Abstract:
A method of assaying for an analyte including the steps of: (i) passing a sample suspected of containing an analyte and reagents comprising a target ligand-analyte receptor conjugate and a detectable tracer containing a label for the analyte through filter apparatus containing a plurality of discrete flow zones wherein at least one zone functions as a capture zone having bonded thereto a receptor ligand for said target ligand; (ii) allowing the sample and accompanying reagents to incubate prior to passage through said at least one zone to facilitate formation of complex(es) of said conjugate and said at least one analyte in a liquid or fluid phase; and (iii) detecting the presence of analyte in the sample by activation of the label in said at least one zone after binding of the complex(es) conjugate to the associated receptor ligand(s).

Description:
FIELD OF THE INVENTION 
     THIS INVENTION relates to an assay method and apparatus suitable for determination of analyte wherein assay apparatus is provided having one or multiple capture zones incorporating a receptor ligand for detection of analyte. 
     BACKGROUND OF THE INVENTION 
     Lateral flow membranes for immunoassays are well known and reference may be made, for example, to U.S. Pat. No. 4,943,522 which refers to a porous membrane capable of non-bibulous lateral flow which is used as an assay substrate. A member of a binding pair is affixed in an indicator zone defined in the substrate. A sample is applied at a position distant from the indicator zone and permitted to flow laterally through the zone. Any analyte in the sample is complexed by the affixed binding partner and detected. A method of detection employs entrapment of observable particles in the complex. 
     Another lateral flow assay is described in U.S. Pat. No. 5,798,273 wherein-the presence or amount of an analyte in a sample may be determined by contacting a sample with anti-analyte antibodies which bind to the analyte or to both analyte and an analyte analog and an assay tracer prior to application to a lateral flow device. A first member of a binding pair is incorporated with the tracer. The lateral flow device comprises a solid support having a sample addition area, a capture area containing analyte or analyte analog which is immobilized thereon and a read out area comprising one or a plurality of zones having a second member for the binding pair immobilized thereon which binds with the first member to detect the presence or amount of analyte in the sample. 
     Lateral flow type assays are also described in European Patent No. EP0291194 which refers to a casing having a dry porous carrier. A liquid test sample may be applied to the dry porous carrier which has a labelled specific binding reagent for an analyte which reagent is freely movable within the porous carrier when in the moist state and unlabelled specific binding reagent for the same analyte which is immobilized in a detection zone on the porous carrier. The liquid sample may pick up labelled reagent and thereafter permeate to the detection zone. The label used is a particulate direct label. 
     Reference may also be made to lateral flow assay devices which are described in U.S. Pat. Nos. 5,607,863, 5,648,274 and 5,468,648 which each refer to devices having a first opposable component and a second opposable component wherein at least one of the opposable components comprises capture and detection zones and at least one of the opposable components includes an absorber for contacting the other of the opposable components for detection of analyte. Each of these references describe capture zones which incorporate specific binding partners for the analyte. U.S. Pat. No. 5,468,648 describes provision of a test strip that can carry out multiple assays simultaneously. 
     Reference may also be made to U.S. Pat. Nos. 5,401,667, 4,855,240, 5,602,037, 5,712,170 and 4,727,019 which all refer to complicated forms of lateral flow assay devices and each of which incorporates capture zones for capture reagent or receptor to bind directly to analyte in a sample being tested. 
     Reference may also be made to U.S. Pat. No. 5,185,127 which refers to a vertical filter stack in an enclosure having a base portion and a lid. The filter stack has an initial hydrophilic membrane having a binder for analyte thereon, a hydrophobic membrane under the hydrophilic membrane and a pad of absorbent material under the hydrophobic membrane. 
     Reference may also be made to the following references which use a lateral flow device described above in U.S. Pat. No. 5,468,648, i.e.: 
     (i) Chew et al., 1998, Clin. Diagn. Lab. Immunol. 5 407-409; 
     (ii) Vaughn et al., 1998, J. Clin. Micro. 36 234-238; 
     (iii) Lam et al., 1998, J. Clin. Virol. 10 75-81; 
     (iv) Cuzzubbo et al.., Jan/Mar 1998, Singapore Microbiologist, 16-17; and 
     (v) Devine et al., 1998, Analytical Testing Technology 15 16. 
