Electric field-induced transient birefringence and light scattering of synthetic liposomes

Abstract

The dynamics of electric field-induced transient birefringence Deltan(t) and light scattering (detected as turbidity) of 190 nm diameter unilamellar vesicles of dioleoylphosphatidylcholine are investigated as a function of applied field strength E, length of the square pulse Deltat, lipid concentration, mean hydrodynamic diameter <Dh>, ionic strength, and temperature. Generally, induced birefringence exclusively is observed at low lipid concentration and below certain threshold values of E and Deltat, whereas concomitant induced turbidity appears at high lipid concentration and above thresholds values of E and Deltat. Turbidity is monitored through the change in transmitted intensity DeltaS parallel(t) and DeltaS perpendicular(t) of light polarized parallel and perpendicular to the applied field E. The field-induced structural changes are reflected in double-exponential forward relaxation and triple-exponential reverse relaxation of the positive birefringence, and in non-exponential relaxations of DeltaS parallel (t) and DeltaS perpendicular(t). Under the field, the associated physical events are interpreted as elongation of the spherical bilayer shells in the direction of E, linear chain formation (pearling) of the induced dipolar liposomes parallel to E, and partial fusion of adjoining vesicles within the chains. Under conditions where electroporation can be detected, pore opening succeeds the elongation of the vesicles. After termination of the field, the vesicles return to their original time average spherical shape, the oriented chains randomize and disintegrate, and the fused structures are converted either to unilamellar or multilamellar vesicles.

On the investigation of the bilayer functionalities of 1,2-di-oleoyl-sn-glycero-3-phosphatidylcholine (DOPC) large unilamellar vesicles using cationic hemicyanines as optical probes: A wavelength-selective fluorescence approach

“…The lipid 1,2-di-oleoyl-sn-glycero-3-phosphatidylcholine (DOPC) T c = −17.3 • C [23,24] in chloroform, as obtained from Avanti Polar Lipids, Inc. (Alabaster Al, USA) was used without further purification. The fluorescent probe 4,(4-(dihexadecylamino) styryl-N -methyl-pyridinium iodide (DIA), from Molecular Probes (Eugene Or), was used as received.…”

Photophysics of a β-carboline based non-ionic probe in anionic and zwitterionic liposome membranes

“…Liposomes serve as valuable model for biological membranes and correspond to the environment in which many drugs, proteins and enzymes display their activity. Since the structure of the biological membranes is complicated due to a wide diversity in their composition, one uses synthetic liposomes that mimic the structure and geometry of the cell membrane (Ashgarian and Schelly, 1999;Moyano et al, 2006). Liposome has important applications in the field of drug loading, diagnostics, food industry, and immunology.…”

High-throughput and real-time study of single cell electroporation using microfluidics: Effects of medium osmolarity

“…In general, most mechanistic studies on electroporation have adopted one of the two approaches: total population methods and single cell methods. Total population methods, such as measuring turbidity changes or following radioactivity of cell suspensions, yield information about average electroporative behavior of cells (Asgharian and Schelly, 1999;Bureau et al, 2004;Chi et al, 2004;Eynard et al, 1992;Frantescu et al, 2005). However, given the heterogeneity of the cell population, it is important to find out whether the average behavior is representative of the individual cells within the population or distinct subpopulations with different responses exist.…”