Description of the background art Molecular separation based on affinity interaction has proven to be a valable tool for the purification of biological or related molecules (Affinity Chromatography: a practical approach, P. D. G. Dean, W. S. Johnson, and F. A. Middle (eds.). IRL Press, Oxford, 1986. Affinity Separations: a practical approach, P. Matejtschuk (ed.) IRL Press, Oxford, 1997). The principe of affinity separation relies on the selective recognition and interaction of the desired biological or related substance, present in a fluid phase, with its complementary ligand immobilised on a solid support as it passes over the support in a column. The desired material is retained on the column whilst most impurities are flushed through. The binding is reversible allowing for the recovery of the desired molecules by applying an appropriate eluting solution to the column which disrupts the ligand-binding interaction, by either changing the ionic strength, the pH, or adding a competing reagent, thereby releasing the desired molecules from the column. The types of ligands which may be used in affinity separation is very broad and include antibodies, antigens, enzymes, peptides, oligonucleotides, isolated receptors, carbohydrates, and recombinant proteins. There is now a wide range of support matrices that have been used in affinity chromatography, e. g. Agarose (Sepharose (Pharmacia)), cross-linked dextran (sephadex (Pharmacia)), cross-linked cellulose (Matrex Cellufine (Amicon)), controlled pore glass (CPG (Pierce)), and silica (Hypersil WP 300 (Shandon)) beads.

Microporous membranes as support matrices have also been used in the art. Ligand immobilised membranes provide a compact, easy to manipulate system allowing for the capture of the desired molecule and the removal of unwanted components in a fluid phase at higher throughput and faster processing times than possible with column chromatography. This is due to the fast diffusion rates possible on membranes. Ligands have been immobilised on support materials in the form of microporous membranes used in affinity chromatography. This has occurred either through simple adsorption or through a chemical reaction between complementary reactive groups present on the membrane and on the ligand resulting in the formation of a covalent bond between the ligand and membrane. In some instances, membranes have been initially coated with a water-insoluble protein such as Zein, collagen, fibrinogen, etc., followed by the immobilisation of the ligand of interest (e. g. U. S. Pat. No. 4407943).

Porous membrane materials used for non-covalent ligand immobilisation in affinity chromatography have included materials such as nylon, nitrocellulose, and hydrophobic polyvinylidene fluoride (PVDF).

Non-covalent binding results in random orientation of the ligand and can also be a problem with small molecules such as peptides, oligonucleotides or oligosaccharides or where competing ions may wash away the adsorbed ligand. To circumvent this problem, peptides and oligonucleotides have been synthesised directly onto membranes as a means of generating the desired membrane affinity supports in which the peptides and the oligonucleotides are not only covalently bound to the support but are also placed in the correct orientation (e. g. U. S. Pat. No.

4923901). This method is limite, as individual membranes would need to be generated, every time, for different peptide and oligonucleotide sequences. More often, peptides may be coupled to a solid support via the C-or N-terminal ends of the peptide which may also result in random coupling via reactive groups on the side chains of the peptide. A number of methods and reagents have been developed to also allow the direct coupling of oligonucleotides onto solid supports (e. g. J. M. Coull et a/., Tetrahedron Lett. 27 3991 ; B. A. Conolly, 1987, Nucleic Acids Res., 15 3131 ; B. A. Conolly and P. Rider, 1985, Nucleic Acids Res., 12 4485).

UV cross-linking of DNA (Church et al., 1984, PNAS, 81 1991) and RNA (Khandjian, et al., 1986, Anal. Biochem., 159 227) to nylon membranes have also been reported.

Many chemical methods have been developed for the immobilisation of proteins as ligands on microporous membranes. For example, activated paper (TransBind. TM., Schleicher & Schuell Ltd., Keene, N. H.) carbodimidazole-activated hydrogel-coated PVDF membrane (Immobilin-IAV. T"", Millipore Corp., Bedford, Mass.), activated nylon (BioDyne. TM., Pall Corp., (Glen Cove, N. Y.), DVS-and cyanogen bromide-activated nitrocellulose. Membranes bound with specific ligands are also known such as the SAM2TM Biotin Capture Membrane (Promega) which binds biotinylated molecules based on their affinity to streptavidin or MAC affinity membrane system (protein A/G) (Amicon).

Some of the disadvantages of covalent attachment of biomolecules as ligands onto activated membranes are :- (a) Most of the chemistries used for covalent ligand attachment couple the ligand randomly through amino residues on the protein which often results in partial or complete loss of binding capacity due to the reduced efficiency of ligand-product binding.

This is mostly due to multi-site attachment of the ligand when the activated support contains an excess of activating groups, making the binding site on the ligand inaccessible due to steric hindrance (Spitznagel, T. M. and Clark, D. S., 1993, Biotechniques, 11 825).