     As is clear from the prior art referred to above, a feature of such prior art is the provision of lateral flow devices or filter stacks which include one or a plurality of capture zones for direct binding of analyte for detection of the analyte. 
     However, it has now been realised that such prior art devices have several disadvantages, the most notable of which is the following: 
     (i) by employing capture zones having a specific binding agent for the analyte, it will be appreciated that such binding agents, which are usually proteins, may in some cases comprise unstable biological material that is usually incapable of being stored at room temperature; 
     (ii) by virtue of (i), it is usual that such prior art devices can only be used once and therefore must be discarded; 
     (iii) only relatively small volumes of sample and accompanying reagents can be accommodated due to the necessity for controlling the flow of sample and accompanying reagents through the prior art device to relatively slow speeds; 
     (iv) often accumulation of complexes occur both in the capture zones and non-capture zones restricting the flow of sample and reagents through the prior art device; 
     (v) often non-specific reactions and aggregation of reactants may cause non-specific binding; and 
     (vi) serious limitations apply to processing detection of multiple analytes in prior art devices. For example, when detection of both multiple specificities of IgG and IgM classes of antibodies is being attempted, it is not possible to use anti-IgG or anti-IgM receptors in the capture zones or antigens specific to IgG or IgM antibodies because of the danger of cross reactions occurring, preventing the differentiation between antibody specificity and immunoglobulin class. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide an assay method to reduce the affect of the abovementioned disadvantages. 
     It is a further object of the invention to provide an assay apparatus which is of simple construction and which can be used for assaying a number of different analytes simultaneously. 
     In accordance with the invention, there is provided a method of assaying for an analyte including the steps of: 
     (i) mixing a liquid sample suspected of containing an analyte and reagents comprising a target ligand analyte receptor conjugate and a detectable tracer containing a label for the analyte whereby if the analyte is present, there is formed in solution a complex of analyte coupled to the conjugate after incubation of the mixture; 
     (ii) passing the mixture through filter apparatus containing a plurality of discrete flow zones wherein at least one zone functions as a capture zone having bonded thereto a receptor ligand for the target ligand; 
     (iii) detecting the presence of analyte in the sample by activation of the label in said at least one zone after binding of the complex to the receptor ligand; and 
     (iv) continuing the passage of the mixture past said at least one zone to a wicking zone for liquid entrapment. 
     Thus, one of the principal features of the present invention is that any analyte complex(es) involving the target ligand-analyte receptor conjugate are formed in a liquid or fluid phase prior to retention on a capture zone when the complex(es) bind to associated receptor ligand(s). 
     The above method is especially adapted for assaying a number of different analytes simultaneously. To this end, the assay apparatus may have a plurality of capture zones which have a different receptor ligand bonded thereto. The sample in step (i) may also be combined with a target ligand-analyte receptor conjugate specific for each analyte being assayed and a detectable tracer incorporating a label for each analyte. In this embodiment, step (ii) facilitates the activation of each analyte by detection of the label in each zone after bonding of each complex to its associated receptor ligand. 
     The method of the invention may be used for detection of a wide variety of different analytes. In this regard, it will be appreciated that the term “analyte” refers to any compound or composition to be detected that is capable of binding specifically to a binding agent. Examples of binding agents are antibodies, antigens or chelating agents or receptor ligands discussed hereinafter. 
     The term “analyte” may also include within its scope analyte analogs as referred to in U.S. Pat. No. 5,624,809 which is herein incorporated by reference in its entirety. 
     Analytes may have a simple binding site (i.e. monovalent) or multiple binding sites (i.e. polyvalent). Polyvalent analytes may comprise polymers inclusive of polypeptides, proteins, polysaccharides, nucleic acids or combinations thereof. 
