A DEVICE FOR ANALYTICAL DETERMINATIONS

Abstract: There is described a device for carrying out analytical determinations such as, for example, immunoassays. The device comprises an assay cassette which includes a series of discrete reagent chambers which contain, successively, the reagents required to perform an analytical determination. A sample loaded into the assay cassette may be brought into alignment with successive reagent chambers by rotation of the reagent chambers relative to the sample.

Description: A DEVICE FOR ANALYTICAL DETERMINATIONS Field of the invention The present invention relates to a device for carrying out analytical determinations and, in particular, to a device for carrying out a specific binding assay such as an immunoassay. Background to the invention There is considerable interest in the field of analytical determinations in the development of simplified assay systems which allow an unskilled user to perform complex assay procedures without undue error. Moreover, there is a great deal of interest in the development of efficient and clean assay systems which require minimal handling of liquid reagents and which can be automated to allow the assay procedure to be performed with minimal intervention from the user. This is particularly relevant in the healthcare field where there is an increasing need for assay systems, especially diagnostics, which can be efficiently and safely operated within the doctor's office, the clinic, the veterinary surgery or even in the patient's home or in the field. One approach to this problem is provided in EP-B- 0,320,240, which describes a device for use in analytical determinations which requires minimal handling of liquid reagents. This device consists of two components: a self-contained assay cassette comprising a series of discrete reagent chambers, separated from one another by means of separation means, which successively contain all the reagents and wash solutions required to carry out an assay procedure and a sample transport body which is adapted for location in the assay cassette. The sample to be tested is loaded on to the sample transport body which is then inserted into the assay cassette. To complete the assay procedure the sample transport body is pushed further into the assay cassette, rupturing the separation means between the reagent chambers as it moves through the cassette, in order to expose the sample to the assay reagents in the successive reagent chambers . Whilst the device of EP-B-0, 320, 240 provides for minimal handling of liquid reagents the design is not particularly suited to automation of the assay procedure, largely because the overall dimensions of the device change during operation as the sample transport body is inserted into the assay cassette. Thus there remains a need for a device which combines the advantages of minimal handling of liquid reagents with capacity for automation of the assay procedure. Description of the invention The inventors have now developed an improved device for use in carrying out analytical determinations which is considerably more amenable to automation because the overall shape and dimensions of the device remain constant during the analytical procedure. This device provides an assay system which is convenient, efficient, clean and easy to operate for the unskilled user. According to the present invention there is provided an assay cassette for use in carrying out analytical determinations, the assay cassette comprising: a sample receiving portion and a reagent holding portion which are rotatable relative to each other, the reagent holding portion having formed therein a series of discrete reagent chambers which contain, successively, the reagents required to perform the analytical determination, the reagent chambers being positioned at an eccentric location relative to the axis of rotation and the sample receiving portion defining an access port also positioned at an eccentric location relative to the same axis of rotation such that it may be brought into alignment with successive reagent chambers by relative rotation of the reagent holding portion and the sample receiving portion. In a preferred embodiment, the assay cassette is adapted for use with a sample loading body in order to form a device for use in analytical determinations. The assay cassette comprises a reagent holding portion, which may be formed from a mouldable plastic material, having a series of discrete reagent chambers formed therein and also a sample receiving portion which is adapted for location of a sample loading body. The reagent chambers of the reagent holding portion contain, successively, the reagents for carrying out the analytical procedure. Advantageously, the series of separate discrete reagent chambers may be positioned substantially along the circumference of a circle centred on the axis of relative rotation of the reagent holding portion relative to the sample receiving portion. It is to be understood that the precise arrangement and contents of the reagent chambers may vary according to the nature of the analytical procedure and is not material to the invention. In the case of an immunoassay, the reagent chambers might comprise a wash chamber, a conjugate chamber, a series of further wash chambers and a final signal detection chamber. One or more of the reagent chambers may be left empty to facilitate removal of excess liquid reagents from the sample collection area. Where the sample collection area comprises an absorbent body or pad of compressible material, these λ liquid removal' chambers may advantageously be smaller in depth than the absorbent body or pad in order to compress it and thereby squeeze out more liquid. Detection/measurement of the read-out of an analytical procedure or assay is usually carried out in the final reagent