(b) Ligand immobilisation is often slow requiring 20-180 minutes for reaction completion.

(c) High ligand concentration is needed for fast ligand immobilisation.

(d) Constant agitation is needed during the immobilisation process that may result in further ligand denaturation and deactivation.

(e) Unsuitable for the immobilisation of unstable recombinant proteins due to immobilisation chemistry, mechanical agitation, and the long incubation times needed at room temperature.

(f) Once the immobilisation process is complete, often a blocking (capping) step is required to remove residual covalent binding capacity.

(g) Covalently bound ligands can not be retrieved from the membrane.

The technique of immobilised metal affinity chromatography (IMAC) has found the widest application in affinity purification of recombinant proteins (e. g. J. Porath, Prot. Express. And Purif., 1992,3 263; Vosters et al., 1992, Protein Expr. Purif., 3 18; Alnemri et al., 1993, Proc. Natl Acad. Sci., 90 6839; C. Tang, and H. L.

Henry, 1993, J. Biol. Chem., 268 5069). In this technique, a metal chelate possessing suitable co-ordination sites is immobilised on a solid support (e. g. Iminodiacetic acid immobilised on sepharose beads (IDA- Sepharose, Pharmacia) or nitrilotriacetic acid immobilised on sepharose (NTA-Sepharose)). Only those proteins with two or three suitable donor ligands in a conformationally favourable arrangement will bind and form a stable complex (E. Sulkowski, 1989, BioEssays, 10,170; K. J. Petty, 1996, Metal-chelate affinity chromatography. In: Current protocols in molecular biology, F. M. Ausubel (ed.), vol 2, John Wiley and Sons, New York). In theory, a wide variety of metal ions with high affinity for electron donor groups can be utilised. Of these, Ni2+ and Zn2+ are the most widely used. Suitable donor ligands include amino acids histidine, cysteine and tryptophan. Since natural proteins rarely contain suitably arranged donor ligands, recombinant proteins are engineered with a metal chelate binding tag at either the C-or N-terminal ends of the protein for purification purposes via IMAC (e. g. Sharma et al., 1992, In Methods: A companion to Methods in enzymology, F. Arnold (ed.) 4 57-67, Academic Press, New York). The most popular tag is the hexahistidine tag although many other tags utilising a combination of histidine and other amino acids such as aspartic acid or tryptophan residues have been used (e. g.

Kasher et al., 1993, Bio/Techniques, 14630).

Metal chelating ligands have been immobilised on solid supports exclusive of microporous filter materials, such as Sepharose (IDA-sepharose, Pharmacia), magnetic beads (Ni-NTA Magnetic Agarose Beads, Qiagen) and microtitre plates (Ni-NTA HisSorb, Qiagen).

Iminodiacetic acid (IDA) has also been covalently attached to a stable epoxy resin and incorporated into a microporous plastic sheet (MPS) matrix (Acti-Disk, Whatman) and used for the selective purification of proteins (U. S. Patent Nos. 3862030,4102746,4169014 and 4689302).

The MPS matrix is an inert polymeric microporous sheet that contains silica that can either be functionalised with ion exchange groups or affinity ligands solely for the purpose of protein purification.

SUMMARY OF THE INVENTION Unexpectedly, it has now been discovered that filter media when processed in accordance with the invention to provide a metal chelate filter or metal chelating species filter may provide a number of surprising advantages and applications as described hereinafter which would not have been contemplated from the prior art discussed above.

Thus use of the filter media of the invention may now provide advantages of faster processing of fluids as well as multiple processing of fluids.

Thus the invention provides a ligand immobilisation procedure for peptides, oligonucleotides and recombinant proteins, which involves site specific attachment of the ligand onto the membrane via use of a metal chelating species or metal chelate thus avoiding the use of harsh chemical reactions and long incubation times as was the case in the prior art. In particular, the invention provides for the capture and separation of these biomolecules from a mixture in a fluid or liquid phase onto a microporous filter matrix. Such a filter matrix processed in accordance with the invention would have valable and widespread applications in the diagnostics, high-throughput screening, and biotechnology industries. In particular the invention has particular application to fluid phase assay systems and methods described in International Publications WO 9932884 and/or WO 9932885which are totally incorporated herein by reference.

The process of the invention includes the following variants :- (i) reaction of a filter with a linker and metal chelating species to produce a metal chelating filter ; (ii) reaction of a filter with a linker and metal chelating species and a metal to produce a metal chelate filter; (iii) reaction of a filter with a metal chelating species to produce a metal chelating filter; and (iv) reaction of a filter with a metal chelate to produce a metal chelate filter.

