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Proceedings Paper

Using differential confocal microscopy to detect the phase transition of the membrane of giant unilamellar liposomes
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Paper Abstract

Giant unilamellar lipsomes (diameter $GTR 10 (mu) m) are important for cell-membrane research and controlled drug delivery. Mechanical properties of unilamellar lipsomes in different physiological conditions are crucial for their applications. For example, liquid-gel phase transition of the bilayer membrane under different temperatures determines the stability and activity of liposomes. Bending rigidity is the most closely related mechanical property to phase transition. Owing to the flexible nature of bilayer membranes, accurate measurements of the bending rigidity of membranes are difficult. Here we report an all-optical technique to directly measure the bending modulus of unilamellar lipsomes. We use differential confocal microscopy, a far-field optical profilmetry with 2-nm depth resolution to monitor the thermal fluctuations and the deformation of unilamellar lipsomes. From the amplitude changes of thermal fluctuations along with temperature we can directly determine the phase-transition temperature of the membrane structure. We then employ optical force to induce sub-micrometer deformation of the unilamellar lipsomes. From the deformation we can obtain their bending rigidity with simple calculation. We find the bending modulus decreases from 8-11 pico-erg to 0.5 to 0.9 pico-erg as the liposomes are heated across the phase-transition temperature. All measurements are done without contacting the samples and the shapes of the liposomes remain the same after the experiments.

Paper Details

Date Published: 4 July 2000
PDF: 9 pages
Proc. SPIE 4082, Optical Sensing, Imaging, and Manipulation for Biological and Biomedical Applications, (4 July 2000); doi: 10.1117/12.390535
Show Author Affiliations
Chau-Hwang Lee, Institute of Applied Science and Engineering Research (Taiwan)
Wan-Chen Lin, Institute of Applied Science and Engineering Research (Taiwan)
Jyh-Yang Wang, Institute of Atomic and Molecular Sciences and National Taiwan Univ. (Taiwan)

Published in SPIE Proceedings Vol. 4082:
Optical Sensing, Imaging, and Manipulation for Biological and Biomedical Applications
Robert R. Alfano; Peng Pei Ho; Arthur E. T. Chiou, Editor(s)

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