Abstract:
Devices and systems for active thermal control of sample holding devices for bDNA testing, polymerase chain reaction testing, chemiluminescent immuno-assay testing, and so forth. The thermal control subsystem includes a fluidic circuit, first and second heater assemblies, a centrifugal pump, and a heat exchange device. The first and second heater assemblies include a heat removal device and a controllable thermo-electric device. One or both of the heater assemblies can include a heat spreader. A controller actively controls the pump, the heat removal device, and the thermo-electric devices, to thermally-control sample-containing vessels retained in the holding device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a divisional application claiming priority from U.S. Ser. No. 12/077,193 filed Mar. 17, 2008 which claims priority to U.S. Provisional Patent Application No. 60/918,190 filed on Mar. 15, 2007, both of which are incorporated by reference herein in their entirety. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    (Not Applicable) 
       BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates to devices and systems for providing active thermal control of sample-containing assay trays and, more specifically, to devices and systems that provide improved, uniform heat transfer from a sample-containing assay tray using thermo-electric devices, heat spreader plates, and liquid heat exchangers. 
         [0004]    Protocols for amplification of RNA or DNA, for example, during polymerase chain reaction (PCR), bDNA, and similar testing, require rapid and uniform heating and cooling of a plurality of sample-containing vessels. Because such testing typically is performed in batches, the rapid and uniform heating and cooling are applied to the plurality of sample-containing vessels simultaneously. 
         [0005]    Conventionally, heat transfer for thermo-electric devices and/or heating elements is accomplished by conduction, while cooling of thermal system components is done by convection, or, more conventionally, by air convection. However, thermal performance of such systems is limited by the space needs of relatively large thermal components. 
         [0006]    Therefore, it would be desirable to provide a liquid heat-transferring concept that transfers heat by liquid convection rather than by air convection to improve heat transfer and to provide a more compact thermal component size. Thermal control of sensitive reagents used in these protocols is also highly desirable. 
       SUMMARY OF THE INVENTION 
       [0007]    An active thermal control subsystem for controlling the temperature of a sample-containing holding device used in connection with bDNA testing, polymerase chain reaction testing, chemiluminescent immuno-assay testing, and the like is disclosed. The thermal control subsystem includes first and second assemblies, a pump, and a heat exchange device that are fluidly-coupled via a fluidic circuit. 
         [0008]    The first and second assemblies include a heat removal device and a thermo-electric device(s). One or more of the first and the second assemblies includes a heat spreader. The heat spreader is further thermally-coupled to the sample-containing holding device, such as a micro-well assay tray. The thermo-electric device(s) is/are disposed between the heat removal device and the heat spreader. Current transmitted to the thermo-electric device(s) is controlled. Depending on the voltage at each junction, heat can be transferred bi-directionally, either from the heat spreader to the heat removal device or from the heat removal device to the heat spreader. 
         [0009]    A testing system having active thermal control of a sample-holding device and/or a reagent-containing device is also disclosed. The system includes the thermal control subsystem described above and a controller. The controller controls operation of the pump, the heat exchange device, and the thermo-electric device(s) associated with the first and second assemblies to control the temperature of the sample-holding device and/or reagent-containing device. 
         [0010]    Optionally, the system can include a holding device for retaining reagent-containing vessels that is fluidly-coupled to the fluidic system and/or a drain line that is fluidly-coupled to the fluidic system for removing heat-transferring fluid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention will be better understood by reference to the following more detailed description and accompanying drawings where like reference numbers refer to like parts: 
           [0012]      FIG. 1  shows a diagram of a well subsystem in accordance with the present invention; 
           [0013]      FIG. 2  shows a diagram of micro-well assay trays disposed between first and second heater plates in accordance with the present invention; 
           [0014]      FIG. 3A  shows a diagram of a plan view of a heat sink (taken from the bottom) in accordance with the present invention; and 
           [0015]      FIG. 3B  shows a diagram of an isometric view of the heat sink of  FIG. 3A . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    U.S. Provisional Patent Application No. 60/918,190 filed on Mar. 15, 2007 and entitled “Active, Micro-well Thermal Control Subsystem”, from which priority is claimed, is incorporated herein by reference. 
