Optical waveguides – Optical waveguide sensor
Patent
1997-03-04
1998-10-13
Ngo, John
Optical waveguides
Optical waveguide sensor
385 37, 385130, 385131, G02B 610
Patent
active
058224726
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for detecting evanescently excited luminescence with a planar dielectric optical sensor platform based on a waveguide. The invention also relates to the use of said process in qualitative affinity sensing and to the use thereof for the selective quantitative determination of luminescent components in optically turbid solutions. The invention further relates to a sensor platform suitable for carrying out the process.
Where light propagates in a waveguide, the lightwave is not completely limited to the actual waveguide: in fact a fraction of the lightwave propagates in the contiguous optically thinner medium. This fraction is termed the evanescent field and is the basis of the variegated use of optical waveguides in sensing technology.
With the evanescent field it is possible in particular to excite luminescence in the optically thinner medium. This excitation is limited to the immediate environment of the interface of the waveguide. Evanescent luminescence excitation is therefore of great interest for analytical purposes.
A planar sensor consists in the simplest case of a 3-layer system: a substrate, a waveconducting layer, and a superstrate that usually constitutes the sample for assaying. Especially in the case of thin waveguides in which the thickness of the waveguiding layer is smaller than the light wave length, the number of diffusible modes of the light field capable of propagation is limited to a few discrete waveguide modes.
In the case of thick waveguides, a host of modes can be guided. In this case the need for a substrate can often be dispensed with, for example for thicknesses in the range of several 1/10 mm and greater.
Prior art methods of detecting evanescently excited luminescence can be differentiated in accordance with the choice of radiation fractions that can be detected: excited by the guided wave is emitted into the full space angle; this fraction can be optically recorded and fed into a detection system. luminescence emitted into the space, this evanescent luminescence is back-coupled as guided wave into the waveguide, transported there and coupled out via the end plane of the waveguide.
Methods and apparatus for detecting the evanescently excited luminescence of antibodies or antigens labelled with luminescent dyes are known and described, inter alia, in U.S. Pat. No. 4,582,809. The arrangement claimed therein uses an optical fibre and endface coupling for the evanescent luminescence excitation. Such optical fibres typically have a diameter of up to 1 millimeter and conduct a host of modes when laser light is coupled thereinto. The evanescently excited luminescence can be measured in simple manner only by the fraction tunnelled back into the fibre. The quite large dimensions of the apparatus and the fact that comparatively large sampling volumes are required are further drawbacks. The apparatus cannot be substantially reduced in size or even miniaturised to integrated optical sensors. An enhancement of the sensitivity is usually associated with an increase in the size of the apparatus.
A further drawback is the sensitivity which is limited by the endface output-coupling: as excitation and luminescence radiation run co-linearly and have to be separated by beam splitters and filters (e.g. cut-off filters or band-pass filters), the discrimination characteristics of the filter unit limits the detection sensitivity.
The use of thick planar multimode waveguides is described by D. Christensen, D. Deyer, D. Fowers, J. Herron in "Analysis of Excitation and Collection Geometries for Planar Waveguide Immunosensors", SPIE 1886, 2(1993) (Fibre Optic Sensors in Medical Diagnostics). Here the excitation radiation is coupled into the waveguide via the endface, and the luminescence light emitted into the space angle is detected. Alternatively it is also possible to use an endface output-coupling. In this latter case, the limitation of sensitivity caused by the necessary beam splitters and filters are a drawback in the same way as in the arrangements describ
REFERENCES:
patent: 5082629 (1992-01-01), Burgess, Jr. et al.
Danielzik Burkhard
Duveneck Gert Ludwig
Heming Martin
Neuschafer Dieter
Segner Johannes
Dohmann George R.
Ngo John
Novartis Corporation
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