Patent Publication Number: US-2010124779-A1

Title: Two-Step Moulded Capillary

Description:
STATEMENT TO SEQUENCE LISTING 
     This application incorporates by reference the sequence listing provided in the ASCII text file entitled “25478 FT_ST25.txt”, dated “Aug. 26, 2009” with 1K bytes, which is identical to the incorporated written sequence listing provided in Table 1. 
     TECHNICAL FIELD 
     Embodiments of the present invention relate to reaction containers used in polymerase chain reaction (PCR) applications, and particularly to plastic capillaries having an optimized volume-to-surface ratio that are suitable for PCR applications as well as a method for the production of the plastic capillaries. 
     BACKGROUND 
     The person skilled in the art knows that for the optimization of vessels towards real time polymerase chain reaction (rtPCR) several aspects need to be considered. For the PCR as such it is of importance that a fast and homogeneous heat transfer through the vessel walls need to be provided. This heat transfer parameter is proportional to the wall thickness and the surface-to-volume ration of the vessel. Consequently, thin capillaries are preferred as PCR vessels. A drawback of this consequence is that with increasing PCR volume longer capillaries are needed and such long capillaries present high demands on the material and the production process of such vessels. 
     From the state of the art plastic as well as glass capillaries for rtPCR applications are known. The person skilled in the art will appreciate that capillaries for rtPCR applications should have a high surface-to-volume ration and thin walls in order to provide good thermal transfer properties, such that fast and accurate thermal cycling is possible. Towards higher surface-to-volume ration glass capillaries are preferred, since the limitations of injection molding of plastic devices with respect to wall thickness and length of a vessel are below the limitations of glass vessels. A drawback of glass capillaries are high material and production costs compared to injection molding using plastic. 
     Commercially available glass capillaries have e.g. a reaction volume of 20 μl based on a reaction section of about 17 mm in length, an outer diameter of 1.55 mm and a wall thickness 0.175 mm (Roche Diagnostics GmbH, Cat. Nr. 04929292001). Moreover, glass capillaries having a reaction volume of 100 μl are available, too (Roche Diagnostics GmbH, Cat. Nr. 03337090001). 
     If such capillary dimensions are intended to be produced using injection molding techniques, one faces several fundamental problems. 
     In state of the art molding techniques (designated as 1-step molding throughout the present application) a molten plastic mass is injected under high pressure into a cavity formed between a core and a mold to obtain a cavity closed at one end (WO 2004/054715). If longer capillaries having thin walls and small diameters are intended, at least the following fundamental hindrances need to be met:
         a) Due to the high pressure of the molten mass and small inaccuracies of the mold, large shear forces occur at the thin core of the mold resulting in deflection of the core and an inhomogeneous filling of the mold cavity (wall displacement). This inhomogeneous filling of the mold results in an one-sided increase of the core force (self-energizing effect due to the advancing flow of the molten mass).   b) For transparent materials (such as COC or PC) necessary for rtPCR, the degassing is of importance to avoid embedding of air bubbles and the degassing becomes problematic with increasing length of the capillaries.       

     The consequences of this fundamental hindrances are at least that:
         a) The inhomogeneous filling of the mold cavity results in an inhomogeneous wall thickness distribution of the capillaries and this provides an inhomogeneous heat expansion during the temperature cycles of the PCR. For rtPCR this deformation of the vessels will affect the optical reading of the vessel fluorescence and such vessels are no longer suitable.   b) Frozen tension within the molded capillary will relax due during the elevated temperatures of PCR cycling, causing deflection and consequently, affecting the optical reading   c) The heat input through the walls having a wall thickness distribution will be inhomogeneous affecting the reaction kinetics of mixtures.   d) Embedded air bubbles will affect the detection of optical information for rtPCR applications.       

     To summarize, as a consequence of the insufficient stability of the core, the 1-step molding production of thin-walled devices closed at one end having sufficient quality for rtPCR applications is restricted with respect to length and diameter. 
     The WO 2004/054715 describes 1-step molded plastic capillaries with a wall thickness of as thin as 0.01 mm, a inner diameter of as small as 0.02 mm and a length of as long as 50 mm, but no experimental data is provided that the minimum values are producible nor that any of the described plastic capillaries are suitable for rtPCR applications. 
     Commercially available are plastic capillaries having the following dimensions:
         a) Roche Diagnostics offers plastic capillaries having a reaction volume of 20 μl (Id.nr. 04924738001). The capillaries have a wall thickness of 0.3 mm, an inner diameter of 1.7 mm and a length of the reaction section of around 8 mm for 20 μl reaction volume.   b) From Osmetech Molecular Diagnostics plastic capillaries are available having a reaction volume of 20 μl, too (SensiTube™). The capillaries have a wall thickness of 0.3 mm, an inner diameter of 1.5 mm and a length of the reaction section of around 11 mm for 20 μl reaction volume.   c) Other plastic capillaries are available from Eurogentech, Eliod and Genaxxon.       

     SUMMARY 
     It is against the above background that an embodiment of the present invention provides a molding technique to produce high quality capillaries for sensitive rtPCR applications. The molding technique enables the production of thinner and longer plastic capillaries according to another embodiment of the invention that are suitable for rtPCR applications. In particular, plastic capillaries produced by the method have an optimized volume-to-surface ratio that are suitable for rtPCR applications. 
     In one embodiment, a reaction container for real-time nucleic acid amplifications made of plastic material is disclosed and comprises a capillary section closed at one end, a tubular section open at both ends, and a linkage between the capillary section and the tubular section, wherein the linkage is a fused joint designed to permanently link the open end of the capillary section to one of the open ends of the tubular section thus forming a reaction container having one opening, the fused joint is producing light scatter upon illumination. 
     In another embodiment, an injection molding method to produce a reaction container is disclosed. The method comprises providing a first mold with a core, performing a first injection step to produce the tubular section of the reaction container, the tubular section is partially surrounding the core, placing the core partially surrounded by the tubular section in a second mold, and performing a second injection step to produce the capillary section of the reaction container, wherein the capillary section becomes permanently linked to the tubular section during the second injection step to form the reaction container having one opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, the invention will be described in further detail, by way of example, with reference to different embodiments. In the figures show: 
         FIG. 1A  is a schematic drawing illustrating in cross section one embodiment of a reaction container formed by a 2-step molding process according to the present invention; 
         FIG. 1B  is an enlarged view taken along section line B in  FIG. 1A ; 
         FIG. 1C  is an enlarged view taken along section line C in  FIG. 1A ; 
         FIG. 1D  is a top view of a reaction container from which a cross section taken along section line A is shown as  FIG. 1A ; 
         FIGS. 2A ,  2 B,  2 C, and  2 D are cross sectional views illustrating a production method of 2-step plastic capillaries according to present invention; 
         FIGS. 3A ,  3 B,  3 C, and  3 D depict rtPCR curves for HybProbe CycA amplification (a: 640 nm plastic; b: 640 nm glass; c: 640/530 nm plastic; d: 640/530 nm glass); 
         FIGS. 4A ,  4 B,  4 C and  4 D depict rtPCR curves and melting curves for SYBR Green I PBGD amplification (a: plastic rtPCR; b: plastic TM; c: glass rtPCR; d: glass TM); and 
         FIG. 5  is a depiction of a photograph of a capillary part comprising a linkage between a capillary section and a tubular section. 
     
    
    