chamber in the series, which may be designated herein the signal detection chamber' . The signal detection chamber may be filled with a final reagent, for example a colorimetric enzyme substrate, or it may be left empty if a measurement of luminescence, fluorescence, radioactivity or the colour intensity of a dye or particulate labels is to be made. It may also be filled with a luminescence triggering reagent such as hydrogen peroxide when a chemiluminescent label is employed in a high sensitivity assay. The signal detection chamber is preferably provided with at least one transparent wall or window through which the result of the analytical procedure may be determined by visual inspection for a qualitative or semi-quantitative result or through which a signal indicating the result of the procedure may be measured by means of a measuring instrument to give a quantitative result. In one embodiment, the entire reagent holding portion may be formed from a transparent material. The interior surface of the reagent holding portion, meaning the surface which is interior when the assay cassette is assembled, may comprise a layer of disruptable material, such as a thin foil. This disruptable layer functions to seal in the contents of the reagent chambers prior to use. Accordingly, the layer may be applied across the entire interior surface or just over the area comprising the reagent chambers . It is an essential feature of the invention that the reagent holding portion of the assay cassette is rotatable relative to the sample receiving portion, which may also be advantageously formed from a moulded plastics material . The reagent chambers of the reagent holding portion are positioned in an eccentric location relative to the axis of rotation of the reagent holding portion, for example in a circular strip. The sample receiving portion contains an access port which is also positioned in an eccentric location relative to the axis of rotation of the reagent holding portion so that it may be brought into alignment with successive reagent chambers by simply rotating the reagent holding portion. In one embodiment the assay cassette may be adapted for use with a sample loading body having a sample collection area located thereon. The sample collection area may advantageously comprise an absorbent body or pad of nylon, polyurethane, PVC, or polyether foam, or cellulose or other compressible material. In the case of an immunoassay, a specific binding agent such as an antibody or an antigen may be immobilised on the sample collection area. The specific binding agents may be directly coupled to the plastic surface using established methods such as passive adsorption or covalent linking. In an alternative embodiment, they may be bound to the absorbent body or pad by passive adsorption or covalent linking. In many cases, the sample to be tested may be pipetted or added without measurement to the sample collection area where it is taken up by the absorbent material. Alternatively, the sample can be measured accurately by pipette. It will be understood that the sample may be any fluid material, including body fluids such as whole blood, serum, plasma, urine, milk etc, and other fluids such as environmental samples. It will be further understood that the device of the invention may be used in a wide range of analytical determinations in addition to immunoassays as described above. Control samples or calibrators may be added to other areas of the sample loading body. These controls may be added immediately prior to commencement of an assay, e.g. at the same time as adding the test sample, or may be added during manufacture. In a preferred configuration, the sample loading body comprises two or more distinct absorbent bodies or pads, at least one to function as a sample collection area for addition of the test sample and at least one for addition of a control sample. In a most preferred configuration, the sample loading body comprises three absorbent bodies, one sample collection area, one for a positive control sample and one for a negative control sample. The access port formed in the sample receiving portion of the assay cassette is preferably adapted to receive at least a portion of the sample loading body, including the sample collection area, so that the latter is correctly positioned relative to the reagent chambers when the device is in use. Preferably, the sample loading body is adapted to locate in a cooperating recess in the outer surface of the sample receiving portion of the assay cassette with the sample collection area being positioned within the access port. Advantageously, the sample loading body may be sealed into the assay cassette, for example by a snap-fit mechanism. The device is thus sealed during and at the end of the analytical procedure, preventing leakage of any liquid reagents. Prior to use, the access port may be covered by a removable covering, for example a peel-off strip or patch, which is removed immediately prior to insertion of the sample loading body. In an alternative embodiment the sample loading body may be fixed to the top surface of the sample receiving portion on the assay cassette. Most preferably, the sample loading body may be fixed to the assay cassette via a flexible joint or hinge which enables the sample loading body to be moved between a first position in which the sample loading body is folded back onto the top surface of the sample receiving portion with the sample collection area facing upward and a second position in which the sample collection area is located in the access port. In this configuration the sample may be pipetted onto the upward facing sample collection area when the sample loading body is held in the first position. The sample loading body is then folded into the second position with the sample