Issue 18, 2011

Ion-mediated changes of supported lipid bilayers and their coupling to the substrate. A case of bilayer slip?

Abstract

Ion-mediated (Ca2+) changes in viscoelastic, structural and optical properties of negatively charged solid supported lipid bilayers (SLBs) on SiO2 surfaces were studied by means of quartz crystal microbalance with dissipation (QCM-D) monitoring and optical reflectometry. Despite the sensitivity of QCM-D to viscoeleastic/structural variations, it has not often been used to probe such changes for SLBs. SLBs were prepared from binary phospholipid mixtures of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC, neutral) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1′-rac-glycerol) (POPG, negatively charged) on SiO2 sensor surfaces in a Ca2+-containing buffer. Interestingly, for bilayers containing POPG fractions above 35%, large QCM-D dissipation shifts occurred, when Ca2+ was removed from buffer in contact with the SLB (while maintaining 100 mM NaCl). The accompanying frequency changes were small. These Ca2+ mediated QCM-D responses are reversible, and a signal for considerable changes in the viscoelastic and structural properties of the SLB. Variation of Ca2+-concentration revealed a threshold concentration of around 0.4 mM for the changes in the SLB to occur. Below this value, at >35% POPG concentration in the SLB, the SLB appears to become more weakly attached to the SiO2 substrate, which is partly attributed to a weakening of the POPG-substrate interaction in the absence of Ca2+. A consequence of this is an oscillation-amplitude dependent dissipation, which we attribute to slip of the bilayer at higher oscillation amplitudes. Complementary experiments using a combined QCM-D/reflectometry instrument showed that the Ca2+-induced changes in the viscoelastic/structural properties of the SLB are accompanied by changes in the optical properties. We discuss different scenarios to explain the observed reversible effect of Ca2+-ions on the dissipative and optical properties of the mixed SLBs. Based on our results we propose the observed phenomenon to be a combination of geometric changes, internal structural changes, changes in the interfacial water layer, and a slip mechanism, i.e. friction between the SLB and the substrate.

Graphical abstract: Ion-mediated changes of supported lipid bilayers and their coupling to the substrate. A case of bilayer slip?

Article information

Article type
Paper
Submitted
13 May 2011
Accepted
04 Jul 2011
First published
02 Aug 2011

Soft Matter, 2011,7, 8582-8591

Ion-mediated changes of supported lipid bilayers and their coupling to the substrate. A case of bilayer slip?

A. Kunze, F. Zhao, A. Marel, S. Svedhem and B. Kasemo, Soft Matter, 2011, 7, 8582 DOI: 10.1039/C1SM05886J

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements