Patent Publication Number: US-8110396-B2

Title: Thermocycling device with a thermal switch comprising a magnetic or metal thermoconducting liquid and a stimulating unit

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of EP Appl. No. 08009215.8 filed May 20, 2008, the content of which is hereby incorporated herein by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to a thermocycling device comprising a thermocycler module, to a method of cooling a heating block in a thermocycler module with a heatsink of a thermocycling device and to an analytical apparatus. 
     DESCRIPTION OF PRIOR ART 
     Thermocycling devices comprising thermocycler modules are mainly used for an automatic procedure of polymerase chain reactions (PCR). During a conduct of a PCR the liquid PCR-samples have to be heated and cooled to several temperatures. Typically, at least two temperatures, preferably an annealing, an incubation and a denaturation temperature, have to be accessed and maintained in repetitive cycles. For denaturation, the heating block of the thermocycling device has to be heated to temperatures up to 105° C. Thus, the time for heating and cooling the sample has a great influence on the overall process time. A decrease in heating and cooling time is essential for an efficient and cost effective process and an increase in throughput of a thermocycling device. 
     So far, mainly thermoelectric modules (TEC) are used for a fast thermocycling device for cooling and heating of a sample block, which carries the samples. A rapid thermocycler is e.g. disclosed in U.S. Pat. No. 6,556,940. This thermocycler comprises a low thermal mass sample block, whose temperature can be modulated by a single TEC. The TEC functions as the heater and cooler of the sample block. On the opposite side of the TEC a heat sink is arranged, which is used as a thermal reservoir. The heat sink is either cooled or heated depending on whether the sample block is heated or cooled, respectively. To enhance thermal connection between the TEC and the sample block and the heat sink, usually a thermal grease or thermal interface material in sheet form (e.g. graphite foil) is applied at the connecting surfaces. 
     Drawbacks of this technology are the need of permanent power for the thermoelectric module, because otherwise, the thermoelectric module is a thermal bridge, which will equalize the temperature on both sides of the module. Furthermore, the permanent change in temperature and the associated thermal expansion and contraction leads to a migration of the thermoelectric module and the thermal interface sheet material and bad thermal contacts between the surfaces of the thermoelectric module and the surface of the device to be temperature controlled. Furthermore, thermoelectric modules are expensive and susceptible to interference. 
     SUMMARY OF THE INVENTION 
     In first aspect the invention relates to a thermocycling device comprising a thermocycler module for heating and/or cooling, said thermocycler module comprising a thermal switch, a heating block, and a heat sink, wherein the thermal switch comprises a thermoconducting liquid and a stimulating unit for moving the thermoconducting liquid to provide in an on-state of the thermal switch, a thermal connection between the heating block and the heat sink and, in an off-state of the thermal switch, a thermal disconnection between the heating block and the heat sink. 
     In a second aspect the invention relates to a method of cooling a heating block in a thermocycler module with a heat sink of a thermocycling device, wherein the heating block is thermally connected to the heat sink said method comprising the step of switching on a thermal switch, and moving a thermoconducting liquid of the thermal switch with a stimulating unit to provide a thermal connection between the heating block and the heat sink. 
     In a third aspect the invention relates to an analytical apparatus comprising a thermocycling device according to the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  shows a perspective cross-sectional schematic view of a first embodiment of a thermocycler module for heating and/or cooling with a magnet in a rest position and a thermal switch in the off-state; 
         FIG. 2  shows a perspective cross-sectional schematic view of the thermocycler module shown in  FIG. 1  with the magnet and the thermal switch in an intermediate state; 
         FIG. 3  shows a perspective cross-sectional schematic view of the thermocycler module shown in  FIG. 1  and  FIG. 2  with the magnet in an active position and the thermal switch in an on-state; 
         FIG. 4  shows a perspective cross-sectional schematic view of a thermal switch of a second embodiment of the thermocycler module for heating and/or cooling with a Lorentz-force unit, the thermal switch being in an off-state; 
         FIG. 5  shows the thermal switch in the on-state in the same view as  FIG. 4 ; and 
         FIG. 6  shows a schematic representation of an analytical apparatus comprising a thermocycling device with a thermocycler module and further modules. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It is an object of the present invention to provide a thermocycling device comprising a thermocycler module allowing quick, e.g. within seconds, heating and cooling steps in a reliable and highly reproducible manner. 
     Further objects of the present invention are to provide a method to cool a heating block in a thermocycler module of a thermocycling device by using a thermal switch and to provide an analytical apparatus. 
     The inventive thermocycling device comprises a thermocycler module for heating and/or cooling. The thermocycler module comprises a thermal switch, a heating block and a heat sink. The thermal switch comprises a thermoconducting liquid and a stimulating unit for moving the thermoconducting liquid. In an on-state of the thermal switch, a thermal connection between the heating block and the heat sink is provided by the thermoconducting liquid and, in an off-state of the thermal switch, the thermal connection is disconnected. 
