METHOD, SYSTEM, AND FILTRATION UNIT FOR THE ISOLATION OF PARTICLES FROM BIOLOGICAL SAMPLES

Abstract

A method and an automated liquid handling system for the isolation of particles from a biological sample are provided. A column, a container and a filtration unit which are adapted to be used in such a method and system are provided. The column can include a section comprising a plurality of microbeads retained there.

Claims

1.-38. (canceled)

39. A method for the isolation of particles from a biological sample, the method comprising: providing a column with an upper opening and a lower opening, the column comprising at least a first section comprising a first plurality of microbeads of a first diameter, the first plurality of microbeads being retained in the column to prevent the first plurality of microbeads from passing through the lower opening, and the first section providing interstices between neighboring microbeads which act as a filter for the biological sample; applying the biological sample onto the first section through the upper opening of the column; separating a first portion of particles of the biological sample from a second portion of particles of the biological sample, the first portion of particles of the biological sample passing through the first section, the first section retaining the second portion of particles of the biological sample, and the retained second portion of particles being trapped within the interstices; suspending the retained second portion of particles of the biological sample and the first section in a buffer solution to form a suspension; and separating the suspended second portion of particles of the biological sample from the suspended first section.

40. The method of claim 39, wherein the first portion of particles of the biological sample is separated from the second portion of particles of the biological sample by means of gravity or by application of a centrifugal force, preferably wherein the separated first portion of particles of the biological sample is collected in a first container.

41. The method of claim 39, wherein the suspended second portion of particles is separated from the suspended first section by means of gravity or application of a centrifugal force.

42. The method of claim 39, wherein the method further comprising: concentrating the separated first or second portion of particles of the biological sample, preferably wherein a centrifugal force is applied for concentrating the separated first or second portion of particles of the biological sample.

43. The method of claim 39, wherein the microbeads are substantially non-compressible and/or substantially non-porous.

44. The method of claim 39, wherein the first diameter is in a range of 20 to 700 μm, preferably 50 to 600 μm, or in a range of 10 nm to 1 μm, preferably 50 nm to 500 nm, more preferably 100 to 300 nm.

45. The method of claim 39, wherein the first section is suspendable.

46. The method of claim 39, wherein in the step of providing the column with an upper opening and a lower opening, the first plurality of microbeads is retained in the column by a constricting means that is positioned at the lower opening.

47. The method of claim 46, wherein the constricting means comprises a second section comprising a second plurality of microbeads of a second diameter, wherein the first diameter is smaller than the second diameter.

48. The method of claim 46, wherein the constricting means comprises a removable plug, and/or wherein the constricting means is provided by a container that is positioned below the column, preferably wherein the constricting means is a centered protrusion of the container and is positioned at the lower opening of the column wherein at least a portion of the protrusion fits into the column.

49. The method of claim 48, wherein the centered protrusion comprises at least an upper portion and a lower portion wherein the upper portion fits into the column, and wherein the lower portion supports the lateral walls of the lower opening of the column; and/or wherein a passage is formed between the lateral walls of the elongated channel and the lateral walls of the centered protrusion of the container, which allows a liquid to flow through the passage and into the container chamber, preferably wherein the passage has a width of between 10 and 40 μm, more preferably about 20 μm.

50. The method of claim 39, further comprising: collecting the suspension in a second container by means of aspirating the suspension and transferring the suspension to the second container; or collecting the suspension in a second container by means of gravity or by application of a centrifugal force.

51. The method of claim 47, wherein the first section and the second section are provided as stacked layers with the first section being the top layer, preferably wherein the column comprises a plurality of sections, two of the sections being the first section and the second section, wherein each section comprises a plurality of microbeads of a specific diameter, the plurality of sections differs at least by the specific diameter of the microbeads, wherein the first diameter of the first section comprises the smallest diameter; more preferably wherein the plurality of sections is provided as stacked layers, the first section being the top layer, and wherein the specific diameter of the microbeads of the plurality of sections increases gradually from the top layer to the bottom layer.

52. The method of claim 51, wherein the plurality of sections comprises three to seven sections.

53. The method of claim 39, wherein the method is used for the isolation of circulating tumor cells, wherein the first diameter is in a range of 80 to 200 μm; or wherein the method is used for the isolation of circulating microemboli, wherein the first diameter is in a range of 200 to 600 μm; or wherein the method is used for the isolation of extracellular vesicles, wherein the first diameter is in a range of 50 nm to 500 nm, preferably 100 to 300 nm.

54. An automated liquid handling system for the isolation of particles from a biological sample, comprising: means for providing a column with an upper opening and a lower opening, the column comprising at least a first section comprising a first plurality of microbeads of a first diameter, the first plurality of microbeads being retained in the column to prevent the first plurality of microbeads from passing through the lower opening, and the first section providing interstices between neighboring microbeads which act as a filter for the biological sample; means for applying the biological sample onto the first section through the upper opening of the column; means for separating a first portion of particles of the biological sample from a second portion of particles of the biological sample, the first portion of particles of the biological sample passing through the first section, and the first section retaining the second portion of particles of the biological sample, and the retained second portion of particles being trapped within the interstices; means for suspending the retained second portion of particles of the biological sample and the first section in a buffer solution to form a suspension; and means for separating the suspended second portion of particles of the biological sample from the suspended first section.

55. A filtration unit comprising: a column; and a container, wherein the column is adapted to be used in a method for the isolation of particles from a biological sample, the column comprising: an upper chamber for receiving the biological sample, and defined on its lateral sides by one or more lateral column walls, extending into a tapered portion on its lower end, an elongated channel extending from the tapered portion downwardly to a lower opening, the elongated channel being at least partially filled with at least a first section comprising a first plurality of microbeads of a first diameter, the first plurality of microbeads being retained in the column to prevent the first plurality of microbeads from passing through the lower opening, and the first section providing interstices between neighboring microbeads which act as a filter for the biological sample such that particles are trapped within the interstices; and wherein the container comprises a container chamber for receiving a part or all of the biological sample, and defined on its lateral sides by one or more lateral container walls, and wherein the container is arranged such that, when the column is placed on top of the container, the elongated channel of the column protrudes into the container chamber.

56. The filtration unit of claim 55, wherein the column further comprises a lid part, which comprises an upper opening through which the biological sample is received, to seal the upper chamber.

57. The filtration unit of claim 55, wherein a constricting means is positioned at the lower opening of the elongated channel to retain the first plurality of microbeads in the column, preferably wherein the constricting means comprises a second section comprising a second plurality of microbeads of a second diameter, wherein the first diameter is smaller than the second diameter.

58. The filtration unit of claim 57, wherein the constricting means further comprises a cross-shaped ending of the lower opening that retains the second section, or wherein the constricting means comprises a porous filter.

59. The filtration unit according to claim 55, wherein the container comprises a centered protrusion as a constricting means to be positioned at the lower opening of the elongated channel of the column, wherein at least a portion of the protrusion fits into the elongated channel of the column.

