Microfluidic receiving element, microfluidic device with a receiving element, method for producing a microfluidic receiving element and method for using a microfluidic receiving element

Abstract

The invention relates to a microfluidic receiving element (110) for a microfluidic device (100) for processing fluids. The receiving element (110) has at least one recess (115) for receiving an aqueous solution, wherein the at least one recess (115) is in the form of a cavity or through-hole. The receiving element is characterised in that at least one protrusion (125) is formed in a side wall (120) of the recess (115), having a preferably hydrophilic surface quality, and the recess (155) has a non-convex cross-sectional area in the plane of an upper side (130) of the receiving element (110).

Description

[0001] R. 399224 - 1 - Description Title Microfluidic receiving element, microfluidic device with receiving element, method for producing a microfluidic receiving element, and method for using a microfluidic receiving element. State of the art The invention is based on a microfluidic receiving element, a microfluidic device with a receiving element, a method for producing a microfluidic receiving element, and a method for using a microfluidic receiving element according to the preamble of the independent claims. The present invention also relates to a computer program. Microfluidic analysis systems, so-called lab-on-chips (LoCs for short), enable automated, reliable, compact, and cost-effective processing of chemical or biological substances for medical diagnostics.By combining a variety of operations for the targeted manipulation of fluids, complex microfluidic processes can be realized.