     The thermocycling device according to the invention has the advantage that only a small thermal load is to be heated. On the other hand, a heat sink is reliably connected and disconnected to the heating block with low thermal boundary resistance and high thermal conductivity. This allows a fast and reliable modulation of a temperature of the heating block without susceptible and expensive parts. Further, no detection of the position of the thermoconducting liquid is required since the thermoconducting liquid moves down under gravity when the stimulating unit is switched off. 
     Heating blocks used in thermocycling devices are heat conductive blocks comprising at least one cavity for receiving a reaction receptacle. Commonly the material of these heating blocks comprises aluminum or silver. In the thermocycling device, the heating block is controlled to change between at least two temperatures, for example an annealing, an incubation and an denaturation temperature, in one cycle. The temperature of the heating block can be changed very quickly by means of the thermal switch, which controls the transfer of heat between the heating block and the thermal sink. The thermal switch controls the thermal connection and disconnection of the heating block and the heat sink. 
     In a certain embodiment of the thermocycling device according to the present invention, the thermoconducting liquid -may comprise or may be a magnetic fluid and the stimulating unit may comprise a magnetic unit for moving the magnetic fluid in order to connect and/or disconnect the thermal connection between the heating block and the heat sink. Alternatively, the thermoconducting liquid may comprise or may be a liquid metal and the stimulating unit comprises a Lorentz-force unit for moving the liquid metal in order to connect and/or disconnect the thermal connection between the heating block and the heat sink. These embodiments have a simple design and work reliably. 
     A further aspect of the present invention is to switch the thermal switch by deforming a surface of the magnetic fluid by the magnetic unit or of the liquid metal by the Lorentz-force unit. 
     Another aspect of the present invention is to arrange the magnetic fluid and the liquid metal, respectively, at least partially between the heat sink and the heating block. In an off-state of the thermal switch, a gap is present between the magnetic fluid and the liquid metal, respectively, and the heating block. Thus, the heating block is thermally isolated with respect to the magnetic fluid and the heat sink. 
     The method for cooling a heating block in a thermocycler module of a thermocycling device according to the invention is based upon switching on a thermal switch, which in an on-state provides a connection between a heating block and a heat sink via a thermoconducting liquid, particularly a magnetic fluid or a liquid metal. 
     An analytical apparatus according to the present invention has the same advantages as the thermocycling device. 
     Further preferred embodiments are endowed with features contained in further depending claims. 
       FIG. 1  shows a thermocycler module  10  with a heating block  12  above a heat sink  14  and a thermal switch  16  in-between. The heating block  12  comprises a base-plate  20  and vial-walls  22  fixed at or integrally formed with the base-plate  20 . A number of reaction vials  24  (only one is shown) are loaded from above in loading recesses formed as blind holes  26 . Due to this configuration, the thermal mass of the heating block  12  is relatively low compared with the heat sink&#39;s  14  thermal mass. The heating block  12  can be heated by an incorporated, well known heater element  23 , e.g. a heated fluid or an electrical heater, indicated by an arrow. 
     A cover  30  of the heating block  12  has a thick circumferential border wall  32 . At corners  34  of the circumferential border wall  32  there are fixation throughput holes  36 . The fixation throughput holes  36  serve to accommodate fixation screws. 
     A frame  38  surrounds the upper border of the heat sink  14  and is fixed to the heat sink  14 , e.g. with further screws. In the corners of the frame  38  there are holes  39  with inner threads arranged as a prolongation of the fixation throughput holes  36 , so that the fixation screws can be screwed in these holes  39  to fix the cover  30  to the frame  38 . An upper inner border part of the frame  38  supports the bottom border part of the base-plate  20 . 
     By fixation of the cover  30 , the base surface of the circumferential border  32  partially presses against the upper circumferential border of the base plate  20  of the heating block  12 . The circumferential border of the base plate  20  is otherwise supported by the frame  38 . Thus, the heating block  12  is fixed via the frame  38  to the heat sink  14 . Additional circumferential grooves  28   a ,  28   b  arranged at upper border parts of the frame  38  and the heat sink  14 , respectively, accommodate an o-seal to seal a space enclosed by the heating block  12 , heat sink  14  and frame  38 . 
     The cover  30  and the frame  38  may be made at their connecting parts of a material with low or no thermal conductivity or the cover  30  and the frame  38  are thermally isolated against the other parts in touch with them. Thus the frame  38  thermally isolates the heating block  12  against the heat sink  14 . This also provides a relative low thermal mass of the heating block  12  and allows a rapid temperature modulation of the heating block i.e. the reagent. 
     The cover  30  comprises in its upper plate  42  vial-throughput-holes  40  above each blind hole  26  of the vial-walls  22  to allow the reaction vials  24  to be placed in the blind holes  26 . The reaction vials  24  are filled with a reagent  44 . 
