Immobilization of ion channels requires of a methodology able to retain the physical properties of the lipid bilayer where their activity is performed. However, most of lipid membrane immobilization methods have been observed to alter the structural properties of the bilayers. Use of sol-gel routes seems to be an interesting alternative, although unstable liposomes were obtained when conventional sol-gel methodology was employed for immobilizing. Recently, we have suggested that use of alcohol-free sol-gel routes combined with negatively charged lipids could minimize effects exerted by host matrix on liposome structure, increasing its stability. Here we confirm this assumption by analysing the physical properties of a series of zwitterionic and anionic liposomes entrapped in a sol-gel matrix and we develop a methodology able to retain the physical properties of the lipid bilayer. This methodology has been successfully used to immobilize the transmembrane ion channel peptide gramicidin. Gramicidin was reconstituted in anionic liposomes and its immobilization was confirmed from changes observed in the photophysical properties of the tryptophan residues. Ion channel activity was determined using the fluorescent dye pyrene-1,3,6,8-tetrasulphonic acid (PTSA) and long term stability of the immobilized system was checked from steady-state fluorescence anisotropy measurements.
Most of the conjugated polymer employed as fluorescent biosensors present low solubility and emission in aqueous
environment. In order to solve this feature, we have reconstituted, in buffer phosphate, a neutral conjugated poly[9,9-
bis(6'-bromohexil)-2,7-fluorene-co-alt-1,4-phenylene], as PFPBr2 (insoluble in water), in the presence of an artificial
zwitterionic phospholipids bilayers, as 1,2-dimyristoyl-sn-glycero-3-phospho-choline (DMPC). Quantum yield of
PFPBr2-DMPC was around 20% in phosphate buffer, it was identical value calculated from ammonium polyelectrolytes
(PFPNMe3+). In addition, the maximum of bluish emission for buffer solution of PFPBr2-DMPC was at 420nm, a red-shift emission with regard to chloroform solution (at 410 nm). The structural study at different concentrations of PFPBr2
and DMPC was carried out using different approaches: steady state fluorescence spectroscopy, confocal fluorescence
microscopy and calorimetry. A positive interaction takes place involving neutral conjugated polymer and zwitterionic
phospholipids bilayer. Novels complexes or associations of poly(fluorene-phenylene) (PFPBr2) and zwitterionic
phospholipids (DMPC) have been suggested and visualized by epifluorescence. Phase transitions of the liposomes have
been also detected by differential scanning calorimetry.
In this work, 4x4 organic light emitting diode passive matrices based on new poli(2,7-fluorene phenylidene) (PFP) derivatives have been developed. The fabrication process has involved spin-cast heterostructures that improve charge carrier injection, processing of devices by means of photolithography, together with metallic contact evaporation. Electroluminescent diodes using different polymer derivatives as active layer, and different geometries, have been fabricated and compared. Electrical characterization was carried out in terms of pulsed current-voltage (I-V) measurements. Dependence of the threshold voltage on active material and structural parameters is obtained from the I-V curves, yielding values from 10 V to 25 V. Electroluminescence spectra recorded from the new PFP based devices, as well as commercial polymers, are in good agreement with similar devices found in literature. Finally, experimental data have been fitted using a theoretical model considering several injection and transport mechanisms, including thermionic, reverse, tunnelling, ohmic and space charge limited currents.
Multilayer structures of alternating polymers, poly(9-vinylcarbazole) and poly(vinyl alcohol), with reflectance peaks centered in the range 500 - 610 nm, have been deposited on silica glass subtrates by spin-coating. The dependence of their reflectance, transmittance and absorbance on the incident wavelength have been characterized by spectrophotometry. Feedback from a similar characterization on thin single layers (≈ 100 nm), together with the evaluation of thicknesses by a non-contact profilometer, have provided the input parameters to modelize numerically the spectral response of structures with 5 or 10 pairs of layers. Despite the approximations assumed, good agreement among theory and experiment has been achieved, opening the way to perform easy and inexpensive resonant cavities, in which the properties of spontaneous emission might be controlled. (Summary only available)
We present the results of the study as holographic recording material of aphotopolymerizable mixture of polyvinyl alcohol and acrylamide, with a photo initiator system formed by a 1:1 molar mixture of the anionic dye Rose Bengal (RB) and the cationic one Methylene Blue (MB), with triethanolamine as coinitiator. Under irradiation with 514 or 633 nm light and comparative conditions, photopolymers with this photo initiator system give rise to a clear sensitivity enhancement, with regard to the use of any of the dyes alone. Still higher enhancements were achieved using as absorbing component an isolated ion-pair from the 1:1 mixture of both dues, with some different properties than those of the physical 1:1 mixture of dyes. Maximum diffraction efficiencies of 35-64 percent with 30-100 mJ.cm-2, and spatial resolution of ca. 1000 lines.mm-1, could be reached. The photo initiator mechanism using either the mixture RB/MB or the isolated ion-pair RB-MB is likely based on charge-transfer processes from the excited chromophores, that seems to be favored in the case of the ion-pair.
