Chemistry: analytical and immunological testing – Optical result – With claimed manipulation of container to effect reaction or...
Patent
1993-04-09
1994-12-20
Redding, David A.
Chemistry: analytical and immunological testing
Optical result
With claimed manipulation of container to effect reaction or...
436805, 436807, 435 4, 435 71, 435808, 422 8205, 356318, 356445, C01N 2155
Patent
active
053745639
DESCRIPTION:
BRIEF SUMMARY
This invention relates to sensors for the detection of chemical species, in particular to sensors for the detection of analytes in solution by the technique of surface plasmon resonance (SPR).
BACKGROUND OF THE INVENTION
SPR is well-known for the detection of chemical species. SPR may be achieved by using the evanescent wave which is generated when a TM-polarised (or p-polarised) light beam is totally internally reflected at the interface between a dielectric medium, e.g. glass, and a thin layer of metal. Any TE-polarised (or s-polarised) component of the radiation cannot excite SPR by the process of total internal reflection and in conventional SPR such components are not employed. The technique is described by Lieberg et al in Sensors and Actuators, 4, 299.
The basis for the application of SPR to sensing is the fact that the oscillation of the surface-plasma of free electrons which exists at a metal-dielectric boundary is affected by the refractive index of the material adjacent to the metal surface. Resonance occurs when the angle of incidence of the radiation has a particular value, and this value is dependent on the refractive index of the material adjacent to the metal. Thus, changes in this refractive index give rise to changes in the angle at which resonance occurs.
A problem which occurs with known SPR devices is that resonance is detected as a reduction in the intensity of the reflected light. This means that the electronic gain of the detector, or the light level from the source, can only be set with respect to the bright background to prevent electronic saturation away from resonance. Small changes in intensity at resonance are difficult to amplify independently for measurement.
We have now devised an SPR device in which resonance is detected as an increase in light intensity. This enables the electronic gain of the detector to be set to suit the strength of the resonance, with associated improvements in sensitivity and measurement accuracy.
SUMMARY OF THE INVENTION
According to the invention, there is provided an SPR sensor, comprising directed onto the device, and device, and TM-polarised components and a polarisation analyser is interposed between the device and the detector such that, at angles away from resonance, little or no light reaches the detector.
According to a preferred aspect of the invention, there is provided a sensor for the qualitative and/or quantitative determination of a biological, biochemical or chemical analyte, which sensor comprises layer of metallic material applied to at least part of a first surface thereof, the metallic layer in turn having a layer of material sensitive to the analyte applied to it, onto said block in such a way as to be reflected off said part of said surface, and and TM-polarised components and a polarisation analyser is interposed between the block and the detector such that, at angles away from resonance, little or no light reaches the detector.
The polarisation analyser may, for instance, comprise a polariser arranged such that its transmission axis is orthogonal to the resultant polarisation of the reflected beam.
For optimal results the incident radiation contains approximately equal amounts of the TE- and TM-polarised components. Away from resonance, the phases of both components behave in a similar way as the angle is changed. This allows a suitable analyser to be arranged so as to substantially prevent the polarised reflected light from reaching the detector at angles away from resonance.
Over the region in which SPR is excited, however, (i.e. as the angle of incidence of the radiation is altered) the phase of the TM-component changes, while the phase of the TE-component remains substantially unchanged. The TM-component also suffers some loss due to the SPR effect but despite this, the resultant polarisation of the reflected beam now has a component that can be transmitted through the analyser, and a signal is detected by the detector. The magnitude of this transmitted component, and hence the signal, increases until the phase chan
REFERENCES:
patent: 4889427 (1989-12-01), Van Veen et al.
Sensors and Actuators, vol. 4, 1983, Lidberg et al., "Surface Plasmon Resonance for Gas Detection and Biosensing," pp. 299-304.
Fisons plc
Redding David A.
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