     The heat sink  14  comprises a body  50  and a cap  52 . The body  50  is formed of a wall-section  51 , a column-section  54  and a bottom-section  56 . The cap  52  and the body  50  enclose a ring-shaped clearance  58  around the column-section  54 . The upper surface of the cap  52  forms a trough  60  which is open towards a bottom side  21  of the base plate  20 . The lower surface of the cap  52  comprises four accommodation recesses  62 , formed as bind-holes with openings facing away from the heating block  12  into the clearance  58 . 
     The thermal switch  16  comprises a stimulating unit  64  designed as a magnetic unit  66  and a thermoconducting liquid  68  in form of a magnetic fluid  70 , e.g. a Ferrofluid (FerroTec APGxxx). The magnetic liquid  70  is carried in the trough  60  of the heat sink  14 . The magnetic unit  66  comprises four permanent magnets  72 , e.g. in a cylindrical form, which are fixed with their bottom parts in openings of a frame-plate  74 . The upper part of the permanent magnets  72  project out of the frame-plate  74  in the direction towards the cap  52 . The frame-plate  74  encloses the column-section  54  and is placed in the clearance  58 , so that the frame plate  74  with the permanent magnets  72  can be displaced vertically along the column-section  54  in the perpendicular direction to the bottom-section  56 . The permanent magnets  72  are shown in the rest position in  FIG. 1 . Well known driving means  79  are connected to the frame-plate  74 . The driving means  79  can also be placed in the wall-section  51  or in the column-section  54 . 
     The magnetic fluid  70  is arranged between the heat sink  14  and the heating block  12 . A space  76  defining a gap is present between the magnetic fluid  70  and the heating block  12  in the off-state of the thermal switch  16 , when the permanent magnets  72  are in their rest-position away from the cap  52 , shown in  FIG. 1 . In particular the gap is present between the upper surface  78  of the magnetic fluid  70  carried in the trough  60  and the bottom side  21 . The upper surface  78  of the magnetic fluid  70  is opposite the bottom side  21 . 
     The space  76  isolates thermally the heat sink  14  from the heating block  12 . The connection via the frame  38  has a high thermal resistance. In the space  76  air or an other gas can be present. According to the present invention, It is also possible to improve the thermal isolation by evacuating the space  76  between the heating block  12  and the heat sink  14  enclosed by the frame  38 . The vacuum may also fix the base plate  20  on the frame  38  and thus the heating block  12  on the heat sink  14 . 
     A thermoelectric module  80  is arranged underneath the bottom-section  56  of the heat sink  14 , to hold a temperature of the heat sink  14  on a constant value or a predetermined temperature profile. 
     In an intermediate position shown in  FIG. 2  the frame-plate  74  is moved by the driving means  79  towards the cap  52 . Due to the increased interference of the magnetic field of the permanent magnets  72  and the magnetic liquid  70 , little bumps are formed in the upper surface  78 . 
       FIG. 3  shows the active position of the permanent magnets  72 . The upper part of the permanent magnets  72  are at least partially accommodated by the accommodation recesses  62 . In the corresponding on-state of the thermal switch  16 , the magnetic field of the magnetic means, i.e. the permanent magnets  72 , deform a surface of the magnetic fluid  70 . The upper surface  78  is at least partially in contact with the bottom side  21  of the base plate  20  of the heating block  12 . A bottom surface of the magnetic fluid  70  is always in contact with a surface of the trough  60 . Thus a thermal connection is provided between the heating block  12  and the heat sink  14  to cool the heating block  12 . This cooling is provided within seconds, because the thermal mass of the heat sink  14  is much higher than the thermal mass of the heating block  12 . Therefore, it is beneficial to design the heating block  12  with a relative low mass as explained above. 
       FIG. 1 ,  FIG. 2 , and  FIG. 3  show a course of action of the thermal switch  16  from an off-state ( FIG. 1 ) to an intermediate state ( FIG. 2 ) up to an on-state ( FIG. 3 ) of the thermal switch  16 . 
     By driving the frame-plate  74  with the driving means  79  and hence, the permanent magnet  72  from a rest position shown in  FIG. 1  to an intermediate position shown in  FIG. 2  up to an active position shown in  FIG. 3  a magnetic field of the permanent magnet  72  interferes more and more with the magnetic liquid  70 . The result is, that the upper surface  78  of the magnetic liquid  70  begins to deform and the surface is partially moved against the base plate  20  of the heating block  12  until the upper surface  78  is at least partially in contact with the heating block  12 . Hence, the thermal switch  16  is switched on. Due to the thermal switch&#39;s low thermal contact resistance, the high thermal conductivity of the magnetic liquid  70  and the heat sink&#39;s relative large thermal mass, the heating block  12  is cooled within seconds to the desired temperature. 
     To switch off the thermal switch  16  the driving means  79  have to move the frame-plate  74  from the active position ( FIG. 3 ) to the rest position ( FIG. 1 ), so that the magnetic field of the permanent magnets  72  have a negligible interference with the magnetic fluid  70 . The heater element  23  is switched alternately with the thermal switch  16 , so that the heater element  23  has to heat only the relative low thermal mass of the heating block  12 . The heating block  12  is heated by the heater-element  23  to the desired temperature within seconds. 
