Faculty of Physics - University of Bucharest

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FACULTY OF PHYSICS

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Conference: Bucharest University Faculty of Physics 2012 Meeting

Section: Biophysics; Medical Physics

Title:

Use of Laurdan stady-state and lifetime spectroscopy to characterize the lipid bilayer fluidity

Authors:

Elena ANGHELUTA (1,2), M. RADU (2), A. POPESCU (1)

Affiliation:

(1)Department of Biophysics,Faculty of Physics,University of Bucharest,405 Atomistilor,Magurele-Ilfov,Romania

(2)“Horia Hulubei” National Institute for Research and Development in Physics and Nuclear Engineering,Magurele-Ilfov,Romania

E-mail

elena_e_ang@yahoo.com

Keywords:

Liposomes,laurdan,The generalized polarization ,anisotropy

Abstract:

Scope: Liposomes are vesicles having a concentric lipid bilayer[1], structure that is very similar with biological membranes. Liposomes are widely used as universal drug delivery system. The lipid bilayer fluidity is one of the most studied parameters sine its importance in the interactions of liposomes with other molecular compounds. Laurdan stady-state and time resolved spectroscopy have been used to explore the fluidity of lipid bilayer in liposomes [2, 3]. Methods: The liposomes were prepared according to thin film hydration method, followed by extruder method (200 nm), using DPPC, DSPC, DMPC as lipids. Laurdan was incorporated in liposomes lipid bilayer at a molar ratio [lipid]/[laurdan] =500. The generalized polarization (GP) was computed from fluorescence stady state spectra for a temperature range covering the transition phase of each type of lipid. Also the anisotropy and lifetime of Laurdan on the same temperature range have been measured. Results: All three investigated parameters show a sigmoid like dependence in function of the temperature allowing to calculate the transition temperature for each type of lipid. If the GP is not sensitive to the type of lipids at the extremes of temperature range (~0.5 - ~-0.5) both the anisotropy and lifetime proves to differentiate among the types of lipids for the temperatures bellow the transition, the results being Conclusion: The Laurdan emission can be used in a more effective way to characterize the fluidity of lipid bilayers expanding the measurements from simple GP to polarized lights and lifetime measurements. References [1] Mohammad Riaz, Liposomes Preparation Methods 1996, pp.65-77. [2] F.M.Harris, K.B.Best, J.D.Bell, Use of Laurdan fluorescence Intensity And Polarization To Distinguish Between Changes In Membrane Fluidity And Phospholipid 1565 (2002) 123-128. [3] S.A. Sanchez, M.A. Tricerri, G.Gunther, E.Gratton 2007.