The invention includes within its scope products produced by the above mentioned alternative variants (i) to (iv).

The term"filter"as used herein means a porous material or filter media having an average pore size in the region of 0.01 to 1000 microns and more preferably 0.1-5 microns. Viral antigen immune complexes would generally be retained by a pore size of 0.05-3 microns while a larger size may be more appropriate for bacterial antigen immune complexes. The filter may be formed from either fully or partly from glass, silica or quartz including their beads, fibres or derivatives thereof, having bound thereto accessible functional groups such as-Si-OH groups or which may be treated with a reagent to provide accessible functional groups including-OH,-Si-OH,-NH2 and other amine containing groups, including alkylamino, thiols, cyanobromides, aldehydes, carboxylates, sulfonylchlorides, ketones, halogens, maleimido, hydrazine, acetyl or other groups combining acetyl including haloacetyl inclusive of chloroacetyl, iodoacetyl or bromoacetyl and epoxy groups. It will also be appreciated that the functional groups may be attached directly to the filter or by an appropriate spacer arm or linker.

It will further be appreciated that porous filter materials comprising polyamides inclusive of nylon, cellulose acetate, nitrocellulose, polyvinylidene fluoride, or other fluoropolymers, polysulfone, paper, or combinations thereof, may also be suitable media for the attachment of linkers and/or a metal chelating species or a metal chelate.

The term"linker"as used herein means any spacer group which can be utilised to link the various entities described above. As such, the linker, prior to use has an appropriate functional group as described above at each end. One group is appropriate for the attachment to the filter and the other group is appropriate for attachment to the metal chelate or metal chelating species. Any suitable linking group, as linker, can be utilised which may include substituted or unsubstituted alkyl groups having from one to twenty, or more preferably one to six carbons, and wherein the alkyl groups may be linear or branched. Linkers may also comprise substituted or unsubstituted aryl or aryl alkyl groups. Thus for example the linking group may be variable comprising a single methylene or a plurality of methylene groups. The linking group may also comprise peptides or branched peptides inclusive of lysine. Other examples of linkers include, for example, both linear, cyclic, and branched polymers of polysaccharides, phospholipids and peptides having either alpha-, beta-, or omega-amino acids, heteropolymers, polyurethanes, polyesters, polycarbonates, polyureas, <BR> <BR> <BR> <BR> <BR> polyamides, polyethyleneimines, polyarylene sulfides, polysiloxanes, polyimides, polyacetates, dendrimers and dendrimeric-like molecules or other polymers as will be readily apparent to those skilled in the art.

It will also be appreciated that the term linker as used herein may also include cross-linking species or reagents used to couple the metal chelate or metal chelating species to accessible functional groups either on the filter or which have been produced by derivatisation.

Such cross-linking species are referred to by way of example to the Pierce Chemical Company Product Catalog 1999-2000 which is totally incorporated herein by reference.

In a preferred embodiment of the invention, microfibre glass filters made from silica are especially adapted for use in the invention. Such filters have silanol (Si-OH) functional groups as part of the filter matrix. These may be derivatised using a suitable reagent to provide appropriate functional groups such as those described above for the attachment of the metal chelating species or metal chelate to the filter or by use of a linker.

In this regard it will be appreciate that such reagents may have an in-built linker or the linker may be pre-attached to the metal chelating species prior to attachment to the functional groups on the filter. It may further be appreciated that these reagents may also comprise the various functional groups inclusive of amine, halogen, or epoxy as described above. Alternatively the metal chelating species may be reacted with the Si-OH groups on the filter if the metal chelating species includes a functional group capable of reacting with Si-OH groups such as triethoxysilane or trimethoxysilane. Such functional groups may also be attached to the metal chelating species by a linker.

Examples of silanisation reagents which may be used for the derivatisation of the glass fibre filters are: 3-aminopropyl triethoxysilane, <BR> <BR> <BR> <BR> <BR> 3-aminopropyltrimethoxysilane,3-(2-aminoethylamino) propyltrimethoxysilane and 3-glycidoxypropyltrimethoxysilane.

In relation to nitrocelluose or cellulose paper such porous filters comprise accessible amine groups on the surface of the filter. In this case the linker or metal chelating species with linker attached may be attached to the filter directly without the need for prior derivatisation using for example standard peptide and conjugation chemistries such as those described in Frank, et al., 1991,"Peptides", Giralt and Andrew Eds, ESCOM Science Pub, pp 151-152, which is directed to facile and rapid "spot synthesis"of large numbers of peptides as linkers on porous membrane filters. This reference is incorporated herein by reference.

Reference also may be made to Furka et al., 1991, Int. J.

