Suspension

Abstract

A suspension comprising particles and an aqueous solution comprising a salt, wherein the aqueous solution has a density of from about 1.5 to about 2.0 g / cm3. Also provided is a suspension comprising p

Description

[0001] This invention relates to a suspension for reducing and / or preventing bead sedimentation in the production of solid materials. In particular, the invention relates to a suspension comprising particles and an aqueous solution with a density of from about 1.5 to about 2.0 g / cm3 BACKGROUND

[0002] Solid supports, such as particles and beads, are widely used in various applications, including analytical and synthetic application. For example, they may be used in binding, isolating and purifying analytes of interest, or in (bio)chemical synthesis. The applications typically involve the suspension of the particles and beads in buffer solutions. These buffer solutions may include various additives (e.g. surfactants) or preservatives to increase shelf life. Exemplary methods for preparing such suspensions of particles are described in US7217762, US6986913, US6984702, US10724031 and US7989065.

[0003] However, known means of producing or storing these particles or beads are prone to sedimentation and I or aggregation of the particles in solution, leading to the loss of homogeneity in solution. Although the sedimentation I aggregation of these particles may be reversible, e.g. by sonication, certain applications do not permit proper agitation of the solutions prior to their use. For example, vigorous agitation or rinsing is not always possible in automated workflows which may affect the quantitative removal of sedimented or aggregated particles from a container.

[0004] It is therefore an aim of the present invention to reduce or prevent particle sedimentation and I or aggregation from suspensions. It is another aim of the invention to reduce caking during storage of the suspension. It is yet another aim of the invention to facilitate quantitative removal of particles from a storage container. It is a further aim of the invention to provide solutions for suspensions that are one or more of non-toxic, nonflammable, aqueous and reusable. BRIEF SUMMARY OF THE DISCLOSURE

[0005] In a first aspect of the invention, there is provided a suspension comprising particles and an aqueous solution comprising a salt, wherein the aqueous solution has a density of from about 1.5 to about 2.0 g / cm3.

[0006] In a second aspect of the invention, there is provided a suspension comprising particles and an aqueous solution comprising a metatungstate salt, wherein the metatungstate salt is present at a concentration in the solution of from about 35% w / w to about 65% w / w.

[0007] The inventors have surprisingly found that bead sedimentation, aggregation and I or caking may be avoided by increasing the density of the solution in which the bead is produced. Without wishing to be bound by theory, it is thought that increasing the density of the solution leads to improved buoyancy of the polymeric bead, resulting in lower sedimentation rates and less dense packing of the beads. The addition of metatungstate represents a means of increasing the density of the solution.

[0008] Metatungstate (H2W12O40), also known under the name polytungstate, is a complex of tungsten. The aforementioned complex is highly soluble in water, and is able to achieve concentrations in excess of 80 % w / w, and solution densities above 3 g / cm3, rendering this complex useful in gravity separation and density gradient centrifugation. In contrast, other heavy salts only achieve densities of up to 1.6 g / cm3. Furthermore, metatungstate is non-toxic, non-flammable, water-soluble and reusable. Thus, the incorporation of metatungstate provides a relatively safe, environmentally friendly suspension system. Up until about 2 g / cm3, or about 60% w / w concentration, this solution has a viscosity that is not significantly greater than water. Having a viscosity that is not significantly greater than water may be advantageous, as many liquid handling systems and devices are not designed to work efficiently with more viscous solutions.

[0009] Without wishing to be bound by theory, it is thought that the addition of metatungstate increases the density of the aqueous solution such that the particles or beads have either an approximately neutral or lower density than the aqueous solution, thereby preventing the particles or beads from sedimenting. Where the particles or beads have a neutral buoyancy, the density of the particles or beads is the same as the density of the solution. Where the particles or beads have a positive buoyancy, the particles or beads have a lower density than the solution and so will float to the surface. Thus, in the suspensions of the invention, the particles or beads are held in suspension for longer periods of time.

[0010] Additionally, without wishing to be bound by theory, when used with magnetic particles or beads, the low viscosity of metatungstate solutions allows the particles or beads to move to the magnet at a similar rate to other water-based solutions. Further, the metatungstate ion can be easily washed away and disposed of or regenerated, it is environmentally friendly, and compatible with automation. In addition, we have determined that it does not interfere with many downstream applications.

[0011] In a third aspect of the invention, there is provided a use of an aqueous solution as defined in the first aspect or second aspect for the suspension of particles.

[0012] In a fourth aspect of the invention, there is provided a method of using particles. The method comprises a) suspending particles in an aqueous solution comprising a metatungstate salt, wherein the metatungstate salt is present at a concentration in the solution of from about 35% w / w to about 65% w / w, said suspending comprising a period of at least about 6 h. The method further comprises b) separating the particles from the solution, to provide separated particles; optionally washing the separated particles; and c) use of the separated particles in an assay.

[0013] In a fifth aspect of the invention, there is provided a method of of storing particles, comprising suspending particles in an aqueous solution comprising a metatungstate salt, wherein the metatungstate salt is present at a concentration in the solution of from about 35% w / w to about 65% w / w, optionally wherein the particles are suspended in the aqueous solution for a period of at least about 6 h.

[0014] In a sixth aspect of the invention, there is provided a method of removing particles from a storage container. The method comprises a) providing particles suspended in an aqueous solution comprising a metatungstate salt, wherein the metatungstate salt is present at a concentration in the solution of from about 35% w / w to about 65% w / w, optionally wherein the particles are suspended in the aqueous solution for a period of at least about 6 h, and b) removing the particles from the storage container.

[0015] In a seventh aspect of the invention, there is provided a kit comprising: a solution as defined in the first aspect or second aspect; and particles. DETAILED DESCRIPTION

[0016] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0017] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0018] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0019] For the avoidance of doubt, it is hereby stated that the information disclosed earlier in this specification under the heading “Background” is relevant to the invention and is to be read as part of the disclosure of the invention.

[0020] All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. Definitions

[0021] The following explanations of terms and methods are provided to better describe the present disclosure and to guide those of ordinary skill in the art in the practice of the present disclosure.

[0022] The terms “magnetic” and “magnetic material” means responds to a magnetic field. When the magnetic material is paramagnetic, the magnetic properties are switched off when the magnetic field is removed. When the magnetic material is superparamagnetic, the magnetic material becomes saturated at relatively low magnetic fields and switching off of the magnetic properties with removal of the magnetic field is very rapid / instant. Paramagnetic and superparamagnetic materials may therefore be considered “magnetisable”, as the magnetic properties are dependent on the application of an external magnetic field. When the magnetic material is ferromagnetic, all of its magnetic atoms within each domain add a positive contribution to the net magnetization. When the magnetic material is ferrimagnetic, some magnetic atoms within each domain are opposed, but overall the material exhibits net magnetization. Both ferromagnetic and ferrimagnetic material retain magnetic properties after an external magnetic field is removed. Above the material’s Currie temperature, ferromagnetic and ferromagnetic material becomes a paramagnetic material. The magnetic properties may also be affected by the size of the magnetic particles in the magnetic material, with some materials being ferromagnetic and ferrimagnetic at larger particle sizes, but superparamagnetic suitably small particle sizes (e.g. nm scale). For example, ferrimagnetic material, e.g. iron oxides, form superparamagnetic crystals when the size of the crystals is sufficiently small (e.g. below about 15 nm scale for iron oxides). Magnetic clusters of the disclosure and invention may be paramagnetic or superparamagnetic, as they comprise nanocrystals of iron oxide.

