Light-emitting particle

Abstract

A light-emitting particle comprising a light-emitting particle core having silica at a surface thereof and a first surface group bound to the silica. The first surface group comprises an alkene unit which may be an acrylate, C1-6 alkyl acrylate or an α-olefins. There may be a linker group covalently bound to the alkene unit at one end and bound at the other end to a surface binding group that can attach to the silica. The surface binding group may be a silicate group. An example of such alkene-linker-surface binding group compounds are acrylate-PEG-silane coupling reagents. The alkene unit may be reacted with a compound carrying a reactive group capable of reacting with the alkene, for example a thiol, and a biomolecule binding group, for example streptavidin. The biomolecule-functionalised nanoparticle may be bound to a probe group, for example a biotinylated probe group.

Description

BACKGROUND Nanoparticles are known for use as markers in a wide variety of applications. US 2020 / 0384130 discloses a gadolinium nanoparticle linked to an anti-B-cell maturation antibody for use as a contrast agent in magnetic resonance imaging (MRI). US 10,933,027 discloses a construct including a porous core, a cargo, a spacer disposed between the core and the cargo and an outer layer composed of a lipid, a polymer or a combination thereof. EP3223013 discloses a fluorescent silica-based nanoparticle having a ligand molecule containing a linear, cyclic or branched peptide containing Arg-Gly-Asp. Ha Na Jeon et al, ‘‘Studies on the Michael Addition Reaction between Secondary Amino Groups on the Silica Surface with Polyethylene glycol) Diacrylates”, Polymer(Korea), vol. 36, Issue 6, p.822-830, 2012 discloses modification of silica nanoparticles to introduce secondary amino groups on the silica surface. These N-H groups were reacted with three different molecular weights of poly(ethylene glycol) diacrylates to introduce different attached layer thicknesses on the silica surface by Michael addition reaction. SUMMARY The present disclosure provides a light-emitting particle comprising a light-emitting particle core having silica at a surface thereof and a first surface group bound to the silica wherein the first surface group comprises an alkene unit. Optionally, the group comprising an alkene unit is selected from acry late; Ci-6 alkyl acrylate; and groups of formula -( R CH2 wherein R11 is H; F; an aromatic or heteroaromatic group; or C1-6 alkyl. Optionally, a first linker unit L1 is covalently bound to the alkene unit at one end thereof and is bound at another end thereof to a surface binding group bound to the silica. Optionally, the surface binding group is a silicate (SiOr) group. Optionally, the first linker unit comprises one or more groups separating the surface binding group and the group comprising the alkene unit is selected from: optionally substituted C1-12 alkylene; optionally substituted arylene or heteroarylene; and a group of formula -0(R120)v- wherein R12 is a C1-3 alkylene group and v is at least 1. Optionally, the light-emitting particle comprises a further surface group which does not comprise an alkene unit. Optionally, the further surface group is a group of formula (II) bound to a surface binding group: - U-R13 (II) wherein L1 is a linker unit and R13 is an inert group. Optionally, R13 is a C1-6 alkyl or C1-6 alkoxy group. Optionally, the light-emitting particle core comprises a silica matrix and a light-emitting material disposed in the silica matrix. Optionally, the light-emitting particle core comprises a central core and a shell comprising silica surrounding the central core. The present disclosure provides a method of forming a biomolecule-functionalised lightemitting particle comprising reacting the light-emitting particle as described herein with a functionalising compound comprising a biomolecule and a group capable of reacting with the alkene unit. Optionally, the group capable of reacting with the alkene unit is a thiol. Optionally, the functionalising compound is a compound of formula (III): Y- L2-Bio (III) wherein Y is the group capable of reacting with the alkene unit to form a covalent bond; L2 is a second linking group; and Bio is the biomolecule. Optionally, the biomolecule is streptavidin, neutravidin, avidin or a recombinant variant thereof. The present disclosure provides a method of forming a light-emitting marker comprising binding a probe group to the biomolecule-functionalised light-emitting particle described herein. DESCRIPTION OF DRAWINGS Figure 1 illustrates formation of a light-emitting particle according to some embodiments by attachment of surface groups to a silica surface of a light-emitting particle; Figure 2 is a graph of signal strength vs. light-emitting particle concentration for a colloid containing light-emitting nanoparticles according to an embodiment of the present disclosure and for a colloid containing comparative light-emitting nanoparticlcs; and Figure 3 is a graph of signal to noise vs. light-emitting particle concentration for the lightemitting nanoparticles of Figure 2. DETAILED DESCRIPTION Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to." Additionally, the words "herein," "above," "below," and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word "or," in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. References to an atom include any isotope of that atom unless stated otherwise. The teachings of the technology provided herein can be applied to other systems, not necessarily the system described below. The elements and acts of the various examples described below can be combined to provide further implementations of the technology. Some alternative implementations of the technology may include not only additional elements to those implementations noted below, but also may include fewer elements. These and other changes can be made to the technology in light of the following detailed description. While the description describes certain examples of the technology, and describes the best mode contemplated, no matter how detailed the description appears, the technology can be practiced m many ways. Details of the system may varv considerably in its specific implementation, while still being encompassed by the technology disclosed herein. As noted above, particular terminology used when describing certain features or aspects of the technology should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the technology with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the technology to the specific examples disclosed m the specification, unless the Detailed Description section explicitly defines such terms. Accordingly, the actual scope of the technology encompasses not only the disclosed examples, but also all equivalent ways of practicing or implementing the technology under the claims. To reduce the number of claims, certain aspects of the technology are presented below in certain claim forms, but the applicant contemplates the various aspects of the technology in any number of claim forms. