Microfluidic device for handling a fluid sample

Abstract

The invention relates to a microfluidic device (100,200,700) for handling a fluid sample by dividing it into a plurality of aliquots, with at least one microfluidic well (105) configured to receive the fluid sample. The at least one microfluidic well comprising an inlet end (120), an outlet end (125) and a microfluidic circuit (110) with a plurality of microchambers (112). The inlet end and the outlet end are respectively coupled to the microfluidic circuit via at least one microfluidic channel (130,130',130'',130'''). The plurality of microchambers is arranged such that each microchamber is at least indirectly via further microchambers fluidly coupled with the inlet end and the outlet end such that each microchamber is configured to receive fluid from the inlet end via the at least one microfluidic channel and to provide gas displaced by the fluid downstream to the outlet end. Furthermore, a storage section (140,240,740) with a microfluidic storage circuit (142,242,342,742) is provided in order to store fluid that does not reach and / or flows beyond the microchambers of the microfluidic well during a filling process of the microfluidic device and can therefore not be provided at the intended reaction space, wherein a storage opening structure (144,344) is provided in the storage section.

Description

Microfluidic device for handling a fluid sampleFIELD OF THE INVENTIONThe invention relates to a microfluidic device for handling a fluid sample by dividing it into aplurality of aliquots. Furthermore, the invention relates to a system for providing a molecularanalysis of a fluid sample, in particular for providing a digital polymerase chain reactionanalysis, and to a corresponding method.BACKGROUND OF THE INVENTIONMicrofluidic devices are well known in the field of molecular analysis. Providing microchambersfor aliquots in order to facilitate certain thermal reactions is particularly well known in the fieldof polymerase chain reaction (PCR) analysis. PCR methods usually rely on thermal cycling,which involves a thermal treatment of reactants permitting different temperature-dependentreactions.Digital PCR describes a PCR analysis where a large number of separate aliquots is analyzedin order to detect after the thermal treatment, whether a molecule of target DNA was presentin the respective aliquot or not. In view of the large number of aliquots, an original concentrationof target DNA can be determined by using Poisson statistics. The use of digital PCR isparticularly advantageous in the case of rare target DNA compared to a background of non-target DNA. The concentration of such rare target DNA can be reliably determined if thenumber of aliquots used for the digital PCR is large enough.US 2021 / 0379593 A1 describes a microfluidic device with a microfluidic circuit including anarray of fluidly coupled microchambers. Each microchamber includes a reaction chamber andan associated vent chamber. The microfluidic circuit may be arranged such that a fluid sampleintroduced to the microfluidic device flows into the reaction chamber and gas present in thereaction chamber is vented from the microchamber through the vent chamber.CN 115 350 735 B relates to a detection system comprising a micro pump, a mixing unit, amultifunctional chamber and at least six microfluidic chips.US 2024 / 042444 A1 states a microfluidic device with a microfluidic circuit including an array offluidly coupled microchambers. Each microchamber includes a reaction chamber and anassociated vent chamber. The microfluidic circuit may be arranged so that a fluid sampleintroduced to microfluidic device flows into the reaction chamber and air or other gas presentin the reaction chamber is vented from the microchamber through the vent chamber. Themicrochamber may be configured to allow only the flow of air into the vent chamber from thereaction chamber until the air has been displaced from the reaction chamber by the fluidsample and / or a predefined volume of the fluid sample has been received in the reactionchamber. The microchamber may be further configured to release the fluid sample to thereafterflow from the reaction chamber into the vent chamber.It is an object of the invention to provide a microfluidic device with an improved usability of theanalyzed fluid sample, in particular with an improved further access to the fluid sample.SUMMARY OF THE INVENTIONAccording to a first aspect of the invention, a microfluidic device for handling a fluid sample bydividing it into a plurality of aliquots is provided.The microfluidic device according to the first aspect of the invention has at least onemicrofluidic well configured to receive the fluid sample, the at least one microfluidic wellcomprisinga microfluidic circuit with a plurality of microchambers, which provide a respective reactionspace for an aliquot of the plurality of aliquots,an inlet end coupled to the microfluidic circuit via at least one microfluidic channel,an outlet end coupled to the microfluidic circuit via the at least one microfluidic channel,wherein the plurality of microchambers is arranged such that each microchamber is at leastindirectly via further microchambers fluidly coupled with the inlet end and the outlet end suchthat each microchamber is configured to receive