The present invention relates to a device for the carrying out of chemical or biological reactions with
- a reaction vessel receiving element for receiving reaction vessels, wherein the reaction vessel receiving element has several recesses arranged in a regular pattern to receive reaction vessels, a heating device for heating the reaction vessel receiving element, and a cooling device for cooling the reaction vessel receiving element.
Such devices are described as thermocyclers or thermocycling devices and are used to generate specific temperature cycles, i.e. to set predetermined temperatures in the reaction vessels and to maintain predetermined intervals of time.
A device of this kind is known from U.S. Pat. No. 5,525,300. This device has four reaction vessel receiving elements, each with recesses arranged in a regular pattern. The pattern of the recesses corresponds to a known pattern of reaction vessels of standard microtiter plates, so that microtiter plates with their reaction vessels may be inserted in the recesses.
The heating and cooling devices of a reaction vessel receiving element are so designed that a temperature gradient extending over the reaction vessel receiving element may be generated. This means that, during a temperature cycle, different temperatures may be obtained in the individual reaction vessels. This makes it possible to carry out certain experiments at different temperatures simultaneously.
This temperature gradient is used to determine the optimal denaturing temperature, the optimal annealing temperature and the optimal elongation temperature of a PCR reaction. To achieve this, the same reaction mixture is poured into the individual reaction vessels, and the temperature cycles necessary to perform the PCR reaction are executed. Such a temperature cycle comprises the heating of the reaction mixture to the denaturing temperature, which usually lies in the range 90°-95° C., cooling to the annealing temperature, which is usually in the range 40°-60° C., and heating to the elongation temperature, which is usually in the range 70-75° C. A cycle of this kind is repeated several times, leading to amplification of a predetermined DNA sequence.
Since a temperature gradient can be set, different but predetermined temperatures are set in the individual reaction vessels. After completion of the cycles it is possible to determine, with the aid of the reaction products, those temperatures at which the PCR reaction will give the user the optimal result. Here the result may be optimised e.g. in respect of product volume or also product quality.
The annealing temperature, at which the primer is added, has a powerful influence on the result. However the elongation temperature too can have beneficial or adverse effects on the result. At a higher elongation temperature, the addition of the bases is accelerated, with the probability of errors increasing with higher temperature. In addition, the life of the polymerase is shorter at a higher elongation temperature.
A thermocycling device, by which the temperature gradient may be set, makes it much easier to determine the desired temperatures, since a reaction mixture my simultaneously undergo cycles at different temperatures in a single thermocycling device.
Another important parameter for the success of a PCR reaction is the residence time at the individual temperatures for denaturing, annealing and elongation, and the rate of temperature change. With the known device, these parameters can not be varied in one test series for an individual reaction vessel holder. If it is desired to test different residence times and rates of change, this can be done in several test series either consecutively on one thermocycling device or simultaneously in several thermocycling devices.
For this purpose there are so-called multiblock thermocycling devices with several reaction vessel receiving elements, each provided with separate cooling, heating and control devices (see U.S. Pat. No. 5,525,300). The reaction mixture to be tested must be distributed over several microtiter plates, for testing independently of one another.
To determine the optimal residence times and rates of temperature change it is necessary to have either several thermocycling devices or a multiblock thermocycling device, or to carry out tests in several consecutive test series. The acquisition of several thermocycling devices or of a multiblock thermocycling device is costly and the carrying-out of several consecutive test series takes too long. In addition, handling is laborious when only part of the reaction vessels of several microtiter plates is filled, with each of the latter being tested and optimised in separate test series. This is especially disadvantageous in the case of device which operate automatically and in which the reaction mixtures are subject to further operations, since several microtiter plates must then be handled separately. It is also extremely impractical when only part of the reaction vessels of the microtiter plates is filled, since the devices for further processing, such as e.g. sample combs for transferring the reaction products to an electrophoresis apparatus, are often laid out on the grid of the microtiter plates, which means that further processing is correspondingly limited if only part of the reaction vessels of the microtiter plate is used.