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of implementations of the disclosed technology. It will be apparent, however, to one skilled in the art that embodiments of the disclosed technology may be practiced without some of these specific details. The present inventors have surprisingly found that light-emitting particles having a reactive alkene group on a silica surface thereof can be used to form functionalised particles that provide a high signal-to-noise ratio. Figure 1 illustrates formation of a light-emitting particle according to some embodiments of the present disclosure. A light-emitting particle having silica at a surface thereof and with hydroxyl surface groups is reacted with a compound having a reactive silicate group linked by a linking group L1 to an acrylate group. The reactive silicate group reacts with the hydroxyl groups at the particle surface to form an acrylate group bound to the particle surface via linker group L1. The acrylate group is reacted with a compound having a thiol group linked via a linker group L2 to streptavidin to bind streptavidin to the surface of the nanoparticle through the linker groups L1 and L2 and the thioalkylene group between linker groups L1 and L2 formed by reaction of the acrylate and thiol groups. It will be understood that the acrylate group of Figure 1 may be replaced with a different reactive double bond group capable of reacting with thiol. Figure 1 illustrates functionalisation of a light-emitting particle with a streptavidin binding group. In use of the light-emitting particles, the streptavidin may be bound to a biotinylated probe group to form a light-emitting marker. It will be appreciated that streptavidin may be replaced with another group capable of binding to biotin, for example neutravidin, avidin or a recombinant variant of streptavidin, neutravidin or avidin. It will be understood that biomolecule binding groups other than streptavidin may be used. Biomolecule binding groups may be selected from, for example, DNA, RNA, nucleotides; peptides, carbohydrates, antibodies, antigens, enzymes, proteins and hormones. The probe group is substituted with a group capable of binding to the biomolecule binding group. As shown in Figure 1, preferably none of the light-emitting particle carrying a reactive doublebond group, the biomolecule-functionalised light-emitting particle and the light-emitting marker have an outer layer, e.g., a lipid or polymer layer, surrounding the surface groups. Light-emitting particle The light-emitting particle carrying a reactive double-bond group on its surface has silica at the particle surface. The light-emitting particle may have a core comprising silica and a light-emitting material. In some embodiments, the silica may be a matrix material containing light-emitting material distributed therein, optionally homogenously distributed; according to these embodiments, the light-emitting material may be partially or entirely encapsulated by the silica. In the case where the light-emitting material is a light-emitting polymer, the core may include light-emitting polymer chains which are entirely encapsulated by the silica and / or light-emitting polymer chains which extend beyond a perimeter of the core defined by the silica matrix. In some embodiments, the light-emitting material may be disposed on a surface of a core comprising or consisting of silica. The light-emitting material may be covalently bound to the silica or mixed with (i.e., not covalently bound to) the silica. In some embodiments, the light-emitting particle core has a shell comprising or consisting of silica and surrounding a central particle core. According to these embodiments, the central particle core may or may not comprise silica. In a preferred embodiment, the light-emitting particle core has a central core comprising silica and a light-emitting material, for example as described above, and a shell consisting of silica. A silica shell may be formed as described in, for example, WO 2021 / 176210, the contents of which are incorporated herein by reference. The light-emitting particle cores, as measured prior to attachment of surface groups, preferably have a polydispersity index as measured by dynamic light scattering of less than 0.3, more preferably less than 0.2, yet more preferably less than 0.15, or yet more preferably less than 0.1. The light-emitting particles are preferably light-emitting nanoparticles. The light-emitting particle cores, as measured prior to attachment of surface groups, preferably have a Z-average diameter of less than 50 nm or less, more preferably 30 nm or 20 nm or less, as measured by dynamic light scattering. To form a light-emitting particle core comprising silica mixed with a light-emitting material, a silane substituted with C1-12 alkoxy groups, for example tetraethylorthosilicate (TEOS), may be reacted in in the presence of a light-emitting material in a solvent or solvent mixture including at least one protic solvent. The or each protic solvent may be water or an alcohol. The protic solvent or solvent mixture preferably comprises or consist of water and / or methanol. The reaction is carried out in the presence of a base, e.g., a metal hydroxide, preferably alkali metal hydroxide, ammonium hydroxide or tetraalkylammonium hydroxide. Following particle formation, the particles may be separated by any method known to the skilled person. In some embodiments, the reaction mixture may be centrifuged to pellet the particles. After removal of the supernatant the particles may be resuspended in a suitable liquid, e.g., water, an alcohol or a mixture thereof, by sonication. In some embodiments, the reaction mixture may be passed through a water-equilibrated desalting column to give an aqueous suspension of particles. Alkene-containing surface group Surface groups containing a reactive alkene unit are bound to a surface of the light-emitting particle core. Preferably, the reactive alkene unit is bound to a first linking unit which in turn is bound to the surface of the light-emitting particle by a surface binding group. Preferably, the alkene-containing surface group is formed by reaction of a compound of formula (I) at the surface of the light-emitting particle: SRG- L'-X (I) wherein SRG is a surface reactive group; L1 is a first linking unit; and X is a group comprising or consisting of an alkene unit. SRG is capable of reacting with a group at the surface of the light-emitting particle to form a covalent bond. It will be appreciated that SRG may be selected according to the group at the light-emitting particle surface. Preferably, silica is at the surface of the light-emitting particle; the silica surface comprises hydroxyl groups; and SRG is a group of formula -Si(OR8) wherein R8 in each occurrence is independently H or a C1-12 hydrocarbyl group, preferably H or a C1-12alkyl. A C1-12 hydrocarbyl group as described anywhere herein is preferably selected from C1-12 alkyl and phenyl which is optionally substituted with one or more C1-6alkyl groups. L1 may comprise one or more of the following groups in a chain separating SRG and X: i. optionally substituted C1-12alkylene; ii. optionally substituted arylene or heteroarylene, preferably phenylene; and iii. a group of formula -0(R120)v- wherein R12 is a C1-3 alkylene group and v is at least 1, preferably 1-50. v is preferably at least 2. R12 is preferably CH2CH2. where L1 comprises two or more groups selected from groups (i)-(iii), these groups may be directly linked or may be linked by a linking unit, optionally a linking unit selected from O; S; NR6; Si(R7)2; C=O; C=O; CONR6; and NR6CONR6 wherein R6 in each occurrence is H or a C1-12 hydrocarbyl group, optionally a C1-12 alkyl group or C1-4 alkyl group; and R7 in each occurrence is a substituent, preferably a C1-12 hydrocarbyl group. L1 may be a polydisperse chain, i.e., a chain having a non-monodisperse molecular weight distribution. Optionally, a polydisperse chain L1 has a weight average molecular weight m the range of 500-10,000. X may comprise or consist of a cyclic or acyclic alkene unit, each of which may be unsubstituted or substituted with one or more substituents. Exemplary acyclic alkene units include acrylate: C1-6 alkyl acrylate, preferably mcthacnlate: and groups of formula -CR"=CH2 wherein R11 is H; F; an aromatic or heteroaromatic group, preferably phenyl; or C1-6 alkyl. Exemplary cyclic alkene units include cyclobutene and norbomene, each of which