Stable, Nanoscale Glycosphingolipid Films for Use in Sensing Applications
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Stable, Nanoscale Glycosphingolipid Films for Use in Sensing Applications Rory Stine2, Cara-Lynne Schengrund1 and Michael V. Pishko*2 1 Department of Biochemistry and Molecular Biology, Milton Hershey Medical Center, The Pennsylvania State University 2 Departments of Chemical Engineering, Chemistry, and Materials Science & Engineering The Pennsylvania State University * Author to whom correspondence should be sent: 104 Fenske Laboratory University Park, PA 16802 [email protected]
Abstract We have developed a means of producing thin, oriented lipid monolayers which are stable under repeated washing and which may be useful in biosensing or surfacecoating applications. Phosphotidylcholine (PC) and the glycosphingolipid (GSL) GM1 were used as representative lipids for this process. Initially, a mixed self-assembled monolayer of octanethiol and hexadecanethiol was constructed on a clean gold surface. This hydrophobic surface was then brought into contact with a thin lipid layer that had been deposited at the air/liquid interface of a solution by evaporating a mixture of lipid in hexane on top of a layer of water. The lipid layer, now deposited on the gold surface, was then heated to cause intercalation of the fatty acid and alkanethiol chains, and cooled to form a highly stable film which withstood repeated rinsing and solution exposure. Presence and stability of the film was confirmed via ellipsometry, FTIR, and QCM, with an average overall thickness of ~3.5 nm. These films may be potentially useful in biotoxin detection or as a protein resistant layer for the prevention of biofouling.
Introduction Traditionally, biosensing has relied on the use of protein-based recognition molecules, such as antibodies, as its means of primary detection. More recently, however, the use of glycolipids has gained acceptance as an effective recognition molecule for biotoxin sensing. Recent studies have successfully used glycolipids in fluorescent,1 plasmon resonance,2 and QCM3 based biotoxin sensors. Glycosphingolipids (GSLs), consisting of a carbohydrate head group attached to a sphingosine-derived tail, make up a small percentage of the lipid component of cell membranes. For many biological toxins, binding to the carbohydrate portion of a GSL is the first step in their interaction with cells.4 Using GSLs in this manner presents several advantages over the traditional use of antibodies. These include the ability to easily orient the carbohydrate portion of the GSL towards the surface/fluid interface through hydrophobic/hydrophilic interactions, more active sites for protein binding per unit area, and the greater stability of GSLs when compared to antibodies under a variety of conditions. Supported lipid bilayers are also an area of increasing interest. Studies on lipid film structure,5-7 electrochemical behavior,8, 9 and biosensing capabilities10, 11 have recently received much attention. One drawback to the use of lipid films, however, is their inherent instability. Cremer and colleagues12 found that lipid bilayers are pro
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