EP3268130B1 - Fluidic structure - Google Patents

Description

The invention relates to a fluidic structure, in particular a microfluidic structure, for controlling one or more fluids, which defines a direction of flow and a cross section that is delimited on all sides by walls and perpendicular to the direction of flow. The invention further relates to a microfluidic chip with a substrate, a cover for the substrate and such a fluidic structure in the substrate. The invention finally relates to a system consisting of the fluidic structure or the microfluidic chip together with a first and a second fluid, which are combined in the fluidic structure or the microfluidic chip.

The generic fluidic structures, in particular microfluidic structures, are used to handle sometimes very small amounts of liquid in the range from a few ml to the μl range. The fluid lines in such structures have lateral dimensions in the range of a few mm and below. Liquids are handled in such a fluidic structure in the flow system, i.e. conveyed through the fluid lines by generating a pressure difference (overpressure and / or underpressure). In addition to the microfluidic chip, technically sophisticated control or operator devices are used for this, which are connected to the microfluidic chip or in which the microfluidic chip is inserted.

The applications of such fluid structures are diverse. From the U.S. 5,972,710 A For example, a fluid structure with a diffusion channel with a V-shaped profile is known, in which an analyte and a detection liquid to a parallel laminar flow are combined in order to detect particles in the analyte by means of diffusion processes.

The US 2011/0100476 A1 discloses a microfluidic structure with a valve formed from a fusible structure within a fluid channel. The meltable structure is used to permanently close the fluid channel in the event of an external energy supply.

In the DE 600 07 128 T2 a valve of a microfluidic system is presented which comprises a fluid channel with an obstacle. The obstacle is formed from an intelligent polymer, which experiences a change in volume when supplied with external energy and thus changes the flow of fluid through the channel.

The US 2013/0167958 A1 deals with microfluidic structures in fluidic logic circuits. The microfluidic structures include, among other things, branch circuits for controlling gas or liquid bubbles in a carrier medium.

In scripture US 2004/0195539 A1 describes a microfluidic valve of a fluid line which is formed in a substrate in the form of a channel and has a channel constriction at the location of the valve. The channel is closed with a self-adhesive cover film. The valve is initially open and can be permanently closed by pressing the self-adhesive film in the area of the constriction. It is also described how this valve can then be opened again by reshaping the substrate material in the region of the channel constriction by means of a stamp that is impressed from the outside.

The font US 2012/0103103427 A1 deals with a microfluidic structure with a fluid channel which successively forms further and narrower sections in the direction of flow. Two fluids flowing through the fluid channel in parallel are optionally focused, mixed or guided in separate paths in the structure.

The font US 2007/0286774 A1 deals with a microfluidic device with a fluid channel which is formed in a substrate and covered with a film. At least 2 sections are formed in the channel, into which a liquid flows due to a capillary effect. The two sections are spaced apart so that the capillary flow between them is interrupted. Such a structure is intended to better control the capillary flow within the channel overall.

A particular problem in the handling of fluids arises when liquids are brought together. For this purpose, fluid line structures are known which have at least two fluid feed lines and an outlet which meet in the area of a T-junction. It is difficult here to ensure that liquid columns of limited volumes, also called "liquid plugs", arrive at the T-junction from the two feed lines at the same time for the purpose of unification. This makes extensive fluid control necessary, for example by means of complex valve circuits and precise position monitoring of the liquid columns, by means of which the delivery pressure is controlled and the position of the liquid columns is regulated. The position is monitored, for example, by means of a light barrier that measures exactly where the beginning and the end of both columns of liquid are. Without such a regulation, gas buffers can be enclosed between the liquid columns, which always separate the liquid columns from one another within the fluid lines. In the case of a separation of the liquid columns by air inclusions, for example, a complete mixing of Liquids are prevented or the functionality of sensory devices is impaired.

The basic aim is to restrict the control or regulation to a necessary minimum. In particular, elaborate precautions on the microfluidic chips, such as moving valve parts, are to be avoided because it is precisely here that the lowest possible manufacturing costs are ensured.

Another way of uniting two liquids is therefore described by DE 10 2009 048 378 B3 . The microfluidic structure described therein comprises a fluid line which widens at a point lateral to the direction of flow to form a fluid chamber. The expansion and surface of the fluid chamber are such that a first volume of liquid passed through the fluid chamber is distributed over the entire cross section of the fluid chamber. Furthermore, another feed line opens into a holding position in the fluid chamber, which is designed in such a way that a second liquid volume transported there remains in the area of the holding position until it is absorbed by the first liquid volume passed through and both liquid volumes are conveyed out of the fluid chamber together. Under certain fluidic conditions (wetting properties), this structure provides an alternative, passive fluid control which makes complex valve switching and / or other active fluid control unnecessary.

A very similar fluidic structure is from the article " Droplet-based microfluidic sensing system for rapid fish freshness determination ", by D. Itoh et al., Sensors and Actuators B 171-172 (2012), pages 619-626 known. The microfluidic structure described there comprises only one supply line and one discharge line for handling two or more separately supplied liquid columns (plugs). These are also fed to a laterally widened fluid chamber, separated from one another by the supply line and by gas bubbles, the volume of which is in any case greater than the volume of the first incoming column of liquid. The fluid chamber is designed in such a way that the liquid only wets one of the opposite side walls. This releases a bypass through which the gas can escape from the gas buffer between the liquid columns. As the delivery pressure continues, the second liquid column catches up with the first liquid still adhering to the side wall and is conveyed out of the fluid chamber together with it. However, this requires as a further condition that the total volume of the two liquids is sufficient to wet both walls of the expanded union chamber.

While the two last-mentioned fluidic structures do not require complex valve switching and fluid control and are therefore conceptually simpler, they have the disadvantage that they do not guarantee a process-reliable process in all cases, especially not for wetting liquids and liquids with high surface tension, because these liquids would tend to advance or retreat into the narrower fluid conduit due to capillary forces.

From the WO 2013/160408 A2 A microfluidic device for measuring a certain amount of liquid is known which has a microfluidic channel with at least one cross-section-narrowing obstacle and at least one side channel with an inlet and an outlet, the side channel being connected to the microfluidic channel in such a way that its outlet meets the obstacle , and wherein the cavity of the inlet and outlet of the side channel is less than the cavity of the side channel at a location between the inlet and the outlet.

From the EP 1 441 131 A1 a microfluidic switch with a first channel and a second channel is known, the first channel and the second channel opening into a common end region and the first channel having a taper at the transition to the end region, at which a fluid flowing in through the channel is stopped. During the stop, the second channel fills with the fluid until this channel is completely filled with fluid up to the common end area and the fluid is then conveyed further through the first channel and the second channel with a time delay.

The object of the present invention is accordingly to create a simple fluidic structure which is suitable for reliably combining liquids which are supplied at a distance from one another by a buffer medium and which wet the walls of the fluid line either more or less than the buffer medium.

The object is achieved by a fluidic structure with the features of claim 1, a microfluidic chip with the features of claim 10 and a system with the features of claim 13.

