CA2263976C - Devices incorporating filters for filtering fluid samples - Google Patents

Abstract

Devices and use thereof, the device comprising a filter and a means for region specific compression of the filter. Alternatively, the device comprises a filter; a region containing the filter; a fluid access port to the region containing the filter; a fluid egress port from the region containing the filter; and a lateral fluid flow path through the filter connecting the fluid access port to the fluid egress port. Alternatively, a single step assay device whereby fluid movement through the device occurs substantially solely due to action of capillary force, the device comprising a filter; a region containing the filter; a fluid access port to the region containing the filter; a means for retarding movement of particles through a peripheral filter surface; a fluid egress port from the region containing the filter a lateral fluid flow path through the filter connecting the fluid access port to the fluid egress port whereby sample fluid substantially devoid of particulate matter is released from the filter through the egress port; and, an exit region fluidly connected to the egress port. Use of the device optionally comprises means for producing an assay result in an exit region of the device.

Description

?WO 98/08606101520253035CA 02263976 1999-02-25PCT/US97/ 149391DESCRIPTIQNDevices Incorporating Filters For Filtering Fluid SamplesField of The InventionThis invention relates to devices comprising filtersfor filtering fluid samples. In a particular embodiment,the filter-containing devices filter cells or particulatematter from biological samples and introduce the filtrateinto a capillary space, and operate without the use of anyexternally applied force.Background ArtWith the advent of point of care testing in hospitalemergency departments, it has become increasingly importantto develop diagnostic products which are simple, rapid andconvenient for the user to perform. This need has arisenbecause health care workers in an emergency department needresults rapidly with a minimum. of time given to theperformance of a diagnostic test. Providing a diagnosticresult in minutes allows a physician to treat a patient assoon as possible.Point of care diagnostic tests frequently are performedCellsand particulate matter in biological samples can interfereon biological samples, such as whole blood or urine.with fluid flow ix: a test device, and thus impair themeasurement of analytes in the biological fluid.in blood,with spectroscopic measurements,For example, red blood cells can interfereand as the hematocritvaries, the volume of plasma in a given volume of bloodvaries. To overcome these problems, red blood cells areseparated from plasma to allow for a more defined anduniform sample.As a further example, urine can contain lymphocytes thatcan affect spectroscopic measurements,Thus,or debris from a biologicaland flow throughfilters and capillaries. a device to filter outcells, particulate matter,?WO 98/086061015202530357CA 02263976 1999-02-25PCT/U S97/ 149392sample can improve the quality of an analytical procedureperformed on the sample.To achieve removal of particulates, incorporation ofa filter into an assay device has been described in theprior art. For example, U.S. Patents 4,477,575; 4,753,776;4,987,085; and 5,135,719 refer to blood filter deviceswhereby a transverse flow of blood through a filter resultsin the separation of red blood cells from plasma. Sealingof the filter in the device to achieve effective filtration,and not allow sample to bypass the filter, has been aproblem in the prior art. A small capillary or gap betweenthe filter and the filter chamber walls often existed dueto poor initial sealing, or because the gap formed withtime. As a consequence, particulates in a fluid sampletravel in the capillary space or gap rather than throughthe filter.filter decreases the filtration efficiency,Particulate matter which travels around therepeatability,and may cause the filter to be unacceptable for certainapplications. Techniques, such as using glues, tapes andthe like have been used to seal a filter into the filterchamber of such devices. The use of these materials toaffectsealing.sealing has produced variable, and often poorAdditionally, these sealing methods resulted inabsorption of variable amounts of the sealing compound intothe filter.Another drawback of prior art filter devices isconsequent to use of a relatively short transverse fluidflow path through a filter.a conventionally shaped filterThe transverse flow path in(a filter with a length,width and substantially thinner depth)between the top and the bottom of the filter, the filterFiltersthis relatively shortis the distancedepth commonly referred to as the filter thickness.are generally 0.1 mm to 6 mm thick,flow path produces relatively poor separation efficiency.A longer flow path would allow more particulates to bethus, increasing the separationU.S. Patents 4,678,757; 5,135,719; 5,262,067removed from fluid,efficiency.?WO 98/08606l0l52O253035CA 02263976 1999-02-25PCT/U S97/ 149393and 5,435,970, comprise filters treated with materials suchas carbohydrates, agglutins and lectins, to affectseparation of red blood cells from plasma. However, due tothe short fluid flow path, the filtrationefficiencies in these teachings are not optimal.Appl. No. 893004l6.8, describes methods and devices whichbind red blood cells to treated polycationic filters.relativelyEuropeanHowever, treatment of filters introduces an additionalprocess in device fabrication. A filter-device design thatdoes not require treatment would be advantageous since thefilter would be too costly and device manufacture would beless complicated; less complicated device designs are easierand more cost—effective to manufacture.Embodiments with longer transverse flow paths have alsoU.S. Patent 5,139,685 (“the’685 patent”), describes a cylinder of stacked filters, soAlthoughthe ‘685 patent has a relatively long transverse fluid flowbeen disadvantageous, however.that the device has a relatively long flow path.path pursuant to stacking of discrete filters, applications‘685 patent,discrete filters are stacked and are under an appliedof this technique are limited. Namely, in thepressure to achieve an efficient filtration of red bloodcells from plasma. The pressurization of the filters isnecessary to achieve a fast and efficient separation ofparticulate matter from the sample.The relatively large amount of space required and theconfiguration of a design of the ‘685 patent does not lenditself to a convenient point of care diagnostic testing.Point of care diagnostic testing is facilitated by smallerand more convenient designs that can be easily manipulatedby a health care worker, designs which are capable of beingfed into hand-held instruments that provide quantitationDevices capable of being fed into hand-should be small andPreferably a point of careof assay results.held instruments (such as a reader)flat, and have smooth surfaces.device would not require an externally applied pressure.?WO 98/08606101520253035CA 02263976 1999-02-25PCT/US97ll49394Thus, there is a need for an efficient, compact, cost-effective filtration device. There is also a need for ameans to effectively seal a filter within a device, wherebythe fluid flow path is optimized, leading to increasedfiltration efficiency. Most desirably, there is a need fora sealing means that makes device fabrication tolerancesless crucial and device manufacture more economical.Description of FiguresFigures 1A, 1B, 1C, and 1D show one embodiment of adevice in which Figure 1A is a top view of base 10. Figure1B is a cross-section of base 10. Figure 1C is a top viewof an assembled device taken along plane 1B-1B in Figure1A. Figure 1D is a cross section of an assembled deviceincluding a filter 20, lid 18,lD—lD in Figure 1C.2B, and 2C show another embodiment of aand base 10 taken along planeFigures 2A,device in which Figure 2A is a top View of base 10. Figure2B is a cross—section of base 10 taken along plane 2B—2Bin Figure 2A. Figure 2C is a cross section taken along thecross—sectional plane in Figure 2B of an assembled deviceincluding a filter 20, lid 18, and base 10.Figures 3A, 3B, and 3C show another embodiment of adevice in which Figure 3A is a top View of base 10. Figure3B is a cross—section of base 10 taken along plane 3B-3Bin Figure 3A. Figure 3C is a cross section taken along thecross—sectional plane in Figure 3B of an assembled deviceincluding a filter 20, lid 18, and base 10.Figures 4A, 4B, 4C,of a device in which Figure 4A is a top View of base 10.4D and 4B show another embodimentFigure 4B is a cross—section of base 10 viewed along theplane 4B—4B of Fig. 4A.the same plane as Fig. 4B, of an assembled device includinga filter 20, lid 18, and base 10.of an embodiment comprising a lid cavity 42,Figure 4C is a cross section, alongFigure 4D is a top Viewdepicted indashed lines. Fig. 4E is a cross section of Fig. 4D takenalong the plane 4E—4E.?1015202530CA 02263976 2004-10-1579565-525Figures 5A, 5B, and 5C show another embodiment ofa device in which Figure 5A is a top View of base 10.Figure 5B is a cross—section of base 10 viewed along theplane 5B—5B of Fig. 5A. Figure 5C is a cross section, alongthe same plane as 5B, of an assembled device including afilter 20, lid 18, and base 10.Figures 6A, 6B, 6C and 6D show another embodimentof a device in which Figure 6A is a top view of base 10.Figure 6B is a cross—section of base 10, viewed alongplane 6B—6B of Fig. 6A. Figure 6C is a top view of anassembled device of this embodiment. Figure 6D is a crosssection, viewed along the plane as 6D—6D of Fig. 6C, of anassembled device including a filter 20, lid 18, and base 10.Disclosure of the InventionThe present invention provides for simple andrapid filtering of biological samples, whereby a sample canbe analyzed in the same device or a different device.