Instructional Review: An Introduction to Optical Methods for Characterizing Liquid Crystals at Interfaces.
(Impact Factor: 4.46).
01/2013; 29(10). DOI: 10.1021/la304679f
This Instructional Review describes methods and underlying principles that can be used to characterize both the orientations assumed spontaneously by liquid crystals (LCs) at interfaces and the strength with which the LCs are held in those orientations (so-called anchoring energies). The application of these methods to several different classes of LC interfaces is described, including solid and aqueous interfaces as well as planar and non-planar interfaces (such as those that define a LC-in-water emulsion droplet). These methods, which enable fundamental studies of the ordering of LCs at polymeric, chemically-functionalized and biomolecular interfaces, are described in this article at a level that can be easily understood by a non-expert reader such as an undergraduate or graduate student. We focus on optical methods because they are based on instrumentation that is found widely in research and teaching laboratories.
Available from: Petr V Shibaev
- "In case of nematic and smectic LC materials one of the major indicators of environmental agents presence was a textural change in the visual appearance of liquid crystals  . Much effort was dedicated to solving the problem of the detection of biological molecules in aqueous media by analyzing morphological changes in free standing low molar mass liquid crystalline films and droplets  or films deposited on functionalized surfaces . Liquid crystalline polymers and polymer networks were also explored for detection of organic solvents, pH changes in water, and amino acids   . "
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ABSTRACT: Films and droplets of liquid crystals may soon become an essential part of sensitive environmental sensors and detectors of volatile organic compounds (VOCs) in the air. In this paper a short overview of recent progress in the area of sensors based on liquid crystals is presented, along with the studies of low molar mass liquid crystals as gas sensors. The detection of VOCs in the air may rely on each of the following effects sequentially observed one after the other: (i) slight changes in orientation and order parameter of liquid crystal, (ii) formation of bubbles on the top of the liquid crystalline droplet, and (iii) complete isotropisation of the liquid crystal. These three stages can be easily monitored by a photo camera and/or optical microscopy. Detection limits corresponding to the first stage are typically lower by a factor of at least 3-6 than detection limits corresponding to isotropisation. The qualitative model taking into account the reorientation of liquid crystals is presented to account for the observed changes.
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ABSTRACT: We report the use of flow cytometry to identify the internal ordering (director configurations) of micrometer-sized droplets of thermotropic liquid crystals (LCs) dispersed in aqueous solutions of adsorbates (surfactants and phospholipids). We reveal that changes in the configurations of the LC droplets induced by the adsorbates generate distinct changes in light scattering plots (side versus forward scattering). Specifically, when compared to bipolar droplets, radial droplets generate a narrower distribution of side scattering intensities (SSC, large angle light scattering) for a given intensity of forward scattering (FSC, small angle light scattering). This difference is shown to arise from the rotational symmetry of a radial LC droplet which is absent for the bipolar configuration of the LC droplet. In addition, the scatter plots for radial droplets possess a characteristic "S-shape", with two or more SSC intensities observed for each intensity of FSC. The origin of the experimentally observed S-shape is investigated via calculation of form factors and established to be due to size-dependent interference effects that differ for the forward and side scattered light. Finally, by analyzing emulsions comprised of mixtures of bipolar and radial droplets at rates of up to 10,000 droplets per second, we demonstrate that flow cytometry permits precise determination of the percentage of radial droplets within the mixture with a coefficient of determination of 0.98 (as validated by optical microscopy). Overall, the results presented in this paper demonstrate that flow cytometry provides a promising approach for high throughput quantification of the internal configurations of LC emulsion microdroplets. Because large numbers of droplets can be characterized, it enables statistically robust analyses of LC droplets. The methodology also appears promising for quantification of chemical and biological assays based on adsorbate-induced ordering transitions within LC droplets.
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ABSTRACT: Glycoproteomics represent the field of study of the dynamic changes occuring amongst glycoconjugates within the cellular compartments. Changes in glycosylation have been linked to various diseases, including metastatic carcinomas in which the 9 carbon sialic acid moiety has been shown to play a prominent role. The common method used to study these aberrant changes most often includes a mass spectrometer at some stage in the workflow. However, serum samples contain many proteins which inhibit the analysis of these glycosylation changes, and ergo, enrichment steps are employed as a measure to help alleviate this ailment. Routinely, this is accomplished using lectins, either alone or in combination, to retrieve proteins with specific sugar linkages within the serum sample. This methodology, although known to be very specific, requires many washing steps, making it a cumbersome addition to a high throughput workflow. Presented here, is an alternative protocol using custom-made amine functionalized magnetic nanoparticles (MNP) which are nearly 4x smaller than used before for similar purposes. The developed protocol is based on both hydrophilic interaction and weak anion exchange principles, allowing it to target glycopeptides, but more specifically those which contain sialylation. For quantification purposes, tandem mass tags from Thermo Scientific™ were utilized to compare the enrichment efficiencies between the magnetic nanoparticle method, and a commercially available glycopeptide enrichment kit offered through EMD Millipore™. The MNP method is fast (~10 min), simple, and can quantitatively and qualitatively enrich sialylated glycopeptides more than the commercially available kit.
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