Optical waveguides – Optical waveguide sensor
Patent
1997-10-28
2000-06-20
Bovernick, Rodney
Optical waveguides
Optical waveguide sensor
385 37, G02B 600
Patent
active
060787058
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a sensor platform based on at least two planar, separate, inorganic dielectric waveguiding regions on a common substrate and to a method for the parallel evanescent excitation and detection of the luminescence of identical or different analytes. The invention relates also to a modified sensor platform that consists of the sensor platform having the planar, separate, inorganic dielectric waveguiding regions and one or more organic phases immobilised thereon. A further subject of the invention is the use of the sensor platform or of the modified sensor platform in a luminescence detection method for quantitative affinity sensing and for the selective quantitative determination of luminescent constituents of optically opaque solutions.
If a lightwave is coupled into a planar waveguide that is surrounded by media of a lower refractive index, it is confined by total reflection at the boundaries of the waveguiding layer. In the simplest case, a planar waveguide consists of a three-layer system: substrate, waveguiding layer, superstrate (or sample to be investigated), the waveguiding layer having the highest refractive index. Additional intermediate layers can further improve the action of the planar waveguide.
In that arrangement, a fraction of the electromagnetic energy enters the media of lower refractive index. That portion is termed the evanescent (=decaying) field. The strength of the evanescent field depends to a very great extent upon the thickness of the waveguiding layer itself and upon the ratio of the refractive indices of the waveguiding layer and of the media surrounding it. In the case of thin waveguides, i.e. layer thicknesses that are the same as or smaller than the wavelength that is to be guided, discrete modes of the guided light can be distinguished.
Using an evanescent field, it is possible, for example, to excite luminescence in media of relatively low refractive index, and to excite that luminescence in the immediate vicinity of the waveguiding region only. That principle is known as evanescent luminescence excitation.
Evanescent luminescence excitation is of great interest in the field of analysis, since the excitation is limited to the immediate vicinity of the waveguiding layer. Methods and apparatus for determining the evanescently excited luminescence of antibodies or antigens labelled with luminescent dyes are known and are described, for example, in U.S. Pat. No. 4,582,809. The arrangement claimed therein uses an optical fibre for evanescent luminescence excitation. Such optical fibres have, typically, a diameter of up to a millimeter and guide a large number of modes when laser light is coupled into them. The evanescently excited luminescence can be measured easily only by means of the portion coupled back into the fibres. A further disadvantage is that the apparatus is relatively large and comparatively large volumes of sample are required. There is little scope for any further substantial reduction in the size of the arrangement, let alone for miniaturising it to produce integrated optical sensors.
Any increase in sensitivity is generally associated with an increase in the size of the arrangement.
Photometric instruments for determining the luminescence of biosensors under evanescent excitation conditions using planar optical waveguides are likewise known and are described, for example, in WO 90/06503. The waveguiding layers used in that specification are from 160 nm to 1000 nm thick and the excitation wave is coupled in without grating couplers.
Various attempts have been made to increase the sensitivity of evanescently excited luminescence and to produce integrated optical sensors. For example, a report in Biosensors & Bioelectronics 6 (1991), 595-607, describes planar monomodal or low-modal waveguides that are produced in a two-step ion-exchange process and in which the excitation wave is coupled in using prisms. The affinity system used is human immunoglobulin G/fluorescein-labelled protein A, the antibody being immobilised on the waveguide and the fl
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Budach Wolfgang
Duveneck Gert Ludwig
Neuschafer Dieter
Pawlak Michael
Pieles Uwe
Bovernick Rodney
Kim Ellen E.
Lopez Gabriel
Novartis AG
Wissing William K.
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