‘A broad aspect of the invention provides a devicecomprising: a lid, a base substantially parallel to the lid,a fluid access port within the lid; a fluid permeable filtercomprising a region for fluid access in fluid communicationwith the fluid access port and a region for fluid egress,wherein the filter comprises a substantially smaller depthdimension in comparison to its length and width dimensions,wherein the length/width plane of the filter is orientedwithin the device substantially parallel to the lid andbase, and wherein the peripheral surfaces of the filter aresealed within the device; a fluid flow path through thefilter that is a lateral flow path from the region for fluidaccess through the filter to the region for fluid egress;?l0152025CA 02263976 2oo4—1o—1579565-525aand a fluid egress port comprising a capillary space fluidlyconnected to the region of fluid egress from the filter,wherein fluid flows from said filter to said capillaryspace.Another broad aspect of the invention provides amethod for assaying fluid samples, the method comprisingadding fluid to the fluid access region of the device asaforesaid.In one embodiment, the present disclosure teachesthe use of lateral flow through filters and the use ofcapillary force to cause the exit of filtrate fluid fromfilters and into a capillary space.Alternative embodiments of a device of theinvention comprise are where the device comprises a filterand a means for region specific compression of the filter.the device comprises a filter;Alternatively, a regioncontaining the filter; a fluid access port to the regioncontaining the filter; a fluid egress port from the regioncontaining the filter; and a lateral fluid flow path throughthe filter connecting the fluid access port to the fluidegress port. Alternatively, a single step assay devicewhereby fluid movement through the device occurssubstantially solely due to action of capillary force, thedevice comprising a filter; a region containing the filter;a fluid access port to the region containing the filter; ameans for retarding movement of particles through aperipheral filter surface; a fluid egress port from the?WO 98/08606l0l520253035CA 02263976 1999-02-25PCT/US97/ 149396region containing the filter; a lateral fluid flow paththrough the filter connecting the fluid access port to thefluid egress port, whereby sample fluid substantially devoidof particulate matter is released from the filter throughand,the egress port; an exit region fluidly connected tothe egress port. Use of the device optionally comprisesmeans for a producing an assay result in an exit region ofthe device.List of Reference Numeralsl0 Base12 Filter Cavity14 Fluid Access Port15 Fluid Access Region of Filter 2016 Fluid Egress Region of Filter 2017 Exit Region18 Lid20 Filter/Filter Matrix/Membrane22 Compression Structure23 Support Bar24 Dead Space of Filter Cavity 1226 Sample Reservoir28 Filter Supports/Posts30 Vent Holes32 Filter Stays34 Grooves36 Lateral Compression Region of Compression Structure 2238 Proximal Compression Region of Compression Structure 2240 Distal Compression Region of Compression Structure 2242 Lid CavityMo es For Ca r in Inven ' nThis invention describes novel devices comprisingfilters for the rapid filtering of samples, particularlychemical, environmental, or biological samples, and prefer-ably for introduction of the filtered sample into acapillary space. This invention can be utilized in any?CA 02263976 2004-10-1579565-52101520253035travels in one direction;7device format in accordance with the teachings providedherein. For example, although assay device filters ofconventional configuration are discussed, it is understoodthat the principles of the application apply to devices withother configurations. ha a preferred embodiment, theinvention is used with the technology of devices described5,458,852 to Buéchler.in U.S. Patent No. .Aspects of the‘invention are discussed below.n v F ‘d wfluid flow will be described as follows:L t r ‘dAs used herein,a conventional filter has a width, length, dimensions andsubstantially smaller depth (“thickness”) dimension.. Fora filter» with transverse flow isperpendicular to the length and width of the filter,is predominantly in a direction parallel to the depth ofthe filter. lateral flow is predominantlyparallel to the length or width planes of a filter.a lateral flow path is a distance greatersuch dimensions,andConversely,Alternatively,than a transverse flow path distance through a filter,Vtypically these flow paths are oriented perpendicular toeach other. In one embodiment of the invention,fluid flow path is through a filter connecting a fluidaccess port to a fluid egress port, where the flow path isgreater than or equal to that of the greatest crosssectional distance of the filter as determined perpendicularto any point along the flow path.Conventional device filters comprise some degree ofcapillarity. To a certain extent, fluid moves through thefilter due to capillary forces created, e.g.,diameter pores or the close proximity of fibers.move through such a filter with or without externalOn a micro scale relative to the filter’s overallby smallFluid maypressure.dimensions, fluid travels in multiple directions as a resultOn a macro scale, fluidthrough the filter in aof capillary forces. however,i.e.,a lateral’?WO 98/08606101520253035CA 02263976 1999-02-25PCT/US97/1 49398predominantly lateral or transverse direction to a locationwhere fluid can exit the filter.To filter a sample, either lateral or transverse fluidflow requires at least one fluid input surface and at leastone fluid egress surface. A fluid input surface is definedas the filter surface where unfiltered sample fluid isplaced in contact with the filter; the fluid egress surfaceis a filter surface from which the majority of a filteredexits.sample fluid (“filtrate” or “filtration liquid”)As discussed below, a smaller amount of fluid can exit fromperipheral surfaces in certain embodiments. A peripheralsurface is defined as being a surface that is not a fluidinput surface and not a fluid egress surface. Fortransverse flow, the input and egress surfaces are the topand bottom surfaces of a conventionally shaped filter, e.g.,the lengthAlternatively, for a filter having lateral fluid flow, inputsurfaces parallel to and width planes.surfaces and egress surfaces can be on the top, bottom orany surface which is not a peripheral filter surface.In accordance with the present disclosure, a preferredflow directionality through a device filter is lateral flow.Compared to transverse flow, lateral flow has severaladvantages. First, the fluid flow path can be dramaticallyincreased in a filter of a standard configuration. For afilter of conventional shape, lateral flow yields greaterfiltration efficiency than transverse flow since the lateralfluid flow path is longer than the transverse fluid flowpath.have a thickness of between 0.1 mm and 6 mm, approximatelyFor example, conventional assay filters generally2 mm is most common, with a length and width substantiallylonger than the thickness usually on the order of severalcentimeters. Thus, lateral flow yielded greater filtrationefficiency with minimum effects on the device's shape.Second, lateral flow within a filter allowed the additionof fluid to any region of the filter that is not a fluidegress region, so long as fluid could laterally flow throughthe filter to the fluid egress region thereof. In lateral?W0 98l08606l0l520253035CA 02263976 1999-02-25PCT/U S97/ 149399flow devices, addition of fluid to regions of the filterwhich are not fluid egress regions allowed fluid to enter2 times)the filter at an effectively larger area (approx.than by entering only on one side. The larger area forfluid entrance provided a more efficient use of the filter,maximizing flow rate through the filter and minimizing thepotential for clogging with particulate matter which is tobe filtered from a sample.Additionally, incorporating a single filter rather thana stack