collection area located in the access port. A snap-fit ensures that the device is sealed. The sample receiving portion of the assay cassette may be further provided with a penetration means, positioned on the interior surface (meaning the surface which is inside the assembled assay cassette) thereof adjacent to the access port. The penetration means is adapted to penetrate through the disruptable layer sealing the reagent chambers in the reagent holding portion of the assay cassette. Preferably, the penetration means comprises a blade or knife able to cut through the disruptable layer. The penetration means may itself be mounted on a spring means or equivalent which allows it to move relative to the interior surface of the sample receiving portion. When an assay cassette comprising a penetration means is in use, the reagent holding portion and the sample receiving portion rotate relative to each other such that the reagent chambers are in turn moved past the penetration means, enabling the penetration means to penetrate through the layer of disruptable material sealing the reagent chamber and then brought into alignment with the sample collection area of the sample loading body positioned in the access port, bringing the sample into contact with the contents of the reagent chamber. The assay cassette may further comprise a layer of absorbent material positioned between the interior surfaces of the reagent holding portion and the sample receiving portion. The layer of absorbent material comprises an opening in alignment with the access port of the sample receiving portion and may comprise a further opening in alignment with a penetration means forming part of the sample receiving portion. The absorbent layer functions to absorb any excess liquid reagents released from the reagent chambers when the device is in use, thereby preventing leakage and minimising the potential for carry-over of reagents between adjacent reagent chambers. The overall fluid absorbing capacity of the absorbent layer should ideally exceed the total volume of liquid reagents incorporated into the device such that when the test is complete all liquid reagents remaining in the device will be absorbed. The device can thus be disposed of in a dry format not requiring liquid containment facilities. The invention also encompasses an assay cassette which can function without a separate sample loading body. In this embodiment a sample collection area is located on the interior surface of the sample receiving portion a short distance from the access port, thus the sample receiving portion also functions as the sample loading body. When the device is in use, the sample is added directly to one of the chambers of the reagent holding portion via the access port in the sample receiving portion. Preferably a cover is then placed over the access port to seal the device, advantageously a snap-fit cover can be used. On rotation of the sample receiving portion relative to the reagent holding portion the sample collection area is brought into contact with the sample. Then successively the other reagent chambers are brought into contact with the sample collection area. In this embodiment a penetration means may be located adjacent to the access port. The radial configuration of the assay cassette provides several advantages over the previously known devices. In particular, the radial configuration permits the inclusion of many more reagent chambers whilst keeping the overall device small by locating the reagent chambers on the circumference of a circle. In addition, because the sample loading body once in place does not move relative to the assay cassette the overall device is fixed in size before and during operation and so is more amenable to automation of the assay procedure. Since the assay cassette is entirely self contained and all reagents are incorporated during manufacture there is no need for complex reagent addition or wash steps. After addition of the sample to the sample collection area the sample loading body is loaded into place so that the sample collection area is positioned in the access port on the sample receiving portion of the assay cassette. Thereafter, the sample loading body remains in place throughout the assay procedure. In the case of an automated assay, the entire device is then placed inside an assay instrument which may carry out the assay procedure according to a pre-determined program. The assay instrument should comprise a motor drive to effect controlled rotation of the reagent holding portion of the assay cassette relative to the sample receiving portion and may also function as a measuring instrument to measure the result or read-out of the assay procedure. A portable hand-held assay instrument containing a motor drive to effect rotation of the assay cassette but no complicated measuring instrumentation may be constructed for use in the patient's home or in the field. A more complex instrument incorporating measuring instrumentation would be more suitable for use in the clinic or the doctor's office. The latter instrument may also be pre-programmed with the calibration data necessary to provide a fully quantitative result. To facilitate correct positioning of the assay cassette relative to the motor drive of the assay instrument the outer surface of the reagent holding portion of the assay cassette may be provided with a location means, such as a cog, positioned substantially centrally on the axis of rotation of the assay cassette. It will be readily apparent that relative rotation of the sample receiving portion and the reagent holding portion can be achieved by retaining the sample receiving portion in a fixed location whilst moving the reagent holding portion and by maintaining the reagent holding portion in a fixed location whilst moving the sample