Abstract:
This invention involves a thermal cycler capable of performing amplification of nucleic acids. This thermal cycler provides for the fully automatic positioning of its movable lid, which can be placed in two positions. The lid is also suitable for heating a plurality of reaction vessels and for shielding them from light from the environment. In addition, the thermal cycler also includes a thermal block having a plurality of chambers each of which receives the lower part of a reaction vessel. Finally, the thermal cycler has a lid carrier for moving the lid from the first position to the second position and vice versa.

Description:
RELATED APPLICATIONS 
     This application is related to the European Patent Application No. 98810400.6 filed on May 4, 1998. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention refers to a thermal cycler for performing amplification of nucleic acids, e.g. by means of a polymerase chain reaction (PCR). 
     2. Description of the Prior Art 
     Thermal cyclers of the above-mentioned kind have a heated lid which is positioned manually to cover a plurality of reaction vessels positioned in chambers of a thermal block of the thermal cycler during thermal cycling of sample-reaction-mixtures contained in the reaction vessels. The lid is also manually removed in order to have access to the reaction vessel after the end of the thermal cycling. Known lids of the latter type have a key disadvantage. They are not suitable for automatic change of their position with respect to the thermal block. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a thermal cycler comprising a heated lid which is automatically positionable to cover and uncover a plurality of reaction vessels positioned in the chambers of a thermal block of the thermal cycler. In addition the heated lid should be suitable to ensure that when the reaction vessels are covered by the heated lid then no external light can reach the interior of the reaction vessels. 
     According to the invention this aim is achieved with a thermal cycler of the above mentioned kind which comprises: 
     a thermal block having a plurality of chambers each of which can receive the lower part of a reaction vessel; 
     a movable lid having heating means positioned within it, said lid having a surface that can cover said thermal block and said reaction vessels positioned in said chambers thereof so that said lid fully shields said vessels from light in the environment of said thermal cycler, said lid being positionable at a first position at which it covers said thermal block and said reaction vessels positioned in said chambers thereof, and at a second position at which said lid does not cover said thermal block and said reaction vessels positioned in said chambers thereof, and 
     transport means for moving said lid from said first position to said second position and vice versa, said transport means being so configured and dimensioned that the path followed by said lid as it is moved from said second position to said first position comprises 
     a first path segment which lies above and at a predetermined distance from said thermal block and along which said lid is moved towards a stopper until it abuts against said stopper, and 
     a second path segment along which said lid is moved downwards until it is vertically aligned with said thermal block and exerts a predetermined pressure on said reaction vessels positioned in said chambers of said thermal block. 
     The thermal cycler of the present invention achieves the above mentioned objectives. In addition, the configuration of the lid and of the mechanism for moving it makes it suitable for obtaining optimum results with regard to both suitable heating effect on the reaction vessels and with regard to automatic processing thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective, cross-sectional view of a thermal cycler with the movable lid at a first position. 
     FIG. 2 is a cross-sectional view of the thermal cycler. 
     FIG. 3 is a perspective exploded view showing parts of the thermal cycler. 
     FIG. 4 is a first schematic perspective view of the movable lid and of parts of the transport means. 
     FIG. 5 is a perspective view, partially in cross-section, of the thermal cycler with the movable lid is at a second position. 
     FIG. 6 is a cross-sectional view of the thermal cycler. 
     FIG. 7 is a perspective view, partially in cross-section, of the thermal cycler with the movable lid at an intermediate position between a first position and a second position. 
     FIG. 8 is a cross-sectional view of the thermal cycler. 
     FIG. 9 is a perspective view, partially in cross-section, of the thermal cycler with the movable lid is another position. 
     FIG. 10 is a cross-sectional view of the thermal cycler. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention refers to a thermal cycler for performing amplification of nucleic acids. 
     As shown in FIG. 1 an embodiment of a thermal cycler according to the present invention comprises a metallic thermal block  71  mounted on a base  48 , a movable lid  14 , and transport means for moving the lid  14 . The reaction vessels  13  containing suitable sample-reagent mixtures and closed by caps are positioned on thermal block  71 . The reaction vessels  13  and their caps are preferably of suitable plastic materials. 
     The movable lid  14  has heating means  15  which are positioned within an inner space of the lid  14 , which inner space is limited by top and side walls of the lid  14 . Heating means  15  are mechanically connected with lid the  14 . This mechanical connection comprises pusher springs  36 ,  37 ,  38  and  39 . 