According to the invention, the fluid line of the fluidic structure mentioned at the outset has a holding section which is extended in the flow direction and free of further inlet and outlet lines, in which the fluid line has a narrow area with a volume V _e and, based on the flow direction, laterally adjacent a wide area with a volume V _w , the narrow area in at least one first direction perpendicular to the flow direction (first lateral direction) having a smaller wall distance h _e than the minimum wall distance h _{w of} the wide area. The fluid line has an outlet section upstream of the one inlet section in the flow direction and downstream of the holding section in the flow direction, the inlet section and the outlet section being stepless in the first direction merge into the narrow area of the holding section or into the wide area of the holding section.

Accordingly, the object is also achieved by a microfluidic chip of the type mentioned at the outset, in which the fluid line is designed in the form of a channel in the substrate and closed by the cover, the channel in the holding section being divided into the narrow and the wide area. The wide area particularly preferably has a greater channel depth than the narrow area. This configuration is particularly simple and can therefore be produced inexpensively. Furthermore, the first lateral direction is preferably perpendicular to a channel base opposite the cover, ie the wall distance h _{e of} the narrow area is determined by the channel depth.

The holding section is therefore generally divided longitudinally into two fluidically connected areas lying next to each other transversely to the flow direction (laterally), one of which is narrower in at least one spatial direction perpendicular to the flow direction, namely the first lateral direction, than the other in any spatial direction. This configuration ensures that a first liquid which wets the walls of the fluid line less or more strongly than the buffer medium surrounding this liquid and the holding section is securely held there in both cases due to capillary forces. The term “lateral” is also used herein for the information “transverse to the direction of flow” or “perpendicular to the direction of flow”. The term "in the direction of flow" is also circumscribed as "longitudinally" or "in the longitudinal direction".

As a section of the fluid line, the holding section has only one feed line and one discharge line in the form of the fluid line itself. Two or more columns of liquid are fed to the holding section, separated by one or more buffer media, through the same feed line and successively Association in the holding section is removed together from the holding section by the same derivative.

A second condition is accordingly, very similar to the fluid chamber in the above-mentioned article, that the holding area is sufficient to completely accommodate the expected volume V _{FI1 of} the first liquid arriving there. In other words, it is necessary that the volume V _{FI1 of} the first liquid is smaller than the volume of the holding area. The "holding area" is either only the narrow or the wide area of the holding section, depending on where the liquid is located depending on its wetting behavior. The volume of the holding area can accordingly be the volume V _{e of} the narrow area of the holding section when the first liquid wets the walls of the fluid line more strongly than the surrounding buffer medium. Then the following must apply: V _FI1 <V _e . The volume of the holding area can, however, also be the volume V _{w of} the wide area of the holding section if the first liquid wets the walls of the fluid line less than the surrounding buffer medium. Accordingly, the following must apply: V _FI1 <V _w . Only under these conditions does the first liquid release the beginning and the end of the laterally adjoining area of the holding section, so that a bypass line is released through this for a buffer medium enclosed between the first liquid and a subsequent second liquid.

A third condition is again very similar to the known solution that the expected total volume of the two or more combined liquids V _Fl1 + V _{Fl2 is} sufficient to close one end of the holding section with liquid. In other words, it is necessary that the total volume of the combined liquids V _Fl1 + V _{Fl2 is} greater than the volume of the holding area. In the case of the more strongly wetting liquids, this is the volume V _{e of} the narrow area of the holding section: V _Fl1 + V _Fl2 > V _e . In the case of the less wetting liquids, it is the volume V _{w of} the wide area of the holding section: V _Fl1 + V _Fl2 > V _w . The volume “V _Fl2 ” here represents the volume of a second liquid or several second liquids. In this way, a total of two, three or more liquids separated by buffer media can be combined in the holding area and then the entire combined liquid volume can be automatically conveyed out of the holding area of the fluid line under continued delivery pressure.

These conditions are reflected in a method for combining two volumes of liquid. This provides that in a fluidic structure with a fluid line which defines a flow direction and a cross-section that is delimited on all sides by walls perpendicular to the flow direction and has a holding section which is extended in the flow direction and free of further supply and discharge lines, in which the fluid line has a narrow area a volume V _e and, based on the flow direction, laterally adjoining a wide area with a volume V _w , the narrow area in at least one first direction perpendicular to the flow direction having a smaller wall distance h _e than the minimum wall distance h _{w of} the wide area , optionally, depending on the wetting behavior, in a step a) a first liquid with the volume V _{FI1 is transported} through the fluid line into the holding section and there due to capillary forces in the narrow area, and then in a step b) at least one previously through a Buffer medium from the first Liquid-separated second liquid with the volume V _{FI2 is transported} through the same fluid line into the holding section, while the buffer medium is conveyed out of the holding section through the wide area past the first liquid until the at least one second liquid reaches the first liquid and both / all _{Liquids are conveyed} out of the holding section together, with the following conditions: V Fl1 <V _e and V _Fl1 + V _Fl2 > V _e ; or in a step c) a first liquid with the volume V _Fl1 through the fluid line into the holding section and there due to capillary forces in the wide area, and then in a step d) at least one second liquid with the volume V _Fl2 previously separated from the first liquid by a buffer medium through the same Fluid line is transported into the holding section, while the buffer medium is conveyed out of the holding section through the narrow area past the first liquid until the at least one second liquid reaches the first liquid and both / all liquids are conveyed out of the holding section together, the conditions the following apply: V _FI1 <V _w and V _Fl1 + V _Fl2 > V _w .

Analogously, these conditions are also reflected in the system according to the invention, which has a fluidic structure or a microfluidic chip of the type described above, a first liquid with a defined volume V _Fl1 , and a second liquid with a defined volume V _Fl2 and a buffer medium, which initially of the holding area is arranged between the first and the second liquid and can be transported through the fluid line together with the first and the second liquid, wherein the first and the second liquid optionally wet the walls of the fluidic structure more strongly than the buffer medium and wherein the conditions apply: V _FI1 <V _e and V _Fl1 + V _Fl2 > V _e , or where the first and the second liquid wet the walls of the fluidic structure less than the buffer medium and where the conditions apply: V _Fl1 <V _w and V _Fl1 + V _Fl2 > V _w .

“The liquids are more strongly wetting liquids” means that the liquid surface forms a contact angle to the surface of the channel of <90 °, preferably <75 ° and particularly preferably <45 °. Conversely, the liquids are called less wetting liquids if the liquid surface forms a contact angle to the surface of the channel of> 90 °, preferably> 105 ° and particularly preferably> 135 °. As a "liquid surface" the interface of the first and second liquids to the adjacent buffer medium is referred to. In the case of an interface with a gaseous buffer medium, one would simply speak of wetting or non-wetting first and second liquids. A medium that is insoluble in the first and in the second liquid is generally referred to as a buffer medium. This can be a gas, such as air, or a liquid, such as an oil-based liquid if the first and the second liquids are water-based, or conversely a water-based liquid if the first and the second liquids are oil-based.

