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Show LATERAL DISTRIBUTION OF ADSORBED PROTEINS ON STABILIZED MIXED SURFACTANT FILMS Thomas T. Goodman Senior Bioengineering tte1@utah.edu Faculty Sponsor: Vladimir Hlady Dept. of Bioengineering Vladimir. Hlady@m. cc.utah.edu Faculty Sponsor: David W. Britt Dept. of Bioengineering Utah State University Protein adsorption to surfaces has important implications in medical applications such as implanted devices and biosensors. A thorough understanding of the factors affecting protein adsorption can aid in designing medical devices to have predictable responses to the proteins encountered in-situ. This study investigated the lateral distribution of protein on previously characterized surfactant monolayers of mixed stearic acid methyl ester (SME) and dioctadecyldimethyl-ammonium bromide (DOMA) transferred from the air/water interface to glass surfaces. These mixed monolayers were shown to have a distinctive topographical pattern and a corresponding pattern of surface potential. Distinctive circular 'domains' of approximately 10-20 um in diameter were observed to have a surface potential approximately 50 mV higher and a height 0.8-1.6 nm greater than surrounding areas. This surface potential difference is too low to correspond to a de-mixing of SME and DOMA, as the pure films (at the air/water interface) have surface potential differences between 200 to 500 mV (increasing with packing density). Thus the height and potential differences are attributed to a more upright surfactant orientation in the circular domains compared to the sur- rounding regions. The more upright the surfactants, the greater the contribution of their hydrocarbon tail dipole moment is to the measured surface potential. The influence of surfactant dipole orientation on Ferritin, a protein with negative charge character, was investigated. Fluorescently labeled protein was exposed to the surfactant monolayers, and the protein adsorption pattern was observed under a fluorescent microscope. The protein was found to preferentially bind to the 'domains' of higher surface potential. When the surfactant orientation was reversed on the surface (carbon tail groups down towards the surface) protein adsorbed preferentially to areas surrounding the domains. Reversal of the surfactant orientation reverses dipole orientation and so our results suggest that the surfactants dipole contribution to surface potential is the main factor affecting protein adsorption. This study and similar future studies, in conjunction with methods for high resolution characterization of surface properties, will help elucidate the influence of surface properties, such as topography and surface potential, on adsorption behavior and help further develop methods for predicting protein adsorption behavior. 54 |
