Optical waveguides – Optical waveguide sensor
Reexamination Certificate
2000-01-19
2001-09-11
Bovernick, Rodney (Department: 2874)
Optical waveguides
Optical waveguide sensor
C385S037000, C422S082110
Reexamination Certificate
active
06289144
ABSTRACT:
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, wave-guiding 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 Bio-sensors & 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 fluorescein-labelled protein A to be detected being added in phosphate buffer to a film of polyvinyl alcohol with which the measuring region of the waveguide is covered.
A considerable disadvantage of that method is that only small differences in refractive index between the waveguiding layer and the substrate layer can be achieved, with the result that the sensitivity is relatively low.
The sensitivity is given as 20 nM of fluorescein-labelled protein A. That is still not satisfactory for the determination of very small traces and a further increase in sensitivity is therefore required. In addition, the coupling-in of light using prisms is difficult to reproduce and to carry out in practice owing to the great extent to which the coupling-in efficiency is dependent upon the quality and size of the contact surface between the prism and the waveguide.
In U.S. Pat. No.5,081,012 a different principle is proposed. The planar waveguiding layer is from 200 nm to 1000 nm thick and contains two gratings, one of which is in the form of a reflection grating, with the result that the coupled-in lightwave has to pass at least twice through the sensor region between the gratings. That is supposed to produce increased sensitivity. A disadvantage is that the reflected radiation can lead to an undesirable increase in background radiation intensity.
WO 91/10122 describes a thin-layered spectroscopic sensor which comprises a coupling-in grating and a physically remote coupling-out grating. It is suitable especially for absorption measurement if an inorganic metal oxide of high refractive index is used as the waveguiding layer. Various embodiments that are suitable for the coupling-in and coupling-out of multi-chromatic light sources are described. The preferred thickness of the waveguiding layer is greater than 200 nm and the grating depth should be approx. 100 nm. Those conditions are not suitable for luminescence measurements in affinity sensing since only low sensitivity is obtained. That is confirmed in Appl. Optics Vol. 29, No. 31 (1990), 4583-4589 by the data for the overall efficiency of those systems: 0.3% at 633 nm and 0.01% at 514 nm.
In another embodiment of the same sensor, a plurality of polymeric planar waveguiding layers that can be used as a gas-mixture analyser are applied to a substrate. Use is made in that case of the change in the effective refractive index or the change in the layer thickness of the polymer waveguide on contact with, for example, solvent vapours. The waveguiding structure is physically altered thereby. However, such changes are totally unsuitable for luminescence measurements in affinity sensing since the coupling-in is altered, increasing scatter occurs and there can be a significant decrease in sensitivity.
The production of planar waveguides is a process in which the planarity of the substrate, the constant thickness and homogeneity of the waveguiding layer and the refractive index of the material used therefor are of extreme importance. That is described, for example, in EP-A-0 533 074, and that specification proposes the application of inorganic waveguides to plastics substrates. That offers the advantage that, for example, the structuring of the grating coupler can be effected in an economical manner by impressing the structure into the plastics. On the other hand, however, the requirements with regard to the optical quality of the plastics substrates are also high.
Planar waveguides offer considerable advantages for industrial production over waveguides based on fibre optics. In particular, it is generally necessary in the case of fibres to polish the cut ends in order to achieve perfect optical quality. Planar waveguides, on the other hand, can be produced in sheet form and then stamped, broken or cut to the desired size. Finishing of the edges is unnecessary in most cases, making mass production more economical.
Further advantages of planar waveguides having grating couplers are simple adjustment in the measuring apparatus or in the measurin
Budach Wolfgang
Duveneck Gert Ludwig
Neuschafer Dieter
Pawlak Michael
Pieles Uwe
Bovernick Rodney
Kim Ellen
Novartis AG
Wenderoth , Lind & Ponack, L.L.P.
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