of several filters in a device conserves devicespace and permits the filter to be easily situated on adevice, allowing a plethora of possible designconfigurations.F" e MVarious filter materials are available for filteringcells and particulate matter from biological samples. Forexample, cellulose fibers, nylon, glass fibers, polyesterfibers or combinations of these materials are useful to makefilters that remove debris from samples, e.g., cells fromurine and red blood cells from plasma.The filter is preferably chosen such that the pores ormatrix of the filter do not getfibrous clogged byparticulate matter from the sample. In the case ofseparating red blood cells from plasma,bind,to separate from blood and pass through the filter.Filtersmaterial.that isBorosilicate glass microfiber filters permit filtration offilters generallyretain or retard the red blood cells and allow plasmacan comprise a fibrous matrix or porousA preferred filter is a fibrous matrix filterborosilicate microfibers.made of glasswhole blood samples by permitting the sample (includingparticulate matter such as red blood cells)the filter. the filter retardsred blood cells and allows plasma to move through the fiberWhen theseand cells and plasma moved through theto penetrateFor whole blood samples,matrix at an nonretarded, higher flow rate.filters were used,?CA 02263976 1999-02-25WO 98/08606 PCT/US97/1493910filter, the plasma moved further ahead of the red bloodcells.101520253035Alternative filters can also be used which have a moreporous structure, for example filters comprisingnitrocellulose, acrylic copolymers, or polyethersulfone.These filters, generally, functioned differently thanfilters comprising fiber matrices, in view of the fact thatthey have pore-like passages typically of uniform diameters.Typically, a porous filter is selected such that the porediameters are smaller than the diameters of the particulatesdesired to be separated from a sample. These filters retainrather than retard the red blood cells,generally do not penetrate the filter beyond its surface.skilled in the will that if theparticulate matter in a sample is approximately the samei.e., red cellsOne art recognizesize or greater than the pores of a filter, the particulatematter will rapidly clog the pores and slow or stop fluidflow therethrough.Thus, in accordance with the present disclosure, variousfilters can be used. A filter may be one of severalcommercially available filters including but not limitedto Ahlstrom Cytosep (Mt. Holly Springs, PA) or MicroFiltration System's (Dublin, CA) glass fiber media. U.S.Patents 5,186,843; 4,774,039; 4,629,563, and 5,171,445,cover the compositions of these and like media.Sample ReservoirPreferably, a sample reservoir accomplishes severalfunctions: 1) it delimits a volume which is sufficient toachieve an assay result, and thus facilitates a deviceuser's ability to provide the suitable volume; 2) itaccomplishes the foregoing while allowing for a diverserange of input volumes in a manner which does not impairan assay result; and, 3) a reservoir that is a capillaryspace helps to prevent fluid escape. Irx a preferredembodiment, the sample reservoir contained a fluid volume?WO 98/08606101520253035CA 02263976 1999-02-25PCT7US97H493911approximately 100 times the volume needed for downstreamprocessing of a sample.6B, 6C and 6D,reservoir 26 comprising a capillary space is incorporatedAs depicted in Figure 6A, a sampleinto the device, whereby sample was contained in thecapillary space of the sample reservoir, and the reservoirwas in fluid communication with an edge, top and/or bottomof the filter 6D).capillary space for introducing the sample to the filteris that the fluid,environmental or biological fluid, contained in a capillary(Fig. An advantage of utilizing afor example, a hazardous chemical,space will tend not to spill or leak from the device.” of of a 'l rPreferably the peripheral surfaces of the filter aresealed within the device: 1) so that fluid must flow throughthe filter; and 2) ‘to prevent the fluid sample, e.g.,particulates, from flowing around the filter in a capillary“Sea ' eri her 1 Sbetween the filter and the device, thus contaminating thefiltrate. Sample that travels around the filter in acapillary space, rather than through the filter, can enterthe exit region 17. When unfiltered fluid enters exitregion 17, the filtering efficiency of the device isdecreased. “Sealing” of the peripheral surfaces need notbe liquid-tight,also comprises the ability to retard to flow of liquid andsealing in accordance with the inventionparticulates, or particulates into spaces between the filterand the walls of the device adjacent to the filter.There are several methods to achieve sealing of theperipheral surfaces of a filter. Preferably the sealingis liquid-tight, although some liquid release is acceptableso long as a low resistance fluid flow path outside thefilter does not result. In one embodiment, the sealingpermits liquid between the device wall and the filter, butretards the development of a capillary space along theperipheral surfaces and the sealing also may serve to retainparticulate matter in the filter and not in any space along?WO 98108606101520253035CA 02263976 1999-02-25PCT/U S97/ 1493912peripheral surfaces, due to compression. In any event,there is preferably particle—tight, more preferably liquid-tight and most preferably fluid—tight sealing of the deviceat or near the fluid access region 15 of filter 20.Regardless of the flow path direction, filter surfacesmay be sealed using one or a combination of the followingtechniques: pressure-adhesive tapes, glues, or sealants.Such techniques require careful placement of the sealantalong edges of the filter and the side walls of filtercavity l2. A preferred liquid sealing of the peripheralsurfaces is achieved by a pressure fit. A pressure fit maybe achieved by placing a slightly oversized filter intofilter cavity 12 such that all the peripheral surfaces ofthe filter are in contact with the walls of the filtercavity. Concerning length and width dimensions, a filteris preferably l—lO% and more preferably 1 to 5% larger thanthe filter cavity into which it is to be placed to ensuredirect contact. Compression of the depth dimension isdiscussed in greater detail below. Direct contact betweenthe filter and the filter cavity walls discourages fluidfrom traveling between the peripheral surfaces of the filterand the filter cavity walls, because a capillary space doesThus, theperimeter or side edges of the filter will maintain contactexist between the filter and the device walls.with the walls of the filter cavity 12 as depicted in Figure1A.The filter must have a degree of resilience such thatTheconventional media described herein have these propertiesit may be squeezed and hold its shape over time.and can be employed as disclosed herein to effectively sealparticulates and/or liquid. The more pliable a filter is,the larger the filter must be relative to the cavity intowhich it is placed, so as to assure that the filter providespressure against the cavity walls and a low resistance fluidflow path is avoided.To prepare a device in accordance with the invention,the shape of the filter must be approximately identical to?WO 98/08606l01520253035CA 02263976 1999-02-25PCT/US97/1493913l2,(Figure 1A).be of any three dimensional shape,Filter cavity 12 maye.g.,A presently preferredthe filter cavity,trapezoidal,rectangular, rounded or the like.filter shape is that of the filter cavity 12 of Figure 1A-1D.Region Specific Compression of the FilterPreferred embodiments of the invention make use ofcompression of the filter in distinct areas to limit or(e.g.,debris) within the filter and to prevent particulate matterretard the movement of particulate matter cells orfrom escaping the filter and traveling along the peripheralfilter surfaces. In the case of preventing fluid fromof thesee Figure 2, 3,along peripheral surfaces filter, a(e.g., 4 or SA)in filter cavity 12 helps to prevent the formation offlowingcompression structure 22capillary gaps between the filter 20 and a surface to whichit is in contact, e.g., lid 18 or a surface defining cavity12. Capillary gaps are to be avoided as they provide a lowresistance flow path to fluid exit region 17, and therebypermit unfiltered sample to contaminate the filtrate.In addition to region specific compression, liquidsealing of the filter peripheral surfaces by use ofcapillary force, glues, pressure—sensitive tapes, orsealants can be used to prevent particulate escape and flowof liquid along the peripheral surfaces. It is advantageousto avoid glues, pressure sensitive tapes or sealants sincethey have a tendency to lose their sealing properties withtime; and the sealant in such materials tends to leachthrough the filters,region specific filter compression leads topotentially affecting the filtrate.In contrast,seal and functions without any additives orthus,fabrication process and avoids potential contamination ofthe filtrate.Structures using region specific compression are shown,a lastingadditional parts; it decreases the complexity of thefor example, in the embodiment depicted in Figure 4.?WO 98/08606101520253035CA 02263976 1999-02-25PC1VUS97?493914Referring to the top View Figure 4A, a compression structure22 isthickness of filter 20 by compression structure 22 and anare 1 to 50%preferably 1 to 30% of the native thickness of the filter.shown. Preferred degrees of compression of theabutting surface such as lid 18, and moreAccordingly, in preferred embodiments of the device onlyspecific regions of a filter are compressed; all regionsand flow rate is notof therapid filtration isof the filter are not compressed,unduly impeded. Thus, one advantagethatpresentinvention is effective andachieved.The cross section view of an assemble device in Figure4C displays a preferred height change between filter cavity12,results in dead space 24and compression structure 22.