60. The filtration unit of claim 59, wherein the centered protrusion comprises at least an upper portion and a lower portion, wherein the upper portion fits into the elongated channel of the column, and wherein the lower portion supports the lateral walls of the lower opening of the elongated channel; and/or wherein a passage is formed between the lateral walls of the elongated channel and the lateral walls of the centered protrusion of the container, which allows a liquid to flow through the passage and into the container chamber, preferably wherein the passage has a width of between 10 and 40 μm, more preferably about 20 μm.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0093] Currently preferred embodiments of the present invention will be described in the following detailed description with reference to the following figures:

[0094] FIGS. 1a to c: show schematic representations of interstices formed by three neighboring microbeads, which can be used as filters according to the present invention.

[0095] FIGS. 2a to c: show schematic representations of a container according to the present invention.

[0096] FIGS. 3a to c: show an illustration of a work-flow of the method according to the present invention.

[0097] FIGS. 4a to e: show schematic representations of a container according to the present invention.

[0098] FIGS. 5a to c: show an illustration of a work-flow of the method according to the present invention.

[0099] FIG. 6: shows an illustration of a work-flow of the method according to the present invention.

[0100] FIG. 7: shows an illustration of a health screen, which can make use of the method, the system, the column and the container according to the present invention.

[0101] FIGS. 8a, b: show microscopic images (760× magnification) of silica beads of 20 μm average diameter (a) and 30 μm average diameter (b).

[0102] FIGS. 9a to g: show microscopic images of buffy coat sample (a), flow-through after application onto a 20 μm microbead matrix (b), separated particles after suspension of the 20 μm microbead matrix (c), flow-through after application onto a 50 μm microbead matrix (d), separated particles after suspension of the 50 μm microbead matrix (e), flow-through after application onto a 50 μm microbead matrix (f), and separated particles after suspension of the 50 μm microbead matrix (g) (FIG. a-e: 350× magnification; FIG. f, g: 760× magnification).

[0103] FIGS. 10a, b: show microscopic images (350× magnification) of agglutinated red blood cells trapped in the interstices of microbeads with an average size of 30 μm.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0104] Preferred embodiments and examples of the invention will be described in the following detailed description. It is emphasized, however, that the present invention is not limited to these embodiments.

[0105] The present invention relates to a method, a system, a column, a container and a filtration unit for the isolation of particles from a biological sample to overcome the above-mentioned limitations and challenges known from the prior art. Advantageously, the method, the system, the column, the container and the filtration unit may provide for a high throughput filtration of large volumes of sample while preserving cell viability and providing high yields and high purity.

[0106] The suggested method as well as the system, the column and filtration unit intended for the isolation of biological are based on or comprise a first section comprising microbeads of a specific diameter. These microbeads form interstices that serve as filters for the biological particles; biological particles of a diameter or size above the size of the interstices are trapped in the section. Advantageously, the interstitial volume between the microbeads, which is shaped as a three-dimensional tunnel structure, provides for a minimized area of contact when targeted particles are trapped within the interstices. At the same time, residual volumes of the interstices, which are not occupied by the trapped particles, reduce the shear stress experienced by the trapped particles, and prevent clogging of the filtration matrix by allowing particles below the critical interstice diameter to pass through. The first section, being a three-dimensional matrix of filtering interstices, is furthermore able to separate and trap particles that usually deform in constrictions, thereby evading being trapped.

[0107] The trapped particles can be recovered from the first section in a straight-forward manner. Importantly, according to the suggested method, the particles remain in a buffered solution, thereby increasing the likelihood of isolating live, non-damaged biological particles.

[0108] FIG. 1a illustrates the formation of an interstice, trapping a round particle 102. The interstice is formed by at least three adjacent microbeads 101. The interstice diameter, formed by three adjacent microbeads can be calculated according to the following formula

[00001]$d=\frac{2-\sqrt{3}}{\sqrt{3}}D$

with d being the diameter of the interstice formed by three microbeads, and D being the diameter of each of the microbeads. FIG. 1b as well as Table 1 comprise calculated interstices for exemplary microbeads of homogeneous size.

[0109] The distribution of a microbeads matrix of the first section is relatively consistent. For example, microbeads with a specific diameter of 500 μm provide constant and precise interstices that capture particles with 80 μm diameter and above. Obviously, in practice, the precise interstice might slightly deviate from the calculated values. However, generally speaking, if for example the microbeads are non-compressible, values corresponding to or very close to the calculated interstice diameter are achieved.

TABLE-US-00001 TABLE 1 Pore diameters for homogeneously sized microbeads. Microbead diameter Interstice (μm) diameter (μm) 1000 150 900 140 800 120 700 110 600 93 500 80 400 60 300 50 200 30 100 15 90 14 80 12 70 11 60 9 50 8 40 6.2 30 4.6 20 3.1 10 1.5 9 1.39 8 1.24 7 1.08 6 0.93

[0110] By using a mixture of differently sized microbeads, the interstice diameter changes, which can be measured or calculated (FIG. 1c, Table 2).

TABLE-US-00002 TABLE 2 Pore diameters for heterogeneously sized microbeads. Microbead diameter Interstice (μm) diameter (μm) 500, 500, 300 64 500, 300, 300 54

[0111] FIG. 2a shows a device according to an embodiment of the present invention in the form of a filtration unit 1 which has a column 2 and a container 3. In different embodiments, the filtration unit 1 (and its column and container 2 and 3, respectively) can have a substantially cylindrical or rectangular shape. In different embodiments, the device can only comprise a column 2, in that case it may be adapted to be coupled to a rack or a reservoir. The column 2 and container 3 of one filtration unit 1 are designed so that they can be assembled together or with any other counterparts from another filtration unit 1 of the same type, for instance a column 2 can be assembled successively with different containers 3.

[0112] Suitable material for the filtration unit 1 includes among other: polypropylene, polyethylene, glass. In one embodiment, the filtration unit 1 is formed via injection molding. It is to be noted that in several embodiments, the various parts of the filtration unit 1 do not need to be made of the same material.

[0113] The column 2 of the filtration unit has an upper chamber 21 for containing one or more biological samples. This upper chamber 21 is formed by the cavity in the middle of one or more lateral walls 22 of the column 2. In an embodiment, the upper chamber 21 can be of a substantially cylindrical shape, thus forming a tube. At its upper end (above its upper chamber 21), the column 2 has an upper opening 24 for introducing the one or more biological samples into and flowing the one or more biological samples out of the upper chamber 21. The upper opening 24 can be provided in its vicinity with a pipetting channel coupling 25 (for connection with a pipetting channel of a laboratory automation system), and/or a cover (not show in FIG. 2a) for closing the upper opening, and thus sealing the upper end of the upper chamber 21. In one embodiment, this cover is an elastomer flap. The presence of a pipetting channel coupling 25 facilitates and eases the direct transfer of samples with pipetting channels instead of specific robotic arms. In either case, it should be specifically designed to match means of delivery samples, even directly vein-punctured.