may be unsubstituted or substituted with one or more substituents. Where present, substituents of a cyclic alkene may be selected from F; C1-12 alkyl which is optionally substituted with one or more F atoms; and C1-12 alkoxy which is optionally substituted with one or more F atoms. Preferably, the alkene-containing surface group contains only one alkene unit. Further surface groups One or more surface groups other than surface groups containing a reactive alkene unit may be bound to the surface of the light-emitting particle core. Further surface groups are preferably selected from inert further surface groups. The presence of further surface groups may prevent aggregation of the light-emitting particles as compared to light-emitting particles substituted with Exemplary further surface groups may be formed by reaction of a compound of formula (II) at the light-emitting particle surface: SRG- LkR13 (II) wherein SRG and L1 are as described above; and R13 is an inert group, preferably a Ci-6 alkyl or Ci-6 alkoxy group. Preferably, the number of further surface groups is greater than the number of alkene-containing surface groups. Optionally, the number of moles of the further surface groups is at least 2 times, preferably 3 times, more preferably at least 5 times, the number of moles of the alkene-containing surface groups. Most preferably, the number of alkene-containing surface groups is less than 10 mol %, optionally up to 5 mol %, of the total number of moles of the alkene-containing and further surface groups. Preferably, the number of alkene-containing surface groups is more than 0.1 mol%, optionally at least 0.5 mol %, of the total number of moles of the alkene-containing and further surface groups. The proportion of alkene containing surface groups and further surface groups may be determined from the proportion of reactive compounds used to form these surface groups. Preferably, the light-emitting particle is substituted with an alkene-containing surface group and a further surface group which differ only in that the further surface group does not comprise an alkene. Surface functionalisation The light-emitting particle comprising an alkene group at a surface thereof may be functionalised by reaction with a functionalising compound comprising a group capable of reacting with the alkene, and a biomolecule group. The functionalising compound may be a compound of formula (III): Y- L2-Bio (III) wherein Y is a group capable of reacting with the alkene of group X of formula (III) to form a covalent bond; L2 is a second linking group; and Bio is a biomolecule. Preferably, Y is SH. L2 may be selected from linking groups described with respect to L1. Preferably, L2 contains a linking unit selected from 0; S; NR6; Si(R')2; C=O; C=O; CONR6; and NR6CONR6. Preferably, the linking unit is linked to Y by a C1-12 alkylene group. The linking unit may be linked to Bio through any suitable group of Bio. For example, in the case where Bio is streptavidin, the linking unit may be linked through an amine-containing side chain of an amino acid residue in streptavidin, for example lysine. Bio is preferably selected from a protein, more preferably streptavidin, neutravidin, avidin or a recombinant variant or derivative thereof for attachment to a biotinylated probe group; DNA; RNA; nucleotides; peptides; carbohydrates; antibodies; antigens; enzymes; and hormones. Light-emitting material The light-emitting material may be an inorganic light-emitting material; a non-polymeric organic light-emitting material; or a light-emitting polymer. Exemplary non-polymenc fluorescent materials include, without limitation: fluorescein, fluorescein isothiocyanate (FITC); fluorescein NHS; Alexa Fluor 488; Dylight 488; Oregon green; DAF-FM; 6-FAM; 2,7-dichlorofluorescein; 3’-(p-aminophenyl)fluorescein; 3’-(hydroxyphenyl)fluorescein; rhodamines, for example Rhodamine 6G and Rhodamine 110 chloride; coumarins; boron-dipyrromethenes (BODIPYs); naphthalimides; perylenes; benzanthrones; benzoxanthrones; benzothiooxanthrones; 2-(4-pyridyl)-5-phenyl-oxazole; 2- quinolinyl-5-phenyl-oxazole; 2-(4-pyridyl)-5-naphthyl-oxazole; 2-(4-pyridyl)-5-phenyl-thiazole; 2-quinolinyl-5-phenyl-thiazole; 2-(4-pyridyl)-5-naphthyl-thiazole; 2-(4-pyridyl)-5-phenyl-thiophene; 2-quinolinyl-5-phenyl-thiophene; 2-(4-pyridyl)- 5-naphthyl- thiophene and salts thereof, each of which may be unsubstituted or substituted with one or more substituents. Exemplary substituents are ionic or non-ionic substituents as described herein, optionally chlorine, alkyl amino; phenylamino; and hydroxyphenyl. Exemplary non-polymeric fluorescent materials include, without limitation: fluorescein and salts thereof, for example, fluorescein isothiocyanate (FITC), fluorescein NHS, Alexa Fluor 488, Dylight 488, Oregon green, DAF-FM, 6-FAM2,7-dichlorofluorescein, 3’-(p-aminophenyDfluorcscein and 3’-(hydroxyphenyl)fluorescein; rhodamines, for example Rhodamine 6G and Rhodamine 110 chloride; coumarins; boron-dipyrromethenes (BODIPYs); naphthalimides; perylenes; benzanthrones; benzoxanthrones; and benzothiooxanthrones, each of which may be unsubstituted or substituted with one or more substituents. Exemplary substituents are chlorine, alkyl amino; phenylamino; and hydroxyphenyl. A light-emitting polymer as described herein may be a homopolymer or may be a copolymer comprising two or more different repeat units. The light-emitting polymer may comprise light-emitting groups in the polymer backbone, pendant from the polymer backbone or as end groups of the polymer backbone. In the case of a phosphorescent polymer, a phosphorescent metal complex, preferably a phosphorescent iridium complex, may be provided in the polymer backbone, pendant from the polymer backbone or as an end group of the polymer backbone. The light-emitting polymer may have a non-conjugated backbone or may be a conjugated polymer. Conjugated polymers are preferred. By “conjugated polymer" is meant a polymer comprising repeat units in the polymer backbone that are directly conjugated to adjacent repeat units. Conjugated light-emitting polymers include, without limitation, polymers comprising one or more of arylene, heteroaiy lene and vinylene groups conjugated to one another along the polymer backbone. The light-emitting polymer may have a linear, branched or crosslinked backbone. The light-emitting polymer may be monodisperse or polydisperse. In some embodiments, the light-emitting polymer is a monodisperse light-emitting polymer comprising at least 4 repeating units. Tire repeating units of the monodisperse light-emitting polymer may be the same or different. In some embodiments, the light-emitting polymer contains at least 4 repeat units that are the same. In some embodiments, the light-emitting polymer contains at least two of two different repeat units. The light-emitting polymer may comprise one or more repeat units in the backbone of the polymer substituted with one or more substituents selected from non-polar and polar substituents. Preferably, the light-emitting polymer comprises at least one polar substituent. The one or more polar substituents may be the only substituents of said repeat units, or said repeat units may be further substituted with one or more non-polar substituents, optionally one or more Ci-40 hydrocarbyl groups. The repeat unit or repeat units substituted with one or more polar substituents may be the only repeat units of the polymer or the polymer may comprise one or more further co-repeat units wherein the or each co-repeat unit is unsubstituted or is substituted with non-polar substituents, optionally one or more Ci-40hydrocarbyl substituents. Ci-40 hydrocarbyl substituents as described herein include, without limitation, C1-20 alkyl, unsubstituted phenyl and phenyl substituted