Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1996-11-25
1999-09-28
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250237G, 385 12, 385 37, 385130, 385131, G02B 610
Patent
active
059592923
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF INVENTION
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.
When a lightwave is coupled into a planar waveguide which is surrounded by optically thinner media it is conducted by total reflectance to the interfaces of the waveguiding layer. A planar waveguide consists in the simplest case of a 3-layer system: a substrate, a wave-conducting layer, and a superstrate (e.g. the sample for assaying), the wave-conducting layer having the highest refractive index. Additional interlayers can enhance the activity of the planar waveguide still further.
A fraction of the light energy penetrates the optically thinner media. This fraction is termed the evanescent (=fading) field. The strength of the evanescent field is very strongly dependent on the thickness of the waveguiding layer itself as well as on the ratio of the refractive indices of the waveguiding layer and of the surrounding media. In the case of thin waveguides, i.e. layer thicknesses of the same or lesser thickness than of the wavelength to be guided, it is possible to distinguish discrete modes of the conducted light. With an evanescent field it is possible, for example, to excite luminescence in optically thinner media, but only directly adjacent to the guided lightwave. This principle is called evanescent luminescence excitation.
Evanescent luminescence excitation is of great interest in the analytical field, as the excitation is limited to the direct environment of the waveguiding layer.
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 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.
Photometric instruments for detecting the luminescence of biosensors under the conditions of evanescent excitation with planar optical waveguides are likewise known and disclosed, inter alia, in WO 90/06503. The waveguiding layers used therein have a thickness of 160-1000 nm, and the coupling of light into the excitation wave is effected without coupling gratings.
Various attempts have been made to enhance the sensitivity of evanescently excited luminescence and to fabricate integrated optical sensors. Thus, for example, Biosensors & Bioelectronics 6 (1991), 595-607 reports on planar monomode or low-mode waveguides which are fabricated in a two-step ion exchange process and in which the coupling of light into the excitation wave is effected with prisms. The affinity system used is human immunoglobulin G/fluorescein-labelled protein A, wherein the antibody is immobilised on the waveguide and the fluorescein-labelled protein A to be detected, in phosphate buffer, is added to a film of polyvinyl alcohol with which the measuring region of the waveguide is covered. A substantial disadvantage of this process is that only minor differences in the refraction indices between waveguiding layer and substrate layer are achievable, resulting in a relatively low sensitivity.
The sensitivity is said to be 20 nm in fluorescein isothiocyanate bonded to protein A. This is stil
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Duveneck Gert L.
Ehrat Markus
Neuschafer Dieter
Dohmann George R.
Kalinchak Stephen G.
Lee John R
Novartis Corporation
Westin Edward P.
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