[0002] R. 399224 - 2 - Disclosure of the Invention Against this background, the approach presented here provides a microfluidic receiving element, a microfluidic device with a receiving element, a method for producing a microfluidic receiving element and a method for using a microfluidic receiving element, furthermore a control device that uses one of these methods, and finally a corresponding computer program according to the main claims. The measures listed in the dependent claims enable advantageous further developments and improvements of the device specified in the independent claim. The microfluidic receiving element presented here can advantageously reduce the pinning occurring at the edges of cavities in a microfluidic device, so that a spatially particularly homogeneous wetting of the receiving element in a flow cell can be achieved.A microfluidic receiving element for a microfluidic device for processing fluids is presented. The receiving element has at least one recess for receiving an aqueous solution, wherein the at least one recess is formed as a cavity or through-hole. The receiving element is characterized in that at least one bulge with a preferably hydrophilic surface quality is formed in a side wall of the recess, and the recess has a non-convex cross-sectional area in the plane of an upper side of the receiving element. The microfluidic device can, for example, be a microfluidic analysis system in the form of a lab-on-chip cartridge (LoC), which can comprise a microfluidic network for processing fluids, for example, for analyzing patient samples. With regard to the provision of a predetermined microfluidic functionality, a suitableDesign of microfluidic structures R. 399224 - 3 - may be indispensable. The design of microfluidic structures, for example structures with holes or cavities, can depend, among other things, on the properties of the liquid(s) involved, such as surface tension, viscosity, density, polarity, and in particular the wetting behavior as well as the specifications of the functionality to be provided. In some cases, the geometry of microfluidic structures that can be used to realize a given functionality can be significantly determined or limited by the wetting properties of the surface. One example of this is microfluidic structures that allow the aliquoting of a sample liquid into a plurality of compartments. Such structures can be realized, for example, by a receiving element with an arrangement of recesses such as cavities or holes that area substrate and thus form a microfluidic receiving element for generating liquid compartments. For this purpose, the recess or a plurality of uniform recesses can be formed, for example, as a cavity or through-hole. Accordingly, the core of the invention presented here is an improved microfluidic receiving element with an arrangement of at least one recess on a surface for receiving an aqueous solution, wherein the at least one recess is formed as a cavity or through-hole. The two-dimensional cross-sectional area of ​​the at least one recess can be described, within the plane defined by a top side of the receiving element, via which the filling of the at least one recess takes place, by a geometric figure which has at least one bulge or indentation, so that the said two-dimensionalThe cross-sectional area of ​​the at least one recess forms a non-convex subset of a Euclidean space. A subset of a Euclidean space is convex by definition if, for any two points belonging to the set, their connecting line also always lies entirely within the set. The design of the recess with at least one bulge and a non-convex cross-sectional geometry has the particular advantage that, in the case of a phase boundary with a significant surface energy or surface tension, the occurrence of so-called pinning (“attachment”) R. 399224 - 4 - of the phase boundary to the edge of the recess can be significantly reduced. This can be justified by the fact that for a phase boundary to be pinned to the edge of a recess in the region of a bulge or indentation, there must be an enlargement of the interface or a strong curvature of the interface, which energeticallyis unfavorable, so that preferably penetration of the liquid into the recess can occur. According to one embodiment, the bulge of the recess can be jagged or have at least one prong. In particular, a part, in particular one side, of the prong can have the shape of an arc. In a special embodiment, the one or more prongs can preferably have a segmented, Archimedean spiral shape. The one or more prongs can thus, for example, be formed piece by piece, alternating from straight and arc-shaped segments. The arc-shaped segments can, for example, be formed as a circular arc or as part of an elliptical arc or as part of a spiral arc. The straight segments can, for example, each be oriented radially from the center of the recess. For example, a radius of a tip of the prong can be less than 25 µm and particularly preferablybe less than 15 µm, or the legs of the prong can, for example, be spread at an angle of less than 90 degrees. This has the particular advantage that pinning of a phase interface at the edge of the recess can be prevented particularly effectively, since with a rounding radius of less than, for example, 25 µm or 15 µm of the tip, a locally strong curvature of the interface would be necessary for pinning at this point, the formation of which, however, can be particularly unfavorable in terms of interfacial energy. The improved pinning behavior is attributable to the surface energy of a phase interface, which must be applied for the attachment of a phase interface to the edge of a recess through the associated deformation of the interface. The surface energy that must be provided for the attachment of a phase interface to an edge of a recessmust, correlates with the R. 399224 - 5 - length of the edge and the associated enlargement of the phase interface. Thus, depending on the design of the edge, the surface energy required for pinning at this edge can be adjusted. In principle, an edge with clearly pronounced bulges and thus a significantly larger edge length (compared to a circular recess) with a comparable volume of the recess can also induce a particularly large surface energy for pinning. However, with the edge length, the surface-to-volume ratio of a recess generally also increases. This, in turn, can be disadvantageous for carrying out, for example, a chemical or biochemical reaction within the recess, especially in the event that undesired adsorption of reactants on the walls of the recess can occur, whichIn particular, it cannot be sufficiently reduced by a suitable coating of the walls of the recess. In general, it may therefore be necessary when designing and constructing a recess to find a suitable compromise between improved filling characteristics on the one hand and increasing the surface-to-volume ratio on the other. Accordingly, in addition to the realization of bulges that are as pronounced as possible and an increase in the edge length, the realization of bulges with the most pointed shape possible, i.e. a small minimum radius at the tip of the bulge, may also be advantageous, since a particularly high interfacial energy may be required locally for pinning at an edge formed in this way. According to a further embodiment, the recess may have at least one second bulge, wherein the bulge and the second bulge are arranged in a predetermined manner relative to one another.can be arranged and / or can be similar to one another in shape and size. For example, the recess can be formed with a plurality of bulges, wherein the bulges can be arranged in a predetermined manner relative to one another and can be similar to one another in shape and size. This has the particular advantage that filling of the recess from different directions, from which the phase boundary can run towards the recess, can be promoted. R. 399224 - 6 - Thus, a substantially direction-independent, i.e. uniform, filling characteristic can be achieved. For example, a recess formed in this way can be used for aliquoting a liquid, such as a sample liquid. After aliquoting, a parallelized analysis of the sample liquid can be carried out, for example, via so-called geometric multiplexing. In particular, the bulges can be arranged such that, for examplea star-shaped shape of the recess can be achieved. A subset of a Euclidean space is star-shaped by definition if there is a point from which every straight connecting line from this point to any point of the set lies entirely within this set. For example, a two-dimensional cross-sectional area can be described by a geometric figure having a circular or hexagonal basic shape, on which the at least one bulge can be arranged. This has the particular advantage that a low surface-to-volume ratio can be achieved. Due to the point-oriented design, the recess can also be advantageously designed to promote filling of the recess in different directions, in which the phase interface can run towards the recess. According to a further embodiment, the side wall of the recess can be coated with a biocompatible coatingbe designed to minimize adsorption of reactants on the side wall of the recess. For example, at least one wall of the recess adjacent to the at least one bulge can have a hydrophilic surface quality. Additionally or alternatively, the at least one bulge of the two-dimensional cross-sectional area can correspond to the formation of at least one side wall lamella of the three-dimensional recess. In particular, if the side wall lamella has a hydrophilic surface quality, the formation of a microfluidic capillary path in the side wall lamella can advantageously be promoted, which can support particularly reliable filling of the recess. The at least one side wall lamella can in particular extend over the entire height of the recess or only over a partial area of ​​the recess, in particular the upper area adjacent to the inlet surface for a liquid. 