fluid from the inlet end via the at least onemicrofluidic channel and to provide gas displaced by the fluid downstream to the outlet end,wherein a storage section with a microfluidic storage circuit is provided in order to store fluidthat does not reach and / or flows beyond the microchambers of the microfluidic well during afilling process of the microfluidic device and can therefore not be provided at the intendedreaction space, andwherein a storage opening structure is provided in the storage section.The microfluidic device according to the first aspect of the invention provides an improvedaccess to the fluid sample after a filling of the microfluidic device. It furthermore enables anamplification of those parts of the fluid sample that did not form parts of the aliquots within themicrofluidic chambers. The invention is based on the finding that a rather large amount of thefluid sample remains unused during the treatment of the microfluidic device. Often, parts of thefluid sample can even not be extracted out of the microfluidic device in view of the microscopicdimensions of the respective microfluidic circuit. The microfluidic device according to the firstaspect of the invention solves this problem by providing the storage section and a relatedstorage opening structure for the fluid that does not belong to the aliquots within themicrochambers.By providing the storage section, the stored fluid in the storage section might also be activatedlike the aliquots within the microchambers. Thus, further analysis after a thermal treatmentmight be possible with the stored fluid. This is particularly advantageous in view of the difficultaccess to the aliquots after the applied thermal treatment. These aliquots are withinmicrostructures on a micrometer scale and therefore hard to remove from the microfluidicdevice in a controlled way. Thus, the provided storage section allows a further analysis ofactivated stored fluid with an easy access to the stored fluid via the provided storage openingstructure.The access to activated stored fluid is particularly advantageous in view of the small volumeof fluid that is typically stored in a respective microchamber. Such small volumes of preferablyless than 100 nanoliters typically do not allow a controlled fluid extraction out of amicrochamber. The storage section according to the first aspect of the invention thus enablesthe access, especially the controlled access, to activated fluid. Against this background, it canbe preferred if the volume of the microfluidic storage circuit is larger than the volume of at leastone of the microchambers, and even more preferred if the volume of the microfluidic storagecircuit is larger than the volume of each of the microchambers.Furthermore, the storage section allows a precise control over the amount of stored fluid thatis extracted after the thermal treatment. A scale, a respective stopping valve or otherarrangements that are obvious for a skilled person within the field of microfluid dynamics mightbe provided in order to enable the extraction of a predefined amount of activated stored fluidafter the thermal treatment via the storage opening structure. Alternatively or additionally, sucharrangements might restrict the amount of sample fluid that is allowed to flow into the storagesection.The storage section can be provided such that fluid that does not reach the microchambersduring the filling process and can therefore not be provided at the intended reaction space canbe stored in the storage section. In this way, it is possible to take advantage of the fact thatduring the filling process, excess fluid usually remains upstream of the microchambers sinceall microchambers are aimed to be filled with the fluid sample. Typically, the division of the fluidsample will not be precise enough to avoid remaining fluid outside the microchambers. For thesame reason, there is usually also excess fluid that passes the microchambers during the fillingprocess. To take advantage of this, the storage section can alternatively or additionally beprovided such that fluid that flows beyond the microchambers during the filling process andcan therefore not be provided at the intended reaction space can be stored in the storagesection. This can be particularly preferred since the amount of excess fluid passing themicrochambers can be particularly difficult to control.The microfluidic device according to this first aspect of the invention is simple to build, sinceonly the storage section has to be added to already available microdevices with a plurality ofmicrochambers.A further advantage is the variability of the provided solution. Different microfluidic circuits canbe improved by providing the storage section, for example at the downstream end of therespective microfluidic well.According to the invention, the microchambers of the microfluidic circuit are coupled to othermicrochambers via a respective microfluidic channel. In one embodiment there is only onemicrofluidic channel that connects all microchambers of the respective microfluidic circuit witheach other. In preferred embodiments, there are several microfluidic channels that formparallel flow paths from the inlet end to the outlet end and thereby connect a respective numberof microchambers. In that sense, the respective microfluidic channel also