The present invention concerns an extraction system, in particular the present invention concerns a method to perform extraction of nucleic acids in a closed system and an extraction system to pursue the method.

Extractions of nucleic acids from cells are important procedures in biochemical work. Such extractions are normally accomplished by chemical or physical denaturation of membranes, followed either by precipitation of the nucleic acid, or by permitting it to bind to a medium with affinity to nucleic acids. Subsequently the nucleic acid is washed or else cleaned.

These operations are normally carried out using conventional procedures in an open handling chain, typically using piston pipets and m crocentrifuge tubes. A disadvantage with this open handling is that the reaction liquid is repeatedly exposed, giving rise to contamination risks.

Such contamination consists predominantly of air-borne particles carrying microorganisms, fragments of nucleic acids and nucleases. The present invention aims to minimize the risk for this type of contamination during extraction of nucleic acids by handling the components of the process (cells, chemicals and binding ^" medium for nucleic acids) in a closed handling chain.

In brief, the principle for the present invention is to utilize a medium (a chemical compound or a suspension of particles) being denser than water and having affinity to specific molecules, e.g. nucleic acids, which is serving as a shuttle, that, using centrifugation or sedimentation, alternately is transferred to desired fluid matter (e.g. washing buffer) , alternately is temporarily stored in a capillary tube, at time for exchange of the desired fluid matter.

The invention will now be more precisly described in relation to the enclosed figures, in which

Fig. 1 is a section view of a reaction vial constituting one of the two parts of an extraction system according to the present invention;

Fig. 2 is a section view of an into the former reaction vial fitting, second reaction vial, constituting the second part of the extraction system according to the present invention; and

Fig. 3. is a diagrammatic view of the extraction system mounted together.

The extraction system according to the present invention is generally designated by reference number 1 in the figures. The extraction system consists of a reaction vial 2 according to Fig. 1 and a reaction vial 3 according to Fig. 2, both having configurations per¬ mitting them to be fitted together with the bottom ends directed upwards and downwards respectively as illustrated in Fig. 3. This fit is generated by means of the reaction vial 2 is provided with an upper, convergent section or lid 4 and the reaction vial 3 is provided with an upper divergent or collared section 8. The angles of the convergent and divergent parties respectively, are the same, leading to a tight fit and, consequently, a closed system when the two reaction vials 2, 3 are mounted together as shown in Fig. 3. As also shown in Fig. 3 the outer diameter of the reaction vial 2 corresponds to the inner diameter of the collared section 8 of the reaction vial 3.

In the lid 4 of the reaction vial 2 is situated one or more (the number corresponds to the number of capillaries 12 below) tube shaped orifices 5 which optionally can be

covered by a permeable membrane 6. The reaction vial 3 is provided with a considerably wider orifice 9 compared with the orifices 5, which orifice 9 has the function to come into the upper section 4 of the reaction vial 2 as is explained above, c.f. Fig. 3.

Within the reaction vial 3, one or more capillaries 12 are longitudinally arranged. This capillaries 12 are fixed, preferrably in the center of the reaction vial 3, as a consequence of its top end being inserted into a bore 11 in a disc, which is situated in the upper section of the reaction vial 3 precisely beneath the collared section 8, and its lower end being firmly attatched to the bottom of the reaction vial 3.

As shown in Fig. 3, the tube shaped orifices 5 is dimen¬ sioned precisely to fit over the upper section of the capillaries 12 and to establish contact with the disc 10.

Below is described a preferred way to use the extraction system according to the invention, for extraction of nucleic acids.

The capillaries 12 are provided with a medium with affinity to nucleic acids 13 (below termed DNA-binder) , which is denser than water. The reaction vial 3, enclosing the capillaries 12, has the shape of a microcentrifuge tube, and has three functions. One is the function to isolate its content from the environment, which reduces the contamination risk as well as the infection risk in case of extraction of contagious matter, another function is to stabilize the capillary during centrifugation, and a third is to function as a stop collar during centrifugation. Stability is achieved due to the bore 11 in the horizontal disc 10 as described above. The function as a stop collar is achieved due to the upper collared section 8 of the reaction vial 3,

leading to an upside down reaction vial 2 will be brought to contact with the diverging walls of the collar, according to the description above.

To a reaction vial 2, here being denoted reaction vial 2A, is provided a membrane denaturating medium 7 (e.g. concentrated saline solution, lysozyme and/or alkali) , followed by the bore 5 in the lid 4 is sealed by a thin membrane 6. To another, not shown, reaction vial 2, here being denoted reaction vial 2B is inserted a washing buffer (a saline solution aimed to rinse the DNA-binder, cleaning it from coagulated proteins, cell-fragments and other impurities, without eluating the DNA from the DNA- binder) , and to yet another, not shown, reaction vial 2, here being denoted reaction vial 2C, is inserted distiHated water, whereafter also the reaction vials 2B and 2C are sealed with thin membranes. The operations described hithereto may be carried out industrially in advance.

The manual handling starts by the sample, e.g. blood, using a syringe, pipet or a measuring capillary is inserted to reaction vial 2A. This is incubated and the content may be boiled up in order to denaturate nucleases, followed by the capillaries 12 are coupled to the reaction vial 2 by bringing the tube shaped orifices 5 over the capillaries 12 until their verges are brought into contact with the disc 10. The reaction vial 2A #and the reaction vial 3 then comprises a closed unit (c.f Fig. 3) , which is placed with the bottom of the reaction vial 2A directed downwards/outwards in a microcentrifuge, followed by a short centrifugation, which transfer the content of each capillary (i.e. DNA-binder) to reaction vial 2A. After powerful mixing, e.g by vortexing, of the content of the reaction vial 2A, the DNA will bind to the DNA-binder.

Subsequently, the closed extraction system 1 is turned and placed with the bottom of the reaction vial 3 downwards, either in a stand for tubes, allowing the DNA- binder 13 with bound DNA to sediment back into the capillaries 12, or in a microcentrifuge with the bottom of the reaction vial 3 directed downwards/outwards, followed by a short centrifugation in which the DNA- binder 13 with bound DNA is returned to the capillaries 12.

The reaction vial 2A with its content is disposed, and the reaction vial 2B containing washing buffer is arranged on the capillaries 12 as described above. After this, the DNA-binder with bound DNA is rinsed by transferring it into reaction vial 2B containing washing buffer, using centrifugation. The content of the reaction vial 2B is mixed, e.g. by vortexing, to achieve effective cleaning of bound DNA. Subsequently the DNA-binder with bound DNA is tranferred back to the capillaries 12 by sedimentation or centrifuga ion according to the same procedure as described above concerning reaction vial 2A. Thereafter also reaction vial 2B with its content is disposed.

If further rinsing is desired, the procedure is repeated one or several times from the point of replacement of reaction vial 2A to the disposing of reaction vial 2B.

If no further rinsing is desired the reaction vial 2B is replaced with reaction vial 2C containing water or other medium bringing DNA into solution. The DNA-binder with bound DNA is centrifuged down into the reaction vial 2C, which is shaken, in which the DNA will dissociate from the DNA-binder and be brought in solution in the water. The DNA-binder without DNA may, if so is preferred, sediment or be pelleted by centrifuga ion, optionally to the bottom of reaction vial 2C or back into the

capillaries 12, which thereafter are disposed together with the connected reaction vial 3.

The DNA now being in solution in the reaction vial 2C, would, due to the closed handling described above, ensure very reliable results in e.g. PCR.

Preferrably, the DNA in reaction vial 2C is dispensed using a dispenser according to the SE application 91 00726-0, to which is referred.