[0114] The lower part of the upper chamber 21 forms a tapered portion 29, whose lateral walls are tapered, i.e. the distance between opposing walls (or the distance between opposing sides of one or more continuous lateral walls) gets smaller when moving in a downward direction (i.e from the top of the upper section to the bottom of the lower section). The tapered portion 29 ends with an opening oriented in the downward direction and opened toward an elongated channel 26, which is joined to the tapered portion 29. In some embodiments, the elongated channel 26 protrudes downwardly from the tapered portion 29 of the column 2. In a preferred embodiment, the elongated channel 26 comprises a filter element 4 (see FIG. 2b) which will be described in more details later in this description. In embodiments with a container 3, the elongated channel 26 may protrude into a container chamber 31 of the container 3. The length and diameter of the elongated channel 26 may be adapted to the type and method of sampling of a given biological sample, i.e. for instance for optimizing the filtration results. For example, in some embodiments, the elongated channel 26 may be long enough to accommodate a filter element 4 in the form of a column filter element. The elongated channel 26 ends at its lower side with a lower opening 27 to enable discharge of a part or parts of the biological sample that was contained in the upper chamber 21. This lower opening 27 may be comprised of a constricting means 271, with a pre-defined spacing that is large enough for allowing the flow of unfiltered biological sample. The constricting means 271 may comprise tapered and angled slopes extending within the elongated channel 26. Alternatively, the constricting means 271 may be a porous filter.

[0115] Preferably, the column 2 of the filtration unit 1 is made in one piece, for example by means of injection molding. However, in some embodiments, the column 2 may comprise a main body and a lid part 210. The lid part 210 may be produced separately from the reminder of the column 2 (also called the “main body”), wherein each part may be produced by injection molding, and then be assembled. This embodiment has proven to be easy to manufacture and to be cost-efficient.

[0116] The lid part 210 may be positioned at the upper end of the column 2. It may comprise lateral walls 211, substantially parallel to the lateral walls 22 of the column 2. The lateral walls 211 are preferably surrounding the lateral walls 22 of the upper section, and may be connected to them by a friction force. In one embodiment, a connection notching 212 is provided for connecting the main body of the column 2 to the lid part 210. This connection notching 212 may be placed on the lateral walls 211 of the lid part 210 or on the lateral walls 22 of the column 2. This connection notching 212 may be placed between the lateral walls 22 and 211 to replace or supplement the friction force maintaining the lid part 210 connected to the main body of the column 2. The lid part 210 may further comprise internal walls 213 substantially parallel to the lateral walls 211 and positioned at the upper end of the main body of the column 2, so that when the lid part 210 is connected to the main body of the column 2, the internal walls 213 and the lateral walls 211 form a slot 214 into which the upper part of the lateral walls 22 of the main body of the column 2 may be clamped, thus ensuring an even more stable connection between the main body of the column 2 and the lid part 210, and ensuring a better sealing of the upper chamber 21.

[0117] For rectangular shaped filtration units 1, the outer surface of the column 2 may comprise anchor protrusions 23, preferably in pairs of two, four, eight etc. The protrusions allow the column 2 to be reliably positioned onto the container 3 of the filtration unit 1 or compatible racks.

[0118] The container 3 of the filtration unit 1 may comprise an open upper end, through which the lower part of the upper section can be entered. The container 3 may comprise a container chamber 31 for collecting for instance separated sample fluid. The container chamber 31 is defined by the spaced formed between the open upper, one or more lateral walls 32 of the container, and a bottom end 34. The lower chamber 31 may also be cylindrical or rectangular. Most preferably, it has the same shape as the column 2 to which it is designed to be attached.

[0119] At its upper opened end, the container 3 may have a flange 33 around its opening (at the top end of the lateral walls 32), for receiving the one or more protrusions 23 of the column 2, and ensuring the connection between the column and container of the filtration unit 1. Such a flange 33 also has the advantage of easing the handling for the detachment and/or positioning onto a centrifuge and/or automated handling system and/or to be positioning on compatible racks.

[0120] The bottom end 34 of the lower chamber 31 may be provided with one or more bottom walls 35 forming a tapering portion (i.e. the distance between opposing walls—or the distance between opposing sides of one or more continuous lateral walls—gets smaller when moving in a downward direction). The bottom end 34 may be further provided with a reduced trap portion 36 at the lower end of the bottom walls 35. In an exemplary embodiment, the container may also include a lid to permit safe transportation of the container 3 and its contents received from the column 2 for further processing, and to reduce the risk of losing and/or contaminating the contents in container 3.

[0121] The container 3 may be further provided with one or more wall extensions 37, which extend the one or more lateral walls 31 of the container 3 in a substantially downward direction. These one or more wall extensions 37 are preferably configured to allow stable footing of the container on a plane surface, irrespective of whether the container is present attached to or separate from the column 2. For instance, these wall extensions 37 may extend at least as far downwardly as the one or more bottom walls 35 or the trap portion 26 of the container 3. These wall extensions 34 may have a substantially horizontal end surface, adapted to support them and ensure a stable contact with an external surface onto which the container 2 may be placed.

[0122] In the preferred embodiment, the column and container are designed in a detachable manner, wherein e.g. a reduced outer surface of the column 2 is smaller than the inner surface of the container 3, so that frictional force is applied when the column and the container are attached together. When the upper section 3 is attached with the container 3, the reduced outer surface of the column 2, the tapered portion 29 of the upper chamber 21 and the elongated channel 26 of column 2 are accommodated into the container chamber 31.

[0123] Referring to FIGS. 2b and 2C, the filter element 4 contained in the elongated channel 26 may be formed of a matrix 41 of microbeads 411 and 412, 413. In this case, one section comprises a plurality of microbeads 411 (upper section, i.e. “first section”) and another section comprises a plurality of microbeads 412 (middle section). Further, one section comprises a plurality of microbeads 413 (lower section, i.e. “second section”), which is configured to retain the microbeads 411 and 412 in the column, while smaller particles (i.e. the “first portion of particles”) and buffer can pass. Thus, the lower or “second” section comprising microbeads (413) of the microbeads matrix 41 is part of a constricting means to retain the above sections 411 and 412 in the column. In some embodiments, the elongated channel 26 of the column 2 has a substantially cylindrical inner surface which is filled with the microbeads matrix 41.

[0124] The microbeads matrix 41 according to the present invention refers to a size-continuous or size-discontinuous matrix of substantially non-compressible microbeads 101. The wording “size-continuous matrix” is intended to mean a gradual increase in size of microbeads 101. The wording “size-discontinuous” is intended to mean that the matrix comprises size-dependent microbeads sections, microbeads within each section have a specific diameter and are randomly diffused within the confinement of the elongated channel structure.