         [0017]    An active control, micro-well thermal breadboard/micro-well thermal subsystem, e.g., for a bDNA testing system, a chemiluminescent immunoassay system, a PCR testing system, and the like, is disclosed. Referring to  FIG. 1 , there is shown an active thermal control subsystem  10  for controlling the temperature of at least one micro-well assay tray (not shown). The micro-well assay tray discussed in this disclosure corresponds to a conventional micro-well titer plate for holding multiple, i.e., 96, sample-containing cuvettes. The invention, however, is applicable to other sample-holding devices. 
         [0018]    The subsystem  10  is structured and arranged to maintain micro-well plate incubation temperatures between about 20 degrees Centigrade (° C.) and about 70° C., which is to say, between about 68 degrees Fahrenheit (° F.) and 158° F., respectively. Moreover, the subsystem  10  is structured and arranged so that the average temperature of the micro-well assay trays can be maintained within approximately ±0.5° C. of the specified or desired temperature and, moreover, so that the temperature difference between adjacent micro-well assay trays does not exceed approximately ±0.5° C. Optionally, the subsystem  10  of the present invention can also be structured and arranged to control the temperature of sensitive reagents used in the course of the PCR, chemiluminescent or other testing. 
         [0019]    The micro-well thermal subsystem  10  of the present invention includes first and second heater trays  14  and  16 , a heat exchanger  15 , a pump  18 , and a fluidic system  19 . Optionally, the micro-well thermal subsystem  10  can include a reagent holding device  12  and/or a system controller  20 , which in  FIG. 1  is shown separate from the micro-well thermal subsystem  10 . 
         [0020]    Each of the first and second heater trays  14  and  16 , the heat exchanger  15 , and the reagent holding device  12  are fluidly-coupled via a common fluidic system  19 . The fluidic system  19  includes fluid conduits, such as flexible tubing, for circulating a heat-transferring liquid. A drain line  17  can be provided to drain the fluidic system  19  and/or to bleed off excess heat-transferring liquid within the fluidic system  19 . 
         [0021]    A centrifugal pump  18 , such as the RD-05CV24 manufactured by Iwaki Co., Ltd. of Tokyo, Japan, is also fluidly-coupled to the fluidic system  19 . The centrifugal pump  18  is adapted to circulate a heat-transferring liquid, such as a water and ethylene-glycol (WEG) mixture, between the first and second heater trays  14  and  16  and the heat exchanger  15 , to transfer heat from or transfer heat to the first and second heater trays  14  and  16 ; between the reagent holding device  12  and the heat exchanger  15 , to transfer heat from or transfer heat to the reagent-containing vessels disposed in the reagent holding device  12 ; and between the fluidic system  19  and a coolant reservoir  25 , to add heat-transferring liquid to or to drain heat-transferring liquid from the fluidic system  19 . 
         [0022]    The reagent holding device  12  of the present invention includes inlet and outlet ports  26  and  28 , respectively, and associated internal fluidic connections (not shown) for controlling the temperature of reagent-containing vessels, e.g., test tubes, disposed in the reagent holding device  12 . The inlet and outlet ports  26  and  28  are releasably attachable to the external fluidic system  19  for circulating a heat-transferring liquid through the fluidic connections and about the reagent-containing vessels, to control the temperature of the reagent-containing test tubes by liquid convection. 
