Sensitive layer

Imaging plates are exposed similar to radiographic films. They are read out by a LASER-scanner to a digital image without any developing process. After optical erasing of the virtual picture the same IP can be used cyclic up to more than 1000 times. The life time is limited by the mechanical stability of the IP s. An IP consists of a flexible polymer carrier which is coated with the sensitive layer. This layer is covered with a thin transparent protective foil. 

The sensitive layer of the systems under investigation eonsists of a mixture of BaFBr with Eu dotation. Other systems are available in the mean time too. X-ray- or y-quants initiate transitions of electrons in the crystal lattice. Electrons are excited from the valence band to the conduction band [2]. Electrons from the conduction band are trapped in empty Br -lattice places. They can return to the valence band via the conduction band after an excitation by... 

The initiation of development in the activator solution is more rapid than in conventional processes because the developer molecules need not diffuse into the light-sensitive layers from the processing solution. In spite of the low activity of the coated developer, some unintentional reduction sensitization may occur, which produces unwanted fog. Therefore, coating the developer in a separate layer usually is preferred. Because of simplicity, rapid access, and solution stabihty, incorporated developer papers have been used for office copying appHcations. 

Negative image in red-sensitized layer Metallized cyan dye developer layer... 

Fuji Peel-Apart Film FP-100. In 1984 Fuji introduced FP-lOO, a peel-apart instant color film rated at ISO 100. The FP-lOO system uses a dye-release process similar to that used in the Fuji integral films. Figure 16b is a schematic cross section of FP-100, and Figure 11b (on the colored plate) is a micrograph of the unprocessed film in cross section. The negative stmcture includes a spacer layer between the red-sensitive layer and the cyan dye-releaser layer that it controls, similar to that shown in the FI-800 stmcture, but there are no spacers between the other emulsions and corresponding dye-releaser layers. 

NANOSCALE LANGMUIR-BLODGETT FILMS AS SENSITIVE LAYERS OF CHEMICAL SENSORS... 

Thermal recording materials consist of a heat-sensitive layer made by dispersing a leuco triphenylmethane dye and a phenol in a binder where the... 

Square-planar ds platinum complexes could perhaps be used as the chemically sensitive layer for a chemical sensor system. These complexes are robust and form colored solid-state materials that respond spectroscopically to a wide range of volatile organic compounds (VOCs) this process has been named vapochromism. The vapochromic shifts occur in the solid-state UV-vis,... 

Haley, N. F. Corbiere. S. L. Method of Making a Lithographic Printing Plate Containing a Resole Resin and a Novolac Resin in the Radiation Sensitive Layer. U.S. Patent 5,372,915, December 13, 1994. 

Figure 3. First fiber optic chemical sensor (from ref. [17] used for sensing oxygen). Alos shown is a cross-sedction of the fiber bundle used. 6 light source 9 photodectectors 16 chemically sensitive layer.

To overcome this drawback, capillary sectorial fibres (Figure 11) were fabricated31. In this case part of the preform ground to the designed shape was inserted into a circularly symmetric silica tube and drawn. The active length of the sensor is defined by the distance between the input and output of the analyte produced in the capillary wall by special diamond tools. Despite promising results achieved, difficulties in the application of sensitive layers on the core surface remain a drawback of this kind of fibres and the... 

Fluorescence resonance energy transfer (FRET) has also been used very often to design optical sensors. In this case, the sensitive layer contains the fluorophore and an analyte-sensitive dye, the absorption band of which overlaps significantly with the emission of the former. Reversible interaction of the absorber with the analyte species (e.g. the sample acidity, chloride, cations, anions,...) leads to a variation of the absorption band so that the efficiency of energy transfer from the fluorophore changes36 In this way, both emission intensity- and lifetime-based sensors may be fabricated. 

Navarro-Villoslada F., Orellana G., Moreno-Bondi M.C., Vick T., Driver M., Hildebrand G., Liefeith K., Fiber-Optic Luminescent Sensors with Composite Oxygen-Sensitive layers and Anti-Biofouling Coatings, Anal. Chem. 2001 73 5150-5156. 

With consideration to the quality of a bio or chemosensor it is therefore necessary to discuss the transduction principle, the quality of the sensitive layer and the data evaluation. These three issues will be discussed in this paper, with the focus on interferometric principles in the area of non-specific measurements using chemosensors and specific interaction processes in the case of biosensing. 

Since the quality of a sensor and its application depends on all components of the sensor system, optical transduction, sensitive layers and chemometrics will be discussed in more detail in dependence on the different approaches. In the final chapter, quite a few applications will demonstrate the feasibility and the quality of such bio or chemosensors. Since miniaturisation and parallelisation are further essential topics in these applications, these approaches will be included. 

After discussing various sensitive layers later, both principles will be applied to monitor effects in biomolecular or chemical sensitive layers. The applications will demonstrate the feasibility of the methods as well as their advantages and their disadvantages. Therefore various applications are given, sometimes even for the same analyte, in order to demonstrate the normal approach in sensor development to select the best transduction principle for a specific application. 

For the quality of a sensor, not only the transduction is essential but also the sensitive layer. In addition, it determines selectivity sensitivity, stability... 

Accordingly, in Figure 8 sensitive layers can demonstrate either a higher reversibility or a higher selectivity. In combination with these properties, polymers usually show a high reversibility since they have poor selectivity and since they are relatively stable in contrast to biomolecular receptor layers where the selectivity and the sensitivity are high, but where the stability is rather poor as is reversibility. 

Notice, that with these extremely good resolutions in case of surface sensing contamination of the sensitive layer with solid particles has to be avoided completely, e.g. by an appropriate filtering of the sample solutions. Notice also that the temperature coefficient of the refractive index of water is about 10-4 per °C. So if applying the surface sensing mode using watery solutions indeed a perfect balance of both branches and low temperature gradients have to be aimed at. 

The other sensor makes use of two dyes, bromophenol blue (BPB) and thymol blue (TB), to cover the range of interest26. The chromophores, immobilised on controlled pore glasses, are fixed at the end of plastic optical fibres. The distal end of the fibres is then heated and the CPGs form a very thin pH-sensitive layer on the fibre tips. The probe has four fibres (two for each chromophore) and its sketch is shown in Figure 5. A Teflon diffuse... 

The first LAPS utilized silicone nitride (S3N4) as a pH-sensitive layer [68], A light-addressable high resolution pH imaging sensor was applied to the detection of spatially resolved metabolic activity of Escherichia coli colonies on agar medium [69], For a silicone substrate thickness of 20 pm the reported spatial resolution was about 10 pm. The observed pH distribution was in good agreement with the results of simulation based on a two-dimensional diffusion model. 

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