Evaluation of the mechanical properties of films of the materials currently employed for recording diffractive optical elements is very important in order to foresee their mechanical behavior during the photochemical processing following recording of the interference pattern. This will also provide information about the mechanical and thermal stability of holograms recorded on these materials, which may be tested in the different environments in which the final application of the optical elements will be used. For quantitative evaluation of these properties in an acrylamide based photopolymeric system, a study was carried out on layers of films of polyvinylalcohol and polyvinylalcohol mixed with triethanolamine. Layers coated on glass substrate were subjected to both a high vacuum and temperature changes. Real time measurements of optical path variations in the film were performed using a vacuum interferometric measurement system.
The response curve D-Log E is the most important method to characterize photographic emulsions. In this work we present the experimental study using a real time technique that can be applied to the improvement of the holographic properties of emulsions. We have exposured an Agfa Gevaert 8E56HD emulsion with an Argon laser tuned at 514 nm. After it, we measured the transmittance curve when the emulsion was into the developer bath function of time at 20 degrees Celsius. This method gives us the possibility of study the dynamics of different developers as a function of the storage energy. It also provides a way to optimize the composition of developers function of the chemical composition, temperature and other secondary factors as superaditivity and non-linear processes.
The spectral sensitivity and the enhancement of the energetic sensitivity are important points to the optimization of photopolymerizable materials. We have studied a polymeric system based on polyvinylalcohol as binder, monomers as acrylamide and dihydroxyethylenbisacrylamide and a photoinitiator system composed by triethanolamine and methylene blue. This system was irradiated with an Ar+ laser tuned at 514 nm, where this material do not absorb. Obtaining diffraction efficiencies of 55% with an energetic expositions of 500 mJcm-2. A possible mechanism of initiation of the photopolymerization process has been proposed by the presence of semireduced methylene blue that has an absorption band at 520 nm.
We study the effect of the addition of a crosslinking agent in a photopolymerizable matrix for real time holography. The optimization of the concentration of this component has been realized attending to the holographic parameters like energetic sensitivity and diffraction efficiency. Diffraction efficiencies near to 80 percent have been obtained with energetic exposures of 12 mJ/cm2.
The quantum efficiency and molar absorption coefficients of dyes are the responsible for holographic efficiency and sensitivity in a photopolymeric holographic recording material. These parameters have been obtained by fitting the experimental transmittance curves as function of time. For this using the mechanism of photo initiation an analytical expression for the transmitted intensity in a photopolymerizable holographic material has been proposed, obtaining good agreement between theory and experience.
New holographic recording material based on photopolymerizable systems have contributed significantly to recent growth of holographic applications. Previously, we report that on photopolymerizable system with the presence of the difunctional monomer, ethylene glycol dimethacrylate improves the behavior of the system and particularly to elucidate the role played by eosin ester with oxooxime group in the production of amine initiator radicals. This comparative study has been carried out in our laboratory using differential scanning photocalorimetry and holography. The results of the new photosensitive recording material for holography indicate that this system can be used for the formation of very promising photopolymer with better performance. The aim of this work has been changed the crosslinking monomer to decrease the energetin sensitivity and know the rest of the behavior. The new photopolymerizable mixture containing pentaethritol triacrylate in the same relation with the ethylene glycol dimethacrylate mixture. A diffraction efficiency of 80% is achieved with a energetic sensitivity of 3 J/cm2 at 514 nm, and the spatial resolution is up to 2000 l/mm.
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