We have investigated the interaction between graphene oxide and lipid membranes, using both supported lipid membranes and supported liposomes. Also, the reverse situation, where a surface coated with graphene oxide was exposed to liposomes in solution, was studied. We discovered graphene oxide-induced rupture of preadsorbed liposomes and the formation of a nanocomposite, bio-nonbio multilayer structure, consisting of alternating graphene oxide monolayers and lipid membranes. The assembly process was monitored in real time by two complementary surface analytical techniques (the quartz crystal microbalance with dissipation monitoring technique (QCM-D) and dual polarization interferometry (DPI)), and the formed structures were imaged with atomic force microscopy (AFM). From a basic science point of view, the results point toward the importance of electrostatic interactions between graphene oxide and lipid headgroups. Implications from a more practical point of view concern structure-activity relationship for biological health/safety aspects of graphene oxide and the potential of the nanocomposite, multilayer structure as scaffolds for advanced biomolecular functions and sensing applications.

Biomolecules such as proteins immediately adsorb on the surface of nanoparticles upon their exposure to a biological environment. The formed adlayer is commonly referred to as biomolecule corona (biocorona) and defines the biological activity and toxicity of the nanoparticle. Therefore, it is essential to understand in detail the biocorona formation process, and how it is governed by parameters like composition of the biological environment, and nanoparticle size, shape and faceting. Here we present a detailed equilibrium and real time in situ study of biocorona formation at SiO-nanoparticle surfaces upon exposure to defined (BSA, IgG) and complex (bovine serum, IgG depleted bovine serum) biological samples. We use both nanofabricated surface-associated Au core-SiO shell nanoparticles (faceted, d = 92-167 nm) with integrated nanoplasmonic sensing function and dispersed SiO nanoparticles (using DLS and SDS-PAGE). The results show that preadsorbed BSA or IgG are exchanged for other proteins when exposed to bovine serum. In addition, the results show that IgG forms a biocorona with different properties at curved (edge) and flat (facet) SiO-nanoparticle surfaces. Our study paves the way for further real time in situ investigations of the biocorona formation and evolution kinetics, as well as the role of molecular orientation in biocorona formation, on nanoparticles with surface faceting.

Surface properties of nanoparticles imposed by particle size, shape, and surface chemistry are key features that largely determine their environmental fate and effects on biological systems. Consequently, development of analytical tools to characterize surface properties of nanomaterials and their relation to toxicological properties must occur in parallel with applications. As a contribution to this quest, we present a nanoplasmonic sensing strategy that enables systematic in situ characterization of molecule−nanoparticle interactions under wellcontrolled conditions, in terms of both nanoparticle size and surface chemistry, with particular focus on the importance of surface faceting in crystalline nanoparticles. We assess the performance of our sensing strategy by presenting two case studies. (i) The first is protein corona formation on faceted Au core−SiO 2 shell nanoparticles of different sizes, and thus different surface facet-to-edge ratios. Based on 2D and 3D models of the investigated structures, we find that for small particles the curved regions between adjacent facets dominate the response of the corona formation process, whereas the facets dominate the response in the large particle regime. (ii) The second is in situ functionalization of Au core−SiO 2 shell nanoparticle surfaces, and analysis of the subsequent protein repellent behavior. Due to the versatility of the presented sensing strategy in studies of nanoparticle surface properties, including in situ surface modifications, and their interactions with (bio)molecules during corona formation, we foresee it to become a valuable tool in the areas of nanomedicine and nanotoxicology.

Synthetic lipid bilayers have similar properties as cell membranes and have been shown to be of great use in the development of novel biomimicry devices. In this study, lipid bilayer formation on mesoporous silica of varying pore size, 2, 4, and 6 nm, has been investigated using quartz crystal microbalance with dissipation monitoring (QCM-D), fluorescent recovery after photo bleaching (FRAP), and atomic force microscopy (AFM). The results show that pore-spanning lipid bilayers were successfully formed regardless of pore size. However, the mechanism of the bilayer formation was dependent on the pore size, and lower surface coverages of adsorbed lipid vesicles were required on the surface having the smallest pores. A similar trend was observed for the lateral diffusion coefficient (D) of fluorescently labeled lipid molecules in the membrane, which was lowest on the surface having the smallest pores and increased with the pore size. All of the pore size dependent observations are suggested to be due to the hydrophilicity of the surface, which decreases with increased pore size.

Nanoplasmonic sensors typically comprise arrangements of noble metal nanoparticles on a dielectric support. Thus, they are intrinsically characterized by surface topography with corrugations at the 10-100 nm length scale. While irrelevant in some bio- and chemosensing applications, it is also to be expected that the surface topography significantly influences the interaction between solids, fluids, nanoparticles and (bio)molecules, and the nanoplasmonic sensor surface. To address this issue, we present a wafer-scale nanolithography-based fabrication approach for high-temperature compatible, chemically inert, topographically flat, and laterally homogeneous nanoplasmonic sensor chips. We demonstrate their sensing performance on three different examples, for which we also carry out a direct comparison with a traditional nanoplasmonic sensor with representative surface corrugation. Specifically, we (i) quantify the film-thickness dependence of the glass transition temperature in poly(methyl metacrylate) thin films, (ii) characterize the adsorption and specific binding kinetics of the avidin-biotinylated bovine serum albumin protein system, and (iii) analyze supported lipid bilayer formation on SiO surfaces.

We have investigated the interaction of graphene oxide (GO) sheets with supported lipid membranes with focus on how the interaction depends on GO sheet size (three samples in the range of 90-5000 nm) and how it differs between small and large liposomes. The layer-by-layer assembly of these materials into multilamellar structures, as discovered in our previous research, is now further explored. The interaction processes were monitored by two complementary, real time, surface-sensitive analytical techniques: quartz crystal microbalance with dissipation monitoring (QCM-D, electroacoustic sensing) and indirect nanoplasmonic sensing (INPS, optical sensing). The results show that the sizes of each of the two components, graphene oxide and liposomes, are important parameters affecting the resulting multilayer structures. Spontaneous liposome rupture onto graphene oxide is obtained for large lateral dimensions of the graphene oxide sheets.

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Different levels of model systems are needed for effect studies of engineered nanoparticles and the development of nanoparticle structure–activity relationships in biological systems.