Liquid crystals (LCs) were used to amplify and transduce receptor-mediated binding of proteins at surfaces into optical outputs. Spontaneously organized surfaces were designed so that protein molecules, upon binding to ligands hosted on these surfaces, triggered changes in the orientations of 1- to 20-micrometer-thick films of supported LCs, thus corresponding to a reorientation of approximately 10(5) to 10(6) mesogens per protein. Binding-induced changes in the intensity of light transmitted through the LC were easily seen with the naked eye and could be further amplified by using surfaces designed so that protein-ligand recognition causes twisted nematic LCs to untwist. This approach to the detection of ligand-receptor binding does not require labeling of the analyte, does not require the use of electroanalytical apparatus, provides a spatial resolution of micrometers, and is sufficiently simple that it may find use in biochemical assays and imaging of spatially resolved chemical libraries.

We report the use of atomic force microscopy (AFM) to characterize quantitatively the structural anisotropy within ultrathin (thickness of ∼10 nm) obliquely deposited films of gold and thereby calculate the influence of this anisotropy on the orientations of liquid crystals (LCs) supported on these surfaces. Whereas visual inspection of AFM images (real space or reciprocal space) reveals no obvious structural anisotropy within these gold films, a quantitative analysis of the AFM profiles does show a subtle level of anisotropy on wavelengths comparable to the lateral dimensions of the gold grains (∼30 nm). Our analysis reveals the root-mean-square (rms) slope of the surface topography to be ∼1°greater in a direction parallel to the direction of deposition of the gold as compared to the perpendicular direction. We also demonstrate the rms curvature of the grains of gold to be greatest in a direction parallel to deposition. Because the amplitude of the surface roughness (∼2 nm) is small compared to its wavelength (∼30 nm), the influence of the surface roughness on the orientations of supported LCs can be described through an elastic mechanism of anchoring. By combining the multimode Berreman-de Gennes model for the elastic free energy density of a nematic LC with AFM profiles of the topography of obliquely deposited gold films, we calculate the azimuthal anchoring energy of the supported LC to be ∼0.015 mJ/m 2 , a value that is consistent with estimates of anchoring energies obtained by fabrication of twisted nematic LC cells. The results reported in this paper provide a route to the characterization of surfaces with designed levels of anisotropy suitable for control of the anchoring of LCs. This capability will, we believe, find application in studies aimed at exploring the use of LCs for amplification and transduction of events of molecular recognition (e.g., antigenantibody) at surfaces.

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.

A normally‐white LC design has been developed for use with an all digital backplane LCoS imager. We detail the optimizations to enhance static and dynamic performance in an LCoS projection engine. Drive voltage, contrast, efficiency and dynamic response have all been optimized. Optimization details are described and results are presented.