[0023] The term “magnetic material precursor” means a substance that may be converted to provide a magnetic material. A magnetic material precursor may comprise solvated transition metal ions (e.g. polyvalent cations of Fe, Ni, Co or a combination thereof, optionally in admixture with polyvalent cations of Al, Mn, Cu, Zn, Ca, Ge, Te, Ti or Sn and / or rare earths). The solvated transition metal ions and / or rare earth ions may be converted to a magnetic material by any process that causes the ions to precipitate, e.g. as oxides. Precipitation may be caused by, for example, a pH change, removal of solvent, or a change in temperature. For example, a magnetic material precursor may be provided by an aqueous suspension of pH less than 6 comprising Fe2+ and / or Fe3+ ions; and the Fe2+ and / or Fe3+ ions may be converted to a magnetic material by precipitation, e.g. by raising the pH to more than 8.

[0024] A “cluster” as used herein means a clump or particle composed of multiple smaller entities. For example, magnetic nanoclusters are nano-sized particles composed of or formed from multiple nanocrystals of iron oxide. Thus, in many instances the terms cluster(s) and particle(s) may be used interchangeably herein. Particles or clusters having a spherical shape are also often referred to as beads.

[0025] The term “nucleic acid” means, unless otherwise stated, a polynucleotide molecule made up of ribonucleotides and / or deoxyribonucleotides as well as synthetic nucleotide residues that are capable of participating in Watson-Crick type or analogous base pair interactions, i.e. "hybridisation" or the formation of a "duplex". Thus, the nucleic acid may be DNA or RNA or any modification thereof, including conformationally restricted or nucleobase analogue-bearing oligomers such as “locked-nucleic acids” (LNA) or “peptide nucleic acids” (PNA) or other derivatives containing non-nucleotide or modified nucleotide backbones (e.g., modifications on the sugars, bases, and / or internucleotide phosphate linkages). The nucleic acid may be a naturally occurring molecule, i.e. DNA or RNA but also include DNA / RNA hybrids where the DNA is in separate strands or in the same strand) in which the 3' position of the pentose of one nucleotide is joined by a phosphodiester linkage to the 5' position of the pentose of the next nucleotide. Nucleic acids used in various embodiments may comprise chemically, enzymatically, or metabolically modified forms of nucleotides or combinations thereof. Non-limiting examples of nucleic acids include primers, probes, oligonucleotides, aptamers, DNA templates, genomic DNA, cellular or cell-free DNA or RNA or fragments thereof, plasmid DNA, PCR fragments, RNA (such as mRNA, siRNA, guide RNA, small nuclear RNA, ribosomal RNA, transfer RNA, antisense RNA, circular RNA, short hairpin RNA etc.).

[0026] “Coating” means a covering that is applied to the surface of a substrate (such as a particle or bead). The coating may be an all-over coating, completely covering the substrate, or it may be a partial coating, only covering a portion of the surface of the substrate. The coating may be applied to the substrate by any suitable type of bonding, for example by at least one of covalent bonding, metallic bonding, ionic bonding, hydrogen bonding, van der Waals interactions, hydrophobic interactions, and the like. Where the substrate comprises a magnetic material (such as magnetic clusters), the coating (or at least a part thereof) may be silica, which may be formed on the surface of the magnetic material by condensation of silicates or orthosilicates. The coating may comprise an organic coating, which may comprise a spacer (such as an oligoethyleneglycol or polyethyleneglycol) and / or a polymer. In embodiments, a coating may comprise functional groups or ligands.

[0027] “Functional group” or “reactive group” means a substituent that is able to undergo characteristic chemical reactions. Exemplary functional groups I reactive groups of the present disclosure include hydroxyl groups, carboxylic acid groups, aldehyde groups, amine groups (e.g. primary or secondary aliphatic amine groups, and aromatic amine groups), thiol groups, epoxy groups, amide groups, chloromethyl groups, or tosyl-activated groups. Functional groups may be present on the surface of a substrate (e.g. the surface of a particle of the invention), for example functional groups may be present on a coating.

[0028] “Ligand” means a molecule that is able to bind to another species. A ligand may be a capture ligand, for example a capture ligand that is useful in an assay. Exemplary ligands include antibodies, antibody fragments, peptides, carbohydrates, haptens, aptamers, and oligonucleotides. Ligands may be bound to a substrate (such as magnetic clusters) comprising functional groups using standard techniques. Examples of such techniques are described in Chapter 14 of G.T. Hermanson, Bioconjugate Techniques, Academic Press, (3rd Edition, 1996).

[0029] The term “antibody”, as used herein, includes: (a) any of the various classes or sub-classes of immunoglobulin (e.g., IgG, IgA, IgM, IgD or IgE derived from any animal e.g., any of the animals conventionally used, e.g., sheep, rabbits, goats, mice, camelids, or egg yolk), (b) monoclonal or polyclonal antibodies, (c) intact antibodies or fragments of antibodies, monoclonal or polyclonal, the fragments being those which contain the binding region of the antibody, e.g., fragments devoid of the Fc portion (e.g., Fab, Fab‘, F(ab')2, scFv, VHH antibodies, VHH antibody fragments, as well as other single domain antibodies), the so called “half molecule” fragments obtained by reductive cleavage of the disulphide bonds connecting the heavy chain components in the intact antibody (Fv may be defined as a fragment containing the variable region of the light chain and the variable region of the heavy chain expressed as two chains), and (d) antibodies produced or modified by recombinant DNA or other synthetic techniques, including monoclonal antibodies, fragments of antibodies, “humanized antibodies”, chimeric antibodies, or synthetically made or altered antibody-like structures.

[0030] An “antibody fragment” refers to a molecule other than an intact antibody that comprises a portion of an intact antibody that binds the antigen to which the intact antibody binds.

