GB2202045A

GB2202045A - Sensors for performing assays

Info

Publication number: GB2202045A
Application number: GB08705648A
Authority: GB
Inventors: Craig George Sawyers
Original assignee: PA Consulting Services Ltd
Current assignee: PA Consulting Services Ltd
Priority date: 1987-03-10
Filing date: 1987-03-10
Publication date: 1988-09-14
Anticipated expiration: 2007-03-10
Also published as: GB8705648D0; GB2202045B

Abstract

A sensor device for use in an assay for the detection of a chemical, biochemical or biological analyte, the said device comprising a substrate having a surface with a pre-formed relief profile formed from or coated with a dielectric material capable of exhibiting a surface plasmon resonance effect when illuminated by light of an appropriate wavelength, wherein the said surface or coated surface carries a material capable of binding the analyte to be assayed. The optical properties of the sensor change due to binding thereto of the species under assay. The dielectric material exhibits negative dielectric constant and thus acts as a metal in the presence of light of the particular wavelength which excites surface plasmons.

Description

Title: Improvements relating to sensors for performing assays This invention relates to sensors by which assays for the qualitative and/or quantitative detection of chemical, biochemical or biological species in a sample may be performed and is particularly concerned with materials employed as coatings for such sensors.

Background to the invention International Patent Publication W084/02578 describes a sensor device comprising a substrate having a surface with a pre-formed relief profile such as a regular sinusoidal grating, coated with a thin metal layer, such as silver or aluminium, which conforms to the relief profile. The metal layer is coated with a material capable of binding the species to be assayed. The sensor surface is optically active with respect to radiation such that there is a change in the optical properties of the sensor when the species to be assayed binds to the surface of the sensor. Light is directed, onto the grating surface such that the polarisation vector is in the plane of incidence, and the plane of incidence contains the grating vector.

The angle of incidence, or the wavelength of light, at which there is a sudden dip in the magnitude of reflected light is then monitored. This change in reflectivity is caused by light energy being coupled into the surface of the grating and causing surface plasmon resonance to occur.

This assay device may alternatively, as described in International Patent Publication WO 86/01901, have a layer of dye-tagged material, which is capable of binding to the species to be assayed, bonded to the profiled surface.

The binding of the complementary binding partner to the dye tagged molecules on the surface of the sensor affects -the fluorescent behaviour of the system, which can be arranged to be fluorescent activating or fluorescent inhibiting on binding of the assayed species, and which can thereby be used as a sensor.

Such sensors rely on the presence of the metal layer at, or near, the surface of the device to support a surface plasmon mode. The presence of a metal as the upper surface of the sensor may not always be advantageous in that it does not always provide a suitable surface for the attachment of the layer which specifically binds the species to be analysed To this end the thin metal layer may be covered with a further layer of a non-metallic material which does form a suitable binding surface for attachment of biological or other molecules capable of binding the species to be analysed. The non-metallic material can also serve as a protective layer to prevent the metal from chemical attack.

Object of the invention It is an object of the present invention to remove the requirement for a metal layer at or near the surface of such a sensor.

Summary of the invention According to the present invention in a sensor of the type described the profiled surface is formed from or coated with a dielectric material which exhibits a negative dielectric constant and therefore acts as a metal in the presence of light the wavelengths of which is capable of exciting the surface plasmon.

Examples of materials which may be so employed as the surface material or surface coating are silicon carbide, strontium fluoride, barium fluoride, strontium titanate, aluminium nitride, gallium phosphide and calcium fluoride.

It will be noted that these are so called dielectric materials and, under normal circumstances, have a positive dielectric constant. However, in accordance with the Restrahlen effect, in a particular, restricted, range of wavelengths, these materials behave as if metallic as a result of the change to a negative dielectric constant in the presence of such wavelengths. Therefore a sensor employing the surface plasmon effect can be constructed entirely from dielectric materials and no metal film need be employed.