Peptide Protein Res. 37 : 487-493, which is totally incorporated herein by reference with regard to use of peptides as linkers. Usually such filters may be treated with a reagent such as ethylenediamine which may be considered as a short linker in a suitable solvent such as acetonitrile and usually in the presence of a catalyst such as triethylamine.

In the case of fluoropolymers, there are no existing functional groups suitable or otherwise for the attachment of a linker of a metal chelating species. Suitable reactive groups may need to be introduced onto the filter by a process which is described in the following publications each of which are incorporated herein by reference ie Vargo et al., 1992, Langmuir 8: 130 ; Vargo et al., 1992, J. Polym. Sci. Part A: Poly. Chem. 29: 555; and Hook et al., 1991, Langmuir 7: 142.

Briefly these processes are called radiofrequency glow discharge (RFGD) plasma using hydrogen gas and methanol vapour which facilitates the introduction of hydroxyl groups to the filter surface.

Such hydroxyl groups can be directly used for the attachment of a filter, metal chelating species or a metal chelate using standard coupling chemistries and protocols such as those described above. Alternatively the hydroxyl groups may be further derivatised with silanisation reagents as described above to introduce the more versatile amino group. This can then be used for the attachment of the linker, metal chelating species or metal chelate.

It will be appreciated from standard texts such as a publication entitled"Affinity Membranes in Bioseparations"by E. Klein which is part of"Membrane Processes in Separation and Purification" 1994, by Crespo and Boddeker Eds, published by Kluwer Academic Publishers which is totally incorporated herein by reference that there is a full description of various microporous membranes which may be utilised in the current invention and also reference to various reagents and processes which may attach the above mentioned functional groups to the filter. Such reagents for example may include cyanogen bromide, tosyl chloride, N-hydroxy succinamide, diamines, hydrazine and its derivatives, dialdehydes such as glutaraldehyde, carbodiimides, and diepoxides. This reference also described the preparation of polyamide filters having accessible functional groups.

The term"metal chelating species" (MCS) as used herein can be any species with electron donating groups such as-NH2,-COOH, -SH,-OH and heterocyclic moieties comprising nitrogen atoms, capable of coordinating with metal ions. Examples of such metal chelating species include iminodiacetic acid, nitrilotriacetic acid, diethylenetriamine -N, N, N', N"-pentoacetic acid and branched superstructures such as dendrimers or dendrimeric-like molecules or polymeric structures with the appropriate donating groups, triethylenetetramine, ethylenediamine, glycine, o-phenanthroline, 4,4-bipyridyl, 2,2-bipyridyl, pyridine and 6- hydroxynicotinic acid The term"metal chelate" (MC) as used herein means the metal chelating species having a metal coordinated thereto. Chelation type associations make use of metal ions such as but not limited to, the metals Fe, Co, Ru, Rh, Rh, Pd, Os, Ir, Pt, Pb, Sn, Ge, Sc, Y, lanthanides and actinides, B, Al, Ga, In, TI, Li, Na, K, Rb, Cs, Fr and Be, Mg, Ca, Sr, Ba, Ra, Cu, Ni, Zn and transition metals.

It will be appreciated that the above mentioned products of the invention which incorporate the metal chelating species can be utilised for immobilisation of metal containing ligands or metal ions. On the other hand metal chelate filters of the invention which include the metal can be used for immobilisation of ligands that coordinate with the metal.

In the above it will be appreciated that the metal chelating species may be attached to the filter by a covalent bond, charge interaction or metal chelation. It will also be appreciated that the metal chelating species may be attached to the filter via a linker by either of the following:- (i) attaching the linker first to the filter followed by attachment of the metal chelating species followed by addition of the metal; (ii) alternatively, the linker may be pre-attached to the metal chelating species followed by attachment of the linker-metal chelate species moiety on to the filter (Ji et a/., 1996, Analy. Biochem., 240 197); (iii) pre-attachment of a linker moiety on the filter in which one of its reactive functional groups is protected by a suitable protecting group will allow for unreacted functional groups on the filter to be blocked. Examples of suitable protecting groups include Fmoc, Boc, trityl groups and any other protecting groups as is known in the art. For example, attachment of an Fmoc group protected linker will allow for uncoupled amine groups on the filter to be blocked by an acetic anhydride/pyridine/DMF blocking procedure. It will also be appreciated that reaction of the linker with branched species such as lysine or branched polymeric species such as dendrimers may increase the number of functional groups on the filter. This may then be reacted with a MCS thereby increasing the metal chelating capacity of the filter. Examples of suitable protecting groups are disclosed in The Peptides, Vol 3. (eds. Gross, E., and J. Meienhofter, Academic Press, 1981).

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 shows a derivatised glass fibre filter with imidodiacetic acid metal chelate attached to the filter with a linker.

