Immunoassay evanescent wave

The detection of flu viruses via a fluorescent sandwich immunoassay was reported by Bucher.(10) However, the method sensitivity was too low for direct detection of the virus. A novel sandwich immunoassay was described by Ogcr((lff7 for the detection of Botulinum Toxin A. Antibodies specific for Clostridium botulinum were covalently attached to the surface of a tapered fiber. After the capture of the antigen, a sandwich was formed with a rhodamine-labeled anti-toxin IgG, and the evanescent wave was measured. The assay was highly specific with detection limits near 5 ppb. 

An example of an evanescent wave fiber optic immunoassay and the associated optics has been described in detail for measurement of anti-rabbit IgG.(130) Rabbit antibody is immobilized on the distal face of an optical fiber. Unlabeled anti-rabbit IgG competes with fluorescein-labeled anti-rabbit IgG for rabbit antibody binding sites... 

R. Sutherland. C. Dahne, R. Slovacek, and B. Bluestein, Interface immunoassays using the evanescent wave, in Alternative Immunoassays (W. P. Collins, ed.). pp. 331-357, John Wiley Sons, New York (1985). 

The utihzation of fluorescence dyes for analytical measurements enhances the sensitivity for the detection of the molecules of interest. First, Cronick and Little made use of evanescent wave excitation for a fluorescence immunoassay, in 1975. By using totally internally reflected light, they excited the fluorescence of a fluorescein-labeled antibody which has become bound to a hapten-protein conjugate adsorbed on a quartz-plate in an antibody solution [41]. Contrary to the label-free high-refractive-index sensors where the mass of the molecule of interest is... 

Immunochromatography, colloidal gold, silver enhancement 10 minutes Evanescent wave fiber-optic immunosensor Colorimetric and chemiluminescence ELISA Immunochromatography, colloidal gold, silver enhancement 10 minutes Sandwich hybrid receptor-immunoassay,... 

This chapter describes an evanescent wave fiber optic biosensor and its application to immunoassays for rapid detection of bacterial cells and pollutants. Whole cells of Burkholderia cepacia G4 5223-PRl (G4) are of interest for their ability to degrade trichloroethylene (TCE) which is one of the most prevalent contaminants of ground water in the United States. The lower limit of detection of the G4 with this system is 10 - 10 cells/ml. In addition to TCE, the explosive trinitrotoluene (TNT) is a known contaminant of ground water. Limits of detection of TNT with this system is 10 ng/ml. 

What is possible, however, is a technique which weights each of these properties in accordance to its importance in a given application. The use of immunoassays in conjunction with an evanescent wave fiber optic biosensor is a unique way of balancing the demands for specificity, sensitivity, rapidity, adaptability, and simplicity. 

Simultaneous with the light s reflection off the internal surface of the fiber is the creation of an electromagnetic field at the external surface of the fiber core. This field extends into the surrounding media and is called the evanescent wave. The intensity of the field decays exponentially as the distance from the surface of the probe increases. The effective distance this field penetrates the external media is less than one wavelength of light and is very sensitive to the incident angle the refractive indexes of the internal media (n ), and external media (n2). For the typical optical fiber used in an immunoassay with a fused silica core surrounded by an aqueous media, the penetration depth of the evanescent wave is on the order of 100 nm. 

A pTAS must miniaturize the steps listed above (and any we may have omitted). There are two types of methods to do this. First, try to miniaturize the existing components used to accomplish these steps. Second, find new methods that accomplish the same result in a novel way appropriate to a pTAS. In the first family would be efforts to make microvalves and pumps, that move solutions around, mix them, and thereby miniaturize conventional chemistry. Homogeneous immunoassays involve efforts to find non-solution equivalents, such as controlled release of encapsulated reagents [14], or virtual separation using an evanescent wave optical signal [15], and are thus in the second category. 

Recently, a novel approach for the detection of Clostridium botulinum neurotoxins was developed (Ogert et al., 1992). This technique involved a two-step sandwich immunoassay utilizing an evanescent wave of light to excite fiuorescently labeled antibodies bound to type A toxin captured on the surface of antibody immobilized fibers. Despite the many... 

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