     DETAILED DESCRIPTION 
     As is discussed herein, reaction containers according to the present invention are assembled from two sections via a linkage, wherein the linkage between the two sections is established by heat, the heat is sufficient to melt the sections at the interface and the linkage forms during subsequent cooling of the interface. The linkage forming during subsequent cooling of the interface is called fused joint throughout the present invention. 
     Assembling a reaction container out of a capillary section, a tubular section and a fused joint as a linkage between both section has the advantage that the production of the reaction container can be divided into sub-steps. This offers the opportunity to produce reaction containers having certain geometrical dimensions and/or a certain quality that are not available by a 1-step production, because for each section as part of the final reaction container the required dimensions and/or quality are easier to fulfill. In other words, the fused joint as linkage between two sections of a reaction container offers the possibility to e.g. enhance the quality, reduce the wall thickness and/or to increase the container length. 
     In a preferred reaction container according to the present invention, the linkage, the capillary section and the tubular section are made of the same plastic material. 
     It is preferred that both sections and the linkage are made from the same material, such that the optical properties of the entire reaction container is as homogeneous as possible. Nevertheless, even with the same material, there will be a certain area with different optical properties at the interface between the sections (see the photograph of  FIG. 5 ), the difference in optical properties at the interface is based on a different morphological structure of the linkage material. 
     As mentioned before, the linkage throughout the present invention is formed by heat in order to locally melt the interface between the two sections. As the person skilled in the art will appreciate, the molecular structure of plastic is highly depending from the production procedures. Throughout the present invention the phrase molecular structure is used as a term to describe the arrangement of the molecules to form a three-dimensional structure (in other words, the morphological or physical structure of the material) and therefore, a material having an identical molecular composition can still form different molecular structures. Consequently, the plastic of the linkage will differ from the rest of the reaction container in terms of its molecular arrangement, because the temporary, local melting of the interface to produce a fused joint will result in a different morphological structure as compared to e.g. the structure based on controlled cooling from a homogeneous mold. 
     In a preferred setup of the reaction container according to the present invention, the capillary section as well as the tubular section are injection molded items. To produce the fused joint as linkage, the molten plastic necessary to form the capillary section in the second production step is allowed to contact the pre-formed tubular section, thereby temporarily melting the boarder of the tubular section and creating a fused joint between both sections during cooling of the mold. 
     In another preferred reaction container according to the present invention, the material of the linkage has a different molecular structure than both the material of the capillary section and the tubular section. Such changes within the molecular structure of the plastic material constitute an optical interface that will produce light scatter. Therefore, it is preferred that the linkage of the reaction container is provided at a position with minimal effect on the real-time detection of the nucleic acid amplification. 
     The photograph of a reaction container according to the present invention in  FIG. 5  (taken with a standard digital camera) shows the light scattering along the fused joint of the container and consequently, it is an intrinsic property of the fused joint permanently linking the capillary section with the tubular section to produce light scatter upon illumination. 
     In yet another preferred reaction container according to the present invention, the capillary section and the tubular section are injection molded items. 
     Injection molded items for the capillary section and the tubular section are preferred mainly because the formation of the linkage between the two section is a direct consequence of the production process. If the two sections of the reaction container are produced successively and the second section is molded directly in contact with the first section, the molten plastic of the second section will locally melt the plastic of the first section and form the linkage upon cooling. 
     In a more preferred reaction container according to the present invention, the capillary section has a wall thickness of about 0.2 to about 0.4 mm. 
     In another more preferred reaction container according to the present invention, the capillary section has an inner diameter of about 0.7 to about 2 mm. 
     Mainly, there are two geometrical parameters that need to be optimized in order to obtain a reaction container that is suitable for real-time nucleic acid amplifications, namely the wall thickness and the surface-to-volume ratio. Nucleic acid amplifications require precise temperature profiles within the target solution and consequently, it is essential to transfer heat fast in both directions through the walls of the reaction container. Therefore, it is obvious that the wall thickness is of importance for the design of the reaction container. 
     Moreover, the heat transfer is proportional to the surface of the interface and the time for heat equilibration within the reaction container increases proportional with the reaction volume. Therefore, the person skilled in the art will appreciate that the reaction container should have a large surface-to-volume ratio. With respect to reaction containers for PCR, the ideal geometry are long and thin capillaries. 
     In yet another preferred reaction container according to the present invention, the tubular section has the same wall thickness and the same inner diameter than the capillary section at the opening permanently linked to the open end of the capillary section. 
     Even though the reaction container according to the present invention comprises two section permanently linked together, it is essential that the reaction container is as homogeneous as possible. Therefore, it is preferred that the wall thickness of both section is adjusted, such that the reaction container does not exhibit steps, at least within the reaction section, where such steps would generate additional light scatter. 
