Toward understanding the interactions between liposomes and graphene for the application of lipidic structures on graphene
- Date
- Thursday 24 October 2024
- Time
- Address
-
Gorlaeus Building
Einsteinweg 55
2333 CC Leiden - Room
- BM.1.23
Thomas J.F. Kocka, Christine M. Vissera, Ankush Singhala, Erik van Geesta, Lars Jeukena, Agur Sevinka, Alexander Krosa, Grégory F. Schneidera
aLeiden Institute of Chemistry, Faculty of Science, Leiden University, Einsteinweg 55, 2333CC Leiden, The Netherlands.
Abstract
Lipidic structures present biomimetic environments that can be used for applications of graphene, for example in graphene liquid cells (GLCs)1 and graphene field effect transistors (GFETs)2, 3. To modulate the lipid structure that forms on the graphene, it is important to understand the interactions between liposomes and graphene. Here, a reliable experimental methodology using a pyrene adhesion layer4 is introduced, to ensure the permanent adhesion of graphene on quartz crystal microbalance sensors. It was found that not only the adhesion of the graphene but also the transfer polymer residues influenced QCM-D measurements with graphene. Therefore, graphene transfer was optimized to obtain the graphene transfer methods with the least amount of transfer polymer residues. Using the optimized experimental methodology, the interactions between graphene and POPC liposomes were investigated, showing that the POPC liposomes ruptured upon coming into contact with graphene. The rupture of the POPC liposomes led to the formation of a POPC lipid monolayer on graphene, evidenced by the obtained average final frequency shift of ∆f5 = -11.1 ± 2.5 Hz. Subsequently, we investigated the experimental conditions that determine whether a liposome ruptures on graphene to form a lipid monolayer, or stays intact. The driving force for the rupture of liposomes on a hydrophobic surface to form a lipid monolayer is the interfacial free energy of the surface5, 6. The rupture of the liposomes comes at a considerable activation energy cost however, which is influenced by the vesicle concentration5, 7. The focus of this work was to understand what vesicle properties, i.e. size (membrane tension) and lipid composition (head group charge, Tm), would influence the activation energy and thereby the resulting lipid structure on graphene. By studying the influence of lipid charge, Tm and the incorporation of cholesterol in the lipid membrane on the formed lipidic structure on graphene, we have found strong indications that liposome rupture on graphene is mediated by lipid-packing defects in the liposome lipid bilayer. Lastly, we demonstrate the utility of lipidic structures on graphene by applying a lipid monolayer for biosensing purposes. We showed that POPC and DOPC lipid monolayers prevents the graphene surface from non-specific binding interactions with proteins. Therefore, a lipid monolayer functionalized with biotin moieties allowed for the selective detection of avidin, a model protein, followed by the detection of biotinylated liposomes. Moreover, the sensing system could be regenerated multiple times, by removing the lipid layer using the surfactant sodium dodecyl sulfate. With this model system we showcase the potential of graphene covered QCM sensors to provide supplemental insights for GFET sensing systems and the study of liposomes in graphene liquid cells.
Acknowledgements
The authors gratefully thank Niek van Hilten and Jeroen Methorst for fruitful discussions.
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