Streptavidin 312 INDEX

Guided mode calculations were also carried out to compare the sensor response of several waveguide systems. In these simulations a model molecular monolayer is represented by a 2-nm thick layer with a refractive index of n 1.5. The optical properties of this model layer are typical of a dense layer of organic molecules on a substrate1 41, and are a reasonable approximation for a streptavidin protein layer bound to a biotinylated surface, the experimental model system we use to characterize our sensors. The ambient upper cladding was assumed to be water with a refractive index of n 1.32. For all examples, the lower cladding was assumed to be Si02 with an index of n 1.44. In the simulations, the effective index of... 

We (K1) attempted to develop a noncompetitive assay based on the anti-idiotype antibodies for a conjugated bile acid metabolite, ursodeoxycholic acid 7-A-acetyl-glucosaminide (UDCA 7-NAG), which is expected to serve as a diagnostic index for an autoimmune disease, primary biliary cirrhosis. In our assay, the hapten UDCA 7-NAG, a /3-type antibody, and a biotin-labeled a-type antibody were simultaneously added to a microtiter plate coated with an F(ab )2 fragment of a specific anti-UDCA 7-NAG antibody, then incubated at room temperature for 8 h. Bound biotin was then detected with HRP-labeled streptavidin, whose enzyme activity was measured using o-phenylenediamine/H202 as a substrate. This noncompetitive assay system provided a subfemtomole-order sensitivity (detection limit 118 amol) that was 7 times lower than the competitive immunoassay using the same anti-hapten antibody (K2), even with a common colorimetric detection (Fig. 13). Somewhat improved specificity was also obtained namely, better... 

Colorimetric resonant reflection Si3N4 [31] 3.4 X 10 An (determined by solvents with defined refractive index) 0.4 pg/ mm dried BSA 0.1-1.0 ng/mL streptavidin to immobilized biotin... 

Surface plasmon resonance (SPR) allows monitoring label-free interactions between biomolecules in real time. In SPR measurements, one of the biomolecules is immobilized on a sensor surface and the other one is transported in solution across the surface. Binding of the second biomolecule will cause an increase in mass and a proportional increase in refractive index that can be monitored. Gold surfaces are the most commonly used ones and they can be modified or functionalized for the specific binding of particular molecules. For example, biotinylated surfaces enable the immobilization of streptavidin-labeled proteins, and surfaces modified with lipophilic groups allow the immobilization of vesicles creating membrane-like structures to study protein association and dissociation with membranes. 

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