Optics: measuring and testing – By dispersed light spectroscopy
Patent
1993-04-15
1995-07-18
McGraw, Vincent P.
Optics: measuring and testing
By dispersed light spectroscopy
356445, G01J 300, G01N 2155
Patent
active
054346630
DESCRIPTION:
BRIEF SUMMARY
This invention relates to sensors, especially those termed biosensors, ie to devices for the analysis of biologically active species such as antigens and antibodies in samples of biological origin. In particular, the invention relates to biosensors based on the principle of resonant attenuated or frustrated total internal reflection.
Many devices for the automatic determination of biochemical analytes in solution have been proposed in recent years. Typically, such devices (biosensors) include a sensitised coating layer which is located in the evanescent region of a resonant field. Detection of the analyte typically utilizes optical techniques such as, for example, surface plasmon resonance (SPR), and is based on changes in the thickness and/or refractive index of the coating layer resulting from interaction of that layer with the analyte. This causes a change, eg in the angular position of the resonance.
Other optical biosensors include a waveguide in which a beam of light is propagated. The optical characteristics of the device are influenced by changes occurring at the surface of the waveguide. One form of optical biosensor is based on frustrated total reflection. The principles of frustrated total reflection (FTR) are well-known; the technique is described, for example, by Bosacchi and Oehrle [Applied Optics (1982), 21, 2167-2173]. An FTR device for use in immunoassay is disclosed in European Patent Application No 2205236A and comprises a cavity layer bounded on one side by the sample under investigation and on the other side by a spacer layer which in turn is mounted on a substrate. The substrate-spacer layer interface is irradiated with monochromatic radiation such that total reflection occurs, the associated evanescent field penetrating through the spacer layer. If the thickness of the spacer layer is correct and the incident parallel wave vector matches one of the resonant mode propagation constants, the total reflection is frustrated and radiation is coupled into the cavity layer. The cavity layer must be composed of material which has a higher refractive index than the spacer layer and which is transparent at the wavelength of the incident radiation.
More recently, FTR biosensors have been described [see, for example, PCT Patent Application WO 90/06503] in which the cavity layer is a thin film of relatively high refractive index material, typically an inorganic oxide.
In devices of this kind, the occurrence of resonance may be detected as a change of phase of the reflected radiation. Measurement of a change of phase is a relatively complex operation and is easily affected by varying birefringence of the substrate or an interposed optical component. This makes the use of inexpensive plastics optics impracticable. It would be desirable if, instead, a device were available which enabled measurements to be made by, for example, detection of the output intensity.
We have now devised a biosensor device based on FTR which enables this to be done.
According to the invention, there is provided a sensor including an optical structure comprising refractive index n.sub.2, of sufficient thickness to support at least one resonant mode, and the arrangement being such that the optical structure may be illuminated by a beam of incident radiation, internal reflection occurring at the interface between the substrate and the spacer layer, wavelength of the incident radiation.
The sensor according to the invention is advantageous primarily in that resonance may be detected as a reduction in the intensity of the reflected radiation. Such a drop in intensity requires a less elaborate detection system than is necessary for the detection of a phase change. Also, relatively inexpensive plastics optical components may be used. This means that simpler instrumentation may be used, with concomitant cost savings.
The cavity layer or spacer layer should absorb sufficiently strongly for a detectable reduction in intensity to be obtained. On the other hand, the absorption should not be so great as to cause significant broadening o
REFERENCES:
patent: 3436159 (1969-01-01), Harrick et al.
patent: 4558012 (1985-12-01), Nygren et al.
Applied Optics, vol. 21, No. 12, Jun. 1982, Bosacchi et al., "Resonant Frustrated-Total-Reflection Technique for the Characterization of Thin Films".
Fisons plc
Hantis K. P.
McGraw Vincent P.
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