receiving portion. In automated systems, the preferred configuration is one in which the sample receiving portion is held fixed and the reagent holding portion is rotated relative to it. In this manner the sample collection area may be held in alignment with a measuring means, such as an optical measuring instrument. The invention provides a clean and efficient device which does not require handling of any liquids and can be operated by an unskilled user to provide rapid quantitative assay results. Such a device is ideally suited to the field of diagnostics, specifically immunoassay or DNA amplification or hybridisation assays. It can be used in the doctor's office or the clinic to assist a physician in diagnosis or in monitoring the progression of disease. One useful example would be in the field of cancer diagnosis and prognosis. Detection/measurement of cancer-associated markers in the blood is becoming an increasingly powerful tool to assist at all stages in the treatment of cancer, including the detection of early neoplasia, the diagnosis of disease, and in monitoring disease progression or response to treatment. Using the device of the invention a physician or nurse will be able to perform rapid and quantitative tests for the presence of cancer- associated markers in the clinic, the doctor' s office or at the patient's bedside. Moreover, because the device is suitable for use by an unskilled user and does not require dispensing or measuring of liquid reagents in order to achieve a quantitative result it is also suited to use in home testing. In a further embodiment of the invention, the assay cassette may be adapted for carrying out a plurality of analytical determinations in parallel. This can be achieved by having two or more series of discrete reagent chambers in the reagent holding portion, each series of chambers containing successively the reagents required for one analytical determination, and a corresponding number of access ports in the sample receiving portion. Conveniently, the two or more series of reagent chambers may be positioned substantially along the circumferences of a series of concentric circles centred on the axis of rotation of the reagent holding portion relative to the sample receiving portion. A sample loading body for use with such an assay cassette may comprise two or more sample collection areas adapted to locate within the two or more access ports when the device is in use. Alternatively, two or more sample loading bodies may be used, each one adapted to locate in a specific position on the sample receiving portion. The feature of multiple access ports may also be included in the embodiment of the assay cassette device adapted to function without a separate sample loading body in order to carry out more than one assay simultaneously. The present invention will be further described with reference to the accompanying schematic drawings, in which: - Figure 1A is a plan view of the sample loading body for use in the device of the invention, Fig IB is an underside plan view of the sample loading body, Figure 2 is a plan view of the assay cassette of the invention, Figure 3 is a plan view of the device of the invention illustrating how the sample loading body is loaded into the assay cassette, Figure 4 is an underside plan view of the assay cassette, Figure 5 is an expanded view of the assay cassette, Figures 6a and βb are cross-sectional views of an analytical device of the invention in operation, Figure 7 is a plan view of an assay cassette according to the invention in which the sample loading body is attached to the sample receiving portion of the assay cassette . Figure 8 is an expanded view of a device according to the invention which does not require a separate sample loading body. Referring to the Drawings, Figures 1A and IB illustrate the sample loading body 1 which is a plastics member having at least one sample collection area. In this embodiment, the sample loading body has three pads of absorbent material 2 bonded thereto. At least one of these pads functions as the sample collection area for addition of the test sample. Positive or negative control samples may be added to the remaining pads. The arrangement of the pads shown in Figure IB is intended to be merely illustrative and alternative configurations may be used. For example, three or more pads may be arranged radially. Figures 2-3 illustrate schematically the assay cassette of the invention. In the preferred configuration, the assay cassette is disc-shaped and formed from a suitable mouldable plastics material. Figure 2 is a plan view illustrating the sample receiving portion of the assay cassette 3. The sample receiving portion is provided with access port 4 and may be further provided with a recess 5 shaped to cooperate with a sample loading body. Figure 3 illustrates schematically how the sample loading body 1 may be located in the recess formed on the sample receiving portion of the assay cassette such that the sample collection area 2 is positioned in the access port 4. Figure 4 is an underside plan view of the assay cassette illustrating the reagent holding portion 6. The reagent holding portion has a series of reagent chambers 7-18 formed therein. The embodiment illustrated in Figure 4 has a total of 12 reagent chambers but it is to be understood that devices can be constructed with varying numbers of reagent chambers, as required. Chamber 18 is the signal detection chamber. A location means 19 is provided on the outer surface of the reagent holding portion to facilitate location of the assay cassette in an assay instrument. In this embodiment, the location means comprises a cog which is adapted to co-operate with a motor drive provided by the assay instrument. Figure 5 is an expanded view illustrating schematically the construction of