FIG. 2 shows a polyacrylamide gel with a low range molecular weight marker in lane 1 and various molar ratios of E5 dendrimer-horseradish peroxidase (HRP) conjugates in lanes 2 to 5. In lanes 2 and 3 free HRP is detected at around 45 kDa. In lane 4 the dendrimer-HRP conjugate at about 73 kDa is readily apparent in the absence of free HRP. In lane 5 the concentration of the dendrimer-HRP conjugate at a 1: 1 ratio has reduced noticeably.

FIG. 3 shows results of an experiment using Zn2+ immobilised on the filter in which HRP, HRP-antibody conjugate and HRP-dendrimer conjugate were passed through metal chelate filter discs at varying concentrations. At 1: 1600, only the dendrimer-HRP conjugate was detectable. Traces of HRP-antibody conjugates were detectable at 1: 400 to 1: 1200 and free HRP was detectable at 1 : 400 only. HRP was detected by applying an HRP substrate (3,3', 5,5'-Tetramethylbenzidine (TMB), insoluble) for 2 minutes after which the discs were then removed, washed with doubly deionised water and dried on filter paper.

FIG. 4 shows free HRP, HRP-antibody and E5 dendrimer- HRP conjugates diluted 1: 100 and passed through different derivatised metal chelate glass fibre filters (Whatman GF/B, GF/C and GF/F). The metal ion used was Zn FIG. 5 shows results of an experiment in which E5- dendrimer conjugate, diluent only, E5 dendrimer only and E5 dendrimer- antibody conjugate were passed through Zn2+ metal chelate filter discs in duplicate. For one set of discs, phosphate buffered saline with Tween 20 only was used to wash the discs to remove unbound reagent. For the other set of discs, 500 mM imidazole was added to the washing buffer.

Then a 1: 1000 dilution of anti-mouse immunoglobulin conjugated to HRP was added to the discs and incubated for 30 minutes at 37EC. After this the discs were washed as before and TMB substrate was applied and washed as described above.

FIG. 6 of a polyacrylamide gel shows that metal chelate filter discs efficiently capture a 6 x histidine tagged protein from a solution. The concentration of the tagged protein was found to be approximately five times higher in material eluted from the discs than material that flowed through the discs.

EXPERIMENTAL EXAMPLE 1 Functionalization of glass fibre membranes with 3-aminopropyltriethoxysilane Twenty sheets (10.5 cm x 14.7 cm) of GF/F glass microfibre filters, as obtained from Whatman, Maidstone, England, were placed in a flat dish and covered with 300 mL of a 10% solution of 3- aminopropyltriethoxysilane in ethanol (99.7-100% v/v). The reaction was allowed to proceed for 48 hours with rocking. The sheets were then washed with ethanol and air dried before they were activated at 110aC for 3 hours. The presence of amine groups was confirme with a 2,4,6- trinitrobenzynesulfonic acid (TNBS) test. A few drops of a 1% TNBS solution in N, N-dimethylformamide (DMF) were added to a small piece of filter membrane and the colour change recorded after I minute.

EXAMPLE 2 Coupling of linker (Fmoc a-aminocaproic acid).

Five sheets (10.5 cm x 14.7 cm) of functionalised GF/F filters were treated with Fmoc a-aminocaproic acid (4.0 mmol), O- Benzotriazole-N, N, N', N',-Tetramethyl-Uronium-Hexafluorophosphate (HBTU) (3.9 mmol), N-Hydroxybenzotriazole (HOBt) (4.5 mmol), and diisopropylethylamine (DIPEA) (5.0 mmol) in 40 mL of dry DMF overnight with rocking. The sheets were washed with methanol, dichloromethane and then air-dried. The extent of coupling was measured with an Fmoc test and gave an Fmoc loading of 0.016 mmol/g of filter. Briefly, accurately weighed filter discs (16 mg) were treated with a 0.4 mL of a 50% solution of piperidine in dichloromethane for 10 minutes with sonication. This volume was then made up to 2.4 mL with dichloromethane and the absorbance of the liberated Fmoc group measured at 301 nm (extinction coefficient at 7,800).

EXAMPLE 3 Coupling of metal chelating species.

Eighty filter discs (5 mm diameter) were treated with a 20% solution of piperidine in DMF for 5 min with sonication to effect the deprotection of the Fmoc group on the linker moiety. The filters were then washed with methanol, dichloromethane and then air-dried. Removal of the Fmoc group was then tested with a TNBS test.

The deprotected filters were treated with nitrilotriacetic acid (1.0 mmol), HBTU (0.9 mmol), HOBt, (1.2 mol), and DIPEA (0.26 mmol) in 6 mL of dry DMF overnight with rocking. The filters were washed with DMF, methanol, and dichloromethane and air-dried. TNBS test indicated efficient coupling of the nitrilotriacetic acid.