         [0023]    The heat exchanger  15  can be a conventional, radiator-type heat exchanger, having a coolant reservoir  22 , a plurality of coils  23 , and at least one fan assembly  21 . The coolant reservoir is adapted to hold heat-transferring liquid that has been heated in the first or second heater trays  14  and  16  and elsewhere in the fluidic system  19  temporarily. The plurality of coils  23  is adapted to circulate heat-transferring liquid from the coolant reservoir  22  to the fluidic system  19 . The fan assembly(ies)  21  is/are adapted to move ambient air against and around the coils  23 , to remove heat from the heat-transferring liquid circulating therein. Once sufficient heat has been removed from the heat-transferring liquid circulating in the coils  23 , the heat-transferring liquid is re-circulated to the first and second heater trays  14  and  16 , to the reagent holding device  12 , and/or to the coolant reservoir  22 . 
         [0024]    Referring to  FIG. 2 , a first side of each of the first and second heater trays  14  and  16  is operationally- and thermally-coupled to the item(s) being thermally-controlled, e.g., at least one 96-position micro-well assay tray  39 . The first side of the second heater tray  16  shown in  FIG. 1  and  FIG. 2  includes two sub-portions  24  and  27 , each of which is adapted for holding a conventional,  96 -position micro-well titer plate  39 . The first side of the first heater tray  14  includes two sealing pads  37  and  38  that are also adapted, in combination with the associated sub-portions  24  and  27  of the second heater tray  16 , for securing the 96-position micro-well titer plates  39  therebetween. 
         [0025]    As shown in  FIG. 2 , the sub-portions  24  and  27  of the second heater plate  16  are thermally-coupled to a heat spreader  31 . Optionally (as shown in  FIG. 2 ), the sealing pads  37  and  38  of the first heater tray  14  also can be thermally-coupled to a heat spreader  32 . Experimentation by the inventors evinced that micro-well thermal performance is more greatly influenced by the second (lower) heater tray  16  than by the first (upper) heater tray  14 . Hence, a heat spreader  32  for the first (upper) heater tray  14  can be omitted to reduce cost and simplify design. 
         [0026]    The heat spreaders  31  and  32  are adapted to avoid hot or cold spots within the micro-well assay trays  39 , especially during rapid, ramp temperature changes. The heat spreaders  31  and  32  also prevent direct heat transfer from thermo-electric devices (TEDs)  35 , which are disposed on the opposite sides of the heat spreaders  31  and  32 , to the center of the micro-well assay trays  39 . 
         [0027]    Heat spreaders  31  and  32  can be manufactured of copper, aluminum or some other relatively-highly thermally-conductive material. More specifically, the heat spreaders  31  and  32  are adapted to ensure that each micro-well assay tray  39  is maintained within approximately ±0.5° C. (±about 1° F.) of the specified temperature; that the temperature difference between adjacent micro-well assay trays  39  does not exceed approximately ±0.5° C.; that the ramp temperature change rate, i.e., “ramping”, for heating or cooling the micro-well assay trays  39  is between approximately 1° C./minute (about 2° F.) and approximately 10° C./minute (about 18° F./minute) and, more preferably, between approximately 1° C./minute and approximately 7° C./minute (about 13° F./minute); and that, during ramping, the upper (or lower) target temperature is not exceeded by more than approximately 0.5° C. 
         [0028]    As mentioned above, one side of each of the heat spreaders  31  and  32  is operationally- and thermally-coupled to a plurality of thermo-electric devices (TED)  35 , which are disposed to be in registration with the sub-portions  24  and  27  and the micro-well assay trays  39 . TEDs  35  are thermal controllers that transfer heat across their thickness by the Peltier effect. According to the Peltier effect, applying voltage to the junctions of two dissimilar metals causes a temperature difference between the two junctions. Hence, by varying the polarity of the voltages applied to the junctions, temperatures can be increased or decreased and, more importantly, heat can be transferred from one side of the TED  35  to the other side of the TED  35  in either direction. 
         [0029]    Advantageously, heat can be transferred from heat removal devices, i.e., heat sinks  11  and  13 , respectively, to the heat spreaders  31  and  32 , when ramping up the temperature of the micro-well assay trays  39 . Alternatively, heat can be transferred from the heat spreaders  31  and  32  to the heat sinks  11  and  13 , respectively, when ramping down the temperature of the micro-well assay trays  39 . 