U.S. Pat. No. 5,819842 discloses a device for the individual, controlled heating of several samples. This device has several flat heating elements arranged in a grid pattern on a work surface. Formed below the heating elements is a cooling device which extends over all the heating elements. In operation a specially designed sample plate is placed on the work surface. This sample plate has a grid plate, covered on the underside by a film. The samples are poured into the recesses of the grid plate. In this device the samples lie on the individual heating elements, separated from them only by the film. By this means, direct heat transfer is obtained. The drawback of this device, however, is that no commonly available microtiter plate can be used.
With increasing automation in biotechnology, thermocyclers are increasingly being used in automated production lines and with robots as one of several work stations. Here it is customary for the samples to be passed in microtiter plates from one work station to the next. If the device according to U.S. Pat. No. 5,819,842 were to be used in such an automated production process, it would be necessary for the samples to be pipetted out of a microtiter plate into the specially designed sample plate before temperature adjustment, and from the sample plate into a microtiter plate after temperature adjustment. Here there is a risk of contamination of the samples. The use of this specially designed sample plate must therefore be regarded as extremely disadvantageous.
The invention is based on the problem of developing the device described above in such a way that the disadvantages described above are avoided and the parameters of the PCR process may be optimised with great flexibility.
To solve this problem the invention has the features specified in claim1. Advantageous developments thereof are set out in the additional claims.
The invention is characterised by the fact that the reaction vessel receiving element is divided into several segments, with the individual segments thermally decoupled and each segment assigned a heating device which may be actuated independently.
By this means the individual segments of the device may be set to different temperatures independently of one another. This makes it possible not only to set different temperature levels in the segments, but also for them to be held for varying lengths of time or altered at different rates of change. The device according to the invention thus permits optimisation of all physical parameters critical for a PCR process, while the optimisation process may be carried out on a single reaction vessel receiving element in which a microtiter plate may be inserted.
With the device according to the invention it is therefore also possible to optimise the residence times and rates of temperature change without having to distribute the reaction mixture over different microtiter plates for this purpose.
The thermocycling device according to the invention is in particular suitable for optimising the multiplex PCR process, in which several different primers are used.
The above problem, and the features and advantages according to the present invention, may be better understood from the following detailed description of preferred embodiments of the present invention and with reference to the associated drawings.
The invention is explained in detail below with the aid of the drawings. These show in:
FIG. 1 a section through a device according to the invention for carrying out chemical or biological reactions in accordance with a first embodiment,
FIG. 2 a section through an area of a device according to the invention for carrying out chemical or biological reactions in accordance with a second embodiment,
FIG. 3 a schematic plan view of the device ofFIG. 2,
FIG. 4 a schematic plan view of a device according to a third embodiment, an area of the device ofFIG. 4 in a sectional view along the line A-A,
FIGS. 6 to 9 schematic plan views of reaction vessel receiving elements with differing segmentation
FIG. 10 a clamping frame in plan view
FIG. 11 a device according to the invention in which segments of a reaction vessel receiving element are fixed by the clamping frame according toFIG. 10, and
FIG. 12 a further embodiment of a device according to the invention in section, in which segments of a reaction vessel receiving element are fixed by the clamping frame according toFIG. 10.
FIG. 1 shows a first embodiment of the device1 according to the invention for carrying out chemical or biological reactions in a schematic sectional view.
The device has ahousing2 with abottom3 andside walls4. Located just above and parallel to thebottom3 is anintermediate wall5, on which are formedseveral bases5a.In the embodiment shown inFIG. 1, a total of sixbases5aare provided, arranged in two rows of threebases5aeach.
Mounted on each of thebases5ais aheat exchanger6, aPeltier element7 and asegment8 of a reactionvessel receiving element9. Theheat exchanger6 is part of a cooling device and thePeltier element7 is part of a combined heating and cooling device. The elements (heat exchanger, Peltier element, segment) mounted on thebases5aare bonded by an adhesive resin with good heat conducting properties, so that good heat transfer is realised between these elements, and the elements are also firmly connected to asegment element10. the device has altogether sixsuch segment elements10. Instead of adhesive resin, a heat conducting film or a heat conducting paste may also be provided.
