Azide coated magnetic particle and its use in qualitative and / or quantitative determination of at least one analyte

Abstract

In a first aspect, the present invention is directed to a magnetic particle having a saturation magnetization ≥ 15 Am2 / kg and having at least one azide group –N=N'-N- bonded to a polymer matrix of the magnetic particle. A second aspect of the invention relates to a process for preparing a magnetic particle, which comprises at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), the polymer matrix (P) comprising on its surface at least a functional group reactive towards amine groups and / or hydroxyl groups. In a third aspect, the invention is directed to the magnetic particle obtained or obtainable from the process of the second aspect. A fourth aspect is related to a process for preparing a magnetic particle having a saturation magnetization ≥ 15 Am2 / kg of the first aspect, and a fifth aspect relates to the magnetic particle obtained or obtainable from the process of the fourth aspect. A sixth aspect is directed to the use of the magnetic particle having a saturation magnetization ≥ 15 Am2 / kg of the first aspect or of the fourth aspect for qualitative and / or quantitative determination of at least one analyte in a fluid or in a gas, and a seventh aspect relates to a method for determining at least one analyte in a fluid using said magnetic particle having a saturation magnetization ≥ 15 Am2 / kg.

Description

[0001] Roche Diagnostics GmbH September 8, 2025

[0002] RD38922PC

[0003] Azide coated magnetic particle and its use in qualitative and / or quantitative determination of at least one analyte

[0004] In a first aspect, the present invention is directed to a magnetic particle having a saturation magnetization > 15 Am2 / kg and having at least one azide group -N=N+-N' bonded to a polymer matrix of the magnetic particle. A second aspect of the invention relates to a process for preparing a magnetic particle, which comprises at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), the polymer matrix (P) comprising on its surface at least a functional group reactive towards amine groups and / or hydroxyl groups. In a third aspect, the invention is directed to the magnetic particle obtained or obtainable from the process of the second aspect. A fourth aspect is related to a process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg of the first aspect, and a fifth aspect relates to the magnetic particle obtained or obtainable from the process of the fourth aspect. A sixth aspect is directed to the use of the magnetic particle having a saturation magnetization > 15 Am2 / kg of the first aspect or of the fourth aspect for qualitative and / or quantitative determination of at least one analyte in a fluid or in a gas, and a seventh aspect relates to a method for determining at least one analyte in a fluid using said magnetic particle having a saturation magnetization > 15 Am2 / kg.

[0005] Related art

[0006] Magnetic particles are widely used for capturing analytes from human samples for diagnostic applications. The magnetic properties allow for a fast and cheap automation on diagnostic systems by avoiding time-consuming centrifugation or filtration steps. Documents such as EP 2 003 455 Al and EP 2 015 074 Al describe the extraction of analytes from human samples by using magnetic particles on an LC / MS system. EP 3 610 262 Al discloses magnetic particles with improved size and improved saturation magnetization.

[0007] Beside the magnetization, also further properties are indispensable, for example, the binding of an analyte should be reliable and quantifiable. For being able to bond analytes, one way is the creation of a porous structure of the magnetic particles’ surface, which is for example, achievable by hypercrosslinking of the polymer matrix (P). The term "hypercrosslinked" as used herein refers to a type of multiple crosslinking resulting in a rigid three-dimensional network with pores, into which analytes can enter. Hypercrosslinking is often achieved by subjecting the already crosslinked polymer to a further chemical reaction, thereby obtaining the hypercrosslinked polymer such as a Friedel-Crafts reaction. In addition or alternatively, the magnetic particles’ surface, i.e. the surface of its polymeric matrix (P), can be modified by addition of functional groups. For surface modification, the magnetic particles may be treated with a suitable base in order to achive a functionalization with hydroxyl groups or the magnetic particles’ surface can be functionalized with carboxyl groups or epoxy groups. For example, EP 3 610 262 Al describes a direct functionalization of the surface of its polymeric matrix (P) with a plurality of functional groups. An orthogonal biofunctionalization of magnetic nanoparticles via “clickable” poly(ethylene glycol) silanes is described by M. Das et al. (M. Das, D. Bandyopadhyay, R. P. Singh, H. Harde, S. Kumar, S. Jain J. Mater. Chem., 2012, 22, 24652). Azide-alkyne reactions (“click chemistry”) for a site-specific modification of nanoparticles with small molecules are also described by E. Sun et al. (E. Y. Sun, L. Josephson, R. Weissleder, Molecular Imaging, Vol. 5, 2, April- June 2006). Coppock et al. (M. B. Coppock, D. N. Strati s-Cullum, Methods 158 (2019) 12-1) describes the functionalization of dyed magnetic microspheres with peptides, wherein however the magnetic microspheres only had a saturation magnetization of < 5 Am2 / kg.

[0008] Magnetic particles available to date have however the disadvantage, especially when considering specific analytes such as steroids and some vitamins, that they bind the analytes non-specifically. Furthermore, analytical separation and quantification of the analytes is sometimes problematic or not possible as the size and / or magnetization are not suitable.

[0009] The objective problem underlying the present invention was thus the provision of specific particles for the binding of analytes, which overcome the disadvantages indicated above.

[0010] Summary of the invention

[0011] This problem is addressed by a magnetic particle, its preparation and use with the features of the independent claims. Advantageous embodiments which might be realized in an isolated fashion or in any arbitrary combinations are listed in the dependent claims as well as throughout the specification.

[0012] As used in the following, the terms “have”, “comprise” or “include” or any arbitrary grammatical variations thereof are used in a non-exclusive way. Thus, these terms may both refer to a situation in which, besides the feature introduced by these terms, no further features are present in the entity described in this context and to a situation in which one or more further features are present. As an example, the expressions “A has B”, “A comprises B” and “A includes B” may both refer to a situation in which, besides B, no other element is present in A (i.e. a situation in which A solely and exclusively consists of B) and to a situation in which, besides B, one or more further elements are present in entity A, such as element C, elements C and D or even further elements.

[0013] Further, it shall be noted that the terms “at least one”, “one or more” or similar expressions indicating that a feature or element may be present once or more than once, typically will be used only once when introducing the respective feature or element. In the following, in most cases, when referring to the respective feature or element, the expressions “at least one” or “one or more” will not be repeated, notwithstanding the fact that the respective feature or element may be present once or more than once.

[0014] Further, as used in the following, the terms "preferably", "more preferably", "particularly", "more particularly", "specifically", "more specifically" or similar terms are used in conjunction with optional features, without restricting alternative possibilities. Thus, features introduced by these terms are optional features and are not intended to restrict the scope of the claims in any way. The invention may, as the skilled person will recognize, be performed by using alternative features. Similarly, features introduced by "in an embodiment of the invention" or similar expressions are intended to be optional features, without any restriction regarding alternative embodiments of the invention, without any restrictions regarding the scope of the invention and without any restriction regarding the possibility of combining the features introduced in such a way with other optional or non-optional features of the invention.

[0015] 1staspect - Magnetic particle

[0016] In a first aspect, the invention thus relates to a magnetic particle having a saturation magnetization > 15 Am2 / kg comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L) to the polymer matrix (P), wherein the linker (L) comprises an element

[0017] ••X-(CR1R2)xi-[Y-(CR3R4)x2]y-Z -(CR1R2)x3•••• (L), wherein R1and R2are independently selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;

[0018] R3is selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;

[0019] R4is selected from the group consisting of hydrogen atom, Cl to C3 straight or branched alkyl group and C(=O)-X1-(CH2)zi-N+(CH3)2-(CH2)z2-SO3' group; xl, x2 are each independently an integer selected from the range of from 1 to 10; x3 is zero or an integer selected from the range of from 1 to 10; y is an integer selected from the range of from 1 to 500; zl, z2 are each independently an integer selected from the range of from 1 to 10;

[0020] X is an -NH- group or an oxygen atom;

[0021] XIis an -NH- group or an oxygen atom;

[0022] Y is an oxygen atom or is absent;

[0023] Z is an oxygen atom or is absent; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0024] The dotted line connected to X represents the covalent bond to the polymer matrix (P) and the dotted line connected to (CR1R2)X3 represents the covalent bond to the azide group.

[0025] The azide groups on the surface can be detected analytically, for example, based on IR, the azide integral can easily be determined via IR spectroscopy, and the complete linker can be separated and analysed by amide cleavage. Furthermore, particles can be easily characterised using established analytical methods.

[0026] Linker (L)

[0027] In some preferred embodiments of the magnetic particle, the linker (L) comprises an element (LI)

[0028] • • • X-(CR1R2)xi - [(CR3R4)x2]y-(CR1R2)x3 •••• (LI), wherein

[0029] R1, R2are independently selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;

[0030] R3is selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group, and is preferably a Cl to C3 straight or branched alkyl group; R4is a C(=O)-X1-(CH2)zi-N+(CH3)2-(CH2)z2-SO3- group; xl, x2, x3 are each independently an integer selected from the range of from 1 to 10; y is an integer selected from the range of from 1 to 500;

[0031] X is an -NH- group or an oxygen atom;

[0032] XIis an -NH- group or an oxygen atom, preferably an oxygen atom; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0033] In some preferred embodiments of the magnetic particle, the linker (L) comprises an element (L2) wherein

[0034] R1, R2, R3, R4are independently selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group; xl, x2 are each independently an integer selected from the range of from 1 to 10; y is an integer selected from the range of from 1 to 500;

[0035] X is an -NH- group or an oxygen atom; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0036] In some preferred embodiments of the magnetic particle, at least one of R3, R4is a hydrogen atom, preferably R3and R4are both hydrogen atoms.

[0037] In some preferred embodiments of the magnetic particle, at least one of R1, R2is a hydrogen atom, preferably R1and R2are both hydrogen atoms.

[0038] In some preferred embodiments of the magnetic particle, xl, x2 and optionally x3 are independently an integer selected from the range of from 2 to 6, preferably 2 or 3.

[0039] In some preferred embodiments of the magnetic particle, y is an integer selected from the range of from 2 to 450, preferably from the range of from 2 to 225, more preferably from the range of from 2 to 110; or wherein y is an integer selected preferably from the range of from 2 to 50, more preferably from the range of from 3 to 40. In some preferred embodiments of the magnetic particle, the linker (L) comprises an element •NH-(CH2)2 -O-[(CH2)2-O]y-(CH2)2 ••••, wherein y is an integer selected from the range of from 1 to 100, preferably selected from the range of from 2 to 50, more preferably from the range of from 3 to 40; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0040] Properties of the magnetic particle

[0041] In some preferred embodiments of the magnetic particle, the magnetic particles have a median of particle size distribution x50 in the range of from 2 to 5 micrometers, as determined according to DIN ISO 9276-2:2018-09.

[0042] In some preferred embodiments of the magnetic particle, the median of particle size distribution x50 has a standard deviation (span), calculated according to (x90 - xlO) / x50, of < 1.1 micrometer, wherein x90, x50 and xlO are determined according to DIN ISO 9276- 2:2018-09.

[0043] In some preferred embodiments, the magnetic particle has a density in the range of from 1.2 to 1.7 g / cm3, determined by gas pycnometry. The determination of the density by gas pycnometry is preferably done according to the method indicated in the European Pharmacopoeia (Ph. Eur.), 11thedition, Chapter 2.9.23.

[0044] In some preferred embodiments, the magnetic particle has a saturation magnetization in the range of from 15 to 25 Am2 / kg, determined by vibrating sample magnetometry, preferably according to ASTM A 894 / A 894M.

[0045] In some preferred embodiments, the magnetic particle has a BET specific surface area in the range of from 2 to 60 m2 / g, determined by nitrogen physisorption according to DIN 66131 : 1993-07.

[0046] Polymer matrix (P)

[0047] In some preferred embodiments of the magnetic particle, the polymer matrix (P) comprises a crosslinked polymer, wherein the crosslinked polymer preferably comprises a co-polymer obtained or obtainable by a method comprising a polymerization of at least two different monomeric building blocks selected from the group consisting of styrene, functionalized styrenes, vinylbenzylchloride, divinylbenzene, vinylacetate, methylmethacrylate and acrylic acid. In some preferred embodiments of the magnetic particle, the at least one monomeric building block used has one or more functional group(s) reactive towards amine groups or amine groups, wherein the functional group reactive towards amine groups and / or hydroxyl groups is preferably selected from the group of halogenated Cl-C3-alkyl group, halogen atom, epoxy group and activated carboxy group, more preferably the functional group reactive towards amine groups and / or hydroxyl groups is a halogenated Cl-C3-alkyl group, more preferably a -CH2-CI group. Preferably, vinylbenzyl chloride is employed as monomeric building block having functional groups reactive towards amine groups and / or hydroxyl groups.

[0048] In some preferred embodiments of the magnetic particle, the at least one further monomeric building block is a crosslinking agent, preferably selected from the group consisting of divi- nylbenzene, bis(vinylphenyl)ethane, bis(vinylbenzyloxy)hexane, bis(vinylbenzyloxy)do- decane, and mixtures of two or more thereof, wherein more preferably the crosslinking agent comprises at least divinylbenzene.

