Patent Publication Number: US-8974751-B2

Title: Apparatus and method for separating components of a sample liquid

Description:
The present invention relates to an apparatus for treating and preferably examining sample liquid, particularly blood, and a process for this purpose. 
     The present invention is particularly concerned with microfluidic systems or apparatus. The following remarks therefore relate particularly to apparatus in which capillary forces come into effect and in particular are critical to the function. 
     There are known apparatus in which blood as the sample liquid is filtered by means of a planar separating device. The filtrate or the permeate is held in a chamber flatly adjoining the separating device and is drained away laterally through an adjacent channel. Usually, the channel has a substantially smaller cross-section than the chamber. It is also known to provide the chamber under the separating device with fluidic structures such as columns or the like, so as to achieve as uniform a distribution as possible and accordingly ensure good removal or drainage through the channel. However, fluidic structures of this kind are not ideal, because of their larger dead volume which varies. 
     Similar apparatus for separating blood are known for example from WO 2005/119211 A1 and WO 2009/106331 A2. According to WO 2009/106331 A2 it is also possible for the flat, thin separating device to be somewhat deformed transversely of its planar dimension, particularly into the chamber adjoining the separating device on the outflow side. 
     Tests have shown that even when the channel extends into the middle of the chamber or below the separating device, with the lowest possible chamber height, i.e. with the smallest possible spacing from the separating device and a correspondingly small dead volume, drainage from the chamber under the separating device is not very uniform. Rather, the pores of the separating device clog up with blood cells or other components that have been filtered out, essentially only in the region of the channel. Accordingly, optimum throughput is not achieved, particularly in processes that operate by capillary force. 
     The present patent application is based on the problem of providing an apparatus and a process for the treatment and preferably investigation of sample liquid, particularly blood, in which the fluidic throughput is optimised by simple means and/or an excessively increased dead volume is avoided. 
     The above problem is solved by an apparatus or a process according to the disclosed embodiments. 
     A fundamental idea of the present invention is to drain off the sample liquid from the chamber adjoining the separating device on the outflow side—particularly directly and/or flatly—not only through one channel but through at least two channels and accordingly not via only one outflow region but via at least two lateral outflow regions. In this way a substantially higher throughput or a substantially larger amount of sample liquid can be drained off easily and/or with minimal increase to the dead volume. This can be explained in particular by the fact that there is better drainage from different areas of the substantially flat or planar chamber and hence also from different areas of the planar separating device. Accordingly, the permeability of the separating device for the sample liquid is better utilised in a larger area than would otherwise be the case when drainage takes place only through one channel with a small cross-section. 
     The sample liquid drained off from the two channels, i.e. the sample liquid such as blood plasma or blood serum filtered by the separating device, can then be supplied for example to a common investigating area or, alternatively, to two separate investigating areas. In the former case the channels preferably converge in a connecting chamber or connecting line which is particularly preferably ventilated to avoid unwanted effects of gas or air, particularly in channels that fill up at different rates. 
    
    
     
       Other advantages, features, properties and aspects of the present invention will become apparent from the claims and the description of preferred embodiments by reference to the drawings, wherein: 
         FIG. 1  is a schematic section through a proposed apparatus; 
         FIG. 2  is a schematic plan view of a carrier of the proposed apparatus according to a first embodiment; and 
         FIG. 3  is a schematic plan view of a carrier of the proposed apparatus according to a second embodiment. 
     
    
    