with one or more C1-20 alkyl groups. As used herein a "polar substituent” may refer to a substituent, alone or in combination with one or more further polar substituents, which renders the light-emitting polymer with a solubility of at least 0.01 mg / ml in an alcoholic solvent, optionally in the range of 0.01-10 mg / ml. Optionally, solubility is at least 0.1 or 1 mg / ml. The solubility is measured at 25°C. Preferably, the alcoholic solvent is a C1-10 alcohol, more preferably methanol. Polar substituents are preferably substituents capable of forming hydrogen bonds or ionic groups. In some embodiments, the light-emitting polymer comprises polar substituents of formula -O(R3O)t-R4 wherein R3 in each occurrence is a C1-10 alkylene group, optionally a C1-5 alkylene group, wherein one or more non-adjacent, non-terminal C atoms of the alkylene group may be replaced with O, R4 is H or C1-5 alkyl, and t is at least 1, optionally 1-10. Preferably, t is at least 2. More preferably, t is 2 to 5. The value of t may be the same in all the polar groups of formula -O(R3O)t-R4 The value of t may differ between polar groups of the same polymer. By “Ci-5 alkylene group" as used herein with respect to R3 is meant a group of formula wherein fis from 1-5. Preferably, the light-emitting polymer comprises polar substituents of formula -O(CH2CH2O)t-R4 wherein t is at least 1, optionally 1-10 and R4 is a C1-5 alkyl group, preferably methyl. Preferably, t is at least 2. More preferably, t is 2 to 5, most preferably q is 3. In some embodiments, the light-emitting polymer comprises polar substituents of formula -N(R5)2, wherein R5 is H or C1-12 hydrocarbyl. Preferably, each R5 is a C1-12 hydrocarbyl. In some embodiments, the light-emitting polymer comprises polar substituents which are ionic groups which may be anionic, cationic or zwitterionic. Preferably the ionic group is an anionic group. Exemplary anionic groups are COO\ a sulfonate group; hydroxide; sulfate; phosphate; phosphinate; or phosphonate. An exemplary cationic group is -N(R5)s wherein R5 in each occurrence is H or C1-12 hydrocarbyl. Preferably, each R5 is a C1-12hydrocarbyl. A light-emitting polymer comprising cationic or anionic groups comprises counterions to balance the charge of these ionic groups. An anionic or cationic group and counterion may have the same valency, with a counterion balancing the charge of each anionic or cationic group. The anionic or cationic group may be monovalent or polyvalent. Preferably, the anionic and cationic groups are monovalent. The light-emitting polymer may comprise a plurality of anionic or cationic polar substituents wherein the charge of two or more anionic or cationic groups is balanced by a single counterion. Optionally, the polar substituents comprise anionic or cationic groups comprising di- or trivalent counterions. The counterion is optionally a cation, optionally a metal cation, optionally Li+, Na+, K+, Cs+, preferably Cs+, or an organic cation, optionally ammonium, such as tetraalkylammonium, ethylmethyl imidazolium or pyridinium. The counterion is optionally an anion, optionally a halide; a sulfonate group, optionally mesylate or tosylate; hydroxide; carboxylate; sulfate; phosphate; phosphinate; phosphonate; or borate. In some embodiments, the light-emitting polymer comprises polar substituents selected from groups of formula groups of formula -N(R5)2, groups of formula OR4 and / or ionic groups. Preferably, the light-emitting polymer comprises polar substituents selected from groups of formula -O(CH2CH2O)tR4, groups of fonnula -N(R5)2, and / or anionic groups of formula -COO". Preferably, the polar substituents are selected from the group consisting of groups of formula -O(R3O)t-R4, groups of formula -N(R5)2, and / or ionic groups. Preferably, the polar substituents are selected from the group consisting of polyethylene glycol (PEG) groups of formula groups of formula -N(R5)2, and / or anionic groups of formula -COO'. R3, R4, R5, and t are as described above. Optionally, the backbone of the light-emitting polymer is a conjugated polymer. Optionally, the backbone of the conjugated light-emitting polymer comprises repeat units of formula (III): (R2)P (Sp)m I (R')„ (ill) wherein Ar1 is an arylene group or heteroarylene group; Sp is a spacer group; m is 0 or 1; R1 independently in each occurrence is a polar substituent; n is 1 if m is 0 and n is at least 1, optionally 1,2,3 or 4, if m is 1; R2 independently in each occurrence is a non-polar substituent; p is 0 or a positive integer, optionally 1, 2, 3 or 4; q is 0 or a positive integer, optionally 1, 2, 3 or 4; and wherein Sp, R1 and R2 may independently in each occurrence be the same or different. Two substituents of Ar1 may be linked to form a ring. Preferably, m is 1 and n is 2-4, more preferably 4. Preferably p is 0. Preferably q is at least 1. Ar1 of formula (III) is optionally a Ce-20 arylene group or a 5-20 membered heteroarylene group. 5 Ar1 is preferably a dibenzosilole group or a C6-20 arylene group, optionally phenylene, fluorene, benzofluorene, phenanthrene, naphthalene or anthracene, more preferably fluorene or phenylene, most preferably fluorene. Exemplary Ar1 groups of formula (III) include groups of formula (IV)-(X): p9 p9 R« / R RX R= R1°R10 10 (IV) p9 p9 R- P R\R’ x zs' R10 \10 (VI) r9 r9 r9 r9 xHhKi \ __( 7 pSA R10 R10 (VIII) ---1—, 1 , o> ---- „ 0 X Y|f <0 11 / WA z 0 K V ° — "n A= >1 1 >0 £ a V / x «5 / A jn-x a: A JJ 1) x I T o> / ^T , T^, rv 1——1 u- wherein R9 in each occurrence is independently H, R1 or R2, preferably H; R10 in each occurrence is independently R1 or R2; R6 is H or a C1-12 hydrocarbyl group, optionally a C1-12 alkyl group or C1-4 alkyl group; c is 0, 1, 2, 3 or 4, preferably 1 or 2; d is 0, 1 or 2; X independently in each occurrence is a substituent, preferably a substituent selected from the group consisting of branched, linear or cyclic C1-20 alkyl; phenyl which is unsubstituted or substituted with one or more substituents, e.g. one or more C1-12 alkyl groups; and F; and Z'-Z2- Z3 is a C2 (ethylene) C3 alkylene (propylene) chain wherein one or two non-adjacent C atoms may be replaced with O, S or NR6. Sp-(R')n may be a branched group, optionally a dendritic group, substituted with polar groups, optionally -NH2 or -OH groups, for example polyethyleneimine. Preferably, Sp is selected from: C1-20 alkylene or phenylene-Ci-20 alkylene wherein one or more non-adjacent C atoms may be replaced with O, S, N or C=O; - a C6-20 arylene or 5-20 membered heteroarylene, more preferably phenylene, which, in addition to the one or more substituents R1, may be unsubstituted or substituted with one or more non-polar substituents, optionally one or more C1-20 alkyl groups. “alkylene" as used herein means a branched or linear divalent alkyl chain. “non-terminal C atom” of an alkyl group as used herein means a C atom other than the methyl group at the end of an n-alkyl group or the methyl groups at the ends of a branched alkyl chain. More preferably, Sp is selected from: Ci-20 alkylene wherein one or more non-adjacent C atoms may be replaced with O, S or CO; and a Ce-20 arylene or a 5-20 membered heteroarylene, even more preferably phenylene, which may be unsubstituted or substituted with one or more non-polar substituents. R1 may be a polar substituent as described anywhere herein. Preferably, R1 is: a polyethylene glycol (PEG) group of formula -O(CH2CH2O)tR4 wherein t is at least 1, optionally 1-10 and R4 is a Ci-s alkyl group, preferably methyl; a group of formula -N(R5)2, wherein R5 is H or C1-12 hydrocarbyk or - an anionic group of formula COC)\ In the case where n is at least two, each R1 may independently in each occurrence be the same or different. Preferably, each R1 attached to a given Sp group is different. In