         [0030]    Heat sinks  11  and  13  are thermal masses used for removing heat by conduction and/or by convection. Heat sinks  11  and  13  are well known to the art and will not be discussed in great detail. However, referring to  FIG. 3A and 3B , heat sinks  11  and  13  can include two opposing, relatively-highly thermally-conductive plates  42  and  44  that are releasably attachable to one another. At least one fluid-carrying channel  45  is disposed between the two plates  42  and  44 . The fluid-carrying channel(s)  45  of the heat sinks  11  and  13  includes an inlet port  49  and an outlet port  47 , which are fluidly-coupled to the fluidic system  19 . 
         [0031]    During operation, the direction of heat transfer between the heat sinks  11  and  13  and the micro-well assay trays  39  depends on whether the TEDs  35  are in a heating or in a cooling mode. During a heating mode, a rapid ramp-up temperature change of the micro-well assay tray(s)  39  is desired. For example, during PCR testing, conventionally, an analyte-containing sample is heated from ambient temperature to about 70° C. (about 158° F.) during the initial de-naturing cycle. 
         [0032]    Accordingly, voltages at the junctions of the TEDs  35  are controlled so that heat is transferred from the heat sinks  11  and  13  to the micro-well assay trays  39 . More specifically, the heat-transferring liquid in the fluidic system  19  is heated to an elevated temperature (or is allowed to remain at an elevated temperature) sufficient to transfer the necessary heat from the heat-transferring liquid to the heat sink(s)  11  and/or  13 . In some instances, the available heat in the heat sink(s)  11  or  13  may be sufficient to rapidly change the temperature of the micro-well assay trays  39  without using a heated liquid to heat the heat sink(s)  11  or  13 . 
         [0033]    During a cooling mode, a rapid ramp-down temperature change of the micro-well assay tray(s)  39  is desired. Accordingly, voltages at the junctions of the TEDs  35  are controlled so that heat is transferred from the micro-well assay trays  39  to the heat sink(s)  11  and/or  13  via the TEDs  35 . Heat-transferring liquid circulating though the channels disposed in the heat sink(s)  11  and/or  13  removes heat from the heat sink(s)  11  and/or  13 . 
         [0034]    A controller  20  ( FIG. 1 ) is electrically-coupled to the system  10 , for the purpose of controlling the centrifugal pump  18 , the heat exchanger  15 , and each of the TEDs  35  associated with the first and second heater trays  14  and  16 . The controller  20  can include electronic hardware, software, and/or applications, driver programs, and other algorithms as well as input/output devices to control the machination of the centrifugal pump  18 , the heat exchanger  15 , and each of the TEDs  35 . More specifically, the controller  20  is adapted to control the temperature of the heat-transferring liquid and, further, to control the heat transfer direction of the TEDs  35 , to heat or cool the micro-well assay tray(s)  39  automatically, and in accordance with the protocol of the PCR, bDNA, and related tests. 
         [0035]    In one aspect of the present invention, the first heater tray  14  is releasably attachable to the second heater tray  16 . Any clamping or other means for temporarily securing the first heater tray  14  to the second heater tray  16  can be used.  FIG. 1  shows a fastener-based embodiment, whereby a plurality of fasteners  51 , e.g., machine screws, bolts, and the like, are disposed through holes  53  in upper and lower clamping portions  52  and  54 , respectively, and, further disposed in associated openings disposed in the second heater tray  16 . As the fastening devices  51  are tightened, the upper and lower clamping portions  52  and  54  secure the upper heater tray  14 . As the fastening devices  51  are tightened more, the upper and lower heater trays  14  and  16  are tightly secured about the micro-well assay tray(s)  39 . 
         [0036]    The invention has been described in detail including the preferred embodiments thereof. However, those skilled in the art, upon considering the present disclosure, may make modifications and improvements within the spirit and scope of the invention.