Each of thesegments8 of the reactionvessel receiving element9 has abase plate11 on which tubular, thin-walledreaction vessel holders12 are integrally formed. In the embodiment depicted inFIG. 1, in eachcase 4×4reaction vessel holders12 are arranged on abase plate11. The distance d betweenadjacent segments8 is such that thereaction vessel holders12 of allsegments8 are arranged in a regular pattern with constant grid spacing D. The grid spacing D is chosen so that s standardised microtiter plate with its reaction vessels may be inserted in thereaction vessel holders12.
By providing the distance d between adjacent segments, an air gap which thermally decouples thesegments8 andsegment elements10 respectively is formed.
Thereaction vessel holders12 of the device shown inFIG. 1 form a grid with a total pf 96 reaction vessel holders, arranged in eight rows each with twelvereaction vessel holders12.
ThePeltier elements7 are each connected electrically to afirst control unit13. Each of theheat exchangers6 is connected via aseparate cooling circuit14 to asecond control unit15. The cooling medium used is for example water, which is cooled in the cool temperature control unit before transfer to one of theheat exchangers6.
Thefirst control unit13 and thesecond control unit15 are connected to acentral control unit16 which controls the temperature cycles to be implemented in the device. Inserted in each coolingcircuit14 is acontrol valve19, which is controlled by thecentral control unit16 to open or close therespective cooling circuit14.
Pivotably attached to thehousing2 is acover17 in whichadditional heating elements18 in the form of Peltier elements, heating films or semiconductor heating elements may be located. Theheating elements18 form cover heating elements, each assigned to asegment8 and separately connected to thefirst control unit13, so that eachheating element18 may be individually actuated.
The mode of operation of the device according to the invention is explained in detail below.
There are three modes of operation.
In the first operating mode all segments are set to the same temperature, i.e. the same temperature cycles are run on all segments. This operating mode corresponds to the operation of a conventional thermocycling device.
In the second operating mode the segments are actuated with different temperatures, wherein the temperatures are so controlled that the temperature difference ΔT ofadjacent segments8 is less than a predetermined value K which amounts for example to 5°-15° C. The value to be chosen for K depends on the quality of the thermal decoupling. The better the thermal decoupling, the greater the value which can be chosen for K.
The temperature cycles input by the user may be distributed automatically by thecentral control unit16 to thesegments8, so that the temperature differences between adjacent segments are kept as small as possible.
This second operating mode may be provided with a function by which the user inputs only a single temperature cycle or PCR cycle, and thecentral control unit16 then varies this cycle automatically. The parameters to be varied, such as temperature, residence time or rate of temperature change, may be chosen by the user separately or in combination. Variation of the parameters is effected either by linear or sigmoidal distribution.
In the third operating mode, only part of the segments is actuated. In plan view (FIG. 3,FIG. 4,FIGS. 6 to 9) thesegments8 have side edges20. In this operating mode, thesegments8 adjacent to the side edges of an actuatedsegment8 are not actuated. If thesegments8 themselves form a regular pattern (FIG. 3,FIG. 4,FIG. 6,FIG. 7 andFIG. 8), then the actuated segments are distributed in a chessboard pattern. In the embodiments shown inFIGS. 1 to 4, three of the sixsegments8 can be actuated, namely the two outer segments of one row and the middle segment of the other row.
In this operating mode the actuated segments are not influenced by the other segments, and their temperature may be set completely independently of the other actuated segments. By this means it is possible to run quite different temperature cycles on the individual segments, with one of the segments for example heated up to the denaturing temperature and another held at the annealing temperature. Thus it is possible for the residence times, i.e. the intervals of time for which the denaturing temperature, the annealing temperature and the elongation temperature are held, also the rates of temperature change, to be set as desired, and run simultaneously on the individual segments. In this way it is possible to optimise not only the temperatures, but also the residence times and the rates of temperature change.
In this operating mode it may be expedient to heat the non-actuated segments8 a little, so that their temperature lies roughly in the range of the lowest temperature of the adjacent actuated segments. This avoids the non-actuated segments forming a heat sink for the actuated segments and affecting their temperature profile adversely.
A second embodiment of the device according to the invention is shown inFIGS. 2 and 3. the basic design corresponds to that ofFIG. 1, so that identical parts have been given the same reference number.
