Abstract:
A microarray storage device includes a cassette having top, bottom and opposite side walls, the front and rear of the cassette being open. The side walls are formed with a multiplicity of parallel rails spaced along the heights of the walls which define compartments in the cassette for supporting a multiplicity of microarrays one above the other. The depth of the cassette is such that the microarrays supported in the compartments project appreciably from the front and/or rear of the cassette. Integral springs are formed in the side walls of the cassette which press down directly on the side edge margins of the microarrays so as to releasably retain the microarrays in their respective compartments. The cassette is designed to be latched to the elevator platform of an associated microwave handling system and a cover may be releasably engaged over the cassette and its contents so that the cover protects those contents and may function as a tool for inserting the cassette into, and removing it from, the associated handling system.

Description:
This invention relates to the automatic quantitative scanning of microarrays. It relates more particularly to a microarray storage device for use in an automated microarray handling system. 
     BACKGROUND OF THE INVENTION 
     Microarrays are arrays of very small samples of purified DNA or protein target material arranged as small spots, usually in the order of 100-200 microns in diameter, on a solid substrate. The spots in the array are exposed to complimentary genetic or protein probe samples derived from cells that have been tagged with fluorescent dyes. The probe material binds selectively to target spots only where complimentary bonding sites occur from a process called hybridization. In other words, probe molecules with a similar sequence to the target will bind or hybridize to the target molecules. Dissimilar probe molecules will not bind to the target molecules and will be washed away in a subsequent rinsing process. By measuring the quantity of bound probe molecules, a researcher can determine the likeness between the probe and the target molecules. This technique is used to measure a variety of biological characteristics including gene expression, genotype and gene sequence. 
     Hybridization experiments must be conducted in large quantities in order to be generally useful. For example, there are approximately one hundred thousand genes in the human genome, several thousand of which are considered in a typical study. Technologies have been developed to allow massively parallel hybridization experiments to be performed on DNA on a very large number of samples comprising a microarray. 
     In a typical hybridization experiment, the reference DNA is spotted onto a substrate, typically a glass slide similar to a microscope slide. The DNA is mixed with a liquid buffer to form a solution that is laid down on the substrate in droplets. The surface of the substrate is treated to control the size of the spots resulting from the drops and to chemically bind the DNA to the substrate. When the microarray dries, it is left with an ordered array of reference DNA samples bound to its surface. 
     Such spotting is accomplished by using an instrument called an arrayer which is a robotic device that can spot forty to a hundred microarrays on a substrate or slide in an automated fashion. Typical spotting times are in the range of eight minutes per slide, the substrates or slides being manually loaded and removed from the arrayer. 
     The next step in the microarray process is to introduce the fluorescently labeled probe DNA. The DNA is mixed in a buffer solution and placed onto the surface of the microarray. A thin piece of glass is then used to sandwich the probe between it and the substrate or slide which causes the probe DNA to spread across the region of the microarray that contains the target DNA. 
     Next the target and probe are hybridized by putting the microarray into a humid, thermally controlled environment and baking at temperatures ranging from 40-60° C. for periods ranging from thirty minutes to twelve hours depending on the nature of the experiment. During this stage, target and probe molecules with similar structures bind. 
     After hybridization, the glass cover is removed and the microarray is rinsed to wash away any probe DNA that did not bind to the target DNA. 
     Finally, the microarray is imaged. For this, the microarray is manually loaded into an imager or scanner where the probe DNA is illuminated by light which excites the fluors in the probe DNA causing the fluors to fluoresce. The brightness of each specimen or spot in the microarray is a function of the fluor density in that specimen or spot. The fluor density is, in turn, a function of the binding affinity or likeness of the probe molecule to the target molecule for each spot. Therefore, the brightness of each spot can be mapped to the degree of similarity between the probe DNA and the target DNA in that spot or sample. In a typical microarray, up to tens of thousands of experiments can be performed simultaneously on the probe DNA allowing for a detailed characterization of complex molecules. 