     The thermal block  71  has a plurality of chambers  72  each of which is apt to receive the lower part of a reaction vessel  13 . 
     The lid  14  is positionable at a first position (lid closed) at which it covers the thermal block  71  and the reaction vessels positioned in the chambers  72  thereof. The lid  14  is also positionable at a second position (lid open) at which the lid  14  does not cover the thermal block  71  and the reaction vessels positioned in the chambers  72  thereof. 
     The lid  14  has a surface which is apt to cover the thermal block  71  and the reaction vessels  13  positioned in the chambers  72  thereof when the lid  14  is in the above-mentioned first position (lid closed). When the lid  14  is in this position, it fully shields reaction vessels  13  from light in the environment of the thermal cycler. This light should not interfere with the measurement of fluorescence light emitted by sample-reagent-mixtures contained in the reaction vessels  13 . 
     The transport means for moving the lid  14  from the first position (lid closed) to the second position (lid open) and vice versa are so configured and dimensioned that the path followed by the lid  14  as it is moved by the transport means from the second position (lid open) to the first position (lid closed) comprises the following path segments: (1) a first path segment which lies above and at a predetermined distance from the thermal block  71  and along which the lid  14  is moved towards a stopper  16  until it abuts against the stopper  16 , and (2) a second path segment along which the lid  14  is moved downwards until it is vertically aligned with the thermal block  71  and exerts a predetermined pressure on the reaction vessels  13  positioned in the chambers  72  of the thermal block  71 . 
     The transport means for moving the lid  14  are comprised of: a stopper  16  positioned in the above-mentioned first path segment of the movement of the lid  14 ; a motor driven lid carrier  17 ; and plates  25  and  26  mounted on the inner surface of the side walls  23  of the lid carrier  17 . 
     The stopper  16  is mounted on the base  48  and has a plane surface  18  which is substantially perpendicular to the above-mentioned first path segment. 
     The lid carrier  17  has a front end wall  21  which is substantially in face of the plane surface  18  of the stopper  16 , a rear end wall  22 , and side walls  23  and  24  extending between the front and rear walls  21  and  22 . The lid carrier  17  has means for holding the lid  14  within it when the lid  14  is in the first position. 
     The transport means for moving the lid  14  further comprise a motor driven spindle  28  for moving the rear wall  22  of the lid carrier  17  along the longitudinal axis of the spindle  28  in both senses, that is towards and away from the stopper  16 , a spindle bearing  29  mounted on a base  48 , and means (not shown) for controlling the operation of the motor (not shown) which drives the spindle  28 . 
     The plate  25  is fixed on the inner surface of a side wall  23  of the lid carrier  17  and the plate  26  is fixed on the inner surface of the other side wall  24  of the lid carrier  17 . Each of the plates  25  and  26  has a pair of guiding slots  31  and  32  respectively for guiding the movement of the lid  14  along the above-mentioned second path segment. 
     As shown in FIGS. 2,  3  and  4 , the lid  14  has an inner and an outer top surface, a front end wall  41  which is substantially in face of the plane surface  18  of the stopper  16 , a rear end wall  42 , and side walls  43  and  44  extending between the front and rear walls and parallel to the side walls  23  and  24  of the lid carrier  17 . The side walls of the lid  14  include outward projecting pins  51 ,  52 ,  53 ,  54  which fit into and slide in guiding slots  31  and  32  of the plate  25 , and guiding slots  33  and  34  of the plate  26 , respectively. 
     In a preferred embodiment, the transport means for moving the lid  14  further comprise a tension spring  61  one end of which is attached to the front end of the inner top surface of the lid carrier  17 , whereas the other end of the spring  61  is attached to the rear part of the top surface of the lid  14 . 
     The operation of the above-described transport means for moving the lid  14  is better understood by referring to FIGS. 5 and 6. These figures show the position of the lid carrier  17  when the lid  14  is in the above-mentioned second position (lid open). When lid  14  and lid carrier  17  are positioned as shown in FIGS. 5 and 6, a reaction tube holder  11  having a plurality of apertures  12  and carrying a plurality of reaction vessels  13  inserted through those apertures can be positioned on the thermal block  71  so that the lower part of each reaction vessel  13  fits into a chamber  72  of the thermal block  71 . 