[0049] In some preferred embodiments of the magnetic particle, the co-polymer is obtained or obtainable by a method comprising a polymerization of at least two different monomeric building blocks selected from the group consisting of the following monomers: with Rv, Rw, Rx, Ryand Rz, are, independently of each other selected from the group consisting of -N3, -NH2, -Br, -I, -F, -NR’R”, -NR’R”R”’, -COOH, -CN, -OH, -OR’, -COOR’, - NO2, -SH2, -SO2, -R’(OH)X, -R’(COOH)X, -R’(COOR”)X, -R’(OR”)X, -R’(NH2)X, - R’(NHR”)X, -R’(NR”R”’)X, -R’(C1)X, -R’(I)X, -R’(Br)x, -R’(F)X, R’(CN)X, -R’(N3)X, - R’(NO2)X, -R’(SH2)X, -R’(SO2)X, alkyl, aryl, cycloalkyl, heteroaryl, heterocycloalkyl and with R’, R” and R’” being, independently of each other, selected from the group consisting of alkyl, aryl, cycloalkyl, heteroaryl, heterocycloalkyl, halides, hydrogen, sulfides, nitrates and amines, and wherein x is an integer in the range of from 1 to 3.

[0050] In some preferred embodiments of the magnetic particle, the polymer matrix is obtained or obtainable by a method comprising co-polymerizing at least one monomeric building block, which is a crosslinking agent, and at least one monomeric building block having functional groups reactive towards amine groups and / or hydroxyl groups, wherein the molar ratio of crosslinking agent : monomeric building block having functional groups reactive towards amine groups and / or hydroxyl groups is in the range of from 10: 1 to 1 :10, preferably in the range of from 5: 1 to 1 :5, more preferably in the range of from 2: 1 to 1 :2, more preferably in the range of from 1.5: 1 to 1 : 1.5, more preferably in the range of from 1.2: 1 to 1 : 1.2.

[0051] In some preferred embodiments of the magnetic particle, at least divinylbenzene is employed as crosslinking agent and at least vinylbenzyl chloride is employed as monomeric building block having functional groups reactive towards amine groups and / or hydroxyl groups.

[0052] In some preferred embodiments of the magnetic particle, the functional group reactive towards amine groups and / or hydroxyl groups is modified in the polymer matrix (P), wherein a modified functional group is still reactive towards amine groups and / or hydroxyl groups and is preferably a carboxyl group and / or an amine group. For example, if vinylbenzyl chloride has been employed as monomeric building block, the functional group is modified into a hydroxyl group, for example, by application of a strong base such as KOH and heat, and, subsequently, the hydroxyl group is transformed into a carboxylic group by oxidation, for example, by using sodium hypochlorite.

[0053] In some preferred embodiments of the magnetic particle, the linker (L) is covalently bonded to the polymer matrix (P) by a structural element derived or derivable from the functional group reactive towards amine groups and / or hydroxyl groups and / or from the modified functional group, which is still reactive towards amine groups and / or hydroxyl groups, wherein the structural element more preferably comprises — W — , wherein the dashed lines • — represent the covalent bond to the polymer matrix (P) and to the X group of the element •X- (CR1R2)xi-[Y-(CR3R4)x2]y-Z -(CR1R2)X3"- of the linker (L), wherein W is selected from - NH- and -C(=O)O-.

[0054] Magnetic core (M)

[0055] In some preferred embodiments of the magnetic particle, the at least one magnetic core (M) comprises a compound selected from the group consisting of metal, metal carbide, metal nitride, metal sulfide, metal phosphide, metal oxide, metal chelate and a mixture of two or more thereof.

[0056] In some preferred embodiments of the magnetic particle, the at least one magnetic core (M) comprises a metal oxide or a metal carbide, more preferably, an iron oxide, in particular an iron oxide selected from the group consisting of FesCU, a-Fe2Os, y-Fe2O3, MnFepOq, CoFepOq, NiFepOq, CuFepOq, ZnFepOq„ CdFepOq, BaFepO and SrFepO, wherein p and q vary depending on the method of synthesis, and wherein p is preferably an integer of from 1 to 3, more preferably 2, and wherein q is preferably 3 or 4 most preferably, FesC

[0057] In some preferred embodiments of the magnetic particle, the at least one magnetic core (M) comprises at least one magnetic nanoparticle, preferably at least one iron oxide nanoparticle, more preferably a FesCU-nan oparticle.

[0058] In some preferred embodiments of the magnetic particle, the at least one magnetic core (M) comprises, more preferably consists of a magnetic nanoparticle and a coating (C).

[0059] Coating (C)

[0060] In some preferred embodiments, the magnetic particle has a a coating (C) on at least a part of the surface of the magnetic core (M), preferably on at least 90 % of the surface of the magnetic core (M), more preferably on the whole surface of the magnetic core (M).

[0061] In some preferred embodiments of the magnetic particle, the coating (C) is selected from the group consisting of silica, silicate, silane, phosphate, phosphonate, phosphonic acid, fatty acid, and mixtures of two or more thereof.

[0062] In some preferred embodiments of the magnetic particle, the coating (C) is selected from the group consisting of silica, tetraethyl orthosilicate, 3 -(trimethoxy silyl)propyl methacrylate, vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, triethoxyvinyl silane, 3 -(trimethoxy silyl)propyl acrylate, trimethoxy(7-octen-l-yl)silane, trimethoxymethylsilane, triethoxymethylsilane, ethyltrimethoxysilane, triethoxy(ethyl)silane, trimethoxyphenylsilane, trimethoxy(2-phenylethyl)silane trimethoxy(propyl)silane, n- propyltriethoxysilane, isobutyl(trimethoxy)silane, isobutyltriethoxysilane, vinylphosphonic acid, dimethyl vinylphosphonate, diethyl vinylphosphonate, diethyl allylphosphonate, diethyl allyl phosphate, diethyl (2-methylallyl)phosphonate, octylphosphonic acid, bu- tylphosphonic acid, decylphosphonic acid, hexylphosphonic acid, hexadecylphosphonic acid, n-dodecylphosphonic acid, lauric acid, myristic acid, palmitic acid, stearic acid, and arachidic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecylic acid, tridecylic acid, pentadecylic acid, margaric acid, nonadecylic acid, heneicosylic acid, behenic acid, tricosylic acid, lignoceric acid, pen- tacosylic acid, cerotic acid, heptacosylic acid, montanic acid, nonacosylic acid, melissic acid, henatriacontylic acid, lacceroic acid, psyllic acid, geddic acid, ceroplastic acid, hexatriac- ontylic acid, heptatriacontanoic acid, octatriacontanoic acid, oleic acid, linoleic acid, linolenic acid, arachidonic acid, hexadecatrienoic acid, stearidonic acid, eicosatrienoic acid, eicosatetraenoic acid, eicosapentaenoic acid, heneicosapentaenoic acid, docosapentaenoic acid, clupanodonic acid, docosahexaenoic acid, tetracosapentaenoic acid, tetracosahex- aenoic acid, calendic acid, eicosadienoic acid, docosadienoic acid, adrenic acid, docosapentaenoic acid, tetraco-satetraenoic acid, tetracosapentaenoic acid, 5-dodecenoic acid, 7- tetradecenoic acid, pal-mitoleic acid, vaccenic acid, paullinic acid, 15-docosenoic acid, 17- tetracosenoic acid, elaidic acid, gondoic acid, mead acid, erucic acid, nervonic acid, rumenic acid, calendic acid, jacaric acid, eleostearic acid, catalpic acid, punicic acid, rumelenic acid, parinaric acid, bosseopentaenoic acid, pinolenic acid, podocarpic acid and mixtures of two or more thereof.

[0063] In some preferred embodiments of the magnetic particle, the polymer matrix (P) comprises a crosslinked polymer based on at least vinylbenzyl chloride and divinyl benzene, wherein the polymer matrix (P) at least partially surrounds the magnetic core (M), wherein the magnetic core (M) comprises at least a FesCU-nanoparticle, a coating (C) on at least a part of the surface of the magnetic core (M), which comprises a fatty acid, preferably oleic acid, the magnetic particle comprising at least one azide group -N=N+-N' bonded via a linker (L) to the polymer matrix (P), wherein the linker (L) comprises an element (L2) as defined in any one of embodiments 3 to 7, the linker (L) preferably comprising an element •••NH-(CH2)2 - O-[(CH2)2-O]y-(CH2)2 • • • •, wherein y is an integer selected from the range of from 1 to 100;or wherein y is an integer selected selected from the range of from 2 to 50, preferably from the range of from 3 to 40; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0064] 2ndaspect - Process for preparing a functionalized magnetic particle

[0065] A second aspect of the invention relates to a process for preparing a functionalized magnetic particle, the magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), the polymer matrix (P) comprising on its surface at least a functional group reactive towards amine groups and / or hydroxyl groups, the process comprising: a) Providing a magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, wherein the polymer matrix (P) comprises on its surface at least one hydroxyl group; b) Contacting the magnetic particle of (a), with an oxidation agent in an aqueous medium at a pH in the range of from 7.8 to 10, thereby obtaining a magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises on its surface at least a COOH group reactive towards amine groups and / or hydroxyl groups (COOH-fimctionalized magnetic particle).

[0066] It turned out that the process for functionalization is sensitive and has some critical issues, which could result in the surface of the magnetic particles coming out of the process severely damaged. Surprisingly, it was found that adjusting the pH value and / or mass based ratio of water : oxidation agent and / or temperature and / or duration of the reaction was critical and that, if suitable parameters are applied, it was possible to achieve COOH-fimctionalized magnetic particles with an undamaged surface.

[0067] In some preferred embodiments of the process for preparing a functionalized magnetic particle, (b) is conducted at a temperature T in the range of from 35 to 80°C, preferably in the range of from 40 to 70°C, more preferably in the range of from 42 to 55°C.

[0068] Preferably, the oxidation agent is selected from the group consisting of sodium hypochlorite, potassium permanganate, 1 -hydroxy cyclohexyl phenyl ketone, potassium dichromate(VI) and mixtures of two or more thereof, wherein the oxidation agent more preferably comprises or is sodium hypochlorite.

[0069] In some preferred embodiments of the process for preparing a functionalized magnetic particle, (b) is conducted at a mass based ratio of NaOCl : H2O in the range of from 1 : 100 to 1 : 10, preferably 1 : 80 to 1 :5.

[0070] In some preferred embodiments of the process for preparing a functionalized magnetic particle, (b) is conducted for a period of time t in the range of from 0.1 to 15 h, preferably in the range of from 3 to 10 h, more preferably in the range of from 4 to 8 h, more preferably in the range of from 5 to 7 h.

[0071] In some preferred embodiments of the process for preparing a functionalized magnetic particle, (b) comprises b.1) Contacting the magnetic particle of (a), with an oxidation agent in an aqueous medium, thereby obtaining an aqueous mixture comprising the magnetic particle of (a) and the oxidation agent, wherein said aqueous mixture has a temperature Ti; b.2) Adding one or more acid(s) to the aqueous mixture of b.1), thereby obtaining an aqueous mixture comprising the magnetic particle of (a) and the oxidation agent, wherein said aqueous mixture has a pH in the range of from 7.8 to 10; b.3) heating the aqueous mixture of b.2) to a temperature T, wherein T > Ti and maintain the aqueous mixture at said temperature T for a period of time t, thereby obtaining a magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises on its surface at least a COOH group reactive towards amine groups and / or hydroxyl groups.

[0072] In some preferred embodiments, the process for preparing a functionalized magnetic particle further comprises: c) Separating the magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises on its surface at least a COOH group reactive towards amine groups and / or hydroxyl groups obtained in (b) from the aqueous mixture, thereby obtaining a separated magnetic particle; d) Optionally washing the separated magnetic particle at least once with an aqueous medium, preferably with water, thereby obtaining a washed separated magnetic particle; e) Optionally modifying the COOH group reactive towards amine groups and / or hydroxyl groups of the separated magnetic particle of c) or of the washed separated magnetic particle of d); thereby obtaining a magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises on its surface at least a (modified) functional group reactive towards amine groups and / or hydroxyl groups.

[0073] The term “(modified) functional group” means either a COOH group or a functional group, which is modified compared to the COOH group. In some preferred embodiments, the (modified) functional group is chosen as a (modified) functional group reactive towards amine groups. In some other preferred embodiments, the (modified) functional group is chosen as a (modified) functional group reactive towards hydroxyl groups. Preferably, the functional group is a COOH group, i.e. optional step (e) is omitted.

[0074] All details, embodiments and preferred embodiments described in the section above related to the first aspect of the invention apply also to the second aspect of the invention. Some details, (preferred) embodiments are outlined below. 3rdaspect - Product-by-process

[0075] A third aspect of the invention is directed to a magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises on its surface at least a (modified) functional group reactive towards amine groups and / or hydroxyl groups, obtained or obtainable from the process of the second aspect.

