Abstract:
A laboratory device design particularly for a multiplate format that includes a tray having at least one well with a support associated with the well, and a removable undercover. The undercover protects the support or membrane from external contamination without causing excessive force on an individual well that can cause membrane flatness. The undercover is easily removable to provide access to the support or membrane. The undercover, when affixed to the underside of the multiwell plate or tray, allows the assembly to be transportable as a single unit while still being in compliance with SBS automation standards.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Test plates for chemical or biochemical analyses, which contain a plurality of individual wells or reaction chambers, are well-known laboratory tools. Such devices have been employed for a broad variety of purposes and assays, and are illustrated in U.S. Pat. Nos. 4,734,192 and 5,009,780, for example. Microporous membrane filters and filtration devices containing the same have become particularly useful with many of the recently developed cell and tissue culture techniques and assays, especially in the fields of virology and immunology. Multiwell plates, used in assays, often utilize a vacuum applied to the underside of the membrane as the driving force to generate fluid flow through the membrane. The microplate format has been used as a convenient format for plate processing such as pipetting, washing, shaking, detecting, storing, etc.  
           [0002]    Typically, a 96-well filtration plate is used to conduct multiple assays simultaneously. In the case of multiwell products, a membrane is placed on the bottom of each of the wells. The membrane has specific properties selected to filter or to support biological or chemical reactions. High throughput applications, such as DNA sequencing, PCR product cleanup, plasmid preparation, drug screening and sample binding and elution require products that perform consistently and effectively.  
           [0003]    One such filtration device commercially available from Millipore Corporation under the name “Multiscreen” is a 96-well filter plate that can be loaded with adsorptive materials, filter materials or particles. The Multiscreen underdrain has a phobic spray applied in order to facilitate the release of droplets. More specifically, the MultiScreen includes an underdrain system that includes a spout for filtrate collection. This spout not only directs the droplets but also controls the size of the droplets. Without the underdrain system, very large drops form across the entire underside of the membrane and can cause contamination of individual wells. Access to the membrane can be had by removing the underdrain. However, assay results are sensitive to liquid collection between the membrane and the underdrain due to membrane weeping. Also, membrane flatness can be problematic depending on the reading technology used. The device also is not compatible with automated robotics equipment such as liquid handlers, stackers, grippers and bar code readers.  
           [0004]    A conventional application for the microplate format that does not involve filtration is enzyme linked immuno-spot (ELISPOT) assays. In an ELISPOT assay, for example, the wells of the ELISPOT plate are coated with an antibody that is specific for the cytokine that is being assayed for. The antibody binds to the nitrocellulose or polyvinylidene fluoride (PVDF) membrane portion of the ELISPOT plate. Activated peripheral mononuclear cells are transferred to the plate, and the cytokines are released during an incubation period. The released cytokines bind to and are therefore captured by the specific antibody. The cells and excess cytokines are washed away, and a second antibody also specific for the cytokine of interest that is coupled to an enzyme capable of converting a substrate into an insoluble colored product is added. The substrate is converted into an insoluble product, forming spots or colors that represent the areas of captured cytokines. The spots can be quantitated using a microscope or digital imaging system. The ELISPOT assay provides an effective method of measuring antibody or cytokine production of immune cells on the single cell level.  
           [0005]    In applications such as ELISPOT assays where the membrane is not used as a filter, but rather as a substrate upon which a biochemical reaction occurs and is detected, the underdrain not only becomes unnecessary, but also can be problematic. The underdrain both hinders access to the membrane for imaging and can cause the membrane to bow, which also deleteriously effects imaging. In addition, leakage or weeping of liquid through the membrane into the area between the membrane and the underdrain can ruin the assay, and may be dangerous to the user if the samples or reagents involved are biohazards, for example.  
           [0006]    The Society for Biomolecular Screening (SBS) has published certain dimensional standards for microplates in response to non-uniform commercial products. Specifically, the dimensions of microplates produced by different vendors varied, causing numerous problems when microplates were to be used in automated laboratory instrumentation. The SBS standards address these variances by providing dimensional limits for microplates intended for automation.  
           [0007]    It would therefore be desirable to provide a multiplate format that allows for easy access to the membrane while reducing or eliminating the deleterious retention of liquid under the membrane, loss of membrane flatness, and/or accidental separation of the wells from the tray.  
           [0008]    It also would be desirable to provide a multiplate format that is automation compatible.  