[0031] The term “monodisperse” means that for a plurality of particles or beads (e.g. at least 100, more preferably at least 1,000) the particles or beads have a coefficient of variation (CV) or % polydispersity of their diameters of less than 20%, for example less than 15%, typically of less than 10% and optionally of less than 8%, e.g. less than 5%. The term monodisperse is used herein to characterize a population of particles or beads with low heterogeneity and a homogenous size distribution. The size distribution of a particle or bead may be defined by the percentage CV (coefficient of variation) which may be determined on a CPS disc centrifuge as described e.g. in the Analytical Methods section of WO2017211913A1 which is incorporated by reference herein. CV is defined as 100 times (standard deviation) divided by average where “average” is mean particle or bead diameter 10 and standard deviation is standard deviation in particle size. The CV for a plurality of particles may for example be within a range of 50 to 100%. For example, a monodisperse particle or beads population may have more than 90%, preferably more than 95% of the particles or beads with sizes within their mean diameter of ± 5 %. Suspension

[0032] An aspect of the invention relates to a suspension comprising particles and an aqueous solution comprising a salt, wherein the aqueous solution has a density of from about 1.5 to about 2.0 g / cm3.

[0033] The aqueous solution may have a density of at least about 1.6 g / cm3, at least about 1.7 g / cm3, or at least about 1.8 g / cm3. The aqueous solution may have a density of not more than about 1.9 g / cm3, not more than about 1.8 g / cm3 or not more than about 1.7 g / cm3

[0034] In embodiments, the aqueous solution has a density of at least about 1.7 g / cm3, and / or wherein the aqueous solution has a density of not more than about 1.9 g / cm3.

[0035] In embodiments, the aqueous solution has a viscosity of less than about 10 x 10’3 Pa.s at 20 °C, less than about 5 x 10’3 Pa.s at 20 °C, less than about 2.5 x 10~3 Pa.s at 20 °C, or less than about 1.5 x 10~3 Pa.s at 20 °C.

[0036] In embodiments, the salt is or comprises a metatungstate salt. The metatungstate salt may be selected from an alkali metatungstate salt, an ammonium metatungstate salt, or a combination thereof. The metatungstate salt may comprise sodium metatungstate.

[0037] The metatungstate salt may be selected from a sodium metatungstate salt, an ammonium metatungstate salt, or a combination thereof. The metatungstate salt may be sodium metatungstate.

[0038] The metatungstate salt may be present at a concentration in the solution of at least about 35% w / w, at least about 40% w / w, at least about 45% w / w, or at least about 50% w / w.

[0039] The metatungstate salt may be present at a concentration in the solution of no more than about 65% w / w, no more than about 60% w / w, or no more than about 50% w / w.

[0040] The metatungstate salt may be present at a concentration in the solution of from about 35% w / w to about 65% w / w. For example, the metatungstate salt may be present at a concentration in the solution of from about 40% w / w to about 60% w / w or from about 45% to about 55% w / w. In embodiments, the metatungstate salt is present at a concentration in the solution of 50% w / w.

[0041] For the avoidance of doubt, the concentration of the metatungstate salt in the aqueous solution given as a % w / w value used throughout this disclosure refers to the concentration of the metatungstate ion and the counter ion in the salt. For example, in the case of sodium metatungstate, the given % w / w value refers to the concentration of metatungstate ion and sodium ion together in the aqueous solution.

[0042] The particles may have a density of at least about 1.2 g / cm3, optionally at least about 1.3 g / cm3. The particles may have a density of not more than about 2 g / cm3.

[0043] The difference in density between the particles and the aqueous solution may be not more than about 0.3 g / cm3. The difference in density between the particles and the solution may be not more than about 0.2 g / cm3.

[0044] The particles may have a diameter of from about 0.1 pm to about 100 pm, from about 0.1 pm to about 50 pm, from about 0.1 pm to about 5 pm, or from about 0.2 pm to about 2 pm.

[0045] The particles may be monodisperse.

[0046] The particles may comprise polymeric material and / or silica. Exemplary polymeric materials include polystyrene, poly(meth)acrylate, polyether, dextran, polyamine, polyester, polyamide and polyurethane.

[0047] The particles may comprise magnetic material. Thus, the particles may comprise magnetic particles or beads.

[0048] In some instances, the magnetic particles may comprise microparticles or nanoparticles. In some examples, the magnetic particles may contain iron oxide. For example, magnetic nanoclusters as described in patent application No. PCT / EP2023 / 070373 which is hereby incorporated by reference may be used.

[0049] The particles may be monodisperse and magnetic.

[0050] The particles may be functionalised. In such embodiment, the functionalised particles may comprise a functional group and / or a ligand.

[0051] The functional group may be selected from a hydroxyl group, a carboxylic acid group, an aldehyde group, an amine group, a thiol group, an epoxy group, an amide group, a chloromethyl group, and a tosyl-activated group.

[0052] The ligand may be a capture ligand. The ligand may be selected from a protein (e.g. an antibody, antigen, streptavidin, avidin, protein A, protein G, a lectin, a receptor), a peptide (e.g. an antibody fragment), a carbohydrate, a hapten, an aptamer, and an oligonucleotide.

[0053] The functionalisation may be selected from a protein (e.g. an antibody, streptavidin, avidin, protein A, protein G, protein A / G and a lectin), a carboxylic acid group, and a tosyl-activated group. Where the functionalisation is a protein, the protein may be selected from an antibody, streptavidin, avidin, protein A, protein G, protein A / G ( / .e., a recombinant protein comprising the IgG binding domains of protein A and G), and a lectin; or the protein may be selected from streptavidin and protein A / G. The functionalisation may be selected from streptavidin, protein A, a carboxylic acid, and a tosyl-activated group.

[0054] The functionalised particles may have a core comprising the magnetic material and a coating comprising the functional group or ligand.

[0055] The particles may be selected from any commercially available particles suitable for use in bio-separation workflows. For example, the particles may be selected from Dynabeads™ MyOne™ Silane, Dynabeads™ MyOne™ Carboxylic Acid, Dynabeads™ M-270™ Carboxylic Acid, Dynabeads™, Oligo(dT)25 magnetic beads (all available from Thermo Fisher Scientific), SeraMag SpeedBeads™ carboxylate-modified or SeraSil-Mag 400 or 700 (Cytiva), BioMagPlus COOH™ and ProMag 1 COOH™ (both Bangs Laboratories, INC Fishers), 4.4 pm fluorescent ferromagnetic beads or 2.0 pm ferromagnetic beads (both available from Spherotech INC Lake Forest, IL), 2 pm beads designated WHM-S001™ or 2 pm beads designated WHM-S002™ (both available from Creative Diagnostics, New York, NY), Silicon Hydroxyl Magnetic Microspheres or Carboxyl Magnetic Microspheres or Oligo(dT) Magnetic Microspheres (available at different nm or pm sizes from VDO Biotech, Suzhou, China), Carboxyl Adembeads (available at 100 nm, 200 nm, 300 nm or 500 nm) or Carboxyl Masterbeads (500 nm) (available from Ademtech, France), MagneSil™ beads (available from Promega), BeaverBeads™ Mag COOH (available from Beaver Biomedical Engineering Ltd.), Lodestars High Bind Carboxyl beads (available from Agilent), Magnosphere™, MS300 Carboxyl, MS 160 Carboxyl or MS160 Carboxyl (all available from JSR Life Sciences), PureProteome Carboxy FlexiBind Magnetic Bead System (available with different bead sizes from Sigma-Aldrich), BioMag™ Carboxl, BioMag™ Maxi Carboxyl or BioMag™ Plus Carboxyl (all available from Polysciences), Carboxyl Super Mag or Mono Mag Magnetic Beads (available at sizes between 0.1 pm and 4.5 pm from Ocean Nanotech), and Carboxyl beads of different sizes available from VdoBiotech.