(e-9-,filter 20 upon placement of filter 20 in cavity 12.This height changein figure 4C) underneathDead space 24 effectively leads to liquid sealing, sinceand thereforeThecapillary force is low for dead space 24 due to a relativelydead space 24 has minimal capillary force,does not draw any fluid away from or out of filter 20.large gap between filter 20 and filter cavity 12.Region specific compression leads to liquid sealing yetThenotalso facilitates rapid fluid flow through the filter.filter the deadcompressed to the same degree as the filter regions betweenregion depicted above space iscompression structure 22 and an abutting surface. The poresor matrices of the filter are not appreciably compressedin this area and fluid flow therethrough is facilitated.It is advantageous to keep the filter noncompressed inembodiments where maximum flow rate from the fluid egressregion is desired.dead certaincompression structure designs and is useful for severalIn summary, space 24 results fromFirst, it has minimal capillary force and drawsThus,along the respective filter surface adjacent the dead space,forcing fluid to flow through the filter. thereasons .no fluid into its cavity. a liquid seal is formedSecond,?WO 98/08606101520253035CA 02263976 1999-02-25PCT/US97/1 493915filter adjacent to the dead space is not compressed andtherefore the pore or fiber structure within the filterremains unchanged; such filter configuration is in contrastto the prior art, and advantageously produces higher flowrates.As noted, preferred degrees of compression of filter20 by compression structure 22 and lid 18 are 1 to 50%,preferably 1 to 30% of the native thickness of the filter.To achieve such compression, compression structure 22 needRather,compression structure 22 may be comprised of Inultiplenot be limited to one uniform level or height.sections at the same or different heights. Figure 5Adisplays an embodiment of the present invention in whichcompression structure 22 is comprised of sub-regionsincluding: support bar 23, lateral compression regions 36,proximal compression region 38, distal compression region40. Each sub—region may be sized to yield compression thatfacilitates sealing, filtration, or flow rate properties.In the embodiment of Figure 5, the combination of supportbar 23, lateral compression regions 36, and distal compres-sion region 38 force filter 20 to be in contact with lid18 forming a preferably liquid tight seal above each sub-region, thus facilitating prevention of flow along theperipheral surfaces of the filter. Distal region 40 doesnot form a liquid~tight seal, but permits liquid to exitfilter 20 is notuniformly compressed, but rather is compressed only aboveat fluid egress region 16. Accordingly,the sub-regions of compression structure 22.Anothercompression is the ability to retard particulate matter fromadvantageous aspect of region specificdesignated regions of the filter. Namely, to retard partic-ulate matter from reaching either the peripheral edges orthe fluid egress region of a filter. Retardation of partic-ulate movement occurs since compression of a filter causesconcomitant compression of the fiber spacing and/or poresin the filter; the compression of these microstructures?WO 98/08606101520253035CA 02263976 1999-02-25PCT/US97/1493916makes it more difficult or impossible for particulate matteror cells to travel therethrough.One skilled in the art will recognize that the selectivecompression of the filter at the compression structure 22is not required for the separation of the particulate matterfrom the sample, but rather, such compression is but oneembodiment than can be utilized for sealing the peripheralsurfaces of the filter in a device and for modulatingparticulate movement. In a preferred embodiment, noparticulate matter can exit along the peripheral surfacesor the fluid egress region of filter 20. In an alternativeembodiment employing compression structure 22, particulatematter is retarded in its movement through the filter, butnevertheless is capable of exiting the filter; in thisembodiment, the exit region preferably holds the amount of(via aliquid that is required to produce an assaymaterial(s) or modality(s) for achieving an assay resultappreciated by those of skill in the art), where that volumeis less than the volume of fluid that flows through hefilter ahead of the retarded particulate matter.Exit Region in Fluid Communication with Fluid Egress Regionof FilterIn a preferred embodiment, after the particulate—freefluid has passed through the filter it is preferably drawnfluid e.g., lD).Preferably, exit region 17 comprises higher capillarity thanfilter 20 to facilitate fluid flow therebetween.preferred embodiment of the invention utilizes capillarityinto a exit region 17 (see, FigThus, aforce, whereby fluid egress area 16 of the filter isimmediately adjacent to exit region 17, and region 17 isa capillary space. Due to the use of capillarity as taughtherein, fluid leaves the filter without an external pressureand uniformly fills the capillary space of exit region 17,and fluid will not enter any region with lower capillaritythan the filter,can be used to cause egress of fluid from the filter ande.g., dead space 24. Thus, capillary force?WO 98/086061O1520253035CA 02263976 1999-02-25PCT/U S97/ 14939l7into an exit region 17 without the application of anexternal pressure such as hydrostatic pressure. In accord-ance with this embodiment, compression of the filter bycompression structure 22, in particular distal compressionregion 40, should not cause the pores of the filter to bemade sufficiently small such that the capillary forceholding the fluid within the filter is greater than thecapillarity of exit region 17.Device AssemblyAdvantageously, devices that incorporate filters thatfunction by lateral flow, can be designed so that theoverall device thickness is not constrained by the filterthickness.Therequire assembly and joining of several parts.described herein generallyLid 18 andbase 10 can be fabricated from conventional materialsfiltration devicescompatible with chemical, environmental or biological fluidsto be assayed, for example: a plastic material such asacrylic, polystyrene, polycarbonate, or like polymericmaterials; as well as silicon composites, such as siliconsemiconductor chips; glass; or metal. In the case of plasticlid 18 and base 10 may be fabricatedusing thermal injection molding technology or machining.polymeric materials,In the case of fabricating the lid and base from siliconcomposites, micromachining and photolithographic techniques,commonly used in the field of electronics, can be utilizedto create chambers and capillaries.The base 10 and lid 18 are contacted together in orderto form the physical configuration desired to achieve aparticular result. Ultrasonic welding, adhesives, physicalinterfitting and heat welding are some of the methods thatmay be used to join base 10 and lid 18. For example, withembodiments comprising a lid of silicon composite orplastic, and a base of plastic or silicon composite, thebase and lid can be joined with adhesives.?CA 02263976 2004-10-1579565-5210152025303518L In a preferred embodiment, the plastic surfaces of base10, lid 18, or both are made hydrophilic or “wettable”,whereby the contact angle between the sample fluid meniscusand the base 10 and lid 18 is decreased. There are severalways to decrease the contact angle including but not limited,to corona discharge, plasma treatment or the drying downof various surfactants or proteins onto surfaces. Inaccordance with standard methodologies, exposing a plasticsurface to a corona discharge or plasma gas results in theformation of functional groups on the surface. The surfacechemistry as well as the degree of hydrophobicity are thusmodified and can be used for a variety of applications.For example, time gates, as described in U.S. Patentn5,458,852 to Buechler,-can be indbrporatedvatwthe.fluidegress region to provide an incubation time for the