399224- 7 - area of ​​the recess. The latter offers the advantage that, on the one hand, improved penetration of a liquid into the recess can occur via the sidewall lamella, and, on the other hand, the discharge of a substance or pre-stored reagent that has dried exclusively at the bottom of the recess can be reduced, since the capillary path created by such a sidewall lamella is not continuous all the way to the bottom of the recess. Advantageously, such a recess can be produced, for example, by a dry etching process in a silicon substrate, wherein the geometry of the recess with the at least one bulge and sidewall lamella at the entry surface is defined lithographically, and due to a partially isotropic nature of the etching process, with increasing depth of etching, there is a continuous weakening of the degree of pronouncedness of the sidewall lamella, so that theThe side wall lamella is formed only in a region of the recess adjacent to the inlet surface. Furthermore, the recess can additionally or alternatively have a slightly bulbous end similar to a wide-necked round-bottomed flask. Additionally or alternatively, the side walls of the at least one recess of the receiving element can have a biocompatible coating, which advantageously minimizes the adsorption of reactants, i.e. components of a reaction mix required for carrying out a biochemical, such as a molecular diagnostic, detection reaction, such as nucleic acids, primers, probe molecules or enzymes such as polymerases, on the walls of the recess. In this way, on the one hand, a design of the at least one recess with bulges is enabled, which increases the surface-to-volume ratio, but on the other hand, improves the filling behavior of the recess in accordance with the invention.In this way, a high reaction efficiency can be achieved. At the same time, a high reaction efficiency can be achieved, since despite a larger surface-to-volume ratio compared to, for example, a cylindrically shaped recess, adsorption of components of the reaction mix on the walls of the recess can be advantageously reduced by the coating. R. 399224 - 8 - According to a further embodiment, the side wall of the recess can be arranged perpendicularly with respect to an upper side of the receiving element within a tolerance range, in particular wherein the side wall can form an angle between 85 and 95 degrees to the upper side. Additionally or alternatively, the bulge can be formed adjacent to the upper side of the receiving element over the entire height of the side wall of the recess. For example, the at least one recess of the receiving element can have almost vertical side walls, which form an angle to the upper side of the receiving element.between 85 and 95 degrees, whereby a cylindrical basic shape can be achieved. This has the particular advantage that the recess can be produced in a particularly simple manner. According to a further embodiment, a surface-to-volume ratio of the recess can be 1.0 to 2.0 times the surface-to-volume ratio of a cylindrical recess of the same volume with a circular cross-sectional area, in particular 1.0 to 1.5 times the surface-to-volume ratio. This has the particular advantage that the surface of the recess, at which adsorption of components of a reaction mix can take place, can be particularly small. In this way, for example, the efficiency of a biochemical detection reaction carried out in a recess can be increased. According to a further embodiment, the recess can have anon-convex, but star-shaped cross-sectional area. For example, the recess can have several bulges, which are arranged in a predetermined manner relative to one another, resulting in a star-shaped cross-sectional area. By means of such an advantageous configuration, for example, on the one hand a low surface-to-volume ratio of the recess can be achieved and, on the other hand, the point-oriented configuration of the recess can promote filling of the recess in different directions, with which the phase boundary surface can run towards the recess adjacent to the plane of the upper side of the receiving element. R. 399224 - 9 - According to a further embodiment, the receiving element can comprise several recesses. For example, the receiving element can have at least one second recess or several further recesses, wherein the recess and the second recess can resemble one another in shape and additionally orAlternatively, the size may be the same within a tolerance range (of, for example, 10 to / or 25 percent). For example, the receiving element may comprise an arrangement or an array of several uniform recesses for carrying out identical reactions or reactions that differ from recess to recess. This has the advantage that analysis processes can be optimized and carried out in the recesses in a parallel manner. According to a further embodiment, the receiving element may have at least one substance that can be pre-stored in the recess and is soluble in an aqueous solution, for example for carrying out a detection reaction, in particular wherein the substance can be arranged or can be arranged in the bulge or adjacent to the bulge. For example, at least one dried substance can be pre-stored in the at least one recess of the receiving element, which substance, when receiving an aqueous solution, enters theRecess can be released. This has the particular advantage that the recess can be used, for example, for carrying out a special detection reaction. With a plurality of recesses in the receiving element, different detection reactions can be carried out in the recesses, for example, by means of different detection reagents stored in the recesses. In a further advantageous embodiment, the substance dried in the at least one recess of the receiving element is present, in particular, in at least one bulge or adjacent to at least one bulge of the at least one recess. This has the particular advantage that the substance is present in regions of the recess which, when the recess is filled in a flow cell in which a continuous liquid flow through the recess can occur at times, can be flowed through less strongly than other regions of theRecess. In this way, for example, flow-induced entrainment of the upstream substance can be minimized. R. 399224 - 10 - Furthermore, the substance upstream into the at least one bulge or adjacent to the at least one bulge can preferably be present largely, for example more than 70% or more than 80% or completely, in the lower half of the recess and in particular at least partially adjacent to the edge of the bottom of the recess. In this way, the substance can be stored in the recess as far as possible from the region of the recess through which the flow is particularly strong, in order to prevent, as far as possible, an undesired discharge of upstream substance from a recess during the microfluidic processing of the receiving element. Furthermore, with a hydrophilic surface quality (at least present in some areas) of the inner walls of the recess with the bulges, a particularly simpleThe introduction of a substance into the recesses can be achieved, for example, by means of a fine dosing system, by first introducing an aqueous solution of the substance into the recess and subsequently causing the solvent to evaporate, whereby the capillary forces acting on the liquid within the recesses can promote the incorporation of the substance in the recesses or a deposition on the walls of the recesses. Furthermore, depending on the geometric design of the recesses and the existing degree of hydrophilicity of the surface of the recesses and the surface tension of the liquid, the ratio of the amount of substance stored in the recesses to the amount of substance stored in the recess outside the volume surrounded by the recesses (in particular on the central bottom area of ​​theRecess) can be adjusted to a variable extent. Overall, the described receiving element is characterized by an improved filling behavior of the inventive recess of the improved microfluidic receiving element. In this case, a particularly high reliability in the wetting of a cavity can advantageously be achieved. In particular, when filling the cavity with a liquid with a significant surface tension, such as an aqueous solution, the inclusion of a gas previously present in the cavity, such as air, in the cavity and in particular at the bottom of the cavity can be prevented. In other words, an improved microfluidic filling behavior of recesses can be achieved. In particular, so-called dead-end structures, such as cavities with a higher aspect ratio, can be completely filled than is the case with conventionally designed, state-of-the-artThis is the case with cavities corresponding to the technology. Furthermore, the device according to the invention can improve the fillability of any shaped recesses, whereby only a slight geometric modulation of the edge properties or parts of the edge is required. The invention thus enables the functionalization of any geometries with regard to improved microfluidic fillability. In addition, the presented receiving element is characterized by reduced pinning of a phase interface to the edge of a recess. In particular, when using a receiving element with a plurality of recesses arranged on a surface in the inventive design, a spatially particularly homogeneous and temporally continuous wetting of the receiving element with the recesses can occur, thereby ensuring particularly high reliability in the microfluidic processing of the receiving element in a flow cell.can be achieved. The particularly advantageous filling behavior can be brought about in particular by the formation of microfluidic capillary paths on the side walls of the recess. The resulting capillary forces can promote wetting of the hydrophilic side walls. Wetting of the side walls can, in particular, prevent undesired inclusion of gaseous media, which may be present in the recess before wetting with the liquid. In addition, pinning of the liquid front hitting the recess to the edge of the recess can be reduced, which can also facilitate complete filling of the recess. Based on the newly established filling mechanism, the recess according to the invention can also be appropriately referred to as a capillary cavity and in particular as a silicon capillary cavity. The latter term arises in particular from the fact that by means of theThe MEMS industry-established process of reactive ion deep etching provides a process