     As can be appreciated, performing the above described microarray process manually is costly and time consuming. A researcher or technician is required to handle each microarray at every step in the process, i.e. spotting, hybridization, washing and imaging. The imaging process is particularly labor intensive because each slide is inserted by hand into the imager for single slide imaging while the user waits to load the next slide. The situation becomes acute for high volume users which process several hundred microarrays a day. They will need to hire several technicians just to keep up with the imaging. Thus, there is a need to reduce the amount of handling required to process microarrays and indeed, to process the microarrays in batches. 
     Also microarrays are susceptible to damage if they are not stored properly. Everything from dust to light can affect the data that is gleaned from the microarrays. Therefore, there is a need for a way to properly store microarrays so that they are not degraded or damaged over time. 
     We should mention that there do exist mechanisms for loading microscope slides bearing biomedical samples, such as Pap smears, into microscopes; see e.g., U.S. Pat. Nos. 4,367,915 and 5,690,892. 
     The former patent describes a system which uses two separate mechanisms for loading slides into, and unloading them from, a cassette or magazine. The magazine is indexed to position each specimen slide for access by a horizontal feed mechanism which transfers the specimen slide onto a microscope stage which has controllable X,Y and Z axes to move the specimen slide into the optical viewing field of the microscope. A duplicate mechanism on the other side of the microscope returns the slide to the magazine. 
     The latter patent describes a system wherein specimen slides are removed from a magazine or cassette by a shuttle which reaches under each slide and lifts up to engage the slide using a complex motion. The weight of the slide is used to keep it in place on the shuttle mechanism, limiting the acceleration that can be applied and the friction forces that can be overcome when transferring the slide to another mechanism. The slides are then passed to a second mechanism which changes the direction of motion of travel into and out of an associated microscope. 
     Aside from being designed for use with biomedical samples instead of fluorescent microarrays, those prior loading/unloading mechanisms exhibit a great deal of complexity which results in increased size, decreased reliability and increased cost. 
     There also exist automated microarray scanning or imaging apparatus which use substrate storage cassettes or magazines. Such apparatus do include mechanisms for holding multiple microarrays. However, they invariably require that each substrate or slide be placed in a metal sub-frame or clip prior to loading it into the storage mechanism or magazine. Both the substrate and the frame are then moved into the scanning field of the apparatus and subsequently scanned. However, as throughput demands increase for microarray processing, this sub-frame approach becomes limiting because of the added manual labor required to place each microarray into a sub-frame. Further, the user needs to gather multiple sub-frames to process a batch of microarrays. The sub-frames also increase the amount of space required by each microarray in the magazine or cassette placing an upper limit on the number of microarrays that can be stored in a magazine of reasonable size. 
     Currently there are no microarray magazines or cassettes that can be used both as a common interface for different types of microarray processing equipment and as a storage device for a batch of microarrays allowing a user to queue batches of microarrays in such storage devices and protect them when they are stored. 
     SUMMARY OF THE INVENTION 
     Thus, an object of the invention is to provide a microarray storage device for use with an automated microarray handling system which can be used as a common platform microarray storage mechanism during the spotting, hybridizing, washing and scanning steps of a microarray process. 
     Another object of the invention is to provide a device of this type which is easily transferable between various elements of a microarray processing system. 
     Yet another object of the invention is to provide a microarray cassette which can function as a storage device or mechanism for a relatively large batch of microarrays. 
     A further object in the invention is to provide a microarray cassette which requires no sub-frames on the microarrays thereby allowing direct-to-glass handling of the microarrays. 
     Yet another object of the invention is to provide a microarray storage device which protects the microarrays therein from light and particulate matter. 
     Another object is to provide a storage device of this type which is relatively easy and inexpensive to manufacture in quantity. 
     Other objects will, in part, be obvious and will, in part, appear hereinafter. 
     The invention accordingly comprises the features of construction, combination of elements and arrangement of parts which will be exemplified in the following detailed description, and the scope of the invention will be indicated in the claims. 