         SUMMARY OF THE INVENTION  
         [0009]    The problems of the prior art have been overcome by the present invention, which provides a laboratory device design particularly for a multiplate format that includes a plate or tray having at least one well with a support associated with the well, and a removable undercover. The undercover protects the support or membrane from external contamination without causing excessive force on an individual well that can interfere with the membrane&#39;s flatness. The undercover is easily removable to provide access to the support or membrane.  
           [0010]    According to a preferred embodiment of the present invention, there is provided a multiwell device including a multiwell plate or tray having a membrane as a support, and an undercover affixed to the underside of the multiwell plate or tray so that the plate or tray and undercover are transportable as a single unit, the undercover being removable from the plate or tray, the multiwell device meeting SBS automation standards even with the undercover in place. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is an exploded perspective view of a multiwell microplate device and undercover in accordance with the present invention;  
         [0012]    [0012]FIG. 2 is a perspective view showing the underside of a multiwell microplate device with the undercover affixed in place in accordance with the present invention;  
         [0013]    [0013]FIG. 3 is a bottom view showing the underside of a multiwell microplate device with the undercover affixed in place in accordance with the present invention;  
         [0014]    [0014]FIG. 4 is a perspective view showing two undercovers stacked in accordance with an embodiment of the present invention;  
         [0015]    [0015]FIG. 5 is a cross-sectional view showing two stacked microplates with undercovers attached in accordance with an embodiment of the present invention;  
         [0016]    [0016]FIG. 6 is a perspective view showing removal of the undercover from the microplate in accordance with the present invention;  
         [0017]    [0017]FIG. 7 is a bottom view of the microplate showing the undercover in phantom in accordance with the present invention; and  
         [0018]    [0018]FIG. 8 is a cross-sectional view of a portion of the microplate with the undercover in place in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    Turning first to FIG. 1, there is shown a multiwell device including an optional removable protective cover  5 , a 96-well plate or tray  10  and an undercover  12 . Although a 96-well plate array is illustrated, those skilled in the art will appreciate that the number of wells is not limited to 96; a single well could be used, or standard multiwell formats with 384, 1536 or fewer or more wells are within the scope of the present invention. The well or wells are preferably cylindrical with fluid-impermeable walls, and have a width and depth according to the desired use and amount of contents to be sampled. Where a plurality of wells is present, the wells are preferably interconnected and arranged in a uniform array, with uniform depths so that the tops and bottoms of the wells are planar. The plate  10  is generally rectangular, although other shapes are within the scope of the present invention, keeping in mind the objective of meeting SBS dimensional standards.  
         [0020]    In the embodiment shown, the plate  10  includes a plurality of wells having an open top and a bottom having a surface to which is sealed a substrate or support  11 , such as a membrane (FIGS. 5 and 8). The sealing can be accomplished by any suitable means, including heat-sealing, sealing with ultrasonics, solvents, adhesives, by diffusion bonding, etc. The type of membrane suitable is not particularly limited, and can include nitrocellulose, cellulose acetate, polycarbonate, polypropylene and PVDF microporous membranes, or ultrafiltration membranes such as those made from polysulfone, PVDF, cellulose or the like. A single support covering all of the wells could be used, or where the device is a plurality of wells, each well can contain or be associated with its own support which can be the same or different from the support associated with one or more of the other wells. Each such individual support is preferably coextensive with the bottom of its respective well.  
         [0021]    Depending on the anticipated mode of assay analysis, the undercover  12  may or may not be made of material sufficiently transparent so as not to interfere with optical imaging processes. It might also be desirable for the material to retain its optical properties through the procedure or assay, including sterilization. For example, some materials tend to yellow with gamma radiation, deleteriously affecting subsequent imaging processes. Suitable materials that have been found to have acceptable optical properties and that retain their optical properties include acrylic, EASTAR polyester copolymer, polystyrene, polycarbonate, polyethylene, polypropylene, cyclic olefin polymer such as ZEONEX and ZEONOR, cyclic olefin copolymer such as TOPAS, and NAS, a copolymer of 70% polystyrene and 30% acrylic. Acrylic is particularly preferred. However, it is within the scope of the present invention to use opaque undercovers where optical imaging is not a concern.  
         [0022]    As shown in FIG. 2, when affixed to the plate  10  to form a unitary assembly, the undercover  12  should cover all of the wells to protect the wells from contamination. The undercover  12  has a length and width smaller than the length and width of the plate  10  so that the undercover  12  is dimensioned to fit inside the skirt  28  of the plate  10 . The undercover  12  also is sufficiently thin so that when assembled to plate  10 , the skirt  28  of plate  10  extends beyond the undercover  12  as best seen in FIG. 5. This configuration therefore does not alter the compatibility of plate  10  with robotics equipment, and maintains the dimensional standards established in the industry.  