EXAMPLE 4 Immobilisation of Zn2+ on filter discs.

Nitrilotriacetic acid derivatised filter discs were each placed on a sintered glass funnel connected to a vacuum pump. The discs were each initially washed with 100 uL of doubly deionised water, 100 uL of 50 mM phosphate buffered saline, pH 7.5, containing 50 mM sodium chloride, and followed by 100 uL of doubly deionised water. Fifty uL of a 0.1 M solution of Zinc sulphate were then allowed to pass through each filter discs followed by washing with a 100 pL of doubly deionised water.

FIG. 1 shows an example of a molecular structure showing the derivatised filter, linker (s) and the metal chelate.

EXAMPLE 5 Preparation of enzyme dendrimer conjugates.

To a solution of HRP (4.3 mg) made up in 30 mM sodium acetate buffer containing 150 mM sodium chloride, pH 4.5, was added 80 pL of a freshly prepared solution of sodium periodate (Na104) and the reaction mixture allowed to incubate for 5 hours in the dark. The mixture was then loaded onto a Sephadex G-25 PD-10 column equilibrated with 20 mM phosphate buffer, pH 6.0, and the activated enzyme eluted with the same buffer. Thirteen pL of a 50 mg/ml solution of generation five dendrimer (E5) (Michigan Molecular Institute) was then incubated with 1.1 mg of the activated HRP enzyme in the presence of 0.70 mg of sodium cyanoborohydride (NaBH3CN) at 4°C for 16 hours. The reaction mixture was then dialyse against 0.1 M NaCI and doubly deionised water. Polyacrylamide gel electrophoresis (PAGE) on a linear gradient gel (4-15%) under SDS reducing conditions revealed the main product to be a 1: 1 conjugate of HRP to E5.

FIG. 2 shows examples of different molar ratios of E5 dendrimer-HRP conjugations.

EXAMPLE 6 HRP-E5 conjugate capture on a glass microfibre meta/chelate filter Metal chelate glass microfibre disc filters prepared as in EXAMPLE 4 were used for the capture of HRP-E5 conjugates. The discs were each washed with 100 uL of 50 mM phosphate buffered saline, pH 7.5, containing 500 mM NaCI and 500 mM imidazole. Fifty, uL of either diluted HRP, HRP-antibody conjugate, or HRP-E5 conjugate were then allowed to pass through the filter followed by a washing step of 100 pL of the imidazole, buffer. The filter discs were then incubated in the presence of an HRP substrate (3,3', 5,5'-Tetramethylbenzidine (TMB) insoluble) for 2 minutes after which the discs were then removed, washed with doubly deionised water and dried on filter paper.

FIG. 3 shows results of an experiment using Zn 2, 1, immobilised on the filter in which HRP, HRP-antibody conjugate and HRP-dendrimer conjugate were passed through metal chelate filter discs at varying concentrations. At 1: 1600, only the dendrimer-HRP conjugate was detectable. Traces of HRP-antibody conjugates were detectable at 1: 400 to 1: 1200 and free HRP was detectable at 1: 400 only.

FIG. 4 shows free HRP, HRP-antibody and E5 dendrimer- HRP conjugates diluted 1 : 100 and passed through different derivatised metal chelate glass fibre filters (Whatman GF/B, GF/C and GF/F). The metal ion used was Zn2+.

EXAMPLE 7 An immunoassay to detect the presence of mouse antibody on a metal chelate filter E5-dendrimer conjugate, diluent only, E5 dendrimer only and E5 dendrimer-antibody conjugate were passed through Zn2+ metal chelate filter discs in duplicate. For one set of discs, phosphate buffered saline with Tween 20 only was used to wash the discs to remove unbound reagent. For the other set of discs, 500 mM imidazole was added to the washing buffer. Then a 1 : 1000 dilution of anti-mouse immunoglobulin conjugated to HRP was added to the discs and incubated for 30 minutes at 37°C. After this the discs were washed as before and TMB substrate was applied and washed as described above.

FIG. 5 shows the results. It can be seen that the presence of 500 mM imidazole inhibited non-specific binding of HRP-conjugated anti-mouse immunoglobulin from the metal chelate filters.

EXAMPLE 8 Recombinant 6 X histidine tagged protein capture on Zn2+ immobilised meta/chelate filter Two metal chelate filter discs (5 mm diameter) immobilised with Zn2+ prepared as in EXAMPLE 4 were incubated with 30 ug of 6 X histidine tagged protein in 400 uL of phosphate buffer for 20 minutes.