     Throughout the present invention the reaction section is defined as the part of the reaction container that will be filled with reagent for the intended use of the reaction container. Moreover, throughout the present invention the geometry of this reaction section is relevant for the performance of the reaction container and consequently, the surface-to-volume (S/V) ration is calculated for this part of the container. 
     The surface-to-volume ration of a reaction container in form of a capillary is only depending upon the inner and outer radius (r in  and r out ) of the container and is independent from its length 1 (S/V=2πr out 1/πr in   2 1=2r out /r in   2 ; neglecting the small surface of the capillary bottom). Therefore, if the volume of a capillary should be increased without affecting the S/V ratio, the length of the capillary must be increased without changing its radius. 
     In still another preferred reaction container according to the present invention, the tubular section has portions with different diameters. 
     In another preferred reaction container according to the present invention, the capillary section has portions with different diameters. 
     In yet another preferred reaction container according to the present invention, the diameter of the tubular section at the opening not linked to the capillary section is larger than the diameter at the opening permanently linked to the capillary section. 
     In still another preferred reaction container according to the present invention, the diameter of the capillary section at the opening linked to the tubular section is larger than the diameter towards the closed end of the capillary section. 
     To provide the reaction container with a large opening and a decreasing diameter towards its closed end has several advantages. First of all, this geometry simplifies the loading of the reaction container with reagents. Moreover, in case of using molding techniques for the production of the reaction container, this geometry enables an easy removal of the container from the core of the mold. 
     In another preferred reaction container according to the present invention, the inner diameter of the tubular section at the opening not linked to capillary section is about 2 to about 10 mm. 
     The inner diameter at the opening of the reaction container needs to be adjusted to the intended application. E.g., if the reaction containers are designed as vessels for automated real-time PCR amplifications, this inner diameter needs to be adjusted to the holding device of the PCR machine intended to be used. 
     In yet another preferred reaction container according to the present invention, the opening of the tubular section not linked to the capillary section is designed such that an air-tight seal with a closure means is obtainable. 
     Throughout the present invention it is preferred that the reaction container has a reaction section constituting only a part of the entire reaction container. The reaction section is placed at the closed end of the reaction container and it is preferred that the reaction section is composed of the entire capillary section and, if necessary a part of the tubular section. Depending on the design of the capillary, the linkage between the capillary section and the tubular section may be part of the reaction section. 
     As mentioned before, the linkage of the reaction container has a different molecular structure than the capillary as well as the tubular section of the container and consequently, the linkage will produce a certain amount of light scatter. Based on this reasoning, it would be preferred to design the reaction container such that the linkage is not within the reaction section. But, as will be discussed later with respect to the method according to the present invention, the quality of the capillary section is depending to some extend on its length, too. To summarize, it may be preferred to design the reaction container with short capillary section, even though the linkage is then within the reaction section. 
     In yet another preferred reaction container according to the present invention, the tubular section has portions with different wall thickness. 
     In contrast to the wall thickness of the capillary section, there is no need to minimize the wall thickness of the tubular section over its entire extent, because only at least a part of the tubular section is also part of the reaction section and only the wall thickness of the reaction section affects the container performance. 
     Consequently, the wall thickness of the tubular section not part of the reaction section can be enlarged in order to provide stability to the reaction container, to provide an opening suitable to enable an air-tight seal or to provide a secure fixation within an analysis device. 
     Similar to the above mentioned discussion with respect to wall thickness, the requirements of the reaction container concerning length and volume can be separated in requirements critical or not critical for the container performance. The length and volume of the reaction section is essential for the performance of the reaction container, because these parameters define the surface-to-volume ration. On the other hand, the overall volume and length of the entire reaction container does not influence the performance, but are of relevance for aspects such as stability, suitability for a certain analyzer or filling with reagents. 
     In still another preferred reaction container according to the present invention, the reaction container has a length of about 30 to about 55 mm. 
     In yet another preferred reaction container according to the present invention, the reaction container has at its closed end a reaction section with constant wall thickness, the reaction section has a volume of about 10 to about 30 μl. 
     In a more preferred reaction container according to the present invention, the reaction section has a length of about 10 to about 30 mm. 
     As mentioned before, the length of the reaction section is the preferred geometric parameter of the reaction container in order to define the container volume without affecting the S/V ratio. 
     In another preferred embodiment of the reaction container according to the present invention at least the reaction section is not cylindrical. But even in this embodiment it is preferred that the wall thickness is constant for the entire reaction section. 
     In a preferred reaction container according to the present invention, the reaction section is a conical reaction section. 
     In a more preferred reaction container according to the present, the conical reaction section has a conical angle of about 0.5° to about 2°. 
     As mentioned before with respect to the reaction container, the conical form of the reaction section is especially preferred, if the container is produced using molding techniques, because this special form enhances the removal of the container from the core of the mold. 