       FIGS. 4 and 5  show an alternative embodiment of the heat sink  14  with thermal switch  16  of the thermocycler module  10 . The thermal switch  16  comprises a Lorentz-force unit  86  as stimulating unit  64  and a liquid metal  88 , e.g. GaInS as thermoconducting liquid  68 . The liquid metal  88  is carried in the trough  60  of the heat sink  14 . The opening of the trough  60  in the form of a cuboid is laterally delimited by four side wall-sections and at the bottom side by a bottom wall-section of the heat sink  14 . A thermoelectric module is arranged underneath the bottom wall-section to hold the temperature of the heat sink  14  on a constant value or a predetermined temperature profile; c.p.  FIG. 1 to 3 . 
     The heating block  12  as shown in  FIG. 1 to 3  is arranged above the heat sink  14  so that the bottom side  21  of the base plate  20  of the heating block  12  delimits the opening of the trough  60  at the upper side. A thermal isolation is present between the heat sink  14  and the heating block  12 . 
     Two opposing side wall-sections of the body of the heat sink  14  comprise each at the surface directed toward the opening of the trough  60  an electrode plate  90   a  and  90   b , respectively. The electrode plate  90   a  of the one of the two side wall-sections is connected to a positive output connection (+) and the electrode plate  90   b  of the other of these two side wall-sections is connected to a negative output connection (−) of an electrical control unit. 
     A permanent magnet  92  is assigned to each of the residual two opposing side wall sections. The permanent magnet  92  generates a magnetic field B in the opening of the trough  60 . 
     As shown in  FIG. 4 , in the off-state of the thermal switch  16  no electrical tension is applied to the electrode plates  90   a ,  90   b  and no electrical current is flowing in the liquid metal  88  being in contact with the electrode plates  90   a ,  90   b . A space  76  defining a thermal isolation gap is present between the liquid metal  88  and the bottom side  21  of the heating block  12 . 
       FIG. 5  shows the on-state of the thermal switch  16 . The electrical control unit applies a voltage to the electrode plates  90   a  and  90   b , thus an electrical current I is flowing through the liquid metal  88  from the electrode plate  90   a  to the electrode plate  90   b . This electrical current I and the magnetic field B generate a force F deforming the liquid metal  88  and moving the upper surface  78  of the liquid metal  88  upwardly until the liquid metal  88  is in contact with the bottom side  21  of the heating block  12 . Thus, the heating block  12  is cooled within seconds to the desired temperature. Thereby, the bottom surface of the liquid metal  88  remains in contact with the bottom wall-section of the trough. 
     A thermocycling device according to the present invention and schematically shown in  FIG. 6  comprises a thermocycler module  10 , two embodiments of this thermocycler module  10  are shown in  FIG. 1 to 5  and described above. 
     The thermocycling device may further comprise a defection unit  96 , for example an optical defection unit for determining the amount of nucleic acid analyte produced during amplification in the thermocycler module  10 . In a certain embodiment, the TaqMan methodology is used for simultaneous amplification and defection of the nucleic acid analyte by measuring the intensity of fluorescent light, as disclosed in WO 92/02638 and the corresponding documents U.S. Pat. No. 5,210,015, U.S. Pat. No. 5,804,375 and U.S. Pat. No. 5,487,972. 
     The thermocycling device may for example also comprise a heated lid  98  for covering the reaction receptacles (e.g. reaction vials  24 ) held by the heating block  12 . 
     As further shown in  FIG. 6 , an analytical apparatus  100  comprises a thermocycling device according to the present invention. The analytical apparatus  100  may further comprise a storage module  102  for storing consumables used during the analytical test. Furthermore, a sample preparation module  104  may be comprised in the analytical apparatus  100 . In the sample preparation module  104 , a sample comprising analyte which was obtained from a biological sample is prepared such that the analyte, preferably a nucleic acid analyte, can be analysed by amplification. In a certain embodiment all steps carried out in the analytical apparatus  100  are fully automated. 
     The use of a thermoconducting liquid  68  has several advantages. The thermal connection can be connected and disconnected with a high reliability. Since the thermoconducting liquid  68  coats the base plate very efficiently, the surface connection to the base plate  20  in the on-state of the thermal switch  16  provides a very low thermal boundary resistance. The thermoconducting liquid  68  itself, in the form of a magnetic fluid  70  or a liquid metal  88 , has a high thermal conductivity compared to thermal greases. In the off-state, the thermoconducting liquid  68  disconnects promptly without any residues at the base plate  20 . Furthermore, in comparison to thermal greases, no degradation due to evaporation of grease compounds and no air enclosures occur. In the off-state no material filaments remain between the heating block  12  and the heat sink  14 . 
     In a further embodiment of the invention the permanent magnets  72  of the embodiment shown in  FIG. 1 to 3  are replaced by electromagnets, e.g. an inductor. The inductors can be switched on and off by simple, well known electrical switching means and can be installed fixed under the magnetic liquid  70 . Thus, this further embodiment of the thermocycler module  10  as well as the embodiment disclosed in  FIGS. 4 and 5  do not require movable parts with the exception of the thermoconducting liquid  68 . The permanent magnets  92  of the Lorentz-force unit  86  can also be replaced by electromagnets. 
     