     Analytes may also include mono-epitopic liquid species, such as drugs, metabolites, pesticides and pollutants. 
     Examples of a wide variety of analytes to which the invention is relevant are mentioned in U.S. Pat. Nos. 4,943,522 and 5,624,809, both of which are incorporated herein by reference. 
     Other analytes include immunoglobulins IgA, IgG, IgE and IgM, enzymes and receptors inclusive of nucleic acids and proteins as described in U.S. Pat. No. 5,624,809. 
     The term “tracer” as made herein may comprise any suitable binding partner specific for analyte(s) of interest contained in a sample being tested. A convenient form of tracer is an antibody specific for an antigen when the analyte of interest. The label may be any conventional marker which after binding of the analyte to the tracer provides a detectable signal. Examples of labels may be a radioactive species, fluorescent species, chemiluminescent species or an enzyme for which a substrate convertible to a coloured product exists such as a peroxidase or alkaline phosphatase. Examples of appropriate tracers or labels are referred to in U.S. Pat. No. 5,208,143, which is herein incorporated by reference, or U.S. Pat. No. 5,624,809 supra. 
     The preferred label in relation to the present invention is colloidal gold which may be conjugated to antibody or paratope thereof or antigen or epitope thereof. Also may be used as labels are coloured microparticles, coloured dendrimers or coloured dendrimer type molecules. 
     The term “receptor ligand” as used herein refers to any species which may be immobilized or bound to a filter zone or flow zone and which is a specific binding partner for a “target ligand”. Examples of receptor ligands are antibodies, antigens including haptens, dendrimers, dendrimetric type molecules, oligomers comprising a sequence of monomers selected from the group consisting of amino acids, carbamates, sulfones, sulfoxides, nucleotides, carbohydrates, ureas, phosphonates, liquids, esters or combination thereof or any other molecule or composition capable of recognizing a particular site of a molecule which may be an epitopic or determinant site. Naturally occurring receptor ligands also include nucleic acids, metal chelates, enzymes, biotin, lectins, oligonucleotides and peptides. Dendrimers or dendrimeric-type molecules may also be used as receptor ligands. 
     The term “target ligand” as used herein refers specifically to the specific binding partner to the “receptor ligand” and thus may include any of the species discussed above for the receptor ligand. It will also be appreciated that the “target ligand” may also be bound to a specific carrier such as dendrimers, microparticles, latex beads, dendrimers, dendrimeric-type molecules, branched polymers, zeolites, fullerenes, streptavidin, avidin or other substance capable of conjugation to the target ligand. 
     The microparticles when used as carriers may be of any convenient size that are suitably small enough that they may form a suspension in aqueous solution to facilitate their coating with an antibody, antigen, oligonucleotide or any of the species discussed above for the receptor ligand or target ligand. The average individual size of the microparticles is about 0.01-50 microns, more preferably 1-10 microns. The microparticles can be selected from any suitable type of particulate material, such as polystyrene, polymethylacrylate, polypropylene, silica, teflon, fluropolymers, latex, polytetrafluoroethylene, polyacrylanitrile or polycarbonate. 
     Reference may also be made to Australian Patent Application Nos. 22431/95 or 22889/95 in the name of Dade International, Inc. or U.S. Pat. No. 5,714,166 for the types of dendrimers that may be used as carriers. Therefore, Australian Patent Application Nos. 22431/95 and 22889/95 and U.S. Pat. No. 5,714,166 are incorporated herein by reference. 
     The attachment between the receptor ligand and the target ligand may utilize covalent, coulombic, hydrophobic (inclusive of hydrogen binding) or chelation type association between mating functional groups of the target ligand and receptor ligand. An example of such functional groups are thiol groups that bond together to form an —S—S— bond. 
     A coulombic interaction is an ionic interaction between two oppositely charged species. For example, dendrimeric polymers with a positive or negative overall charge may be attracted to a receptor ligand with an opposite charge. 
