| Abstract
| - We report an experimental investigation of the role of molecular-level interactions in determining theanchoring of liquid crystals supported on surfaces possessing nanometer-scale topography on whichimmunoglobulins (IgG) are specifically bound to immobilized antigens. Molecular-level interactions aremanipulated by using self-assembled monolayers (SAMs) of organosulfur compounds formed on thin filmsof gold that possess an anisotropic, nanometer-scale topography (corrugation). We compare the orientationalresponse of liquid crystal to the presence of anti-biotin IgG specifically bound to mixed SAMs formed frombiotin-(CH2)2[(CH2)2O]2NHCO(CH2)11SH and either CH3(CH2)6SH or CH3(CH2)7SH on the gold films. Whenusing SAMs that contain 70% alkanethiolate, we measure the orientational (and thus optical) responseof the liquid crystal to IgG to depend on whether the alkanethiolate within the mixed SAM is CH3(CH2)6Sor CH3(CH2)7S. We conclude, therefore, that molecular-level interactions controlled by the structure of thealkanethiolates, in addition to long-range (elastic) interactions that result from the nanometer-scaletopography of the gold film, influence the response of liquid crystal to the IgG specifically bound to thesesurfaces. The influence of the nanometer-scale topography does, however, dominate the response of theliquid crystal. The molecular interactions appear to influence the lifetimes of line defects formed as nematicphases spread across these surfaces: the defects are observed to anneal quickly (∼seconds) on SAMscontaining CH3(CH2)7S but slowly (>days) on those containing CH3(CH2)6S. The pinning of defects withinthe liquid crystal when using SAMs containing CH3(CH2)6S causes these surfaces to be more sensitive tobound IgG than surfaces containing CH3(CH2)7S.
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