[0056] The particles may remain suspended in the aqueous solution for at least about 6 h without mixing or agitation. The particles may remain suspended in the aqueous solution for at least about 24 h, 36 h, 48 h, 60 h, or 72 h without mixing or agitation. For the avoidance of doubt, the particles may be said to be suspended in the aqueous solution if no sedimentation of particles in the aqueous solution is observed during the specified period of time, e.g. particles are considered suspended for at least about 6 h if no sedimentation is observed by the end of the specified about 6 h period. Sedimentation may be observed by visual inspection of the sample with the naked eye (e.g. upon sedimentation of particles or beads the solution may change its colour from opaque / turbid to clear / transparent while a pellet may form at the bottom of the tube or vial containing the sample).

[0057] The suspension may further comprise one or more surfactants. Each surfactant may be a non-ionic surfactant. A non-ionic surfactant comprises molecules having both a hydrophilic moiety and a hydrophobic moiety which does not comprise any charged moieties.

[0058] The non-ionic surfactant may be selected from the group consisting of Ecosurf™ EH-9 (Ethylene oxide-propylene oxide copolymer mono(2-ethylhexyl) ether), Ecosurf™ SA-9 (seed oil alcohol ethoxylate 9 EO or polyethylenglykolether), Tergitol™ 15-S-9 (sek-alkoxypolyethylenglykol) or Tween-20 or Eco Tween™-20 or Eco Tween™-80 (100% bio-based ethoxylated (20) or (80) sorbitan ester based on a natural fatty acid (lauric acid)).

[0059] The non-ionic surfactant may be a non-toxic, biodegradable surfactant. For example, the surfactant may be selected from ECOSURF™ EH, ECOSURF™ SA or ECOSURF™ LFE specialty surfactants (The Dow Chemical Company (“Dow”)).

[0060] The non-ionic surfactant may comprise ethylene oxide-propylene oxide copolymer mono(2-ethylhexyl) ether or seed oil alcohol ethoxylate 9 EO, or polyethylenglycolether.

[0061] Without wishing to be bound by theory, it is thought that such surfactants prevent aggregation of magnetic particles in aqueous solution and reduce stickiness, thereby increasing the ease of handling the suspension in both manual and automated bead-based workflows. Additionally, the surfactants may be employed at low concentrations to reduce foaming in bead samples.

[0062] The non-ionic surfactant may be used in a lysis and / or binding buffer, washing buffer or storage buffer for magnetic bead-based separations.

[0063] The suspension may further comprise one or more preservatives. In particular, the suspensions of the invention used for storage purposes may require a biocide effective against microbial growth to maintain product quality and extended shelf life. Preferably, a preservative having a broad spectrum of activity against all types of bacteria, fungus or yeasts should be used. Preferably, a preservative that is non-toxic and environmentally friendly should be used, presenting no health hazards, toxicology problems, or disposal issues.

[0064] Exemplary preservatives include: 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl—4-isothiazolin-3-one (Acticide™ MV), 2-methyl-4-isothiazolin-3-one and 5-chloro2-methyl-4-isothiazolin-3-one (Acticide™ 14), 1,2-benzisothiazolin-3-one (2.5%) and 2- methyl-4-isothiazolin-3-one (2.5%) (Acticide™ MBS), 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (MIT) (ProClin™300), methylchloroisothiazolin and methylisothiazolin (Kathon™LX), 2-methyl-4-isothiazolin-3-one (MIT) or 5- chloro-2-methyl-4-isothiazolin-3-one (CMIT) or 1,2-benzisothiazolin-3-one, ora mixture thereof. The preservative may comprise 2-methyl-4-isothiazolin-3-one or 5-chloro-2-methyl-4-isothiazolin-3-one or 1,2-benzisothiazolin-3-one or a mixture thereof.

[0065] A preservative or preservative mixture may be provided at minimum concentration required to achieve the desired biocidal effect. In many instances, a suitable concentration (e.g., in a storage buffer) may be between about 0.01% and about 2% by volume, preferably at a concentration of between about 0.05% and about 2% by volume or between about 0.07% and about 1.5% by volume.

[0066] The suspension may further comprise one or more buffers. The one or more buffers may comprise a phosphate buffer. For example, the phosphate buffer may be selected from phosphate buffered saline (PBS) or Tris-buffered saline (TBS). The pH of the composition of buffer may vary depending on the intended use and application but may generally be within a range of between about 2 and about 9, preferably between about 5 and about 8. For example, a physiological pH (e.g., a pH of about 7.0 or about 7.5) may be used.

[0067] In some embodiments, the suspension buffer may comprise both, a nonionic surfactant and a preservative and optionally one or more buffers as listed above. For example, the suspension buffer may comprise an ECOSURF™ and an Acticide™ and / or a phosphate buffer. In some examples, the surfactant in a suspension buffer may be ethylene oxide-propylene oxide copolymer mono(2-ethylhexyl) ether or seed oil alcohol ethoxylate 9 EO or polyethylenglykolether and the preservative may be 2-methyl-4-isothiazolin-3-one or 5-chloro-2-methyl-4-isothiazolin-3-one or 1,2-benzisothiazolin-3-one, or a mixture thereof.

[0068] Another aspect of the invention relates to a suspension comprising particles and an aqueous solution comprising a metatungstate salt, wherein the metatungstate salt is present at a concentration in the solution of from about 35% w / w to about 65% w / w.

[0069] The metatungstate salt may be selected from an alkali metatungstate salt, an ammonium metatungstate salt, or a combination thereof. The metatungstate salt may comprise sodium metatungstate.

[0070] The metatungstate salt may be selected from a sodium metatungstate salt, an ammonium metatungstate salt, or a combination thereof. The metatungstate salt may be sodium metatungstate.

[0071] The metatungstate salt may be present at a concentration in the solution of from about 40% w / w to about 60% w / w or from about 45% to about 55% w / w. In embodiments, the metatungstate salt is present at a concentration in the solution of 50% w / w.

[0072] The aqueous solution may have a density of from about 1.5 to about 2.0 g / cm3. In embodiments, the aqueous solution has a density of at least about 1.6 g / cm3, at least about 1.7 g / cm3 or at least about 1.8 g / cm3. In embodiments, the aqueous solution has a density of not more than about 1.9 g / cm3, not more than about 1.8 g / cm3 or not more than about 1.7 g / cm3.

