| Abstract
| - This paper reports a strategy for the oriented immobilization of protein receptors on gold films possessingnanometer-scale topographies and the detection of protein binding events to these receptors by using liquidcrystals. The approach revolves around the use of self-assembled monolayers (SAMs) formed fromnitrilotriacetic acid (NTA)-terminated alkanethiols, 1, and tri(ethylene glycol)-terminated alkanethiols,2. The SAMs are formed on ultrathin gold films that are deposited from a vapor onto silica substratesoriented at an oblique angle of incidence. Single-component SAMs formed from 2 on these gold films resistnonspecific protein adsorption (using cell lysates) and promote uniform planar anchoring of the nematicliquid crystal, 4-cyano-4‘-pentylbiphenyl (5CB). Surprisingly, the azimuthal orientation of nematic 5CBis parallel to the direction of maximum roughness within the gold film when using SAMs formed from 2but perpendicular to the direction of maximum roughness when tetra(ethylene glycol)-terminated SAMsare formed on the gold films. Mixed SAMs formed from 1 and 2 bind the hexahistidine-tagged protein MEKvia specific complexation of the hexahistidine tags of MEK to the NiII−NTA complexes on the surface.When gold films are prepared by oblique deposition at an angle of 30° from the normal, we measure boundMEK to disrupt the uniform orientation of 5CB, thus leading to an easily visualized change in the opticalappearance of the liquid crystal. However, by using gold films deposited at an angle of 40° from the normal,we report that bound MEK does not disrupt the alignment of the liquid crystal whereas anti-MEK IgGbound to the MEK does lead to a nonuniform alignment. These results, when combined with appropriatecontrol experiments, suggest that nanostructured surfaces presenting NTA and ethylene glycol terminatedSAMs form a useful interface for imaging proteins bound to histidine-tagged, surface-immobilized receptors.
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