Optics: measuring and testing – Refraction testing
Patent
1987-01-27
1989-03-28
Rosenberger, Richard A.
Optics: measuring and testing
Refraction testing
350 9619, 350136, G01N 2141, G01N 2175, G01N 3353
Patent
active
048158437
DESCRIPTION:
BRIEF SUMMARY
The present invention refers to an optical sensor according to the main patent claim. A well-known device for measuring refractive index changes in liquid, solids and porous samples is the refractometer which determines the angle of total internal reflexion between two media where the reference medium is a high index prism of known refractive index. A well-known device for the detection of chemisorbate layers and of chemically bound layers on surfaces in the ellipsometer analysing the state of polarisation of th elight being reflected at the chemisorbate layer (cf. R. Azzam et al., Physics in Medicine and Biology 22 (1977) 422-430; P. A. Cuypers et al., Analytical Biochemistry 84 (1978), 56-67), These devices are voluminous and the required sample volume is rather big what can be a great disadvantage in case of expensive samples. Furthermore the measurement accuracy of an ellipsometer is limited since the cell containing the liquid can influence the state of polarisation of the light. Another well-known instrument for the detection of adsorbed antigens, antibodies and haptens is the refractometer described in EP 0073980. A relatively new method for the detection of adsorbate layers is based on the excitation of surface plasmons at metal layer interfaces with or without using a diffraction grating (cf. B. Liedberg et al., Sensors and Actuators 4 (1983), 299 and EP 0112721). Thin metal films are not very stable and show ageing effects in their optical properties, what may be causing problems in practical applications.
The methods mostly used for the immunological determination of antibodies, antigens and haptens and for the determination of concentrations of metabolites such as glucose are based on the use of markers such as radioisotopes, enzymes or fluorescent tracers (EP 0103426, U.S. Pat. No. 4,344,438), which are chemically bound to a counter ligand, that is, to a complementary biomolecule. Sometimes, however, labeling leads to a perturbation of the binding behaviour of the corresponding biomolecule what means a decrease of the binding affinity.
Ellipsometry, reflectometry and excitation of surface plasmons allow a direct measurement of the immunological reaction (without using labels), but have the disadvantages mentioned above. Nephelometry is another direct measurement method but it is not very sensitive.
The invention as characterized in the claims solves the problem to provide an optical sensor which shows one or several of the following characteristic properties, namely
(1) enabling a selective detection of specific substances contained in gaseous, liquid, solid or porous samples
(2) resolving changes in surface coverage of less than a hundredth of a monomolecular layer
(3) resolving refractive index changes in gases, liquids, solids or porous materials of less than 1.10.sup.-5
(4) distinguishing simultaneously and continuously between surface coverage and refractive index change
(5) requiring very small sample volumes
(6) requiring little space
(7) working multifunctionally by integration of several detectors on a single chip.
The invention will be now described by way of example with reference to the accompanying drawings in which
FIG. 1 is a schematic diagram of the basic elements of the invention where a waveguiding structure located at the surface of a substrate and depicted in the subsequent drawings as a planar waveguiding film is provided with a diffraction grating and, optionally, with an additional layer
FIG. 2 is in accordance with the invention a schematic view of a measuring device operating as an input grating coupler
FIG. 3 is in accordance with the invention a schematic view of a measuring device operating as an output grating coupler
FIG. 4 is in accordance with the invention a schematic view of a measuring device operating as a Bragg reflector
FIG. 5 is an extended schematic diagram of the basic elements of the invention where outside the grating region the waveguiding structure is coverred by a protective layer
FIG. 6 is an extended schematic diagram of the basic elements of the
REFERENCES:
patent: 3856404 (1974-12-01), Hershler
patent: 4344438 (1982-08-01), Schultz
Tiefenthaler et al. "Integrated optical switches and gas sensors", Optics Letters vol 10, No. 4 (Apr. 1984) pp. 137-139.
Chabay, I. "Optical Waveguides" Analytical Chemistry, vol. 54, No. 9 (Aug. 1982) pp. 1071A-1080A.
Lukosz et al "Embossing technique for fabricating integrated optical components in hard inorganic waveguide materials", Optics Letters, vol. 8, No. 10 (Oct. 1983) pp. 537-539.
Sutherland et al "Optical Detection of Antibody-Antigen Reactions at a Glass-Liquid Interface", Clinical Chemistry, vol 30, No. 9 (1984) pp. 1533-1538.
Lukosz Walter
Tiefenthaler Kurt
Oerlikon-Buhrle Holding AG
Rosenberger Richard A.
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