Chemistry: analytical and immunological testing – Involving an insoluble carrier for immobilizing immunochemicals
Patent
1991-05-21
1994-09-06
Scheiner, Toni R.
Chemistry: analytical and immunological testing
Involving an insoluble carrier for immobilizing immunochemicals
385 12, 385129, 385130, 385131, 422 55, 422 57, 422 58, 422 8205, 422 8208, 435808, 436172, 436524, 436525, 436527, 436537, 436805, 436807, G01N 33552
Patent
active
053447840
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a device for the enhancement of fluorescence and in particular to a device for use in fluorometric systems and methods for the assay of chemical or biochemical entities.
Methods of assay involving the use of fluorescence biosensors and employing evanescent wave coupling techniques are known, see for example EP-A-170376. The present invention provides means for carrying out assays employing evanescent wave coupling techniques whereby an improved signal-to-noise ratio and enhanced sensitivity may be obtained.
U.S. Pat. No. 4,649,280 describes a device for enhancing fluorescence comprising a waveguide defined by a dielectric layer of predetermined thickness having layers of fluorescent and of conductive material on opposite surfaces of the said layer. The present invention avoids the need for a conductive layer, thereby reducing the cost of materials and increasing the ease of fabrication of the device. The invention also allows greater design flexibility in producing sensors and allows a greater range of wavelengths of light to be used. Furthermore, methods according to the present invention are not polarisation dependant.
According to the present invention there is provided a sensor device for use in assaying chemical or biochemical substances by optical methods which sensor comprises an optical structure comprising:
(a) a dielectric substrate transparent at least at the wavelengths of radiation involved in the assay;
(b) a thin film waveguide of dielectric material having a refractive index higher than that of the substrate, the waveguide carrying a layer (continuous or discontinuous) of a reagent appropriate to the assay to be carried out, the said reagent being immobilized directly or indirectly on the surface of the waveguide remote from the substrate; and
(c), interposed between (a) and (b), a buffer layer of dielectric material of refractive index lower than that of the substrate; the thicknesses of the buffer layer and the waveguide being such that, in use, one or more guided modes may be propagated within the waveguide.
In a preferred embodiment, the thicknesses of the buffer layer and the waveguide are such that a single transverse magnetic (TM) and/or single transverse electric (TE) guided mode may be propagated within the waveguide.
A practical advantage accruing from use of an optical structure containing no metal layers is that fabrication of such devices is possible without the need for vacuum evaporation techniques; for example, spun-coated phosphate glasses may be used.
Furthermore, using a given combination of refractive indices of substrate, buffer layer, waveguide and solution it is possible in principle to design a device wherein the evanescent field is more highly confined than in previously known devices. When the device is used in fluorometric methods of assay this therefore leads to better discrimination between fluorophores bound to the surface of the device and fluorophores in solution. Additionally, the intensity of the evanescent field is enhanced resulting in greater excitation of the fluorophores within the evanescent field thereby improving the intensity of the emitted light compared to previously known devices.
Suitable materials for the substrate include glass, acrylic and polystyrene plastics, silica and quartz; suitable materials for the buffer layer include any material of suitably low refractive index which can be formed as an optically transparent thin film, such as magnesium fluoride, lithium fluoride, silicon dioxide and phosphate glasses; suitable materials for the waveguide layer include any material of suitably high refractive index which can be formed as an optically transparent thin film, such as zinc sulphide, zinc selenide, phosphate glasses lithium niobate, tin oxide and suitable polymers, e.g. polystyrene.
Preferably the buffer layer is 0.1 to 2 microns thick (for example, a buffer layer of SiO.sub.2 may be 0.6 microns thick and a buffer layer of MgF.sub.2 may be 0.7 microns thick) and the waveguide layer is 0.16 to 1.0 microns thick
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Applied Research Systems ARS Holding N.V.
Chin Christopher L.
Scheiner Toni R.
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