comprises channelsegments between microchambers.The microfluidic storage circuit is fluidly coupled with the microfluidic circuit. Thereby, the fluidthat passes the storage section can preferably flow directly into the microchambers and / or thefluid that passes the microchambers can preferably flow directly into the storage section.Irrespective of this, the microfluidic storage circuit can be fluidly coupled with the outlet endsuch that fluid can flow, preferably directly, from the microfluidic storage circuit into the outletend. Thus, if too much fluid reaches the storage section, the amount of fluid that is too muchcan simply flow into the outlet end.The storage opening structure is preferably arranged at an end, downstream end or upstreamend, of the microfluidic storage circuit. At such a location the whole amount of fluid stored inthe storage section can be extracted at once.The microfluidic storage circuit can consist of a single channel, preferably a single microfluidicchannel.In the following, embodiments of the microfluidic device according to the first aspect of theinvention will be described.In a preferred embodiment of the microfluidic device according to the first aspect of theinvention, the storage section is arranged between the inlet end and the microfluidic circuit. Inthis way, fluid not reaching the microchambers during the filling process can be easily storedin the storage section. Then the inlet end is in particular fluidly coupled to the microfluidic circuitvia the microfluidic storage circuit. In addition, the storage section can be arrangedgeometrically between the inlet end and the microfluidic circuit. With respect to an easy storageof fluid flowing beyond the microchambers during the filling process, it can alternatively oradditionally be preferred if the storage section is arranged between the microfluidic circuit andthe outlet end. Then, the microfluidic circuit is in particular fluidly coupled to the outlet end viathe microfluidic storage circuit. The position of the microfluidic storage circuit downstream,preferably right before, the outlet end allows storage of all the fluid that has passed themicrochambers of a certain microfluidic channel during the filling process. Irrespective of this,the storage section can additionally be arranged geometrically between the microfluidic circuitand the outlet end.Irrespective of the arrangement of the storage section, it can be preferred if the storageopening structure is provided between the microfluidic circuit and the microfluidic storagecircuit. Such a position of the storage opening structure ensures the presence of fluid at thestorage opening structure. While it is hard to predict, how much of the volume of the microfluidicstorage circuit is filled with fluid, it is clear that fluid is present at least between the microfluidiccircuit and the microfluidic storage circuit.In a further embodiment, the storage opening structure is configured to stay closed during thefilling process of the plurality of microchambers and to allow a retrieval of a storage sample ofthe stored fluid by an external device which pierces the storage opening structure. The storageopening structure of this embodiment avoids a contamination of the fluid sample prior to theretrieval of the storage sample. Using an external device, such as a syringe or the like, topierce the storage opening structure is a secure way to avoid any contamination of the storagesample during the retrieval. Furthermore, after the storage sample is in the syringe, it can beeasily used for further steps of analysis.In a preferred variant of the aforementioned embodiment, the microfluidic device comprises acover layer that is arranged to hold the storage opening structure closed during the fillingprocess. Such a cover layer is particularly suitable for avoiding a contamination of the fluid. Ina preferred example of this embodiment, the cover layer also holds the inlet end and the outletend of the microfluidic device closed during the filling process, after the fluid sample has beeninserted into the inlet end. Irrespective of this, the cover layer can be an adhesive cover layer.An adhesive cover layer allows easy and at the same time reliable closure of the storageopening structure. Alternatively or additionally, the cover layer can be a film, preferably a plasticfilm. This can be simple and functional.In a preferred embodiment, the microfluidic storage circuit comprises a meander-like structure.Such a meander-like structure can lead to small dimensions of the storage section, comparedto an elongated structure of the microfluidic storage circuit. In addition, a meander-likestructure, in particular ribs between adjacent sections of the meander-like structure, canprovide good support for a layer resting on the storage section, for example the cover layerand / or a sealing layer. In a preferred variant of this embodiment, the microfluidic storage circuitconsists of a single channel, especially a single microfluidic channel. This can lead to a robuststructure that is easy to manufacture.The meander-like structure has preferably a spiralled configuration. In a preferred variant, thespiralled configuration comprises a plurality of circuit sections wherein these circuit sectionsrespectively comprise a linear channel and the circuit sections of