     Briefly, our microarray storage device comprises a generally rectangular cassette having top and bottom walls connected by opposite side walls, the front and rear of the cassette being open. The interior surfaces of the side walls are provided with a multiplicity of parallel rails spaced along the heights of those walls which define compartments for supporting a multiplicity of microarrays so that the microarrays are closely spaced one above the other in the cassette. Preferably, the depth of the cassette is designed so that the microarrays supported in the compartments project appreciably from the front and/or rear of the cassette. 
     Preferably also, the side walls of the cassette are formed with integral springs which press down on the microarrays supported in the cassette to releasably secure the microarrays within their respective compartments both when the cassette is in use and when it is being transported. As will be seen later, these springs bear directly against the substrates of the microarrays at the side edge margins thereof so that they do not contact experimental spots that are present on the upper surfaces of the substrates. 
     In use, the cassette may be positioned on the elevator platform of the microarray or loading/unloading handling system for an integrated microarray scanning instrument of the type disclosed in our co-pending application Ser. No. 09/390,013 filed Sep. 3, 1999, entitled MICROARRAY LOADING/UNLOADING SYSTEM, which application is hereby incorporated herein by reference. A latching mechanism to be described later fixes the cassette to that platform. The platform then lowers the cassette into the handling apparatus so that the apparatus feeder mechanism has access to the ends of the microarrays protruding from the cassette to enable the apparatus to transfer, in turn, microarrays from the cassette to the associated scanner or other instrument and vice versa. The projecting ends of the microarrays also enable the user to handle the microarrays without risk of finger contact with the experimental spots present on the substrates. 
     The microarray storage device preferably also includes a cover which may be engaged over the cassette to protectively enclose the microarrays in the cassette when they are not being processed. Desirably, the cover and the cassette are composed of an opaque material which blocks the ambient light which could photobleach the microarrays stored in the device. Thus, the cover shields the microarrays from light, dust and other particulate matter that could degrade the microarrays. 
     As will be seen, both the cassette and the cover may be molded of a suitable rigid, impact resistant plastic material. Therefore, the storage device can be made in quantity at relatively low cost. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in connection with the accompanying drawings, in which: 
     FIG. 1 is an exploded perspective view of a microarray storage device incorporating the invention; 
     FIG. 2 is a fragmentary perspective view in section showing the interior of the cassette component of the FIG. 1 device in greater detail; 
     FIG. 3 is a side elevational view with parts broken away of the storage device showing the device&#39;s cover installed on the cassette, and 
     FIG. 4 is a top plan view of a microarray of the type stored in the FIG. 1 storage device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, our microarray storage device comprises a cassette shown generally at  10  for supporting a multiplicity of vertically spaced microarrays  12 , and a cover  14  arranged to engage over cassette  10  and its contents to protectively enclose the microarrays  12  when they are not being processed. 
     Cassette  10  is a generally rectangular structure having a top wall  16   a , a bottom wall  16   b  and a pair of opposite side wall  16   c  connecting the top and bottom walls. Preferably, the front and rear edges of cassette  10  are finished off by a pair of front and rear bezels  18  and  22  which define the front and rear openings into cassette. 
     For reason that will be described later, the cassette side walls  16   c  are formed with horizontal shoulders  24  near the lower edges of those walls between the bezels  18  and  22 , the shoulders  24  projecting slightly beyond the sides of those bezels. As we shall see, the shoulders  24  may be used to retain the cassette  10  in a microarray handling apparatus so that microarrays  12  in the cassette can be processed by an instrument associated with the handling apparatus. 
