Abstract:
Methods of and systems for applying blocking material to assay substrates are disclosed. A method includes supplying an assay substrate having at least one surface. A first portion of the surface of the substrate has at least one analysis feature thereon, and a second portion of the surface of the substrate lacks analysis features. The method also includes generating a spray of a blocking material in proximity to the surface of the substrate and continuing the spray generation in proximity to the surface of the substrate at least until the second portion of the surface of the substrate is substantially covered by the blocking material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 61/372,552, filed on Aug. 11, 2010, entitled Method of and System for Applying Blocking Material to Assay Substrates, incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field of Invention 
         [0003]    The present invention relates to the preparation of assay substrates, and, more specifically, to the application of a blocking material to an assay substrate that has been printed with features. 
         [0004]    2. Description of Related Art 
         [0005]    An assay substrate is a surface upon which various chemical and/or biological analyses can be performed. Examples include microarray plates, glass slides, and microtiter plates. A microtiter plate is a flat plate that has multiple “wells” formed in its surface. Each well can be used as a small test tube into which various materials can be placed for the purposes of performing chemical analysis. One illustrative use of microtiter plates includes an enzyme-linked immunosorbent assay (ELISA), which is a modern medical diagnostic testing technique. 
         [0006]    In ELISA, in general, a capture antibody is printed in the bottom of a well in a microtiter plate. The capture antibody has specificity for a particular antigen for which the assay is being performed. A sample to be analyzed is added to the well containing the capture antibody, and the capture antibody “captures” or immobilizes the antigen contained in the sample. A detect antibody is then added to the well, which also binds and/or forms a complex with the antigen. Further materials are then added to the well which cause a detectable signal to be produced by the detect antibody. For example, when light of a specific wavelength is shone upon the well, the antigen/antibody complexes will fluoresce. The amount of antigen in the sample can be inferred based on the magnitude of the fluorescence. In another example, a compound can be added to the well that causes the detect antibody to emit light within a predetermined wavelength (e.g., 400-500 nm). This light can be read by a CCD camera to measure the optical brightness of the emitted light. 
       BRIEF SUMMARY 
       [0007]    In one aspect, the invention features methods of and systems for applying blocking material to assay substrates. 
         [0008]    In another aspect, the invention features a method including supplying an assay substrate having at least one surface. A first portion of the surface of the substrate has at least one analysis feature thereon, and a second portion of the surface of the substrate lacks analysis features. The method also includes generating a spray of a blocking material in proximity to the surface of the substrate and continuing the spray generation in proximity to the surface of the substrate at least until the second portion of the surface of the substrate is substantially covered by the blocking material. 
         [0009]    In a further aspect, the at least one analysis feature has a first surface in contact with the surface of the substrate and a second surface not in contact with the surface of the substrate. The method also optionally includes continuing the spray generation in proximity to the surface of the substrate until the second surface of the analysis feature is substantially covered by the blocking material. 
         [0010]    In yet another aspect, the spray of the blocking material is generated by an airbrush. Optionally, the airbrush generates a spray pattern having a central axis, and the airbrush is held in relation to the substrate to maintain the central axis of the spray pattern substantially normal to the at least one surface of the substrate. 
         [0011]    In still a further aspect, the airbrush, in operation, has a blocking material flow rate through the airbrush and an air supply pressure. The flow rate through the airbrush ranges from about 5 ml/min to about 20 ml/min, and the air supply pressure ranges from about 34 kPa to about 207 kPa. 
         [0012]    In an aspect of the invention, the spray of the blocking material originates at a nozzle, and the surface of the substrate is within about 2 cm to about 41 cm of the nozzle. 
         [0013]    In another aspect, the spray of the blocking material originates at a nozzle, and the method further includes moving at least one of the nozzle and the assay substrate relative to each other to distribute the blocking material over substantially the entire surface of the substrate. 
         [0014]    Optionally, the method includes disposing the assay substrate on a conveyor, a portion of the conveyor being disposed below the nozzle, and actuating the conveyor to bring the assay substrate into the spray of blocking material. 
         [0015]    In yet another aspect, the assay substrate is a microtiter plate. The microtiter plate has a plurality of wells, and the at least one analysis feature is disposed within one of the wells. Optionally, the method also includes, adding blocking material to at least one well via a pipette. 
         [0016]    In still a further aspect, the assay substrate is a functionalized slide. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  shows a cross-sectional side view of a single well in a microtiter plate. 
           [0018]      FIG. 2A-C  show a series of cross-sectional side views of a well during a known method of adding a blocking material to a well. 