the case where p is a positive integer, optionally 1, 2, 3 or 4, the group R2 may be selected from: - alkyl, optionally C1-20 alkyl; and aryl and heteroaryl groups that may be unsubstituted or substituted with one or more substituents, preferably phenyl substituted with one or more C1-20 alkyl groups; - a linear or branched chain of and or heteroaryl groups, each of which groups may independently be substituted, for example a group of formula -(Ar3)s wherein each Ar’ is independently an aryl or heteroaryl group and s is at least 2, preferably a branched or linear chain of phenyl groups each of which may be unsubstituted or substituted with one or more C1-20 alkyl groups; and - a crosslinkable-group, for example a group comprising a double bond such and a vinyl or acrylate group, or a benzocyclobutene group. Preferably, each R2, where present, is independently selected from Ci-40 hydrocarbyl, and is more preferably selected from C1-20 alkyl; unsubstituted phenyl; phenyl substituted with one or more C1-20 alkyl groups; and a linear or branched chain of phenyl groups, wherein each phenyl may be unsubstituted or substituted with one or more substituents. A polymer as described herein may comprise or consist of only one form of the repeating unit of formula (111) or may comprise or consist of two or more different repeat units of formula (III). Optionally, the polymer comprising one or more repeat units of formula (III) is a copolymer comprising one or more co-repeat units. If co-repeat units are present then the repeat units of formula (III) may form between 0.1-99 mol % of the repeat units of the polymer, optionally 50-99 mol % or 80-99 mol %. Preferably, the repeat units of formula (I) form at least 50 mol% of the repeat units of the polymer, more preferably at least 60, 70, 80, 90, 95, 98 or 99 mol%. Most preferably the repeat units of the polymer consist of one or more repeat units of formula (I). The or each repeat unit of the polymer may be selected to produce a desired colour of emission of the polymer. Arylene repeat units of the polymer include, without limitation, fluorene, preferably a 2,7-linked fluorene; phenylene, preferably a 1,4-linked phenylene; naphthalene, anthracene, indenofluorene, phenanthrene and dihydrophenanthrene repeat units. The polystyrene-equivalent number-average molecular weight (Mn) measured by gel permeation chromatography of the light-emitting polymers or the silica polymers described herein may be in the range of about IxlO3 to IxlO8, and preferably IxlO4 to 5xlO6 The polystyrene-equivalent weight-average molecular weight (Mw) of the polymers described herein may be IxlO3 to IxlO8, and preferably 5xl03 to IxlO7. Polymers as described herein are suitably amorphous polymers. Colloids The particles may be provided as a colloidal suspension comprising the particles suspended in a liquid. Preferably, the liquid is selected from water, C1-10 alcohols and mixtures thereof. The liquid preferably has a pH greater than 10. The liquid may be a buffer solution. The salt concentration of a buffer solution may be in the range of about 1 mmol IL - 200 mmol / L. The concentration of the particles in the colloidal suspension is preferably in the range of 0.1-20 mg / mL optionally 5-20 mg / mb In some embodiments, the particles may be stored as a colloidal suspension, optionally a colloidal suspension having a particle concentration greater than 0.1 mg / mL, preferably at least 0.5 mg / mL or 1 mg / mL. Colloids The particles may be provided as a colloidal suspension comprising the particles suspended in a liquid. Preferably, the liquid is selected from water, Ci-io alcohols and mixtures thereof. The liquid may be a buffer solution. The salt concentration of a buffer solution may be in the range of about 1 mmol / L 200 mmol / L. The concentration of the particles in the colloidal suspension is preferably in the range of 0.1-20 mg / mL, optionally 5-20 mg / mL. Applications Optionally the light-emitting marker is for use in fluorescence microscopy, flow cytometry, DNA sequencing, luminescent imaging applications for example in-vivo imaging, or any other application where a light-emitting marker is brought into contact with a sample to be analysed. The analysis may be performed using time-resolved spectroscopy. The applications can medical, veterinary, agricultural or environmental applications whether involving patients (where applicable) or for research purposes. In use the the light-emitting marker may comprise a probe configured to bind to target biomolecules which include without limitation DNA, RNA, peptides, carbohydrates, antibodies, antigens, enzymes, proteins and hormones. The target biomolecule may or may not be a biomolecule, e.g., a protein, at a surface of a cell. A sample to be analysed may brought into contact with the light-emitting marker, for example the light-emitting marker dissolved in a solution or a particulate light-emitting marker in a colloidal suspension. In some embodiments, the sample is analysed by flow cytometry. In flow cytometry, the lightemitting marker or markers are irradiated by at least one wavelength of light, optionally two or more different wavelengths, e.g., one or more wavelengths including at least one of about 355, 405, 488, 530, 561 and 640 nm, each of which may be ± 10 nm. Light emitted by the lightemitting marker(s) may be collected by one or more detectors. To provide a background signal for calculation of a staining index, measurement may be made of a light-emitting marker mixed with cells which do not bind to the light-emitting marker. In some embodiments, e.g., a plate assay, any target antigen in the sample may be immobilised on a surface which is brought into contact with the particles. The light-emitting particles as described herein may be used in nucleic acid sequencing. A method of sequencing nucleic acids may comprise: contacting a primed template nucleic acid molecule with a polymerase and a test nucleotide; incorporating the test nucleotide into a primed strand of the primed template only if it comprises a base complementary' to the next base of the template strand; irradiating the primed strand; and determining from luminance of the primed strand if the test nucleotide has been incorporated into the primed strand, wherein the test nucleotide of the irradiated primed strand is bound to a light-emitting particle as described anywhere herein. In some embodiments, the sequencing method comprises the detection of single nucleotides as they are incorporated at the 3’ end of the primer or 3’ end of the nascent growing strand. In some embodiments, nucleotides are added to a nucleic acid primer thereby extending the primer in a template-dependent manner. Detection of the order and type of nucleotides added to the primer can be used to determine the sequence of the template. At least some of the nucleotides are labelled with a light-emitting nanoparticle as described herein which may be used to detect and identify the nucleotide. During each sequencing cycle, a nucleotide which is the next complementary nucleotide (i.e., comprises a base complementary to the next base of the template strand), is incorporated into the nucleic acid chain in a template-dependent manner due to complementary hydrogen bonding with the corresponding nucleotide in the template fragment. A polymerase enzyme may subsequently catalyze the chemical addition of the next complementary nucleotide into the nucleic acid chain. In each sequencing cycle, the next complementary nucleotide is identified by irradiation of the nucleotide and detection of any luminescence attributable to a marker that the nucleotide is labelled with. A plurality of different species of test nucleotide may be included in the reaction mixture in a single sequencing