the storage circuit arearranged such that the linear channels are at least partially parallel to each other. Preferably,the linear circuit sections of said spiralled configuration are at least partially identical to eachother. In a related variant of this embodiment, the circuit sections show essentially identicalgeometric measurements. Preferably, two successive circuit sections of the spiralledconfiguration are connected to each other via a respective turning point that redirectsrespective fluid from a first linear channel of a first circuit section to a second linear channel ofa second circuit section. Preferably, the storage circuit comprises between 3 and 12 turningpoints, especially between 5 and 10 turning points, in particular at least 6 turning points. In apreferred variant, adjacent circuit sections show a similar length of the respective linearchannel. In a preferred variant, all linear channels of the microfluidic storage circuit have asimilar length.As an alternative or in addition to the meander-like structure, the microfluidic storage circuitcan comprise a receiving space for the fluid to be stored. Then, a plurality of spacers, forexample at least 5, 10, 15 or 20, can be arranged in the receiving space. Such a structure canfor example be preferred if, in addition to thermal cycling, a continuous imaging of afluorescence signal (RT-PCR) is to be performed. The spacers can then support a layer restingon the storage section, for example the cover layer and / or the sealing layer. In this way, it ispossible to easily and reliably keep the layer out of the receiving space. Irrespective of this,the spacers can be simply and expediently designed as pillars. Alternatively or additionally, thereceiving space can for example be defined by a basin-like structure of the storage section.In a preferred embodiment, a depth of the microfluidic storage circuit is essentially equal to adepth of the microchambers. Similar depths of microfluid storage circuit and microchambersof the respective microfluidic well ensure a similar thermal treatment during the activation ofthe sample fluid.In a preferred embodiment, the cross section of the microfluidic storage circuit is essentiallyequal to the cross section of the at least one microfluidic channel. Similar cross sections enablea reduced fluidic resistance compared to different cross sections.In a preferred embodiment, the microfluidic storage circuit is configured to store at least 5 µL,preferably at least 10~\mu L of the fluid sample. This amount of fluid sample is usually enough fora future processing, e.g. sequencing, of unusual and / or particularly interesting stored fluid.Therefore, the microfluidic storage circuit of this embodiment is very advantageous for the useof the microfluidic device for a polymerase chain reaction analysis, such as a digitalpolymerase chain reaction analysis, since it allows a further sequencing if enough sample fluidhas been inside the microfluidic storage circuit.With respect to a sufficiently large amount of fluid sample for a future sequencing, it canalternatively or additionally be preferred if the volume of the microfluidic storage circuit is atleast 50 times the volume of at least one of the microchambers. For the same reason it can beeven more preferred if the volume of the microfluidic storage circuit is at least 200 times,preferably at least 500 times, the volume of at least one of the microchambers. Alternatively oradditionally, it can also be particularly preferred in this context if the volume of the microfluidicstorage circuit is larger than the volume of each of the microchambers by a respective factor.In an embodiment of the microfluidic device according to the first aspect of the invention, theat least one microfluidic channel comprises at least one fluidic delay structure, which isconfigured to delay a fluid flow, in particular in the direction of the microfluidic storage section.The fluidic delay structure of this embodiment allows a control of the filling of the storagesection with fluid. In a variant of this embodiment, the at least one fluidic delay structure cancomprise at least one fluidic stop structure, which is configured to inhibit a fluid flow until apredefined fluid pressure is reached. A fluidic stop structure allows particularly good control ofthe filling of the storage section. Only after reaching the predefined fluid pressure, the fluid canpass the fluidic stop structure and reach those parts of the microfluidic circuit and / or of themicrofluidic storage circuit that are behind the stop structure in a downstream direction.Possible designs of such stop structures are well-known in the art. Typically, the hydrodynamiccharacteristics of such a stop structure are based on capillary forces that act due to differentcross sections, on hydrophobic characteristics of a chosen material and / or surface, and / or ona turbulent flow guidance that decelerates a fluid flow.In a further variant of the aforementioned embodiment, the at least one fluidic delay structurecomprises alternatively or additionally to the at least one fluidic stop structure at least one delaychannel section which is, preferably at least 1.5 times, in particular at least 2 times, particularlypreferably at least 3 times, longer than the geometrical distance between a fluid inlet and