Novel Temperature Dependence of the Smectic−C Tilt in the Polymeric Liquid Crystal, C−6 Polysiloxane: A High−Resolution X−Ray Study

High-resolution x-ray scattering measurements of the smectic-C phase of the polymeric liquid crystal, C-6 polysiloxane, show that the smectic-C tilt angle φp decreases continuously upon decreasing temperature. This behavior, opposite to that observed in monomeric liquid crystals, is caused by stiffening in the polymeric backbones and spacers

Nematic−Smectic−C phase transition in the polymeric liquid crystal C−6 polysiloxane: A high resolution x−ray study

We report on the first x-ray scattering measurements of pretransitional smectic-C fluctuations in the nematic phase of a side-chain polymeric liquid crystal, C-6 polysiloxane. The data are well described by the mean-field theory of Chen and Lubensky suggesting that the mesogenic side groups are only weakly coupled to the polymeric backbone. Because of disorder in the polymer backbone, the correlation lengths, in the vicinity of the nematic-smectic-C phase transition, are weak functions of temperature and their magnitudes are smaller than those of conventional monomeric liquid crystals

Real-time sensing of cell morphology by infrared waveguide spectroscopy.

We demonstrate that a live epithelial cell monolayer can act as a planar waveguide. Our infrared reflectivity measurements show that highly differentiated simple epithelial cells, which maintain tight intercellular connectivity, support efficient waveguiding of the infrared light in the spectral region of 1.4-2.5 µm and 3.5-4 µm. The wavelength and the magnitude of the waveguide mode resonances disclose quantitative dynamic information on cell height and cell-cell connectivity. To demonstrate this we show two experiments. In the first one we trace in real-time the kinetics of the disruption of cell-cell contacts induced by calcium depletion. In the second one we show that cell treatment with the PI3-kinase inhibitor LY294002 results in a progressive decrease in cell height without affecting intercellular connectivity. Our data suggest that infrared waveguide spectroscopy can be used as a novel bio-sensing approach for studying the morphology of epithelial cell sheets in real-time, label-free manner and with high spatial-temporal resolution

Probing of the microwave radiation effect on the green fluorescent protein luminescence in solution

Abstract Microwaves have a larger effect on the green fluorescent protein (GFP) fluorescence intensity than is observed by conventional thermal heating. Our measurements show that thermally heating a GFP solution from 7 to 40 • C results in a ∼1% decrease in fluorescence for every 1 • C. On the other hand, under 250 mW of localized microwave irradiation, the fluorescence can decrease by up to 3-10% with an accompanying temperature rise of only 1 • C

Schematic representation of intracellular leaky waveguide mode propagation in a living cell monolayer.

<p>A. Waveguide mode excitation in a living cell monolayer. An electromagnetic wave penetrates at an incident angle <i>θ_inc</i> from the high-refractive-index substrate into a cell monolayer having a lower refractive index, <i>n_cell</i>_,. Because <i>n_medium</i> is lower than <i>n_cell</i>_, this wave undergoes total internal reflection at the cell-medium interface. The wave then impinges on the cell-substrate interface where it is partially reflected (solid red arrow) and refracted (pale red arrow). Excitation of the radiative (leaky) waveguide mode occurs when the reflected and refracted waves at the substrate-cell interface interfere destructively, confining the energy within the cell layer. B. XZ-section of epithelial MDCK cell monolayer stably expressing LifeAct-GFP as imaged by confocal microscopy. Scale bars: 10 µm.</p

Excitation of intracellular waveguide modes using a collimated broadband infrared beam.

<p>A. Experimental setup. A cell layer was cultured on an Au-coated ZnS prism as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0048454#s4" target="_blank">Materials and Methods</a>. During the measurement, the cells in the flow chamber were exposed to culture medium at constant flow. The collimated and polarized infrared beam from the FTIR spectrometer impinges on the gold layer at angle <i>θ_inc</i> and excites waveguide modes within the cell layer (panel C). The intensity of the reflected beam is measured by an MCT detector. Simultaneously, the cells are optically imaged by a CMOS camera attached to the optical microscope. B. Wavelength-dependent reflectivity measurement (<i>I_p/I_s</i>, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0048454#s4" target="_blank">Materials and Methods</a>) from the ZnS/Au/MDCK cells/medium assembly at <i>θ_inc</i> = 34.8°. The reflection minima correspond to the surface plasmon (SP) resonance and to the waveguide mode resonances (TM₁ and TM₂). C. Schematic representation of the electric field distribution for the surface plasmon and TM₁ waveguide mode propagating in the cell layer. The surface plasmon penetrates only up to ∼2 µm into the cell layer and is thus sensitive mainly to the cell-substrate interface. The TM₁ mode penetrates much further, it is confined within the entire cell volume and can be used to measure the cell height <i>h</i>. D. Angular-resolved reflectivity spectra from the ZnS/Au/MDCK cells/medium assembly. The strong reflectivity minimum (deep blue) arises from the surface plasmon resonance. Its angular dependence mimics the dispersion of the water refractive index. A shallow minimum at lower angles (light blue) corresponds to the TM₁ waveguide mode. This mode does not appear in the absence of cell layer (i.e., in a bare Au substrate; see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0048454#pone.0048454.s001" target="_blank">Figure S1</a>).</p