     Chelation type associations make use of metal ions such as, but not limited to, the metals Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Pb, Sn, Ge, Sc, Y, lanthanides and actinides, B, Al, Ga, In, Tl, Li, Na, K, Rb, Cs, Fr and Be, Mg, Ca, Sr, Ba, Ra and transition metals. Metal ions immobilized onto solid supports such as membrane filters or microparticles may comprise receptor ligands which will chelate with appropriate coordinating groups on the target ligand. An example of a receptor ligand is iminodiacetic acid complexed with Ni 2+  binds with target ligands that have an affinity for Ni 2+  acid, such as polyhistidine. 
     The term “analyte receptor” as used herein refers to any specific binding partner for the analyte and thus may comprise antibodies, antigens, oligonucleotides, peptides, proteins or other species discussed above for the receptor ligand or target ligand. 
     The term “analyte receptor-target ligand conjugate” as used herein refers to the analyte receptor when conjugated to the target ligand and thus may comprise, for example, a peptide, nucleic acid or combinations of species of analyte receptor referred to above and target ligand referred to above. This term may also refer to the presence of a carrier as described above in relation to the target ligand. 
     In another aspect of the invention, there is provided assay apparatus comprising a plurality of discrete flow zones characterized in that there is provided an incubation zone upstream of one or more capture zones which only incorporate immobilized receptor ligand which does not bind directly to analyte in use. 
     The assay apparatus may comprise a lateral strip as shown hereafter in the illustrated embodiment and thus comprise a plurality of discrete flow zones arranged linearly or in end-to-end, overlapping or abutting relationship. 
     Preferably the assay apparatus also incorporates a wicking chamber for entrapment of liquids after they have passed through the plurality of discrete zones. 
     More suitably, however, the assay apparatus may comprise a strip of annular form arranged into each of the discrete zones. Advantageously, there is provided a multiplicity of different capture zones with each capture zone having immobilized thereto a different receptor ligand which does not bind directly with analyte in use. Preferably each of the capture zones is separated from each other by incubation zones. 
     These also may be provided an incubation chamber or vessel which contains the sample and each of the reagents described above. The mixture of sample and reagents may then flow to an initial zone of the assay apparatus before passing though the or each capture zone before passing into the wicking chamber. 
     The assay apparatus of the invention comprises, in a preferred form, a plurality of filter discs preferably spaced by spacer discs wherein each of the filter discs are contained in a cartridge. The cartridge may be located above the wicking chamber containing wicking material. 
     It will also be appreciated that the filter discs or annular or linear strips referred to above may be formed from filter material. 
     Typical filter materials comprise hydrophilic and liquid permeable polymers inclusive of polyvinylidene fluoride, polyamide, polyester cellulose acetate and, nitrocellulose. Use may also be made of fibres formed from polyvinyl chloride, teflon or other fluoropolymers, polysulfone, nylon, polycarbonate, paper, glass, quartz, silica, ceramic or metallic materials or combinations thereof. Use may also be made of wicking materials referred to hereinafter. 
     The incubation chamber or vessel discussed above may be in the form of wells which are cylindrical, conical, square or other shape dependent upon the requirements of the user. The wells are suitably formed from a substantially rigid, water insoluble, fluid-impervious, thermoplastic material chemically unreactive with assay reagents and samples. Suitable materials include polyvinyl chloride with or without copolymers, teflon or other fluoropolymers, polyethylene, polystyrene, and the like. The preferred material is polystyrene. 
