadet, Laboratoire de Biologie et de Pharmacologie appliquées, ENS
Cachan, Cachan, France.