Chemistry: analytical and immunological testing – Involving an insoluble carrier for immobilizing immunochemicals
Patent
1994-12-12
1997-05-20
Chin, Christopher L.
Chemistry: analytical and immunological testing
Involving an insoluble carrier for immobilizing immunochemicals
356317, 356318, 356243, 356246, 385 12, 385129, 422 58, 422 61, 422 8205, 422 8208, 422 8211, 422 57, 4352871, 4352872, 4352887, 435808, 435810, 435967, 435975, 436164, 436172, 436527, 436805, G01N 33543, G01N 33552
Patent
active
056311702
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a method of improving measurement precision in optical biosensor assays employing evanescent wave detection, to devices for use in such a method and to the use of such devices.
DESCRIPTION OF THE PRIOR ART
Of the large variety of chemical and biochemical techniques used for analysis or assay, a particularly useful and sensitive one is an optical system employing the principles of internal reflection spectroscopy. Especially useful for immunoassays, such an optical system employs an optical waveguide, a portion of one surface of which generally carries an immobilised reagent, for example, a specific binding partner to the ligand to be assayed in the sample solution. A light beam directed into the waveguide will be totally internally reflected in the dense medium of the waveguide and will generate an electromagnetic waveform, known as the evanescent wave component at the surface of the waveguide. This component characteristically extends only a fraction of a wavelength across the interface between the waveguide and the sample solution. This penetration, however, is sufficient to permit substantial optical interaction between the evanescent wave component and entities close to or at the surface of the waveguide, and only minimal interaction with species in the bulk solution. Hence in the example of an immunoassay for a ligand where a specific binding partner to the ligand is immobilised onto the waveguide, the evanescent wave component will interact with this immobilised species and with any species complexed to it. By employing an optically labelled reagent in the assay which complexes with the immobilised species as a function of the amount of ligand present, the interaction of the evanescent wave component with this labelled reagent can be determined. Since there is only minimal interaction with the labelled reagent in the bulk solution, this then permits one to assay the ligand of interest. The two principal forms of optical detection which have been used are those based on the optical absorbance or fluorescence characteristics of the species to be measured i.e. Attenuated Total Reflection (ATR) and Total Internal Reflection Fluorescence (TIRF).
Such techniques and their application to assays are described, for example, by I. Chabay in Analytical Chemistry, Vol. 54. No. 9, (1982) and in EP-A-103426, and biosensors employing such techniques are described in, for example, Biosensors: fundamentals and applications, Eds. Turner, Karube and Wilson, pp. 655-678, OUP, 1987, Biosensors Vol. 1, 321-353, (1985), EP-A-171148 and WO-90/14590.
However, such optical assay systems suffer from two particular sources of imprecision which it would be desirable to reduce or eliminate. In particular, deficiencies in the surface quality of the waveguide, for example surface roughness, the overall flatness of the waveguide and the level of tilt of its surface relative to its longitudinal axis, will modulate the evanescent signal, these effects hereinafter being denoted as "edge effects"; these deficiencies will also lead to a scattering effect. In addition the intrinsic properties of the waveguide material and, for example, the presence of bulk inhomogeneities in the waveguide will also result in a scattering effect of the excitation light, of the signals from species in the bulk solution and the signals from species at or near the waveguide surface. Hence such edge effects and scattering effects, hereinafter collectively denoted "waveguide effects", can significantly affect the background signal of an assay system and the sensitivity range of an assay method, therefore introducing errors.
It is thus desirable to develop an assay method in which a reference measurement can be taken within the assay procedure in order to compensate for the various factors, such as those indicated above, which may alter the level of the observed assay measurement. An example of such a principle is illustrated in EP-A-093613 in which a reference signal is obtained from appropriate reagents
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Database WPI, Section Ch, Week 9119, Derwent Publications Ltd., London, GB; Class J04, AN 91-135984 & JP, A, 3 072 262 (Daikin KOgyo KKO, Mar. 27, 1991.
Applied Research Systems ARS Holding N.V.
Chin Christopher L.
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