     In the figures, the same reference numerals are used for identical or similar parts, where corresponding or comparable properties and advantages are obtained even if the description is not repeated. 
       FIG. 1  shows, in schematic section, a proposed apparatus  1  for the treatment and preferably investigation of sample liquid  2 , particularly blood or another human or animal bodily fluid. The apparatus  1  comprises a flat separating device  3  for treating the sample liquid  2 , particularly for separating components such as particles or cells, from the sample liquid  2 . In particular, the separating device  3  is used for filtering. It preferably comprises a filter element, a membrane or the like. The separating device  3  may be configured in a single layer or in several layers. It is preferably flat or planar in configuration. 
     Particularly preferably, the separating device  3  may be formed by or provided with a membrane as described in WO 2009/106331 A2, which is thus incorporated by reference as a supplementary disclosure. 
     The apparatus  1  comprises a chamber  4  for receiving sample liquid  2  flowing through the separating device  3 . In particular, the chamber  4  thus receives sample liquid  2  such as blood plasma or blood serum that has been treated or filtered by the separating device  3 . 
     The chamber  4  is preferably directly adjacent, with its flat side, to the separating device  3  on the outflow side. In particular the chamber  4  is arranged under the separating device  3 . In the embodiment shown the separating device  3  is larger in surface area than the chamber  4 . In particular, the separating device  3  projects laterally beyond the chamber  4 , most preferably on all sides in the embodiment shown. 
     Particularly preferably, the sample liquid  2  is guided within the chamber  4  without any side walls. In the embodiment shown this is achieved in particular by the fact that, laterally adjoining a base  5  of the chamber  4 , is a capillary stop which is particularly preferably formed by an encircling or laterally adjacent trench  6 . However, other design solutions are also possible. 
     In the embodiment shown the chamber  4  is particularly formed between the base  5  of the chamber  4  on the one hand and the opposite region of the separating device  3 . Because of the small spacing between these two opposing surfaces, the sample liquid  2  is preferably held in the chamber  4  by capillary forces, without any side walls. The capillary forces or the capillary stop prevent the sample liquid  2  from flowing into the trench  6  that is laterally adjacent in the embodiment shown. In particular, the trench  6  forms the capillary stop by its abrupt increase in cross-section—i.e. its greater depth in relation to the height of the chamber (distance of the base  5  from the separating device  3 ). 
     In the embodiment shown the apparatus  1  preferably comprises a carrier  7 , an associated cover  8  and/or a receiving element  9 . 
     The carrier  7  is preferably plate-shaped and/or rigid in its construction. 
     The carrier  7  is preferably made of plastics and/or by injection moulding. The carrier  7  preferably comprises microfluidic structures for the sample liquid  2  and/or venting structures or the like, which will be discussed in more detail hereinafter. These structures are preferably—at least partly—covered by the cover  8 . 
     The cover  8  is preferably made of plastics and/or embodied as a film. The cover  8  is preferably laminated or stuck onto the carrier  7  or attached thereto by some other method. 
     The cover  8  preferably extends at least substantially continuously or over the entire surface of the carrier  7 . 
     The receiving element  9  preferably serves to hold the separating device  3  and/or receive the sample liquid  2 , such as a drop of blood, as shown in  FIG. 1 . The receiving element  9  comprises for this purpose a receiving region  10 , for example, such as an aperture, opening or the like. 
     The separating device  3  may for example be held in an annular shoulder or the like on the receiving element  9 . 
     The separating device  3  is attached to or held by the receiving element  9  and/or the carrier  7  or cover  8  for example by gluing, clamping and/or welding or by any other suitable method. 
     In the embodiment shown the receiving element  9  is mounted on the cover  8  or attached thereto. However, the receiving element  9  may also be directly connected to the carrier  7  and/or formed thereby. 
     In order to achieve a preferably lateral venting of the chamber  4 , the trench  6  is preferably connected to the atmosphere through a venting channel  11 . Particularly preferably, the venting channel  11  is formed in the carrier  7 . However, other design solutions for venting are also possible. 
     In the present description, the sample liquid  2  that flows through or is filtered by the separating device  3  is also referred to as the sample liquid  2 .  FIG. 1  shows, purely schematically, that the sample liquid may contain, upstream of the separating device  3 , larger components, shown schematically for example, which are no longer present in the sample liquid  2  after it has flowed through the separating device  3 , i.e. in the chamber  4 . In particular, the substance present in the chamber  4  or further on in the direction of outflow is then the treated or filtered sample liquid  2  or its permeate. The remainder of the description should be understood in this sense, in particular. 