[0076] All details, embodiments and preferred embodiments described in the section above related to the first aspect of the invention or in the section above related to the second aspect of the invention apply also to the third aspect of the invention.

[0077] 4th aspect - Process for preparing a magnetic particle with a linker bound azide group

[0078] A fourth aspect of the invention is directed to a process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L), which is as defined in the section above related to the first aspect of the invention, to the polymer matrix (P),

[0079] (i) Providing a magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises at least a (modified) functional group reactive towards amine groups and / or hydroxyl groups, preferably a magnetic particle of the third aspect of the invention as described in the section above;

[0080] (ii) providing a linker precursor molecule HiX-(CR1R2)xi-[Y-(CR3R4)X2]y-Z-(CR1R2)X3- N3, wherein

[0081] R1and R2are independently selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;

[0082] R3is selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;

[0083] R4is selected from the group consisting of hydrogen atom, Cl to C3 straight or branched alkyl group and C(=O)-X1-(CH2)ZI-N+(CH3)2-(CH2)Z2-SO3' group; xl, x2 are each independently an integer selected from the range of from 1 to 10, preferably from the range of from 2 to 6, more preferably 2 or 3; x3 is zero or an integer selected from the range of from 1 to 10; y is an integer selected from the range of from 1 to 500; zl, z2 are each independently an integer selected from the range of from 1 to 10;

[0084] X is an -NH- group or an oxygen atom;

[0085] XIis an -NH- group or an oxygen atom

[0086] Y is an oxygen atom or is absent;

[0087] Z is an oxygen atom or is absent; and i is 1 or 2;

[0088] (iii) reacting the (modified) functional groups reactive to amine groups and / or hydroxyl groups of the magnetic particle provided in (i) with the amine groups and / or the hydroxyl groups of the molecule provided in (ii); thereby obtaining the magnetic particle having a saturation magnetization > 15 Am2 / kg, the magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L).

[0089] All details, embodiments and preferred embodiments described in the section above related to the first aspect of the invention, in the section above related to the second aspect of the invention, and in the section above related to the third aspect of the invention, apply also to the fourth aspect of the invention. Some details, (preferred) embodiments are outlined below.

[0090] Reacting the (modified) functional groups reactive to amine groups and / or hydroxyl groups of the magnetic particle provided in (i) with the amine groups and / or the hydroxyl groups of the molecule provided in (ii) according to (iii) is preferably done in aqueous solution by methods known to a person skilled in the art.

[0091] In some preferred embodiments, a suitable combination of X and (modified) functional group is chosen so that the bond formed between them is an amide bond. Thus, in some preferred embodiments, when X is an -NH- group, the (modified) functional group is chosen as a (modified) functional group reactive towards amine groups. In some other preferred embodiments, when X is an oxygen atom, the (modified) functional group is chosen as a (modified) functional group reactive towards hydroxyl groups. In some preferred embodiments, X is an -NH- group and thus the (modified) functional group is chosen as a (modified) functional group reactive towards amine groups and is preferably a (modified) carboxyl group.

[0092] In some preferred embodiments of the process, one or more coupling agent(s) are added in (iii), wherein suitable coupling agents, especially for formation of an amide bond, especially those also resulting in an activation of a functional group such as a carboxy group, are known to the skilled person; for example, coupling agents are carbodiimides, such as l-ethyl-3-(3- dimethylaminopropyl)carbodiimide hydrochloride, EDC HC1) or triazine based coupling reagents such as cyanuric chloride (CC).

[0093] Linker

[0094] In some preferred embodiments of the process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the linker (L) comprises an element (LI)

[0095] • • • X-(CR1R2)xi - [(CR3R4)x2]y-(CR1R2)x3 •••• (LI), wherein

[0096] R1, R2are independently selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;

[0097] R3is selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group, and is preferably a Cl to C3 straight or branched alkyl group;

[0098] R4is a C(=O)-X1-(CH2)zi-N+(CH3)2-(CH2)z2-SO3- group; xl, x2, x3 are each independently an integer selected from the range of from 1 to 10; y is an integer selected from the range of from 1 to 500;

[0099] X is an -NH- group or an oxygen atom;

[0100] XIis an -NH- group or an oxygen atom, preferably an oxygen atom; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0101] In some preferred embodiments of the process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the linker (L) comprises an element (L2) wherein

[0102] R1, R2, R3, R4are independently selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group; xl, x2 are each independently an integer selected from the range of from 1 to 10; y is an integer selected from the range of from 1 to 500;

[0103] X is an -NH- group or an oxygen atom; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively. Preferably, at least one of R3, R4is a hydrogen atom, more preferably R3and R4are both hydrogen atoms. Preferably, at least one of R1, R2is a hydrogen atom, more preferably R1and R2are both hydrogen atoms. Preferably, xl, x2 and optionally x3 are independently an integer selected from the range of from 2 to 6, more preferably 2 or 3. Preferably, y is an integer selected from the range of from 2 to 450, more preferably from the range of from 2 to 225, more preferably from the range of from 2 to 110; or wherein y is an integer selected preferably from the range of from 2 to 50, more preferably from the range of from 3 to 40.

[0104] In some preferred embodiments of the process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the linker (L) comprises an element •••NH-(CH2)2 - O-[(CH2)2-O]y-(CH2)2 ••••, wherein y is an integer selected from the range of from 1 to 100, preferably selected from the range of from 2 to 50, more preferably from the range of from 3 to 40; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0105] Polymer matrix (P)

[0106] In some preferred embodiments of the process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the polymer matrix (P) comprises a crosslinked polymer, wherein the crosslinked polymer preferably comprises a co-polymer obtained or obtainable by a method comprising a polymerization of at least two different monomeric building blocks selected from the group consisting of styrene, functionalized styrenes, vinylben- zylchloride, divinylbenzene, vinylacetate, methylmethacrylate and acrylic acid. Preferably, at least one monomeric building block used has one or more functional group(s) reactive towards amine groups or amine groups, wherein the functional group reactive towards amine groups and / or hydroxyl groups is preferably selected from the group of halogenated C1-C3- alkyl group, halogen atom, epoxy group and activated carboxy group, more preferably the functional group reactive towards amine groups and / or hydroxyl groups is a halogenated Cl- C3-alkyl group, more preferably a -CH2-CI group. Preferably, vinylbenzyl chloride is employed as monomeric building block having functional groups reactive towards amine groups and / or hydroxyl groups.

[0107] In some preferred embodiments of the process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, at least one further monomeric building block is a crosslinking agent, preferably selected from the group consisting of divinylbenzene, bis(vi- nylphenyl)ethane, bis(vinylbenzyloxy)hexane, bis(vinylbenzyloxy)dodecane, and mixtures of two or more thereof, wherein more preferably the crosslinking agent comprises at least divinylbenzene. In some preferred embodiments of the process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the co-polymer is obtained or obtainable by a method comprising a polymerization of at least two different monomeric building blocks selected from the group consisting of the following monomers: with Rv, Rw, Rx, Ryand Rz, are, independently of each other selected from the group consisting of -N3, -NH2, -Br, -I, -F, -NR’R”, -NR’R”R”’, -COOH, -CN, -OH, -OR’, -COOR’, - NO2, -SH2, -SO2, -R’(OH)X, -R’(COOH)X, -R’(COOR”)X, -R’(OR”)X, -R’(NH2)X, - R’(NHR”)X, -R’(NR”R’”)X, -R’(C1)X, -R’(I)X, -R’(Br)x, -R’(F)X, R’(CN)X, -R’(N3)X, - R’(NO2)X, -R’(SH2)X, -R’(SO2)X, alkyl, aryl, cycloalkyl, heteroaryl, heterocycloalkyl and with R’, R” and R’” being, independently of each other, selected from the group consisting of alkyl, aryl, cycloalkyl, heteroaryl, heterocycloalkyl, halides, hydrogen, sulfides, nitrates and amines, and wherein x is an integer in the range of from 1 to 3.

[0108] In some preferred embodiments of the process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the polymer matrix is obtained or obtainable by a method comprising co-polymerizing at least one monomeric building block, which is a crosslinking agent, and at least one monomeric building block having functional groups reactive towards amine groups and / or hydroxyl groups, wherein the molar ratio of crosslinking agent : monomeric building block having functional groups reactive towards amine groups and / or hydroxyl groups is in the range of from 10: 1 to 1 : 10, preferably in the range of from 5: 1 to 1 :5, more preferably in the range of from 2: 1 to 1 :2, more preferably in the range of from 1.5:1 to 1 : 1.5, more preferably in the range of from 1.2: 1 to 1 : 1.2.

[0109] Preferably, at least divinylbenzene is employed as crosslinking agent and at least vinylbenzyl chloride is employed as monomeric building block having functional groups reactive towards amine groups and / or hydroxyl groups.

[0110] Preferably, the functional group reactive towards amine groups and / or hydroxyl groups in the polymer matrix (P) is modified, wherein a modified functional group is still reactive towards amine groups and / or hydroxyl groups and is preferably a carboxyl group and / or an amine group. In some preferred embodiments of the process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the linker (L) is covalently bonded to the polymer matrix (P) by a structural element derived or derivable from the functional group reactive towards amine groups and / or hydroxyl groups and / or from the modified functional group, which is still reactive towards amine groups and / or hydroxyl groups, wherein the structural element more preferably comprises — W — , wherein the dashed lines • — represent the covalent bond to the polymer matrix (P) and to the X group of the element • •X-(CR1R2)XI-[Y- (CR3R4)x2]y-Z -(CR1R2)X3"- of the linker (L), wherein W is selected from -NH- and - C(=O)O-.

[0111] Magnetic core (M)

[0112] In some preferred embodiments of the process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the at least one magnetic core (M) comprises a compound selected from the group consisting of metal, metal carbide, metal nitride, metal sulfide, metal phosphide, metal oxide, metal chelate and a mixture of two or more thereof.

[0113] In some preferred embodiments of the process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the at least one magnetic core (M) comprises a metal oxide or a metal carbide, more preferably, an iron oxide, in particular an iron oxide selected from the group consisting of FesCU, a-Fe2Os, y-Fe2O3, MnFepOq, CoFepOq, NiFepOq, CuFepOq, ZnFepOq„ CdFepOq, BaFepO and SrFepO, wherein p and q vary depending on the method of synthesis, and wherein p is preferably an integer of from 1 to 3, more preferably 2, and wherein q is preferably 3 or 4 most preferably, FesC

[0114] In some preferred embodiments of the process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the at least one magnetic core (M) comprises at least one magnetic nanoparticle, preferably at least one iron oxide nanoparticle, more preferably a Fe3O4-nan oparticle.

[0115] In some preferred embodiments of the process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the at least one magnetic core (M) comprises, more preferably consists of a magnetic nanoparticle and a coating (C). Coating (C)

[0116] In some preferred embodiments of the process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the magnetic particle has a coating (C) on at least a part of the surface of the magnetic core (M), preferably on at least 90 % of the surface of the magnetic core (M), more preferably on the whole surface of the magnetic core (M). Preferably, the coating (C) is selected from the group consisting of silica, silicate, silane, phosphate, phosphonate, phosphonic acid, fatty acid, and mixtures of two or more thereof. More preferably, the coating (C) is selected from the group consisting of silica, tetraethyl orthosilicate, 3 -(trimethoxy silyl)propyl methacrylate, vinyltrimethoxy silane, vinyltri ethoxy silane, allyltrimethoxysilane, allyltriethoxysilane, triethoxyvinylsilane, 3 -(trimethoxy silyl)propyl acrylate, trimethoxy(7-octen-l-yl)silane, trimethoxymethylsilane, triethoxymethylsilane, ethyltrimethoxysilane, triethoxy(ethyl)silane, trimethoxyphenylsilane, trimethoxy(2-phe- nylethyl)silane trimethoxy(propyl)silane, n-propyltriethoxysilane, isobutyl(tri- methoxy)silane, isobutyltriethoxysilane, vinylphosphonic acid, dimethyl vinylphosphonate, diethyl vinylphosphonate, diethyl allylphosphonate, diethyl allyl phosphate, diethyl (2- methylallyl)phosphonate, octylphosphonic acid, butylphosphonic acid, decylphosphonic acid, hexylphosphonic acid, hexadecylphosphonic acid, n-dodecylphosphonic acid, lauric acid, myristic acid, palmitic acid, stearic acid, and arachidic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecylic acid, tridecylic acid, pentadecylic acid, margaric acid, nonadecylic acid, heneico- sylic acid, behenic acid, tricosylic acid, lignoceric acid, pentacosylic acid, cerotic acid, hep- tacosylic acid, montanic acid, nonacosylic acid, melissic acid, henatriacontylic acid, lac- ceroic acid, psyllic acid, geddic acid, ceroplastic acid, hexatriacontylic acid, heptatri aconta- noic acid, octatriacontanoic acid, oleic acid, linoleic acid, linolenic acid, arachidonic acid, hexadecatrienoic acid, stearidonic acid, eicosatrienoic acid, eicosatetraenoic acid, eicosapentaenoic acid, heneicosapentaenoic acid, docosapentaenoic acid, clupanodonic acid, docosahexaenoic acid, tetracosapentaenoic acid, tetracosahexaenoic acid, calendic acid, eicosadienoic acid, docosadienoic acid, adrenic acid, docosapentaenoic acid, tetraco-satetraenoic acid, tetracosapentaenoic acid, 5-dodecenoic acid, 7-tetradecenoic acid, pal-mitoleic acid, vaccenic acid, paullinic acid, 15-docosenoic acid, 17-tetracosenoic acid, elaidic acid, gondoic acid, mead acid, erucic acid, nervonic acid, rumenic acid, calendic acid, jacaric acid, eleostearic acid, catalpic acid, punicic acid, rumelenic acid, parinaric acid, bosseopentaenoic acid, pinolenic acid, podocarpic acid and mixtures of two or more thereof.