     In another preferred reaction container according to the present invention, the reaction section has a surface-to-volume ratio of about 1 to about 15 mm −1 . 
     In yet another preferred reaction container according to the present invention, the plastic material is cyclo-olefin copolymer (COC), cyclo-olefin polymer (COP) or polycarbonate (PC). 
     In general, the plastic materials suitable for the reaction containers according to the present invention must combine a very high level of light transmission with a good thermal stability under the thermal conditions of PCR cycling. 
     With respect to the preferred materials mentioned above, COC and COP provide a very good stability. In addition, COC shows a low level of self-fluorescence, whereas the self-fluorescence is of course a critical parameter for rtPCR based on fluorescence detection. Certain COP materials need nitrogen as cover gas during processing to avoid discoloring of the material. PC has a cheap material price and therefore, it is economically advantageous. COP has very good technical properties, but is rather high priced. 
     Suitable materials are e.g. the COC material Topas 5013S, the PC material Makrolon CD 2005 or the COP material Zeonex 690R. 
     With reference now made to  FIGS. 1A-1D , a reaction container  10  for real-time nucleic acid amplifications is shown. In the illustrated embodiment, the reaction container  10  is formed as a 2-step molded capillary that is made of a plastic material. The reaction container  10  comprises a capillary section  12  closed at one end, a tubular section  14  open at both ends, and a linkage  16  between the capillary section  12  and the tubular section  14 . As best shown by  FIG. 1C , the linkage  16  is a fused joint designed to permanently link the open end of the capillary section  12  to one of the open ends of tubular section  14  thus forming the reaction container  10  with one opening  8 . It is to be appreciated that the fused joint  16  produces light scatter upon illumination. 
     With reference made to  FIGS. 2A-2D , another aspect of the present invention is an injection molding method to produce a reaction container, such as reaction container  10 , according to the present invention. In a first step shown by  FIG. 2A , the method comprises providing a first mold  18  with a core  20 . In a second step shown by  FIG. 2B , the method comprises performing a first injection step (e.g., blow molding the plastic material into injection (inlet) ports  22  and  24 ) to produce the tubular section  14  of the reaction container. It is to be appreciated that as the molten plastic material is blown into inlet ports  22  and  24 , air escapes from injection (outlet) ports  26  and  28  such that the tubular section  14  can partially surround the core  20  as shown by  FIG. 2B . Next, as shown by  FIG. 2C , the method comprises placing the core  20  that is partially surrounded by the tubular section  14  in a second mold  30 . In the illustrated embodiment, the second mold  30  is displaced relative to the core  20  such that an additional inlet port  32  is provided. Next, the method comprises performing a second injection step using the inlet port  32  to produce the capillary section  12  of the reaction container. It is to be appreciated that the capillary section  12  becomes permanently linked to the tubular section  14  during the second injection step to form the reaction container  10  having the one opening  8 . After the second injection step, the molded reaction container  10  is removed from the second mold  30  as well as from a guidance block  34 . 
     It is to be appreciated that during the first step of the production process according to the present invention the core  20  is initially stabilized by the guidance block  34  which surrounds the core  20  while being partially coated with molten plastic material. Based on the guidance block  34  surrounding the sides of the core  20 , the core resists the pressure of the molten plastic material during the first injection step and stays concentric within the surrounding cavity  36  ( FIG. 2A ) of the first mold  18 . The core  20  partially surrounded by plastic material (i.e., the tubular section  14 ) is then placed into (provided with) a second cavity  38  of the second mold  30  such that a tip  40  of the core  20  ( FIG. 2C ), which was sticking in a recess  42  of the first mold  18  during the first injection step ( FIG. 2A ), becomes surrounded by additional molten plastic material provided during the second injection step ( FIGS. 2C and 2D ). 
     Based on this 2-step production process a capillary closed at one end having a thin wall with a homogeneous thickness distribution can be obtained that are of importance in the field of rtPCR (no wall displacement, no deformation during temperature cycles, no embedded air bubbles). Moreover, the 2-step production process enables an easy degassing of each mold during the two injection steps, such that the formation of air bubbles in the plastic material can be avoided 
     The 2-step production process according to the present invention provides not only the possibility to produce long capillaries with thin walls, but also to produce them with high accuracy, the accuracy is sufficient to apply them to highly sensitive rtPCR applications. For rtPCR applications it is of utmost importance that the capillaries do not deform during the temperature cycles, that the heat transfer through the capillary walls is homogeneous and that no air bubbles are embedded in the capillary walls. 
     The requirement towards temperature deformation is even higher for capillaries that should be used in rtPCR machines applying a rotary motion of the capillaries in order to place them into the detection position (e.g. the LightCycler® devices of Roche Diagnostics GmbH). Here, in addition to the thermal stress a centrifugal force need to be balanced. If such a deformation of the capillaries can not be avoided, the position with respect to the detection optic will differ between different capillaries and the comparability of the capillaries is no longer warranted. 
     During the first injection step, the flow direction of the molten plastic material is preferably parallel to the core  20 . This flow direction pushes air within the cavity  36  formed between the first mold  18  and the guidance block  34  parallel to the core  20  towards de-aeration spots and avoids the enclosure of air bubbles. 