sample1-wi*1ih':in‘ th-‘e 'fiil't',"er.ucamnlss 7One skilled in the art will recognize, in view of thepresent disclosure, that the filter cavity can have manypossible design configurations or embodiments.tion concepts disclosed herein can be incorporated into avariety of devices that can be used in various assays. Thepresentlyfollowing examples demonstrateembodiments and are not intended to limit the invention.E_x.amL>_l:;Qn_eAn embodiment of the present invention is shown inFigure 1. Base 10 was fabricated using injection moldingtechnology and was made of white acrylic copolymer (PolysarNAS@ 30, Polysar, CT). The overall devicelength, width and thickness were 8.7, 3.5 and 0.26 cmrespectively; The surface of base 10 was made hydrophilicby a corona discharge treatment.In accordance with standard methodologies, filter cavity12 (Figure 1A, 1B) was formed into base 10. The filtercavity had a bilaterally symmetrical trapezoidal shape, withInc., Madison,The filtra-preferred‘?WO 98/0860610152O253035CA 02263976 1999-02-25PCT/U S97/ 1493919parallel sides 1.0 and 1.34 cm long and 0.72 cm apart. Afilter 20, slightly oversized 1—30% preferably l—5% relativeto filter cavity 12, was fitted into the cavity (Figure 1D).The filter (# GBlOOR, (“MFS”),Dublin, CA) consisted of borosilicate glass fibers;thickness was 0.038 cm and had an absorption volume ofMicro Filtration Systemsitsapproximately 50 ul.A clear plastic lid 18 (Figure 1C, 1D)base 10 by ultrasonically welding using a Branson 941 ABDanbury CT) set at 50 joules and 40Bonding lid 18 to base 10 slightly compressed thewas coupled towelder (Branson Inc.,psi.filter 20.prevent fluid and particle flow around the peripheral edgesof filter 20.14 was located directly over the filter.This compression created a seal that served toReferring now to Figure 1D, fluid access portLid 18 and base10 formed a capillary space in exit region 17 adjacent tofluid egress region 16 of filter 20. Despite the increasein capillarity by compressing filter 20, exit region 17comprised sufficient capillarity to draw filtrate fluid,e.g. plasma, out of filter 20. In this embodiment the exitregion comprised a capillary space, where a cross sectionof exit region 17 immediately abutting fluid egress regionof filter 20 had dimensions approximately 25 pm by 1.0 cm.The volume encompassed by this exit region is preferablya volume sufficient to permit enough fluid to flow throughthe device so that an effective assay result is obtained(via a material or modality appreciated by one of ordinaryskill in the art),with fluid and flow stops;(not illustrated)gaseous fluids but not liquid fluids.after which the exit region is filledfor such an embodiment an escapeport is present that permits release ofA use of the embodiment depicted in Figure 1 was asfollows: fresh human whole blood (70 ul), that was drawnin a Vacutainer® Blood Collection Tube with acid citratedextrose (ACD), was added to fluid access port 14. Someof the blood was immediately absorbed into filter 20 andthe remainder formed a small droplet covering fluid access?CA 02263976 1999-02-25WO 98/08606 PCT/US97/1493920port 14. As the fluid moved by lateral flow through filter20, two distinct flow fronts formed. Since the filter10l520253035retarded flow of particulates, the two flow fronts consistedof a clear plasma front preceding a dark front of red bloodcells. Thus, the plasma front reached egress region 16 ofthe filter before the red cells, and particulate depletedfiltrate entered exit region 17 before the red blood cellflow front reached the end of the filter.Example TwoAnother embodiment of this invention is depicted inFigure 2. Base 10 is fabricated using injection moldingtechnology and is made of white acrylic copolymer (PolysarNAS® 30, CT).length, width and thickness were 8.7,The overall device3.5 and 0.26 cmThe surface of base 10 was made hydrophilicPolysar, Inc., Madison,respectively.by a corona discharge treatment.Base 10 comprising compression structure 22 was formedby conventional methods. A slightly oversized filter20(Figure 2C) was fitted over compression region 22 causingdead space 24 to be defined (Figure 2C). The filter wasl—30%, preferably l—5% larger than the portion of the filtercavity 12 which did not include the dead spare 24. Thefilter (MFS filter, GBl00R Micro FiltrationSystems, Dublin, CA) consisted of borosilicate glass fibers.cat. no.Its thickness was 0.038 cm and had an absorption Volume ofapproximately 50 ul. Thus, there was sealing between fluidaccess port 14 and fluid access region 15 of filter 20, sothat essentially the only way sample could enter the filterwas through region 15.Advantageously, this embodiment comprises dead space2C). fluid couldaccumulate jJ1 a capillary space between the filter and24 (Figure In prior art devices,device walls around the filter. The formation of fluid inthe capillary space is believed to result from a relativelyhigh capillary force created by the close contact of thefilter with the filter cavity and by the deformability of?WO 98/08606101520253035CA 02263976 1999-02-25PCT/U S97/ 1493921the filter.since it can provide a route whereby sample does flowFluid formation in such regions is undesirableentirely within the filter, and if particulates enter thespace separation efficiency is decreased. The presentinvention decreases potential fluid formation between filter20 and a wall of cavity 12 by means of a space24)long as capillary force is used to move fluid through the(dead spacethat has virtually no capillary force. Therefore, sofilter fluid exits only from the designated region, namely,fluid egress region 16.A clear plastic lid 18 (Figure 2C) was coupled to thebase by ultrasonic welding using a Branson 941 AE welderset at 50 joules and 40 psi. Bonding of lid 18 to base 10slightly compressed filter 20 above compression structure22: the filter was compressed by 1—50%, preferably l—30%relative to its native thickness. This region specificcompression created a sufficient seal to serve to preventfluid flow over the peripheral surfaces of the filter atthat region and to retard particles within the filtercompressed at that region. Fluid access port 14 was locateddirectly over the trapezoid—shaped filter. As shown in Fig.2C,the filter 16 adjacent to the downstream edge of filter 20.lid l8 and base 10 defined a fluid egress region fromA cross section of exit region 17 immediately adjacent fluidegress region 16 had dimensions approximately 25 um by 1.0cm.a thin filmlamination may be applied to the filter to increase theFor the embodiment depicted in Fig. 2,filter’s rigidity, to avoid having the filter fall into deadspace 24 when sample is added. The lamination also preventsbending of the filter in a region where the filter islead to flow of fluidparticulates along a peripheral surface causing contamina-tion of the filtrate,Pressure sensitive tape such as ARcare ®7396Glen Rock, PA) isunsupported; bending can andand is generally to be avoided.(AdhesivesResearch, Inc., one example of a?WO 98/08606101520253035CA 02263976 1999-02-25PCT/US97/1493922commercially available plastic lamination film which hasbeen used.The embodiment of Figure 2 was used as follows: Freshhuman whole blood (70 ul), was drawn in a Vacutainerm BloodCollection Tube with ACD, and was added to fluid access port14.20, and the remainder formed a small droplet covering fluidSome of the fluid was immediately absorbed into filteraccess port 14.through the filter, as the fluid laterally moved throughfilter 20,fronts consisted of a clear plasma front preceding a darkDue to the retarding of particulate flowtwo distinct flow fronts formed. The two flowfront of particulate matter comprising red blood cells.Thus, the plasma front reached the downstream edge of filter20 before the red cells, and by the time particulate matterreached the downstrean1 edge, clear plasma had alreadyentered exit capillary 17. Exit capillary 17 containedmaterial(s)/modality(s) for conducting an assay on thefiltrate fluid, e.g., plasma, thus an assay was performedsubstantially without contamination from particulate matter,e.g., red blood cells.In general, fluid continues to flow from filter egressregion 16 into exit region 17 until the fluid sample ataccess port 14 is depleted into the device or until theWith thisconcept in mind, an embodiment of a device of the inventionvolume that exit region 17 can contain is filled.was designed to hold a specific volume of filtrate (e.g.,in exit region 17, as in devicesPatent 5,458,852 to Buechler;exit region contained the specified volume of liquid, fluidThe fluid flow stoppedwhether or not sample remained at the access port 14 orplasma) for example,described in U.S. once theflow through the device stopped.sample reservoir 26; thus, the addition of too much samplehad no negative affect on device function.As depicted in Table 1, use of the embodiment of Example2 yielded a flow rate of plasma out of filter 20 of up to8 ul/min. Use of this embodiment