that enables high-precision manufacturing of such capillary cavities with capillary channels formed on the micrometer scale on the side walls of the cavities based on silicon. Furthermore, pre-storage of reagents in the recesses is recommended, for example, to be able to carry out different reactions in the recesses (geometric multiplexing). The recess presented here can have a positive effect on the carryover behavior of at least one reagent pre-stored in a recess, i.e., in particular, discharge from the at least one reagent pre-stored in the recess can be reduced when filling the recess. Furthermore, a microfluidic device for processing fluids with a variant of the previously presented microfluidic receiving element is presented.The device can, for example, be a lab-on-chip cartridge. The combination of the microfluidic device with the receiving element has the advantage that all of the previously described advantages for processing a fluid or for analyzing sample components dissolved in the fluid can be optimally implemented. In addition, a method for producing a variant of the previously presented microfluidic receiving element is presented. The method comprises a step of defining a geometry of at least one recess with a bulge arranged in the side wall of the recess. This definition step can, for example, be carried out as a separate step in which, for example, a photoresist can be exposed accordingly. Alternatively, the definition step can also be carried out parallel to a step of introducing the at least one recess into a substrate. In the introduction step,For example, the recess can be created in, for example, a silicon substrate by means of reactive ion deep etching. According to one embodiment, a plurality of recesses, each with the same geometry, can be defined in the defining step, wherein the plurality of recesses can be introduced into the substrate in parallel in the introducing step. For example, a parallel R. 399224 - 13 - forming of a plurality of recesses in a silicon substrate can be carried out by reactive ion deep etching of the silicon substrate, wherein the geometry of the recesses can be defined beforehand via a lithographic step. This has the advantage that the effectiveness of the end product is increased and, at the same time, time and costs in production can be saved through parallelization. In addition, a method for using a variant of the previously presented microfluidic receiving element is presented. TheThe method comprises a step of introducing an aqueous solution into the recess of the receiving element and a step of detecting a parameter of a reaction carried out in the receiving element using the introduced aqueous solution. For example, in the step of introducing, the surface of the microfluidic receiving device with the arrangement of recesses can be brought into contact with an aqueous solution and the at least one recess can be filled with the aqueous solution. For example, at least one bulge of a cavity can be wetted first and, starting therefrom, the bottom of the cavity can be wetted with liquid and finally the entire volume of the cavity can be filled with liquid. Subsequently, a reaction can be carried out within the recess, for example using upstream reagents and additionally or alternatively by heating the receiving element. In the step ofDuring detection, a parameter of the reaction, such as an optical signal, in particular a fluorescence signal, is detected in order to obtain an analysis result. These methods can be implemented, for example, in software or hardware or in a mixed form of software and hardware, for example in a control unit. The approach presented here further creates a control unit that is designed to carry out, control, or implement the steps of a variant of a method presented here in corresponding devices. The object underlying the invention can also be achieved quickly and efficiently by this embodiment of the invention in the form of a R. 399224 - 14 - control unit. For this purpose, the control unit can have at least one computing unit for processing signals or data, at least one memory unit for storing signals or data, at least one interface to a sensor or an actuator for reading inSensor signals from the sensor or for outputting data or control signals to the actuator and / or at least one communication interface for reading in or outputting data that is embedded in a communication protocol. The processing unit can be, for example, a signal processor, a microcontroller, or the like, wherein the storage unit can be a flash memory, an EEPROM, or a magnetic storage unit. The communication interface can be designed to read in or output data wirelessly and / or via a wired connection, wherein a communication interface that can read in or output wired data can, for example, read this data electrically or optically from a corresponding data transmission line or output it to a corresponding data transmission line. In the present case, a control unit can be understood as an electrical device that processes sensor signals and, depending on them,and / or outputs data signals. The control unit can have an interface, which can be implemented in hardware and / or software. In a hardware implementation, the interfaces can, for example, be part of a so-called system ASIC, which contains a wide variety of functions of the device. However, it is also possible for the interfaces to be separate integrated circuits or to consist at least partially of discrete components. In a software implementation, the interfaces can be software modules, which are present, for example, on a microcontroller alongside other software modules. Also advantageous is a computer program product or computer program with program code, which can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory, or an optical memory and is used to carry out, implement, and / or control the steps of the method.according to one of the embodiments described above, in particular when the program product or program is executed on a computer or a device. Embodiments of the approach presented here are illustrated in the drawings and explained in more detail in the following description. It shows: Fig. 1 is a schematic cross-sectional view of a microfluidic device according to an embodiment; Fig. 2A is a schematic plan view of an embodiment of a recess; Fig. 2B is a schematic plan view of an embodiment of a recess; Fig. 2C is a schematic plan view of an embodiment of a recess; Fig. 3A is a schematic plan view of an embodiment of a recess; Fig. 3B is a schematic plan view of an embodiment of a recess; Fig. 3C is a schematic plan view of an embodiment of aRecess; Fig. 3D is a schematic top view of an embodiment of a recess; Fig. 4A is a schematic top view of an embodiment of a recess; R. 399224 - 16 - Fig. 4B is a schematic top view of an embodiment of a recess; Fig. 4C is a schematic top view of an embodiment of a recess; Fig. 5A is a schematic top view of an embodiment of a recess; Fig. 5B is a schematic top view of an embodiment of a recess; Fig. 6A is a schematic top view of an embodiment of a recess; Fig. 6B is a schematic top view of an embodiment of a recess; Fig. 7 is a schematic top view of an embodiment of a recess; Fig. 8 is a schematic top view of an embodiment of a recess; Fig. 9A is a schematic top viewof an embodiment of a receiving element; Fig. 9B is a microscopic top view of an embodiment of a receiving element; Fig. 10 is a microscopic cross-sectional view of an embodiment of a receiving element; Fig. 11A is a fluorescence microscopic top view of an embodiment of a receiving element during microfluidic processing of the receiving element in a microfluidic device with a fluorescent aqueous solution; Fig. 11B is a fluorescence microscopic top view of an embodiment of a receiving element during microfluidic processing of the receiving element in a microfluidic device with a fluorescent aqueous solution; Fig. 11C is a fluorescence microscopic top view of an embodiment of a receiving element during microfluidic processing of the receiving element in a microfluidic devicewith a fluorescent aqueous solution; Fig. 12 is a flow diagram of an embodiment of a method for producing a microfluidic receiving element; Fig. 13 is a microscopic top view of an embodiment of a lithographically structured photoresist on a silicon wafer; Fig. 14 is a flow diagram of an embodiment of a method for using a microfluidic receiving element; Fig. 15A is a schematic top view of an embodiment of a receiving element during a method step of insertion; Fig. 15B is a schematic cross-sectional view of an embodiment of a receiving element during a method step of insertion; Fig. 15C is a schematic top view of an embodiment of a receiving element during a method step of insertion; Fig. 15D is a schematic cross-sectional view of an embodiment of a receiving elementduring a method step of introduction; Fig. 16A shows a schematic sequence of a method step of introduction; R. 399224 - 18 - Fig. 16B shows a schematic sequence of a method step of introduction; Fig. 16C shows a schematic sequence of a method step of introduction; and Fig. 17 shows a block diagram of an embodiment of a control device for producing a microfluidic receiving element. In the following description of favorable embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and having a similar effect, whereby a repeated description of these elements is omitted. Figure 1 shows a schematic cross-sectional view of a microfluidic device 100 according to an embodiment. The device 100 is designed to process fluids and thus, for example, substances dissolved in a fluid. For this purpose, it comprisesThe device 100 comprises a microfluidic receiving element 110, which in this exemplary embodiment is arranged on a flow cell 105. The receiving element 110 has a recess 115 for receiving an aqueous solution, wherein a bulge 125, which can also be referred to as a sidewall lamella, is formed in a side wall 120 of the recess 115. In one exemplary embodiment, the lateral dimensions of the entire microfluidic device 100 are merely exemplary 30 x 50 mm² to 80 x 220 mm², and the dimensions of the flow cell 105 are exemplary 5 x 5 x 0.5 mm³ to 15 x 15 x 1 mm³. In one