[0125] Non-limiting suitable non-compressible materials to be used for the microbeads 101 include stainless steel, magnetic, silica; insoluble and immiscible in blood and non-reactive therewith. Such microbeads 101 can also be made of other material, such as glass or ceramics, and/or one or more polymers, such as, for example, nylon, polytetrafluoroethylene (TEFLON™), polystyrene, polyacrylamide, sepharose, agarose, cellulose, cellulose derivatives, or dextran, and/or can comprise metals. Examples of microbeads 101 include, but are not limited to, magnetic isolation, magnetic particles, plastic particles, ceramic particles, carbon particles, glass isolation, metal particles, particles of complex compositions, microfabricated free-standing microstructures, etc.

[0126] In FIG. 2b, the column 2 of the filtration unit 1 is filled with a matrix 41 of microbeads which has three sections of microbeads 411, 412, and 413. While the section comprising a plurality of microbeads 411 acts as a filter, section 413 is part of the constricting means. As explained above, the microbeads in each of the sections of the microbeads 411, 412, and 413 may be preferably of substantially uniform size, i.e., comprising the distribution of diameters as usual for commercially available microbeads (cf. above). It is to be noted that the matrix 41 of microbeads may also have less sections (i.e. two or one) or more sections than the three sections disclosed in this illustrative example. The sections are arranged in layers, wherein the microbeads of the top layer have the smallest diameter (e.g. 80 μm), and the microbeads of the bottom layer have the largest diameter (e.g. 300 μm). The middle layer comprises microbeads with a diameter of for example 200 μm. The bottom layer is arranged at the lower opening of the column, such that the microbeads clog or constrict the aperture. The 80 μm sized microbeads of the top layer form effective interstices of about 10 μm and can be applied for separating CTCs, CICs and CTM.

[0127] A mode of implementation of the method for isolation of circulating rare cells is illustrated in FIGS. 3a to c. The biological sample 8 may be for example a buffy coat or whole blood sample. The whole blood sample may be diluted or the biological particles of interest may be enriched by any means, before application of the sample onto the microbeads matrix. For example, the density gradient centrifugation methods described in PCT/CN2017/072654, filed on behalf of the present applicant, can be applied to enrich the biological particles in the sample before applying onto the filtration matrix.

[0128] All of the methods steps described in the following can be performed manually or in an automated liquid handling system.

[0129] In the example method of FIGS. 3 a to c, 2 ml whole blood is used as a sample fluid for detecting circulating tumor cells, circulating immune cells (CICs) and/or microemboli. The sample is first separated by a density gradient centrifugation, resulting in two fractions, i.e. approximately 1 ml of plasma and mononuclear cells (MNCs), and 1 ml of RBCs and heavy cells, and/or CTC/CIC/microemboli caught with the RBC. The fraction containing the RBC and heavy cells is then applied onto a filtration matrix 41 comprised in a column 2. The filtration matrix comprises three sections of uniformly sized microbeads 411, 412, and 413. The sections are arranged in layers, wherein according to a preferred embodiment the microbeads of the top layer have the smallest diameter (50 μm), and the microbeads of the bottom layer have the largest diameter (300-500 nm). The middle layer comprises microbeads with a diameter larger than 60 nm, preferably 100-220 μm. The 50 μm sized microbeads of the top layer form effective interstices of about 7.7 μm and can therefore be applied for separating CTCs, CICs and CTM. The bottom layer of microbeads clogs the lower opening of the column. Thereby, the upper layers of microbeads are stably positioned in the column above the bottom microbead layer.

[0130] Filling of the microbeads matrix into the column can be performed by pipetting microbead suspensions (e.g. microbeads in water or in 20% ethanol) consecutively into the column 2 through the upper opening 24, with each suspension comprising microbeads of a specific size. The suspension with the smallest microbeads (“first section”) is pipetted into the column at last. The microbeads matrix can then be dried by centrifugation, and washed with buffer, e.g. PBS, before application of the biological sample.

[0131] In step a of FIG. 3a, the biological sample 8, optionally enriched after a density gradient centrifugation and potentially comprising CTCs, CICs and/or CTM is applied onto the microbeads matrix 41 through the upper opening 24. The biological sample 8 thereby slowly enters the first section, and biological particles that are larger than the interstice diameter of the first section, i.e. the top microbead layer, are retained. In step b of FIG. 3a, the column 2, which may be part of the filtration unit 1, and further may be positioned onto the container 3, is centrifuged for example at 5-20 g for 2 to 5 minutes, preferably 2 to 3 minutes. The centrifugation parameters may vary, depending on the sample and which biological particles are to be extracted. By centrifugation, the first portion of particles of the biological sample can run through the first section, as well as the microbeads of the other sections, including the second section at the lower opening of the column, and exit the column at the lower opening. In principle, gravity would suffice to allow the first portion of particles to pass the microbeads matrix, however, by centrifugation, the time for this passage can be reduced significantly. Such reduction in time is advantageous, as it reduces turn-around time and the likelihood that the particles of the biological sample are damaged during processing. After centrifugation, the fluid 812, e.g. blood plasma or the buffer used during enrichment of the biological particles, of the biological sample, and the first portion of particles 811, that have diameters or sizes below the critical size of 10 μm (i.e. the size of the interstices of the microbead layer with the smallest sized microbeads) have passed the microbeads matrix 41 with sections 411, 412, 413 and are collected in the container 3, while the second portion of particles 813 above the critical value, if any, are retained above or within the effective interstices of the microbeads. These particles of the second portion have sizes or diameters above 10 μm and are, therefore, trapped in the interstices of the smallest sized microbeads, i.e. the microbeads of the first section.

[0132] In step c of FIG. 3a, the container 3 and the column 2 are separated. The container 3, comprising the first portion of particles 811 below the critical value can be discharged or further processed, in particular by the method according to the invention. Thus, in step a″ of FIG. 3a, the particles 811 can be applied onto a further column comprising a plurality of microbeads having a diameter, which is smaller than the diameter of the beads in section 411. For example, the column can comprise microbeads with a diameter of 40 μm forming the first section, thereby providing filtering interstices of about 6 μm. By applying the first portion of particles to such column, a further separation into a fraction of particles, that have a size or diameter above 6 μm, and a fraction of particles, having a size below 6 μm, can be achieved.

[0133] The second portion of particles, trapped in the interstices of the matrix 41 of microbeads can be further processed according to the method of the present invention. In step d of FIG. 3b, the matrix 41 of microbeads and the second portion of particles are suspended in a buffer solution. For example, 2 ml PBS can be sufficient to form a suspension of particles and microbeads. By suspending the particles and the microbeads, the defined structure of the sections 411, 412 and 413 is lost, and the particles are released from the first section 411 into the buffer solution. This procedure ensures that all particles being trapped can now be isolated from the suspension, while being in a physiological, aqueous environment.