provided recovery of atleast 6 ul of plasma. The effect of varying the area of?WO 98/08606101520253035CA 02263976 1999-02-25PCT/U S97/ 1493923filter compression at the distal compression region 40 isshown in Table 1. As the area of the distal compressionregion 40 was decreased from 0.041 in2 to 0.004 1&3, thepercent area of compression of the filter 20 concomitantlyto 3%,through the filter increased from 1 ul/min to 8 Ml/min ata constant filter compression of 40%. This data showed thatthe flow rate of fluid from the filter can be controlleddecreased from 32% and the flow rate of plasmaby the area of the filter that is compressed.Table 1EFFECT ON FLOW RATE BY VARIATIONS OF FILTERAREA COMPRESSED AT DISTAL REGION 40(40% FILTER THICKNESS COMPRESSION)FLOW RATEAREA1 % AREA COMP2 ul/MIN0.041 32 10.028 22 20.014 11 40.004 3 81 Surface area of region 40 of structure 22 in square inches2 9o of total filter area that is compressedEx 1 4Figure 3 represents an alternative embodiment of aThefabricated by conventionalfiltration device in accordance with this invention.embodiment in Figure 3 ismethodologies, such as described in Examples 1 and 2. Anaspect of this embodiment is the extension of compressionstructure 22 along two additional sides (lateral compressionof base 10.regions 36 capable of compressing the filter,regions 36) Providing lateral compressiondiminishedthe possibility that fluid could create a low resistancepath along the peripheral surfaces of the filter, whereby?WO 98/08606lO1520253035CA 02263976 1999-02-25PCT/US97/1 493924particulate matter could contaminate the filtrate. Inaddition, the lateral compression regions of compressionstructure 22 provided additional support for the filter 20,minimizing the potential for the filter 20 to touch thebottom of filter cavity l2 in any aspect of dead space 24.Example FgurFigure 4 represents an alternative embodiment of aThisfabricated in accordance with standardfiltration device in accordance with the invention.embodiment wasmethodologies, such as those described in Examples 1 and2. An aspect of this embodiment is compression structure22 which comprises lateral compression regions 36 andproximal compression region 38 so that the perimeter offilter 20 is supported and capable of being compressed.A compression structure 22, as shown in Figure 4A, isparticularly useful when a large bolus of sample is addedThus,given along the edges of the filter will minimize thepotential for the filter to touch the bottom of the filterto the device at a rapid rate. the extra supportcavity 12 in any aspect of dead space 24.The embodiment described in this example, and depictedin Figure 4, provides a larger and more stable compressionstructure 22 for filter 20.dead space 24 is beneficial because it has essentially noAs previously described herein,capillary force, and therefore, dead space 24 remains freeof fluid throughout the operation of the embodiment depictedin Figure 4.Depending on the manner of sample addition to thefiltration device, that is, whether a large bolus of sampleis added quickly to the filter,of the filter at the compression region can be increasedto about 50% of the filter thickness.compression, impacts the flow rate through thefilter. Generally, as the filter is compressed more thanabout 5% of the filter thickness, the flow rate of thesample moving in the filter is decreased.the degree of compressionThis amount ofhowever,?WO 98/08606101520253035CA 02263976 1999-02-25PCT/US97/1493925As illustrated in Figure 4D and 4E, lid 18 incorporatesa lid cavity 42 which is positioned above filter 20 whenlid 18 is assembled to base 10; the lid cavity does notextend into the area above the filter at the compressionstructure 22. Thus, compression structure 22 is capable ofcompressing filter 20 to any degree necessary to seal andhold filter 20 in filter cavity 12 without compressing thecomplete filter 20 against the lid 18, thereby potentiallyslowing overall fluid flow through filter 20.Table 2 shows the effect of varying the areas of theproximal 38 and lateral 36 regions, wherein the area ofdistal compression region 40 was held constant. The resultsshowed that as the total areas were increased from havingno lateral or proximal compression region to a combined areaof 0.05 inz, the flow rate decreased from 5 ul/min to 0.5ul/min.Thus, Table 2 provides data showing the impact on flowrate due to variations in the combined area of proximalregion 38 and lateral region 36 of compression structure22.EFFECT OF VARIATION OF COMBINED AREAS OFPROXIMAL REGION 38 AND LATERAL REGION 36,ON FLUID FLOW RATE(AREA OF 40 WAS CONSTANT)FLOW RATEAREA} % AREA COMP2 pl/MINO O 50.01 8 20.025 20 10.05 39 0.51 Combined area of proximal region 38 and lateral regions36 of structure 22 in square inches2 % of total filter area that is compressed?WO 98/086061015202530CA 02263976 1999-02-25PCT/US97/1493926Example FiveFigure 5 illustrates another embodiment of compressioncompression structure 22 wasSB), thatinto two separate dead spaces.structure 22. Specifically,extended to comprise support bar 23 (Figure 5A,divided dead space 24Support bar 23 of compression structure 22 added additionalsupport to the filter in the area of the filter 20 whichis adjacent and slightly downstream to fluid access port14.differential compression as compared to other regions ofIn addition, support bar 23 can provide for athe compression structure 22. Support bar 23 can providejust enough compression on a small surface area of thefilter such that flow of sample between a peripheral filtersurface and the cavity wall is eliminated, but not so muchcompression as to impede or cease fluid flow through thedevice.Table 3 depicts data for flow rate based on variationsin the area of distal compression region 40 of compressionstructure 22. Table 3 provides empirical data that relatesflow rate, plasma recovery volume, and % filter compressionThus, Table 3illustrates that compressing filter 20 from 4% to 31% offor the embodiment shown in Figures 5A—C.the native filter thickness at distal compression region40, decreased the flow rate from about 3 ul/min to 2 ul/minThe dataof Table 3 was taken by adding fresh human whole blood towhile maintaining region specific compression.the inlet port of devices embodied as illustrated in Figure5. Each such device consisted of base 10 (Polysar,Incorporated, Madison, CT, NAS® 30)to lid 18 with filter 20 (Ahlstrom Cytosep,0.066 cm thick)Polysarultrasonically bondedLot 94—49B,placed therebetween.?WO 98/08606101520253035CA 02263976 1999-02-25PCT/US97/ 1493927Table 3Distal Filter Flow rate ofCompression(%) Filter(ul/min.)4 315 323 2.531 2Plasma RecoveryVolume(111)Plasma Exiting®CDO\OWthe of thestructure 22 that contacts filter 20 is held to a minimum.the flow ratePreferably, surface area compressionIf one were to compress the entire filter,and filtrate fluid recovery from filter 20 would substan-tially decrease because the effective porosity of the totalfilter would be lowered.In each of Examples 2-5, the sealing of filter 20comprised use of compression in certain regions of filter20.sion structure 22 was made.With each example, a variation in the shape of compres-The choice of a compressionregion configuration for use with a particulate sample isappreciated readily by one of ordinary skill in the art inView of the present disclosure, based on the extent to whichone wishes to emphasize parameters such as filter support,flow rate or particle retardation. For example, inclusionof compression structure 22 in Figure 3 reduced the leakageof red blood cells into the plasma and increased separationefficiency while maximizing flow rate.Exa e 6Figure 6A-D illustrates a presently preferred embodimentThis(Figure 6D)of the invention. embodiment provided a samplereservoir 26 which safely contains a fluidsample. Sample reservoir 26 preferably comprises acapillary space, and is in fluid communication with filter20 and exit region 17.?WO 98/08606l01520253035CA 02263976 1999-02-25PCT/US97/ 1493928The embodiment depicted in Figure 6 was fabricated asfollows: base 10 was fabricated using injection moldingtechnology and was made of white acrylic copolymer (PolysarNAS® 30). The overall device length, width and thicknesswere approximately 8.7, 3.5 and 0.26 cm, Thesurface of base 10 was made hydrophilic by treatment withrespectively.a gas plasma in accordance with standard methodologies,alternatively corona discharge treatment was used to makethe surface hydrophilic.As depicted in Figure 6D, a slightly oversized filter20 was fitted over compression structure 22 and a dualregion dead space 24. Filter 20 (Ahlstrom CytoSep® filter,PA)and polyester fibers.Mt. Holly Springs, comprised a mixture of cellulose,borosilicate glass, Its thicknesswas 0.063 cm and had an absorption volume of approximately200 pl.added,and positioning of filter 20.Lid 18,welded to base 10. The lid had dimensions of approximately8, 2.5 and 0.1 cm. Bonding lid 18 to base 10 resulted ina slight