embodiment, the lateral dimensions of the receiving element are 1105 x 5 mm² to 15 x 15 mm², and the height is, for example, 300 µm to 800 µm. In other embodiments, the lateral dimensions of the device can be, for example, 10 x 10 mm² to 200 x 200 mm², and the dimensions of the flow cell can be, for example, 3 x 3 x 0.3 mm³ to 30 x 30 x 3mm³, the dimensions of the R. 399224 - 19 - receiving element are, for example, 3 x 3 mm² to 30 x 30 mm² and the height is 200 µm to 1100 µm. In the exemplary embodiment shown here, the recess also has, for example, a second bulge 127, which in the illustration shown here is arranged opposite the bulge 125 merely by way of example. In this exemplary embodiment, the bulge 125 and the second bulge 127 are of the same shape and size. The side wall 120 of the recess is arranged, for example only, at an angle of 90 degrees perpendicular to an upper side 130 of the receiving element 110. In other exemplary embodiments, the side wall can be arranged perpendicular to the upper side of the receiving element within a tolerance range, for example at an angle between 85 and 95 degrees to the upper side. In addition, the side wall 120 in this embodiment is adjacent to the bulges 125, 127 onlyFor example, it is formed with a hydrophilic surface finish. In another exemplary embodiment, the side wall can additionally or alternatively comprise one or more side wall lamellae formed with the one or more bulges, for example, with a variable cross-sectional profile, i.e., side wall lamellae that are formed only, for example, over a partial region of the recess, in particular the upper region of the recess adjacent to the upper side of the receiving element, and additionally or alternatively, a biocompatible coating, for example, to minimize the adsorption of reactants on the surface of the recess. In this exemplary embodiment, the receiving element 110 comprises, merely by way of example, in addition to the recess 115, a second recess 135, as well as, merely by way of example, a third recess 140, a fourth recess 142, a fifth recess 144, and a sixth recess 146.wherein all recesses 115, 135, 140, 142, 144, 146 are identical in shape and size. By designing the recesses 115, 135, 140, 142, 144, 146 with bulges 125, 127 or with sidewall lamellae, the filling behavior of the recesses 115, 135, 140, 142, 144, 146 can be improved by these lamellae, which can also be referred to as capillary paths, when liquids are brought into controlled contact with the microfluidic receiving element 110 via the R. 399224 - 20 - flow cell 105, since the sidewall lamellae enable improved wetting of the microcavity. The capillary forces acting on the liquid during wetting of a recess 115, 135, 140, 142, 144, 146 correlate on the one hand with the affinity of the liquid to the side wall 120 and on the other hand with the width of the bulge 125, 127. For example, aqueous (polar) solutions, a hydrophilic nature of theSide walls are particularly advantageous; on the other hand, a narrow width of the side wall lamellae allows for a particularly strong influence of the surface forces acting on the liquid when wetting the side wall lamellae. In other embodiments, the size and number of recesses can vary. For example, to specify the receiving element for carrying out a multiplex detection with reagents stored in the recesses, the number of recesses can be 1 to 1,000, preferably 10 to 200, and the volume of a recess can be, for example, 2 nl to 110 nl, preferably 10 nl to 50 nl. The diameter of a recess can be, for example, 110 µm to 1,100 µm, preferably 200 µm to 500 µm. For an exemplary specification of the recording element for carrying out a digital detection, the number of recesses can be, for example, 110 to 110,000, preferably 1,000 to 30,000, the volume of aThe cavity can be 10 pl to 50 nl, preferably 110 pl to 10 nl, and the diameter of a cavity can be, for example, 20 µm to 200 µm, preferably 30 µm to 110 µm. Figures 2A, 2B, and 2C each show a schematic plan view of an exemplary embodiment of a recess 115. The recess 115 shown here corresponds to or is similar to the recess described in the previous figure. The geometries of such recesses with a circular (2A), hexagonal (2B), or square (2C) shape outlined here correspond, by way of example, to the current state of the art. R. 399224 - 21 - A circular geometry shown in Figure 2A, for example, has the particular advantage that the surface-to-volume ratio of a liquid or reaction compartment is particularly low. In this way, for example, the influence of an interaction of components of an aqueous solution in the liquid compartment withthe walls of the liquid compartment can be minimized. For example, the efficiency of a chemical or biochemical reaction carried out in the liquid compartment can be increased if necessary. A hexagonal geometry shown in Figure 2B, for example, has the particular advantage that the liquid volume that can be analyzed on a given area can be maximized with a hexagonally densest arrangement of the reaction compartments and a constant, predetermined minimum wall thickness between the reaction compartments. A square geometry shown in Figure 2C, for example, has the particular advantage that such compartments can be produced in a particularly simple manner by potassium hydroxide-based etching of silicon with high precision in a silicon substrate of suitable crystallographic orientation. In more general terms, a two-dimensional cross-sectional area of ​​a recess115 for the formation of a microfluidic liquid or reaction compartment, which forms a convex subset of a Euclidean space. A subset of a Euclidean space is convex by definition if, for any two points belonging to the set, their connecting line also always lies entirely within the set. In other words, such cavities or through-holes, i.e. generally recesses used to form microfluidic liquid or reaction compartments in a receiving element, according to the prior art have a two-dimensional cross-sectional area with a mostly circular, hexagonal, or more rarely square shape, through which an entry of a mostly aqueous liquid, such as a sample liquid, into the R. 399224 - 22 - liquid compartment occurs. According to the prior art, through-holes are used for this purpose, since these are completely filled witha liquid flowing in from one side of the substrate, without the possibility of air being trapped during filling, as this can escape on the opposite side of the substrate. However, such through-holes make it difficult, for example, to introduce reagents into the compartments, as these can only be deposited on the side walls of the through-holes, but cannot be dried on the bottom of a recess (as is the case with a cavity). Therefore, cavities are also used in particular to provide reaction compartments with introduced, upstream reagents. The reagents can be introduced into the cavities and dried in a controlled and technically established manner, for example by means of a contactless fine dispensing system. In addition, a receiving element with cavities offers the possibility of surface contact of theSubstrate underside, for example with a heating and / or cooling device, in order to enable direct, i.e. as immediate as possible, temperature control of the receiving element. In addition to the aforementioned advantages of such cavity-based microfluidic receiving elements, there is, however, a particular risk that gas, especially air, is trapped in the cavities, thus preventing complete filling of the cavities with a liquid, for example with an aqueous solution with significant surface tension. In particular, cavities with a high aspect ratio are susceptible to the inclusion of air or gas bubbles in the cavities when the receiving element is brought into contact with an aqueous liquid to fill the cavities. This behavior can be explained in particular by the fact that the liquid meniscus is pinned to the edge of the cavity at the edge present here, the cavity from thePhase interface – stabilized by surface tension – is spanned, and then this is suddenly crossed. Consequently, an inclusion of air or gas bubbles in the cavities and thus only an incomplete filling of the cavities is caused. R. 399224 - 23 - Furthermore, for example, when using a flow cell for a controlled contact of at least one liquid with a receiving element, the pinning of the liquid meniscus present at the edges of the individual cavities, for example of an air-water interface, can lead to a spatially and temporally inhomogeneous wetting of the receiving element, which in turn, in addition to promoting an incomplete filling of the individual cavities, can also lead to an incomplete wetting of the receiving element as a whole. When using a three-phase system known from the prior art consisting of a gaseous phasesuch as air, an aqueous phase such as a sample liquid for filling the cavities and a third, immiscible phase as a sealing liquid, such as a fluorinated hydrocarbon for sealing the cavities, it can happen, particularly when sealing the cavities previously filled with the aqueous phase using a flow cell and a limited volume of the aqueous phase, that the third phase breaks through the limited volume of the aqueous phase, i.e. the sample liquid-sealing liquid interface breaks through the sample liquid-air interface, so that a sealing liquid-air interface is present, whereby the filling of all cavities of the receiving device with the aqueous phase can be impaired in a particularly disadvantageous way, for example in the case that sealing liquid penetrates into a cavity before it can contact thecomes into contact with sample liquid. Figures 3A, 3B, 3C and 3D each show a schematic plan view of an embodiment of a recess 115. The recess 115 shown here corresponds to or is similar to the recess described in the previous figures, wherein a plurality of uniform bulges 125 of the recess 115 are jagged in shape. Due to an underlying circular or cylindrical geometry of the recess 115, an overall star-shaped shape results. Mathematically, the geometries of the two-dimensional cross-sectional areas of the recess 115 R. 399224 - 24 - shown here can be easily described in a polar coordinate system and can be distinguished from one another