     After positioning the reaction vessels  13  on the thermal block  71 , motion of the lid  14  from its second position (lid open) to its first position (lid closed) is initiated by horizontal displacement of the lid carrier  17  towards the stopper  16  by rotation of the spindle  28  in a first sense. In this way, the lid  14  is moved horizontally towards the stopper  16  until front end wall  41  of the lid  14  abuts against the plane surface  18  of the stopper  16 . After this point of the movement of the lid  14  and since lid  14  cannot move further in the horizontal direction, further displacement of the lid carrier  17  towards the stopper  16  causes a downwards displacement of the lid  14  away from the top wall of the lid carrier  17 . During this displacement of the lid  14 , the tension spring  61  is stretched and the movement of the lid  14  is guided by the sliding of pins  51 ,  52  and  53 ,  54  along guiding slots  31 ,  32 ,  33  and  34  respectively. The lid  14  is displaced in this sense until heating means  15  carried by the lid  14  abut on the caps of the reaction vessels  13  and exert on these caps a predetermined pressure. At this point, the lid  14  has reached its first position (lid closed) represented in FIGS. 1 and 2. 
     The predetermined pressure exerted by the heating means  15  on the caps of the reaction vessels  13  when the lid  14  is at its first position (lid closed) is determined by the last part of the downwards displacement of the lid  14  guided by the lower part of the slots  31 ,  32 ,  33  and  34  and also by the mechanical characteristics of the pusher springs  36  to  39 . 
     FIGS. 7 and 8 illustrate the position of the lid carrier  17  and other related parts of the transport system for moving the lid  14 , at the point of time where front end wall  41  of the lid  14  abuts against the plane surface  18  of the stopper  16 . At that point, the direction of the motion of the lid  14  changes from a horizontal motion towards the lid carrier  17  to a downward motion away from the stopper  16 . 
     To bring the lid  14  from its first position (lid closed) to its second position (lid open), the lid carrier  17  is moved away from the stopper  16  by rotation of the spindle  28  in a second direction opposite to the first. This causes motion of the lid  14  along the same path described above, but in the reverse direction. Pulled by tension the spring  61  and guided by the slots  31 ,  32 ,  33  and  34  the lid  14  moves initially upwards towards the top wall of the lid carrier  17  and towards the stopper  16  until the lid  14  is again within the lid carrier  17  and close to the top wall thereof. After that the lid  14  moves with the lid carrier  17  further away from the stopper  16  until the lid  14  and the lid carrier  17  reach their positions shown by FIGS. 5 and 6. 
     In a further preferred embodiment, the transport means for moving the lid  14  further comprise ejector means  62 ,  63 ,  64 ,  65 ,  66  and  67  for separating or removing the lower part of the reaction vessels  13  from the chambers  72  of thermal block  71  when the transport means move the lid  14  from the second position to the first position. The need for such ejector means arises from the fact that at the end of a thermal cycling process the lower parts of the reaction vessels  13  tend to remain stuck in the chambers  72  of the thermal block  71 . 
     The above-mentioned ejector means comprise an ejector frame  66  which receives the reaction vessel holder  11  and which is arranged between the latter holder and the thermal block  71 . The ejector frame  66  has on the outer surface of its side walls ramp guides  67  and  68  which enter into contact with the inwards projecting pins  62 ,  63 ,  65  and  66  of the plates  25  and  26  when the lid carrier  17  is moved to bring the lid  14  from its first position (lid closed) to its second position (lid open). 
     The operation of the above-described ejection means for separating reaction vessels  13  from the chambers  72  of the thermal block  71  is described herein. 
     During the vertical upwards movement of the lid  14  as it is moved from its first position (lid closed) to its second position (lid open), relative movement of plates  25  and  26  and of pins  62  to  65  which belong to them brings these pins into contact with the ramp guides  67  and  68  of the ejector frame  66 . As represented in FIGS. 9 and 10, the shape of the ramp guides  67  and  68  is such that the relative movement mentioned causes pins  62  to  65  to push the ejector frame  66  and the reaction vessel holder  11  which is positioned on the frame  66  upwards, and this causes removal of the lower parts of the reaction vessels  13  from the chambers  72  of the thermal block  71 . 
     Within the scope of the instant invention, the thermal block  71  is used for heating and cooling the reaction vessels  13 . For heating and cooling purposes, the lower part of the thermal block  71  is mechanically and thermally coupled with a Peltier element. 
     It should be understood, however, that the present invention herein illustrated and described is intended to be representative only, as many changes may be made therein without departing with the clear teachings of the invention. Accordingly, reference should be made to the following claims in determining the full scope of the invention, as it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the subjoined claims.