The second embodiment differs from the first embodiment by virtue of the fact that the side edges20 of thesegments8 adjacent to theside walls4 of thehousing2 engage in aslot21 running round the inner face of theside walls4, and are fixed therein for example by bonding. By this means theindividual segment elements10 are fixed in space, thereby ensuring that despite the form of the gaps between thesegment elements10, allreaction vessel holders12 are arranged in the pattern of the reaction vessels of a microtiter plate. Theside walls4 of thehousing2 are made of a non heat conducting material. This embodiment may also be modified such that theslot21 is introduced in a frame formed separately from thehousing2. The frame and the segments inserted in it form a part which may be handled separately during production and is bonded to the heating and cooling devices.
A third embodiment is shown schematically inFIGS. 4 and 5. In this embodiment, ties22 of non heat conducting material are located somewhat below thebase plates11 of thesegments8 in the areas between thesegment elements10 and between thesegment elements10 and theside walls4 of thehousing2. On the side edges20 of thesegments8 and of thebase plates11 respectively are formedhook elements23 which are bent downwards. Thesehook elements23 engage in corresponding recesses of the ties22 (FIG. 5), thereby fixing thesegments8 in their position. Thehook elements23 ofadjacent segments8 are offset relative to one another. Theties22 thus form a grid, into each of the openings of which asegment8 may be inserted.
This type of position fixing is very advantageous since the boundary areas between thesegments8 and theties22 are very small, so that heat transfer via theties22 is correspondingly low. Moreover this arrangement is easy to realise even in the confined space conditions between adjacent segment elements.
Shown in schematic plan view inFIGS. 6 to 9 are reactionvessel receiving elements9 which represent further modifications of the device according to the invention. In these reactionvessel receiving elements9, theindividual segments8 are joined bywebs24 of a thermally insulating material joined to form a single unit Theties22 are arranged between the side edges20 of thebase plates11, to which they are fixed for example by bonding.
The segmentation of the reaction vessel receiving element ofFIG. 6 corresponds to that of the first and second embodiment (FIG. 1-3), in which 4×4 reaction vessel holders are arranged on eachsegment8.
The reactionvessel receiving element9 shown inFIG. 7 is comprised of24segments8 each with 4×4reaction vessel holders12, while thesegments8 are in turn connected by means of thermally insulatingwebs24.
In the reactionvessel receiving element9 shown inFIG. 8, eachsegment8 has only a singlereaction vessel holder12.
For the relatively finely sub-divided reactionvessel receiving elements9 it is expedient to integrate temperature sensors in the thermocycling device. These temperature sensors sense the temperatures of the individual segments, so that the temperature of thesegments8 is regulated in a closed control loop on the basis of the temperature values determined by the temperature sensors.
Infrared sensors may for example be used as temperature sensors, located e.g. in the cover. With this sensor arrangement it is possible to sense the temperature of the reaction mixture directly.
FIG. 9 shows a reactionvessel receiving element9 with sixsegments8, rectangular in plan view, and a segment8ain the form of a double cross formed by three intersecting rows ofreaction vessel holders12. The sixrectangular segments8 are each separated from the next rectangular segment by a row or column of reaction vessel holders. This segmentation is especially advantageous for the third operating mode described above, since therectangular segments8 are not in contact with one another and may therefore be actuated simultaneously as desired, with only the segment8ain the form of a double cross not being actuated.
Thesegments8 of the reactionvessel receiving element9 are made from a metal with good heat conducting properties, e.g. aluminium. The materials described above as non-heat conducting materials or thermally insulating materials are either plastics or ceramics.
A further embodiment of the device according to the invention is shown inFIG. 11. In this embodiment theindividual segments8bof the reactionvessel receiving element9 are fixed in position by means of a clamping frame25 (FIG. 10).
The clampingframe25 is grid-shaped and formed bylongitudinal ties26 and cross ties, wherein theties26,27 span openings. Through these openings extend thereaction vessel holders12 of thesegments8b.In the present embodiment, theties26,27 are for instance in positive contact with thereaction vessel holders12 and with thebase plate11 which protrudes from the reaction vessel holders. The25 is provided withholes28, through which passbolts29 for fixing the clamping frame to a thermocycling device1.