based on the type of edge. Thus, the jagged edge ^(^) = ^0 + ^ f(^ / (2^) ^) with a triangular wave function f(^) can be described by Figures 4A, 4B and 4C each show a schematic top view representationAn embodiment of a recess 115, wherein a plurality of uniform protrusions 125 of the recess 115 are formed as curved prongs. Due to the underlying circular or cylindrical geometry of the recess 115, an overall segmented, Archimedean spiral shape results. Mathematically, the geometries of the two-dimensional cross-sectional areas of the recess 115 shown here can be easily described in a polar coordinate system. Thus, the segmented Archimedean spiral modulated edge can be described with the formula: ^(^) = ^0 + ^ Mod(^ ^, 2^) Figures 5A and 5B each show a schematic plan view of an embodiment of a recess 115. The recess 115 shown here corresponds to or is similar to the recess described in the previous figures, wherein a plurality of uniform bulges 125 of the recess 115 are designed as rounded protrusionsare formed. Due to an underlying circular or cylindrical geometry of the recess 115, an overall sinusoidally undulating shape results. Mathematically, the geometries of the two-dimensional cross-sectional areas of the recess 115 shown here can be easily described in a polar coordinate system. Thus, the sinusoidally undulating edge can be described with the formula: R. 399224 - 25 - ^(^) = ^0 + ^ sin(^ ^) Figures 6A and 6B each show a schematic plan view of an embodiment of a recess 115. The recess 115 shown here corresponds to or is similar to the recess described in the previous figures, wherein a plurality of uniform bulges 125 of the recess 115 are formed as flat spikes or rays. Due to an underlying circular or cylindrical geometry of the recess 115, an overall truncated-divergingmodulated shape. Mathematically, the geometries of the two-dimensional cross-sectional areas of the recess 115 shown here can be easily described in a polar coordinate system. Thus, the truncated-diverging modulated edge can be described with the formula: ^(^) = ^0 + ^ min[ abs[ 10 tan(^ ^)], ^] Figure 7 shows a schematic plan view of an embodiment of a recess 115. The recess 115 shown here corresponds to or is similar to the recess described in the previous figures, wherein a plurality of uniform bulges 125 of the recess 115 are formed as rounded points or curves. Due to an underlying circular or cylindrical geometry of the recess 115, an overall sinusoidal, jagged shape results. Mathematically, the geometry of the two-dimensional cross-sectional area of ​​the recess 115 shown here can be easily described in aPolar coordinate system. Thus, the sinusoidal jagged edge can be described with the formula: ^(^) = ^0 + ^ sig [sin(^ ^)] sin(^ ^) with the signum function R. 399224 - 26 - Figure 8 shows a schematic plan view of an embodiment of a recess 115. The recess 115 shown here corresponds to or is similar to the recess described in the previous figures, wherein a plurality of uniform bulges 125 of the recess 115 are shaped as steps. Due to an underlying circular or cylindrical geometry of the recess 115, an overall step-like modulated shape results. Mathematically, the geometry of the two-dimensional cross-sectional area of ​​the recess 115 shown here can be easily described in a polar coordinate system. Thus, the step-like modulated edge can be described with the formula: ^(^) = ^0 + ^ sig [sin(^ ^)] where ^0, ^, ^, ^ each represent fixed, but adjustable geometric parameters.In other words, the preceding Figures 3, 4, 5, 6, 7, and 8 can be described as follows: In these exemplary embodiments, the recess 115 is formed with a non-convex and star-shaped cross-sectional area based on a circular cross-sectional area whose edge is modulated in different ways. The recess 115 can be used advantageously for the microfluidic generation of liquid compartments in the recess 115. In advantageous exemplary embodiments, depending on the choice of the geometric parameters, the surface-to-volume ratio of the recess can be 1.0 to 2.0 times the surface-to-volume ratio of a cylindrical recess of the same volume with a circular cross-sectional area, in particular 1.0 to 1.5 times the surface-to-volume ratio.Among the configurations described above, depending on the choice of configuration and geometric parameters for a given application, as well as the selected surface coating, particularly advantageous embodiments arise, in particular with regard to the properties of the at least one recess 115 of the receiving element, such as the surface-to-volume ratio, surface texture, and the wetting properties of the surface. Furthermore, a configuration according to the invention results in advantages with regard to the process parameters that can be selected for use of the device, such as the flow rate when introducing the liquid into the flow cell, the spatial / direction-dependent uniformity of the filling characteristics, and the choice of the properties of the liquids used, such as polarity and viscosity.Advantages also arise with regard to application-specific requirements, such as the adsorption behavior of reactants involved in a detection reaction, the acceptable amount of reagent discharged from a recess during microfluidic processing, or the robustness of a detection reaction with respect to fluctuations in reactant concentration. Figures 9A and 9B each show a schematic (Figure 9A) and a microscopic (Figure 9B) top view of an embodiment of a receiving element 110. The receiving element 110 shown here corresponds to or is similar to the receiving element described in the preceding Figure 1. In these embodiments, the receiving element 110 each has an arrangement of a plurality of recesses 115, which are formed, merely by way of example, with the cross-section of an eight-segmented Archimedean spiral.In this exemplary embodiment, the receiving element 110 is formed purely by way of example on the basis of a silicon substrate, wherein the recesses 115, which can also be referred to as capillary cavities, were introduced into the silicon substrate, for example, by means of reactive ion deep etching. The (almost) vertical side walls thus created have bulges 125 or sidewall lamellae formed down to the bottom of the capillary cavity, which lead to particularly advantageous filling behavior of a capillary cavity configured in this way. In the receiving element 110 shown in Figure 9B, purely by way of example, a substance R. 399224 - 28 - 900 soluble in an aqueous solution is arranged in each recess 115 for carrying out a detection reaction. The scale bar shown in Figure 9B corresponds to a length of 500 µm.Figure 10 shows a microscopic cross-sectional view of an exemplary embodiment of a receiving element 110. The receiving element 110 shown here corresponds to or is similar to the receiving element described in the preceding Figures 1 and 9. The figure shown here shows a broken view along the cross section of a recess 115 or a capillary cavity with a plurality of bulges 125 or sidewall lamellae. The sidewall lamellae are realized along the entire height of the capillary cavity. The scale bar has a length of 100 µm. Figures 11A, 11B and 11C each show a microscopic top view of an exemplary embodiment of a receiving element 110. The receiving element 110 shown here corresponds to or is similar to the receiving element described in the preceding Figures 1, 9 and 10.This illustrates, by way of example, the filling of the microfluidic receiving element 110 with an arrangement of recesses 125 or capillary cavities with a colored aqueous solution 1100 and the sealing of the capillary cavities with a second liquid 1105 that is immiscible with the aqueous solution. For this purpose, the microfluidic receiving element 110 with the capillary cavities is implemented, by way of example, in a flow cell, which enables controlled contact of the receiving element 110 with the liquids 1100, 1105. The three figures 11A, 11B, and 11C show the filling in chronological order.Figures 11A, 11B, 11C particularly illustrate the advantageous filling mechanism which results from the wetting of the capillary cavities with the aqueous phase due to the cavity shape according to the invention: As can be seen in Figure 11A, immediately after the liquid meniscus describing the phase interface comes into contact with a bulge 125 of a capillary cavity, the aqueous solution R. 399224 - 29 - 1100 penetrates into the cavity, the bottom of the cavity being wetted with the solution 1100 and in particular also the other bulges of the cavity.The wetting process of the bulges is particularly favored by the capillary forces acting on the liquid within the bulges. This is because, on the one hand, the bulges have a particularly hydrophilic surface texture and, on the other hand, the small spatial dimensions of the bulges, which are particularly below the capillary length of the liquid used, lead to a wetting behavior driven by surface forces. In this way, wetting of the bulges is particularly favored, and the bulges initially exhibit the highest fluorescence signal of all areas of a cavity. The scale bar in Figure 11A corresponds to a length of 200 µm. Following wetting of the bulges, the almost cylindrical basic volume of the capillary cavities enclosed by the bulges is filled.Filling occurs continuously, starting from the bottom of the cavity and moving upwards to the top of the receiving element 110, with the capillary cavities being completely filled without any gas being trapped. Almost complete filling of a capillary cavity can be achieved even before the meniscus of the phase interface completely migrates over the capillary cavity. This is particularly indicated by the similar fluorescence signal level of the capillary cavities in Figures 11B and 11C, which can be observed before a cavity migrates over the phase interface and after a cavity is covered with a second immiscible (and non-fluorescent) liquid 1105. The spatially homogeneous fluorescence signal of the capillary cavities in Figure 11C indicates in particular that complete filling of the capillary cavities could be achieved overall without any gas bubbles being trapped.Figure 12 shows a flow diagram of an embodiment of a method 