Abstract:
A slide heater for use in a slide processing apparatus in which an interface surface between the slide heater and the slide has a plurality of slots or channels terminating in an edge thereof, for gathering and venting gas bubbles.

Description:
TECHNICAL FIELD 
     The present invention relates to slide processing apparatus, and more particularly to improvements in heaters for slides for biological reaction analysis slide processing systems. 
     BACKGROUND ART 
     Immunostaining and in situ DNA analysis are useful tools in histological diagnosis and the study of tissue morphology. Immunostaining relies on the specific binding affinity of antibodies with epitopes in tissue samples, and the increasing availability of antibodies which bind specifically with unique epitopes present only in certain types of diseased cellular tissue. Immunostaining requiring a series of treatment steps conducted on a tissue section mounted on a glass slide to highlight by selective staining certain morphological indicators of disease states. Typical steps include pretreatment of the tissue section to reduce non-specific binding, antibody treatment and incubation, enzyme labeled secondary antibody treatment and incubation, substrate reaction with the enzyme to produce a fluorophore or chromophore highlighting areas of the tissue section having epitopes binding with the antibody, counterstaining, and the like. Each of these steps is separated by multiple rinse steps to remove unreacted residual reagent from the prior step. Incubations typically are conducted at around 40° C., while cell conditioning steps typically are conducted at somewhat higher temperatures, e.g. 90-100° C. In-situ DNA analysis relies upon the specific binding affinity of probes with unique nucleotide sequences in cell or tissue samples and similarly involves a series of process steps, with a variety of reagents and process temperature requirements. 
     Automated systems have been proposed to introduce cost savings, uniformity of slide preparation, and reduction of procedural human errors. Stross, W. et al, J. Clin. Pathol. 42: 106-112 (1989) describes a system comprising a series of baths positioned under the circumference of a circular, rotatable disc from which slide trays are suspended. The disc is lifted to lift slide trays from their baths, turned to position the slide trays above the next consecutive bath, and lowered to immerse the slide trays in the baths. This operation can be automated with suitable timers and switches. This system exposes each of the slides to the same treatment and relies on dipping for application of reactants and rinsing. 
     Stark, E. et al, J. Immunol. Methods. 107: 89-92 (1988) describes a microprocessor controlled system including a revolving table or carousel supporting radially positioned slides. A stepper motor rotates the table, placing each slide under one of the stationary syringes positioned above the slides. A predetermined volume of liquid, determined by a dial, is delivered to a slide from each syringe. Microprocessor controls are provided. 
     Cosgrove, R. et al, ACL. pp 23-27 (December, 1989) describe an immunostaining apparatus for auto-pipetting reagents into a slide well from a carousel holding up to 18 reagent vials. Below each well, a coverplate spaced from the surface of each slide provides cover and defines a reagent flow channel. The slides are suspended at a steep angle. Reagent from the well flows downward over the slide surface. A row of slides are suspended for sequential treatment. Washing is accomplished by a 3 to 4 minute continuous running wash over the sample, yielding an estimated 20:1 wash/reagent ratio. 
     Brigati, D. et al, J. Histotechnology 11: 165-183 (1988) and Unger, E. Brigati, D. et al, et al, J. Histotechnology. 11: 253-258 (1988) describe the Fisher automated work station using capillary gap technology. A coverplate is placed over the slide, forming a capillary gap. Liquid is introduced into the capillary gap by placing the lower edge of the plate-slide pair in a liquid. Liquid is removed by placing the lower edge of the plate-slide pair on a blotter. The system is further described in U.S. Pat. Nos. 4,777,020, 4,798,706 and 4,801,431. The previously known devices are listed in their performance and unable to satisfy the needs for automated, high precision immunohistology. 
     The foregoing discussion of the prior art derives in large part from U.S. Pat. No. 5,654,200 to Copeland et al., who describe an automated biological processing system comprising a reagent carousel cooperating with a sample support carousel to apply a sequence of preselected reagents to each of the samples with interposed mixing, incubating, and rinsing steps cooperating therewith. This patented automated biological processing system, which is available from Ventana Medical Systems, Inc. of Tucson, Ariz. includes a slide support carousel having a plurality of slide supports thereon and drive means engaging the slide support carousel for consecutively positioning each of a plurality of slide supports in a reagent receiving zone. The reagent carousel has a plurality of reagent container supports thereon and drive means engaging the reagent carousel for rotating this carousel and positioning a preselected reagent container support and associated reagent container in a regent supply zone. The apparatus has a reagent delivery actuator means positioned for engaging a reagent container positioned on a container support in the reagent supply zone and initiating reagent delivery from the reagent container to a slide supported on a slide support in the reagent receiving zone. 
       FIG. 1 , which largely corresponds to FIG. 3 of U.S. Pat. No. 5,654,200 is a partial exploded isometric view of an automated biological processing system, with the cabinet, liquid and air supply tubing and electrical wiring omitted in the drawings for the purposes of clarity. 