cycle. Thus, labels associated with each different nucleotide species may be distinguishable and identifiable, for example on the basis of different luminescence emission spectra. Tn these embodiments, the luminescence emission that is detected is used to determine which of the different species of test nucleotides is incorporated into the primed strand and, thus represents the next complementary nucleotide. In these embodiments, at least one of the different nucleotide species is labelled with a light-emitting nanoparticle as described herein. In some embodiments, one or more of the nucleotides may be pre-labelled with the relevant marker prior to inclusion in the reaction mixture and / or prior to incorporation into the primer or nascent strand of the nucleic acid that is being sequenced, wherein at least one of the nucleotides is pre-labelled with a light-emitting nanoparticle marker as described herein. In other embodiments, one or more of the nucleotides may be labelled after correctly base pairing with the relevant nucleotide in the template strand, and / or after incorporation into the growing strand, wherein the labels include at least one light-emitting nanoparticle as described herein. In some sequencing methods, each nucleotide is associated with a different luminescent label that may be used to detect and identify the nucleotide, wherein at least one of the different luminescent labels is a light-emitting nanoparticle as described herein. Thus, the number of possible different nucleotides to be detected is equal to the number of different labels used, and the number of detection channels required. In some sequencing methods, the number of possible different nucleotides is greater than the number of different labels used and / or the number of detection channels required, wherein at least one of the different luminescent labels is a light-emitting nanoparticle as described herein. In some embodiments, one of the nucleotides is not labelled and all other nucleotides are labelled. The presence of the unlabeled nucleotide may be determined if no luminescence arising from a luminescent marker is detected. In some sequencing methods, emissions from at least two different markers are detectable by the same detector, i.e. emissions from the at least two different markers are the a single nucleotide is labelled with a first and second marker, wherein the first and second markers can be excited by the different laser frequency to produce emissions having first and second peak wavelengths wherein the first and second peak wavelengths are detectable by the same detector. In any event, at the point of detection, such as for example, when electromagnetic radiation at an excitation wavelength is applied to an emitter, the nucleotide that is being detected comprises the label, in the sense that the label is associated with the nucleotide in such a way that it may be used to specifically detect and identify the nucleotide. The linker attaching a light-emitting nanoparticle to the nucleotide in the disclosed method may be cleavable or otherwise arranged to allow dissociation of the label from the nucleotide. Thus, after incorporation and identification of the test nucleotide, the emitter or other label may be removed to allow the next sequencing cycle to commence and the next complementary nucleotide to be identified. The result is base-by-base sequencing of the template fragment nucleic acids. The term “linker” is intended to mean a chemical bond or moiety that bridges two moieties, for example by covalent linkage or the formation of a stable complex. A linker can be, for example, the sugar-phosphate backbone that connects nucleotides in a nucleic acid moiety. A linker may be used to conjugate a test nucleotide to a light-emitting nanoparticle or other label. The linker can include, for example, one or more of a nucleotide moiety, a nucleic acid moiety, a nonnucleotide chemical moiety, a nucleotide analogue moiety, amino acid moiety, polypeptide moiety, or protein moiety. The terms “cleave”, “cleavage site”, and similar terms, refer to a moiety in a molecule, such as a linker, which can be modified or removed to physically separate two other moieties of the molecule. EXAMPLES Measurements Particle size as described herein is a number average diameter, or as an intensity average diameter (x), as measured by dynamic light scattering (DLS), for example using a Malvern Zetasizer Nano ZS. using a 4mW 633 nm He-Ne laser. Nanoparticle suspensions were measured either in methanol or water m single use UV transparent plastic cuvettes. Hie machine was operated in Backscatter mode at an angle of 173°. Samples are equilibrated to 25°C if the solvent is methanol or 20°C if the solvent is water for 60 seconds prior to measurement. The viscosity values of methanol (0.5476cP) and water (l.OOOOcP) and refractive index values of methanol (1.326) and water (1.330) were inputted into the software SOP before measurement. The sample is defined as Polystyrene 10 latex (RI: 1.590, Absorption: 0.0100). The automatic measurement duration setting is used, with automatic measurement positioning and automatic attenuation. The ‘general purpose’ analysis model is used, with the default size analysis parameters along with a refractive index of 1.59 for the sample parameter. A single measurement is taken for each sample. Cumulants analysis calculation is defined in ISO 13321 and ISO 22412 and provides a width parameter known as the Polydispersity Index (Pdl). Poly dispersity Index is calculated as the standard deviation divided by the intensity average squared (o / x2). Sizes of particles as described herein are sizes of the nanoparticle cores without any surface groups thereon. Light-Emitting Nanoparticle Silica nanoparticles containing LEP1, illustrated below, were formed. Synthesis of LEP1 is described in WO 2021 / 001663, the contents of which are incorporated herein by reference. 1.0 mg / mL LEP solution was prepared by dissolving the LEP in methanol in a sealed vial. The 5 solution was heated at 60°C followed by sonication for 5 min. The process was repeated until a clear solution w as obtained. The solution was filtered using 0.45 pL syringe filter before use. 1.0 mL of LEP solution was taken in a screw cap amber vial containing a 4.5 x 12.5 mm stirrer bar. Methanol (6.3 mL) and 1 -octanol (2.2 mL) were added and mixed properly before addition of ammonium hydroxide (0.6 mL, aq. 28-30%). The reaction vial was heated at 60°C in a 10 preheated oil bath for 10 min then a methanol solution of tetraethyl orthosilicate (TEOS) (0.1 mL TEOS in 0.5 mL methanol) was injected into the reaction mixture using a long needed and syringe. After 1 hour a second methanolic TEOS solution (0.06 mL TEOS in 0.5 mL methanol) was injected to form a shell around the silica and light-emitting polymer, and heating was continued for additional 1 hour before cooling down to room temperature. 15 Zeba desalting columns (7K MWCO) were equilibrated with ultrapure water according to the manufacturer’s recommendations. Hie crude reaction mixture was loaded on top of column and eluted to collect nanoparticles in water. The nanoparticles as measured by DLS using a Malvern Zetasizer Nano S had a number average diameter of 30-35 nm; an intensity average diameter of 43-48 nm; and a polydispersity index (PDI) of less than 0.1 Acrvlate-functionalised nanoparticle 68.6 mg of mPEG-silane (“mPEG-silane, MW Ik”, illustrated below, available from Creative PEGWorks) was weighed into a 40 mL amber vial with septum lid. .0 o H H NYN^^^Si(OEt)3 o mPEG-silane n - 23 (average Mw of PEG = 1000) 5 A 10 mg / mL solution of acrylate-PEG-silane (“AC-PEG-Silane, Mw Ik”, illustrated below, available from Creative PEGWorks) was made by dissolving 5mg of AC-PEG-silane in 500 pL of deionised water. Acrylate-PEG-silane n ~ 23 (average Mw of PEG = 1000) 140 pL of acrylate-PEG-silane solution was added to the 40 mL amber vial containing mPEG-10 silane. The vial was shaken gently and the mPEG-silane was allowed to dissolve. 