[0073] In embodiments, the aqueous solution has a density of at least about 1.7 g / cm3, and / or wherein the aqueous solution has a density of not more than about 1.9 g / cm3.

[0074] In embodiments, the aqueous solution has a viscosity of less than about 10 x 10’3 Pa.sat20 °C, less than about 5 x 10’3 Pa.s at 20 °C, less than about 2.5 x 10~3 Pa.s at 20 °C, or less than about 1.5 x 10~3 Pa.s at 20 °C.

[0075] The particles may have a density of at least about 1.2 g / cm3, optionally at least about 1.3 g / cm3. The particles may have a density of not more than about 2 g / cm3.

[0076] The difference in density between the particles and the solution may be not more than about 0.3 g / cm3. The difference in density between the particles and the solution may be not more than about 0.2 g / cm3.

[0077] The particles may have a diameter of from about 0.1 pm to about 100 pm, from about 0.1 pm to about 50 pm, from about 0.1 pm to about 5 pm, or from about 0.2 pm to about 2 pm.

[0078] The particles may be monodisperse.

[0079] The particles may comprise polymeric material and / or silica.

[0080] The particles may comprise magnetic material. Thus, the particles may comprise magnetic particles or beads.

[0081] In some instances, the magnetic particles may comprise microparticles or nanoparticles. In some examples, the magnetic particles may contain iron oxide. For example, magnetic nanoclusters as described in patent application No. PCT / EP2023 / 070373 which is hereby incorporated by reference may be used.

[0082] The particles may be monodisperse and magnetic.

[0083] The particles may be functionalised. In such embodiment, the functionalised particles may comprise a functional group or a ligand.

[0084] The functional group may be selected from a hydroxyl group, a carboxylic acid group, an aldehyde group, an amine group, a thiol group, an epoxy group, an amide group, a chloromethyl group, and a tosyl-activated group.

[0085] The ligand may be a capture ligand. The ligand may be selected from a protein (e.g. an antibody, antigen, streptavidin, avidin, protein A, protein G, a lectin, a receptor), a peptide (e.g. an antibody fragment), a carbohydrate, a hapten, an aptamer, and an oligonucleotide.

[0086] The functionalisation may be selected from a protein (e.g. an antibody, streptavidin, avidin, protein A, protein G, protein A / G, and a lectin), a carboxylic acid group, and a tosyl-activated group. Where the functionalisation is a protein, the protein may be selected from an antibody, streptavidin, avidin, protein A, protein G, protein A / G, and a lectin; or the protein may be selected from streptavidin and protein A / G. The functionalisation may be selected from streptavidin, protein A, a carboxylic acid, and a tosyl-activated group.

[0087] The functionalised particles may have a core comprising the magnetic material and a coating comprising the functional group or ligand.

[0088] The particles may be selected from any commercially available particles suitable for use in bio-separation workflows. For example, the particles may be selected from Dynabeads™ MyOne™ Silane, Dynabeads™ MyOne™ Carboxylic Acid, Dynabeads™ M-270™ Carboxylic Acid, Dynabeads™, Oligo(dT)25 magnetic beads (all available from Thermo Fisher Scientific), SeraMag SpeedBeads™ carboxylate-modified or SeraSil-Mag 400 or 700 (Cytiva), BioMagPlus COOH™ and ProMag 1 COOH™ (both Bangs Laboratories, INC Fishers), 4.4 pm fluorescent ferromagnetic beads or 2.0 pm ferromagnetic beads (both available from Spherotech INC Lake Forest, IL), 2 pm beads designated WHM-S001™ or 2 pm beads designated WHM-S002™ (both available from Creative Diagnostics, New York, NY), Silicon Hydroxyl Magnetic Microspheres or Carboxyl Magnetic Microspheres or Oligo(dT) Magnetic Microspheres (available at different nm or pm sizes from VDO Biotech, Suzhou, China), Carboxyl Adembeads (available at 100 nm, 200 nm, 300 nm or 500 nm) or Carboxyl Masterbeads (500 nm) (available from Ademtech, France), MagneSil™ beads (available from Promega), BeaverBeads™ Mag COOH (available from Beaver Biomedical Engineering Ltd.), Lodestars High Bind Carboxyl beads (available from Agilent), Magnosphere™, MS300 Carboxyl, MS 160 Carboxyl or MS160 Carboxyl (all available from JSR Life Sciences), PureProteome Carboxy FlexiBind Magnetic Bead System (available with different bead sizes from Sigma-Aldrich), BioMag™ Carboxl, BioMag™ Maxi Carboxyl or BioMag™ Plus Carboxyl (all available from Polysciences), Carboxyl Super Mag or Mono Mag Magnetic Beads (available at sizes between 0.1 pm and 4.5 pm from Ocean Nanotech), and Carboxyl beads of different sizes available from VdoBiotech.

[0089] The particles may remain suspended in the aqueous solution for at least about 6 h without mixing or agitation. The particles may remain suspended in the aqueous solution for at least about 24 h, 36 h, 48 h, 60 h, or 72 h without mixing or agitation. For the avoidance of doubt, the particles may be said to be suspended in the aqueous solution if no sedimentation of particles in the aqueous solution is observed during the specified period of time, e.g. particles are considered suspended for at least about 6 h if no sedimentation is observed by the end of the specified about 6 h period. Sedimentation may be observed by visual inspection as outlined above.

[0090] The suspension may further comprise one or more surfactants. Each surfactant may be a non-ionic surfactant. A non-ionic surfactant is a substance having both a hydrophilic moiety and a hydrophobic moiety in a molecule and exhibiting non-ionic properties upon dissociation.

[0091] The non-ionic surfactant may be selected from the group consisting of Ecosurf™ EH-9 (Ethylene oxide-propylene oxide copolymer mono(2-ethylhexyl) ether), Ecosurf™ SA-9 (seed oil alcohol ethoxylate 9 EO or polyethylenglykolether), Tergitol™ 15-S-9 (sek-alkoxypolyethylenglykol) or Tween-20 or Eco Tween™-20 or Eco Tween™-80 (100% bio-based ethoxylated (20) or (80) sorbitan ester based on a natural fatty acid (lauric acid)).

[0092] The non-ionic surfactant surfactant may be a non-toxic, biodegradable surfactant. For example, the surfactant may be selected from ECOSURF™ EH, ECOSURF™ SA or ECOSURF™ LFE specialty surfactants (The Dow Chemical Company (“Dow”)).

[0093] Without wishing to be bound by theory, it is thought that such surfactants prevent aggregation of magnetic particles in aqueous solution and reduce stickiness, thereby increasing the ease of handling the suspension in both manual and automated bead-based workflows. Additionally, the surfactants may be employed at low concentrations to reduce foaming in bead samples.

[0094] The non-ionic surfactant may be used in a lysis and / or binding buffer, washing buffer or storage buffer for magnetic bead-based separations.