Application examples include reaction mixtures for molecular-biological reactions in which, in aqueous liquid volumes, nucleic acids are supplied as the first liquid and enzymes as the second liquid to the fluidic structure according to the invention and are combined therein according to the method in order to enable a reaction. Mineral oils, silicone oils, fluorinated oils, or organic polymers (e.g. "Novec 7500" (hydrofluoroether (C7F150C2H5)) can be considered as a possible buffer medium.

A lateral transition between the narrow area and the wide area is preferably designed in the form of a shoulder extended in the direction of flow.

One or more of such shoulders can rise from one or more walls delimiting the fluid line. The narrow area is preferably formed in each case between a plateau of the shoulder and an opposing wall section, the first lateral direction being perpendicular to the plateau. The shoulder can have sharp or rounded or beveled edges.

In the case of the microfluidic chip, for example, the channel base in the inlet section and in the outlet section merges continuously into the channel base of the narrow area or into the channel base of the wide area. The channel bottom of the narrow area preferably forms the above-mentioned plateau.

“Stepless” comprises, on the one hand, a transition from the inlet section to the narrow or wide area of the holding section and from there to the outlet section without any change in cross section in the first lateral direction. In one embodiment, this is achieved, for example, in that the inlet section and the outlet section each have a wall distance h _in and h _out in the first direction perpendicular to the flow direction, which is equal to the minimum wall distance h _{e of} the narrow area.

In this case, the dimension of the fluid line does not change in the first lateral direction when it flows through the narrow area in the holding section. In this embodiment, the wide area of the holding section forms an expansion of the cross section of the fluid line in the first lateral direction.

On the other hand, "stepless" also includes a continuous transition between the sections. “Continuous” denotes a continuous, non-abrupt change in cross-section. In an alternative embodiment, the inlet section accordingly has a wall spacing h _in > h _e in the first lateral direction, the fluid line having a first transition section in the flow direction after the inlet section and in front of the holding section, in which the lateral wall spacing in the flow direction is from h _in on h _e steadily tapered.

In an analogous manner, the outlet section has a wall distance h _out > h _e in the first lateral direction, the fluid line in the flow direction has a second transition section behind the holding section and in front of the outlet section, in which the lateral wall distance widens steadily _{in the direction of flow from h e} to h _out.

In this embodiment, the channel cross-section of the fluid line tapers in the first lateral direction on the inlet side towards the holding section to the wall distance of the narrow area and widens again in a corresponding manner on the outlet side. The narrow area thus forms a narrowing of the line cross-section.

In order to prevent the flow speed of the liquids from increasing too much due to constrictions in the line cross-section, an advantageous embodiment of the invention provides that the fluid line in the holding section in a second direction perpendicular to the flow direction (second lateral direction) opposite the inlet section and the outlet section is expanded laterally. A second advantage of the expansion is that larger volumes of liquid can be handled without the space requirement of the structure on the microfluidic chip increasing too much. In contrast, a correspondingly lengthened channel would require more space even if it meanders.

In particular, the fluid line can be widened on the side of the narrow area, on the side of the wide area or on both sides in the second lateral direction.

It is particularly advantageous if the wide area is arranged offset in the second direction perpendicular to the flow direction relative to the inlet section and / or relative to the outlet section.

This refinement has the advantage that the flow of the fluids is deflected less strongly or not at all when passing the narrow area in the holding section, so that the risk of turbulence is reduced.

A further advantageous embodiment of the invention provides that the fluid line has at least one stop structure in the direction of flow in front of and / or behind the holding section.

The at least one stop structure is preferably designed in the form of a shoulder interrupting the course of at least one of the walls of the fluid line.

Paragraphs in this sense form, for example, one or more hollow shapes in the at least one wall of the fluid line or one or more projections along the at least one wall of the fluid line, or both. The hollow shape can be formed, for example, by a laterally extending channel or an indentation. A multiplicity of projections can form a comb-like structure, for example. In all cases it is crucial that the stop structure cannot be overcome by using capillary forces alone. The stop structure thus prevents the first liquid from flowing past the end of the holding section when it flows into it or from being drawn back into the inlet section by the capillary forces. In this way, it supports the holding function of the narrow area and makes the flow process even more reliable when two liquids are brought together.

Figur 1a-c

ein nicht zur Erfindung gehörendes Beispiel in drei Ansichten;

Figur 2a-c

eine Ausführungsform der Erfindung in drei Ansichten;

Figur 3a-c

eine Ausführungsform der Erfindung in drei Ansichten;

Figur 4a-e

eine Ausführungsform der Erfindung in fünf Ansichten;

Figur 5a-c

drei Momentaufnahmen in den Halteabschnitt der Fluidikstruktur gemäß Figur 1 einströmender Flüssigkeit;

Figur 6

ein nicht zur Erfindung gehörendes Beispiel mit alternativer Ausgestaltung der Stoppstrukturen vor dem Halteabschnitt;

Figur 7

eine Ausführungsform der Erfindung mit alternativer Ausgestaltung des Absatzes zwischen dem engen Bereich und dem weiten Bereich des Halteabschnittes;

Figur 8

eine Ausführungsform der Erfindung mit alternativer Ausgestaltung des Absatzes zwischen dem engen Bereich und dem weiten Bereich des Halteabschnittes;

Figur 9a-c

ein nicht zur Erfindung gehörendes Beispiel in drei Ansichten;

Figur 10a-c

ein nicht zur Erfindung gehörendes Beispiel in drei Ansichten und

Figur 11a-c

drei Momentaufnahmen in den Halteabschnitt der Fluidikstruktur gemäß Figur 9 einströmender Flüssigkeit.

Further advantages of the invention are explained below with reference to figures. Show it:

Figure 1a-c

an example not belonging to the invention in three views;

Figure 2a-c

an embodiment of the invention in three views;

Figure 3a-c

an embodiment of the invention in three views;

Figure 4a-e

an embodiment of the invention in five views;

Figure 5a-c

three snapshots in the holding section of the fluidic structure according to FIG Figure 1 inflowing liquid;

Figure 6

an example not belonging to the invention with an alternative configuration of the stop structures in front of the holding section;

Figure 7

an embodiment of the invention with an alternative configuration of the shoulder between the narrow area and the wide area of the holding portion;

Figure 8

an embodiment of the invention with an alternative configuration of the shoulder between the narrow area and the wide area of the holding portion;

Figures 9a-c

an example not belonging to the invention in three views;

Figure 10a-c

an example not belonging to the invention in three views and

Figure 11a-c

three snapshots in the holding section of the fluidic structure according to FIG Figure 9 inflowing liquid.

In Figure 1a a plan view of a first example not belonging to the invention is shown. Figure 1b shows a longitudinal section and Figure 1c a cross-section at each of the in Figure 1a marked positions. Is shown a substrate 10 of a schematically greatly simplified microfluidic chip in which only one fluid line 12 is formed in the form of a channel. A fluid, not shown, flows through the fluid line 12, operated by pressure, in the direction indicated by the arrow 13, also referred to as the flow or longitudinal direction. The fluid line or the channel have a cross section that is delimited on all sides by walls transversely to the direction of flow. This is limited in a first direction perpendicular to the flow direction by a channel base 14 and the one cover (not shown) at the position 16 opposite the channel base.

