Evanescent excitation

T. P. Burghardt and N. L. Thompson, Effect of planar dielectric interfaces on fluorescence emission and detection Evanescent excitation with high aperture collection, Biophys. J. 46, 729-737 (1984). 

J. D. Andrade, W. M. Reichert, D. E. Gregonis, and R. A. VanWagenen, Remote fiber-optic biosensors based on evanescent-excited fluoro-immunoassay Concept and progress, IEEE Trans. Electron Devices ED-32, 1175-1179 (1985). 

Fluorescence from labeled adsorbed protein has also been excited with the evanescent surface wave created by integrated optics. Both optical fiber I60) and flat rectangular waveguides193) have been used. Interesting use of optical fiber as a remote protein sensor was demonstated the excitation light was sent down the fiber whose tip was immersed in protein solution, evanescently excited fluorescence was collected by the same fiber and delivered to a scanning monochromator 160). 

Duveneck GL, Neuschafer D, Ehrat M (1995) Process for detecting evanescently excited luminescence. International Patent GolN 21/77, 21/64... 

For example, several strategies have been used for immunoassay techniques with fiber-optic biosensors. In the sandwich format, the receptor is immobilized on the stu"face of the fiber waveguide and a secondary or tracer antibody (which is labelled with a fluorescent dye) is added to the solution. In the absence of the analyte, the tracer remains in solution and little fluorescence is observed. However, after addition of the analyte, a molecular sandwich is formed on the sensor smface within the evanescent excitation volume. The sandwich assay is usually more sensitive than a competitive-binding assay because the fluorescence intensity increases with analyte concentration. 

Figure 3. Collected power versus fluorophore position. The glass coverslip (z < 0) has a refraction index of 520 and the water sample 1.335, respectively. In the region of an evanescent excitation field (z < the trans-illumination setup I with aNAof 1,20 collects less power (dotted curve) than the epi-illumination reference system (Pq ), whereas the epi-illumination setup II with aNAof 1,45 collects two times more power (solid curve).

The production rate of a single enzyme can be observed by detecting the Rhl23 emission at the single enzyme-single molecule level. As the evanescent excitation confines the excitation to the surface-immobilized enzyme, the... 

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