Phospholipid/Aromatic Thiol Hybrid Bilayers

Abstract

Gold-supported hybrid bilayers comprising phospholipids and alkanethiols have been found to be highly useful in biomembrane mimicking as well as biosensing ever since their introduction by Plant in 1993 (Plant, A. L. Langmuir 1993, 9, 2764−2767). Generalizing the mechanism (i.e., hydrophobic/hydrophobic interaction) that primarily drives bilayer formation, we report here that such a bilayer structure can also be successfully obtained when aromatic thiols are employed in place of alkanethiols. Four aromatic thiols were studied here (thiophenol, 2-naphthalene thiol, biphenyl-4-thiol, and diphenylenevinylene methanethiol), all affording reliable bilayer formation when 1-palmitoyl-2-oleoylsn-glycero-3-phosphocholine liposomes were incubated with self-assembled monolayers of these thiols. Characterization of the resultant structures, using cyclic voltammetry, impedance analysis, and atomic force microscopy, confirmed the bilayer formation. Significant differences in electrochemical blocking and mechanical characteristics of these new bilayers were identified in comparison to their alkanethiol counterparts. Taking advantage of these new features, we present a new scheme for the straightforward biorecognition of a lipolytic enzyme (phospholipase A2) using these phospholipid/aromatic thiol bilayers. In order to present the thesis in a clear manner, this synopsis provides a brief summary of the chapters and contents. Chapter 1 presents a detailed literature review on the simplified lipid bilayer membrane model systems, and the meaningfulness of my work. Additionally, a brief introduction of cyclic voltammetry, impedance spectroscopy and atomic force microscopy are given at the end of chapter 1. Chapter 2 describes the preparation and characterization experiments of the aromatic thiol SAMs and phospholipid/thiol hybrid bilayers. Chapter 3 illustrates the characterization results of four aromatic thiols and their corresponding hybrid bilayers, via cyclic voltammetry, impedance analysis, and atomic force microscopy. Besides, a new method for the straightforward biorecognition of a lipolytic enzyme (phospholipase A2) was explored by using these phospholipid/aromatic thiol bilayers. Chapter 4 provides a summary of this research work and an outline for possible future directions that would follow this work.