Sol-gel-layer

For trace analysis in fluids, some Raman sensors (try to) make use of the SERS effect to increase their sensitivity. While the basic sensor layout for SERS sensors is similar to non-enhanced Raman sensors, somehow the metal particles have to be added. Other than in the laboratory, where the necessary metal particles can be added as colloidal solution to the sample, for sensor applications the particles must be suitably immobilised. In most cases, this is achieved by depositing the metal particles onto the surfaces of the excitation waveguide or the interface window and covering them with a suitable protection layer. The additional layer is required as otherwise washout effects or chemical reactions between e.g. sulphur-compounds and the particles reduce the enhancement effect. Alternatively, it is also possible to disperse the metal particles in the layer material before coating and apply them in one step with the coating. Suitable protection or matrix materials for SERS substrates could be e.g. sol-gel layers or polymer coatings. In either... 

In order to verify the enhancement provided by the cones, a sol-gel layer doped with a fluorescent ruthenium complex was deposited onto a chip in a configuration similar to that shown in Figure 15. Blue LED excitation of the fluorescent sol-gel layers was employed. The resultant fluorescence was recorded using a CMOS camera and the resultant image is shown in Figure 16. 

The bright rings surrounding lower intensity spots correspond to the additional fluorescence signal from the sol-gel layer on the surface of the cones. The isolated spots (i.e., those without a surrounding ring) correspond... 

The pH optical fiber sensor without any pH-sensitive dye was also described70. Porous silica layer made by the sol-gel method was cladded onto optical fibre core and was exploited as the optical transducer. Acid-base properties of silica surface caused that the surface charge of silica changed with pH of the solution. For example saturation of the sol-gel layer with cations leads to an increase of the electron density of the film, hence, the refractive index of the film. Since the surface charge of silica depends on pH, the refractive index of silica film varies also with pH. Thus, changes of... 

The design and implementation of a portable fiber-optic cholinesterase biosensor for the detection and determination of pesticides carbaryl and dichlorvos was presented by Andreou81. The sensing bioactive material was a three-layer sandwich. The enzyme cholinesterase was immobilized on the outer layer, consisting of hydrophilic modified polyvinylidenefluoride membrane. The membrane was in contact with an intermediate sol-gel layer that incorporated bromocresol purple, deposited on an inner disk. The sensor operated in a static mode at room temperature and the rate of the inhibited reaction served as an analytical signal. This method was successfully applied to the direct analysis of natural water samples (detection and determination of these pesticides), without sample pretreatment, and since the biosensor setup is fully portable (in a small case), it is suitable for in-field use. 

To reduce further the pore size and/or to introduce specific interactions between the solid surface and the liquid or gaseous medium in the pores, sol-gel layers need to be modified. In principle this is done by precipitation or by adsorption of components from a gaseous or liquid medium followed by heat treatment of the formed products inside the pores or the pore entrance. This will be further discussed in Section 2.7. 

Immobilization of nanoparticles and enzymes onto electrode surfaces using various entrapment chemistries, that is, sol-gels, layered polyions, and hydrogels, has allowed for greater functionality and improved stability. Crumbliss and coworkers demonstrated the direct electron transfer between the redox center of HRP by evaporation... 

Surface Activation of PMR-15 by sulfonation has been described.17 BMI surfaces were made hydrophilic by surface oxidation with UVOCS and/or depositing a sol gel layer of Si02.18 Kapton surfaces were activated with a UVOCS cleaner or by air-plasma. Their water contact angle fell from 64° to 0°. 

An optical sensing device for surface plasmon resonance (SPR) was proposed for determination of the concentration of phenolic compounds in water. The phenols become adsorbed on a thin gold or silver film that has been spin-coated with a sol-gel layer containing receptor molecules. Best SPR signals for phenolic compounds were obtained when the receptors were viologen-type polymers with polymeric counterions (179). The SPR signal intensity was concentration dependent and had to be calibrated for individual phenolic compounds . ... 

Write et al. explored direct detection of various phenohc compoimds (phenol, hydroquinone, resorcinol, phloroglucinol, and catechol) using an SPR sensor with intensity modulation and synthetic receptors loaded in a polymer or sol-gel layer [39]. Their preUminary experiments, consisting of the detection of phenols in buffer, suggested that detection of phenols at mUlimolar concentration levels ( 100 iJigmL ) is feasible using this approach. 

Figure 3. Micrographs of sol-gel YSZ layers (a) fracture surface of intermediate sol-gel layer (b) fracture surface of top sol-gel layer on sintered intermediate electrolyte layers, (c) surface of top sol-gel layer, fired at 600 °C (d) surface of top sol-gel layer with large pores, fired at 1040 "C,...

The helium leakage value was tested on the half cells in the oxidized state before the coating of cathode. Helium is suitable to be used as the test gas because its molecular is smaller than all the gases under the operation condition of SOFC cells. The helium flowed through the half cell at a pressure difference of 1000 hPa. The shown values in this test were normalised to the measurement area and to a pressure difference of 100 hPa, which was typical for an SOFC stack. One large squared area of 16cm was measured per cell. The leak rate value of samples without polymeric sol-gel layers was around 5-10" (hPa dmV(s cm ). By applying a polymeric sol-gel layer on top of the colloidal-sol-derived intermediate layers, the leak rate value of samples was improved to 1.5-10 (hPa dm ( s cm ). 

Despite the above-mentioned advantages of cerium oxide and a-alumina especially for the conversion of alcohols, a wide variety of investigations have dealt with alkene conversion on y-alumina-supported active species [16, 28, 41]. For sol-gel layers, which can also be used as a support for CPO [8], the determination of the aluminum phase is often not reported (e.g. [42]) as calcination temperatures between 300 and 700 °C could result in a considerable contribution of amorphous phases to gamma phases and at 800-1000 °C there is an additional transition to a delta phase [43]. 

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