afluid outlet of the delay channel section. Then, the fluid preferably has to cover a relatively longdistance to get through the fluidic delay structure compared to the extent of the delay structure.In this way, with a compact design of the delay structure, a significant pressure loss can becreated in the fluid so that the fluid flow is slowed down considerably. This allows a precisecontrol of the fluid. The at least one delay channel section can for example have a meander-like form. A meander-like form can be particularly preferred with regard to compactness and alarge pressure drop, and is also simple to manufacture.In a further variant of the aforementioned embodiment, at least one further delay structure isprovided within the microfluidic circuit. Thereby, the fluidic delay structure might enable ahomogenous filling of the microchambers. Delay structures can lead to a filling that preventsgas from the microchambers to be trapped in the circuit. A trapping of gas might occur, if amicrofluidic channel is completely filled with fluid that flows into the storing section while afurther microfluidic channel is not completely filled so that gas that cannot vent through thefilled storing section is trapped within this channel. Therefore, in the present embodiment, atrapping of gas might be avoided.In a preferred variant of the aforementioned embodiment, the at least one fluidic delaystructure, in particular the at least one fluidic stop structure, is arranged between the pluralityof microchambers and the microfluidic storage circuit. This allows particularly good control ofthe filling of the storage section with fluid. In the case of the at least one fluidic stop structure,preferably, the storage section is not filled with fluid and the sample fluid rests in the microfluidiccircuit, as long as the predefined fluid pressure is not reached. But after reaching the fluidpressure during the filling process, the fluidic stop structure opens for the fluid and, preferably,the storage section gets filled with fluid that has passed the microfluidic circuit.In a further embodiment of the microfluidic device, a cross section of the microfluidic storagecircuit is larger than a cross section of the at least one microfluidic channel such that capillaryforces do not cause a flow of fluid into the storage section. In this embodiment, the physicalstructure of the respective circuit can ensure that fluid is not brought into the storage sectionby capillary forces without any applied pressure. Thereby, it can be ensured that fluid is notaccidentally within the storage section. It can be furthermore ensured that fluid is not pressedout of a microchamber by capillary forces of the storage section.In a preferred embodiment, the microfluidic device comprises a sealing layer that covers themicrofluidic circuit at least partially, preferably at least substantially. This can help to avoid acontamination of the fluid sample in the microfluidic circuit. For simplicity, the sealing layer andthe cover layer can be the same layer. However, this does not necessarily have to be the case.Irrespective of this, the sealing layer can be a film, preferably a plastic film. This can be simpleand functional. For the same reason, the sealing layer can alternatively or additionally be anadhesive sealing layer. Regardless of whether the sealing layer is adhesive or not, the sealinglayer can be configured to fluidly separate the microchambers from each other. A sealing layerallows easy and reliable fluidic separation of the microchambers and thus of the aliquotscontained therein. This applies even more if the sealing layer is configured to fluidly separatethe microchambers by deformation, for example elastic deformation and / or plastic deformation,into channel segments of the at least one microfluidic channel that fluidly couple themicrochambers. Then, the sealing layer can seal the channel segments and can thus causefluidic separation of the microchambers. A deformation of the sealing layer into the channelsegments can be achieved, for example, by heating the sealing layer. However, fluidicseparation of the microchambers can be achieved particularly easily and reliably if the sealinglayer is configured to deform into the channel segments upon application of a compressiveforce to the sealing layer. As a result of the applied compressive force, the sealing layer canthen be pressed into the channel segments. The compressive force can for example be appliedby means of a roll and / or a clamping plate.In principle, it is conceivable that the microchambers have the same depth and width aschannel segments of the at least one microfluidic channel fluidly coupling the microchambers.In this case, the microfluidic device can comprise a forming layer, for example a forming plate,having one or more protrusions configured to press the sealing layer into the channel segmentswhen the forming layer is pressed against the sealing layer. However, for the sake of simplicity,it is preferred if the microchambers have a greater depth and, preferably, a greater width thanchannel segments of the at least one microfluidic channel that fluidly couple themicrochambers. Then, the microfluidic device does not have to comprise a respective forminglayer, although this should not be excluded in principle.The inlet end can be fluidly