compression of filter 20 of approximately 4%To enhance filter support, filter posts 28 werethese posts are believed to improve the stabilityformed of clear plastic, was ultrasonicallyrelative to its native thickness. Region-specificcompression at structure 22 created a seal that helped toprevent fluid and particle flow over peripheral surfacesof filter 20.Tables 4-6 contain flow rate data for exit region 17.The data for Tables 4-6 were obtained from experimentswherein at least 15 pl of filtrate fluid was obtained.For example, as indicated in Table 4, a 25% compressionof filter 20 by compression structure 22 slowed the flowin the filter.Increasing the compression to about 50% decreased the flowrate of the sample by’ as much as 23%rate by up to 61%.?WO 981086061015202530CA 02263976 1999-02-25PCT/U S97/ 1493929Table 4EFFECT ON FLUID FLOW BY FILTER COMPRESSION (THICKNESS)BYDISTAL COMPRESSION REGION 40 OF COMPRESSION STRUCTURE 22% Flow Rate % decreaseCompression pl/min in fluidflow1 6.4 Control25 4.9 23%50 2.5 61%Table 5 shows the effect of filter compression bysupport bar 23 on the fluid flow from the filter. A con-stant 1% compression of filter 20 at the distal compressionAs the compression of the filtertheregion 40 was the control.thickness by support bar 23 increased from 1% to 50%,flow rate dropped from 6.4 ul/min to 1.7 M1/min.laDl:_§EFFECT ON FLUID FLOW BY FILTER COMPRESSION (THICKNESS)BY SUPPORT BAR 23% Flow Rate % decreaseCompression ul/min in fluidflow1 6.4 Control25 3.0 53%50 1.7 73%Table 6 shows the effect of filter compression at bothdistal region 40 and support bar 23, on fluid flow rate fromthe filter.compression from 1% to 50%,6.4 #1/min to 1.8 Ml/min.As the compression regions increased filterthe flow rate decreased from?WO 98/08606101520253035CA 02263976 1999-02-25PCT/U S97/ 1493930Table 6EFFECT ON FLUID FLOW BY FILTER COMPRESSIONDISTAL REGION 40 AND SUPPORT BAR 23(THICKNESS) BY% Flow Rate % decreaseCompression ul/min in fluidflow1 6.4 Control25 2.9 55%50 1.8 72%The sample flow rate decreased since pores or matricesof the filter are made smaller by compression and theresistance to flow is increased. As disclosed herein,compression of the filter at compression structure 22 canbe as great as 50% if lid 18 has been modified to compriselid cavity 42, as shown in Figure 4D, without a substantialdecrease in fluid flow rate.Fluid access port 14 was located over sample reservoir26.access port 14 can be situated over the sample reservoir26, Lid 18and base 10 formed a fluid exit region 17 (Figure 6D)One skilled in the art will recognize that the fluidas well as a portion of filter 20 (Figure 6D).adjacent to the downstream edge of filter 20 (i.e., adjacentfluid egress region 16 of filter 20). The fluid exit regionpreferably can comprise a capillary space. In an embodimentwhere exit region 17 comprised a capillary, exit region 17had cross—sectional dimensions adjacent filter egress region16 of 25 pm by 1.0 cm to create a capillary gap (alsoreferred to herein as a capillary space). The dimensionof a fluid egress region comprising a capillary can varyfrom about 0.1 pm to about 100 um, and most preferably fromabout 10 pm to 50 pm.The capillarity of exit region 17 was important forembodiments where fluid was drawn into the exit regionwithout an external applied pressure at any point before?“K)%M?M101520253035CA 02263976 1999-02-25PCT/U S97/ 1493931or along the flow path. For such embodiments, the relativecapillarity of filter 20 and the exit region 17 weredesigned to provide fluid movement from the filter into theexit capillary. Thus, exit region 17 will have the highestfilter 20 will have intermediate capillarityThecapillarity of the sample reservoir should not be so greatcapillarity,and sample reservoir 26 will have lowest capillarity.as to prevent fluid from. entering the filter and thedownstream capillaries of the device, particularly devicesPatent 5,458,852.As depicted in Figure 6D,as described in U.S.sample reservoir 26, is influid communication with the top, bottom and edge of filter20.area of the filter in contact with fluid in sample reservoirOne skilled in the art will recognize that the surface26 can be varied, and that maximizing the surface area ofthe filter in contact with fluid will improve the filtrationcharacteristics of the filter because particulate matterincapable of penetrating the filter is spread out over alarger area, whereby the filter will have a lower tendencyto clog.Sample reservoir 26 also facilitates addition of variousvolumes of sample to the device. One skilled in the artwill recognize that the volume of the sample reservoir 26should be adjusted to accommodate the volume of sample tobe assayed by the device. Preferred volumes for the samplereservoir are between 0.1 ul and 1000 ul, and particularlypreferred volumes are between 5 ul and 300 ul.In one embodiment, sample reservoir 26 comprises acapillary space when a lid 18 is attached to the base 10;therefore, the dimensions of the capillary gap of thereservoir 26 are designed in accordance with the capillarityof the regions of the entire device, so that there will befluid flow and filtration.the fluidreservoir 26 held the fluid sample within the reservoir andAdvantageously, capillary force of theminimized the risk of spilling or expulsion of fluid samplefrom the device. This is particularly advantageous when?WO 98/0860610l520253035CA 02263976 1999-02-25PCT/US97/1493932the fluid sample is, a biological fluid that may bee.g.,contaminated with hazardous bacteria or virus, or is anenvironmental water sample contaminated with pollutants.Preferably, reservoir 26 comprises vent holes 30 in lid18.during filling with the fluid sample,Vent holes 30 allow escape of air from reservoir 28and facilitate morecomplete filling of the reservoir.A particularly preferred embodiment of the samplereservoir 26, as illustrated in Figure 6, comprises grooves34 on the floor of reservoir 26 and on the filter stay 32.whenIn the absence of grooves (or other suitable texture),the floor of the sample reservoir 26 was flat, some samplefluid was retained by capillary action in the corners ofthe sample reservoir 26. In one embodiment, grooves 34 areapproximately 0.013 cm deep and 0.043 cm wide and areoriented such that the sample fluid is directed to filterThus,completely drained from the corners of the sample reservoir20 by flowing along grooves 34. the sample fluid26, since grooves 34 served to break the capillary tensionof the sample fluid meniscus that formed in the corners ofsample reservoir 26 that occurred as sample fluid wasdepleted from the reservoir.One skilled in the art will recognize that the size andorientation of the grooves can be changed and the groovescould beprotruding from the floor of the sample reservoir withoutsubstituted for a surface texture of postschanging the scope of this invention.In the particular embodiment with dimensions discussedin this example, (220 pl),in a Vacutainerm Blood Collection Tube with EDTA, was addedfresh human whole blood drawninto sample reservoir 26; theBloodcontinued to move from sample reservoir 26 into filter 20through fluid access port 14,fluid simultaneously began to flow into filter 20.because filter 20 had a stronger capillary force than sampleThe fluid flowed laterally through filterand two distinct flow fronts developed,reservoir 26.20,front being clear plasma and the trailing front comprisingthe leading?WO 98/0860610152025CA 02263976 1999-02-25PCT/US97/1493933particulate material such as red blood cells. The plasmafront reached the downstream edge of filter 20 (i.e., fluidegress region 16) after about 50 seconds at which point theplasma front was approximately 2 mm ahead of the red bloodcell front. Within filter 20 having dimensions disclosedabove, the volume of plasma that a 2 mm distance cor-responded to was approximately 20 to 30 ul. This volumerepresented the amount of plasma available for an assaybefore the red blood cells reached the downstream edge offilter 20 17; thisconfiguration was selected because a volume of 15 to 20 ulFluid flow throughfilter 20 was enhanced by the capillary force of exit region17.space, and plasma exited the filter and entered exit regionand could move into exit regionwas necessary to obtain an assay result.As noted above, exit region 17 comprised a capillary17 by capillary action, at a flow rate of approximately 7ul/min. Approximately 15 to 20 ul of plasma was recoveredand was devoid of red blood cells.In a preferred embodiment, to minimize the possibilitythat a filtrate fluid in exit region 17 might be contamin-ated with particulate matter, the exit region was designedto accommodate a volume which corresponded to the volumeof fluid that was equal to or less than that which precedesthe particulate matter front for a given device embodiment.the withdimensions as set forth above, the exit region was designedThus, in embodiment depicted in Figure 6,to accommodate 20-30 ul or less.