         [0023]    Preferably a gap  17  is provided between the edge of the undercover  12  and the edge of the plate  10  to allow for insertion of a finger or tool  19  between the undercover  12  and the plate  10  to pry away the undercover  12  from the plate  10  for removal, as depicted in FIG. 6. Thus, by removing the undercover  12 , the operator can gain access to the membrane or support. The gap  17  need not be uniform along the perimeter of the undercover  12 .  
         [0024]    Turning now to FIG. 4, details of the features of the undercover  12  and plate  10  to enable the undercover  12  to be removably affixed to the plate  10  are illustrated. In the embodiment shown, the undercover  12  has a tab  20  extending in a vertical direction relative to the surface of the undercover  12 . The tab  20  is preferably centrally located along, adjacent or slightly spaced from the side edge  18  of the undercover  12 . The opposite side edge  18 ′ also has a similar tab  20 ′. The tab  20  is dimensioned to be received between two spaced, preferably parallel ribs  21  (FIG. 7) that extend from each side  18  of the plate  10  to outer walls of respective wells  25  in the underside of plate  10 . Each rib  21  can include a cylindrical post  22  that provides structural integrity to the rib  21  and further serves to position the tab  20 . The width of the tab  20  is only slightly bigger than the distance between the spaced ribs  21 , so that force is necessary to push the tabs into that space and to remove the tabs from that space. As best seen in FIG. 8, the tab  20  thus fits laterally between the two ribs  21  and longitudinally between the outer walls of two consecutive wells  25 A,  25 B and two consecutive rib posts  22  to assist in locating and securing the undercover  12  to the plate  10 . One or more tabs  20  can be used for each side edge  17 .  
         [0025]    [0025]FIG. 4 also shows pins  26  that extend in a vertical direction relative to the surface of the undercover  12 . The pins  26  are located at or near opposite corners of each side edge  17  as shown, spaced from the tab  20 . The pins  26  also are dimensioned to fit between two adjacent spaced ribs  21  that extend from the side  17  of the plate  10  to outer walls of respective wells  25  in the plate  10 , and assist in aligning the undercover  12  with the plate  10 . It is not necessary that the pins  25  contact the ribs  21  or the outer walls of the wells  25 . The height of the pins  26  is preferably chosen so that the pins  26  contact the underside of the plate  10  to provide a stop to hold the undercover  12  a fixed and minimum distance from the surface of the membrane to prevent the undercover  12  from contacting the membrane when affixed to the plate  10 . That is, a clearance  29  (FIGS. 5 and 8) between the surface of the undercover and the surface of the membrane or support  11  is ensured by sizing the pins  26  appropriately based upon the distance each well extends from the underside of the plate  10 . A suitable clearance  29  has been found to be between about 0.8-1.0 mm. The pins  26  also add to the structural integrity of the undercover  12 , avoiding too much flex, assist in the stackability of the undercovers (FIG. 4) and protect the tabs  20 . As seen in FIG. 2, apertures  32  can be formed in the undercover  12  axially aligned with the pins  26 , the apertures  32  being configured to receive corresponding pins  26  from another undercover  12  to enhance stackability.  
         [0026]    Alternatively or in addition to configuring the pins  26  so as to ensure the clearance  29  between the undercover  12  and the membrane or support  11 , the undercover  12  may also include a raised rim  30  at or near the perimeter, as best seen in FIG. 4. The rim  30  may be continuous and encompass the entire perimeter of the undercover  12 , or may be discontinuous. The height of the rim  30  is chosen to contact the top surface of the ribs  21  and therefore also act as a stop to prevent the undercover from contacting the membrane or support  11 . The top surface of lateral ribs  23  that extend from inwardly towards wells  25  from the longitudinal edges  24 ,  24 ′ of the undercover  12  also may be contacted and provide a stop to form the clearance  29 .  
         [0027]    It also is within the scope of the present invention to include one or more vertical pins in the center region of the undercover  12 . These additional pins can interlock with the plate and further prevent inadvertent contact between the undercover and the bottom of wells anywhere in the plate, especially the center.  
         [0028]    Since the undercover  12  is not fixed to each individual well, unnecessary strain on each well is avoided. Such strain can create membrane bowing that can deleteriously effect imaging.  
         [0029]    The clearance between the undercover  12  and the plate skirt of the plate  10  allows for plate stackability, with or without cover  5 , as shown in FIG. 5.  
         [0030]    In the event it is desirable to have the undercover  12  contact the membrane  11  to support the membrane, the clearance  29  can be eliminated by proper sizing of the rim  30  and pins  26 .