[0134] According to one of the preferred embodiments according to the invention, the column 2 of the filtration unit 1 comprising the matrix 41 of microbeads and the trapped biological particles is transferred onto a container 3′, which is filled with a buffer solution 9, e.g. 2 ml PBS. In this case, the lower opening 27 of the column 2 of the filtration unit 1 is immersed in the buffer solution in the container 3′. By aspirating the buffer solution into the column 2 via the lower opening 27 and repeated dispensing with a pipetting channel, the matrix 41 of microbeads is disrupted at least to a large extent. In particular, the bottom layer of the microbeads matrix comprising large microbeads to initially constrict the lower opening, i.e. to act as a constricting means, is disrupted and mixed with the smaller microbeads of the other microbead layers. Thus, the lower opening is no longer clogged by the larger microbeads, and the biological particles and the smaller microbeads can enter the container chamber 31 of the container 3′ through the lower opening 27 of the column 2.

[0135] According to one embodiment of the present invention, the microbeads of the second section, i.e. the microbeads with the larger diameter that clog the lower opening to act as a constricting means, are magnetic. Thereby, by placing the column 2 of the filtration unit 1 through or aside of a magnetic element, the magnetic microbeads are pulled away from the lower opening 27 and facilitate passing of the biological particles of the second portion of particles and smaller (non-magnetic) microbeads of the first section. The second portion of particles and the microbeads of the first section are thus collected in a second container 3′ (step e of FIG. 3b).

[0136] Alternatively, the lower opening 27 of the column 2 may be sealed, e.g. with a lid that fits onto the lower opening. In this case, the buffer solution 9 is applied through the upper opening 24 of the column 2 of the filtration unit 1 and the matrix 41 is suspended in the buffer solution by repeated dispensing and aspiration. This results at least in a partial disruption of the matrix 41. The trapped biological particles are thus released into the buffer solution, and microbeads, particles and the buffer solution form a suspension in the column. The suspension is then aspirated and transferred to a second container 3′ (step e of FIG. 3b).

[0137] In principle, the process of suspension and aspiration can be repeated so that all targeted particles are extracted from the filtration matrix.

[0138] In step f of FIG. 3b, the second container 3′ is centrifuged to allow separation of the microbeads 421 from the suspension 814 comprising the second portion of particles. For example, the container can be centrifuged at 200 g for 5 seconds, which allows complete separation of the microbeads and the particles due to the density and/or size difference. Alternatively, the separation of the particles and the microbeads can be achieved by means of gravity. Due to the density and/or size difference, the microbeads eventually settle at the bottom of the container, while the particles remain in solution. Furthermore, the container can be pre-filled with a separation gel or mineral oil with a lighter density than the microbeads part of the solution. This ensures that no particles are trapped in the microbeads pellets, thereby improving the overall capture efficiency. Moreover, use of a separation gel or mineral oil allows for an easy aspiration of the particles, as a distinct separation line is formed. This is important, for example, to ensure purity for downstream application.

[0139] After the microbeads have been separated from the suspension, the suspension 814 comprising the second portion of particles can be transferred to a further container 3″ (step g of FIG. 3b). This transferring step can be performed manually or by means of an automated liquid handling system. In the following step h of FIG. 3b, the suspension may be centrifuged at least at 100 g for 1 minute to pellet the targeted particles 815. For example, the container may comprise a reduced trap portion 36, where the pellet of particles forms. Such a trap portion can facilitate complete removal of the solution, e.g. by pipetting of decanting (step i of FIG. 3b). After removal of the solution, the particles can be suspended in a further buffer (step j of FIG. 3b). The particles can be suspended, for example, in appropriate buffers for staining or immune-affinity assays. Thus, the centrifugation step h of FIG. 3b allows an effective buffer exchange, streamlining any further down-stream assays. Alternatively, after step f, the second portion of particles may be directly transferred to a downstream assay, such as microscopic analysis, without transferring to a new container, concentrating, and buffer-exchange.

[0140] FIG. 3c exemplifies different downstream processes. The second portion of particles can be, for example, stained (step k of FIG. 3c), washed (step 1 of FIG. 3c), suspended (step m of FIG. 3c) before being analyzed by morphology imaging or other validation assays. These assays allow quantification of the particles, e.g. CTCs or CICs, in the sample.

[0141] Advantageously, multiple columns 2 and containers 3 can be processed in parallel, and easily integrated in automated liquid handling platforms. Thereby, throughput can dramatically increase. Moreover, the sample can be split during the method according to the invention. As explained above, the first filtrate comprising the first portion of particles can be further processed, such as by a further separation method or directly by validation assays. On the other hand, the second portion of particles, e.g. comprised in the suspension 814, can be further processed, e.g. by applying the suspension to another column comprising a first section or a microbeads matrix with interstices that are larger than the interstices of the first section 411 of the microbeads matrix 41. For example, a first section that effectively filters at a critical size of 18 μm can be used to separate particles below and above this size.

[0142] FIG. 4a shows a further device according to a preferred embodiment of the present invention in the form of a filtration unit 1 with a column 2 and a container 3. As described above for FIG. 2a, the filtration unit 1 (and its column and container 2 and 3, respectively) can have a substantially cylindrical or rectangular shape. The device can only comprise a column 2, in that case it may be adapted to be coupled to a rack or a reservoir. The column 2 and container 3 of one filtration unit 1 are designed so that they can be assembled together or with any other counterparts from another filtration unit 1 of the same type, for instance a column 2 can be assembled successively with different containers 3. Suitable material for the filtration unit 1 includes among other: polypropylene, polyethylene, glass. The filtration unit 1 may be formed via injection molding. It is to be noted that in several embodiments, the various parts of the filtration unit 1 do not need to be made of the same material.

[0143] According to this embodiment, the column 2 of the filtration unit, the upper chamber 21, the one or more lateral walls 22, anchor protrusions 23, the upper opening 24, the pipetting channel coupling 25, the tapered portion 29, the elongated channel 26, which is joined to the tapered portion 29, the lower opening 27 are formed as described for FIG. 2a. The elongated channel 26 may contain a filter element 4, as described above for FIGS. 2b and 2C (see FIG. 4b).

[0144] As described for FIG. 2a, the column 2 of the filtration unit 1 can be made in one piece, for example by means of injection molding, or the column 2 may comprise a main body and a lid part 210.

[0145] The lid part 210, its lateral walls 211, a connection notching 212, internal walls 213 and a slot 214 may be provided as described for FIG. 2a.

[0146] The container 3 of the filtration unit 1 may comprise an open upper end, through which the lower part of the upper section can be entered. The container 3 may comprise a container chamber 31, one or more lateral walls 32 of the container, a flange 33, bottom walls 35, one or more wall extensions 37, as described for FIG. 2a.

