Colloids and Surfaces B: Biointerfaces 160 (2017) 117–125 Contents lists available at ScienceDirect Colloids and Surfaces B: Biointerfaces j o ur nal ho me pa ge: www.elsevier.com/locate/colsurfb Full Length Article The effect of thiolated phospholipids on formation of supported lipid bilayers on gold substrates investigated by surface-sensitive methods Abdulhalim Kılıc ¸ a , M. Fazeli Jadidi b , Hakan Özgür Özer b , Fatma Nes ¸ e Kök a,c,∗ a Istanbul Technical University, Molecular Biology-Genetics and Biotechnology Program, MOBGAM, Maslak, Istanbul, Turkey b Istanbul Technical University, Physics Engineering Dept., Maslak, Istanbul, Turkey c Istanbul Technical University, Molecular Biology and Genetics Dept., Maslak, Istanbul, Turkey a r t i c l e i n f o Article history: Received 22 May 2017 Received in revised form 19 August 2017 Accepted 6 September 2017 Available online 8 September 2017 Keywords: Supported lipid bilayer thiol-terminated phospholipids Quartz CrystalMicrobalance Surface Plasmon Resonance a b s t r a c t Most of the model lipid membrane studies on gold involve the usage of various surface-modification strategies to rupture liposomes and induce lipid bilayer formation since liposomes with polar surfaces do not interact with bare, hydrophobic gold. In this study, a thiol-modified phospholipid, 1,2-Dipalmitoyl- sn-Glycero-3-Phosphothio ethanol (DPPTE) was incorporated into phosphatidylcholine (PC) based liposomes to form supported lipid bilayer (SLB) on gold surfaces without further modification. The binding kinet- ics of liposomes with different DPPTE ratio (0.01 to 100% mol/mol) and diameters were monitored by Quartz Crystal Microbalance with Dissipation (QCM-D). The dissipation change per frequency change, i.e. acoustic ratio, which is evaluated as a degree of the viscoelasticity, considerably decreased with the presence of DPPTE (from 162.3 GHz −1 for flattened PC liposomes to ca. 89.5 GHz −1 for 100% DPPTE lipo- somes) when compared to the results of two reference rigid monolayers and two viscoelastic layers. To assess the quality of SLB platform, the interpretation of QCM-D data was also complemented with Sur- face Plasmon Resonance. The optimum thiolated-lipid ratio (1%, lower thiol ratio and higher rigidity) was then used to determine the dry-lipid mass deposition, the water content and the thickness values of the SLB via viscoelastic modelling. Further surface characterization studies were performed by Atomic Force Microscopy with high spatial resolution. The results suggested that model membrane was almost contin- uous with minimum defects but showed more dissipative/soft nature compared to an ideal bilayer due to partially fused liposomes/overlapped lipid bilayers/multilayer islands. These local elevations distorted the planarity and led the increase of overall membrane thickness to ∼7.0 nm. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Supported lipid bilayer systems prepared by surface-mediated liposome fusion allow researchers to isolate and study one or few biological membrane components. These non-fouling biomimetic surfaces that resist cell/protein adhesion can be modified/functionalized by changing their lipid composition or incorporating membrane-associated proteins or molecules. Func- tionalization by different components helps to develop biosyn- thetic systems such as drug-screening platforms, membrane-based molecular biosensors, and then utilized in medical diagnostics, bio- material improvement, and various other biomedical assays [1–8]. Taking the advantage of high stability and flat geometry, SLBs make long-term experimentation possible and allow the usage of surface sensitive characterization tools such as quartz crys- ∗ Corresponding author at: Istanbul Technical University, Molecular Biology and Genetics Department, 34469 Maslak, Istanbul, Turkey. E-mail address: kokf@itu.edu.tr (F.N. Kök). tal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance (SPR), atomic force microscopy (AFM) and flu- orescence recovery after photobleaching (FRAP) within aqueous environments [4,9–12]. Silica, mica and glass are well-established and most commonly employed solid supports for the preparation of SLBs since their hydrophilicity and negative charge at neutral pH provide lipo- somes a surface to adsorb, deform, flatten and finally rupture to form a bilayer [8]. In that case, the lipid layer is attached to the support by noncovalent bonds. These systems generally have high fluidity because of underlying water layer, but low stability due to weak interactions [13]. Liposomes with polar surfaces, on the other hand, neither interact with bare, hydrophobic gold surfaces [14], nor rupture on oxidized gold surfaces [15]. However, to take the advantages of the attractive properties (such as biocompatibility, electrical conductance) of gold [16,17], an efficient chemisorption method, gold-thiol bond chemistry is often used. For that, a self- assembled monolayer (SAM) is first formed onto the gold using this chemistry, and then a single phospholipid monolayer is attached on http://dx.doi.org/10.1016/j.colsurfb.2017.09.016 0927-7765/© 2017 Elsevier B.V. All rights reserved.