     In a preferred method according to the present invention, the core  20  is fixed at both ends during the first injection step e.g., at one end to first mold  18  and at a second end (tip  40 ) being form-fitted and fixed releasably into the recess  42  of an upper mold block  44  of the first mold  18  as shown by  FIG. 2A . In this preferred embodiment of the method according to the present invention the core  20  is arranged such that both ends of the core  20  are fixed during the first injection step in order to ensure a stable positioning of the core  20  within the flow field of the molten plastic material mass, such that the tubular section  14  with two open ends forms around the core  20 . This fixation of the core  20  also enables an increase of the producible reaction container length. 
     It is preferred that the molten plastic material flows along the core  20  starting at the suspended part forming the opening  8  of the reaction container in the direction of the fixed part (i.e., tip  40 ) of the core forming the capillary section of the reaction container. Consequently, the degassing occurs at the interface between the core and the recess fixation of the core. 
     In yet another preferred method according to the present invention, the first injection step is performed using at least two injection ports (e.g., ports  22 ,  24 ). 
     Due to the use of two injection ports for the first injection step, an additional increase in length of the capillary can be reached. This is based on two different flow fields of the molten mass generated by two injection ports and the at least partial balancing of their shear forces. This is in contrast to state of the art injection techniques based on only one injection port, where the balancing of negative shear forces can only be attempted by molt temperature and injection pressure. 
     It is preferred that the mass flow through both injection ports are equal such that tensions within the reaction container are minimized and a homogeneous flow field parallel to the core is provided. 
     For the subsequent process step, the core of the first injection step still surrounded by the tubular section is used as the core for the mold of the second injection step. 
     In a more preferred method according to the present invention, in the step illustrated by  FIG. 2C , the second end of the core  20 , i.e., tip  40  which was sticking out from the tubular section  14  formed in first injection step, is placed within a recess  46  provided by the second mold  30  to form the capillary section  12  during the second injection step, wherein the capillary section  12  is linked to the tubular section  14  due to local melting of the tubular section. 
     During the second injection step, the flow direction of the molten plastic material is preferably perpendicular to the core  20  and the degassing occurs again at the interface between the core  20  and the tubular section  14  produced during the first injection step. This degassing procedure pushes air around the core  20  and based on an optimized flow profile it is possible to avoid degassing in the optically sensitive region of the capillary section  12 . 
     In still another preferred method according to the present invention, the second injection step is performed using one injection port (e.g., port  32 ). For the second injection step producing the capillary section  12  of the reaction container  10  it is suitable to perform the molding with only one injection port due to several aspects. For the production of the capillary section  12  it is not longer possible to fix both sides of the core  20  as for the first injection step. Therefore, it is preferred to design the reaction container  10  with a small capillary section, because for a long capillary section the free tip  40  of the core  20  is susceptible to deformation in the flow field risking the production of inhomogeneous containers. Because at least compared to the tubular section the capillary section is small requiring only a small amount of molten plastic, the requirements for this injection step can be fulfilled even with one injection port. 
     Moreover, the entire capillary section  12  is within the reaction section and therefore, the homogeneity is essential for the optical properties of the container. Therefore, it is preferred to have only one injection port, because each injection port will generate an area with inhomogenities within the final product. This statement holds true also for the degassing ports (i.e., ports  26 ,  28 ) and therefore, it is preferred to arrange the degassing at the interface (i.e., linkage or fused joint  16 ) between capillary and tubular sections  12 ,  14 , wherein the interface provides the linkage of the container with unavoidable inhomogenities. 
     In a preferred method according to the present invention, molten plastic material having a temperature of about 240 to about 290° C. is used for the first injection step. 
     With respect to the injection temperature, two aspects need to be considered. On one hand, high temperatures reduce the viscosity of the molten plastic material and facilitate the filling, but on the other hand, at higher temperatures the material may become yellow, which influences the light transmission. Hence, the temperature of the molten plastic material before injection should not exceed 290° C. Moreover, overheated material may become brittle. 
     In another preferred method according to the present invention, molten plastic material is injected with a pressure of about 600 to about 1000 bar for the first injection step. 
     Throughout the present invention, a high injection pressure is preferred in order to fill the cavity rapidly, such that the deflection of the core  20  can be minimized. 
     In a more preferred method according to the present invention, the pressure for the first injection is about 800 bar. 
     In yet another preferred method according to the present invention, the molten plastic material has a temperature of about 240 to about 290° C. is used for the second injection step. 
     In still another preferred method according to the present invention, the molten plastic material is injected with a pressure of about 200 to about 400 bar for the second injection step. 
     In a more preferred method according to the present invention, the pressure for the first injection is about 300 bar. 
     Hereafter experimental examples are provided to further aid in the understanding of the embodiments of the present invention. 
     EXPERIMENTAL SETUP 
     The plastic capillaries according to the present invention that were used for the following examples have the following characteristics:
         a) wall thickness of the capillary section: 0.3 mm;   b) inner diameter of the capillary section: 1.09 mm;   c) reaction container length: 42 mm;   d) inner diameter tubular section at opening not linked to capillary section: 3.98 mm;   e) reaction section volume: 20 μl;   f) reaction section length: 19.26 mm; and   g) conical angle of conical reaction section: 1°.       