     Any convenient bibulous absorbent solid material may be formed as the wicking material which allows for capillary transport of liquids from the filter material. Various materials include cellulose particles, silica gel, cellulosic beads, glass fibres, or filter paper. Preferably the wicking material is porous and can be moulded into complex sizes and shapes from thermoplastic polymers including light density polyethylene, ultra high molecular weight polyethylene, polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, nylon, polyethersulfone and ethyl vinyl acetate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Reference may now be made to a preferred embodiment of the invention as shown in the attached drawings, wherein: 
     FIG. 1 is a plan view of assay apparatus in the form of a filter disc having a plurality of discrete zones for use in accordance with the invention; 
     FIG. 2 is a plan of a linear filter strip having a plurality of discrete zones for use with the invention; 
     FIG. 3 is a similar view to FIG. 2 but showing an alternative embodiment of linear strip; 
     FIG. 4 is an exploded perspective view of assay apparatus in accordance with the invention; 
     FIG. 5 is an exploded perspective view of assay apparatus in accordance with the invention different to that shown in FIG. 4; 
     FIG. 6 is a perspective view of assay apparatus shown in FIG. 5 incorporating an absorbent paddle for drawing up a mixture of sample and reagents from an incubation chamber into the! assay apparatus; 
     FIG. 7 is a similar view to FIG. 6 showing the absorbent paddle in use; 
     FIG. 8 is an exploded perspective view of another embodiment of assay apparatus in accordance with the invention; and 
     FIG. 9 is a perspective view of another embodiment of assay apparatus in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference may now be made to FIG. 1 wherein a circular filter assembly  10  can be used in a general sense in conjunction with four different target ligands or molecules (i.e. T 1 , T 2 , T 3  and T 4 ) and four different carrier molecules (i.e. C 1 , C 2 , C 3  and C 4 ) so as to provide selective capture of immune complexes in a rapid multi-analyte assay as described hereinafter. The assay of FIG. 1 is a three analyte assay and allows the simultaneous detection of IgM antibodies and IgG antibodies to an infectious agent as well as detection of antigenic component(s) of the infectious agent itself in human blood, serum, saliva, cerebrospinal fluid and other body fluids. It will be noted that the circular filter assembly  10  of FIG. 1 comprises filter zones  10   c ,  10   d  and  10   e , each of which have been treated with receptor ligand or capture reagent as hereinafter described and which are all relatively narrow compared to filter zones  10   a  and  10   g  which do not incorporate capture reagent and incubation zones  10   b  which are located between zones  10   a  and  10   c ,  10   c  and  10   d ,  10   d  and,  10   e  and  10   e  and  10   f  as shown in FIG.  1 . 
     Zones  10   c ,  10   d  and  10   e  are each impregnated with specific receptors ligand R 1 , R 2 , R 3  and R 4  which are able to bind with high affinity target ligands T 1 -T 4  which may be conjugated to carriers C 1 -C 4  such as dendrimers, dendrimeric-type molecules, microparticles, streptavidin, avidin or any other carrier, antibody oligonucleotide or other substance. 
     Such carriers are capable of conjugation to bio-active agents such as antibodies, peptides and oligonucleotides or molecules mimicking the same. It is also possible to conjugate the target ligands directly to bio-active agents such as antibodies, peptides and oligonucleotides or molecules mimicking the same, eliminating the need to use carriers. 
     The receptor ligands and target ligands may be small oligonucleotide pairs, small peptides or other organic or non-organic substances which each bind the other with high affinity. 
     The carriers C 1 -C 4  in this embodiment are conjugated to antibodies directed against human IgG, human IgM and a viral protein. A carrier C 4  is also conjugated to antibodies to human albumin which serves as a control. 
     A sample and the reagent mixture are added successively or concurrently to filter zone  10   a  initiating flow through filter assembly  10 . If the sample is whole blood, zone  10   a  may be constituted by a blood filter to remove blood cells if desired. 
     Immune complexes carried on C 1  (anti-IgG, IgG antibody from sample and gold labelled antigen) are trapped in filter zone  10   c  by specific binding of the T 1  ligand or molecule on the carrier with the R 1  ligand or molecule. This results in accumulation of gold and red banding of filter zone  10   c.    
     Immune complexes carried on C 2  (anti-IgM, IgM antibody from sample and gold labelled antigen) are trapped in filter zone  10   d  by specific binding of the T 2  ligand on the carrier with the R 2  ligand. This results in accumulation of gold and red banding of filter zone  10   d.    
