Particles

1 . A coated magnetic particle comprising an optionally porous magnetic polymer particle of a matrix polymer, said polymer particle having on a surface and/or in the pores thereof superparamagnetic crystals, said coated particle having a coefficient of variation (CV) of less than 10% and having a coat formed of a coating polymer, wherein said coated magnetic particle is essentially non-autofluorescent.

2 . A coated magnetic particle as claimed in claim 1 having a level of autofluorescence corresponding to a difference in the Mean Grey Value (ΔMGV) at an excitation wavelength of 450±25 nm for an exposure time of 500 ms or 600 ms of less than 600.

3 . A coated magnetic particle as claimed in claim 2 having a level of autofluorescence corresponding to a difference in the Mean Grey Value (ΔMGV) at an excitation wavelength of 450±25 nm for an exposure time of 500 ms or 600 ms of less than 300.

4 . A coated magnetic particle as claimed in claim 1 being essentially free of conjugated delocalized electron systems (except those within benzene rings).

5 . A coated magnetic particle as claimed in claim 1 wherein said coating polymer is formed from at least one epoxide.

6 . A coated magnetic particle as claimed in claim 5 wherein said coating polymer is formed from at least two epoxides.

7 . A coated magnetic particle as claimed in claim 6 wherein the epoxides are selected from epichlorohydrin, epibromohydrin, isopropylglycidyl ether, butyl glycidyl ether, allylglycidyl ether, 1,4-butanediol diglycidyl ether (1,4-bis (2,3-epoxypropoxy) butane), ethylhexylglycidylether, methyl glycidylether neopentylglycol diglycidyl ether, ethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycidol, and glycidyl methacrylate.

8 . A coated magnetic particle as claimed in claim 1 wherein the polymer particle is porous.

9 . A coated magnetic particle as claimed in claim 1 wherein the polymer particle has a diameter in the range 0.8 to 10 μm.

10 . A coated magnetic particle as claimed in claim 9 wherein the particle is in the range 2 to 10 μm in diameter.

11 . A coated magnetic particle as claimed in claim 1 wherein said matrix polymer is a combination of a styrenic polymer, a styrenic/acrylic polymer and an acrylic polymer.

12 . A coated magnetic particle as claimed in claim 1 wherein the particle surface carries free amino groups.

13 . A coated magnetic particle as claimed in claim 1 additionally comprising a fluorophore or mixture of different fluorophores.

14 . A coated magnetic particle as claimed in claim 13 wherein said fluorophore is attached to the external coating polymer via an amino linkage or is swollen into the coating polymer and entrapped therein.

15 . A coated magnetic particle as claimed in claim 13 wherein said fluorophore is Bodipy 630/650, Bodipy 650/655, DY-647 or AMCA-X.

16 . A coated magnetic particle as claimed in claim 13 wherein said fluorophore emits in the blue/green region of the electromagnetic spectrum.

17 . A coated magnetic particle as claimed in claim 1 additionally comprising an affinity ligand.

18 . A mixture of coated magnetic particle as claimed in claim 1 wherein the CV of the polymer particle diameters is less than 8%.

19 . A mixture of coated magnetic particles as claimed in claim 1 comprising at least a first set of coated magnetic particles carrying a first fluorophore and second set of coated magnetic particles carrying a second fluorophore, the particles of said first and second sets being of differing diameters.

20 . A process for the preparation of coated magnetic particles as claimed in claim 1 being free of conjugated delocalised electron systems, said method comprising reacting porous magnetic polymer particles essentially free from surface nitro groups and having superparamagnetic crystals on the surface and/or in the pores thereof with polymer-forming monomers selected from epoxides.

21 . Use of a coated magnetic particle or particles as claimed in claim 1 in an assay.

22 . Use as claimed in claim 21 wherein said assay comprises the steps of:

i) adding a coated magnetic particle comprising a first fluorophore and an affinity ligand to a sample in which a target analyte may be present;

ii) allowing said affinity ligand to bind with said analyte if present to form a complex;

iii) contacting the complex with a reporter to allow binding of said reporter to said analyte wherein said reporter optionally carries a second fluorophore;

iv) magnetically separating said particles from said sample; and

v) detecting said first fluorophore and if present said second fluorophore.

23 . Use as claimed in claim 22 wherein detection is carried out using a flow cytometer or by microscopy.

24 . Use as claimed in claim 22 wherein the particles form part of a bead array, which is analysed to detect the position of each bead type and the presence of second fluorophore.

25 . Use as claimed in claim 22 wherein said reporter is biotin or a second fluorophore which is different from said first fluorophore.

26 . Use as claimed in claim 21 wherein step (i) additionally comprises the step of:

adding at least a second coated magnetic particle carrying a further affinity ligand (specific for other analytes which may be present in the sample) and a further fluorophore to said sample, said first and further affinity ligands and said first and further fluorophores being different.

27 . Use as claimed in claim 26 wherein said second coated magnetic particle is of different diameter to said first coated magnetic particle.

28 . Use as claimed in claim 22 wherein said reporter is biotin and said complexes are contacted with a streptavidin coated surface prior to fluorophore detection.

29 . Use as claimed in claim 21 wherein said assay comprises the steps of:

i) contacting a coated magnetic particle comprising a first fluorophore and an affinity ligand with a sample in which a target analyte may be present and in which an analyte carrying a reporter capable of competing with said target analyte for the affinity ligand is present:

ii) allowing said affinity ligand to bind to said analyte, if present, or said analyte carrying a reporter;

iii) magnetically separating said particles from said sample; and

iv) detecting the first fluorophore.

30 . Use as claimed in claim 29 wherein said reporter is biotin and said complexes are contacted with a streptavidin coated surface prior to fluorophore detection.

31 . An optionally porous magnetic polymer particle comprising a matrix polymer, with disposed on the surface and/or in the pores thereof superparamagnetic crystals, said matrix polymer being essentially free of conjugated delocalized electron systems and optionally being surface functionalised with groups selected from sulphonic acid, carboxylic acid, amine, and epoxy groups, said particle being essentially non-autofluorescent.