[0117] In some preferred embodiments of the process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the polymer matrix (P) comprises a crosslinked polymer based on at least vinylbenzyl chloride and divinyl benzene, wherein the polymer matrix (P) at least partially surrounds the magnetic core (M), wherein the magnetic core (M) comprises at least a FesCU-nanoparticle, a coating (C) on at least a part of the surface of the magnetic core (M), which comprises a fatty acid, preferably oleic acid, the magnetic particle comprising at least one azide group -N=N+-N' bonded via a linker (L) to the polymer matrix (P), wherein the linker (L) comprises an element (L2) as defined in any one of embodiments 3 to 7, the linker (L) preferably comprising an element •NH-(CH2)2 -O-[(CH2)2-O]y- (CH2)2 ••••, wherein y is an integer selected from the range of from 1 to 100;or wherein y is an integer selected selected from the range of from 2 to 50, preferably from the range of from 3 to 40; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0118] 5thaspect - product-by-process

[0119] A fifth aspect of the invention is directed to a magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L), which is as defined in the section related to the first aspect of the invention hereinabove, to the polymer matrix (P), obtained or obtainable from the process of the fourth aspect as described herein above, the magnetic particle having a saturation magnetization > 15 Am2 / kg.

[0120] All details, embodiments and preferred embodiments described in the section above related to the first aspect of the invention, the section above related to the second aspect of the invention, the section above related to the third aspect of the invention, and the section above related to the fourth aspect of the invention apply also to the fifth aspect of the invention. Some details, (preferred) embodiments are outlined below.

[0121] Properties of the magnetic particle

[0122] Preferably, the magnetic particle has a median of particle size distribution x50 in the range of from 2 to 5 micrometers, as determined according to DIN ISO 9276-2:2018-09.

[0123] Preferably, the magnetic particle’s median of particle size distribution x50 has a standard deviation (span), calculated according to (x90 - xlO) / x50, of < 1.1 micrometer, wherein x90, x50 and xlO are determined according to DIN ISO 9276-2:2018-09.

[0124] Preferably, the magnetic particle has a density in the range of from 1.2 to 1.7 g / cm3, determined by gas pycnometry. The determination of the density by gas pycnometry is preferably done according to the method indicated in the European Pharmacopoeia (Ph. Eur.), 11thedition, Chapter 2.9.23.

[0125] Preferably, the magnetic particle has a saturation magnetization in the range of from 15 to 25 Am2 / kg, preferably determined by vibrating sample magnetometry, more preferably according to ASTM A 894 / A 894M.

[0126] Preferably, the magnetic particle has a BET specific surface area in the range of from 2 to 60 m2 / g, determined by nitrogen physisorption according to DIN 66131 : 1993-07.

[0127] 6thaspect - Use of the magnetic particle

[0128] A sixth aspect of the invention is directed to the use of a magnetic particle having a saturation magnetization > 15 Am2 / kg, the magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L), which is as defined in the section hereinabove related to the first aspect of the invention, to the polymer matrix (P), preferably of the magnetic particle as defined in the section hereinabove related to the first aspect of the invention or of the magnetic particle as described hereinabove in the section related to the fifth aspect of the invention, for qualitative and / or quantitative determination of at least one analyte in a fluid or in a gas.

[0129] All details, embodiments and preferred embodiments described in the section above related to the first aspect of the invention, the section above related to the second aspect of the invention, the section above related to the third aspect of the invention, the section above related to the fourth aspect of the invention, and the section above related to the fifth aspect of the invention apply also to the sixth aspect of the invention. Some details, (preferred) embodiments are outlined below.

[0130] The use is preferably for qualitative and / or quantitative in vitro determination of an analyte in a body fluid sample of a mammal.

[0131] Preferably, the analyte is selected from the group of steroids, sugars, vitamins, drugs, organic compounds, proteins, nucleic acids, sugars and mixtures of two or more thereof.

[0132] Preferably, the analyte is enriched by the magnetic particles as described hereinabove in the section related to the first aspect of the invention or of the magnetic particle as described hereinabove in the section related to the fifth aspect of the invention. Preferably, the analyte is determined by mass spectrometry, UV-vis, NMR, IR, more preferably by at least mass spectrometry, more preferably by liquid chromatography coupled with mass spectrometry (LC MS).

[0133] 7thaspect - Method for determining an analyte in a fluid

[0134] A seventh aspect of the invention relates to a method for determining at least one analyte in a fluid, the method comprising:

[0135] (A) Providing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L), which is as defined in the section hereinabove related to the first aspect of the invention, to the polymer matrix (P), preferably of the magnetic particle as defined in the section hereinabove related to the first aspect of the invention or of the magnetic particle as defined in the section hereinabove related to the fifth aspect of the invention;

[0136] (B) Providing a fluid sample comprising or suspected to comprise the at least one analyte;

[0137] (C) Contacting the magnetic particle of (A) with the fluid sample comprising or suspected to comprise the at least one analyte of (B); and

[0138] (D) determining the at least one analyte eluted from the said magnetic particle.

[0139] All details, embodiments and preferred embodiments described in the section above related to the first aspect of the invention, the section above related to the second aspect of the invention, the section above related to the third aspect of the invention, the section above related to the fourth aspect of the invention, the section above related to the fifth aspect of the invention, and the section above related to the sixth aspect of the invention apply also to the seventh aspect of the invention. Some details, (preferred) embodiments are outlined below.

[0140] Typically, the determination referred to in this context is a qualitative or quantitative determination.

[0141] Typically, step (C) of the method is carried out for a time and under conditions sufficient to allow for binding of the at least one analyte to the magnetic particle. Thus, preferably in step (C) at least a portion, preferably all of, the analyte is bounded to the particle. In case, the determination is a quantitative determination, preferably substantially all of the anlalyte present in the fluid sample is bound to the particle. Preferably, step (C) further comprises step:

[0142] (Cl) washing the magnetic particle to which at least a portion of the at least one analyte is bounded to, preferably under conditions which do not elute the at least one analyte; and / or

[0143] (C2) eluting the at least one analyte from the magnetic particle under conditions suitable to allow the elution of the at least one analyte.

[0144] More specifically, the qualitative or quantitative determination in (D) may comprise the determination of the presence or absence of bound analyte on the magnetic particle or the determination of the amount of analyte bound to the magnetic particle.

[0145] It is to be understood that the washing step in (Cl) may be carried as single washing step. Alternatively more than one washing step may be carried out.

[0146] More specifically, the qualitative determination may comprise the following further step as part of step (C) and / or (D): determining whether the at least one analyte was bound to the magnetic particle, or not.

[0147] Using the magnetic particles of the invention or obtainable by the process of the invention, advantageously reduces the matrix carry-over of the said fluids in applications.

[0148] Analytes to be determined by the magnetic particles of the invention or the magnetic particles obtained by the process of the invention or analytes to be determined in accordance with the aforementioned uses are, preferably, chemical compounds present in biological fluid samples, environmental samples or solutions of mixtures of chemical compounds. Accordingly, the fluid sample referred to in accordance with the present invention is, preferably, selected from the group of body fluids.

[0149] In a preferred embodiment the fluid sample as used herein refers to a biological sample obtained for the purpose of evaluation in vitro. In the methods of the present invention, the fluid sample or patient sample preferably may comprise any body fluid.

[0150] Preferred body fluid samples are whole blood, serum, plasma, bronchioalveolar lavage (BAL), epithelial lining fluid (ELF), urine or sputum, with plasma or serum being most preferred. In one embodiment, the sample is a clinical sample. In another embodiment, the sample is used in a diagnostic assay. The term body fluid sample includes biological samples that have been manipulated in any way after their procurement, such as by treatment with reagents, solubilization, or enrichment for certain components, such as proteins or polynucleotides. Typically, the body fluid sample is a liquid sample.

[0151] Depending on the nature of the body fluid sample, different classes of chemical compounds are to be detected. Preferably, the analyte in accordance with the present invention may be selected from the group of steroids, sugars, vitamins, drugs including medicaments and drugs for abuse, organic compounds, proteins, nucleic acids and mixtures of two or more thereof.

[0152] The aforementioned applications for determining analytes in body fluid samples may, preferably, be applied or are involved in diagnostic purposes, drug of abuse testing, environmental control, food safety, quality control, purification or manufacturing processes. In diagnostic applications, the qualitative or quantitative determination of an analyte may allow aiding the diagnosis if the analyte is, e.g., a biomarker for a disease or medical condition.

[0153] Preferably, the analyte is determined by mass spectrometry, UV-vis, NMR, IR, preferably by at least mass spectrometry, more preferably by liquid chromatography coupled with mass spectrometry (LC MS).

[0154] Summarizing and without excluding further possible embodiments, the following embodiments may be envisaged:

[0155] Embodiment 1 : A magnetic particle having a saturation magnetization > 15 Am2 / kg comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L) to the polymer matrix (P), wherein the linker (L) comprises an element

[0156] ••X-(CR1R2)xi-[Y-(CR3R4)x2]y-Z -(CR1R2)x3•••• (L), wherein

[0157] R1and R2are independently selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;

[0158] R3is selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;

[0159] R4is selected from the group consisting of hydrogen atom, Cl to C3 straight or branched alkyl group and C(=O)-X1-(CH2)ZI-N+(CH3)2-(CH2)Z2-SO3' group; xl, x2 are each independently an integer selected from the range of from 1 to 10; x3 is zero or an integer selected from the range of from 1 to 10; y is an integer selected from the range of from 1 to 500; zl, z2 are each independently an integer selected from the range of from 1 to 10;

[0160] X is an -NH- group or an oxygen atom;

[0161] XIis an -NH- group or an oxygen atom;

[0162] Y is an oxygen atom or is absent;

[0163] Z is an oxygen atom or is absent; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0164] Embodiment 2: The magnetic particle according to embodiment 1, wherein the linker (L) comprises an element (LI)

[0165] • • • X-(CR1R2)xi - [(CR3R4)x2]y-(CR1R2)x3 •••• (LI), wherein

[0166] R1, R2are independently selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;

[0167] R3is selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group, and is preferably a Cl to C3 straight or branched alkyl group;

[0168] R4is a C(=O)-X1-(CH2)zi-N+(CH3)2-(CH2)z2-SO3- group; xl, x2, x3 are each independently an integer selected from the range of from 1 to 10; y is an integer selected from the range of from 1 to 500;

[0169] X is an -NH- group or an oxygen atom;

[0170] XIis an -NH- group or an oxygen atom, preferably an oxygen atom; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0171] Embodiment 3: The magnetic particle according to embodiment 1, wherein the linker (L) comprises an element (L2) wherein

[0172] R1, R2, R3, R4are independently selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group; xl, x2 are each independently an integer selected from the range of from 1 to 10; y is an integer selected from the range of from 1 to 500;

[0173] X is an -NH- group or an oxygen atom; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0174] Embodiment 4: The magnetic particle according to embodiment 3, wherein at least one of R3, R4is a hydrogen atom, preferably R3and R4are both hydrogen atoms.

[0175] Embodiment 5: The magnetic particle according to any one of embodiments 1 to 4, wherein at least one of R1, R2is a hydrogen atom, preferably R1and R2are both hydrogen atoms.

[0176] Embodiment 6: The magnetic particle according to any one of embodiments 1 to 5, wherein xl, x2 and optionally x3 are independently an integer selected from the range of from 2 to 6, preferably 2 or 3.

[0177] Embodiment 7: The magnetic particle according to any one of embodiments 1 to 6, wherein y is an integer selected from the range of from 2 to 450, preferably from the range of from 2 to 225, more preferably from the range of from 2 to 110; or wherein y is an integer selected preferably from the range of from 2 to 50, more preferably from the range of from 3 to 40.

[0178] Embodiment 8: The magnetic particle according to any one of embodiments 1 to 7, wherein the linker (L) comprises an element •NH-(CH2)2 -O-[(CH2)2-O]y-(CH2)2 ••••, wherein y is an integer selected from the range of from 1 to 100, preferably selected from the range of from 2 to 50, more preferably from the range of from 3 to 40; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0179] Embodiment 9: The magnetic particle according to any one of embodiments 1 to 8, wherein the magnetic particles have a median of particle size distribution x50 in the range of from 2 to 5 micrometers, as determined according to DIN ISO 9276-2:2018-09.