[0095] The suspension may further comprise one or more preservatives. In particular, the suspensions of the invention used for storage purposes may require a biocide effective against microbial growth to maintain product quality and extended shelf life. Preferably, a preservative having a broad spectrum of activity against all types of bacteria, fungus or yeasts should be used. Preferably, a preservative that is non-toxic and environmentally friendly should be used, presenting no health hazards, toxicology problems, or disposal issues.

[0096] Exemplary preservatives include: 5-chloro-2-methyl—4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (Acticide™ MV), 2-methyl-4-isothiazolin-3-one and 5-chloro2-methyl-4-isothiazolin-3-one (Acticide™ 14), 1,2-benzisothiazolin-3-one (2.5%) and 2- methyl-4-isothiazolin-3-one (2.5%) (Acticide™ MBS), 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (MIT) (ProClin™300), methylchloroisothiazolin and methylisothiazolin (Kathon™LX), 2-methyl-4-isothiazolin-3-one (MIT) or 5- chloro-2-methyl-4-isothiazolin-3-one (CMIT) or 1,2-benzisothiazolin-3-one, ora mixture thereof.

[0097] A preservative or preservative mixture may be provided at minimum concentration required to achieve the desired biocidal effect. In many instances, a suitable concentration (e.g., in a storage buffer) may be between about 0.01% and about 2% by volume, preferably at a concentration of between about 0.05% and about 2% by volume or between about 0.07% and about 1.5% by volume.

[0098] The suspension may further comprise one or more buffers. The buffers may comprise a lysis buffer, and / or a binding buffer, and / or a washing buffer and / or an elution buffer. As the skilled person will appreciate, the specific composition of a given buffer will depend on the assay and target analyte(s). For example, where the assay comprises isolation of nucleic acid, the buffers may comprise a lysis buffer (e.g. an exemplary lysis solution described herein), and / or a nucleic acid binding buffer, and / or a washing buffer, and / or an elution buffer.

[0099] The one or more buffers may comprise a phosphate buffer. For example, the phosphate buffer may be selected from phosphate buffered saline (PBS) or Trisbuffered saline (TBS). The pH of the composition of buffer may vary depending on the intended use and application but may generally be within a range of between about 2 and about 9, preferably between about 5 and about 8. In many instances, a physiological pH (e.g., a pH of about 7.0 or about 7.5) may be used.

[00100] In some embodiments, the suspension buffer may comprise both, a non-ionic surfactant and a preservative and optionally one or more buffers as listed above. For example, the suspension buffer may comprise an ECOSURF™ and an Acticide™ and / or a phosphate buffer. In some examples, the surfactant in a suspension buffer may be ethylene oxide-propylene oxide copolymer mono(2-ethylhexyl) ether or seed oil alcohol ethoxylate 9 EO or polyethylenglykolether and the preservative may be 2-methyl-4-isothiazolin-3-one or 5-chloro-2-methyl-4-isothiazolin-3-one or 1,2-benzisothiazolin-3-one, or a mixture thereof.

[00101] Use and methods of using the aqueous solution for the suspension of particles

[00102] A further aspect of the invention provides a use of an aqueous solution as defined in the first or second aspect for the suspension of particles.

[00103] The particles of this aspect may be as defined elsewhere in the description, for example as defined above in the section titled “Suspension”.

[00104] The use may comprise keeping the particles suspended in the solution for at least about 6 h, optionally at least about 12 h. For example, the particles may be kept suspended in the aqueous solution for at least about 24 h, 36 h, 48 h, 60 h, or 72 h without mixing or agitation. For the avoidance of doubt, the particles may be said to be kept suspended in the aqueous solution if no sedimentation of particles in the aqueous solution is observed during the specified period of time, e.g. particles are kept suspended for at least about 6 h if no sedimentation is observed by the end of the specified about 6 h period.

[00105] The use may comprise, after the suspension of the particles, providing separated particles by separating the particles from the aqueous solution (e.g. by filtration, magnetic separation etc.). The particles may be monodisperse, and / or functionalised, and / or comprise magnetic material.

[00106] The use may further comprise the use of the separated particles in an assay. The assay may comprise immunoprecipitation, nucleic acid capture, immunoassay, and / or lateral flow assay.

[00107] The use may further comprise the use of the separated particles for isolating, purifying, fractionating, depleting, concentrating and / or analysing one or more of cells, viruses, vesicles, organelles, exosomes, small molecules, analytes cations, anions, ions, toxins, pathogens, nucleic acids, proteins or peptides.

[00108] An additional aspect of the invention provides a method of using particles, comprising: a) suspending particles in an aqueous solution comprising a salt, wherein the aqueous solution has a density of from about 1.5 to about 2.0 g / cm3, said suspending comprising a period of at least about 6 h; b) separating the particles from the solution, to provide separated particles; and c) use of the separated particles in an assay.

[00109] Step b) of the method may comprise filtering the particles using a membrane or filter material with a pore size less than the diameter of the used particles. Alternatively, where the particles used are magnetic particles step b) may comprise applying a magnetic field to the sample (e.g. exposing the sample to a magnet) to concentrate the magnetic particles and removing the aqueous solution comprising the metatungstate salt from the sample. Optionally, one or more washing steps with a suitable washing solution may be performed after separation of the particles (e.g. to remove traces of the salt or equilibrate the particles for downstream assay formats).

[00110] The particles of this aspect may be as defined elsewhere in the description, for example as defined above in the section titled “Suspension.

[00111] The method may comprise keeping the particles suspended in the solution for at least about 12 h. For example, the particles may be kept suspended in the aqueous solution for at least about 24 h, 36 h, 48 h, 60 h, or 72 h without mixing or agitation. For the avoidance of doubt, the particles may be said to be kept suspended in the aqueous solution if no sedimentation of particles in the aqueous solution is observed during the specified period of time, e.g. particles are kept suspended for at least about 6 h if no sedimentation is observed by the end of the specified about 6 h period.

[00112] The particles may be monodisperse, and / or functionalised, and / or comprise magnetic material.

[00113] The assay may comprise immunoprecipitation, nucleic acid capture, immunoassay, and / or lateral flow assay.

[00114] The method may further comprise the use of the separated particles for isolating, purifying, fractionating, depleting, concentrating and / or analysing one or more of cells, viruses, vesicles, organelles, exosomes, small molecules, analytes cations, anions, ions, toxins, pathogens, nucleic acids, proteins or peptides.

[00115] A further aspect of the invention provides a method of using particles, comprising: a) suspending particles in an aqueous solution comprising a metatungstate salt, wherein the metatungstate salt is present at a concentration in the solution of from about 35% w / w to about 65% w / w, said suspending comprising a period of at least about 6 h; b) separating the particles from the solution, to provide separated particles; and c) use of the separated particles in an assay.