Claims (19)

CLAIMS:

1. A device comprising:
a lid, a base substantially parallel to the lid, a fluid access port within the lid;
a fluid permeable filter comprising a region for fluid access in fluid communication with the fluid access port and a region for fluid egress, wherein the filter comprises a substantially smaller depth dimension in comparison to its length and width dimensions, wherein the length/width plane of the filter is oriented within the device substantially parallel to the lid and base, and wherein the peripheral surfaces of the filter are sealed within the device;
a fluid flow path through the filter that is a lateral flow path from the region for fluid access through the filter to the region for fluid egress; and a fluid egress port comprising a capillary space fluidly connected to the region of fluid egress from the filter, wherein fluid flows from said filter to said capillary space.

2. The device of claim 1, wherein the peripheral surfaces of the filter are sealed within the device in a fluid tight manner.

3. The device of claim 1, further comprising a dead space defined by a peripheral surface of the filter and a region of the device.

4. The device of claim 1, further comprising a means for retarding movement of any particulate matter in the filter through a peripheral surface of the filter.

5. The device of claim 4, wherein the filter is sealed in a particle-tight manner on all peripheral surfaces, whereby for a sample comprising particulate matter, any particulate matter in the filter is retained in the filter and any fluid in a capillary space along a peripheral surface of the filter is free of particulate matter.

6. The device of claim 5, wherein the filter is sealed in a liquid-tight manner on all peripheral surfaces.

7. The device of claim 5, wherein the filter is sealed in a fluid-tight manner on all peripheral surfaces.

8. The device of claim 1, further comprising a means for region-specific compression.

9. The device of claim 8, wherein the means for region-specific compression further comprises use of fluid-impermeable glue, a sealant, or a pressure adhesive tape.

10. The device of claim 8, wherein the means for region-specific compression comprises compressing the filter matrix between two or more solid surfaces.

11. The device of claim 1 further comprising a sample reservoir fluidly connected to the sample access region of the filter.

12. The device of claim 11 wherein the sample reservoir comprises a capillary space.

13. The device of claim 1 wherein the capillary space fluidly connected to the fluid egress region comprises a means for producing an assay result.

14. A method for assaying fluid samples, the method comprising adding fluid to the fluid access region of the device of claim 11.

15. The device of claim 1 wherein the capillary space fluidly connected to the fluid egress port comprises a means for producing an assay result, wherein the assay means requires a set volume of liquid to produce an assay result.

16. The device of claim 15 wherein the capillary space fluidly connected to the fluid egress port is adapted to contain a volume that is at least the set volume of liquid required to produce an. assay result.

17. A method for producing an assay result, the method comprising adding a volume of fluid sample to the sample access port of the device of claim 15, wherein the volume is greater than or equal to the volume required by the assay means to produce an assay result.

18. The device of claim 8, wherein the means for region-specific compression comprises compression of the filter by 1-50% of the native thickness of the filter.

19. The device of claim 1, wherein sample fluid substantially devoid of particulate matter is released from the filter through the fluid egress port.