     Immune complexes carried on C 3  (anti-antigen, antigen from sample and gold labelled anti-antigen antibody) are trapped in filter zone  10   e  by specific binding of the T 3  ligand on the carrier C 3  with the R 3  ligand. This results in accumulation of gold and red banding of filter zone  10   d.    
     Immune complexes carried on C 4  (anti-albumin, albumin from sample and gold labelled anti-albumin antibody) are trapped in filter zone  10   f  by specific binding of the T 4  ligand on the carrier C 4  with the R 4  ligand. This serves as a sample control and demonstrates that (a) sample was added, (b) reagents were added, and (c) indicates how a positive band should appear. 
     The fluid flow is then directed into filter zone  10   g  under which is wicking material that draws in the fluid. Flow is physically prevented from re-entering segment  10   a  by barrier  13 . 
     Using the same reagents as described in FIG.  1  and the sample fluid, FIG. 2 shows formation of the same complexes to filter zones  20   c ,  20   d ,  20   e  and  20   f  of a linker filter strip  20 . There are also provided incubation zones  20   a  and  20   b  and wicking zone  20   g.    
     Each of the zones  20   a  through  20   f  of FIG. 2 may be joined in abutting relationship or overlapping relationship as shown in FIG. 3 in regard to linear filter strip  20 A. In another embodiment, each zone  20   a  through  20   f  may be connected by linker strips (not shown) or be constituted by an integral strip having receptor ligand(s) applied thereto at one or more spaced locations. 
     Reference may now be made to another embodiment shown in FIG. 4 wherein filter apparatus  30  comprises a G-shaped filter pad  31  having filter zones  31   a ,  31   b ,  31   c ,  31   d ,  31   e  and  31   f  wherein each of zones  31   c ,  31   d ,  31   e  and  31   f  has receptor ligand bound thereto. There is also zones  31   b  which are incubation zones bounding each of zones  31   c ,  31   d  and  31   e  while zone  31   f  also has zone  31   g  adjacent thereto. 
     There is also provided a plastics cover  32  having aperture  33  that mates with filter zone  31   g  and a capillary tube  34  attached thereto. There is also provided plastics housing  35  containing wicking material  36  which has a central elongate aperture  37  for accommodation of capillary tube  34 . There is also provided incubator well  39 . 
     The flow of reagent and sample mixture occurs upwardly from incubation well  39  as shown by the arrows in full outline through capillary tube  34  and into filter zone  31  a and subsequently through each of zones  31   c ,  31   d ,  31   e  and  31   f  as described in FIG. 1 before being transferred into wicking material  36 . 
     Another embodiment is shown in FIG. 5 wherein reference is made to filter assembly  40  which includes filter pad  41  having incubation zones  41   b , zones  41   c ,  41   d ,  41   e  and  41   f  which incorporate bound receptor ligand and wicking zone  41   g . There is also provided a cup  42  formed from plastics material having a slot  43  and a peripheral flange  44  which mates with wicking zone  41   g . There is also provided a plastics housing or container  45  having a central recess  46  for retention of cup  42  as shown. Wicking material  47  is located inside container  45  and is exposed to slot  43  through an open top  48  of container  45 . There also may be provided a pierceable water resistant or plasticized paper or plastics cover  49  to seal cup  42 . 
     The embodiment of FIG. 5 functions in a similar manner to the FIG. 4 embodiment. 
     Reference may now be made to another embodiment shown in FIGS. 6-7 wherein the same filter assembly  40  as discussed in FIG. 5 incorporates an additional component in the form of a paddle  50  in the form of a capillary strip or tube preferably formed from plastics material having an angled shank  51  and support part  52  with a hinge  53  interconnecting shank  51  and support part  52 . The paddle  50  is attached to filter assembly  40  as shown in FIG. 6 wherein support part  52  is supported on filter pad  41  and shank  51  is then bent downwardly to penetrate liquid contained in cup or well  42  as shown in FIG.  7 . 