[00116] Step b) of the method may comprise filtering the particles using a membrane or filter material with a pore size less than the diameter of the used particles. Alternatively, where the particles used are magnetic particles step b) may comprise applying a magnetic field to the sample (e.g. exposing the sample to a magnet) to concentrate the magnetic particles and removing the aqueous solution comprising the metatungstate salt from the sample. Optionally, one or more washing steps with a suitable washing solution may be performed after separation of the particles (e.g. to remove traces of the salt or equilibrate the particles for downstream assay formats).

[00117] The particles and / or aqueous solution of this aspect may be as defined elsewhere in the description, for example as defined above in the section titled “Suspension.

[00118] The method may comprise keeping the particles suspended in the solution for at least about 6 h, optionally at least about 12 h. For example, the particles may be kept suspended in the aqueous solution for at least about 24 h, 36 h, 48 h, 60 h, or 72 h without mixing or agitation. For the avoidance of doubt, the particles may be said to be kept suspended in the aqueous solution if no sedimentation of particles in the aqueous solution is observed during the specified period of time, e.g. particles are kept suspended for at least about 6 h if no sedimentation is observed by the end of the specified about 6 h period.

[00119] The particles may be monodisperse, and / or functionalised, and / or comprise magnetic material.

[00120] The assay may comprise immunoprecipitation, nucleic acid capture, immunoassay, and / or lateral flow assay.

[00121] The method may further comprise the use of the separated particles for isolating, purifying, fractionating, depleting, concentrating and / or analysing one or more of cells, viruses, vesicles, organelles, exosomes, small molecules, analytes cations, anions, ions, toxins, pathogens, nucleic acids, proteins or peptides.

[00122] An additional aspect of the invention provides a method of storing particles, comprising suspending particles in an aqueous solution comprising a metatungstate salt, wherein the metatungstate salt is present at a concentration in the solution of from about 35% w / w to about 65% w / w, optionally wherein the particles are suspended in the aqueous solution for a period of at least about 6 h.

[00123] The particles and / or aqueous solution of this aspect may be as defined elsewhere in the description, for example as defined above in the section titled “Suspension.

[00124] The method may comprise keeping the particles suspended in the solution for at least about 12 h. For example, the particles may be kept suspended in the aqueous solution for at least about 24 h, 36 h, 48 h, 60 h, or 72 h without mixing or agitation. For the avoidance of doubt, the particles may be said to be kept suspended in the aqueous solution if no sedimentation of particles in the aqueous solution is observed during the specified period of time, e.g. particles are kept suspended for at least about 6 h if no sedimentation is observed by the end of the specified about 6 h period.

[00125] The particles may be monodisperse, and / or functionalised, and / or comprise magnetic material.

[00126] The method of storing particles may further comprise storing the suspended particles in a storage container, wherein the container may have any suitable size, dimension or form such as e.g., a vial, a tube, a multi-well plate, a bag, a box, a cartridge, a microfluidic chip etc.

[00127] The method of storing particles may further comprise storing the suspended particles at ambient temperature, or at a temperature of between about 0°C and about 10 °C, or at a temperature below 0°C, such as e.g. at about -20°C or at about -70°C.

[00128] An additional aspect of the invention provides a method of removing particles from a storage container, comprising a) providing particles suspended in an aqueous solution comprising a metatungstate salt, wherein the metatungstate salt is present at a concentration in the solution of from about 35% w / w to about 65% w / w, optionally wherein the particles are suspended in the aqueous solution for a period of at least about 6 h, and b) removing the particles from the storage container.

[00129] The particles and / or aqueous solution and / or storage container of this aspect may be as defined elsewhere in the description, for example as defined above or in the section titled “Suspension.

[00130] In embodiments, the removing may comprise applying a magnetic force, suction, pipetting and the like. The particles may be removed quantitatively from a storage container such that at least 90% of the particles, preferably at least 95%, more preferably at least 98% of the particles are removed from the container. Kit

[00131] A further aspect of the invention provides a kit comprising a solution as defined in the first aspect or second aspect, and particles. The particles may be as defined in embodiments relating to the first or second aspect.

[00132] The kit may further comprise reagents for desired separation or analytic methods. The reagent can be any suitable reagent (e.g., lysis and / or binding buffers, precipitating reagents, wash buffers, elution buffers, columns, plates, cartridges, microfluidic chips, or containers and the like) that can be used while processing or analyzing a sample, for example, analyzing the sample for the presence of a particular analyte, such a biological molecule.

[00133] The kit may also comprise an instruction manual. The "instruction manual" is a printed matter describing how to use the kit, for instance, the method of preparing reagents, recommended preparation conditions, and the like. The instruction manual includes those appearing on labels attached to the kit, packages housing the kit, and the like, as well as handling brochures in a pamphlet or leaflet form. In addition, the instruction manual includes information that is disclosed or provided via an electronic medium such as the internet. EXAMPLES General Workflow Procedure

[00134] The following represents an example method for keeping particles in suspension using a 40-60% w / w solution of sodium metatungstate in water. 1. Prepare 10 g of 50% sodium metatungstate solution in water by dissolving 5 g of sodium metatungstate in 5 g of water. The resulting total volume is around 5,5 mL. 2. Take out 1 mL of 10 mg / mL suspension of particles (e.g. Dynabeads™ MyOne™ Streptavidin T1) into a tube. 3. Place the tube onto a magnet rack. Wait 30 seconds, then aspirate and remove the supernatant. 4. Remove the tube from the magnet, add 1 mL of sodium metatungstate solution. Vortex for 30 seconds to resuspend the beads into the solution. Thusly prepared suspension of particles is slow to settle and the particles do not aggregate easily. Gentle stirring can hold the particles in suspension indefinitely. 5. From this suspension, take out 100 pL and transfer it into a new tube. 6. Place the tube onto a magnet rack. Wait 30 seconds, then aspirate and remove the supernatant. 7. Remove the tube from the magnet, add 100 pL of 50 mM phosphate buffer pH 7.4 (or other buffer of choice). Vortex for 30 seconds to resuspend the particles into the solution. 8. Repeat steps 6 and 7 twice more. The particles are now in a new solution, free from metatungstate and ready for downstream applications. Using this method and similar procedures, it is possible to reduce sedimentation of solid particles. Depending on the particle density, it may be necessary to adjust the concentration of metatungstate to achieve optimal particle suspension over long periods of time (>72 hours). Example 1: Dynabeads™ MyOne™ T1

[00135] 20 mg of Dynabeads— MyOne— T1 beads ware suspended in 5 mL of 50% w / w aquatic solution of sodium metatungstate, in a 15 mL tube. Another 20 mg of Dynabeads™ MyOne— T1 beads were suspended in 5 mL of water. Upon mixing, the beads in the tubes were left to sediment at room temperature. The beads in the tube with the metatungstate solution did not fully sediment even after 3 days. The beads stored in water fully sedimented within 3 hours, and after 3 days they formed a compact cake which needed strong mixing to break up and resuspend again. The metatungstate solution could afterwards easily be removed from the beads using standard magnetic separation for the superparamagnetic Dynabeads™ magnetic beads. Example 2: Other Exemplary Particles