     Refer for a moment to FIG. 4 which shows a microarray  12  in greater detail. It comprises a generally rectangular substrate  32  similar to a microscope slide, e.g., its dimensions are in the order of 1 in.×3 in.×0.04 in. Typically, the substrate is made of soda lime float glass and at least its upper surface is chemically treated to control the size of DNA spots S deposited on substrate  32  and to chemically bind the DNA to the substrate. In the illustrated microarray  12 , the spots S are arranged in columns and rows in three arrays more or less centered on the upper surface of the substrate so that relatively wide, e.g., in the order of 1.5 mm. substrate edge margins  32   a  at both sides of the substrate are free of spots. Even wider, e.g., at least 10 mm, margins  32   b  are provided at the ends of the substrate. 
     As shown in FIGS. 1 and 2, the side walls of cassette  10  (including those of bezels  18  and  22 ) are designed to define a series of vertically spaced parallel compartments  36  for releasably supporting a stack of microarrays  12 . Preferably, the cassette stacks the microarrays so as to provide a very small spacing, e.g., 0.02 inch, although the spacing may vary depending on the associated handling apparatus. A typical cassette may hold up to twenty microarrays  12  at a pitch tighter than 8/inch. 
     As best seen in FIGS. 1 and 3, the front to rear depth of cassette  10  is less than the lengths of the substrates  32  so that when the microarrays are positioned in the cassette as shown, their opposite ends project appreciably, e.g., 10 mm, from the front and rear of the cassette. This permits the automatic feeder of the associated handling apparatus to grasp the ends of the substrates  32  projecting from the rear (or front) of the cassette in order to withdraw them from, or insert them into, the cassette. The other projecting ends may be used for manually handling the microarrays. Preferably only the unspotted end margins  32   b  of the substrate  32  project from the cassette so that all of the experimental spots S on the substrates remain within the boundaries of cassette  10 . 
     As best seen in FIG. 2, each compartment  36  in cassette  10  is defined by a pair of rails  38  formed at the inner surfaces of the cassette side walls  16   c . These rails extend from the front of cassette  10  all the way to the rear thereof. Preferably a recessed notch  42  is formed in the front and rear walls of cassette  10  (i.e., bezels  18  and  22 ) just above the opposite ends of each rail  38  to introduce, and help guide, the ends of the microarrays  12  onto the rails  38  in the various compartments  36 . Each microarray  12  may be slid along the rails  38  in the corresponding compartment  36  until the microarray is more or less centered in the cassette, ie., so that equal lengths of the microarray substrate  32  project from the front and rear of the cassette as shown in FIG.  3 . 
     In order to releasably retain each microarray  12  in the cassette, a pair of downwardly bowed, relatively low force leaf springs  44  are formed integrally in the cassette side walls  16   c  at the location of each compartment  36 . Each pair of leaf springs  44  overlies the corresponding pair of rails  38  and is arranged to bear down on the substrate side edge margins  32   a  of the microarray  12  positioned on the rails  38  of that compartment. Thus, each microarray is releasably retained in its compartment by frictional forces exerted by the rails  38  and the springs  44  bearing against the opposite surfaces of the substrate side edge margins  32   a  of the substrate itself midway between the ends of the substrate. Thus, the position of each microarray  12  in its compartment  36  is fixed in all three dimensions by housing side walls  16   c , rails  38  and springs  44  without any need for sub-frames. In fact, the illustrated storage device is able to secure each microarray  12  with dimensional tolerances of 76 mm+0.0 mm−1.0 mm in length, 26 mm±0.5 mm in width and 0.09 mm to 1.30 mm in height or thickness. 
     The bias exerted by the springs  44  on the microarrays in the various compartments  36  is strong enough to prevent the microarrays from moving within their respective compartments during normal handling of cassette  10 . However, when a sufficient pulling force is exerted on a projecting end of a microarray by the associated feeder mechanism (or by a user), the microarray may be withdrawn easily from cassette  10  or inserted back into the cassette. 