[0147] The bottom end 34 of the lower chamber 31 may be provided with a centered protrusion 39 with an upper portion 391 and a lower portion 392. The centered protrusion 39 is provided to fit through the lower opening 27 of the column 2 into the elongated channel 26, thereby preventing that the filtration matrix localized in the elongated channel 26 enters the container chamber 31. Preferably, a passage is formed between the lateral walls of the elongated channel and the lateral walls of the protrusion, which allows a liquid to flow through the passage and into the container chamber. Such passage may, for example, have a width of 10 to 40 μm, preferably about 20 μm. Thus, while liquid and smaller particles can flow from the column into the container chamber through the passage, larger particles, in particular microbeads above this size, are stably positioned in the column.

[0148] The container may also include a lid to permit safe transportation of the container 3 and its contents received from the column 2 for further processing, and to reduce the risk of losing and/or contaminating the contents in container 3.

[0149] In the preferred embodiment, the column and container are designed in a detachable manner, wherein e.g. a reduced outer surface of the column 2 is smaller than the inner surface of the container 3, so that frictional force is applied when the column and the container are attached together. When the upper section 3 is attached with the container 3, the reduced outer surface of the column 2, the tapered portion 29 of the upper chamber 21 and the elongated channel 26 of column 2 are accommodated into the container chamber 31. The centered protrusion 39 can then fit into the elongated channel 26.

[0150] FIG. 4b illustrates a container 3, comprising a centered protrusion with an upper portion 391 and a lower portion 392. In this embodiment, the upper portion has a diameter that fits into the lower opening 27 of the elongated channel 26 (not shown), while the diameter of the lower portion 392 does not fit into the lower opening of the elongated channel, but supports the lateral walls of the lower opening. The lower portion 392 thereby acts as a holding device that ensures that the protrusion 39 does not completely fill the elongated channel 26.

[0151] FIG. 4c illustrates a column 2 and a container 3, wherein the elongated channel 26 of the column 2 is filled with a matrix 41 of microbeads. The microbeads matrix 41 comprises one section of microbeads 411, which act as a filter. The centered protrusion 39 of the container 3 serves as a constricting means that prevents the microbeads of the first section to pass through the lower opening 27 of the elongated channel 26.

[0152] FIG. 4d illustrates a column 2 and a container 3 according to the invention. While the column 2 is provided as described for FIG. 4a, comprising an upper chamber 21, one or more lateral walls 22, anchor protrusions 23, an upper opening 24, a pipetting channel coupling 25, a tapered portion 29, an elongated channel 26, a lower opening 27 and a lid part 210, lateral walls 211, a connection notching 212, internal walls 213 and a slot 214, the container 3 comprises an open upper end, through which the lower part of the upper section can be entered, a container chamber 31, one or more lateral walls 32 of the container, a flange 33, bottom walls 35, one or more wall extensions 37, as described for FIG. 4a, but is devoid of a centered protrusion. Such container can be used for processing steps not requiring a constricting means, or for processing steps where a constriction means is provided in alternative forms, e.g. as second section of microbeads, plug, or porous filter positioned at the lower opening of column 2. The container 3 may be provided as described in FIG. 2. In particular, the bottom end 34 of the lower chamber 31 may be provided with one or more bottom walls 35 forming a tapering portion (i.e. the distance between opposing walls—or the distance between opposing sides of one or more continuous lateral walls—gets smaller when moving in a downward direction). The bottom end 34 may be further provided with a reduced trap portion 36 at the lower end of the bottom walls 35 (not shown).

[0153] FIG. 4e illustrates a filtration unit 1 comprising a column 2 and a container according to FIG. 4d, wherein the column 2 is positioned on top of the container 3. As the container does not contain a protrusion, the lower opening of the column 2 is not blocked by the container, but rather does not contact walls of the container 3.

[0154] In the example method of FIGS. 5a and b, the filtration unit according to FIG. 4a to e is applied. As described for FIG. 3a to c, 2 ml whole blood can be used as a sample fluid for detecting circulating tumor cells, circulating immune cells (CICs) and/or microemboli. After density gradient centrifugation, the fraction containing the RBC and heavy cells is then applied onto a microbeads matrix 41 comprised in a column 2. The microbeads matrix contains one section of uniformly sized microbeads. This section acts as a filter. The microbeads preferably have a diameter of about 50 μm, thereby forming effective interstices of about 7.7 μm. The protrusion of the container 3, acting as a constricting means, blocks the lower opening of the column and thereby retains the section of microbeads in the column. Preferably, a passage is formed between the lateral walls of the elongated channel and the lateral walls of the protrusion, which allows a liquid to flow through the passage and into the container chamber. Such passage may, for example, have a width of 10 to 40 μm, preferably about 20 μm. Thus, while liquid and smaller particles can flow from the column into the container chamber through the passage, larger particles, in particular microbeads above this size, are stably positioned in the column. The effective sealing of the lower opening of the column by the protrusion of the container in particular also facilitates the suspension step, wherein (after separation of the first portion of particles) the second portion of particles and the microbeads of the first section are suspended in buffer solution.

[0155] Filling of the section of microbeads into the column can be performed by pipetting microbead suspensions (e.g. microbeads in water or in 20% ethanol) consecutively into the column 2 through the upper opening 24. The section can then be dried by centrifugation, and washed with buffer, e.g. PBS, before application of the biological sample, in order to prevent formation of air bubbles. Moreover, by centrifugation a dense and compact matrix is obtained. Filling can be done by the same automated liquid handling system.

[0156] In step a′ of FIG. 5a, the biological sample 8, optionally enriched after a density gradient centrifugation and potentially comprising CTCs, CICs and/or CTM is applied onto the microbeads matrix 41, i.e. the first section comprising a plurality of microbeads, through the upper opening 24. The biological sample 8 thereby slowly enters the microbeads matrix, and biological particles that are larger than the interstice diameter of the microbeads are retained at the top of the microbeads matrix. In step b′ of FIG. 5a, the column 2, which may be part of the filtration unit 1, and further may be positioned onto the container 3, is centrifuged, at 5-20 g for 2-5 minutes, preferably 2-3 minutes, depending on the sample. Thereby, the first portion of particles of the biological sample can run through the microbeads matrix, exit the column at the lower opening, and run through the passage formed between the lateral walls of the elongated channel of the column and the protrusion of the container. In principle, gravity would suffice to allow the first portion of particles to pass the microbeads of the section, however, by centrifugation, the time for this passage can be reduced significantly. After centrifugation, the fluid 812, e.g. non-targeted particles or the buffer used during enrichment of the biological particles, of the biological sample, and the first portion of particles 811, that have diameters or sizes below the critical size of 10 μm (i.e. the size of the interstices of the microbead section) have passed the microbeads matrix 41 and are collected in the container 3, while the second portion of particles 813 above the critical value are retained above or within the effective interstices of the microbeads. These particles of the second portion have sizes or diameters above 10 μm and are, therefore, trapped in the interstices of the microbeads.

[0157] In step c′ of FIG. 5a, the container 3 and the column 2 are separated. The container 3, comprising the first portion of particles 811 below the critical value can be discharged or further processed, in particular by the method according to the invention, as described for FIG. 3a, step a″.

