Hybrid nanoparticle-lipids multilayers have attracted great interest as potential novel materials for applications such as drug delivery, energy harvesting or sensing, and as model system in fundamental research. Different nanoparticles such as silica, cadmium telluride, or iron-platinum can be incorporated into lipid multilayers in different ways, e.g. drop casting from mixed particle-lipid dispersions1, adding particles to pre-existing multilayers via chemical vapour deposition2, and thermal deposition followed by rehydration3. To fully explore the potential of lipid-nanoparticle composites, it is important to understand how the structure and stability of lipid multilayers could be affected by the presence of nanoparticles.
In the current work, the structure of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) multilayers were investigated at the mica surface using X-ray reflectometry (XRR). The samples were made by drop casting aqueous mixtures of nanoparticles and lipid liposomes on freshly cleaved mica and then drying them in vacuo. Negatively charged polystyrene (24 nm in diameter) and anionic, cationic and neutral 4th-generation poly(amidoamine) dendrimers (~4.5 nm in diameter) were used.
The analysis of the distinct Bragg peaks in XRR curves indicates ordered and polycrystalline domains with tens of bilayers stacked approximately parallel to the substrate. The thickness of single lipid bilayers is ~4-5 nm when dry. The effect of temperature, water addition and the presence of different nanoparticles on the structure of the lipid multilayers will be discussed.
1. Yuan, B., et al., Nanotechnology (2011) 22 (31)
2. Gupta, G., et al., ACS Nano (2013) 7 (6), 5300
3. Terheiden, A., et al., Journal of Chemical Physics (2004) 121 (1), 510
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