coupled to the microchambers, via a, in particular common, fillingchannel. The filling channel can for example be part of the at least one microfluidic channel.However, this does not have to be the case. Irrespective of this, it can be preferred for technicalreasons if the filling channel has at least substantially the same depth as one or more,preferably at least substantially all, of the microchambers. This can contribute to a simplemanufacture of the microfluidic device. As an alternative or in addition, the filling channel canhave a depth of at least 20 µm, preferably at least 40 µm, in particular at least 50 µm. This canbe useful for good and reliable filling of the at least one microfluidic channel and thus of themicrochambers. With respect to an economic use of the fluid sample and a flat design of themicrofluidic device, it can alternatively or additionally be preferred if the filling channel has adepth of at most 800 µm, preferably at most 600 µm, particularly at most 500 µm. Irrespectiveof its depth, the filling channel can have a width of at least 50 µm, preferably at least 75 µm, inparticular at least 100 µm. This can also be useful for good and reliable filling of themicrochambers. Alternatively or additionally, the filling channel can have a width of at most300 µm, preferably at most 250 µm, in particular at most 200 µm. This can not only beadvantageous with respect to an economic use of the fluid sample but can also ensure thatthe fluorescence signal of the fluid cycled in the filling channel does not outshine the signal ofthe fluid in the microchambers and thus contribute to a reliable analysis.The microchambers can have a depth of at least 20 µm, preferably at least 40 µm, in particularat least 50 µm. This helps to ensure that the microchambers can accommodate a sufficientvolume of the fluid sample. As an alternative or in addition, the microchambers can have adepth of at most 800 µm, preferably at most 600 µm, particularly at most 500 µm. This cancontribute to a compact design of the microfluidic device and an economic use of the fluidsample. For the same reasons, the microchambers can alternatively or additionally have awidth of at least 25 µm, preferably at least 40 µm, in particular at least 50 µm, and / or of at most130 µm, preferably at most 105 µm, particularly at most 85 µm. The depth and the volume ofthe microchambers depend in particular on the purpose of the analysis to be performed withthe microfluidic device. Depending on the type of application, many small microchambers or afew large microchambers or a combination thereof can be expedient.The at least one microfluidic channel can have a depth of at least 5 µm, preferably at least 10µm, in particular at least 15 µm. This can not only be useful with respect to a reliable filling ofthe microchambers but also with respect to the fluidic separation of the microchambers. Thisis because if the sealing layer is deformed into the microfluidic channel by applying acompressive force to the sealing layer, a channel depth that is too small leads to excessivevariations in back pressure as the production tolerance of the microfluidic channel is typicallyat least + / - 2 µm. As an alternative or in addition, the at least one microfluidic channel can havea depth of at most 80 µm, preferably at most 60 µm, in particular at most 50 µm. This allowsthe microfluidic channel to be reliably sealed in a simple manner. Irrespective of its depth, theat least one microfluidic channel can have a width of at least 5 µm, preferably at least 10 µm,and / or of at most 120 µm, preferably at most 100 µm, particularly at most 80 µm. In this way,a good filling behavior can be ensured for different kinds of fluids. Irrespective of this, the atleast one microfluidic channel can have the respective depth and / or width preferably at leastin channel segments fluidly coupling the microchambers.The microchambers can be fluidly coupled to the microfluidic storage circuit via a, in particularcommon, collecting channel. The collecting channel can for example be part of the at least onemicrofluidic channel. However, this does not have to be the case. Irrespective of this, thecollecting channel can have a depth of at least 55 µm, preferably at least 85 µm, in particularat least 110 µm. This can be useful to provide a sufficient collection volume. As an alternativeor in addition, the collecting channel can have a depth of at most 330 µm, preferably at most275 µm, in particular at most 220 µm. This can contribute to a flat design of the microfluidicdevice. Irrespective of its depth, it can be preferred with respect to a sufficient collection volumeif the collecting channel has a width of at least 50 µm, preferably at least 75 µm, in particularat least 100 µm. Alternatively or additionally, the collecting channel can have a width of at most300 µm, preferably at most 250 µm, particularly at most 200 µm.For technical reasons, it can be preferred if the microfluidic storage circuit has at leastsubstantially the same depth as one or more, preferably at least substantially all, of themicrochambers. This can contribute to a simple manufacture of the microfluidic device.Irrespective of this, the microfluidic storage circuit can have a depth of at least 20 µm,preferably at least 40 µm, in particular at least 50 µm. This allows