[0158] The second portion of particles, trapped in the interstices of the microbeads matrix 41 can be further processed according to the method of the present invention. In step d′ of FIG. 5a, the column 2 of the filtration unit 1 comprising the microbeads matrix 41 and the trapped biological particles is transferred onto a container 3′, which is filled with a buffer solution 9, e.g. 2 ml PBS. In this case, the container 3′ does not comprise a centered protrusion, but is formed to accommodate the elongated channel of the column such that the lower opening of the elongated channel is not blocked by any wall of the container 3′ when the column 2 is positioned onto the container 3′. Transferring can be in particular performed, when the microbeads matrix is substantially dry. The lower opening 27 of the column 2 of the filtration unit 1 is immersed in the buffer solution in the container 3′ (FIG. 5b, step e′).

[0159] As shown in FIG. 5b, step f, the filtration matrix and the trapped particles can enter the container chamber of the container 3′. The buffer solution may furthermore be aspirated into the column 2 via the lower opening 27 and repeatedly dispensed with a pipetting channel to ensure that the microbeads matrix 41 is disrupted and exits the column through the lower opening. Thereby, the biological particles and the microbeads of the first section can enter the container chamber 31 of the container 3′ through the lower opening 27 of the column 2 and form a suspension.

[0160] The empty column is then removed from the container (step g′).

[0161] Further processing of the sample in step h′ to separate the microbeads from the sample can be performed as described above for FIG. 3b, step f. Processing of the sample in step i′ to transfer the separated second portion of particles from the microbeads to a new container can be performed as described above for FIG. 3b, step g. Concentrating the second portion of particles at the bottom of the container, e.g. by centrifugation, in step j′ can be performed as described above for FIG. 3b, step h. Removing the supernatant and resuspending the second portion of particles in an appropriate buffer in step k′ can be performed as described above for FIG. 3b, steps i and j. Finally, process steps k to m as described above for FIG. 3c can be performed. Alternatively, and as explained above for FIG. 3b, after step f, the separated second portion of particles may be directly transferred to a downstream analysis, e.g. microscopic analysis.

[0162] FIG. 6 illustrates a general work-flow for the method of this invention. At first, a column is provided comprising at least a first section of microbeads. A biological sample is then applied to the first section, and the particles in the sample are separated from each other. The first portion of particles passes the filtration matrix and is collected in the flow-through. The second portion of particles remains in the interstices of the first section. The separation can be achieved by gravity or centrifugal force. The first portion of particles can be either discarded or collected. The collected first portion of particles can be applied onto a further column. The second portion of particles is suspended in a buffer solution. The suspension can be collected, for example by means of gravity or a centrifugal force. In the following, the second portion of particles is separated from the microbeads of the first section, e.g. by means of gravity or a centrifugal force. After separation, the particles may be concentrated and analyzed.

[0163] According to the invention, an automated liquid handling system may be capable of carrying out the work-flow as illustrated in FIG. 6. Modern laboratory equipment comprises the means of e.g. filling a column with microbeads forming a matrix, filling a column with a biological sample, positioning a column in a rack or centrifuge, means for aspirating a liquid sample, means for centrifugation, etc. Thus, according to the present invention, there may also be provided a computer program that is stored on a non-transitory computer readable medium and that contains instructions that, when executed by one or more processors of an automated liquid handling system, carries out the method according to any of the embodiments described herein. For example, the instructions may follow the work-flow as illustrated in FIG. 6.

[0164] FIG. 7 illustrates a health screen routine which can make use of the method according to the present invention. As a first step, whole blood samples are taken from the cancer patient, and particles are isolated according to the method of the present invention. The cell morphology of the isolated particles is analyzed by imaging. If microemboli are detected, further assays such as NAATs (nucleic acid amplification techniques) or CLIA (chemiluminescence immunoassays) are performed to validate the metastatic potential of the detected microemboli.

Examples

Size Distribution of Microbeads

[0165] In order to quantify the size distribution of commercially available microbeads, silica beads with average diameters of 20 μm and 30 μm were analyzed by light microscopy. As shown in FIG. 8a and FIG. 8b, image analyses were performed on several imaged microbeads (assuming perfectly circular microbeads), illustrating a deviation of about 1 μm to 2.4 μm in diameter for beads having an average diameter of 20 μm, and of up to 4 μm for beads having an average diameter of 30 μm, respectively.

[0166] Filter performance on buffy coat Four columns, each comprising an elongated channel with the lower opening formed as a cross to support microbeads, were prepared by filling each column with a microbead matrix composed of three layers. For all columns, the bottom layer was formed from 500 μm sized microbeads, and the middle layer was formed from 220 μm sized microbeads. The microbeads of the top layers were of size 20 μm (column ID W1031-20), 30 μm (column ID W1031-30), 40 μm (column ID W1031-40) and 50 μm (column ID W1031-50) for the four columns, respectively, thereby providing interstice sizes of 3.1 μm, 4.6 μm, 6.2 μm and 7.7 μm.

[0167] Buffy coat was conventionally prepared by centrifugation (about 300 g for 15 minutes) of in total 8 ml whole blood that had been collected using an anticoagulant, e.g. EDTA, and that was split in four centrifugation tubes. In total 840 μl of the buffy coat layer was aspirated from the four tubes and pooled. A 20 μl sample was taken, and the cell content (white blood cells (WBC), red blood cells (RBC), platelets (PTL)) was analyzed with a Sysmex XS-500i system. The remaining isolated buffy coat layer sample was split into four 200 μl aliquots, and each aliquot was pipetted onto one of the above referenced four microbead matrix columns. The four columns were centrifuged at less than 20 g for 2 minutes and each flow-through was collected for analysis with the Sysmex XS-500i system. These flow-through samples contained the first portion of particles of the buffy coat layer sample. After centrifugation, 200 μl buffer solution (PBS) was pipetted onto each microbead matrix, dispensed and aspirated several times to form a suspension of microbeads and the second portion of particles in the buffer solution. The suspensions were transferred to four new containers, and the containers were centrifuged at 50 g for 3 minutes in order to separate the second portion of particles from the microbeads. Samples were taken from the supernatants containing the second portion of particles and subsequently analyzed with the Sysmex XS-500i system.

[0168] Cell concentrations, as obtained from the Sysmex XS-500i analysis, are compiled in Table 3.