[00136] Other exemplary particles were tested with metatungstate solutions in accordance with the protocol of Example 1. Particles with different sizes, compositions, surface properties and functionalisation were tested, as indicated in Table 1. Each type of tested particles remained in suspension and did not aggregate during the 24h test period. The beads were then tested in downstream assays, confirming that the beads maintained their activity. Table 1 - details of other exemplary particles tested using the protocol of Example 1 Particle Diameter (pm) Polymer core? Approximate density (g / cm3) Surface property Functionality tested Dynabeads™ Protein A beads 2.8 Yes 1.4-1.5 protein Yes Dynabeads™ MyOne™ Streptavidin C1 beads 1 Yes 1.7-1.9 protein Yes Dynabeads™ M-270 2.8 Yes 1.7-1.9 carboxylic acid, hydrophilic Yes Carboxylic acid beads Dynabeads— M-280 T osylactivated beads 2.8 Yes 1,7-1.9 tosylated alkyl, hydrophobic Yes DynaGreen™ Protein A beads 0.3 No 1,8-2,0 protein No

Claims

1. A suspension comprising particles and an aqueous solution comprising a salt, wherein the aqueous solution has a density of from about 1.5 to about 2.0 g / cm3.

2. The suspension of claim 1, wherein the aqueous solution has a density of at least about 1.7 g / cm3, and / or wherein the aqueous solution has a density of at not more than about 1.9 g / cm3.

3. The suspension of claim 1 or claim 2, wherein the aqueous solution has a viscosity of less than about 10 x 10’3 Pa..s at 20 °C, optionally than about 5 x 10’3 Pa.s at 20 °C; further optionally less than about 2.5 x 10’3 Pa.s at 20 °C (e.g. less than about 1.5 x 10'3 Pa.s at 20 °C).

4. The suspension of any preceding claim, wherein the salt is or comprises a metatungstate salt, optionally wherein the metatungstate salt is present at a concentration in the solution of from about 35% w / w to about 65% w / w.

5. A suspension comprising particles and an aqueous solution comprising a metatungstate salt, wherein the metatungstate salt is present at a concentration in the solution of from about 35% w / w to about 65% w / w.

6. The suspension of claim 4 or claim 5, wherein the metatungstate salt is selected from an alkali metatungstate salt, an ammonium metatungstate salt, or a combination thereof; optionally wherein the metatungstate salt is or comprises sodium metatungstate.

7. The suspension of any of claims 4 to 6, wherein the metatungstate salt is selected from a sodium metatungstate salt, an ammonium metatungstate salt, or a combination thereof.

8. The suspension of any preceding claim, wherein the particles have a density of at least about 1.2 g / cm3; and / orwherein the particles have a density of not more than about 2 g / cm3.

9. The suspension of any preceding claim, wherein the difference in density between the particles and the solution is not more than about 0.3 g / cm3, optionally not more than about 0.2 g / cm3.

10. The suspension of any preceding claim, wherein the particles are monodisperse.

11. The suspension of any preceding claim, wherein the particles comprise polymeric material and / or silica.

12. The suspension of any preceding claim, wherein the particles comprise magnetic material.

13. The suspension of any preceding claim, wherein the particles are functionalised.

14. The suspension of claim 13, wherein the functionalised particles comprise a functional group and / or a ligand.

15. The suspension of claim 14, wherein the functional group is selected from a hydroxyl group, a carboxylic acid group, an aldehyde group, an amine group, a thiol group, an epoxy group, an amide group, a chloromethyl group, and a tosyl-activated group.

16. The suspension of claim 14 or claim 15, wherein the ligand is a capture ligand.

17. The suspension of any of claims 14 to 16, wherein the ligand is selected from a protein (optionally an antibody, antigen, streptavidin, avidin, protein A, protein G, protein A / G, a lectin, a receptor), a peptide (optionally an antibody fragment), a carbohydrate, a hapten, an aptamer, and an oligonucleotide.

18. The suspension of any preceding claim, wherein the particles remain suspended in the aqueous solution for at least about 6 h without mixing or agitation;optionally where in the particles remain suspended in the aqueous solution for at least about 24 h, 36 h, 48 h, 60 h, or 72 h without mixing or agitation.

19. The suspension of any preceding claim, further comprising one or more of a non-ionic surfactant, a preservative and / or a buffer,optionally wherein the non-ionic surfactant comprises ethylene oxide-propylene oxide copolymer mono(2-ethylhexyl) ether or seed oil alcohol ethoxylate 9 EO, or polyethylenglycolether; and / oroptionally wherein the preservative comprises 2-methyl-4-isothiazolin-3-one or 5-chloro-2-methyl-4-isothiazolin-3-one or 1,2-benzisothiazolin-3-one or a mixture thereof; and / oroptionally wherein the buffer comprises phosphate buffered saline or Tris.

20. Use of an aqueous solution as defined in any of claims 1 to 7 for the suspension of particles.

21. The use of claim 20, wherein the particles are as defined in any of claims 8 to 17.

22. The use of claim 20 or 21, wherein the use comprises keeping the particles suspended in the solution for at least about 6 h, optionally at least about 12 h.

23. The use of any of claims 20 to 22, wherein the use comprises, after the suspension of the particles, providing separated particles by separating the particles from the aqueous solution;optionally wherein the particles are monodisperse, and / or functionalised, and / or comprise magnetic material.

24. The use of claim 23, further comprising use of the separated particles in a manufacturing step or in an assay.

25. The use of claim 24, wherein the assay comprises immunoprecipitation, nucleic acid capture, immunoassay, and / or lateral flow assay.

26. The use of claim 23, further comprising use of the separated particles for isolating, purifying, fractionating, depleting, concentrating and / or analysing one or more of cells, viruses, vesicles, organelles, exosomes, small molecules, analytes cations, anions, ions, toxins, pathogens, nucleic acids, proteins or peptides.

27. A method of using particles comprisinga) suspending particles in an aqueous solution comprising a metatungstate salt, wherein the metatungstate salt is present at a concentration in the solution of from about 35% w / w to about 65% w / w, said suspending comprising a period of at least about 6 h;b) separating the particles from the solution, to provide separated particles; optionally washing the separated particles, andc) using the separated particles in an assay.

28. A method of storing particles comprising suspending particles in an aqueous solution comprising a metatungstate salt, wherein the metatungstate salt is present at a concentration in the solution of from about 35% w / w to about 65% w / w, optionally wherein the particles are suspended in the aqueous solution for a period of at least about 6 h.

29. The method of claim 27 or claim 28, wherein the solution is as defined in any of claims 1-7 or 19, and optionally wherein the particles are as defined in any of claims 8-17.

30. A kit comprising:a solution as defined in any of claims 1-7; andparticles, optionally wherein the particles are as defined in any of claims 8 to 17.