In practice, microfluidic chips usually have several fluid lines and functional elements such as reaction chambers, mixer structures, valves or the like. Furthermore, the channel is closed on its open top by means of a film laminated to the substrate, precisely that cover. In the Figures 1a to 1c The cover is not shown for the sake of simplicity.

The channel 14 is functionally divided in the flow direction into an inlet section 18, downstream a holding section 20 and further downstream an outlet section 22.

The holding section 20 is in turn subdivided laterally, that is to say transversely to the direction of flow, into a narrow area 24 and a wide area 26 adjacent to it laterally.

_{In the narrow region 24, the fluid line has a wall distance h e} in a first lateral direction between the channel base 14 and the cover (position 16), which in this case is determined by the channel depth. The minimum wall spacing of the wide area 26 is identified by h _w and extends in a different lateral direction in the example shown. As in the cross-sectional view of the Figure 1c can be seen, the distance h _{e is} smaller than the minimum wall _{distance h w of} the wide area. This condition is solely decisive for ensuring that a wetting liquid flowing into the holding section 20 (better than a surrounding buffer medium) due to capillary forces in the narrow area 24 or a liquid flowing into the holding section 20 less than a surrounding buffer medium or non-wetting liquid in the wide area 26 is held. In principle, it is not decisive whether wall distances in the same or different directions are compared with one another. It is also irrelevant whether the narrow area in the second lateral direction is wider or narrower than that of the minimum wall distance h _{w of} the wide area.

In the present case, in which h _e coincides with the channel depth, the channel depth in the wide area, which is greater than or equal to the minimum wall distance h _w , must also be greater than the channel depth in the narrow area.

In the cross-sectional view of the Figure 1b It can also be seen that the inlet section in the first lateral direction has a wall distance h _in and the outlet section 22 has a wall distance h _out and that both h _in and h _{out are} just as large as the wall _{distance h e} in the narrow area of the holding section 20. The inlet section 18 and the outlet section 22 thus merge steplessly into the narrow region 24 in the first lateral direction. In other words, the channel base 14 continues in the inlet and outlet sections and in the narrow area 24 of the holding section 20.

The wide area 26, on the other hand, forms a depression starting from the channel base 14. The total depth of the wide area 26 is even greater than its width, which in this example defines _{the minimum wall distance h w.} The recess is between the narrow area 24 and the wide area 26, a lateral transition in the form of a shoulder 28 extended in the direction of flow is formed. The shoulder 28 in turn has a sharp edge 29 in this exemplary embodiment. In principle, a sharp edge offers greater process reliability, since a greater amount of energy has to be expended here in order to let the liquid flow over the edge. Responsible for this is the contact angle hysteresis, which ensures that the contact lines formed by the interface and the wall stick to edges and kinks. On the other hand, there is no arbitrarily sharp edge for manufacturing reasons anyway and it is also not functionally necessary. In this sense, the term edge deliberately also includes rounded or beveled edges.

In the Figures 2a to 2c a schematically greatly simplified embodiment of the fluidic structure according to the invention is shown. Once again, a fluid line 32 in the form of a channel is formed in a substrate 30 of a microfluidic chip, which is closed in a first lateral direction by the channel base 34, 34 'and on its upper side 36 by a cover or film (not shown).

In contrast to the example according to Figure 1 the fluid line 32 has, one after the other in the flow direction, an inlet section 38, a first transition section 39, a holding section 40, a second transition section 41 and, downstream, an outlet section 42. The holding section 40 is in turn subdivided laterally into a narrow area 44 and a wide area 46 adjoining it laterally. Here, too, the wide section 46, starting from the level of the channel bottom 34 in the narrow section 44, forms a depression so that the lateral transition between the narrow area 44 and the wide area 46 is in the form of a shoulder 48 with a sharp edge 49 that is extended in the direction of flow is trained.

In the longitudinal section of the Figure 2b it can be seen that the wall distance h _in between the channel bottom 34 'and the top side 36 in the inlet section is greater than the wall _{distance h e} in the narrow area 44 of the holding section 40 a ramp-like channel bottom 35 is bridged. In other words, the distance from the wall in the flow direction 13 tapers continuously _{from h in} to h _e.

In an analogous manner, the wall distance h _{out of} the outlet section 42 is greater than the wall distance h _{e of} the narrow area and here, too, the second transition section 41 with the ramp-like channel bottom 35 'serves to compensate for the level difference or the wall distance in the flow direction in the second transition section 41 of h _{e to widen} steadily to h out. In this example, too, the inlet section 38 and the outlet section 42 merge into the narrow region 44 of the holding section 40 without a step in the direction of flow.

From the point of view of the flowing fluid, the narrow region 44, proceeding from the cross section of the inlet section 38, thus forms a significant cross-sectional constriction which, with constant volume delivery, leads to an increase in the flow velocity.

To avoid this, the fluidic structure, as in the Figures 3a to 3c shown, modified. As before, this embodiment comprises a microfluidic chip with a substrate 60 in which the fluid line 62 is incorporated in the form of a channel. The fluid flowing in the flow direction 13 first again flows through an inlet section 68, then a first transition section 69, then the holding section 70, then the second transition section 71 and, downstream, finally the outlet section 72. The holding section 70 is again laterally in a narrow area 74 one Wall distance h _{e divided} in a first lateral direction and an adjacent wide area 76 with a minimum wall distance h _w in the longitudinal direction. Here too, h _e <h _w applies. Furthermore, as in the exemplary embodiment, the Figure 2 Here, too, the wall distance h _in in the inlet section 68 and the wall _{distance h out} in the outlet section 72 are greater than the wall _{distance h e} in the narrow area 74 of the holding section 70. Accordingly, the first and second transition sections 69 and 71 each have a ramp-like channel base 65, 65 'which form a step-free transition.

In contrast to the exemplary embodiment according to FIG Figure 2 is the fluid line 62 in the embodiment shown in FIG Figure 3 in the holding section 70 in a second direction perpendicular to the flow direction 13 with respect to the inlet section 68 and laterally with respect to the outlet section 72. The lateral widening is configured symmetrically to the central axis of the fluid line 64, while the wide area 76, as in the two previous examples, is located in the second lateral direction at an edge of the fluid line 62. In other words, the fluid line 62 is widened in the second lateral direction both on the side of the narrow area and on the side of the wide area.

The lateral widening primarily benefits the narrow area 74 in that it is wider in the second direction than the inlet and outlet sections. The cross-sectional loss due to the tapering in the first lateral direction from h _in to h _e can thus be partially compensated and the flow velocity in the narrow region 74 can be reduced with a constant volume flow.

