Polarity-sensitivity

Toleutaev B N, Tahara T and Hamaguchi H 1994 Broadband (1000 cm multiplex CARS spectroscopy application to polarization sensitive and time-resolved measurements Appl. Phys. 59 369-75... 

Oudar J-L, Smith R W and Shen Y R 1979 Polarization-sensitive coherent anti-Stokes Raman spectroscopy Appi. Rhys. Lett. 34 758-60... 

Pott, A., Dork, T., Uhlenbusch, J. et al. (1998) Polarization-sensitive coherent anti-Stokes Raman scattering applied to the detection of NO in a microwave discharge for reduction of NO, J. Phys. D Appl. Phys. 31, 2485-98. 

There are two important drawbacks of such an approach (1) a polarity scale based on a particular class of probes, in principle, does not account, for example, sizes of probes, which should strongly effect the interactions (2) betain dyes do not fluoresce, which restrict essentially the field of application of this approach, because in many cases, absorption spectrum could not be measured accurately (small volumes of samples, study of cells, and single molecules spectroscopy). Therefore, polarity-sensitive fluorescent dyes offer distinct advantage in many applications. 

Sackett, D. L. and Wolff, J. (1987). Nile red as a polarity-sensitive fluorescent-probe of hydrophobic protein surfaces. Anal. Biochem. 167, 228-234. 

A novel approach for ion sensing is based on the use of potential-sensitive or polarity-sensitive dyes (PSDs) and was presented first106 in 1987. PSDs are charge dyes and typically located at the interface between a lipophilic sensor phase and a hydrophilic sample phase. The transport of an ion into the lipophilic sensor layer causes the PSD to be displaced from the hydrophilic/hydrophobic interface into the interior of the respective phase (or vice versa), thereby undergoing a significant change in its fluorescence properties107 110. 

The ion sensing scheme based on the use of potential-sensitive or polarity-sensitive dyes (PSDs) was extended to other anions. Both the clinically significant chloride ion124 and the environmentally important nitrate anion125 can be sensed in the desired concentration ranges. Such sensors have the unique advantage of having a virtually pH-insensitive response. 

Huber Ch., Werner T., Krause Ch., Wolfbeis O.S., Novel Chloride-Selective Optode Based on Polymer-Stabilized Emulsions Doped with a Lipophilic Fluorescent Polarity-Sensitive Dye. Analyst 1999 124 1617. 

Potential-sensitive or polarity-sensitive dyes are known to optically respond to changes in their micro-environment such as changes in polarity or lipophilicity. 

Polarity plays a major role in many physical, chemical, biochemical and biological phenomena. This chapter aims to describe how local polarity can be estimated using a fluorescent probe. But what is polarity This apparently simple question deserves some attention before describing the methodologies based on polarity-sensitive fluorescent probes. 

The sensitivity of betain dyes to solvent polarity is exceptionally high, but unfortunately they are not fluorescent. Yet polarity-sensitive fluorescent dyes offer... 

Helix is the most common higher-order structure of synthetic polymers such as peptides, polymethacrylates, polychloral, polyisocyanides, polyisocyanates, and polysilanes. Polyacetylenes bearing appropriate substituents also form a helix. Substituted helical polyacetylenes are promising candidates for enantioselective permeable materials, polarization-sensitive electro-optical materials, asymmetric electrodes, and hence their synthesis is currently under intensive research. This section overviews the synthesis and properties of helical polyacetylenes recently reported. 

A full description of polarization-sensitive CARS signal generation that takes the polarization properties of the pump, Stokes, and CARS fields and the tensor character of the nonlinear susceptibility components (cf. (6.5)-(6.7)) into account can be found elsewhere [16]. 

Second, the absorption characteristic of each Rhodonine chromophore is highly directional (15R). This anisotropic absorption is only observed for radiation applied perpendicular to the surface of the film, i.e., parallel to the axis of the Outer Segment. The peak absorption wavelength for resonant absorption by these chromophores is nominally either 342,437, 532 or 625 nm. The chromophore is not polarization sensitive for excitation along this axis. For radiation applied along other axes, such as transverse to the axis of the OS, only the intrinsic absorption characteristic due to conjugate absorption and shared by all retinoids of the Vitamin A Group will be observed. This intrinsic spectrum has a nominal spectral peak at 502 nm at 37C. 

Even in-vivo, careful experimentation using transverse radiation relative to the OS will always exhibit the intrinsic conjugate absorption spectra with a peak near 502 nm. This conjugate spectrum is polarization sensitive. It is maximum when the E-field of the radiation is parallel to the mechanical axis of the individual molecules, generally parallel to the axis of the OS. 

The absorption spectrum of the disk stack is not polarization sensitive to radiation applied perpendicular to the surface of the individual chromophoric films, i.e., along the axis of the OS. There is some data that the individual film layers... 

Because of the unique spatial characteristics of the absorption properties of the chromophores of vision, the literature can be misleading. There are frequent references to the orientation of the chromophores with relation to the surface of the disks (or the axis of the disk stack). These references generally proclaim that the long axis of the chromophores is located in the plane of the disks and are, in order to avoid polarization sensitivity, randomly oriented in that plane (See previous reference to Wyszecki Stiles). Such an assumption is based on the additional assumption that the molecules show maximum sensitivity to radiation applied with a Poynting vector that is perpendicular to the long axis... 

In the end-fire configuration, also known as the slow-wave configuration in antenna theory, the orientation of the E-field of the Poynting vector is irrelevant. To achieve polarization sensitivity, animals use a different chromophore arrangement and orientation, such as rod-shaped microvilli of the arthropod photoreceptor cells. 

Palacios, A. Srivastava, R. Goldsmith, T. (1998) Spectral and polarization sensitivity of photocurrents of amphibian rods in the visible and ultraviolet Visual Neurosci vol. 15, pp 319-331... 

T. Parasassi, E.K. Krasnowska, L. Bagatolli, E. Gratton, Laurdan and prodan as polarity-sensitive fluorescent membrane probes. J. Fluor. 8,365 (1998)... 

The Degree Angular Scale Interferometer (DASI) is a very small interferometric array that operates at 26-36 GHz and the South Pole. After measuring the angular power spectrum of the anisotropy (Halverson et al., 2002) the instrument was converted into a polarization sensitive interferometer which detected the E mode polarization at 5.5a by looking at a small patch of sky for most of a year of integration time (Kovac et ah, 2002). The level agreed well with the solid predictions for adiabatic primordial perturbations. Since the measured quantity was the EE autocorrelation, the 5.5a corresponds to a 9% accuracy in the polarization amplitude. 

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