[0180] Embodiment 10: The magnetic particle according to embodiment 9, wherein the median of particle size distribution x50 has a standard deviation (span), calculated according to (x90 - xlO) / x50, of < 1.1 micrometer, wherein x90, x50 and xlO are determined according to DIN ISO 9276-2:2018-09. Embodiment 11 : The magnetic particle according to any one of embodiments 1 to 10, having a density in the range of from 1.2 to 1.7 g / cm3, determined by gas pycnometry.

[0181] Embodiment 12: The magnetic particle according to any one of embodiments 1 to 11, having a saturation magnetization in the range of from 15 to 25 Am2 / kg, determined by vibrating sample magnetometry, preferably according to ASTM A 894 / A 894M.

[0182] Embodiment 13: The magnetic particle according to any one of embodiments 1 to 12, having a BET specific surface area in the range of from 2 to 60 m2 / g, determined by nitrogen physisorption according to DIN 66131 : 1993-07.

[0183] Embodiment 14: The magnetic particle according to any one of embodiments 1 to 13, wherein the polymer matrix (P) comprises a crosslinked polymer, wherein the crosslinked polymer preferably comprises a co-polymer obtained or obtainable by a method comprising a polymerization of at least two different monomeric building blocks selected from the group consisting of styrene, functionalized styrenes, vinylbenzylchloride, divinylbenzene, vinylacetate, methylmethacrylate and acrylic acid.

[0184] Embodiment 15: The magnetic particle according to embodiments 14, wherein at least one monomeric building block used has one or more functional group(s) reactive towards amine groups or amine groups, wherein the functional group reactive towards amine groups and / or hydroxyl groups is preferably selected from the group of halogenated Cl-C3-alkyl group, halogen atom, epoxy group and activated carboxy group, more preferably the functional group reactive towards amine groups and / or hydroxyl groups is a halogenated Cl-C3-alkyl group, more preferably a -CH2-CI group.

[0185] Embodiment 16: The magnetic particle according to embodiment 15, wherein vinylbenzyl chloride is employed as monomeric building block having functional groups reactive towards amine groups and / or hydroxyl groups.

[0186] Embodiment 17: The magnetic particle according to any one of embodiments 14 to 16, wherein at least one further monomeric building block is a crosslinking agent, preferably selected from the group consisting of divinylbenzene, bis(vinylphenyl)ethane, bis(vinylben- zyloxy)hexane, bis(vinylbenzyloxy)dodecane, and mixtures of two or more thereof, wherein more preferably the crosslinking agent comprises at least divinylbenzene.

[0187] Embodiment 18: The magnetic particle according to any one of embodiments 14 to 17, wherein the co-polymer is obtained or obtainable by a method comprising a polymerization of at least two different monomeric building blocks selected from the group consisting of the following monomers: with Rv, Rw, Rx, Ryand Rz, are, independently of each other selected from the group consisting of -N3, -NH2, -Br, -I, -F, -NR’R”, -NR’R”R”’, -COOH, -CN, -OH, -OR’, -COOR’, - NO2, -SH2, -SO2, -R’(OH)X, -R’(COOH)X, -R’(COOR”)X, -R’(OR”)X, -R’(NH2)X, - R’(NHR”)X, -R’(NR”R”’)X, -R’(C1)X, -R’(I)X, -R’(Br)x, -R’(F)X, R’(CN)X, -R’(N3)X, - R’(NO2)X, -R’(SH2)X, -R’(SO2)X, alkyl, aryl, cycloalkyl, heteroaryl, heterocycloalkyl and with R’, R” and R’” being, independently of each other, selected from the group consisting of alkyl, aryl, cycloalkyl, heteroaryl, heterocycloalkyl, halides, hydrogen, sulfides, nitrates and amines, and wherein x is an integer in the range of from 1 to 3.

[0188] Embodiment 19: The magnetic particle according to any one of embodiments 14 to 18, wherein the polymer matrix is obtained or obtainable by a method comprising co-polymer- izing at least one monomeric building block, which is a crosslinking agent, and at least one monomeric building block having functional groups reactive towards amine groups and / or hydroxyl groups, wherein the molar ratio of crosslinking agent : monomeric building block having functional groups reactive towards amine groups and / or hydroxyl groups is in the range of from 10:1 to 1 : 10, preferably in the range of from 5: 1 to 1 :5, more preferably in the range of from 2: 1 to 1 :2, more preferably in the range of from 1.5: 1 to 1: 1.5, more preferably in the range of from 1.2:1 to 1 : 1.2.

[0189] Embodiment 20: The magnetic particle according to any one of embodiments 14 to 19, wherein at least divinylbenzene is employed as crosslinking agent and at least vinylbenzyl chloride is employed as monomeric building block having functional groups reactive towards amine groups and / or hydroxyl groups.

[0190] Embodiment 21 : The magnetic particle according to any one of embodiments 13 to 20, wherein the functional group reactive towards amine groups and / or hydroxyl groups is modified in the polymer matrix (P), wherein a modified functional group is still reactive towards amine groups and / or hydroxyl groups and is preferably a carboxyl group and / or an amine group. Embodiment 22: The magnetic particle according to any one of embodiments 14 to 21, wherein the linker (L) is covalently bonded to the polymer matrix (P) by a structural element derived or derivable from the functional group reactive towards amine groups and / or hydroxyl groups and / or from the modified functional group, which is still reactive towards amine groups and / or hydroxyl groups, wherein the structural element more preferably comprises — W — , wherein the dashed lines • — represent the covalent bond to the polymer matrix (P) and to the X group of the element ••••X-(CR1R2)xi-[Y-(CR3R4)X2]y-Z -(CRJR2)x3 •••• of the linker (L), wherein W is selected from -NH- and -C(=O)O-.

[0191] Embodiment 23: The magnetic particle according to any one of embodiments 1 to 22, wherein the at least one magnetic core (M) comprises a compound selected from the group consisting of metal, metal carbide, metal nitride, metal sulfide, metal phosphide, metal oxide, metal chelate and a mixture of two or more thereof.

[0192] Embodiment 24: The magnetic particle according to any one of embodiments 1 to 23, wherein the at least one magnetic core (M) comprises a metal oxide or a metal carbide, more preferably, an iron oxide, in particular an iron oxide selected from the group consisting of FesCU, a-Fe2O3, y-Fe2O3, MnFepOq, CoFepOq, NiFepOq, CuFepOq, ZnFepOq„ CdFepOq, BaFepO and SrFepO, wherein p and q vary depending on the method of synthesis, and wherein p is preferably an integer of from 1 to 3, more preferably 2, and wherein q is preferably 3 or 4 most preferably, FesCE

[0193] Embodiment 25: The magnetic particle according to any one of embodiments 1 to 24, wherein the at least one magnetic core (M) comprises at least one magnetic nanoparticle, preferably at least one iron oxide nanoparticle, more preferably a FesCU-nan oparticle.

[0194] Embodiment 26: The magnetic particle according to any one of embodiments 1 to 25, wherein the at least one magnetic core (M) comprises, more preferably consists of a magnetic nanoparticle and a coating (C).

[0195] Embodiment 27: The magnetic particle according to any one of embodiments 1 to 26, having a coating (C) on at least a part of the surface of the magnetic core (M), preferably on at least 90 % of the surface of the magnetic core (M), more preferably on the whole surface of the magnetic core (M).

[0196] Embodiment 28: The magnetic particle according to any one of embodiments 1 to 25, wherein the coating (C) is selected from the group consisting of silica, silicate, silane, phosphate, phosphonate, phosphonic acid, fatty acid, and mixtures of two or more thereof. Embodiment 29: The magnetic particle according to any one of embodiments 1 to 28, wherein the coating (C) is selected from the group consisting of silica, tetraethyl orthosilicate, 3 -(trimethoxy silyl)propyl methacrylate, vinyltrimethoxy silane, vinyltri ethoxy silane, allyltrimethoxysilane, allyltriethoxysilane, triethoxyvinylsilane, 3 -(trimethoxy silyl)propyl acrylate, trimethoxy(7-octen-l-yl)silane, trimethoxymethylsilane, triethoxymethylsilane, ethyltrimethoxysilane, triethoxy(ethyl)silane, trimethoxyphenylsilane, trimethoxy(2-phe- nylethyl)silane trimethoxy(propyl)silane, n-propyltriethoxysilane, isobutyl(tri- methoxy)silane, isobutyltriethoxysilane, vinylphosphonic acid, dimethyl vinylphosphonate, diethyl vinylphosphonate, diethyl allylphosphonate, diethyl allyl phosphate, diethyl (2- methylallyl)phosphonate, octylphosphonic acid, butylphosphonic acid, decylphosphonic acid, hexylphosphonic acid, hexadecylphosphonic acid, n-dodecylphosphonic acid, lauric acid, myristic acid, palmitic acid, stearic acid, and arachidic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecylic acid, tridecylic acid, pentadecylic acid, margaric acid, nonadecylic acid, heneico- sylic acid, behenic acid, tricosylic acid, lignoceric acid, pentacosylic acid, cerotic acid, hep- tacosylic acid, montanic acid, nonacosylic acid, melissic acid, henatriacontylic acid, lac- ceroic acid, psyllic acid, geddic acid, ceroplastic acid, hexatriacontylic acid, heptatri aconta- noic acid, octatriacontanoic acid, oleic acid, linoleic acid, linolenic acid, arachidonic acid, hexadecatrienoic acid, stearidonic acid, eicosatrienoic acid, eicosatetraenoic acid, eicosapentaenoic acid, heneicosapentaenoic acid, docosapentaenoic acid, clupanodonic acid, docosahexaenoic acid, tetracosapentaenoic acid, tetracosahexaenoic acid, calendic acid, eicosadienoic acid, docosadienoic acid, adrenic acid, docosapentaenoic acid, tetraco-satetraenoic acid, tetracosapentaenoic acid, 5-dodecenoic acid, 7-tetradecenoic acid, pal-mitoleic acid, vaccenic acid, paullinic acid, 15-docosenoic acid, 17-tetracosenoic acid, elaidic acid, gondoic acid, mead acid, erucic acid, nervonic acid, rumenic acid, calendic acid, jacaric acid, eleostearic acid, catalpic acid, punicic acid, rumelenic acid, parinaric acid, bosseopentaenoic acid, pinolenic acid, podocarpic acid and mixtures of two or more thereof.

[0197] Embodiment 30: The magnetic particle according to any one of embodiments 1 to 29, wherein the polymer matrix (P) comprises a crosslinked polymer based on at least vinylben- zyl chloride and divinyl benzene, wherein the polymer matrix (P) at least partially surrounds the magnetic core (M), wherein the magnetic core (M) comprises at least a FesCU-nanopar- ticle, a coating (C) on at least a part of the surface of the magnetic core (M), which comprises a fatty acid, preferably oleic acid, the magnetic particle comprising at least one azide group -N=N+-N' bonded via a linker (L) to the polymer matrix (P), wherein the linker (L) comprises an element (L2) as defined in any one of embodiments 3 to 7, the linker (L) preferably comprising an element •••NH-(CH2)2 -O-[(CH2)2-O]y-(CH2)2 ••••, wherein y is an integer selected from the range of from 1 to 100;or wherein y is an integer selected selected from the range of from 2 to 50, preferably from the range of from 3 to 40; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0198] Embodiment 31 : A process for preparing a functionalized magnetic particle, the magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), the polymer matrix (P) comprising on its surface at least a (modified) functional group reactive towards amine groups and / or hydroxyl groups, the process comprising: a) Providing a magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, wherein the polymer matrix (P) comprises on its surface at least one hydroxyl group; b) Contacting the magnetic particle of (a), with an oxidation agent in an aqueous medium at a pH in the range of from 7.8 to 10, thereby obtaining a magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises on its surface at least a COOH group reactive towards amine groups and / or hydroxyl groups.

[0199] Embodiment 32: The process of embodiment 31, wherein the pH in (b) is in the range of from 8 to 9.5, preferably in the range of from 8.1 to 9.0.

[0200] Embodiment 33: The process of embodiment 31 or 32,_wherein the pH in (b) is adjusted by addition of one or more acid(s), preferably one or more organic acid(s), preferably one or more organic acid(s), having a pKs value in the range of from 4 to 7, preferably in the range of from 4.5 to 5.5, more preferably the one or more acid(s) comprise at least acetic acid, more preferably the pH in (b) is adjusted by addition of acetic acid.

[0201] Embodiment 34: The process of any one of embodiments 31 to 33, wherein (b) is conducted at a temperature T in the range of from 35 to 80°C, preferably in the range of from 40 to 70°C, more preferably in the range of from 42 to 55°C. Embodiment 35: The process of any one of embodiments 31 to 34, wherein the oxidation agent is selected from the group consisting of sodium hypochlorite, potassium permanganate, 1 -hydroxy cyclohexyl phenyl ketone, potassium dichromate(VI) and mixtures of two or more thereof, wherein the oxidation agent preferably comprises or is sodium hypochlorite.