           [0019]      FIG. 3  shows a top view of a number of printed features after the application of a blocking material using a known method. 
           [0020]      FIG. 4  shows a method of preparing a microtiter plate in accordance with some embodiments. 
           [0021]      FIGS. 5A-B  show a series of cross-sectional side views of a well during a method of adding a blocking material to a well in accordance with some embodiments. 
           [0022]      FIG. 5C  shows a cross-sectional side view of a well during an optional step of a method of adding a blocking material to the well in accordance with some embodiments. 
           [0023]      FIG. 6  shows a top view of a number of printed features after the application of a blocking material in accordance with some embodiments. 
           [0024]      FIGS. 7A-B  show a series of cross-section sides views of an assay substrate on a conveyor passing under a spray of blocking material. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1  shows an illustration of a cross-sectional side view of a single well in a microtiter plate  100 . The bottom of the well is formed of a polystyrene base  105 . During the preparation of a microtiter plate for use in an ELISA, many different capture antibody “spots” or “features”  110  are printed in the well and adhere to the polystyrene base  105 . The features can be about 320-380 gm in diameter, for example. After printing the capture antibody features  110 , a blocking material is added to the well to block plate binding sites  115  that remain on the plate  100 . This prevents non-selective binding of sample antigens to the base of the well during the ELISA, which would give false readings. 
         [0026]      FIGS. 2A-C  show a series of cross-sectional side views  200  of a well  205  during a known method of adding a blocking material to a well during the preparation of an ELISA plate. After the features  210  have been printed, a micropipette  215  containing a solution of blocking material  220  is used to add about 200 μL of the solution to the well  205 . However, this method can introduce undesirable effects inside the plate well. Specifically, applying a blocking material solution directly above one or more of the printed features  210  can destroy the shape of the feature due to the force of the blocking material solution impacting the printed feature. Thus, a typical approach is to apply the blocking solution along a portion of the wall  220  of the well  205 . 
         [0027]    Such an approach can reduce the impact force experienced by the printed features  210 . However, in some cases, the printed features  210  can still be “toppled” by the incoming blocking material solution washing over the top of the printed feature (as shown in  FIG. 2B ). The toppled features can then form large deformed spots  225  on the surface of the bottom of the well plate (as shown in  FIG. 2C ). 
         [0028]      FIG. 3  shows a top view  300  of a number of printed features after the application of a blocking material using the known method illustrated in  FIGS. 2A-2C . As shown in  FIG. 2 , several of the features have toppled and spread across larger portions of the bottom surface of the well plate. Thus, these features lack a clearly defined circle when viewed from above. These altered features can be more difficult to detect or “read”. For example, an automated ELISA reader may misread a malformed feature, the toppled feature may interfere with an adjacent feature, and/or the intensity of the feature may be affected. Moreover, a user of a plate with malformed features may perceived the plate as lacking quality, or the user may lack confidence in the results of the analysis. 
         [0029]      FIG. 4  shows a method  400  of preparing a microtiter plate in accordance with some embodiments. Method  400  reduces or eliminates malformation and/or toppling of features during the addition of blocking material to the microtiter wells. As used herein, a “target plate” is a plate that is to be prepared (e.g., printed, blocked, and processed for later usage) for a particular set of analyses. Whereas, a “source plate” is a microtiter plate that has a supply of the material to be printed onto a target plate. For example, the wells of a source plate can be filled with various types of antibodies that are to be printed onto target plates. 
         [0030]    In accordance with method  400 , the source plate is prepared for the printing process (step  410 ). This can include filling the wells of the source plate with the desired material to be printed onto the target plate. Next, the target plate is prepared for printing (step  420 ). This can include washing and/or other surface treatments to enable the material to be printed to properly adhere to the bottom surface of the plate well. The source and target plates are then fit into a printing apparatus (e.g., a 2470 Arrayer available from Aushon Biosystems, Inc. of Billerica, Mass.) (step  430 ). Features are printed in the wells of the target plate (step  440 ), the printed target plate is incubated for a period of time (step  450 ), and the target plate is dried (step  460 ). 
         [0031]    Next, a blocking material is applied to the target plate via a spraying process (step  470 ).  FIGS. 5A-B  show a series of cross-sectional side views  500  of a well  505  during the spraying step in accordance with one implementation. In the implementation shown, an airbrush  510  (e.g., a Paasche Talon model TG0210) is used to apply the blocking material  515  to the bottom surface of the well  520  of the plate. During the spraying step, approximately 10 ml of a blocking material solution is sprayed over the entire surface of the plate. The blocking material is propelled by a compressed air source, e.g., a standard air compressor that supplies clean and dry air, at a pressure of about 138 kPa (20 psig). The flow rate of the airbrush is set to about 10 ml/min. 