     The apparatus has an upper section  2 , intermediate section  4  and lower section  6 . In the upper section  2 , reagent bottle support carousel  10  is mounted for rotation about its central axis on upper support plate  8 . Reagent bottles  12  required for the immuno-histochemical reactions to be conducted during slide treatment cycle are supported by the carousel  10 , mounted in reagent bottle receptors  11 . These receptors  11  are configured to receive volumetric pump outlet tubes (not shown). The receptors  11  are preferably equally spaced in a circular pattern axially concentric with the carousel axis. The number of receptors  11  provided should be sufficient to accommodate the number of different reagent bottles  12  required for a cycle or series of cycles. The carousel  10  is rotated by the stepper motor  14  and drive belt  16  to a position placing a selected reagent bottle  12  in the reagent delivery position under an air cylinder reagent delivery actuator  18  over a slide to be treated with reagent. Reagent tray motor driver  20  is connected to stepper motor  14 . 
     The intermediate section  4  comprises support plate  22  upon which the slide support carousel  24  is rotatably mounted. The carousel  24  supports slide supports  26 . In the intermediate section  4 , a stepper motor  48  rotates the slide support carousel  24 , engaging drive belt  25  engaging the perimeter of the slide support carousel  24 . Splash guard  50  is a wall which surrounds the sides, back and part of the front of the carousel  24 , and contains liquid spray and droplets produced in the processing. Splash guard  50  extends upward from the intermediate plate  22  to a position adjacent the upper plate  8 , leaving an air flow gap between the upper edge of the splash guard  50  and the underside of the plate  8 . Lower section  6  includes slide carousel stepper motor driver  72  and relay  74 , power supplies  76  and  78 , and control systems all mounted on plate  40 . 
     Referring to  FIGS. 2 and 3 , slide support  26  comprises a molded plastic base  80  on which is mounted a metal plate  82 . An electrical resistance heater shown in phantom at  84  is mounted in direct contact to the underside of metal plate  82 . Corner pins  86  locate a specimen carrying glass slide  88  on the surface of metal plate  82 . Metal plate  82  has a top surface that is essentially flat and smooth. Flatness and smoothness facilitates glass plate position stability and thermal conduction uniformity. 
     In practice, water and other fluids employed in the slide processing may spill over the edges of the slides, and work their way under the slides where the fluids may boil, causing the slides to “pop” or dislocate. Moreover, since heater surfaces are not perfectly flat, in order to insure good thermal contact between metal plate  82  and glass slide  88 , a thin layer  90  of oil may be applied to the top surface of metal plate  82 . However, using oil as an interfacial heating medium, may exacerbate the problem of slide popping or dislocation due to gas formation from water or other fluid getting under the slide, mixing with the oil and then boiling off in an uncontrolled fashion. Dislocation of a slide may cause that slide to set up on a post, thereby compromising the processing of that one slide, or in a worse case scenario result in a domino or train wreck effect where the one dislocated slide hits a neighboring slide causing that slide to dislocate, and so forth. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention overcomes the aforesaid and other disadvantages of the prior art, by patterning the slide heater upper surface and/or the glass slide underside surface with ridges or slots, whereby gas bubbles generated by boiling of water trapped between the slide heater and the slide may be channeled, to edges of the slide heater, where the gas may escape or vent without lifting or otherwise dislocating the glass slide. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the present invention will be seen from the following detailed description, taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a partial exploded isometric view of a prior art automated slide processing apparatus; 
         FIG. 2  is a top plan view of a prior art slide support and heater; 
         FIG. 3  is a side elevational view of a prior art slide support and heater; 
         FIG. 4  is a top plan view of a slide support heater made in accordance with a first embodiment of the present invention; 
         FIG. 5  is a side elevational view, in cross-section, of a slide support heater of  FIG. 4 ; 
         FIG. 6  is an enlarged detail view, in cross-section, of a portion of the slide heater of  FIG. 5 ; 
         FIG. 7  is a view similar to  FIG. 4  showing details of an alternative slide support heater in accordance with the present invention; 
         FIG. 8  is a side elevational view of the slide support heater of  FIG. 7 ; 
         FIG. 9  is an enlarged detail view of the slide support heater of  FIG. 8 ; 
         FIGS. 10 and 11  are views, similar to  FIG. 9 , of yet other embodiments of slide support heaters made in accordance with the present invention; 
         FIGS. 12-14  are views similar to  FIG. 4  of yet other embodiments of slide support heaters made in accordance with the present invention; 
         FIGS. 15-17  are views similar to  FIGS. 4-6 , respectively, of still another alternative of the present invention; and 
         FIGS. 18 and 20  and  19  and  21 , are views similar to  FIGS. 6 and 17 , respectively, of still other alternative of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention is based on the discovery that ridges or slots formed on the upper surface of the slide heater and/or on the lower surface of the slides serve to route or channel bubbles formed by the boiling of water or other fluid trapped between the slide heater and slide, to edges of the slide, where the bubbles may vent without dislodging the slide. As mentioned supra, heater surfaces are not perfectly flat. Thus, slight variations in surface heaters may result in a bias or pooling of gas, i.e., steam bubble migration to low areas, and/or in the case of a slide having an interfacial layer or oil, into and through regions of deeper oil. In the case of prior art slide heaters, the migrating gas could pool to a vapor pocket which could “pop” the slide. The present invention takes advantage of the phenomena of gas bubble migration by creating channels for the gas which terminate at open edges of the slide heater. Gas bubbles forming on the surface of the heater migrate to the channels, displace any oil present in the channels, and run to the ends of the channels, where the migrating gas bubbles vent harmlessly from the slide heater edges without dislodging the slide. 