the assay cassette, comprising a sample receiving portion 3 and a reagent holding portion 6. The reagent holding portion is coupled to the sample receiving portion so as to be rotatable relative to the sample receiving portion about a common axis of rotation. In the embodiment shown in Figure 5 this is be achieved is by extending the edge of the sample receiving portion to form a lip 20, making the outer circumference of the reagent holding portion slightly smaller than the inner circumference of the lip of the sample receiving portion such that the reagent holding portion fits and is able to rotate within the sample receiving portion. The assay cassette is further provided with a layer of disruptable material 21 such as a thin foil which, when the assay cassette is assembled, is bonded to the upper surface of the reagent holding portion in order to seal the reagent chambers. A layer of absorbent material 22 is provided between the disruptable layer and the sample receiving portion. The absorbent layer contains a first opening 23 which is aligned in registration with the access port formed in the sample receiving portion and a second opening 24 which is aligned in registration with a penetration means attached to the underside of the sample receiving portion (not shown) so that the penetration means is able to contact the layer of disruptable material when the assay cassette is assembled. Figures 6A and 6B illustrate stages in the operation of an analytical device of the invention. The sample loading body 1 is positioned within a cooperating recess on the sample receiving portion, positioning the absorbent material forming the sample collection area 2 within the access port. Figure βa shows a cross section of the device in a first position with the access port in alignment with one of the reagent chambers 13. The absorbent material projects through the sample holding body and through the absorbent layer 22 in order to contact the contents of the reagent chamber. The disruptable layer 21 sealing reagent chamber 13 has previously been cut by the action of the penetration means 25 which is positioned adjacent to the access port and attached to the interior surface of the sample receiving portion. The penetration means is shown in the process of cutting the disruptable layer sealing reagent chamber 14, reagent chamber 15 remains sealed. As shown in Figure 6A, the reagent chambers are entirely separate from one another. The direction of movement of the reagent chambers relative to the absorbent body 2 and the penetration means 25 is indicated. Figure 6B shows a cross section of the device in a second position, the reagent holding portion having been rotated relative to the sample receiving portion in the direction indicated. The absorbent body 2 is now positioned between reagent chambers 14 and 15, illustrating how the absorbent body may be compressed between the surface of the reagent holding portion and the sample loading body as it moves between reagent chambers. This compression assists the removal of excess liquid from the absorbent body. Reagent chamber 15 is shallower than reagent chambers 13, 14, 16 and 17 and does not contain liquid reagents. The absorbent body will be compressed as it moves through chamber 15 facilitating the removal of further excess liquid reagents. The penetration means is positioned between reagent chambers 15 and 16 which is still sealed by an intact disruptable layer 21. Figures 6A and 6B illustrate how the penetration means is able to move relative to the interior surface of the sample loading portion. In Figure 6A the penetration means is shown in an extended position within a reagent chamber, whilst in Figure 6B it is shown in a retracted position as it is moved between reagent chambers . Figure 7 illustrates an assay cassette wherein the sample loading body is attached to/formed integrally with the sample receiving portion and is movable about a flexible or hinged joint 26. Figure 8 illustrates a further embodiment of the invention which is an assay cassette which does not require a separate sample loading body. The sample collection area 2 is located on the inner surface of the sample receiving portion close to the access port 4. Alternative arrangements of the sample collection area are possible, for example in may be formed in a circumferential ring around the access port. Opening 23 in the absorbent layer is elongated in order to align with the access port and accommodate the sample collection area. In use, the sample to be tested is loaded into the first chamber of the reagent holding portion of the device through the access port 4. The access port is then sealed by closure 27. The pads forming the sample collection area project down into the chambers of the reagent holding portion and thus come into contact with the sample added to the first chamber and then successively with the reagents required to complete an assay. The construction and operation of the device of the invention will be further understood with reference to the following experimental examples, together with the accompanying Figures in which: Figure 9 shows the results of an assay for human IgA using the device of the invention, as described in Example 4. The concentration (ng/ml) of the IgA solution added to the foam pads on the sample loading body is shown on the x-axis and colour density of the foam pads on completion of the assay on the y-axis, Figure 10 illustrates the effect of wash number on signal-to-noise ratio in an IgA assay using the device of the invention, as described in Examples 4 and 5. Number of washes is shown on the x-axis and colour density of the foam pads on the y-axis. Figures 11 and 12 show standard curves for the detection of c-erbB2 using the device of the invention, as described in Example 7. The concentration (HNU/ml) of the c-erbB2 solution added to the foam pads of the sample loading body is shown on the x-axis and the colour density of the foam pads on completion of the assay on the y-axis. Example 1 Preparation of foams bonded -to sample loading body- Open cell PVC foam (supplied by Duflex Ltd., Derby, UK) supplied in sheets at 3mm thickness was positioned over the flat sector at the end of a sample loading body and an ultrasound welding horn (supplied by Renfrew Stylengineering Ltd, Leicester, UK) configured to weld the extremity of the foam, but leaving interior Λ pillows', was used to bond the foam to the material of the sample loading body. A period of 30 seconds at 100 watts was used to ensure secure bonding between the foam and the plastic surface. This procedure created foam reaction zones on the end of the sample loading body which were securely held in place by the welding process. Example 2 The procedure for coating foams with antibody In this example the foams were coated with an anti human IgA antibody. The foam segments on the sample loading body were washed once in 0.01 M Tris/Cl buffer pH 7.5. The foam pieces were coated with mouse monoclonal anti -human IgA antibody (supplied by Zymed Laboratories, Inc. USA) at 10 μg/ml in 0.01 M Tris/Cl pH 7.5 by adding 20μl to each foam sector. Coating proceeded for 12-16 hours at 4°C in a sealed moist chamber. Control foam segments on the sample loading body were washed once in 0.01 M Tris/Cl pH 7.5 buffer and three times in 0.01 M Tris/Cl pH 7.5 containing 0.05% (v/v) Tween 20. Both coated foams and controls were glazed in 0.01 M Tris/Cl pH 7.5 buffer containing 0.1 % (w/v) BSA and 1 % (w/v) lactose by washing three times. The sample loading body could then be used immediately in an assay. Reagent suppliers were as follows: Trizma-base, Sigma Chemical Co. /Sigma-Aldrich Chemie Gmbh; NaCl, J. T. Baker 0278 or Sigma S7653; Tween 20, Merck/KEBO lab Denmark; bovine serum albumin (BSA) Fraction V, Sigma A4503; α-Lactose, Sigma L3625; MgCl 2 , J. T. Baker; distilled water, Bie & Berntsen, Denmark. To test the coating of the antibody on the foam sectors the entire sample loading body was placed in SuperBlock (supplied by Pierce Chemical Co. USA) for 2 min at room temperature (22°C) . The foams were then pressed to remove excess fluid using absorbent paper. Then 25μl of human IgA, at the concentrations shown in Table 1, in 0.05 M Tris/Cl pH 7.5 containing 0.1 M NaCl, 1 mM MgCl 2 , 1% (w/v) BSA and 0.1 % (v/v) Tween 20 was added to all three foam sectors on the sample loading body. The foams were then incubated at room temperature (22°C) for 5 min and blotted dry. Then 25 μl of alkaline phosphatase conjugated rabbit anti-human IgA (supplied by DAKO A/S, Denmark) diluted 1:25 in 0.05 M Tris/Cl buffer pH 7.5 containing 0.1 M NaCl, 1 mM MgCl 2 , 1% (w/v) BSA and 0.1 (v/v) % Tween 20 was added to each foam sector for a further incubation period of 5 min. The foams were washed three times in 0.01 M Tris/Cl pH 7.5 containing 0.05% (v/v) Tween 20 and then, after blotting, 25μl of BCIP/NBT substrate (supplied by Zymed Laboratories, Inc. USA) was added to each foam sector. After incubating for 5 minutes at room temperature (22°C) the foams were washed with distilled water to stop the colour development reaction and the foams were then scanned for colour density using a DUOSCAN T1200 (supplied by AGFA, Germany) connected to a PC running the software program "Cream for Windows, version 1.0" (supplied by Kem-En-Tech A/S, Denmark) . The Cream software provides a quantitative measure of the colour density in the foams. The results in Table 1 show that the foams are coated with specific antibody, a standard curve is obtained with increasing concentrations of IgA and the backgrounds on the uncoated foams are low. Table 1: Colour density signal from the AGFA scanner/Cream software. Example 3 Preparation of the assay cassette base The reagent holding portion was supplied by Renfrew Stylengineering Ltd, Leicester, UK. The component was fabricated from PVC sheet (1.5 mm thickness) using a vacuum forming process. The reagent holding portion was placed in a holder and the appropriate chambers were filled with fluid reagents according to the specific assay procedure. A sheet of aluminium foil (with one side coated with lacquer) was then cut to fit the diameter of the reagent holding portion and was placed over the component with the lacquered surface juxtaposed to the surface of the reagent holding portion. A domestic iron set to "silk" was then used to seal the foil to the surface of the reagent handling portion. The component was then examined for leaks and for signs of overheating in the reagent chambers. To complete the reagent handling portion the foil was trimmed around the edge and the foil surface covering the first chamber was removed to allow positioning of the sample loading body. Example 4 An assay for human IgA in the assay cassette This example describes an assay for human IgA run in the assay cassette. A manually driven rig was constructed into which the reagent holding portion, as prepared in Example 3, is seated. A sheet of absorbent material (supplied by Renfrew Stylengineering Ltd) was applied to the upper surface of the reagent holding portion and then the sample receiving portion of the assay cassette was clipped in place. The sample receiving portion of the assay cassette has a knife placed in the interior surface that is adapted to pierce the foil of the reagent chambers, thus allowing the fluid to reach the foam sample collection area on the sample loading body. To run the assay the sample was added to the foam sample collection area on the sample loading body and, after a short incubation to allow the IgA to bind to the antibody on the foam surface, the sample loading body was clipped in place on