7.0 mL of the light-emitting nanoparticle suspension described above was added to the 40 mL amber vial. A solution of dilute base was prepared by adding 10 pL NH4OH (28-30%) to 9.99 mL milliQ water in to a 15 mL centrifuge tube. 140 pL of the dilute base was added to the 40 mL amber 15 vial. The vial lid was secured to the vial and an empty 1 mL syringe with needle was inserted so that it sits in the head space above the reaction mixture (to release any pressure build up). The reaction vial was placed in a pre-heated oil bath at 60 °C, ensuring the level of tire reaction mixture is below the level of the oil bath and stirred at 300 rpm for 16 hours, after which the vial was removed from the oil bath and left to cool to room temperature for 10 minutes. The reaction mixture was divided between 7x1.5 mL Eppendorf tubes which were centrifuged at 12,298 RCF for 20 minutes to pellet the nanoparticles. Tire supernatant was removed from each Eppendorf tube with a pipette and 1 mL of deionised water was added to each tube. The pellet was resuspended by sonication using a Fisherbrand™ 505 Sonicator with cuphom 5 accessory (20% amp, 5 pulses on for 30 seconds). Completion of resuspension was checked by looking under a UV light. The sonication process was repeated until resuspension was complete. The steps from centrifuging onwards were repeated to wash the nanoparticles and the contents of the Eppendorf tubes were pooled. Streptavidin functionalisation 10 The acrylate-substituted nanoparticle was reacted with a thiol-substituted streptavidin to form a fluorescent tag functionalised with streptavidin: c nh2 Streptavidin Reaction occurs on streptavidin lysine residue Streptavidin^ Deprotection .OH H2N Streptavidin^, 7 mg Streptavidin was dissolved in 1 mL of 50 mM HEPES buffer pFI 7.4. A 100 mM solution of SATP was prepared by adding 40.8 pL DMSO for every mg of SATP. 15 A “dilute SATP"’ solution was prepared by diluting 12 pL of the SATP solution with 438 pL of HEPES buffer (37.5-fold dilution). 100 pL of the dilute SATP solution was added for every 1 mL of 7 mg / mL Streptavidin solution and the mixture was incubated for 1.5 hours on rollers. 100 pL of 1 M Tris HC1 buffer (pH 8) per ml of solution was added and incubated for 15 minutes. The mixture was eluted down a 26 / 10 desalting column with borate buffer (50 mM, pH 8.4) on an Akta Start system (available from Cytiva). The fractions from the first UV-absorbing peak observed on the UV detector of an Akta Start system were eluted were combined and the liquid was concentrated in a Vivaspin 20 10 kDa MCWO spin concentrator to roughly the same volume as the original 7 mg / mL Streptavidin solution. A solution of 0.5 M hydroxylamine in PBS pH 7.2 was used to deacetylate the SATP-streptavidin product. To 1 ml of SATP-Streptavidin-containing solution was added 100 pL of the deacetylation solution and the mixture was incubated for 1.5 hours on rollers. The mixture was eluted down a 26 / 10 desalting column with borate buffer (50 mM, pH 8.4) on an Akta Start system (available from Cytiva). The fractions from the first UV-absorbing peak were combined and the liquid was concentrated in a Vivaspin 20 lOkDa MCWO spin concentrator to about 1 mLpermLofthe original SATP-streptavidin solution. Nanoparticle functionalization 1 mg of acrylate functionalised nanoparticles in water was pipetted into a 1.5 mL Eppendorf tube which was then centrifuged for 20 minutes at 20,817 RCF to form a pellet. The supernatant was removed and replaced with 100 pL of phosphate buffer, pH 8.5. The pellet was resuspended by sonication as described above. 1 mL of concentrated deacetylated SATP-Streptavidin solution was added and placed on rollers for 2 hours. The mixture was then centrifuged for 20 minutes at 20,817 RCF to form a pellet. The supernatant was removed and the nanoparticles were resuspended in 1 mL of 10 mg / mL BSA in borate buffer (50 mM, pH 8.4) using sonication as described above. The centrifuge and resuspension steps were repeated and the suspension was centrifuged again at 20,817 RCF to form a pellet. The supernatant was removed and the nanoparticles were resuspended in 99 pL of 10 mg / mL BSA in borate buffer with sonication conditions as described above and 10 pL of 100X halt protease inhibitor was added. Assay An assay was carried out to compare the performance of the acrylate-functionalised nanoparticles described above to fluorescent tags linked to streptavidin via an azide group. A 96 well microplate was prepared as follows: Sample wells 4.84 mL of a 50 pg / mL solution of Bovine Serum Albumen (BSA) in citrate buffer (200 mM, pH 4.5) was added to a 15 mL tube. 20 pL of a 50 pg / mL solution of biotinylated BSA (available from Fisher Scientific) in citrate buffer (200 mM, pH 4.5) was added and the tube was vortexed. 80 pL of this solution was added to each of the sample wells and incubated at room temperature for 1 hour. The solutions were removed and replaced with 80 pL of a 10 mg / mL solution of BSA in citrate buffer (200 mM, pH 4.5). The plate was incubated for a further 1 hour. The solutions were then removed and the wells w ashed three times with 120 pL citrate buffer to remove any unbound material. Negative wells &blank wells 80 pL of a 10 mg / mL solution of BSA in citrate buffer (200 mM, pH 4.5) was added to the negative and blank wells. The solutions were incubated for 2 hours. The solutions were then removed and the wells washed three times with 120 pL citrate buffer to remove any unbound material. The assay was run as follows: Solutions of the streptavidin-functionalised nanoparticles were made up in borate buffer (50 mM, pH 8.4) with 10 mg / mL BSA. The streptavidin-functionalised nanoparticle concentrations ranged from 250 pg / mL down to 15.6 pg / mL. 60 pL of these solutions were added to the sample and negative wells on the 96 well microplate as prepared above such that each concentration of nanoparticles occupied four sample wells and three negative wells. 60 pL of a control solution of FITC-streptavidin (available from Fisher Scientific) was added to one column on the microplate (again, using four sample wells and three negative wells). The concentration of this control solution w as 2.5 pg / mL of FITC-streptavidin in 10 mg / mL BSA borate buffer (50 mM, pH 8.4). 60 pL of 10 mg / mL BSA in borate buffer (50 mM, pH 8.4) was added to the blank wells. A lid was added and the microplate was incubated at room temperature for 30 mins. The solutions from all the wells were removed and all the wells were washed three times with 120 pL borate buffer to remove any unbound material. Borate buffer was added to all the wells and the 5 microplate was imaged on a BMG ClarioStar plate reader. Hie signal and noise values for each well were calculated by subtracting the average blank well signal from the sample and negative well values. Signal to noise ratios were calculated from (positive signal-blank) / (negative signal-blank). With reference to Figure 2, the signal for nanoparticles carrying streptavidin linked through a 10 group formed by reaction of an alkene is stronger at all measured concentrations of the nanoparticle than for the comparative nanoparticle carrying streptavidin linked through a group formed by reaction of an azide. With reference to Figure 3, the signal to noise ratio for every concentration of nanoparticles carrying streptavidin linked through a group formed by reaction of an alkene is higher than the 15 highest signal-to-noise ratio of the comparative nanoparticles.

