Influence of nanometer-scale topography of surfaces on the orientational response of liquid crystals to proteins specifically bound to surface-immobilized receptors

We report procedures based on oblique deposition of gold that lead to the preparation of ultrathin, semitransparent films of gold that possess systematic differences in their nanometer-scale topography. The nanometer-scale topography of these surfaces is controlled by the angle of incidence of the gold during the oblique deposition of each film. The topography is quantified by using atomic force microscopy (AFM) in terms of the azimuthal dependence of the contour length and local curvature of the surface. We use these surfaces to test our hypothesis that control of nanometer-scale topography permits manipulation of the orientational response of liquid crystal to proteins bound to receptors immobilized on surfaces. We measure the orientational response of nematic phases of 5CB to anti-biotin immunoglobulin G (IgG) bound to biotin-terminated self-assembled monolayers to depend strongly on the nanometer-scale topography of the surfaces. The response of the liquid crystal correlates closely with quantitative measures of the surface topography obtained by AFM and thus demonstrates that it is possible to tune the sensitivity of nematic liquid crystals to the presence of specifically bound IgG by manipulating the nanometer-scale topography of surfaces. The surfaces with the smallest local curvatures were found to be the most sensitive to the presence of bound IgG. We also calculate the anchoring energy of liquid crystal on the surfaces by using continuum elastic theory and the topography obtained from the AFM images. Although the sensitivity of the liquid crystal to the bound protein increases with decreasing anchoring energy, it is not possible to provide a complete account of the orientational behavior of the liquid crystal on these surfaces on the basis of continuum elastic theory.