the sample receiving portion of the assay cassette and the sample receiving portion turned manually to bring the foam sectors successively through the ruptured reagent compartments. To run the assay on the assay cassette a sample loading body was prepared according to the procedure in Example 2. After coating with antibody using 25μl of mouse monoclonal anti human IgA the foam sectors were washed with 0.01M Tris/Cl pH 7.5 and the entire sample loading body was placed in SuperBlock (supplied by Pierce Chemical Co.) for 2 min at room temperature (22°C) . After blotting 25μl of human IgA at 400, 200, 100, 50, 25, or 0 ng/ l in 0.05 M Tris/Cl pH 7.5 containing 0.1 M NaCl, 1 mM MgCl 2 , 1% (w/v) BSA and 0.1 % (v/v) Tween 20 was added to all three foam sectors on the sample loading body. The foams were then incubated at room temperature 22°C for 3 min. The sample loading body was then clipped into place on the sample receiving portion of the assay cassette and the foam sectors were transported through the first chamber of the reagent holding portion, which was filled with 250 μl SuperBlock and then into the second chamber containing 250 μl alkaline phosphatase conjugated rabbit anti-human IgA (supplied by DAKO A/S, Denmark) diluted 1:25 in 0.05 M Tris/Cl buffer pH 7.5 containing 0.1 M NaCl,l mM MgCl 2 , 1% (w/v) BSA and 0.1 % (v/v) Tween 20. The incubation time in the second chamber was 6 min. The foams were then transported through the next seven chambers which were filled with 250 μl wash buffer of 0.01 M Tris/Cl pH 7.5 containing 0.05% (w/v) Tween 20. The final chamber (the 10th) contained 250 μl of the substrate BCIP/NBT (supplied by Zymed Laboratories, Inc. USA) . The foams were incubated for 6 min and colour development took place in the foam structure. Then the sample loading body was removed from the sample receiving portion of the assay cassette, the foams were washed with distilled water to stop the colour development reaction and the foams were then scanned for colour density using a DUOSCAN T1200 (supplied by AGFA, Germany) connected to a PC running the software program "Cream for Windows, version 1.0" (supplied by Kem-En-Tech A/S, Denmark) . The Cream software provides a quantitative measure of the colour density in the foams. The results of a typical assay are presented in Figure 9. Example 5 Investigating the effect of wash number in the assay cassette An assay for human IgA was carried out essentially as described in Example 4. A powered version of the rig was used where the rotation of the assay cassette was controlled by a stepper motor under the control of a timing device. The incubation period in the mouse anti-human alkaline phosphatase conjugate was 4 min 25 seconds. After the incubation in the conjugate the motor transported the sample loading body through eight wash chambers which either contained 275 μl of wash buffer or were empty. The final (10th) chamber contained the substrate BCIP/NBT (supplied by Zymed Laboratories, Inc. USA) and the incubation period was 4 min 25 seconds. The results in Figure 10 indicate that the optimal signal to noise ratio in the powered version of the assay cassette was achieved at seven washes. Example 6 Coating foams with SKBR-3 extract In this example PVC foam used for the sample collection area on the sample loading body was coated with an ammonium sulphate extract of SKBR-3 cells (supplied by University of Southern Denmark, Odense) . The extract contains the human protein c-erb at 320,000 HNU/ l (measured by an ELISA kit supplied by Oncogene Sciences Inc) which is produced by the cells in culture. The cell extract was diluted to give varying concentrations of c-erb in 0.01 M Tris/HCl buffer pH7.5 and 25 μl was added to each foam piece. The foams were incubated at 4°C overnight. They were then washed with the Tris/Cl wash buffer and then incubated with Superblock for ten minutes. After blotting 25 μl of anti c-erb monoclonal antibody (Mab 15, supplied by Neomarkers Inc., USA) at 1/100 dilution in Tris/Cl buffer was added to the foam pieces and incubated for 5 minutes at 22°C. After washing three times and blotting 25 μl of anti-mouse IgG alkaline phosphatase conjugate (supplied by Amdex A/S, Denmark) was added to the foams and incubated for a further five minutes. After washing for a further three times with Tris/Cl buffer and blotting 25 μl of the substrate BCIP/NBT (supplied by Zymed Laboratories, Inc. USA) was added to the foam pieces and after 10 minutes the foams were washed with distilled water and the colour density was read with the AGFA/Cream system. The results in Table 2 show that the c-erb in the cell extract binds to the foam pieces and can be detected by specific mouse monoclonal antibody in a quantitative assay. Table 2 Example 7 An assay for c-erb in the assay cassette In this example the foam sample collection areas on a sample loading body were coated with different concentrations of c-erb as described in Example 6 and incubated with the mouse monoclonal anti-c-erb antibody at 1/100 dilution in Tris/Cl buffer for 15 minutes. After 3 washes with Tris/Cl wash buffer the sample loading body was clipped into the sample receiving portion of the assay cassette and the manual rig was used to continue the assay. The first chamber contained anti mouse IgG-alkaline phosphatase conjugate at 1/500 in Tris/Cl conjugate buffer and the incubation time was five minutes. Then the sample loading body was rotated through seven washes using 275 μl of Tris/Cl wash buffer, reaching the substrate BCIP/NBT with a final incubation period of 10 min before removal from the assay cassette and washing with distilled water to stop the reaction. The results from the Agfa/Cream system are presented in Figures 11 and 12 and show that the assay cassette is capable of generating a standard curve for c-erb.