       
         
           
               
             
               
                   
               
               
                 Reference numerals 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 10 
                 thermocycler module 
               
               
                 12 
                 heating block 
               
               
                 14 
                 heat sink 
               
               
                 16 
                 thermal switch 
               
               
                 20 
                 base-plate 
               
               
                 21 
                 bottom side base plate 21 
               
               
                 22 
                 vial-walls 
               
               
                 23 
                 heater element 
               
               
                 24 
                 reaction vials 
               
               
                 26 
                 blind holes 
               
               
                  28a 
                 circumferential groove 
               
               
                  28b 
                 circumferential groove 
               
               
                 30 
                 cover 
               
               
                 32 
                 circumferential border wall 
               
               
                 34 
                 corners of circumferential border wall 32 
               
               
                 36 
                 throughput holes 
               
               
                 38 
                 frame 
               
               
                 39 
                 holes 
               
               
                 40 
                 vial-throughput-holes 
               
               
                 42 
                 upper plate 
               
               
                 44 
                 reagent 
               
               
                 50 
                 body of heat sink 14 
               
               
                 51 
                 wall-section 51 of body 50 
               
               
                 52 
                 cap 
               
               
                 54 
                 column-section of body 50 
               
               
                 56 
                 bottom-section of body 50 
               
               
                 58 
                 ring-shaped clearance 
               
               
                 60 
                 trough 
               
               
                 62 
                 recesses 
               
               
                 64 
                 stimulating unit 
               
               
                 66 
                 magnetic unit 
               
               
                 68 
                 thermoconducting liquid 
               
               
                 70 
                 magnetic fluid 
               
               
                 72 
                 permanent magnet 
               
               
                 74 
                 frame-plate 
               
               
                 76 
                 space 
               
               
                 78 
                 upper surface of the magnetic fluid 
               
               
                 79 
                 driving means 
               
               
                 80 
                 thermoelectric module 
               
               
                 86 
                 Lorentz-force unit 
               
               
                 88 
                 liquid metal 
               
               
                  90a 
                 electrode plate 
               
               
                  90b 
                 electrode plate 
               
               
                 92 
                 permanent magnet 
               
               
                 96 
                 defection unit 
               
               
                 98 
                 heated lid 
               
               
                 100  
                 apparatus 
               
               
                 102  
                 storage module 
               
               
                 104  
                 preparation module 
               
               
                   
               
            
           
         
       
     
     While the foregoing invention has been described in some detail for purposes of clarity and understanding, it will be clear to one skilled in the art from a reading of this disclosure that various changes in form and detail may be made without departing from the true scope of the invention. For example, the systems and methods described above may be used in various combinations. All publications cited in this application are incorporated by reference in their entirety for all purposes to the same extent as if each individual publications were individually indicated to be incorporated by reference for all purposes.