1200 for producing a microfluidic receiving element. The method 1200 comprises a step 1205 of defining a geometry of at least one recess with a bulge arranged in the side wall of the recess, and a step 1210 of introducing the at least one recess into a substrate. In this embodiment, purely by way of example, in the defining step 1205, a plurality of recesses, each with the same geometry, are defined, wherein in the introducing step 1210, the plurality of recesses are introduced into the substrate in parallel. In one embodiment, the geometry of at least one recess with a non-convex cross-sectional area can be defined in the defining step.In an advantageous embodiment of the method for producing an improved microfluidic receiving element, a plurality of recesses can be introduced into a silicon substrate in the insertion step by reactive ion deep etching of the silicon substrate, wherein the geometry of the recesses can be defined beforehand via a lithographic definition step. In an advantageous further development of the method for producing an improved microfluidic receiving element, a coating step can additionally be carried out after the insertion step, in which an at least partial coating of the receiving element and in particular a partial coating of the surface of the recesses takes place in order to provide a particularly hydrophilic and additionally or alternatively a particularly biocompatible surface quality of the recesses.For example, the coating can, on the one hand, improve wetting of the capillary cavities and, on the other hand, reduce adsorption of reactants on the surface of the recess. For example, the coating can be a silanization coating with a polyethylene glycol molecule. Figure 13 shows a microscopic top view of an embodiment of a lithographically structured photoresist 1300 on R. 399224 - 31 - a silicon wafer 1305. This was produced, for example, in a definition step as described in the previous Figure 12, in order to then introduce (capillary) cavities into the silicon wafer by means of, for example, reactive ion deep etching. The scale bar in the upper left image corresponds, for example, to a length of 500 µm.The 15 images each show sections of arrangements of openings in the photoresist for forming the cavities and creating various microfluidic receiving elements. On the left, three different convex (circular, hexagonal, square) openings in the photoresist are shown, whereas on the right, twelve different non-convex (but star-shaped) openings in the photoresist are shown. It can be seen that the lithographic definition of the structuring by means of exposure and development of a photoresist enables the highly precise production of the various capillary cavities, particularly those designed with recesses or indentations.In one embodiment, exposure can be carried out, for example, using an exposure unit with a mask or using a direct laser beam writer, whereby a precision in the µm range can be achieved in each case. In this way, for example, subsequent reactive ion deep etching can be used to precisely produce sidewall lamellae or capillary channels on the sidewalls of the cavities. Due to the hydrophilic wetting properties of the sidewalls of the cavity, high capillary pressures are generated in the capillary channels in one embodiment, which lead to rapid wetting of the cavity sidewall. After wetting of the sidewall, any trapped air bubbles are moved out of the cavity by the acting buoyancy force. Figure 14 shows a flow diagram of an embodiment of a method 1400 for using a microfluidic receiving element.The method 1400 comprises a step 1405 of introducing an aqueous solution into the recess of the receiving element and a step 1410 of detecting a parameter of a reaction carried out in the receiving element using the introduced aqueous solution. R. 399224 - 32 - In one embodiment, the step 1405 of introducing comprises, for example, bringing into contact, wherein the surface of the microfluidic receiving device having an arrangement of recesses is brought into contact with an aqueous solution and then the at least one recess is filled with the aqueous solution. In one embodiment, during filling, at least one bulge of a cavity is first wetted and then, for example, the bottom of the cavity is wetting with liquid. Subsequently, purely by way of example, the entire volume of the cavity is filled with liquid.Figures 15A, 15B, 15C, and 15D each show schematic representations of an exemplary embodiment of a receiving element 110 during an insertion process step, as described in the preceding Figure 14. Specifically, Figures 15A and 15B outline a filling characteristic of a conventional circular cavity, and Figures 15C and 15D outline a characteristic for a recess 115 with, for example, hydrophilic protrusions 125. As outlined in Figures 15A and 15B, in a cavity with a circular cross-sectional area, pinning occurs at the upper edge of the cavity, thus spanning the cavity by a phase boundary. This may lead to undesired air inclusion and thus to incomplete filling of a cavity.This can be the case, for example, in particular if the liquid has a high surface tension or the upper side of the receiving element has a hydrophobic surface quality, at least in some areas, which leads to the formation of a large contact angle > 90° upon contact with an aqueous phase. In contrast, in a capillary cavity with hydrophilic sidewall lamellae—as outlined in Figures 15C and 15D—as soon as the liquid meniscus of the phase interface encounters the edge of the cavity, capillary forces-induced wetting of the hydrophilic sidewall lamellae of the cavity occurs, whereby wetting of the cavity floor also occurs. Consequently, the inclusion of air in the cavity and thus incomplete filling of the cavity can be prevented.Even when an improved microfluidic receiving element 110 is brought into contact with an aqueous liquid at a high propagation velocity of the phase interface, i.e., in particular at a velocity at which the inertia of the introduced liquid initially does not allow complete filling of the cavity, complete filling of the cavity can ultimately be expected (with suitable alignment of the receiving element), since the air initially trapped in the cavity, after wetting of the side walls induced by capillary forces, can be displaced from the cavity by the buoyancy force acting on them, resulting in complete filling of the cavity with the aqueous liquid. Figures 16A, 16B, and 16C each show a schematic sequence of an introduction process step, as described in the preceding Figure 14.In Figure 16A, the recess 115 is merely exemplary circular in shape, in Figure 16B, the recess 115 is merely exemplary with a serrated edge, and in Figure 16C, the recess 115 is merely exemplary with a segmented, Archimedean spiral-shaped modulated edge. In this case, the recess 115 shown in each case comprises merely exemplary a substance 900 disposed upstream, which can also be referred to as a reagent. In addition to advantageous filling characteristics, a capillary cavity with sidewall lamellae can be advantageous, in particular in combination with a reagent disposed upstream in the capillary cavity, in order to minimize the carryover of a reagent disposed upstream in the cavity induced during filling of the cavity. The reagent disposed upstream is first introduced into the capillary cavity in the form of a solution, for example by means of a fine dosing system, and is then dried therein.The dried reagent is deposited particularly at the edge of the bottom and the lower region of the side walls of the cavity—due to the distribution of the liquid solution within the cavity caused by capillary forces. This is schematically illustrated in the top view on the left side of Figures 16A, 16B, and 16C. In capillary cavities with sidewall lamellae, i.e., with at least one bulge 125, the reagent is deposited and stored within the sidewall lamellae, as shown merely by way of example in Figure 16C.While in a circular (or generally convex) cross-sectional geometry of a cavity, the deposited reagent is located close to the area of ​​the cavity through which liquid flows, incorporation of the reagent in sidewall lamellae can provide better shielding of the reagent from the area through which liquid flows. This is schematically illustrated by the flow lines 1600 in the cross-sectional views on the right-hand side of Figures 16A and 16B. Furthermore, to create liquid compartments in recesses 115 in the form of circular cavities or through holes in a substrate, it is first necessary to fill the recesses with the mostly aqueous liquid. This can lead to undesirable inclusion of gas, such as air, at the bottom of the cavity, particularly when using cavities.Furthermore, pinning of a phase interface, such as an air-water interface, can occur at the edge of the recess 115, via which filling occurs. This can also have a detrimental effect on the filling behavior of a recess and, moreover, also on the filling behavior of an arrangement comprising a plurality of recesses in a substrate, i.e., a receiving element, which is present in particular in a flow cell. An improved geometric design of the recesses 115 for forming liquid or reaction compartments, i.e., in particular, by modifying the geometry of the cavities or through-holes, as shown in Figures 16B and 16C, allows for improved filling of the recesses, particularly with aqueous solutions (with a significant surface tension).Figure 17 shows a block diagram of an embodiment of a control device 1700 for producing a microfluidic receiving element. The control device 1700 comprises a defining unit 1705 for controlling the definition of a geometry of at least one recess with a bulge arranged in the side wall of the recess. In addition, the control device 1700 comprises an insertion unit 1710 for controlling the insertion of the at least one recess into a substrate. If an embodiment comprises an "and / or" connection between a first feature and a second feature, this is to be interpreted as meaning that, according to one embodiment, the embodiment comprises both the first feature and the second feature, and according to another embodiment, either only the first feature or only the second feature.