       FIG. 2  shows in schematic plan view a preferred fluidic structure for draining the sample liquid  2  away from the chamber  4  of the proposed apparatus  1  according to a first embodiment. In particular,  FIG. 2  shows in schematic plan view the carrier  7  with no cover  8 , receiving element  9 , separating device  3  or sample liquid  2 . 
     The apparatus  1  comprises a first channel  12  which laterally adjoins the chamber  4  in a first outflow region  13 . The apparatus  1  further comprises at least one second channel  14 , which laterally adjoins the chamber  4  in a second outflow region  15 . 
     The apparatus  1  thus comprises a plurality of channels  12 ,  14  and outflow regions  13 ,  15  for draining sample liquid  2  out of the chamber  4 . 
     The channels  12 ,  14  have a substantially smaller cross-section compared with the chamber  4 . The channels  12 ,  14  preferably each have a minimum or average cross-section or a cross-section in the vicinity of the respective outflow region  13 / 15  which is less than 20%, preferably less than 15%, particularly less than 10%, particularly preferably less than 5% of the maximum cross-section of the chamber  4 . The maximum cross-section of the chamber  4  is to be understood here as being, in particular, the product of the chamber height by the average or maximum diameter of the base  5 . 
     The chambers  12 ,  14  or outflow regions  13 ,  15  are preferably offset on the edges of the chamber  4  or are arranged on or attached to opposite sides. Accordingly, the sample liquid  2  is drained from the chamber  4  from different areas or at different points, as a result of which the throughput of the apparatus  1  or the separating or filtering performance of the apparatus  1  or separating device  3  can surprisingly easily be increased substantially, as already explained hereinbefore. 
     Of course, more than two channels and outflow regions for draining sample liquid  2  out of the chamber  4  may be laterally connected to the chamber  4 . Thus the throughput or drainage of sample liquid  2  can be increased still further. A cross-shaped arrangement of four channels and outflow regions on the chamber  4  is possible, for example. 
     It can be seen from  FIG. 2  that the lateral trench  6  is subdivided by the outflow regions  13 ,  15  into two trench sections which surround the chamber  4  or its base  5  in the manner of annular segments, in particular. The outflow regions  13 ,  15 , in particular, thus form strut-like or bridge-like connections over the trench  6  to the chamber  4  or its base  5 . However, other design solutions are also possible. 
     The channels  12 ,  14  are preferably formed by channel- or groove-like recesses, particularly in the carrier  7 . 
     The channels  12 ,  14  preferably extend into or over the outflow regions  13 ,  15 , particularly preferably into the chamber  4  or the base  5  and/or under the separating device  3 . In particular, the channels  12 ,  14  towards the separating device  3  are open-ended in their respective end regions. The cover  8  that otherwise covers the channels  12 ,  14  may, if necessary, also extend, especially like a tongue, into or over the outflow regions  13 ,  15  and/or into the chamber  4  or over the base  5 , i.e. it may form tongue-like protuberances  16 , as shown by dotted lines in  FIG. 2 . 
     The channels  12 ,  14  may extend at least substantially into the centre of the chamber  4  and/or be connected to one another in the chamber  4  or in the base  5 , as shown by dotted lines in  FIG. 2 . 
     In the embodiment shown the apparatus  1  has a preferably chamber-like investigating region  17  for investigating sample liquid  2  drained from the chamber  4 . For supplying sample liquid  2  from the chamber  4  into the investigating region  17 , in the embodiment shown, both the first channel  12  and also the second channel  14  are fluidically connected to the investigating region  17 . This may be chosen to be done directly or optionally through a connecting line  18  and/or a connecting chamber  19 , as shown in  FIG. 2 . The connecting line  18  and the connecting chamber  19  are thus optional, in particular, and may be omitted if desired. 
     In the embodiment shown the two channels  12  and  14  are initially combined and the sample liquid  2  drained off from the chamber  4  is then conveyed through the common connecting line  18  to the investigating region  17 . The optional connecting chamber  19  is preferably formed at the junction of the two channels  12  and  14  or at the transition to the connecting line  18 . However, as already stated, this is purely optional and may be omitted if desired. 
     Preferably, a vent is provided for the investigating region  17  and/or for the connecting line  18  and/or connecting chamber  19 . In the embodiment shown the connecting line  18  or connecting chamber  19  is preferably vented through a venting channel  20  which is preferably connected directly or indirectly to the environment, for example, and/or may be in gas exchange and/or may be vented through or connected to the investigating region  17  and/or trench  6 . 