         [0032]    The nozzle of the airbrush is positioned about 15 cm (6 inches) from the surface of the plate, and the airbrush is swept across the entire surface while keeping the nozzle perpendicular to the surface of the plate. In other words, the center of the spray pattern  525  is essentially normal to the surface of the plate. The spraying is continued at least until the parts of the surface of the plate without printed features thereon is substantially covered in blocking material. Optionally, the spraying is continued at least until the level of blocking material in the well covers the printed features  530 . After that level of blocking material is achieved, additional blocking material can be added by continuing the spraying process, or, optionally, additional blocking material can be added via micropipette, as described above (step  480 ).  FIG. 5C  shows a cross-sectional side view of the well during this optional step of adding blocking material to the well via pipette. 
         [0033]    The target plate is then processed for usage or storage using known methods (step  490 ). For example, the target plate can be incubated at about 4° C. overnight. Alternatively, excess blocking material (e.g., the blocking material that has not bound to the bottom of the well) can be removed from the target plate, the plate can then be dried, and then the plate can be placed into a moisture-resistance package for storage. The disclosed method of applying the blocking material reduces or eliminates malformation and/or toppling of features during the addition of blocking material to the microtiter wells.  FIG. 6  shows a top view  600  of a number of printed features  605  after the application of a blocking material in accordance with some embodiments. As shown in the figure, the printed features  605  have well-defined circular borders and do not have the misshapen features that appear in the plate prepared according to the known methods. Thus, plates prepared according to the methods disclosed herein have superior feature uniformity. 
         [0034]    The scope of the invention is not limited to applications involving microtiter plates having wells therein. In another embodiment of the invention, the techniques described herein are applicable to functionalized slides (e.g., functionalized glass slides). In such an implementation, the functionalized slides lack the wells found in microtiter plates. Instead, the functionalized slide contains surface portions that have been modified by binding various compounds to the surface portions. For example, a surface of a functionalized slide can have portions to which a long-chain polymer, having certain functional groups, has been covalently linked. The functional groups enable biomolecules to be captured by the functionalized slide. When applied to a functionalized slide, the techniques herein permit portions of the slide (e.g., those parts that have not been functionalized) to be blocked while reducing disruption to the functionalized areas of the slide. 
         [0035]    The application of the blocking material as described herein can be applied by-hand. In some implementations, the blocking can be applied by automated machinery. For example, after printing, incubating, and drying (steps  440 ,  450 , and  460 ), the plate can be placed on a conveyor over which is mounted one or more spray nozzles. The rate of the conveyor is controlled to ensure adequate residence time of the plates within the spray pattern  525  of the one or more nozzles. For example, if the total flow rate of all of the nozzles is about 10 ml/min, the conveyor speed can be controlled to provide that at least some portion of the surface of the plate is under the spray pattern for 1 minute. In another illustrative implementation, the plate can be held is a fixed position and an automated arm can direct one or more spray nozzles above the surface of the plate. 
         [0036]    The specific operational parameters provided above are merely illustrative, and other values are within the scope of the invention. For example, the blocking material flow rate can vary between 5-20 ml/min, the distance between the airbrush flow nozzle and the surface of the plate can vary between 2-41 cm (1-16 inches), and the air pressure can vary between 34-207 kPa (5-30 psig). It is understood that these ranges are merely illustrative and are not intended to be limiting. 
         [0037]      FIGS. 7A-B  show a series of cross-section side views of an assay substrate on a conveyor passing under a spray of blocking material. In the implementation shown, an spray nozzle  710  is used to apply the blocking material  715  to the surface of an assay substrate  720  (e.g., a microtiter plate or a functionalized slide). The assay substrate  720  is placed on a conveyor  725 , and the conveyor is actuated in the direction shown by arrow  730  to move the assay substrate  720  under the spray of blocking material  715 . Although not shown, a series of assay substrates can be loaded on to conveyor in series. 
         [0038]    The spray nozzle  710  can be a spray nozzle of an airbrush, as described in more detail above. In addition, the spray nozzle  710  can be stationary, or the spray nozzle  710  can be moved side-to-side (relative to the direction of travel of the substrate  730 ) so as to provide even coverage of blocking material  715  over the entire surface of the assay substrate  720 . 
         [0039]    The terms and expressions that are employed herein are terms of description and not of limitation. There is no intention in the use of such terms and expressions of excluding the equivalents of the feature shown or described, or portions thereof, it being recognized that various modifications are possible within the scope of the invention as claimed.