Fibre configuration

Spectroscopic techniques are popular as a means of detection on chips. Examples include the determination of flavins and DNA by fluorescence. Spectrophotometric techniques are often used for biological samples . Mass spectrometry has also been used. Benetton et al. coupled electrospray ionisation MS to a chip while Sillon et al. developed a low cost mass spectrometer which incorporated the ionisation chamber, filter and detector on the chip. A fibre optic coupler has been developed as a detector. The dual optical fibre configuration (one transmitting, one receiving, (Eigure 10.5)) in the chip forms the microchannel as well as the detector itself and measures refractive index changes but can also be used to measure absorbance . 

Figure 10.5 / dual optical fibre configuration can serve as both microchannel and detector. 

Acoustics strong damping of resonance frequencies, even enhanced by isotropic fibre configuration (beneficial for loudspeaker applications). 

A dual-fibre optical probe has been developed for Raman spectroscopic monitoring of a number of polymer processes. In the dual-fibre configuration the internal bundles transmit the light to the sample and the outer fibres carry the signals back to the spectrometer for processing. 

The second way to increase the membrane area per volume of reactor is adopting the hollow fibre configuration. For example, in the case of perovskite membranes, the membrane flux is generally quite low and the hollow fibre configuration is quite interesting. The main investigators of hollow fibre MRs are summarized in Table 3.3. 

The fibre volume fraction depends heavily on the method of manufacture. A uni directional composite may have a fibre volume fraction as high as 75%. However, this can only be achieved if all the fibres are highly aligned and closely packed. A more typical fibre volume fraction for uni directional composites is 65%. If the fibre configuration is changed to put fibres in other directions, then the maximum fibre packing is reduced further. A typical fibre volume fraction for bi-directional reinforcement (woven fibre) is 40% and a typical volume fraction for random in-plane reinforcement (chopped strand mat) is 20%. 

Despite the wide availability of flat-sheet membranes and the impressive permeability they offer, the hollow fibre configuration is usually preferred due to its high packing density. The membrane surface area of commercial hollow fibre membrane modules varies in the contactor volume range of 1500-3000 m /m (Kumar et al, 2002), whereas in conventional contactors (bubble column, packed and plate columns) it is in the range of 100-800 mVm. Table 2.4 clearly shows that MC offers a much larger contact area per unit volume than other conventional absorbers (Yan et al, 2007). 

Simulation of Supported Liquid Membranes in Hollow Fibre Configuration... 

The manner in which the fibres are assembled into a web has profound effect on the web properties. The fibre configuration will have an effect on packing, pore size, capillary dimensions, capillary orientation, etc. The absorbency properties of the nonwoven stmcture can also be expected to be sensitive to the nature of fibre arrangement in the web. Web formation can also be supplemented by localized rearrangement of fibres rendering bundling of fibres, which enhance the fabric wicking capabilities. 

Figure 3.6 Partially debonded fibre configuration and the interfacial shear stresses to calculate combined elastic and frictional resistance to pull-out.

Principles and Characteristics Solid-phase microextraction (SPME) is a patented microscale adsorp-tion/desorption technique developed by Pawliszyn et al. [525-531], which represents a recent development in sample preparation and sample concentration. In SPME analytes partition from a sample into a polymeric stationary phase that is thin-coated on a fused-silica rod (typically 1 cm x 100 p,m). Several configurations of SPME have been proposed including fibre, tubing, stirrer/fan, etc. SPME was introduced as a solvent-free sample preparation technique for GC. 

Another approach, developed in our laboratory, consists of the compartmentalization of the sensing layer25"27. This concept, only applicable for multi-enzyme based sensors, consist in immobilizing the luminescence enzymes and the auxiliary enzymes on different membranes and then in stacking these membranes at the sensing tip of the optical fibre sensor. This configuration results in an enhancement of the sensor response, compared with the case where all the enzymes are co-immobilized on the same membrane. This was due to an hyperconcentration of the common intermediate, i.e. the final product of the auxiliary enzymatic system, which is also the substrate of the luminescence reaction, in the microcompartment existing between the two stacked membranes. 

Since ideally, a biosensor should be reagentless, that is, should be able to specifically measure the concentration of an analyte without a supply of reactants, attempts to develop such bioluminescence-based optical fibre biosensors were made for the measurements of NADH28 30. For this purpose, the coreactants, FMN and decanal, were entrapped either separately or together in a polymeric matrix placed between the optical fibre surface and the bacterial oxidoreductase-luciferase membrane. In the best configuration, the period of autonomy was 1.5 h during which about twenty reliable assays could be performed. 

All of the above trends make a planar platform configuration the ideal choice for the development of such sensors due to the compatibility of this geometry with a range of microfabrication technologies, the availability of low-cost materials for the production of such platforms and the robust nature of planar configurations when compared with alternatives based on optical fibres. 

Astbury, W. T. Street, A., X-ray Studies of the Structure of Hair, Wool and Related Fibres. I. General. Trans. R. Soc. London 1931, A230,75 Astbury, W. T. Woods, H. J., II. The Molecular Structure and Elastic Properties of Hair Keratin. ibid. 1934, A232, 333 Astbury, W. T. Sisson, W. A., III. The Configuration of the Keratin Molecule and its Orientation in the Biological Cell, Proc. R. Soc. London 1935, A150, 533. 

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