At the same time, the wide region 76 is arranged offset in the second lateral direction with respect to the inlet section 68 and with respect to the outlet section 72. He is so broadly chosen that he is trained in the expansion Bulge takes place. The lateral transition or shoulder 78 extending in the flow direction 13 between the narrow area 74 and the wide area 76 is therefore in alignment with a side wall 79 of the fluid line 62 in the inlet section 68 and in the outlet section 72. This causes the flow of the fluid When passing through the narrow area 74 in the holding section 70, there is less deflection overall. The risk of turbulence is therefore significantly reduced by the design of the extension.

In Figure 4 an even more refined configuration of the fluidic structure is shown. As before, the fluid line 82 is embodied in the form of a channel in the substrate 80 of a microfluidic chip. The fluid line 82 has, one after the other in the flow direction 13, an inlet section 88, a first transition section 89, a holding section 90, a second transition section 91 and, downstream, an outlet section 92. The holding section 90 is in turn divided laterally into a narrow area 94 and laterally adjoining it into a wide area 96. Here, too, the wide area 96, starting from the level of the channel bottom 84 in the narrow area 94, forms a depression, so that the lateral transition between the narrow area 94 and the wide area 96 is in the form of a step 98 with a sharp edge extending in the direction of flow 13 99 is formed. As before, the relevant wall distance h _{e of} the narrow area 94 is determined by the channel depth. Unlike before, however, the direction of the minimum wall distance h _w in the wide area 96 coincides with the first lateral direction. In other words, the minimum wall distance h _w in the wide area 96 is also determined by the channel depth there. According to the invention, the following also applies here: h _e <h _w .

The lateral expansion of the fluid line in the transition sections and the holding section serves, as before, to at least partially compensate for a lateral tapering of the line cross-section in the narrow area, and so on to lower the flow velocity here. In this embodiment, the wide area 96 is also positioned again in such a way that the shoulder 98 forming the lateral transition to the narrow area 94 is in alignment with the side wall 100 of the inlet and outlet sections.

In contrast to the embodiment according to Figure 3 the walls 101, 102 in the first transition section 89, holding section 90 and second transition section 91 have rounded or “continuously differentiable” contours. This favors the flow and all the more prevents turbulence from forming at the section transitions. In addition, such continuous contours minimize the holding forces on the contact line between the interface between liquid and gas and the surface of the channel (solid), as above with reference to the sharp edge 29 in FIG Figure 1 already addressed. At the transition discussed here, in contrast to the edge 29 discussed above, it is desired that the wall contact leaves without increased expenditure of energy in order to release the bypass. Therefore "round" or "soft" or "continuously differentiable" contours are advantageous here.

The further area is also a little more complex in this embodiment than before. It has approximately the shape of a walking stick with a “handle” at the outlet-side end of the holding section, which faces away from the narrow area 94. As a result, this end of the wide area 96 forms a dead end 104. This has proven to be very advantageous if liquid should inadvertently run into the wide area. A gas cushion enclosed at the dead end 104 then prevents the liquid from being able to completely wet the wide area. There is thus always a boundary surface which ensures the starting point for a liquid separation and thus a complete emptying of the wide area. Finally, in this embodiment, there are two stop structures 105, 106 in the opposite walls 101 and 102 of the fluid line 82 in front of the holding section 90. The stop structures 105, 106 are designed as a hollow shape, more precisely as dead channels, in the two walls 101, 102 and interrupt the The course of the same is such that a fluid flowing into the narrow region 94 of the holding section 90 does not flow back into the inlet section 98 due to capillary forces.

The Figures 5a to 5c show a sequence of a in the fluidic structure according to FIG Figure 1 inflowing liquid. All three snapshots show the same section of the microfluidic chip 110, shown schematically in greatly simplified form, with the substrate 120, in which the fluid line 122 is incorporated in the form of a channel. A cover 125 in the form of a film is shown here, which closes the channel, which is open laterally on one side.

The fluid line 122 is shown cut in the area of the holding section, in which it has a narrow area 134 with a smaller channel depth and laterally adjoining a wide area 136 with a greater channel depth. A first fluid 140 flowing in in the direction 13 has a front front or interface 142, which at the point in time according to FIG Figure 5a is still in the inlet section.

In Figure 5b the first fluid 140 has advanced further so that its rear interface 144 can already be seen in the inlet section. The first fluid 140 forms a so-called fluid column. The front interface has already reached the holding section of the fluid line and, due to capillary forces, enters the flat area 134, while it does not wet the wide area 136.

Behind the liquid column there is a buffer medium 146 which spatially separates the first fluid 140 from a subsequent second fluid 150, which in Figure 5c appears in the inlet section. As the two fluid columns advance further, the rear boundary surface 144 of the first fluid column 140 at some point also arrives at the beginning of the wide area 136 of the holding section. At this point, the rear boundary surface 144 of the first liquid column 140 tears away from the wall of the fluid channel 122, on which the wide area 136 is located. The wide area 136 then releases a bypass line through which the medium from the buffer 146, a gas or liquid insoluble in the first and second fluid, can escape, as symbolized by the arrow 152. The first fluid column 140 meanwhile remains in the holding area because it no longer feels any delivery pressure. As a result, the following column of liquid 150 can be transported further in the direction of the first column of liquid 140 until both columns of liquid are combined. Then both will be promoted together. This can either be set up in such a way that the combined column of liquid runs completely around an air cushion in the bypass line or that it first empties the bypass line and only then leaves the holding area completely. The process depends on the details of the shape of the transition sections.

It is in Figure 5 that is to say about the system with a fluidic structure or with a microfluidic chip in which the narrow region 134 has a volume V _e , with a first liquid 140 with a defined volume V _Fl1 , with a second liquid 150 with a defined volume V _Fl2 , and with a buffer medium 146, which is arranged at the entrance of the holding area between the first and the second liquid and can be transported together with the first and the second liquid through the fluid line 122, wherein the first and the second liquid 140, 150 wet the walls of the fluidic structure more than the buffer medium 146 and where the conditions apply: V _Fl1 <V _e and V _Fl1 + V _Fl2 > V _e . The buffer medium 146 can be gas, for example or oil if the fluids 140 and 150 are water-based and the wall of the fluid line is hydrophilic.

In Figure 6 an alternative embodiment of a fluidic structure is shown, which in terms of the shape of the fluid line 158 that of the Figures 1 and 5 corresponds to. The only difference is a stop structure 160 which has a plurality of projections 162 along a wall or, more precisely, the channel base 163 of the fluid line. The projections 162 taken together form a comb-like structure at the end of the narrow area 164. This generally hinders the flow of a wetting liquid and thus in particular prevents it from inadvertently flowing back from the narrow area of the holding section into the outlet section of the fluid line.