     Referring to FIGS. 1 and 3, the other component of the storage device, namely cover  14 , may be a simple generally rectangular structure having end walls  14   a , side walls  14   b  a top wall  14   c  and an open bottom. The cover is sized to fit over a cassette  10  filled with microarrays  12 . The cover  14  is dimensioned so that its end walls  14   a  provide adequate clearance for the projecting ends of the microarrays. Also as shown in FIG. 3 sufficient clearance is provided between the side wall  16   c  of the cassette and the side walls  14   b  of the cover so that when the storage device is positioned on the platform P of a microarray handling apparatus such as the one described in the above co-pending application, retaining or latching means extending up from platform P may releasably engage the cassette. Such retaining means are shown here as latches or spring clips C having noses C which can resiliently engage the shoulders  24  at the opposite sides of the cassette as shown in FIG.  3 . Of course, other latching means are possible; see the above co-pending application. 
     Desirably also, the handling apparatus has sufficient space around the platform P to provide clearance for cover  14 . 
     To facilitate lowering cover  14  on and removing it from cassette  10 , a handle  52  may be provided at the cover top wall  14   c  as shown in FIG.  3 . Also, means may be included for releasably locking or latching cover  14  to cassette  10 . In the illustrated embodiment, the locking means comprise a keyhole  54  formed in the top wall  14   a  of housing  14  as shown in FIGS. 1 and 3. Keyhole  54  is designed to receive a spring-loaded key  56  mounted to the cover top wall  14   c  at the handle  52  thereof. Key  56  may comprise a shaft  57  whose inner end  57   a  is formed as a T and whose outer end is formed as a button  57   b . A spring  58  is compressed between button  57   b  and handle  52  so that the shaft  57  is biased upwardly. 
     When cover  14  is placed on cassette  10  as shown in FIG. 3 with shaft end  57   a  aligned with keyhole  54 , key  56  may be pushed down into the keyhole. By turning button  57   b  approximately 90°, key  56  will become locked to the cassette. With the cover locked in place, a technician or other person, using handle  52 , may properly position the storage device on the platform P of the associated handling apparatus so that the clips C latch onto shoulders  24  of cassette  10 . Then, following rotation of the button  57   b  to its unlocked position, cover  14  may be removed from the cassette and withdrawn from the apparatus. 
     Similarly, when it is time to remove cassette  10  from the microarray handling apparatus following completion of a microarray process, the technician may lower cover  14  into the apparatus so that the cover engages over cassette  10 . After the cover is secured to the cassette using lock  56 , the technician may exert sufficient upward force on handle  52  to retract the housing shoulders  24  from spring clips C so that the entire storage device can be removed from the handling apparatus. 
     A wide variety of other locking mechanisms may be used to secure cover  14  to cassette  10 . For example, a conventional push-detent type of latch may be employed. The objective is to be able to lower cover  14  onto cassette  10  and releasably latch the cover to the cassette so that the cover can be used as a tool to insert a cassette into and withdraw it from the associated handling apparatus. In this way, the microarrays  12  in the cassette are protected by the storage device unless they are actually in the handling apparatus. 
     As noted above, cassette  10  and its cover  14  are made of an opaque plastic material so that any microarrays contained within the storage device are not affected by ambient light. Preferably also, cassette  10  (and perhaps cover  14  also) is formed of a conductive plastic as indicated by the conductive particles CP in FIG.  3 . This prevents prevents the buildup of any static charge that could adversely affect electronic components present in the handling apparatus or other apparatus in which the cassette is installed or with which it is used. 
     It is apparent from the forgoing that the our microarray storage device greatly reduces the handling required for microarrays, thus reducing labor costs and data microarray degradation and offers a convenient way to sort and safely store microarrays in batches and to introduce the microarrays into and withdraw them from processing apparatus having a common feeder platform. 
     It will thus be seen that the objects set forth above, among those made apparent from preceding description, are efficiently attained. Also, certain changes may be made in the above construction without departing from the scope of the invention. For example, our storage device may be used to store other small plate-like articles such as microscope slides and the like. Also, the storage device may include an opaque base for cover  14  that fits under cassette  10  so that the cassette and its contents may be fully enclosed and protected. Therefore, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention described herein.