Lipid Nanodomains on Modified Gold Surfaces - A Biomimetic Platform to Study Electroactive Biomolecule-Membrane Interactions

Abstract

Biomimetic platforms based on supported lipid bilayers (SLB) on gold are becoming prominent due to their wide applications in biosensor developing and redox biology studies. A recent innovation was the use of multicomponent lipid bilayers with phase coexistence (Marques et al. 2013). Here, the formation of ternary (DOPC/DPPC/Cholesterol 2:2:1) SLBs exhibiting lipid rafts in modified gold will be described. Surface modifications are required to confer hydrophilicity to gold facilitating the formation of a planar and uniform bilayer. Two surface modifications, 11-mercaptoundecanoic acid (MUA) which generates a long and compact self-assembled monolayer (SAM) and L-cysteine (Cys) which forms a short and non-compact SAM, were used. Similar kinetics was observed for lipid vesicle adsorption on both SAM by surface plasmon resonance and quartz crystal microbalance. On both modified electrodes a continuous lipid bilayer with topographical details assigned to lipid rafts was imaged by atomic force microscopy. Moreover the thickness estimated by ellipsometry lies in the range expected for a bilayer.Since the compact MUA monolayers hinder the electronic exchange between electroactive molecules and the gold electrode, Cysteine emerges as a suitable solution to develop lipid-based interfaces to study electrochemical phenomena. Cys-modified electrodes with raft-containing SLB were employed to study membrane-interactions of a redox active biomolecule, epinephrine. Cyclic voltammetric results revealed an influence of lipid composition on the membrane-adsorbed epinephrine. Interestingly, fluorescence spectroscopy revealed a rather weak interaction between epinephrine and lipid bilayers in suspension, highlighting the applicability of the platform cys-SLB to investigate and detect membrane-associated processes with high sensitivity.Marques, JT, de Almeida, RFM, Viana, AS, 2013, Electrochim. Acta (in press).This work was financed by Portuguese national funds through FCT: Ph.D. fellowship: SFRH/BD/64442/2009, grant PEst-OE/QUI/UI0612/2013, and IF2012 initiative (POPH, Fundo Social Europeu).