[0202] Embodiment 36: The process of any one of embodiments 31 to 35, wherein (b) is conducted at a mass based ratio of NaOCl : H2O in the range of from 1 : 100 to 1 : 10, preferably 1 : 80 to 1 :5.

[0203] Embodiment 37: The process of any one of embodiments 31 to 36, wherein (b) is conducted for a period of time t in the range of from 0.1 to 15 h, preferably in the range of from 3 to 10 h, more preferably in the range of from 4 to 8 h, more preferably in the range of from 5 to 7 h.

[0204] Embodiment 38: The process of any one of embodiments 31 to 37, wherein (b) comprises b.1) Contacting the magnetic particle of (a), with an oxidation agent in an aqueous medium, thereby obtaining an aqueous mixture comprising the magnetic particle of (a) and the oxidation agent, wherein said aqueous mixture has a temperature Ti; b.2) Adding one or more acid(s) to the aqueous mixture of b.1), thereby obtaining an aqueous mixture comprising the magnetic particle of (a) and the oxidation agent, wherein said aqueous mixture has a pH in the range of from 7.8 to 10; b.3) heating the aqueous mixture of b.2) to a temperature T, wherein T > Ti and maintain the aqueous mixture at said temperature T for a period of time t, thereby obtaining a magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises on its surface at least a COOH group reactive towards amine groups and / or hydroxyl groups.

[0205] Embodiment 39: The process of any one of embodiments 31 to 38, further comprising: c) Separating the magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises on its surface at least a COOH group reactive towards amine groups and / or hydroxyl groups obtained in (b) from the aqueous mixture, thereby obtaining a separated magnetic particle; d) Optionally washing the separated magnetic particle at least once with an aqueous medium, preferably with water, thereby obtaining a washed separated magnetic particle; e) Optionally modifying the COOH group reactive towards amine groups and / or hydroxyl groups of the separated magnetic particle of c) or of the washed separated magnetic particle of d); thereby obtaining a magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises on its surface at least a (modified) functional group reactive towards amine groups and / or hydroxyl groups.

[0206] Embodiment 40: A magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises on its surface at least a (modified) functional group reactive towards amine groups and / or hydroxyl groups, obtained or obtainable from the process of any one of embodiment 31 to 39.

[0207] Embodiment 41 : A process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L), which is as defined in any one of embodiments 1 to 30, to the polymer matrix (P),

[0208] (i) Providing a magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises at least a (modified) functional group reactive towards amine groups and / or hydroxyl groups, preferably a magnetic particle of embodiment 40;

[0209] (ii) providing a linker precursor molecule HiX-(CR1R2)xi-[Y-(CR3R4)X2]y-Z-(CR1R2)X3- N3, wherein

[0210] R1and R2are independently selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;

[0211] R3is selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;

[0212] R4is selected from the group consisting of hydrogen atom, Cl to C3 straight or branched alkyl group and C(=O)-X1-(CH2)ZI-N+(CH3)2-(CH2)Z2-SO3' group; xl, x2 are each independently an integer selected from the range of from 1 to 10, preferably from the range of from 2 to 6, more preferably 2 or 3; x3 is zero or an integer selected from the range of from 1 to 10; y is an integer selected from the range of from 1 to 500; zl, z2 are each independently an integer selected from the range of from 1 to 10; X is an -NH- group or an oxygen atom;

[0213] XIis an -NH- group or an oxygen atom

[0214] Y is an oxygen atom or is absent;

[0215] Z is an oxygen atom or is absent; and i is 1 or 2;

[0216] (iii) reacting the (modified) functional groups reactive to amine groups and / or hydroxyl groups of the magnetic particle provided in (i) with the amine groups and / or the hydroxyl groups of the molecule provided in (ii); thereby obtaining the magnetic particle having a saturation magnetization > 15 Am2 / kg, the magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L).

[0217] Embodiment 42: The process according to embodiment 41, wherein the linker (L) comprises an element (LI)

[0218] • • • X-(CR1R2)xi - [(CR3R4)x2]y-(CR1R2)x3 •••• (LI), wherein

[0219] R1, R2are independently selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;

[0220] R3is selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group, and is preferably a Cl to C3 straight or branched alkyl group;

[0221] R4is a C(=O)-X1-(CH2)zi-N+(CH3)2-(CH2)z2-SO3- group; xl, x2, x3 are each independently an integer selected from the range of from 1 to 10; y is an integer selected from the range of from 1 to 500;

[0222] X is an -NH- group or an oxygen atom;

[0223] XIis an -NH- group or an oxygen atom, preferably an oxygen atom; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0224] Embodiment 43: The process according to embodiment 41, wherein the linker (L) comprises an element (L2) wherein R1, R2, R3, R4are independently selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group; xl, x2 are each independently an integer selected from the range of from 1 to 10; y is an integer selected from the range of from 1 to 500;

[0225] X is an -NH- group or an oxygen atom; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0226] Embodiment 44: The process according to embodiment 43, wherein at least one of R3, R4is a hydrogen atom, preferably R3and R4are both hydrogen atoms.

[0227] Embodiment 45: The process according to any one of embodiments 41 to 44, wherein at least one of R1, R2is a hydrogen atom, preferably R1and R2are both hydrogen atoms.

[0228] Embodiment 46: The process according to any one of embodiments 41 to 45, wherein xl, x2 and optionally x3 are independently an integer selected from the range of from 2 to 6, preferably 2 or 3.

[0229] Embodiment 47: The process according to any one of embodiments 41 to 46, wherein y is an integer selected from the range of from 2 to 450, preferably from the range of from 2 to 225, more preferably from the range of from 2 to 110; or wherein y is an integer selected preferably from the range of from 2 to 50, more preferably from the range of from 3 to 40.

[0230] Embodiment 48: The process according to any one of embodiments 41 to 47, wherein the linker (L) comprises an element •••NH-(CH2)2 -O-[(CH2)2-O]y-(CH2)2 ••••, wherein y is an integer selected from the range of from 1 to 100, preferably selected from the range of from 2 to 50, more preferably from the range of from 3 to 40; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0231] Embodiment 49: The process according to any one of embodiments 41 to 48, wherein the polymer matrix (P) comprises a crosslinked polymer, wherein the crosslinked polymer preferably comprises a co-polymer obtained or obtainable by a method comprising a polymerization of at least two different monomeric building blocks selected from the group consisting of styrene, functionalized styrenes, vinylbenzylchloride, divinylbenzene, vinylacetate, methylmethacrylate and acrylic acid. Embodiment 50: The process according to embodiments 49, wherein at least one monomeric building block used has one or more functional group(s) reactive towards amine groups or amine groups, wherein the functional group reactive towards amine groups and / or hydroxyl groups is preferably selected from the group of halogenated Cl-C3-alkyl group, halogen atom, epoxy group and activated carboxy group, more preferably the functional group reactive towards amine groups and / or hydroxyl groups is a halogenated Cl-C3-alkyl group, more preferably a -CH2-CI group.

[0232] Embodiment 51 : The process according to embodiment 50, wherein vinylbenzyl chloride is employed as monomeric building block having functional groups reactive towards amine groups and / or hydroxyl groups.

[0233] Embodiment 52: The process according to any one of embodiments 49 to 51, wherein at least one further monomeric building block is a crosslinking agent, preferably selected from the group consisting of divinylbenzene, bis(vinylphenyl)ethane, bis(vinylbenzyloxy)hexane, bis(vinylbenzyloxy)dodecane, and mixtures of two or more thereof, wherein more preferably the crosslinking agent comprises at least divinylbenzene.

[0234] Embodiment 53: The process according to any one of embodiments 49 to 52, wherein the co-polymer is obtained or obtainable by a method comprising a polymerization of at least two different monomeric building blocks selected from the group consisting of the following monomers: with Rv, Rw, Rx, Ryand Rz, are, independently of each other selected from the group consisting of -N3, -NH2, -Br, -I, -F, -NR’R”, -NR’R”R”’, -COOH, -CN, -OH, -OR’, -COOR’, - NO2, -SH2, -SO2, -R’(OH)X, -R’(COOH)X, -R’(COOR”)X, -R’(OR”)X, -R’(NH2)X, - R’(NHR”)X, -R’(NR”R”’)X, -R’(C1)X, -R’(I)X, -R’(Br)x, -R’(F)X, R’(CN)X, -R’(N3)X, - R’(NO2)X, -R’(SH2)X, -R’(SO2)X, alkyl, aryl, cycloalkyl, heteroaryl, heterocycloalkyl and with R’, R” and R’” being, independently of each other, selected from the group consisting of alkyl, aryl, cycloalkyl, heteroaryl, heterocycloalkyl, halides, hydrogen, sulfides, nitrates and amines, and wherein x is an integer in the range of from 1 to 3. Embodiment 54: The process according to any one of embodiments 49 to 53, wherein the polymer matrix is obtained or obtainable by a method comprising co-polymerizing at least one monomeric building block, which is a crosslinking agent, and at least one monomeric building block having functional groups reactive towards amine groups and / or hydroxyl groups, wherein the molar ratio of crosslinking agent : monomeric building block having functional groups reactive towards amine groups and / or hydroxyl groups is in the range of from 10:1 to 1 :10, preferably in the range of from 5: 1 to 1:5, more preferably in the range of from 2: 1 to 1 :2, more preferably in the range of from 1.5: 1 to 1 : 1.5, more preferably in the range of from 1.2:1 to 1 : 1.2.

[0235] Embodiment 55: The process according to any one of embodiments 49 to 54, wherein at least divinylbenzene is employed as crosslinking agent and at least vinylbenzyl chloride is employed as monomeric building block having functional groups reactive towards amine groups and / or hydroxyl groups.

[0236] Embodiment 56: The process according to any one of embodiments 49 to 55, wherein the functional group reactive towards amine groups and / or hydroxyl groups in the polymer matrix (P) is modified, wherein a modified functional group is still reactive towards amine groups and / or hydroxyl groups and is preferably a carboxyl group and / or an amine group.

[0237] Embodiment 57: The magnetic particle according to any one of embodiments 41 to 56, wherein the linker (L) is covalently bonded to the polymer matrix (P) by a structural element derived or derivable from the functional group reactive towards amine groups and / or hydroxyl groups and / or from the modified functional group, which is still reactive towards amine groups and / or hydroxyl groups, wherein the structural element more preferably comprises — W — , wherein the dashed lines • — represent the covalent bond to the polymer matrix (P) and to the X group of the element ••••X-(CR1R2)xi-[Y-(CR3R4)X2]y-Z -(CRJR2)x3 •••• of the linker (L), wherein W is selected from -NH- and -C(=O)O-.

[0238] Embodiment 58: The process according to any one of embodiments 41 to 57, wherein the at least one magnetic core (M) comprises a compound selected from the group consisting of metal, metal carbide, metal nitride, metal sulfide, metal phosphide, metal oxide, metal chelate and a mixture of two or more thereof.

[0239] Embodiment 59: The process according to any one of embodiments 41 to 58, wherein the at least one magnetic core (M) comprises a metal oxide or a metal carbide, more preferably, an iron oxide, in particular an iron oxide selected from the group consisting of FesCU, a-Fe2O3, y-Fe2O3, MnFepOq, CoFepOq, NiFepOq, CuFepOq, ZnFepOq„ CdFepOq, BaFepO and SrFepO, wherein p and q vary depending on the method of synthesis, and wherein p is preferably an integer of from 1 to 3, more preferably 2, and wherein q is preferably 3 or 4 most preferably, FesCE

[0240] Embodiment 60: The process according to any one of embodiments 41 to 59, wherein the at least one magnetic core (M) comprises at least one magnetic nanoparticle, preferably at least one iron oxide nanoparticle, more preferably a FesCU-nanoparticle.

[0241] Embodiment 61 : The process according to any one of embodiments 41 to 60, wherein the at least one magnetic core (M) comprises, more preferably consists of a magnetic nanoparticle and a coating (C).

[0242] Embodiment 62: The process according to any one of embodiments 41 to 61, wherein the magnetic particle has a coating (C) on at least a part of the surface of the magnetic core (M), preferably on at least 90 % of the surface of the magnetic core (M), more preferably on the whole surface of the magnetic core (M).

[0243] Embodiment 63 : The process according to embodiment 62, wherein the coating (C) is selected from the group consisting of silica, silicate, silane, phosphate, phosphonate, phosphoric acid, fatty acid, and mixtures of two or more thereof.

