Understanding the fluorescence contrast in liquid-gel phases

Jia Ru Yu^1,2*, He Chun Chou¹, Wei Ssu Liao², Chi Chen¹

¹Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan
²Department of Chemistry, National Taiwan University, Taipei, Taiwan

* Presenter:Jia Ru Yu, email:puddingdes@gmail.com

Fluorescence tagging of the supported lipid bilayers (SLB) is an essential technique for imaging the particular components in the biological membrane. It is generally believed that the tagged lipids would participate on the liquid-disordered (fluid) phase rather the liquid-ordered (gel) phase. Such partition behavior of tagged lipids usually guides the interpretation of the fluorescence-bright or dark domain on membrane. Here, we demonstrate that there is no particular partition for the fluorescence tag, Texas red-DHPE, in the fluid or in the gel phases. However, in the gel phase, the fluorescence would be quenched by the efficient excitation energy transfer (EET) in nearly “frozen” molecular environments. The packing and relative motion among neighborhood lipids determine the dipole orientation and therefore, lead to distinct EET efficiency between the gel and the fluid phase. Thus, the bright/dark constrast in between the fluid/gel phases is a result of EET quenching of the fluoresence in the gel phase. Our results not only reveal the fundamental mechanism of the fluorescence/partition contrast of the lipid domains, but also offers a practical guide in interpreting the constrast of the fluorescence imaging.

Keywords: Supported lipid bilayer, Fluorescence tag partition, Xxcitation energy transfer (EET), Atomic force microscopy (AFM), Scanning near field optical microscope (SNOM)