     In use, approximately 50 μl of serum or other suitable sample is pipetted into well  42  by pipette  54  as shown in FIG. 6 which pierces the cover  49  and at the same time pushing the shank  51  into well  42 . The serum mixes with a reagent mixture in well  42  and begins to flow up the filter  51  and then into filter zone  41   a . The flow of liquid then continues as indicated by the arrows in full outline. 
     In FIG. 8, reference is made to a filter assembly  59  including a plurality of filter discs  60  which are arranged in a vertical array as shown to facilitate vertical flow of sample and reagents. Each of the filter discs are designated  60   a  through  60   f  inclusive as shown and each of filter discs  60   c ,  60   d ,  60   e  and  60   f  each have incorporated receptor ligand so as to capture various species as already described above in relation to FIG.  1 . Filter discs  60   b  are wicks consisting of polyethylene or other porous material and allow for incubation of the mixture of sample and reagents in its flow down the filter assembly  59 . The array of filters may be housed in a housing (not shown) for ease of convenience and there may also be provided frits or spacers (not shown) made from polyethylene or other porous material to allow mixtures of sample and reagents to pass at a controlled rate of passage. Each filter disc may be housed in individual cartridges (not shown) for ease of assembly and removal if desired. 
     There is also provided an incubation cup or well  61  which may have a restriction  62  to prevent passage of sample and reagents until additional fluid is added. Alternatively, a cup  63  without restriction may be utilized. 
     The sample may be added to cup  61  or  63  followed immediately by the reagent mixture. Filter  60   a  may comprise a blood filter to remove blood cells from the mixture if desired. There is also provided container  64  containing wicking material  65 . 
     FIG. 9 refers to a filter column  66  comprising successive filters  67   a ,  67   c ,  67   d ,  67   e  and  67   f . These filters are useful for containing microparticles, resins, beads or other particulate matter. Each of these filters are therefore useful in having a receptor ligand attached thereto for the capture of a target substance. Thus, for example, filters  67   c ,  67   d ,  67   e  and;  67   f  have attached thereto complexes as previously described in FIG.  1 . There are also provided frits  67   b  of porous non-binding material such as polyethylene. 
     There is also provided wicking module  67   g  and it will be appreciated that each of modules  67   a  through  67   g  may be readily attached to each other through the use of frits  67   b . There is also shown the use of wells  61  or  63  as discussed above in FIG.  8 . 
     The filter assembly  66  would be suitable for the testing of water or other liquid samples in which large volumes of sample would need to be passed through the device. 
     In the case of large volume sample testing, it would be necessary to load the column of filters  67   a  through  67   g  with the dendrimer, microparticle or other target labelled carrier, antibody, oligonucleotide, etc. before adding the sample, so as to facilitate capture of the analytes from the sample. After sample addition, the other reagents including gold, enzyme or other labelled detecting agent or tracer is added. 
     The assay apparatus of the invention has a plurality of uses and may be utilized, for example, as a rapid detection test of multiple pathogens and other substances in environmental, food and clinical samples as well as a replacement test for immunoblot antibody assays used as confirmatory assays, e.g. Hepatitis C and HIV antibodies. Filter assembly  59  and  66  may also be used for testing samples from 1 ml clinical samples to 100 litre samples of water when used in environmental testing. 
     It is also considered that the invention will, also have special relevance to high throughput screening; of combinatorial chemistry libraries. A combinatorial chemistry library of randomly or non-randomly synthesized oligomers may be prepared on solid support materials such as particles, microparticles, resin beads, and the like with many compositions. Libraries prepared on such particles are used in the art by companies searching for new bioactive compounds such as drugs and for compounds useful as diagnostic agents or vaccines (e.g. synthetic amino acid sequences mimicking discontinuous epitopes derived from micro-organisms such as bacteria and viruses). 
     The assay apparatus of the invention may be used to incubate such a library of compounds with molecules of interest such as cell surface receptor molecules, enzymes or antibodies. These molecules of interest may be labelled with substances such as enzymes, fluorescent compounds, biotin or other molecules and thus may function as a tracer. Following incubation of the library particles with the labelled tracers, the mixture may be added to incubation well  39 ,  42 ,  61  or  63 . 