Figure 7 FIG. 9 shows a simplified microfluidic chip 170 with an alternative configuration of the fluid line 172, more precisely of the shoulder 178 which is extended in the flow direction and which forms the lateral transition between the narrow region 174 and the wide region 176. As in the example according to FIG Figure 4 the wall distance h _{e of} the narrow area 174 as well as the minimum wall distance h _{w of} the wide area 176 are determined by the respective channel depth. However, in contrast to all of the embodiments shown above, the shoulder 178 does not have a sharp, but a rounded edge 180. In addition, the shoulder 178 also merges into the channel bottom 182 of the wide area 176 in the form of a rounding 184. The transition therefore has a curved cross-section without a jump or kink, with the effect that the wall distance increases from the narrow area 174 in the lateral direction to the wide area 176 in a continuously differentiable form.

Figure 8 shows a simplified microfluidic chip 190 with yet another alternative configuration of the fluid line 192, more precisely that forming the lateral transition between the narrow area 194 and the wide area 196, heel extended in the direction of flow. As in the example according to Figure 7 the wall distance h _{e of} the narrow area 194 as well as the minimum wall distance h _{w of} the wide area 196 are again determined by the respective channel depth and the shoulder has a rounded edge and a rounding in the transition from the channel bottom 202 of the wide area 196 to the shoulder 198 . In contrast to the previous example or the example according to Figure 1 the wide area 196, starting from the channel bottom 203 in the narrow area 196, does not form a depression. Conversely, the holding section is shaped here in such a way that the narrow region 194, starting from the channel base 202, forms an elevation or a plateau. This shape is compatible with the exemplary embodiments according to FIGS Figures 2 to 4 related. In contrast to this, however, the channel bottom 202 continues from the inlet section 208 via the first transition section 209, the wide area 196 of the holding section 210, the second transition section 211 to the outlet section 212 without a transition at the same level. In other words, the transition sections 209, 211 do not extend over the entire width of the channel.

In Figure 9a is analogous to Fig. 1a a plan view of a further example not belonging to the invention. Figure 9b shows a longitudinal section and accordingly Figure 9c a cross-section at the in Figure 9a marked positions. A substrate 310 of a schematically greatly simplified microfluidic chip is shown, in which only one fluid line 312 is formed in the form of a channel. A fluid (not shown) flows through the fluid line 312, operated by pressure, in the direction indicated by the arrow 13. The fluid line or the channel have a cross section that is delimited on all sides by walls transverse to the direction of flow. This is limited in a first direction perpendicular to the flow direction by a channel base 314 and a cover (not shown) at the position 316 opposite the channel base.

In the flow direction, the channel 312 is again functionally divided into an inlet section 318, downstream a holding section 320 and further downstream an outlet section 322.

The holding section 320 is divided laterally, that is to say transversely to the flow direction 13, into a narrow region 324 and a wide region 326 adjoining it laterally.

_{In the narrow region 324, the fluid line has a wall distance h e} in a first lateral direction between the channel base 314 and the cover (position 316), which in this case is determined by the channel depth. The minimum wall distance of the wide area 326 is marked with h _w and extends in a different lateral direction in the example shown.

As in the cross-sectional view of the Figure 9c can be seen, the distance h _{e is} smaller than the minimum wall _{distance h w of} the wide area. This condition is solely decisive for ensuring that a better wetting liquid flowing into the holding section is held in the narrow area 324 due to capillary forces or a less wetting liquid flowing into the holding section is held in the wide area 326. Here, too, it is not decisive whether wall distances in the same or different directions are compared with one another. It is also irrelevant whether the narrow area in the second lateral direction is wider or narrower than that of the minimum wall distance h _{w of} the wide area.

In the present case, in which h _e coincides with the channel depth, it also applies in particular that the channel depth in the wide area 326 is greater than its width, which in this example defines _{the minimum wall distance h w.}

In the Figures 9a to 9c it can also be seen that the inlet section 318 and the outlet section 322 have wall _{distances h in} and h _out perpendicular to the channel base 314 in the first lateral direction, which correspond to the channel depth in the wide area 324 of the holding section 420. The inlet section 318 and the outlet section 322 thus merge steplessly into the wide area 324 in the first lateral direction. In other words, the channel base 314 continues in the inlet and outlet section and in the wide area 324 of the holding section 320.

In contrast, the narrow region 326, starting from the channel base 314, forms a lateral transition in the form of a shoulder 328 which is extended in the flow direction 13. In this exemplary embodiment, the shoulder 328 again has a sharp edge 329.

In the Figures 10a to 10c are analogous to the Figures 9a to 9c a plan view, a longitudinal and a cross section of a further example not belonging to the invention. The substrate of a schematically greatly simplified microfluidic chip is denoted by 410, in which only one fluid line 412 is formed in the form of a channel. A fluid (not shown) flows through the fluid line 412, operated by pressure, in the direction indicated by the arrow 13. The fluid line or the channel have a cross section that is delimited on all sides by walls transverse to the direction of flow. This is limited in a first direction perpendicular to the direction of flow by a channel base 414 and a cover (not shown) at the position 416 opposite the channel base 414.

In the flow direction, the channel 412 is again functionally divided into an inlet section 418, downstream a holding section 420 and further downstream an outlet section 422.

The holding section 420 is divided laterally, that is to say transversely to the flow direction 13, into a narrow area 424 and a wide area 426 adjoining it laterally.

In contrast to the exemplary embodiment according to FIG Figure 9 is the fluid line 412 in the example according to FIG Figure 10 in the holding section 420 analogous to the example in FIG Figure 3 widened laterally in a second direction perpendicular to the flow direction 13 in relation to the inlet section 418 and in relation to the outlet section 422. The wide area 426 is located in the second lateral direction at an edge of the fluid line 412 and is thus arranged offset in the second lateral direction with respect to the inlet section 418 and with respect to the outlet section 422.

The lateral widening again benefits the narrow area 424, which is wider in the second direction than the inlet and outlet sections. The cross-sectional loss due to the tapering in the first lateral direction from h _in to h _e can thus be partially compensated and the flow velocity in the narrow region 424 can be reduced with a constant volume flow.

Otherwise, like the example in FIG Figure 9 in the narrow region 424 in a first lateral direction between the channel base 414 and the cover (position 416) a wall distance h _e which is determined by the channel depth. The minimum wall distance of the wide area 426 is marked with h _w and extends in a different, second lateral direction.

As in the cross-sectional view of the Figure 10c can be seen, the distance h _{e is} smaller than the minimum wall _{distance h w of} the wide area. This condition is only decisive for ensuring that a better wetting liquid flowing into the holding section due to capillary forces in the narrow area 424 or a less wetting liquid flowing into the holding section is held in the wide area 426. Here, too, it is not decisive whether wall distances in the same or different directions are compared with one another. It is also irrelevant whether the narrow area in the second lateral direction is wider or narrower than that of the minimum wall distance h _{w of} the wide area.

In the present case, in which h _e coincides with the channel depth, it is again true that the channel depth in the wide area 426 is greater than its width, which in this example defines _{the minimum wall distance h w.}

In the Figures 10a to 10c it can also be seen that the inlet section 318 and the outlet section 422 have wall _{distances h in} and h _out perpendicular to the channel bottom 414 in the first lateral direction, which correspond to the channel depth in the wide area 424 of the holding section 420. The inlet section 418 and the outlet section 422 thus merge steplessly into the wide area 424 in the first lateral direction. In other words, the channel base 414 continues in the inlet and outlet section and in the wide area 424 of the holding section 420.