Claims: Claims : 1. An assay cassette for use in carrying out analytical determinations, the assay cassette comprising: a sample receiving portion and a reagent holding portion which are rotatable relative to each other, the reagent holding portion having formed therein a series of discrete reagent chambers which contain, successively, the reagents required to perform the analytical determination, the reagent chambers being positioned at an eccentric location relative to the axis of rotation and the sample receiving portion defining an access port positioned at an eccentric location relative to the same axis of rotation such that it may be brought into alignment with successive reagent chambers by relative rotation of the reagent holding portion and the sample receiving portion. 2. An assay cassette as claimed in claim 1 wherein the interior surface of the reagent holding portion comprises a layer of disruptable material operable to seal the reagent chambers prior to use. 3. An assay cassette as claimed in claim 2 wherein the sample receiving portion further comprises a penetration means positioned adjacent to said access port, the penetration means being adapted to penetrate through the disruptable layer sealing the reagent chambers in the reagent holding portion. 4. An assay cassette as claimed in claim 3 wherein the penetration means is a blade. 5. An assay cassette as claimed in claim 3 or claim 4 wherein the penetration means is mounted on spring means. 6. An assay cassette as claimed in any one of the preceding claims which further comprises a layer of absorbent material located between the reagent holding portion and the sample receiving portion, the layer of absorbent material comprising an opening in alignment with the access port. 7. An assay cassette as claimed in any one of the preceding claims wherein the signal detection chamber is provided with at least one transparent wall or a window. 8. An assay cassette as claimed in any one of the preceding claims wherein the reagent holding portion has one series of separate discrete reagent chambers positioned substantially along the circumference of a circle centred on the axis of rotation. 9. An assay cassette as claimed in any one of claims 1 to 8 wherein the series of reagent chambers contains the reagents required to carry out a particular analytical determination. 10. An assay cassette as claimed in any one of claims 1 to 9 which comprises at least one sample collection area for the collection of a sample to be analysed. 11. An assay cassette as claimed in claim 10 wherein the sample collection area comprises an absorbent body affixed to the interior surface of the sample receiving portion proximal to the access port. 12. A device for use in analytical determinations comprising an assay cassette as claimed in any one of claims 1 to 9 and a sample loading body comprising at least one sample collection area for the collection of a sample to be analysed. 13. A device as claimed in claim 12 wherein the sample collection area comprises an absorbent body bonded to the sample loading body. 14. A device as claimed in claim 12 or claim 13 wherein the sample loading body is adapted to locate in a recess formed on the outer surface of the sample receiving portion of the assay cassette such that the sample collection area is positioned in the access port, thereby enabling the sample collection area to be sequentially brought into alignment with successive reagent chambers when the device is in use by relative rotation of the reagent holding portion and the sample receiving portion. 15. An assay cassette device for carrying out a plurality of analytical determinations which is adapted for use with a sample loading body, the assay cassette comprising: a sample receiving portion and a reagent holding portion which are rotatable relative to each other, the reagent holding portion having formed therein two or more distinct series of separate discrete reagent chambers being positioned substantially along the circumferences of a series of concentric circles centred on the axis of rotation, each series of reagent chambers containing, successively, the reagents required to perform an analytical determination the sample receiving portion defining two or more access ports positioned at eccentric locations relative to the rotation axis, wherein each one of the access ports is aligned in registration with one of the series of reagent chambers formed in the reagent holding portion such that the access ports may be brought into alignment with successive reagent chambers by relative rotation of the reagent holding portion, j 16. A device for use in analytical determinations comprising an assay cassette as claimed in claim 15 and a sample loading body adapted for use therewith. 17. An assay cassette substantially as described herein with reference to and as illustrated in any one of Figures 2, 3, 4, 5 or 7 of the accompanying drawings . 18. A device for use in analytical determinations substantially as described herein with reference to and as illustrated in any one of Figures 6A, 6B or 8 of the accompanying drawings.

Inventors: RENFREW BRUCE, STANLEY CHRISTOPHER JOHN, RENFREW, BRUCE, STANLEY, CHRISTOPHER, JOHN
Applicants: MEDIC GROUP EUROP AS, RENFREW BRUCE, STANLEY CHRISTOPHER JOHN, MEDIC GROUP EUROPE A/S, RENFREW, BRUCE, STANLEY, CHRISTOPHER, JOHN
Application year: 2000
Main classification: B01L3
IPC codes: B01L3, G01N33, G01N35