Located below each of thesegments8bis a separatelyactuable Peltier element7 and acooling element30 which extends over the area of all thesegments8b. Located in each case between the coolingelement30 and thePeltier element7, and between thePeltier element7 and therespective segment8bis aheat conducting foil31. Thecooling element30 is provided with holes through which extend thebolts29, each fixed by anut32 to the side of thecooling element30 facing away from the reactionvessel receiving element9.
The clampingframe25 is made from a non heat conducting material, in particular POM or polycarbonate. It therefore allows a fixing of thesegments8bof the reactionvessel receiving element9 wherein the individual elements between thesegments8band thecooling element30 are under tension, thereby ensuring good heat transfer in the vertical direction between the individual elements. Since the clamping frame itself has poor heat conducting properties, the heat transfer between twoadjacent segments8bis kept low. For further reduction of heat transfer between two adjacent segments, the surfaces of the clampingframe25 in contact with thesegments8bmay be provided with narrow webs, so that in the areas adjoining the webs, air gaps are formed between the clampingframe25 and thesegments8b.
In the embodiment shown inFIG. 11, a so-calledheat pipe33 is fitted between every two rows ofreaction vessel holders12. Such a heat pipe is distributed for example by the company THERMACORE INTERNATIONAL, Inc., USA. It is comprised of a gastight jacket, in which there is only a small amount of fluid. The pressure in the heat pipe is so low that the fluid is in a state of equilibrium between the liquid and the gaseous aggregate state, and consequently evaporates at a warmer section of the heat pipe and condenses at a cooler section. By this means, the temperature between the individual sections is equalised. The fluid used is, for example, water or freon.
Through integration of such a heat pipe in thesegments8bof the reactionvessel receiving element9, a temperature equalisation is effected over thesegment8b. By this means it is ensured that the same temperature is present over thewhole segment8b.
A further embodiment of the thermocycling device1 according to the invention is shown inFIG. 12. The design of this thermocycling device1 is similar to that ofFIG. 11, therefore similar parts have been given the same reference numbers.
Thesegments8cof this thermocycling device1, however, have no heat pipe. Instead of heat pipes, atemperature equalisation plate34 is provided in the area beneath each of thesegments8c.Thesetemperature equalisation plates34 are flat elements with a surface corresponding to the basic surface of one of thesegments8c.Thesetemperature equalisation plates34 are hollow bodies with a small amount of fluid, and work on the same principle as the heat pipes. By this means it is once again ensured that there are no temperature variations within asegment8c.
The temperature equalisation plate may however be made from materials with very good heat conducting properties, such as e.g. copper. Additional heating and/or cooling elements, e.g. heating foils, heating coils or Peltier elements, may be integrated in such a temperature equalisation plate. The heating and cooling elements support homogeneity and permit more rapid heating and/or cooling rates. A Peltier element, which generally does not have an even temperature distribution, is preferably combined with a flat heating element.
The invention is described above with the aid of embodiments with96 recesses for receiving a microtiter plate with96 reaction vessels. The invention is not however limited to this number of recesses. Thus for example the reaction vessel receiving element may also have384 recesses to receive a corresponding microtiter plate. With regard to features of the invention not explained in detail above, express reference is made to the claims and the drawing.
In the embodiments described above, a cooling device with a fluid cooling medium is used. Within the scope of the invention it is also possible to use a gaseous cooling medium, in particular air cooling, instead of a fluid cooling medium.
The reaction vessel receiving elements described above are comprised of a base plate with roughly tubular reaction vessel holders. Within the scope of the invention it is also possible to use a metal block, in which recesses to receive the reaction vessels of the microtiter plate are made.
List of References- 1thermocycling device25 clamping frame
- 2housing26 longitudinal tie
- 3 bottom27 cross tie
- 4side wall28 hole
- 5intermediate wall29 bolt
- 5abase30 cooling element
- 6heat exchanger31 heat conducting foil
- 7Peltier element32 nut
- 8segment33 heat pipe
- 8asegment in the form of a34 temperature equalisation plate double cross
- 9 reaction vessel receiving element
- 10 segment element
- 11 base plate
- 12 reaction vessel holder
- 13 first control unit
- 14 cooling circuit
- 15 second control unit
- 16 central control unit
- 17 cover
- 18 heating element
- 19 control valve
- 20 side edge
- 21 slot
- 22 ties
- 23 hook element
- 24 web