The protein solution was then removed and concentrated (flow through) and the filters washed with 400 uL of phosphate buffer. Bound protein was then eluted from the filter by incubation with 400 uL of 500 mM imidazole in phosphate buffer for 20 minutes (eluate). This fraction was concentrated and along with the flow through fraction was subjected to PAGE under SDS denaturating conditions.

FIG. 6 of a polyacrylamide gel shows that metal chelate filter discs efficiently captured a hexahistidine tagged protein from a solution and that the concentration of the tagged protein was approximately five times higher in filter eluates than in the flow through.

APPLICATIONS MC and MCS filters may be incorporated into an immunoassay filter plate, column, syringe filter housing or tube for a wide range of diagnostics, high-throughput screening, recombinant protein assays, and research applications. The MC and MCS filters may also be embodied with a second type filter such as an FTAT" Gene Guard System (Fitzco Inc, a member of the Whatman Group) filter which will perform a complementary function to the MC or MCS filters. The MC and MCS filters may further embodied with a second filter such as to restrict the flow of fluids through the MC and MCS filters.

Molecular and immunoassay diagnostics (1) FTA coated filters are known to capture nucleic acids after spontaneously lysing cells introduced to it. Once captured the genetic material is maintained in a bound form for any length of time without damage. The bound genetic material such as human genomic DNA can be ultimately removed by use of reagents such as restriction endonucleases.

The fragments of the restriction digest, can be incubated in the presence of a MC filter harbouring dendrimer-bound gene specific capture probes, to which genes of interest will bind and ultimately be detected.

(2) Immobilisation of oligonucleotide probes for genomic assays. Such probes could be derivatised at their 5' or 3'ends with a metal chelate tail such as a hexahistidine tag or dendrimer, e. g. PAMAM dendrimers (Dendritech Inc, Midland, Michigan, USA) or dendrimeric-like structure for the hybridization capture of genomic DNA. E. g. traditional methodology (other than FTA) of purification yields genomic DNA as a soluble fraction. After restriction digest, or in vitro transcription, template nucleic acid can be produced that is in a position to be captured by such oligonucleotide probes. Alternatively, these probes may be mixed with the genomic DNA whereby the DNA/probe hybrids formed can be captured on MC filter through their metal chelate tail on an MC filter.

A second probe conjugated to a detector label, e. g. an enzyme can then be added.

(3) Oligonucleotides, mRNA and cDNA coupled to dendrimers or other species capable of acting as a ligand, for example a hexahistidine tag, can be immobilized onto a MC filter. Incorporation of metal chelate filters into multi-well filterplates provides a platform for microarray analysis. It will also be appreciated that nucleic acids tagged with dendrimers or a hexahistidine may be added directly to a MC filter sheet to form a microarray suitable for analysis without the need for a multi-well plate format.

(4) Recombinant proteins may be directly immobilized on a metal chelate without the need for a purification step. Proteins with a hexahistidine tag will be captured on the filter while the culture supernatant is washed away. Such proteins may then be detected or utilised in an immunoassay or similar type of analysis.

(5) Site-directed immobilisation of recombinant proteins for use in immunoassays. Recombinant fusion proteins including a hexahistidine tail may be immobilised on a metal chelate filter. This will ensure that the majority of the proteins have their active site (s) available for ligand binding resulting in more efficient antigen usage and more sensitive immunoassays.

(6) Unstable recombinant protein may be immobilized on MC filters quickly and at room temperature without the need for covalent bond formation involving harsh chemical reactions which may damage the protein.

Hiqh-throuqhput screeninq (HTS) (1) Microplates and filterplates in a 96-well or greater format are widely used in HTS. A filterplate incorporating an MC filter would enable the user to rapidly immobilize potential drugs or target molecules labelled with a specific tag, e. g. hexahistidine.

(2)"DELphi" (Cytos Biotechnology Ag, Zurich, Switzerland) is a virus-based expression and screening system that allows reproduction of all proteins from a chosen tissue or cell type using cDNA libraries converted into alphaviral expression libraries that are used to infect cell cultures expressing the original proteins in a"one-gene-per- cell"or"one-gene-per-plaque"format (WO 99/50432, WO 99/25876, C. Blaser, et al., Genetic Engineering News 2000 ; 20 (6): 32-35). If the cDNA were co-expressed with 6-his this would permit rapid capture of the expressed protein. The method could also be combined with a FTA filter for simultaneous capture of the amplifie viral DNA for sequencing either after or without the need for RT-PCR. The MCF-captured proteins may then be tested for function in bioassays.

