New SAXS paper published by ILO team

A new paper has recently been published by Wuge Briscoe and colleagues from the University of Bristol in collaboration with scientists from Diamond Light Source, including the Industrial Liaison team's SAXS specialist, Claire Pizzey. The team used high pressure small angle X-ray scattering (SAXS) for biophysical measurements aimed at understanding changes in cell membrane structure in the presence of nanoparticles. SAXS is an ideal technique for exploring the phase diagrams of lipids.

Different lipid phases give rise to very different SAXS signals and so the SAXS pattern can be used to identify the particular phase present. These specific phases can be mapped with variable temperature and pressure to detect how the phase diagram of the lipid changes with the addition of nanoparticles. By varying the temperature and pressure experienced by the sample and collecting SAXS data at all different conditions, it is possible to use the SAXS signal to identify the phase(s) present and construct a phase diagram.

The paper reports a SAXS investigation of the effect of adding nanoparticles of different types on the microstructure of model cell membranes. Using a membrane comprising the phospholipid dioleoyl phosphatidylethanolamine (DOPE), the SAXS study showed how phase transitions between lipid phases were altered in the presence of nanoparticles. The spherical nanoparticles used were made from silica and were or comparable size although one was hydrophilic and the other had a polydimethyl siloxane (PDMS) coating to provide a hydrophobic surface. Phase diagrams based on SAXS data were constructed for both hydrophobic and hydrophilic particles interacting with DOPE and were constructed for each particle type at a number of different particle concentrations. Hydrophobic nanoparticles in particular were shown to promote a lamellar to inverted hexagonal transition.

The lamellar to inverted hexagonal transition of phospholipids is energetically analogous to the membrane fusion process so a greater knowledge of how this process is influenced by the presence of nanoparticulate additives may help to understand the effect of nanoparticles on biological processes. Using SAXS to understand these processes is also of direct relevance in areas related to the design of drug delivery systems or gene therapy where challenge is to deliver the target molecule or gene across the cell wall (in a similar way to the action of a virus). There are also implications for the toxicity of nanoparticles and understanding their interactions with model cell membranes is an important step in understanding toxicity. SAXS can provide a powerful tool to detect and identify changes in lipid phases in the presence of nanoparticles which could be used for further related studies.

The full publication is available online:

"Hydrophobic nanoparticles promote lamellar to inverted hexagonal transition in phospholipid mesophases" Jennifer M. Bulpett, Tim Snow, Benoit Quignon, Charlotte M. Beddoes, T-Y. D. Tang, Stephen Mann, Olga Shebanova, Claire L. Pizzey, Nicholas J. Terrill, Sean A. Davis and Wuge H. Briscoe, SoftMatter, 2015, DOI: 10.1039/c5sm01705j

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