[0244] Embodiment 64: The process according to embodiment62 or 63, wherein the coating (C) is selected from the group consisting of silica, tetraethyl orthosilicate, 3 -(trimethoxy silyl)pro- pyl methacrylate, vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, triethoxyvinylsilane, 3 -(trimethoxy silyl)propyl acrylate, trimethoxy(7- octen-l-yl)silane, trimethoxymethylsilane, triethoxymethylsilane, ethyltrimethoxysilane, triethoxy(ethyl)silane, trimethoxyphenylsilane, trimethoxy(2-phenylethyl)silane tri- methoxy(propyl)silane, n-propyltriethoxysilane, isobutyl(trimethoxy)silane, isobutyltriethoxysilane, vinylphosphonic acid, dimethyl vinylphosphonate, diethyl vinylphosphonate, diethyl allylphosphonate, diethyl allyl phosphate, diethyl (2-methylallyl)phosphonate, oc- tylphosphonic acid, butylphosphonic acid, decylphosphonic acid, hexylphosphonic acid, hexadecylphosphonic acid, n-dodecylphosphonic acid, lauric acid, myristic acid, palmitic acid, stearic acid, and arachidic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecylic acid, tridecylic acid, pen- tadecylic acid, margaric acid, nonadecylic acid, heneicosylic acid, behenic acid, tricosylic acid, lignoceric acid, pentacosylic acid, cerotic acid, heptacosylic acid, montanic acid, non- acosylic acid, melissic acid, henatriacontylic acid, lacceroic acid, psyllic acid, geddic acid, ceroplastic acid, hexatriacontylic acid, heptatriacontanoic acid, octatriacontanoic acid, oleic acid, linoleic acid, linolenic acid, arachidonic acid, hexadecatrienoic acid, stearidonic acid, eicosatri enoic acid, eicosatetraenoic acid, eicosapentaenoic acid, heneicosapentaenoic acid, docosapentaenoic acid, clupanodonic acid, docosahexaenoic acid, tetracosapentaenoic acid, tetracosahexaenoic acid, calendic acid, eicosadienoic acid, docosadienoic acid, adrenic acid, docosapentaenoic acid, tetraco-satetraenoic acid, tetracosapentaenoic acid, 5-dodecenoic acid, 7-tetradecenoic acid, pal-mitoleic acid, vaccenic acid, paullinic acid, 15-docosenoic acid, 17-tetracosenoic acid, elaidic acid, gondoic acid, mead acid, erucic acid, nervonic acid, rumenic acid, calendic acid, jacaric acid, eleostearic acid, catalpic acid, punicic acid, rume- lenic acid, parinaric acid, bosseopentaenoic acid, pinolenic acid, podocarpic acid and mixtures of two or more thereof.

[0245] Embodiment 65: The process according to any one of embodiments 41 to 64, wherein the polymer matrix (P) comprises a crosslinked polymer based on at least vinylbenzyl chloride and divinyl benzene, wherein the polymer matrix (P) at least partially surrounds the magnetic core (M), wherein the magnetic core (M) comprises at least a FesCU-nan oparticle, a coating (C) on at least a part of the surface of the magnetic core (M), which comprises a fatty acid, preferably oleic acid, the magnetic particle comprising at least one azide group -N=N+-N' bonded via a linker (L) to the polymer matrix (P), wherein the linker (L) comprises an element (L2) as defined in any one of embodiments 3 to 7, the linker (L) preferably comprising an element •••NH-(CH2)2 -O-[(CH2)2-O]y-(CH2)2 ••••, wherein y is an integer selected from the range of from 1 to 100;or wherein y is an integer selected selected from the range of from 2 to 50, preferably from the range of from 3 to 40; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

[0246] Embodiment 66: A magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L), which is as defined in any one of embodiments 1 to 30, to the polymer matrix (P), obtained or obtainable from the process of any one of embodiments 41 to 65, the magnetic particle having a saturation magnetization ^ 15 Am2 / kg.

[0247] Embodiment 67: The magnetic particle according to embodiment 66, wherein the magnetic particles have a median of particle size distribution x50 in the range of from 2 to 5 micrometers, as determined according to DIN ISO 9276-2:2018-09.

[0248] Embodiment 68: The magnetic particle according to embodiment 66 or 67, wherein the median of particle size distribution x50 has a standard deviation (span), calculated according to (x90 - xlO) / x50, of < 1.1 micrometer, wherein x90, x50 and xlO are determined according to DIN ISO 9276-2:2018-09.

[0249] Embodiment 69: The magnetic particle according to any one of embodiments 66 to 68, having a density in the range of from 1.2 to 1.7 g / cm3, determined by gas pycnometry.

[0250] Embodiment 70: The magnetic particle according to any one of embodiments 66 to 69, having a saturation magnetization in the range of from 15 to 25 Am2 / kg, preferably determined by vibrating sample magnetometry, preferably according to ASTM A 894 / A 894M.

[0251] Embodiment 71 : The magnetic particle according to any one of embodiments 66 to 70, having a BET specific surface area in the range of from 2 to 60 m2 / g, determined by nitrogen physisorption according to DIN 66131 : 1993-07.

[0252] Embodiment 72: Use of a magnetic particle having a saturation magnetization > 15 Am2 / kg, the magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L), which is as defined in any one of embodiments 1 to 30, to the polymer matrix (P), preferably of the magnetic particle of any one of embodiments 1 to 30 or of the magnetic particle of any one of embodiments 66 to 71, for qualitative and / or quantitative determination of at least one analyte in a fluid or in a gas.

[0253] Embodiment 73: The use according to embodiment 72 for qualitative and / or quantitative in vitro determination of an analyte in a body fluid sample of a mammal.

[0254] Embodiment 74: The use of embodiment 72 or 73, wherein the analyte is selected from the group of steroids, sugars, vitamins, drugs, organic compounds, proteins, nucleic acids, sugars and mixtures of two or more thereof.

[0255] Embodiment 75: The use of any one of embodiments 72 to 74, wherein the analyte is enriched by the magnetic particles of any one of embodiments 1 to 30 or of the magnetic particle of embodiment 61.

[0256] Embodiment 76: The use of any one of embodiments 72 to 75, wherein the analyte is determined by mass spectrometry, UV-vis, NMR, IR, preferably by at least mass spectrometry, more preferably by liquid chromatography coupled with mass spectrometry (LC MS). Embodiment 77: A method for determining at least one analyte in a fluid, the method comprising:

[0257] (A) Providing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L), which is as defined in any one of embodiments 1 to 8, to the polymer matrix (P), preferably of the magnetic particle of any one of embodiments 1 to 30 or of the magnetic particle of any one of embodiments embodiment 66 to 71;

[0258] (B) Providing a fluid sample comprising or suspected to comprise the at least one analyte;

[0259] (C) Contacting the magnetic particle of (A) with the fluid sample comprising or suspected to comprise the at least one analyte of (B); and

[0260] (D) determining the at least one analyte eluted from the said magnetic particle.

[0261] EXAMPLES

[0262] The following Examples shall merely illustrate the invention. They shall not be construed, whatsoever, to limit the scope of the invention.

[0263] Reference Example 1: Oleic-coated magnetic nanoparticles

[0264] In a general procedure 126 g FeCE ■ 4 H2O (0.63 mol) and 248 g FeCh (1.53 mol) were added under stirring to 3 L water and heated to 55 °C. 460 mL NH4OH (28% in H2O) were added and after 15 min the black precipitate was separated with a magnet. The supernatant was discarded and the magnetic nanoparticles were washed three times with water. The magnetic nanoparticles were resuspended in 2000 mL and the pH was adjusted to 7-9 with NaOH (10 M). After ultrasonication for 30 min the suspension was transferred in a 4 L reactor and 1 L water was added. While stirring 120 mL oleic acid were added and the suspension was stirred for 45 min at 25 °C. The magnetic nanoparticles were separated with a magnet and the supernatant was discarded. The oleic acid -coated nanoparticles were washed three times with water and ethanol and stored in ethanol to give oleic acid-coated magnetic nanoparticles (203 g). Example 1: Preparation of magnetic polymer particles by suspension polymerisation

[0265] 1.1 Preparation of aqueous phase:

[0266] An aqueous mixture having 2-3.2% (w / w) polyvinyl alcohol with Mw of 7200 g / mol (PVA 72000) was prepared in a 30 liter glass reactor, equipped with propeller stirrer. The mixture was heated to 23 °C and stirred at 100 rpm.

[0267] 1.2 Preparation of organic phase:

[0268] 1425 g of oleic acid coated magnetic particles obtained from Reference Example 1 were magnetically washed two times with 750 ml toluene per washing, each time followed by removal of the liquid supernatant. 1500 ml vinylbenzyl chloride and 1500 ml divinyl benzene were added, as well as 200 ml toluene. The resulting organic phase was stirred with an overhead stirrer for 10 min at 1050 rpm for resupension. Homogenizing was done in loop with an inline disperser (Kinematica Megatron MT 5100 S2, Aggregate MTG 40 / 6F) at 11000 rpm for 15 min. After this time, 30 g of azobi si sobutyronitrile (AIBN) were added as radical starter, followed by 2 min homogenization in loop. Afterwards, the homogenized organic phase was transferred into the 30 liter glass reactor, which already contained the aqueous phase of 1.1.

[0269] 1.3 Polymerization:

[0270] The combined content was stirred in the 30 liter glass reactor at 150 rpm, followed by homogenization of organic and aqueous phase in loop with the inline disperser (Kineatica Megatron MT 5100 S2, aggregate MTG 40 / 6F) for 65 min at 8250 rpm, in order to obtain a desired droplet size. After 50 min of homogenization, the temperature of the reaction volume was raised to 43 °C. After the complete homogenization time (65 min), the mixture was stirred at 200 rpm and the temperature was further elevated to 73 °C with a ramp of 10°C / h. After reaching 73°C, the temperature was maintained for 3.1 hours. Thereafter, 14 liter desalted water were added for cooling and the resulting volume was filled into 5 liter Schott bottles for magnetic washing. Magnetic washing of the magnetic polymer particles obtained was then carried out three times with desalted water, three times with ethanol and again three times with desalted water, thereby obtained washed magnetic polymer particles. Example 2: Functionalization

[0271] 2.1 OH functionalization:

[0272] 1800 g magnetic polymer particles obtained from Example 1 were magnetic washed three times with desalted water, thereby obtaining further washed magnetic polymer particles. Afterwards, 4.5 liter KOH solution (I M) were introduced into a 30 liter reactor and heated to 45 °C under stirring at 150 rpm. The further washed magnetic polymer particles were introduced into the 30 liter reactor, as well as water until a final volume of 18 liters was achieved. Afterwards, the reactor content was heated to 60 °C for 6 h under stirring, thereby obtaining OH-functionalized magnetic polymer particles. The reactor content was then filled into 5 liter Schott bottles for magnetic washing, which was done ten times with desalted water.

[0273] 2.2 COOH functionalization:

[0274] For COOH functionalization of the OH-functionalized magnetic particles of 2.1, initially a procedure known in the art via suspending the OH-functionalized magnetic particles of 2.1 in NaClO-solution (10-15 weight-% available chlorine in H2O) and stirring at elevated temperature of 70°C for 1.5h was applied. It turned out that this procedure resulted in a severely damaged surface of the magnetic particles as determined by scanning electron microscopy (SEM).

[0275] Thus, modifications of the COOH functionalization procedure were investigated, in that a certain mass of magnetic beads from 2.1 (mbeads) was suspended in a certain volume of NaClO-solution (10-15 weight-%) (VNaoci), which was then diluted with a certain volume of water (VH2O) and stirred at a certain temperature T for a certain period of time t. wherein the applied conditions and results (relative analysis of SEM pictures) are summarized in Table 1 below:

[0276] Table 1

[0277] COOH functionalization trials with NaOCl and varying dilution, time and temperature

[0278] It turned out that irrespective of dilution, temperature and time, the surface of the magnetic particles came out of the process severely damaged. Thus, a pH adjustment was investigated, for which acetic acid was used. The applied conditions and results (relative analysis of SEM pictures) are summarized in Table 2 below:

[0279] Table 2

[0280] COOH functionalization trials with NaOCl and varying dilution, time and temperature and pH adjustement

[0281] It was found that adjusting the pH value of the suspension comprising magnetic beads of 2.1, water and NaOCl to be in the range of from 7.8 to 10, preferably in the range of from 8 to 9.5, more preferably in the range of from 8.1 to 9.0 resulted in COOH functionalized magnetic particles with an almost non-damaged surface. A temperature in the range of from 35 to 80°C, preferably in the range of from 40 to 70°C, more preferably in the range of from 42 to 55°C was identified as suitable temperature range, as well as a mass based ratio of NaOCl : H2O in the range of from 1 : 100 to 1 : 10, preferably 1 : 80 to 1 :5. A reaction time in the range of from 0.1 to 15 h, preferably in the range of from 3 to 10 h, more preferably in the range of from 4 to 8 h, more preferably in the range of from 5 to 7 h was identified as suitable period of time. Based on these findings, the following optimized procedure was used:

[0282] From the content of the 5 liter Schott bottles containing OH-fimctionalized magnetic polymer particles of 2.1, the supernatant of was removed and 1800 g of the obtained OH- functionalized magnetic polymer particles were re-suspended in a 2 liters desalted water. The suspension comprising the OH-fimctionalized magnetic polymer particles was transferred into a 30 liter glass reactor, in which the suspension was stirred at 150 rpm. 6670 ml sodium hypochlorite solution (10-15 weight-%) were added into the 30 liter glass reactor, followed by dilution with desalted water until a reaction volume of 20 liters was achieved. It was heated to 20 °C, followed by adjusting the pH of the suspension to be in the range of from 8.2-8.9 with acetic acid, followed by heating to 47 °C for 6 h. The suspension comprising the obtained COOH-fimctionalized magnetic polymer particles was then transferred into 5 liter Schott bottles for magnetic washing, which was done ten times with desalted water.

