Sandwich methods

The extent of bleeding in a plastic is evaluated with a test known as the sandwich method. The test sample is placed between a white, smooth surface of plasticized PVC on the top and a standardized sheet of filter paper underneath. The resulting sandwich is then placed between layers of foam material, which in turn are covered by glass plates. The resulting sandwich is allowed to remain in an exposure chamber at 50°C for 72 hours [48]. 

Massayeff, R. and Maillini, R. (1975) A sandwich method of enzyme immunoassay. Application to rat and human a-fetoprotein. J. Immunol. Methods 8,223-234. 

There are certain specimen preparations that create problems for some of the sandwich methods. Frozen or fresh cell preparations may have inherent avidin-binding properties, as some fixed preparations can have. While this should not preclude the use of these methods, one should be aware of the potential limitations and have alternate methodologies available for confirmatory testing. 

Vodakhov, Y. A., et al., Doping Peculiarities of SiC Epitaxial Layers Grown by Sublimation Sandwich-Method, Springer Proc. Phys., Vol. 56, 1992, pp. 329-334. 

Among the many immunological assay methods, the enzyme-linked immunosorbent assay methods (ELISA) are the most popular methods. ELISA can detect both antigen molecules and antibody molecules with only a slight modification of the procedure. The direct-binding and sandwich methods that are used for the... 

When usingthe sandwich method (Figure 11.12b), the antibody molecules specific to a target antigen were first bound to the surface of a well. Then, after washing... 

Figure 11.12 Schematic figures of ELISA (a) direct-binding method and (b) sandwich method.

The second method is sandwich method which was developed from the two-layer method and used first for the analysis of the single mammalian cell lysates [67], The first thin layer is formed by the matrix-only solution. It is followed by deposition of the analyte solution and then deposition of second layer of matrix on the top of analyte layer. The sample is basically sandwiched between the two matrix layers and preparation results in a matrix-sample-matrix sandwich. This method is specifically used for detecting protein and peptides [67-69], The three-layer matrix-sample preparation method was also used as matrix-matrix-sample mode [70],... 

Vodakov et al [9] grew 15 mm free-standing GaN crystals using the sublimation sandwich method with sapphire and SiC as seeds. The FWHM of 00.4 reflection was 430 - 520 arc sec. 

In this Datareview, bulk growth of GaN and AIN by a sublimation method and of GaN by a sublimation sandwich method is described. The source powder was analysed. The bulk GaN obtained was characterised by XRD (X-ray diffraction), TEM (transmission electron microscopy), and so on. 

The sublimation sandwich method (SSM) is similar to the sublimation method, except for the small distance between source powder and substrate, 2-5 mm [10-12], Ga or GaN was used as a source and the substrate was sapphire or 6H-SiC. The optimal growth temperature was around 1200°C as temperatures lower than 1150°C caused the formation of structural defects such as voids and micropipes. Polycrystalline GaN was grown under 1050°C. At higher temperatures, GaN was thermally decomposed. The growth rate is much higher, up to 300 pm/hr [10] or 0.2 - 1.1 mm/hr [12], and crystalline GaN with the maximum thickness of 500 pm could be obtained. 

Bulk growth of GaN and AIN has been achieved by a sublimation method and a sublimation sandwich method. Bulk GaN and AIN bulk crystals were proved to have high crystallinity. It will improve the quality of nitride-based optoelectronic devices, if these bulk crystals are used as substrates for homoepitaxial growth. The size of the bulk GaN, however, is not large enough at this moment, and enlargement of bulk GaN may be necessary. 

Fluorescence Excitation Transfer. This modified-sandwich method (shown in Eq. 6.7) has both antibodies labeled, but with different fluorophores (FI and F2) that are chosen so that the emission spectrum of one overlaps with the excitation spectrum of the other. Internal quenching thus occurs when FI and F2 are held in close proximity. If FI and F2 are close, the emission of FI is quenched... 

Zhang J et al (2012) Extracellular matrix promotes highly efficient cardiac differentiation of human pluripotent stem cells the matrix sandwich method. Circ Res 111 (9) 1125-1136... 

The use of two different antisera in sandwich methods may increase specificity in AA assays. 

The anti-IgG nature of RF and the high detectability of ElA may be responsible for high background reactions in sandwich methods (Section 14.2.2) which, however, can be reduced to insignificant levels using different methods (Section 14.5.2). 

Crook and Payne (1980) compared the direct (Section 14.2.1.1), indirect (Section 14.2.1.2) and the double-antibody sandwich methods (variant A) for their ability to detect and discriminate between several granulosis viruses. The indirect method was the most sensitive (1 ng/ml), the direct method was the least sensitive (15 ng/ml) and method A had an intermediate detectability (10 ng/ml). 

Nakagami et al. (1991) proposed a different universal probe system. In their procedure, phagemids are used to obtain strand-specific ss DNA molecules, one with the insert complementary to the target sequence and a second without the insert and with the opposite polarity (Fig. 7.23). The ss DNA without insert is labeled with any label (usually a secondary label) and this labeled DNA is hybridized with the complementary strand containing the insert. This leaves only the probe sequence ss whereas the tag sequence is ds. This method has several advantages (i) like the sandwich method it leaves the probe sequence single-stranded (ii) hybridization of the tag sequences in solution instead of on the solid phase as in a sandwich assay is much faster (iii) no fragmentation is required. 

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