The narrow region 426 again, starting from the channel base 414, forms a lateral transition in the form of a shoulder 428 that is extended in the direction of flow 13. The shoulder 428 again has a sharp edge 429 in this exemplary embodiment.

The Figures 11a to 11c show analogous to the Figures 5a to 5c a sequence of one in the fluidic structure, this time the fluidic structure according to Figure 9 , inflowing liquid. All three snapshots show the same section of the microfluidic chip 510, shown schematically in a greatly simplified manner, with the substrate 520, into which the fluid line 522 is incorporated in the form of a channel is. Here again a cover 525 is shown in the form of a film which closes the channel, which is open on one side laterally.

The fluid line 522 is shown in section in the area of the holding section, in which it has a narrow area 534 with a smaller channel depth and, laterally adjacent, a wide area 536 with a greater channel depth. A first fluid 540 flowing in in the direction 13 has a front front or interface 542, which at the point in time according to FIG Figure 11a is still in the inlet section.

In Figure 11b the first fluid 540 has advanced further so that its rear boundary surface 544 can already be seen in the inlet section. The first fluid 540 forms a so-called fluid column. The front interface 542 has already reached the holding section of the fluid line and, due to capillary forces, enters the wide area 536 while avoiding the narrow area 534. In this case, the capillary forces act opposite to those in, due to the reversed wetting behavior Figure 5 .

Behind the liquid column there is a buffer medium 546 which spatially separates the first fluid 540 from a subsequent second fluid 550, which in Figure 11c appears in the inlet section. As the two fluid columns advance further, at some point the rear boundary surface 544 of the first fluid column 540 also arrives at the beginning of the wide area 536 of the holding section. At this point, the rear boundary surface 544 of the first column of liquid 540 tears away from the wall of the fluid channel 522, at which the narrow region 534 is located. The narrow area 534 then releases a bypass line through which the medium can escape from the buffer 546, as symbolized by the arrow 552. The first fluid column 540 meanwhile remains in the holding area because it no longer feels any conveying pressure. As a result, the following liquid column 550 can continue in the direction of first liquid column 540 are transported until both liquid columns are combined. Then both will be promoted together. This can either be set up in such a way that the combined column of liquid runs completely around an air cushion in the bypass line or that it first empties the bypass line and only then leaves the holding area completely. The process depends on the details of the shape of the transition sections.

The example in Figure 11 that is, the system with a fluidic structure or with a microfluidic chip in which the wide area 536 has a volume V _w , with a first liquid 540 with a defined volume V _Fl1 , with a second liquid 550 with a defined volume V _Fl2 , and with a buffer medium 546, which is arranged at the entrance of the holding area between the first and the second liquid and can be transported together with the first and the second liquid through the fluid line 522, the first and the second liquid 540, 550 wetting the walls of the fluidic structure less than the buffer medium 546 and where the conditions apply: V _Fl1 <V _w and V _Fl1 + V _Fl2 > V _w . The buffer medium 546 can be gas or oil, for example, if the fluids 540 and 550 are water-based and the wall of the fluid line is hydrophobic.

List of reference symbols

10

Substrate

12th

Fluid line / channel

13th

Direction of flow

14th

Canal bottom

16

Top of the channel

18th

Inlet section

20th

Holding section

22nd

Outlet section

24

narrow area

26th

wide area

28

paragraph

29

Edge

30th

Substrate

32

Fluid line

34

Canal bottom

34 '

Canal bottom

35

ramp-like canal bottom

35 '

ramp-like canal bottom

36

Top of the channel

38

Inlet section

39

first transition section

40

Holding section

41

second transition section

42

Outlet section

44

narrow area

46

wide area

48

paragraph

49

Edge

60

Substrate

62

Fluid line / channel

65

ramp-like canal bottom

65 '

ramp-like canal bottom

68

Inlet section

69

Transition section

70

Holding section

71

second transition section

72

Outlet section

74

narrow area

76

wide area

78

paragraph

79

lateral wall of the fluid line

80

Substrate

82

Fluid line / channel

84

Canal bottom

88

Inlet section

89

Transition section

90

Holding section

91

second transition section

92

Outlet section

94

narrow area

96

wide area

98

paragraph

99

Edge

100

lateral wall of the inlet and outlet section

101

Walls in the transition sections and in the holding section

102

Walls in the transition sections and in the holding section

104

dead end of the wide area

105

Stop structure / hollow form / dead channel

106

Stop structure / hollow form / dead channel

110

microfluidic chip

120

Substrate

122

Fluid line

125

Cover / foil

134

narrow area

136

wide area

140

first fluid / fluid column

142

front interface of the first column of fluid

144

rear interface of the first column of fluid

146

Buffer medium

150

second fluid / fluid column

152

Flow arrow

158

Fluid channel

160

Stop structure

162

head Start

163

Canal bottom

164

narrow area

170

microfluidic chip

172

Fluid line / channel

174

narrow area

176

wide area

178

paragraph

180

Edge

182

Wide area canal bottom

184

Rounding

190

microfluidic chip

192

Fluid line / channel

194

narrow area

196

wide area

202

Canal bottom (in a wide area)

203

Canal bottom in the narrow area

208

Inlet section

209

first transition section

210

Holding section

211

second transition section

212

Outlet section

310

Substrate

312

Fluid line / channel

314

Canal bottom

316

Top of the channel

318

Inlet section

320

Holding section

322

Outlet section

324

narrow area

326

wide area

328

paragraph

329

Edge

410

Substrate

412

Fluid line / channel

414

Canal bottom

416

Top of the channel

418

Inlet section

420

Holding section

422

Outlet section

424

narrow area

426

wide area

428

paragraph

429

Edge

510

microfluidic chip

520

Substrate

522

Fluid line

525

Cover / foil

534

narrow area

536

wide area

540

first fluid / fluid column

542

front interface of the first column of fluid

544

rear interface of the first column of fluid

546

Buffer medium

550

second fluid / fluid column

552

Flow arrow

Claims (13)