Claims

R. 399224 - 36 - Claims 1. Microfluidic receiving element (110) for a microfluidic device (100) for processing fluids, wherein the receiving element (110) has at least one recess (115) for receiving an aqueous solution, wherein the at least one recess (115) is formed as a cavity or through-hole, characterized in that at least one bulge (125) with a preferably hydrophilic surface condition is formed in a side wall (120) of the recess (115) and the recess (115) has a non-convex cross-sectional area in the plane of a top surface (130) of the receiving element (110).

2. Microfluidic receiving element (110) according to claim 1, wherein the protrusion (125) of the recess (115) is jagged or has at least one jagged point, wherein preferably the radius of the tip of the jagged point is less than 25 µm and particularly preferably less than 15 µm. 3.

4. Microfluidic receiving element (110) according to any one of the preceding claims, wherein the recess (115) has at least one second protrusion (127), wherein the protrusion (125) and the second protrusion (127) are arranged relative to each other in a predetermined manner.

5. Microfluidic receiving element (110) according to any one of the preceding claims, wherein the side wall (120) of the recess (115) is formed with a biocompatible coating to minimize the adsorption of reactants on the side wall (120) of the recess (115).

6. Microfluidic receiving element (110) according to any one of the preceding claims, wherein the side wall (120) of the recess (115) is arranged perpendicular to the top (130) of the receiving element (110) within a tolerance range, in particular wherein the side wall (120) forms an angle between 85° and 8°. R. 399224 - 37 - and 95 degrees to the top (130), and / or wherein the bulge (125) adjacent to the top (130) of the receiving element (110) is formed over the entire height of the side wall (120) of the recess (115).

6. Microfluidic receiving element (110) according to one of the preceding claims, wherein a surface-to-volume ratio of the recess (115) has a surface-to-volume ratio of 1.0 to 2.0 times that of a cylindrical recess (115) of the same volume with a circular cross-sectional area, in particular a surface-to-volume ratio of 1.0 to 1.5 times that of a cylindrical recess (115).

7. Microfluidic receiving element (110) according to any one of the preceding claims, wherein the recess (115) in the plane of the top surface (130) of the receiving element (110) has a non-convex, but star-shaped cross-sectional area. 8.Microfluidic receiving element (110) according to any one of the preceding claims, comprising at least one substance (900) soluble in an aqueous solution that can be pre-stored in the recess (115) for carrying out a detection reaction, in particular wherein the substance (900) is arranged or can be arranged in the indentation (125).

9. Microfluidic device (100) for processing fluids with a microfluidic receiving element (110) according to any one of the preceding claims.

10. Method (1200) for producing a microfluidic receiving element (110) according to any one of the preceding claims 1 to 9, wherein the method (1200) comprises the following steps (1205, 1210): R. 399224 - 38 - Defining (1205) a geometry of at least one recess (115) with a protrusion (125) arranged in the side wall (120) of the recess (115); and introducing (1210) the at least one recess (115) into a substrate.

11. Method (1200) according to claim 10, wherein in the defining step (1205) a plurality of recesses, each with the same geometry, are defined, and wherein in the introducing step (1210) the plurality of recesses are introduced parallel into the substrate.

12. A method (1400) for using a microfluidic receiving element (110) according to any one of the preceding claims 1 to 9, wherein the method (1400) comprises the following steps (1405, 1410): introducing (1405) an aqueous solution into the recess (115) of the receiving element (110); and detecting (1410) a parameter of a reaction carried out in the receiving element (110) using the introduced aqueous solution. 13.Control unit (1700) configured to execute and / or control the steps (1205, 1210; 1405, 1410) of one of the methods (1200; 1400) according to one of the preceding claims in corresponding units (1705, 1710).

14. Computer program configured to execute and / or control the steps (1205, 1210; 1405, 1410) of one of the methods (1200; 1400) according to one of the preceding claims. R. 399224 - 39 - 15. Machine-readable storage medium on which the computer program according to claim 14 is stored.

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