(3) An indicator of cellular events is the change in kinase activity. Interaction at the cell surface is translated to gene expression via a multitude of pathways consisting of discrete quinces. This process is known as signal transduction, and is the mechanism by which a cell interacts with its environment. Kinases are therefore regarded as useful drug targets as their (de) activation can alter the behaviour of a cell. To this end many assay techniques to detect kinase activity exist. In the microplate format, typically, a synthetic kinase substrate is incubated with the kinase sample of interest and the level of phosphorylation of the substrate measured post incubation. Difficulty has always arisen when attempting to isolate the substrate in a purified form to facilitate detection. If the substrate was engineered to contain a 6xHis tag, it could therefore be readily captured on a MC filterplate that is incorporated within a multiwell device. A MC filter will have greater specificity than Promega's streptavidin filter that is commonly used together with biotin tagged peptides.

(4) Antibodies, enzymes and other molecules (targets) required to be tested against solid phase or liquid phase combinatorial chemistry libraries may be tagged with hexahistadine or dendrimers. Following an incubation, the reacted mixtures are passed through a MC filter and washed. The hexahistidine or dendrimer tagged targets are retained by the MC filter together with any combinatorial library compound of"hit"compound. The isolated library compound may then be further interrogated to determine its identity as is known in the art. As an alternative the target molecule may be conjugated to a dendrimer or hexahistidine tag either of which may be itself tagged with a dye, fluorescent compound, enzyme, etc. Following an incubation, the"hit"library compounds either on a resin particle or in free solution, are labeled by the tagged dendrimer or hexahistidine and may then be further interrogated.

(5) Peptide immobilisation for epitope mapping.

Overlapping peptide sequences may be tagged with a hexahistidine tail or dendrimers and immobilised onto metal chelate filters for subsequent screening.

(6) Filterplates with 96,384,1536 or more wells with metal chelate filter bottoms could be used to capture hexahistidine or dendrimer tagged or target molecules.

(7) When searching for reporter genes, ie those that switch on or off in response to a drug, the gene product may be engineered to bear a hexahistidine sequence. This product may then readily be captured onto a metal chelate filter.

Biotechnolo-gy applications (1) A deep well multiwell plate encapsulating a MC filter at the bottom of each well may be constructed with a hydrophobic filter layer placed directly beneath the chelate filter to act as a liquid retention barrier. Within each well may be carried out mammalian, yeast or bacterial culture without fluid dripping through the filter bottoms. Protein, recombinant or otherwise, either secreted from the cells in culture, obtained via periplasmic harvesting or lysis will bind to the metal chelate filter at the bottom of the well if it has a hexahistidine tag.

Application of vacuum to the well will remove cellular debris; leaving recombinant protein bound to the filter. After washing steps the captured protein may be released with an elution procedure as is known in the art.

(2) Simultaneous capture of library DNA and recombinant protein. A device encapsulating both FTA and MC filter materials within the same device (tube, column or multiwell) may be constructed.

Upon application of a cellular population containing an expression library, the cells will lyse, the episomal and/or genomic DNA will bind to the FTA, and the recombinant protein containing an engineered hexahistidine tag will bind to the chelate filter. With the addition of imidazole elution buffer, the recombinant protein can be harvested and assayed. If the protein collecte is of interest (desired level, activity, interaction, etc.), the exact DNA that produced it can be collecte using the FTA techniques.

(3) Immobilization of metalloproteases.

Metalloproteases are implicated with the onset of metastasis, being part of the mechanism utilised by transformed cells during the break through of epithelial layers. The action of metalloprotease is currently of interest to the drug discovery community as they provide a good anti-cancer target. The ability to rapidly harvest and assay for metalloproteases is advantageous. Such proteases will specifically bind to MC or MCS filters.

(4) Recombinant proteins and enzymes expressing a tag such as a hexahistidine tail, may be assayed directly from culture to determine a) levels of expression, b) enzyme activity, c) the best construct, d) best culture medium to use thereby eliminating tedious column chromatography work for simple assay determinations.

(5) Immobilisation of metalloproteins for purification and quantitation.

(6) Western blot and dot blot applications.

(7) Immunoassays where it is desirable to capture, for example, dendrimer or hexahistidine tagged peptides, proteins, nucleic acids or other substances onto a MC or MCS filter.

Other applications (1) Multi-layer MC or MCS filterplates, tubes or columns. Several layers of MC or MCS filter within each tube, column or well will amplify the capacity to isolate and harvest compounds tagged with dendrimers or hexahistidine or other suitable substances.

(2) Environmental samples incubated with specific dendrimer or hexahistidine conjugated reagents may be passed through columns containing large rolled up sheets of MC or MCS filters. This approach allows for large volumes processing of fluids such as water supplies. Captured pollutants and microorganisms or parts of microorganisms such as antigens or nucleic acids may then be assayed using methods well known in the art.

(3) The inclusion of a flow restriction filter beneath the MC or MCS filter may be used to control flow through of fluids.

(4) Large and small scale filter devices for heavy metal removal systems using the MC or MCS filter.