1. Fluidic structure which is configured to control one or more fluids with a fluid line (12, 32, 62, 82, 122, 172, 192, 312, 412, 522) which defines a flow direction (13) and a cross-section which is delimited at all sides by walls perpendicular to the flow direction (13), wherein the fluid line (12, 32, 62, 82, 122, 172, 192, 312, 412, 522) has a retention portion (20, 40, 70, 90, 210, 320, 420) which is expanded in the flow direction (13) and which is free from additional inlets and outlets and in which the fluid line (12, 32, 62, 82, 122, 172, 192, 312, 412, 522) has a narrow region (24, 44, 74, 94, 134, 174, 194, 324, 424, 534) having a volume V_e and, with respect to the flow direction, in a laterally adjacent manner a wide region (26, 46, 76, 96, 136, 176, 196, 326, 426, 536) having a volume V_w, wherein the narrow region (24, 44, 74, 94, 134 164, 174, 194, 324, 424, 534) has in at least a first direction perpendicular to the flow direction (13) a smaller wall spacing h_e than the minimum wall spacing h_w of the wide region (26, 46, 76, 96, 136, 176, 196, 326, 426, 536),
   characterised in that the fluid line (12, 32, 62, 82, 122, 172, 192, 312, 412, 522) has in the flow direction (13) upstream of the retention portion (20, 40, 70, 90, 210, 320, 420) an inlet portion (18, 38, 68, 88, 208, 318, 418) and in the flow direction (13) downstream of the retention portion (20, 40, 70, 90, 210, 320, 420) an outlet portion (22, 42, 72, 92, 212, 322, 422), wherein the inlet portion (18, 38, 68, 88, 208, 318, 418) and the outlet portion (22, 42, 72, 92, 212, 322, 422) merge in the first direction in a stepless manner into the narrow region (24, 44, 74, 94, 134, 164, 174, 194) of the retention portion (20, 40, 70, 90, 210) or into the wide region (176, 196, 326, 426, 536) of the retention portion (210, 320, 420).
2. Fluidic structure according to claim 1,
   characterised in that a lateral transition between the narrow region (24, 44, 74, 94, 134, 164, 174, 194, 324, 424, 534) and the wide region (26, 46, 76, 96, 136, 176, 196, 326, 426, 536) is constructed in the form of a shoulder (28, 48, 78, 98, 178, 328, 428) which is expanded in the flow direction (13) .
3. Fluidic structure according to claim 2,
   characterised in that the narrow region is formed (24, 44, 74, 94, 134, 164, 174, 194, 324, 424, 534) between a plateau of the shoulder (28, 48, 78, 98, 178, 328, 428) and an opposing wall portion, wherein the first direction is located perpendicularly to the plateau.
4. Fluidic structure according to claim 3,
   characterised in that the inlet portion (18,) and/or the outlet portion (22,) in the first direction perpendicular to the flow direction (13) has/have a wall spacing h_in or h_out which is equal to the wall spacing h_e of the narrow region (24) .
5. Fluidic structure according to claim 3,
   characterised in that the inlet portion (38, 68, 88, 208) has in the first direction perpendicular to the flow direction (13) a wall spacing h_in > h_e and in that the fluid line (32, 62, 82, 192) has in the flow direction (13) downstream of the inlet portion (38, 68, 88, 208) and upstream of the retention portion (40, 70, 90, 210) a first transition portion (39, 69, 89, 209), in which the wall spacing in the flow direction (13) continuously tapers from h_in to h_e.
6. Fluidic structure according to either claim 3 or claim 4,
   characterised in that the outlet portion (42, 72, 92, 212) has in the first direction perpendicular to the flow direction (13) a wall spacing h_out > h_e, and in that the fluid line (32, 62, 82, 192) has in the flow direction (13) downstream of the retention portion (40, 70, 90, 210) and upstream of the outlet portion (42, 72, 92, 212) a second transition portion (41, 71, 91, 211), in which the wall portion continuously expands in the flow direction (13) from h_e to h_out.
7. Fluidic structure according to any one of claims 1 to 6,
   characterised in that the fluid line (62, 82, 412) has in the flow direction (13) upstream of the retention portion (70, 90, 420) an inlet portion (68, 88, 418) and in the flow direction (13) downstream of the retention portion (70, 90, 420) an outlet portion (72, 92, 422), wherein the fluid line (62, 82, 412) is laterally expanded in the retention portion (70, 90, 420) in a second direction perpendicular to the flow direction (13) with respect to the inlet portion (68, 88, 418) and the outlet portion (72, 92, 422).
8. Fluidic structure according to claim 7,
   characterised in that the wide region (76, 96, 426) is arranged offset in the second direction perpendicular to the flow direction (13) with respect to the inlet portion (68, 88, 418) and/or with respect to the outlet portion (72, 92, 422) .
9. Fluidic structure according to any one of claims 1 to 8, characterised in that the fluid line (82, 158) has in the flow direction (13) upstream of and/or downstream of the retention portion (90) at least one stop structure (105, 106, 160), preferably constructed in the form of a shoulder which interrupts the path of at least one of the walls of the fluid line (82, 158).
10. Microfluidic chip (110, 170, 190, 510) having a substrate (10, 30, 60, 80, 120, 310, 410, 520), a cover (125, 525) for the substrate (10, 30, 60, 80, 120, 310, 410, 520) and a fluidic structure according to any one of claims 1 to 9 in the substrate (10, 30, 60, 80, 120, 310, 410, 520), characterised in that the fluid line (12, 32, 62, 82, 122, 172, 192, 312, 412, 522) is constructed in the form of a channel in the substrate (10, 30, 60, 80, 120, 310, 410, 520) and is closed by the cover (125, 525), wherein the channel in the retention portion (20, 40, 70, 90, 210, 320, 420) is subdivided into the narrow region (24, 44, 74, 94, 134, 164, 174, 194, 324, 424, 534) and the wide region (26, 46, 76, 96, 136, 176, 196, 326, 426, 536), preferably with a greater channel depth in the wide region than in the narrow region.
11. Microfluidic chip (110, 170, 190, 510) according to claim 10,
    characterised in that the first direction is located perpendicularly to a channel base (14, 34, 34', 84, 163, 202, 203, 314, 414) opposite the cover (125, 525).
12. Microfluidic chip (110, 170, 190, 510) according to claim 11,
    characterised in that the channel base (14, 34', 84, 163, 202, 314, 414) merges in an inlet portion (18, 38, 68, 88, 208, 318, 418) in the flow direction upstream of the retention portion (20, 40, 70, 90, 210, 320, 420) and in an outlet portion (22, 42, 72, 92, 212, 322, 422) in the flow direction downstream of the retention portion (20, 40, 70, 90, 210, 320, 420) in a stepless manner into the channel base of the narrow region (24, 44, 74, 94, 134, 164, 174, 194), which preferably forms a plateau in the sense of claim 5, or into the channel base of the wide region (176, 196, 326, 426, 536) .
13. System having a fluidic structure according to any one of claims 1 to 9 or having a microfluidic chip (110, 510) according to any one of claims 10 to 12, wherein the narrow region (134, 154) has a volume V_e and the wide region (136, 536) has a volume V_w,
    having a first fluid (140, 540) having a defined volume V_F11, having a second fluid (150, 550) having a defined volume V_F12, and having a buffer medium (146, 546) which is arranged at the inlet of the retention portion between the first and second fluid and which can be transported together with the first and the second fluid through the fluid line (122, 522), wherein optionally

    - the first fluid and the second fluid wet the walls of the fluidic structure to a greater extent than the buffer medium and wherein the conditions apply:
    V_F11 < V_e and V_F11 + V_F12 >V_e,
    or

    - the first fluid and the second fluid wet the walls of the fluidic structure to a lesser extent than the buffer medium and wherein the conditions apply:
    V_F11 < V_w and V_F11 + V_F12 >V_w.

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