[0283] 2.3 Sizing / Classification:

[0284] 850 g of COOH-fimctionalized magnetic polymer particles from 2.2 were sized in one round in that two 50 liter containers, each containing 425 g COOH-fimctionalized magnetic polymer particles, were each filled up to 42.5 liter with desalted water to obtain a particle concentration of 10 g / liter. The 50 liter contained were positioned in a centrifuge (Heinkel V300), which was operated at 3500 rpm, pump speed 1 55 liter / h, and pump speed 2 255 liter / h. The desired sized product having X50 in the range of from 3 to 4 pm and X5 of 1 pm, with the part of particles with size <1 pm being less than 5 weight-% based on the total weight of the product, was collected in the centrifuge drum. Dilution and removal of desired product were done with pump speed 2. The sized product, i.e. the sized COOH-functionalized magnetic polymer particles, was / were then collected in 5 liter Schott bottles.

[0285] Example 4: Syntheses of azide coated magnetic polymer particles

[0286] 1600 g sized COOH-fimctionalized magnetic polymer particles from 2.3 were transferred into a 30 liter reactor and stirred at 75 rpm. For Examples 4.1 to 4.4, specific amounts of azide linker H2N-CH2-CH2-O-(CH2-CH2-O)X-CH2-CH2-N3 and coupling agent (l-ethyl-3- (3-dimethylaminopropyl)carbodiimide hydrochloride, EDC HC1) or cyanuric chloride (CC)) as indicated in Table 3 were added, followed by addition of desalted water until a reaction volume of 16 liter was achieved. The temperature in the reactor was set to 21 °C and the reaction was carried out for a reaction time in the range of from 4 to 16 hours. Table 3

[0287] Afterwards, the reactor content was filled into 5 liter Schott bottles and magnetically washed one time with potassium phosphate buffer having a pH value of 9.3, followed by four times washing with desalted water. The resulting azide coated magnetic polymer particles were transferred into 5 L HDPE containers (HDPE = high density polyethylene), followed by dilution with storage buffer potassium phosphate having a pH value of 7.4 to a volume of 3 liters.

[0288] The resulting azide coated magnetic polymer particles were analyzed regarding particle size, saturation magnetization, remanence, density, and azide integral:

[0289] For particle size analysis, laser diffraction according to DIN ISO 9276-2:2018-09 was applied For saturation magnetization measurements and determination of remanence, vibrating sample magnetometry was applied according to ASTM A 894 / A 894M. Density was determined by gas pycnometry according to the method described in Pharm.Eur., 11thedition, Chapter 2.9.23. The azide integral was determined via IR specroscopy.

[0290] The resulting azide coated magnetic polymer particles had a particle size (xso,3) in the range of from 2 to 4 pm (mean), < 1.1 (span), a density in the range of from 1.2 to 1.7 g / cm3, a magnetization > 15 Am2 / kg and a separation time of < 4 seconds as detailed in Table 4:

[0291] Table 4

[0292] Characteristics of the azide coated magnetic polymer particles

[0293] The azide integral showed a successful surface coating (> 0.05) with the linker.

[0294] Cited Prior Art

[0295] - EP 2 003 455 Al

[0296] - EP 2 015 074 Al

[0297] EP 3 610 262 Al

[0298] M. Das, D. Bandyopadhyay, R. P. Singh, H. Harde, S. Kumar, S. Jain, J. Mater. Chem., 2012, 22, 24652

[0299] E. Y. Sun, L. Josephson, R. Weissleder, Molecular Imaging, Vol. 5, 2, April- June 2006

[0300] M. B. Coppock, D. N. Strati s-Cullum, Methods 158 (2019) 12-1 Pharm.Eur., 11thedition, Chapter 2.9.23

Claims

Roche Diagnostics GmbH September 8, 2025RD38922PCClaims1. A magnetic particle having a saturation magnetization > 15 Am2 / kg comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L) to the polymer matrix (P), wherein the linker (L) comprises an element••X-(CR1R2)xi-[Y-(CR3R4)x2]y-Z -(CR1R2)x3•••• (L), whereinR1and R2are independently selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;R3is selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;R4is selected from the group consisting of hydrogen atom, Cl to C3 straight or branched alkyl group and C(=O)-X1-(CH2)ZI-N+(CH3)2-(CH2)Z2-SO3' group; xl, x2 are each independently an integer selected from the range of from 1 to 10; x3 is zero or an integer selected from the range of from 1 to 10; y is an integer selected from the range of from 1 to 500; zl, z2 are each independently an integer selected from the range of from 1 to 10;X is an -NH- group or an oxygen atom;XIis an -NH- group or an oxygen atom;Y is an oxygen atom or is absent;Z is an oxygen atom or is absent; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

2. The magnetic particle according to claim 1, wherein the linker (L) comprises an element (LI)• • • X-(CR1R2)xi - [(CR3R4)x2]y-(CR1R2)x3 •••• (LI), whereinR1, R2are independently selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;R3is selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group, and is preferably a Cl to C3 straight or branched alkyl group;R4is a C(=O)-X1-(CH2)zi-N+(CH3)2-(CH2)z2-SO3- group; xl, x2, x3 are each independently an integer selected from the range of from 1 to 10; y is an integer selected from the range of from 1 to 500;X is an -NH- group or an oxygen atom;XIis an -NH- group or an oxygen atom, preferably an oxygen atom; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

3. The magnetic particle according to claim 1, wherein the linker (L) comprises an element (L2)whereinR1, R2, R3, R4are independently selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group; xl, x2 are each independently an integer selected from the range of from 1 to10; y is an integer selected from the range of from 1 to 500;X is an -NH- group or an oxygen atom; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+-N' respectively.

4. The magnetic particle according to claim3, wherein at least one of R3, R4is a hydrogen atom, preferably R3and R4are both hydrogen atoms; and / or wherein at least one of R1, R2is a hydrogen atom, preferably R1and R2are both hydrogen atoms; and / or wherein xl, x2 and optionally x3 are independently an integer selected from the range of from 2 to 6, preferably 2 or 3; and / or wherein y is an integer selected from the range of from 2 to 450, preferably from the range of from 2 to 225, more preferably from the range of from 2 to 110; orwherein y is an integer selected preferably from the range of from 2 to 50, more preferably from the range of from 3 to 40.

5. The magnetic particle according to any one of claims 1 to 4, wherein the linker (L) comprises an element •NH-(CH2)2 -O-[(CH2)2-O]y-(CH2)2 ••••, wherein y is an integer selected from the range of from 1 to 100, preferably selected from the range of from 2 to 50, more preferably from the range of from 3 to 40; wherein the dotted lines •••• indicate the covalent bond(s) to the polymer matrix (P) and to the azide group -N=N+- N’ respectively.

6. The magnetic particle according to any one of claims 1 to 5, wherein the magnetic particles have a median of particle size distribution x50 in the range of from 2 to 5 micrometers, as determined according to DIN ISO 9276-2:2018-09; and / or wherein the magnetic particle have a saturation magnetization in the range of from 15 to 25 Am2 / kg, determined by vibrating sample magnetometry, preferably according to ASTM A 894 / A 894M.

7. A process for preparing a functionalized magnetic particle, the magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), the polymer matrix (P) comprising on its surface at least a (modified) functional group reactive towards amine groups and / or hydroxyl groups, the process comprising: a) Providing a magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, wherein the polymer matrix (P) comprises on its surface at least one hydroxyl group; b) Contacting the magnetic particle of (a), with an oxidation agent in an aqueous medium at a pH in the range of from 7.8 to 10, thereby obtaining a magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises on its surface at least a COOH group reactive towards amine groups and / or hydroxyl groups.

8. The process of claim 7, wherein (b) is conducted at a temperature T in the range of from 35 to 80°C, preferably in the range of from 40 to 70°C, more preferably in the range of from 42 to 55°C; and / or wherein (b) is conducted at a mass based ratio of NaOCl : H2O in the range of from 1 : 100 to 1 : 10, preferably 1 :80 to 1 :5; and / orwherein (b) is conducted for a period of time t in the range of from 0.1 to 15 h, preferably in the range of from 3 to 10 h, more preferably in the range of from 4 to 8 h, more preferably in the range of from 5 to 7 h.

9. The process of claim 7 or 8, wherein (b) comprises b.l) Contacting the magnetic particle of (a), with an oxidation agent in an aqueous medium, thereby obtaining an aqueous mixture comprising the magnetic particle of (a) and the oxidation agent, wherein said aqueous mixture has a temperature Ti; b.2) Adding one or more acid(s) to the aqueous mixture of b.1), thereby obtaining an aqueous mixture comprising the magnetic particle of (a) and the oxidation agent, wherein said aqueous mixture has a pH in the range of from 7.8 to 10; b.3) heating the aqueous mixture of b.2) to a temperature T, wherein T > Ti and maintain the aqueous mixture at said temperature T for a period of time t, thereby obtaining a magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises on its surface at least a COOH group reactive towards amine groups and / or hydroxyl groups.

10. The process of any one of claims 7 to 9, further comprising: c) Separating the magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises on its surface at least a COOH group reactive towards amine groups and / or hydroxyl groups obtained in (b) from the aqueous mixture, thereby obtaining a separated magnetic particle; d) Optionally washing the separated magnetic particle at least once with an aqueous medium, preferably with water, thereby obtaining a washed separated magnetic particle; e) Optionally modifying the COOH group reactive towards amine groups and / or hydroxyl groups of the separated magnetic particle of c) or of the washed separated magnetic particle of d); thereby obtaining a magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises on its surface at least a (modified) functional group reactive towards amine groups and / or hydroxyl groups.

11. A magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises on its surface at least a (modified) functional group reactive towards amine groups and / or hydroxyl groups, obtained or obtainable from the process of any one of claims 7 to 10.

12. A process for preparing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L), which is as defined in any one of claims 1 to 6, to the polymer matrix (P),(i) Providing a magnetic particle comprising a polymer matrix (P) and at least one magnetic core (M), wherein the polymer matrix (P) comprises, preferably consists of, at least one crosslinked polymer, which comprises at least a (modified) functional group reactive towards amine groups and / or hydroxyl groups, preferably a magnetic particle of claim 11;(ii) providing a linker precursor molecule HiX-(CR1R2)xi-[Y-(CR3R4)X2]y-Z- (CRJR2)x3-N3, whereinR1and R2are independently selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;R3is selected from the group consisting of hydrogen atom and Cl to C3 straight or branched alkyl group;R4is selected from the group consisting of hydrogen atom, Cl to C3 straight or branched alkyl group and C(=O)-X1-(CH2)ZI-N+(CH3)2- (CH2)Z2-SO3- group; xl, x2 are each independently an integer selected from the range of from 1 to 10, preferably from the range of from 2 to 6, more preferably 2 or 3; x3 is zero or an integer selected from the range of from 1 to 10; y is an integer selected from the range of from 1 to 500; zl, z2 are each independently an integer selected from the range of from 1 to 10;X is an -NH- group or an oxygen atom;XIis an -NH- group or an oxygen atomY is an oxygen atom or is absent;Z is an oxygen atom or is absent; and i is 1 or 2;(iii) reacting the (modified) functional groups reactive to amine groups and / or hydroxyl groups of the magnetic particle provided in (i) with the amine groups and / or the hydroxyl groups of the molecule provided in (ii); thereby obtaining the magnetic particle having a saturation magnetization > 15 Am2 / kg, the magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L).

13. A magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L), which is as defined in any one of claims 1 to 6, to the polymer matrix (P), obtained or obtainable from the process of claim 12, the magnetic particle having a saturation magnetization > 15 Am2 / kg.

14. Use of a magnetic particle having a saturation magnetization > 15 Am2 / kg, the magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L) to the polymer matrix (P), which is as defined in any one of claims 1 to 6 or of the magnetic particle claim 13, for qualitative and / or quantitative determination of at least one analyte in a fluid or in a gas.

15. A method for determining at least one analyte in a fluid, the method comprising:(A) Providing a magnetic particle having a saturation magnetization > 15 Am2 / kg, the magnetic particle comprising at least one magnetic core (M), a polymer matrix (P) comprising a crosslinked polymer at least partially surrounding the magnetic core (M), and at least one azide group -N=N+-N' bonded via a linker (L) to the polymer matrix (P), which is as defined in any one of claims 1 to 6 or of the magnetic particle claim 13;(B) Providing a fluid sample comprising or suspected to comprise the at least one analyte;(C) Contacting the magnetic particle of (A) with the fluid sample comprising or suspected to comprise the at least one analyte of (B); and(D) determining the at least one analyte eluted from the said magnetic particle.

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