     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Sequences used in Examples 1 and 2 
               
               
                 SEQUENCE LISTING 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 &lt;110&gt; F. Hoffmann-La Roche AG 
                   
               
               
                   
               
               
                 &lt;120&gt; Capillary 
               
               
                   
               
               
                 &lt;130&gt; 25478 
               
               
                   
               
               
                 &lt;150&gt; 08020060.3 
               
               
                 &lt;151&gt; 2008-Nov.-18 
               
               
                   
               
               
                 &lt;160&gt; 4 
               
               
                   
               
               
                 &lt;170&gt; PatentIn version 3.5 
               
               
                   
               
               
                 &lt;210&gt; 1 
               
               
                 &lt;211&gt; 18 
               
               
                 &lt;212&gt; DNA 
               
               
                 &lt;213&gt; Artificial 
               
               
                   
               
               
                 &lt;220&gt;  
               
               
                 &lt;223&gt; artificial DNA, forward primer CycA 
               
               
                   
               
               
                 &lt;400&gt; 1 
               
               
                 ggccgcgtct cctttgag 
                 18 
               
               
                   
               
               
                 &lt;210&gt; 2 
               
               
                 &lt;211&gt; 23 
               
               
                 &lt;212&gt; DNA 
               
               
                 &lt;213&gt; Artificial 
               
               
                   
               
               
                 &lt;220&gt;  
               
               
                 &lt;223&gt; artificial DNA, reverse primer CycA 
               
               
                   
               
               
                 &lt;400&gt; 2 
               
               
                 cgagttgtcc acagtcagca atg 
                 23 
               
               
                   
               
               
                 &lt;210&gt; 3 
               
               
                 &lt;211&gt; 20 
               
               
                 &lt;212&gt; DNA 
               
               
                 &lt;213&gt; Artificial 
               
               
                   
               
               
                 &lt;220&gt;  
               
               
                 &lt;223&gt; artificial DNA, 3′ Fluorescein probe CycA 
               
               
                   
               
               
                 &lt;400&gt; 3 
               
               
                 ggccatggag cgctttgggt 
                 20 
               
               
                   
               
               
                 &lt;210&gt; 4 
               
               
                 &lt;211&gt; 26 
               
               
                 &lt;212&gt; DNA 
               
               
                 &lt;213&gt; Artificial 
               
               
                   
               
               
                 &lt;220&gt; 
               
               
                 &lt;223&gt; artificial DNA, 5′ Red 640 probe CycA 
               
               
                   
               
               
                 &lt;400&gt; 4 
                 26 
               
               
                 aatggcaaga ccagcaagaa gatcac 
               
               
                   
               
            
           
         
       
     
     Example 1 
     CycA with HybProbe-Format 
     In this experiment plastic capillaries (20 μl) according to the present invention are compared with glass capillaries (20 μl, Id.Nr. 11 909 339 001, Lot 3529565-00, Roche) for a rtPCR amplification of CycA using the HybProbe format for RNA using a LightCycler (Roche, Software-Version: LCS4 4.0.5.415). The plastic capillaries were produced using COC Topas5013. 
     The PCR was performed according to the following procedure: 
     Kit: LightCycler RNA Amplification Kit HybProbe, IdNr. 12 015 145 001, Lot 13419720; 
       
                            Primer/Probe:                 SEQ ID NO: 1                         forward primer CycA:                             SEQ ID NO: 2                         reverse primer CycA:                       3′ Fluorescein probe CycA:                 (SEQ ID NO: 3)                         GGC CAT GGA GCG CTT TGG GT-Fluorescein                       5′ Red 640 probe CycA:                 (SEQ ID NO: 4)                         Red 640-AAT GGC AAG ACC AGC AAG AAG ATC AC;            
Template: Universal Human Reference RNA (Stratagene Cat. No. 740000-41, Lot 1139623 with concentrations 20, 2 ng/μl, 200, 20, 2 pg/μl);
 
     Mastermix: 
       
                                         20 x                                                    H 2 O   184           LC RT-PCR Reaction Mix, 5x   80           MgCl 2  [25 mM]   48           CycA Primer-Probe-Mix [10x]   40           LC RT-PCR Enzym Mix, 50x   8           total   360 μl                        
Run protocol: 18 μl mastermix per capillary plus 2 μl RNA (threefold)
 
                                                             Cycles   Analysis   Temp.   Time   Rate   Acquisition                                                                        RT   1x       50° C.   10   min   20°   C./s   —       Denaturation   1x       95° C.   1   min   20°   C./s for glass cap.   —                               1°   C./s for plastic cap.       Amplification   50x    Quantificat.   95° C.   0   s   20°   C./s for glass cap.   —                               1°   C./s for plastic cap.                   55° C.   10   s   20°   C./s   single                   72° C.   18   s   3°   C./s   —       Cooling   1x       40° C.   30   s   20°   C./s   —                    
Analysis performed at 640 nm:
 
                                                    Plastic capillary       Glass capillary                                     Template   Cp   STABW   Cp   STABW               20 ng RNA   19.36   0.46   20.43   0.26        2 ng RNA   22.13   0.16   22.74   0.04       200 pg RNA    24.72   0.08   24.66   0.10       20 pg RNA   25.77   0.21   25.36   0.19        2 pg RNA       NTC                    
Analysis performed at 640/530 nm:
 
     
       
         
           
               
               
               
               
               
            
               
                   
                   
               
               
                   
                 Plastic capillary 
                   
                 Glass capillary 
                   
               
            
           
           
               
               