The use of non-metallic materials t:o replace the metal layer has the added benefit that such materials provide a suitable surface for attachment of the specific binding molecules and the need for additional layers having this function is thereby reduced. It may be possible to select a non-metallic material which is better able to withstand chemical attack, and the use of such a material in sensors of the type described will in that event make the use of protective layers unnecessary.

It is to be noted that although reference is made herein to the use of the invention with an antibody or an antigen as the ligand; the invention is not to be taken as being limited to assays of antibodies or antigens. Examples of ligands which may be assayed by the method of the invention are given in Table 1 below, together with an indication of a suitable specific partner in each instance.

Table 1 Ligand Specific Binding Partner antigen specific antibody antibody antigen hormone hormone receptor hormone receptor hormone polynucleotide complementary polynucleotide strand strand avid in biotin biotin avid in protein A immunoglobulin immunogobulin protein A enzyme enzyme cofactor (substrate) enzyme cofactor enzyme (substrate) lectins specific carbohydrate specific carbohydrate lectins of lectins It will be understood that the term "antibody" used herein includes within its scope: a.) any of the various classes or sub-classes of immunoglobulin, eg. IgG, IgM, derived from any of the animals conventionally used, eg. sheep, rabbits, goats or mice, b.) monoclonal antibodies, c.) intact molecules or 'fragments" of antibodies, monoclonal or polyclonal, the fragments being those which contain the binding region of the antibody, ie.

fragments devoid of the Fc portion (eg. Fab, Fab', F(ab')2) or the so-called "half-molecule" fragments obtained by reductive cleavage of the disulphide bonds connecting the heavy chain components in the intact antibody.

The method of preparation of fragments of antibodies is well known in the art and will not be described herein.

The term "antigen" as used herein will be understood to include both permanently antigenic species (for example, proteins, bacteria, bacteria fragments, cells, cell fragments and viruses) and hastens which may be rendered antigenic under suitable conditions.

Examples In a sensor in which the profiled surface is coated with (or formed from) Silicon carbide, a surface plasmon effect can be obtained with excitation light having a wavelength of the order of 12 microns.

In a sensor in which the profiled surface is coated with (or formed from) Barium fluoride a surface of plasmon effect can be obtained with excitation light having a wavelength of the order of 40 microns.

In a sensor in which the profiled surface is coated with (or formed from) Aluminium nitride a surface of plasmon effect can be obtained with excitation light having a wavelength of the order of 13.3 microns.

In a sensor in which the profiled surface is coated with (or formed from) Gallium phosphide a surface of plasmon effect can be obtained with excitation light having a wavelength of the order of 27 microns.

In a sensor in which the profiled surface is coated with (or formed from) Calcium fluoride a surface of plasmon effect can be obtained with excitation light having a wavelength of the order of 35 microns.

Claims

1. A sensor device for use in an assay for the detection of a chemical, biochemical or biological analyte, the said device comprising a substrate having a surface with a pre-formed relief profile formed from or coated with a dielectric material capable of exhibiting a surface plasmon resonance effect when illuminated by light of an appropriate wavelength, wherein the said surface or coated surface carries a material capable of binding the analyte to be assayed.

2. A sensor device as claimed in claim 1 wherein the saia pre-formed relief profile is a regular sinusoidal grating.

3. A sensor device as claimed in claim 1 or claim 2 wherein said material is silicon carbide, strontium fluoride, barium fluoride, strontium titanate, aluminium nitride, gallium phosphide or calcium fluoride.

4. A sensor device as claimed in any one of the preceding claims wherein the material capable of binding the species to be assayed is an antibody or an antigen.

5. A sensor device as claimed in claim 1 substantially as described herein.

6. A method of assaying a species in a sample which comprises contacting said sample with a sensor as claimed in any one of the preceding claims and determining whether, and if desired the extent to which, there is a change in the optical properties of the sensor due to binding thereto of the species under assay.

7. A method as claimed in claim 6 substantially as described herein.