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Visualization of Membrane Rafts Using a Perylene Monoimide Derivative and Fluorescence Lifetime Imaging

Anca Margineanu ^*, Jun-ichi Hotta ^*, Mark Van der Auweraer ^*, Marcel Ameloot , Alina Stefan ^*, David Beljonne , Yves Engelborghs , Andreas Herrmann ^¶, Klaus Müllen ^¶, Frans C. De Schryver ^* and Johan Hofkens ^*

^* Laboratory of Photochemistry and Spectroscopy, Katholieke Universiteit Leuven, Leuven, Belgium; Biomedical Research Institute, Hasselt University and Transnational University Limburg, Diepenbeek, Belgium; Laboratory for Chemistry of Novel Materials, University Mons-Hainaut, Mons, Belgium; Laboratory of Biomolecular Dynamics, Katholieke Universiteit Leuven, Leuven, Belgium; and ^¶ Max Planck Institut für Polymerforschung, Mainz, Germany

Correspondence: Address reprint requests to J. Hofkens, Tel.: 32-16-327804; E-mail: johan.hofkens{at}chem.kuleuven.be.

A new membrane probe, based on the perylene imide chromophore, with excellent photophysical properties (high absorption coefficient, quantum yield (QY) 1, high photostability) and excited in the visible domain is proposed for the study of membrane rafts. Visualization of separation between the liquid-ordered (Lo) and the liquid-disordered (Ld) phases can be achieved in artificial membranes by fluorescence lifetime imaging due to the different decay times of the membrane probe in the two phases. Rafts on micrometer-scale in cell membranes due to cellular activation can also be observed by this method. The decay time of the dye in the Lo phase is higher than in organic solvents where its QY is 1. This allows proposing a (possible general) mechanism for the decay time increase in the Lo phase, based on the local field effects of the surrounding molecules. For other fluorophores with QY < 1, the suggested mechanism could also contribute, in addition to effects reducing the nonradiative decay pathways, to an increase of the fluorescence decay time in the Lo phase.