               
               
               
            
               
                 Template 
                 Cp 
                 STABW 
                 Cp 
                 STABW 
               
               
                   
               
               
                 20 ng RNA 
                 19.78 
                 0.22 
                 20.90 
                 0.21 
               
               
                  2 ng RNA 
                 22.39 
                 0.22 
                 23.09 
                 0.03 
               
               
                 200 pg RNA  
                 24.89 
                 0.06 
                 24.80 
                 0.11 
               
               
                 20 pg RNA 
                 25.88 
                 0.08 
                 25.42 
                 0.19 
               
               
                  2 pg RNA 
                 26.13 
               
               
                 NTC 
               
               
                   
               
            
           
         
       
     
     Example 1 
     Summary 
       FIGS. 3A ,  3 B,  3 C, and  3 D depict rtPCR curves for HybProbe CycA amplification ( FIG. 3A : 640 nm plastic;  FIG. 3B : 640 nm glass;  FIG. 3C : 640/530 nm plastic; and  FIG. 3D : 640/530 nm glass). The Cp values and the standard deviation are similar for the plastic as well as for the glass capillaries. For the analysis at 640/530 nm the PCR curves for the plastic capillary look similar as compared to the glass capillaries and the standard deviation are even lower. 
     Example 2 
     PBGD with SYBR Green I Format 
     In this experiment plastic capillaries (20 μl) according to the present invention are compared with glass capillaries (20 μl, Id.Nr. 11 909 339 001, Lot 3529565-00, Roche) for a rtPCR amplification of PBGD using the SYBR Green I format for DNA using a LightCycler (Roche, Software-Version: LCS4 4.0.5.415). The plastic capillaries were produced using COC Topas5013. 
     The PCR was performed according to the following procedure: 
     Kit: LightCycler FastStart DNA Master PLUS  SYBR Green I, IdNr. 03 515 885 001, Lot 13828500; 
     Primer: according to the “LightCycler h-PBGD Housekeeping Gene Set” (Cat. No. 03 146 073 001, Roche);
 
Template: cDNA synthesis was performed using the “1st strand cDNA Synthesis Kit for RT-PCR” (Cat. No. 11 483 188 001, Roche);
 
     Mastermix: 
       
                                         20 x                                                    H 2 O   240           PBGD for/rev [each 5 μM]   40           SGI Master, 5x   80           total   360 μl                        
Run protocol: 18 μl mastermix per capillary plus 2 μl RNA (threefold)
 
                                                             Cycles   Analysis   Temp.   Time   Rate   Acquisition                                                                        Denaturation   1x       95° C.   10   min   20°   C./s for glass cap.   —                               1°   C./s for plastic cap.       Amplification   45x    Quantificat.   95° C.   10   s   20°   C./s for glass cap.   —                               1°   C./s for plastic cap.                   58° C.   10   s   20°   C./s   —                   72° C.   15   s   20°   C./s   single       Melting   1x   Melting C.   95° C.   0   s   20°   C./s   —                   42° C.   15   s   20°   C./s   —                   80° C.   0   s   0.1°   C./s   cont.       Cooling   1x       40° C.   30   s   20°   C./s   —                    
Analysis Cp values:
 
                                                    Plastic capillary       Glass capillary                                             Template   Cp   STABW   Cp   STABW                                                     cDNA 1 - 5*10 5 c   21.56   0.29   23.28   0.30           cDNA 2 - 5*10 4 c   25.38   0.07   27.18   0.10           cDNA 3 - 5*10 3 c   28.93   0.08   31.04   0.11           cDNA 4 - 500c   32.73   0.11   34.97   0.04           cDNA 5 - 50c   35.82   0.16   40.00   0.00           cDNA 6 - NTC   0.00   0.00   0.00   0.00                        
Analysis melting curve:
 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Plastic capillary 
                 Glass capillary 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 MW 
                 89.17 
                 88.62 
               
               
                   
                 STABW 
                 0.19 
                 0.11 
               
               
                   
                   
               
            
           
         
       
     
     Example 2 
     Summary 
       FIGS. 4A ,  4 B,  4 C and  4 D depict rtPCR curves and melting curves for SYBR Green I PBGD amplification ( FIG. 4A : plastic rtPCR;  FIG. 4B : plastic TM;  FIG. 4C : glass rtPCR; and  FIG. 4D : glass TM). SYBR Green I as detection format works very good using the plastic capillary according to the present invention. The PCR curves are well formed and the Cp values of the plastic capillaries are even lower compared to the glass capillaries. The standard deviation of both capillaries are comparable. The melting curves are similar having good standard deviations. 
     Although preferred embodiments of the invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations obvious to the skilled artisan are to be considered within the scope of the claims that follow and their equivalents.