     The mixture is allowed to pass through the filter and the filter of the invention may be washed to remove unwanted reagents. The aim is to identify those particles bearing oligomers that have bound to the tracer. This can be done by performing an enzyme assay for the presence of the tracer, which will result in a colour change of the labelled particles. If an encoding system was used during the manufacture of the particle library, it may be possible to decode the oligomer identity directly. 
     Another means of identifying those particles bearing oligomers that have bound to the tracer molecules would be to use tracer molecules conjugated to a specific ligand (e.g. biotin) that will be trapped by a receptor ligand on the filter assembly (e.g. streptavidin). Thus, when the mixtures pass through the filter, particles that have bound the biotinylated tracer molecules will be retained on the filter assembly by biotin-streptavidin binding and all other particles pass through the filter assembly. After washing, the filter assembly will only have on it particles with oligomers that specifically bind to the tracer molecules. Other examples of ligand pairs include oligonucleotide pairs, small peptide binding pairs and metal chelates binding to polyhistidine. 
     Reference may also be made to test kits constructed in accordance with the invention comprising the abovementioned filter assemblies in the form of linear strip(s), annular strip(s) or filter column(s) together with reagent containers containing target ligand-analyte receptor conjugate(s) and detectable tracer(s). Preferably all of the reagents is accommodated in a single reagent container. 
     In another aspect of the invention, there is provided assay apparatus in the form of a column of filter members characterized in that there is provided a filter member used for incubation of sample and reagents to facilitate formation of a complex between an analyte and an analyte receptor upstream of one or more filter members used as capture zones. 
     Advantages applicable to the assay method and apparatus of the invention include: 
     (1) Because the method and apparatus are independent of analyte, this simplifies the form of packaging that may be utilized in that pre-packaged linear or annular strips or columns could be utilized for a variety of different assays. For example, packages only containing the linear strips may be used in developing countries; 
     (2) Kits may be marketed in accordance with the invention that include different sets of reagent bottles applicable to different assays together with linear, annular strips or columns. For example, a kit may have multiple different reagent mixture bottles. A first screening bottle may contain Dengue IgM antibody, Japanese encephalitis IgM antibody and malaria IgM antibody reagents. These reagents may be used for an initial screening test. Patients testing negative for all three analytes could be retested using a second set of reagents in a single bottle containing a mixture of reagents for the detection of Dengue virus antigen(s), Japanese encephalitis virus antigen and malaria antigen(s). Patients testing positive for Dengue virus IgM antibody could be retested using a third set of reagents in a single bottle containing a mixture of reagents that differentiated between primary and secondary Dengue virus infection providing for the detection of high level IgG antibody and IgM antibody. For all or any of these procedures, a single universal linear or annular strip or column would be provided. This approach provides for previously unavailable flexibility of use for in vitro diagnostics; 
     (3) Production of diagnostic kits will be greatly simplified with this invention. Since each analyte or multiple analyte kit does not require manufacture of a filter material impregnated with reagents different from others, a single filter impregnated with one, two, three or more capture zones will serve for the analysis of any analyte or combination or analytes; 
     (4) The filter media produced for the system should have a greatly extended shelf life as preferentially, non-biological material or highly stable bio-oligomers will be used for the production of the receptors on the filter media; 
     (5) Large volumes of sample may be tested with many variants of this system. This will allow greater sensitivity in analyzing samples such as water and other environmental materials for pathogens, chemicals, pollutants and the like. They will also allow the testing of body fluids such as urine in relatively large volumes for the presence of low-level analytes, resulting, in greater test sensitivities and probably earlier detection of analytes in diseases such as leptospirosis and legionellosis in which pathogen specific antigens are excreted in the urine; 
     (6) Manufacture of the assay apparatus of the invention in the form of strips or columns would be facilitated by manufacture in various arrays commensurate with the relevant utility; and 
     (7) in relation to the assay apparatus of the invention, particularly in the form of filter columns, it will be appreciated that such columns may be reusable.