TABLE-US-00003 TABLE 3 Cell concentrations (white blood cells (WBC), red blood cells (RBC), platelets (PTL)) for the buffy coat sample, the flow-through after the first centrifugation (first portion of particles), and the supernatant after the second centrifugation (second portion of particles). Composition of Composition of second Composition of first buffy coat portion of particles portion of particles WBC RBC PLT Column WBC RBC PLT WBC RBC PLT 10.sup.9/L 10.sup.12/L 10.sup.9/L ID Volume 10.sup.9/L 10.sup.12/L 10.sup.9/L 10.sup.9/L 10.sup.12/L 10.sup.9/L Average 6.2-9.4 7-8.5 2-4 diameter (μm) Cell 15.41 0.06 1693 W1031-20 200 μl 14.24 0.04 1198 0 0 571 concentration W1031-30 200 μl 8.74 0.02 490 3.59 0.05 1380 W1031-40 200 μl 5.31 0.02 251 10.98 0.05 1467 W1031-50 200 μl 0.87 0.01 108 14.35 0.05 1584

[0169] As can be derived from the obtained cell concentrations before and after processing, the column comprising 20 μm sized microbeads in the top layer (column ID W1031-20) successfully retained white blood cells and red blood cells, while filtering out smaller sized platelets to a significant extent. Red blood cells were not retained by columns comprising larger microbeads with effective interstices of 40.6 μm, 6.2 μm and 7.7 μm (column IDs W1031-30, W1031-40, W1031-50). On the other hand, white blood cells were partially retained by columns with 30 μm and 40 μm sized microbeads. Considering the average sizes of the analyzed cell populations, these results demonstrate that the average diameter of the microbeads in the top layer determines the cut-off value for the filtration process. Furthermore, the data demonstrate that RBCs, which are able to deform and to squeeze through capillaries of only 3 μm in diameter (e.g. Jones et al., Measurement science in the circulatory system, Cell Mol Bioeng. 2014; 7(1):1-14)), are still retained in the microbeads matrix with 20 μm sized microbeads, providing interstices of 3.1 μm. Hence, the method is also suitable to enrich cells that are in general prone to deformation.

[0170] To further study the cell distributions with respect to the cell sizes, in the Sysmex XS-500i analysis tool the group of white blood cells was broken down into neutrophils, lymphocytes, monocytes and basophils. The results are compiled in Table 4.

TABLE-US-00004 TABLE 4 Cell concentrations (neutrophils (NEUT), lymphocytes (LYMPH), monocytes (MONO), basophils (BASO)) for the buffy coat sample, the flow-through after the first centrifugation (first portion of particles), and the supernatant after the second centrifugation (second portion of particles). Composition of Composition of second Composition of first buffy coat portion of particles portion of particles NEUT LYMPH MONO BASO Column NEUT LYMPH MONO BASO NEUT LYMPH MONO BASO 10.sup.9/L 10.sup.9/L 10.sup.9/L 10.sup.9/L ID 10.sup.9/L 10.sup.9/L 10.sup.9/L 10.sup.9/L 10.sup.9/L 10.sup.9/L 10.sup.9/L 10.sup.9/L Average 10-12 6-18 12-20 12-15 10-12 6-18 12-20 12-15 10-12 6-18 12-20 12-15 diameter (μm) Cell 0.6 11.74 2.86 0.21 W1031-20 0.61 10.95 2.25 0.16 0 0 0 0 concentration W1031-30 0.39 6.35 1.87 0.13 0.08 3.34 0.07 0.1 W1031-40 0.3 3.45 1.4 0.16 0.38 8.86 1.63 0.1 W1031-50 0.08 0.61 0.17 0.01 0.56 11.17 2.4 0.22

[0171] The results in Table 4 give a more differentiated view on the filtration efficiency of the microbeads matrix versus cell populations. The filtration efficiency is not equal for all cell types within the group of WBCs, but rather varies significantly for columns with 30 and 40 μm sized microbeads. While neutrophils are retained to 83% and monocytes to even 96% by 30 μm sized microbeads, lymphocytes and basophils are only retained to 66% and 57%, respectively. Using microbeads of 40 μm diameter, the filtration efficiency for these four cell types ranges from 28% to 62%. Hence, it is possible to specifically enrich a certain cell population from a heterogeneous sample by choosing microbeads of a specific diameter.

[0172] Samples of the buffy coat and the separated blood cells, as described in Tables 3 and 4, were also analyzed by light microscopy. For this process, the samples were transferred to new containers, centrifuged at 80 g for 5 minutes and the supernatant was discarded. The pelleted cells were resuspended in 50 μl buffer (PBS), stained with Romanowsky stain and 2 μl of each sample was pipetted onto a conventional microscope cover slip. FIG. 9a shows a microscope image of the buffy coat sample, as isolated from the whole blood sample by centrifugation. This sample contains a distribution of heterogeneously sized cells. FIG. 9b shows a microscope image of a sample, as obtained as flow-through after application of the buffy coat sample onto column W1031-20 and centrifugation. FIG. 9c shows a microscope image of a sample, as obtained after suspension of the trapped cells and the microbeads matrix of column W1031-20 and centrifugation. Compared to FIG. 9b, a significant amount of larger sized cells is observed in FIG. 9c, thereby qualitatively confirming the results of Table 3. FIG. 9d shows a microscope image of a sample, as obtained as flow-through after application of the buffy coat sample onto column W1031-50 and centrifugation. FIG. 9e shows a microscope image of a sample, as obtained after suspension of the trapped cells and the microbeads matrix of column W1031-50 and centrifugation. Comparing FIG. 9d and FIG. 9e, it is evident that the column with 50 μm sized microbeads did only retain a small fraction of cells, while the majority of cells was found in the flow-through. Cells that were retained by the matrix comprising 50 μm sized microbeads were further analyzed with respect to their sizes. FIGS. 9f and 9g show microscope images in accordance with FIG. 9d and FIG. 9e, respectively, except that the magnification was increased. The diameter of the encircled cells was analyzed (assuming perfectly circular cells) and the results are summarized in the following Table 5.

TABLE-US-00005 TABLE 5 Image analysis of cells, as obtained in the flow-through (first portion of particles) and retained in the microbeads matrix (second portion of particles) Diameter [μm] First portion of Second portion of particles (FIG. 9f) particles (FIG. 9g) Min 9.35 13.12 Max 11.03 14.41 Average 10.53 13.93 Count 6 4

[0173] Based on these data, at least a trend towards larger cells in the retained portion can be derived.

Filter Performance on a Red Blood Cell Suspension

[0174] A column with a microbead matrix with three layers was prepared. The top layer consisted of microbeads of 30 μm diameter, the middle layer consisted of microbeads of 220 μm diameter, and the bottom layer was formed from 50 μm sized microbeads. The effective interstice diameter of the top layer was 4.6 μm.

[0175] A 0.8% red blood cell (RBC) suspension was added onto the microbead matrix, and the column was centrifuged at less than 20 g for 2 minutes. After centrifugation, the column was placed under a light microscope to visualize the top layer (FIGS. 10a, 10b). Agglutinated RBCs (3 to 10 cells) could be observed to be trapped within the interstices of the top layer (exemplary spots labeled with arrows).

[0176] Importantly, RBCs and agglutinated RBCs, which are relatively constant in size, can be used as a reference ladder for optimizing the microbeads matrix to other target cells, such as circulating tumor cells.