Claims

1. A light-emitting particle comprising a light-emitting particle core having silica at a surface thereof and a first surface group bound to the silica wherein the first surface group comprises an alkene unit.

2. The light-emitting particle according to claim 1 wherein the group comprising an alkene unit is selected from acrylate; Ci-6 alkyl acrylate; and groups of formula -CR11=CH2 wherein R11 is H; F; an aromatic or heteroaromatic group; or Ci-6 alkyl.

3. The light-emitting particle according to claim 1 or 2 wherein a first linker unit L1 is covalently bound to the alkene unit at one end thereof and is bound at another end thereof to a surface binding group bound to the silica.

4. The light-emitting particle according to claim 3 wherein the surface binding group is a silicate (SiOr) group.

5. The light-emitting particle according to claim 3 or 4 wherein the first linker unit comprises one or more groups separating the surface binding group and the group comprising the alkene unit is selected from:i. optionally substituted C1-12alkylene;ii. optionally substituted arylene or heteroarylene; andiii. a group of formula 0( R120k- wherein R12 is a C1-3 alkylene group and v is at least 1.

6. The light-emitting particle according to any one of the preceding claims wherein the light-emitting particle comprises a further surface group which does not comprise an alkene unit.

7. The light-emitting particle according to claim 6 wherein the further surface group is a group of formula (II) bound to a surface binding group:- L’-R13(II)wherein L1 is a linker unit and R13 is an inert group.

8. The light-emitting particle according to claim 7 wherein R13 is a Ci-6 alkyl or Ci-6 alkoxygroup.

9. The light-emitting particle according to any one of the preceding claims wherein the light-emitting particle core comprises a silica matrix and a light-emitting material disposed in the silica matrix.

10. The light-emitting particle according to any one of the preceding claims wherein the light-emitting particle core comprises a central core and a shell comprising silica surrounding the central core.

11. A method of forming a biomolecule-functionalised light-emitting particle comprising reacting the light-emitting particle according to any one of the preceding claims with a functionalising compound comprising a biomolecule and a group capable of reacting with the alkene unit.

12. The method according to claim 11 wherein the group capable of reacting with the alkene unit is a thiol.

13. The method according to claim 11 or 12 wherein the functionalising compound is a compound of formula (III):Y- L2-Bio(III)wherein Y is the group capable of reacting with the alkene unit to form a covalent bond; L2 is a second linking group; and Bio is the biomolecule.

14. The method according to any one of claims 11-13 wherein the biomolecule is streptavidin, neutravidin, avidin or a recombinant variant thereof.

15. A method of forming a light-emitting marker comprising binding a probe group to the biomolecule-functionalised light-emitting particle according to any one of claims 11-14.33

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