     The venting provided is preferably configured so that even when the channels  12 ,  14  are filled at different rates with sample liquid  2  drained from the chamber  4  there is, if possible, no undesirable inclusion of gas or air in the investigating region  17  or in the sample liquid  2  supplied to the investigating region  17 . 
     The venting is preferably also formed by channel- or groove-like depressions and/or openings or the like in the carrier  7  and/or if required in the cover  8 . 
     The connecting chamber  19  is preferably used primarily only for venting and therefore preferably has only a minimal volume. 
     A second embodiment of the proposed apparatus  1  or microfluidic structure is hereinafter explained by reference to  FIG. 3 . Only essential differences from the first embodiment are described. The remarks and explanations provided hereinbefore thus apply in a complementary or corresponding capacity. 
       FIG. 3  shows a plan view corresponding to  FIG. 2 . Some aspects such as the optional venting and the possible protuberances  16  in the cover  8  into the drainage regions  13 ,  15  or chamber  4  have been omitted but can still be implemented. 
     In the second embodiment, the two channels  12 ,  14  are connected to separate investigating regions  17  and  21 . Thus, in addition to the (first) investigating region  17  the apparatus  1  comprises a further or additional investigating region  21  which is supplied with sample liquid  2  by the second channel  14 . 
     The two embodiments or individual aspects thereof may also be combined with one another in any desired manner. For example, the connecting line  18  or connecting chamber  19  may also, in addition to the investigating region  17 , be connected to another separate investigating region  21  for re-separating or dividing up the sample liquid  2  that has been drained from the chamber  4  after the joining of the channels  12 ,  14 . 
     Alternatively or additionally, it is also possible, for example, for four channels to drain off the sample liquid  2  from the chamber  4  and to join up in pairs in order to supply the sample liquid  2  to the separate investigating regions  17  and  21 . 
     Generally the following comments can be made on the present invention and the two embodiments: 
     In particular, the apparatus  1  is a microfluidic device. 
     The volumes of the apparatus  1  or individual ones or all of the microfluidic structures such as the chamber  4 , the channels  12 ,  14 , the connecting line  18 , the connecting chamber  19  and/or the investigating regions  17 ,  21 , are preferably less than 1 ml, particularly less than 500 μml, particularly preferably substantially 100 μl or less. 
     The volume of the channels  12 ,  14  is preferably less than 20%, more particularly less than 10%, of the volume of the chamber  4 . 
     The preferred draining of the sample liquid  2  from the chamber  4  through a plurality of channels  12 ,  14 , albeit smaller in cross-section than the chamber, has the advantage that even with a minimal volume for the chamber  4 , particularly a minimal chamber height or very little or no micro-structuring of the chamber  4  or chamber  5  in order to minimise the dead volume, a good throughput or a high separating performance can be achieved. Alternatively or additionally, even when a channel  12  or  14  is out of commission or blocked, the sample liquid  2  can be treated and in particular investigated if the two channels  12 ,  14  are fluidically connected to a common investigating region. When the liquid is drained into separate investigating regions  17  and  21 , by using a plurality of channels  12 ,  14 , it is also possible to achieve faster filling of the investigating regions  17  and  21  compared with the prior art. 
     The channels  12  and  14  preferably extend at least substantially in the main plane of extent of the chamber  4  or carrier  7  and/or in a plane parallel thereto. 
     The apparatus  1  may be used in particular to investigate the sample liquid  2  or to measure an analyte in the sample liquid  2  or the like. For example, the apparatus  1  may be used to carry out an immunoassay reaction or the like. For example, the apparatus  1  may be used to measure or analyse certain analytes or other values of the sample liquid  2 . 
     LIST OF REFERENCE NUMERALS 
     
         
           1  apparatus 
           2  sample liquid 
           3  separating device 
           4  chamber 
           5  base 
           6  trench 
           7  carrier 
           8  cover 
           9  receiving element 
           10  receiving region 
           11  venting channel 
           12  first channel 
           13  first drainage region 
           14  second channel 
           15  second drainage region 
           16  protuberance 
           17  investigating region 
           18  connecting line 
           19  connecting chamber 
           20  venting channel 
           21  additional investigating region