     An important feature and requirement of any slide heater is to provide substantially uniform heating across a slide since non-uniformity of heating could result in unreliable analytical results. Thus, the general wisdom has been to make heater surfaces and slide surfaces as smooth as possible, i.e., so as to achieve maximum contact or match. Unexpectedly, it has been found that up to about 50% of the slide heater upper surface and/or glass slide may be removed, i.e., by patterning with channels or slots, without adversely affecting thermal conduction uniformity and temperature uniformity distribution across the interface between the slide heater and the glass slide. In other words, provided about at least 50% of the slide heater and glass slide facing surfaces are retained, there is sufficient thermal conduction uniformity between the heater and the slide to mediate slight thermal differences between the low and high parts of the slots or channels resulting in substantially uniform heating of the slide. 
     The slots or channels may be formed by machining, casting or etching, and should be spaced close enough together so that nucleating gas bubbles do not have to travel too far before reaching a slot or channel. Typically, the slots or channels are spaced about 2 to 5 millimeters on center, preferably about 3 to 4 millimeters. Spacing the slots or channels more than about 10 millimeters apart, on center, may permit gas bubble pooling and thus may not provide sufficient glass slide stability. On the other hand, forming slots or channels closer than about 3 millimeters, on center, may result in removal of a greater percentage of the surface than ideal for uniform thermal conductivity, depending on the width of the slots or channels. Also, placing the slots or channels too close together, and/or forming a large number of narrow slots or channels, adds to initial fabrication costs and may make cleaning more difficult; and, making the channels or slots overly narrow could restrict free venting of gas. 
     Preferably the slots or channels are similar in size and shape, and run parallel or near parallel to one another, and preferably run from side edge to side edge of the heater. The aspect ratio of the slots or channels per se appears to have little affect on the ability to gather and vent nucleating gas bubbles. Nor does the cross-sectional shape of the slots or channels significantly affect the ability to gather and vent nucleating gas bubbles provided the slots or vents are not overly narrow. As a practical matter, rounded or square edge slots or channels, which could be formed simply by machining, are preferred. Alternatively, the slots or channels can be cast. 
     Referring now to  FIGS. 4-6 , there is shown a first embodiment of slide heater made in accordance with the present invention. (For clarity, details other than the heater surface have been omitted). The heater  100  has an upper surface  102  in which are formed  15  substantially parallel grooves  104 . Slots or channels  104  have a rounded bottom of about 0.4 millimeter radius, and run from side to side of the heater  100 . The slots or channels  104  are approximately 0.25 millimeter at their deepest point, and are spaced at about 3 millimeters on center. 
     Referring to  FIGS. 7-9 , where there is shown an alternative slide heater made in accordance with the present invention. The  FIGS. 7-9  embodiment differs from the embodiment of  FIGS. 4-6  in that the slots or channels are “v” shaped. 
     In yet another embodiment illustrated in  FIG. 10 , the slots or channels are rectilinear in shape, and have a depth-to-width ratio of about 0.2 to 2, preferably about 0.3 to 0.5.  FIG. 11  is similar to  FIG. 10 , in which the slots or channels have a different depth-to-width ratio. 
     Various changes may be made in the invention without departing from the spirit and scope thereof. For example, as shown in  FIG. 12 , the slots or channels may be formed blind at one end. 
     It also may be possible to orient the slots or channels to run the length rather than the width of the heaters ( FIG. 13 ), or at a diagonal ( FIG. 14 ). However, doing so increases the length of the slots or channels, and could result in pooling of gas bubbles in an individual slot or channel, as well as increased transit time to the edges of the slots or channels before the gas could be vented. Accordingly, for optimization purposes, it is preferred that the slots or channels are made as short as possible and run side to side with no interconnections from slot to slot, i.e. the slots should not intersect. In yet another embodiment of the invention, illustrated in  FIGS. 15-17 , slots or channels  200 , similar in arrangement to slots or channels  104 , may be provided on the underside of a glass slide  202 , and provide similar function. 
     Yet other changes may be made without departing from the spirit and scope of the invention. For example, instead of machining or casting referring to  FIGS. 18-21 , slots in channels in the interface surface of the heater or the glass slide, spaced raised regions  300  may be formed on the interface surface of the heater  302  on the glass slide  304  by applying a thermally conductive decal much as a patterned metal foil  306 , or by printing with a thermally conductive ink or coating  308  or the like, so as define slots or channels therebetween.