the storage circuit to store asufficient amount of the fluid sample. Alternatively or additionally, the microfluidic storagecircuit can have a depth of at most 800 µm, preferably at most 600~\mu m, in particular at most500 µm. This can contribute to a flat design of the microfluidic device. Irrespective of its depth,a width of the cross section of the microfluidic storage circuit, in particular of the meander-likestructure, can be at least 35 µm, preferably at least 55 µm, in particular at least 65 µm. Thiscan also help to provide a sufficient storage volume. As an alternative or in addition, a width ofthe cross section of the microfluidic storage circuit, in particular of the meander-like structure,can be at most 300 µm, preferably at most 250 µm, in particular at most 200 µm. This can notonly help to provide good support for a layer, for example the cover layer, resting on the storagesection, but can also ensure that the fluorescence signal of the fluid cycled in the microfluidicstorage circuit does not outshine the signal of the fluid in the microchambers and thuscontribute to a reliable analysis.According to a second aspect of the invention, a system for providing a molecular analysis ofa fluid sample, in particular for providing a digital polymerase chain reaction analysis, isprovided. The system comprisingthe microfluidic device of at least one of the aforementioned embodiments,an analysis apparatus configured to receive the microfluidic device and to amplify the pluralityof aliquots within the plurality of microchambers by providing a predefined thermal treatment,andwherein the microfluidic storage circuit is arranged such that the fluid stored in the storagesection is also amplified by the analysis apparatus.The system according to the second aspect of the invention comprises the microfluidic deviceaccording to the first aspect and therefore all mentioned advantages of the first aspect of theinvention.The position of the storage section and of the microchambers at the microfluidic device ispreferable a position at a surface of the microfluidic device so that the amplification of thestored fluid and of the aliquots is similar to each other. Details concerning the amplificationprocess are well known in the art and therefore not described in the following.The analysis apparatus can be configured to, preferably optically, analyze the fluid stored inthe storage section during the amplification. In this way, the result of the molecular analysiscan be further improved.In the following, embodiments of the system according to the second aspect of the inventionwill be described.In a preferred embodiment, the analysis apparatus is further configured to provide thepredefined fluid pressure to a fluid within the microfluidic device in order to enable a flow of therespective fluid through the microfluidic circuit and at least partly through the microfluidicstorage circuit. In order to provide the fluid pressure, the analysis apparatus comprises in avariant of this embodiment a number of pistons that are arranged to be pressed inside the inletend after it has been filled with the fluid sample. In an alternative variant, the analysis apparatusprovides a fluid flow, preferably a gas flow, in order to provide the fluid pressure. In thisalternative variant, the fluid flow, preferably the gas flow, is pressed inside the inlet end after ithas been filled with the fluid sample. Preferably, a membrane is provided in order to prevent acontact of surrounding laboratory and / or device with the fluid sample. The membrane ispreferably a semi-permeable membrane covering the inlet end. Then, the gas flow can beapplied to the fluid within the microfluidic device through the membrane. At the same time, themembrane can effectively prevent the release of the fluid and / or of aerosols from themicrofluidic device, in particular during the amplification of the fluid. If a fluidic stop structure isprovided in the microfluidic device, the pressure applied to the fluid within the inlet endpreferably exceeds at least at a certain moment of the filling process the predefined pressurethreshold of the respective fluidic stop structure. In a preferred variant, the analysis apparatusis configured to provide different predefined fluid pressures for different stop structures withinthe microfluidic circuit.In a preferred embodiment, the system further comprises optical means, which are arrangedand configured to enable an analysis of a present filling state of the at least one microfluidicwell. The optical means are furthermore advantageous in order to analyze the result of thereactions within the microchambers. In a preferred embodiment, the analysis apparatus isconfigured to provide different predefined fluid pressures for different stop structures within themicrofluidic circuit.In a further embodiment, the optical means are connected to a control unit of the analysisapparatus and the control unit is configured to control a filling of the microfluidic circuit as afunction of data provided by the optical means. In an advantageous variant of this embodiment,the pressure provided by the analysis apparatus to provide a fluid flow of the sample fluiddepends on the data provided by the optical means.As an alternative or in addition to the optical means for the analysis of the present filling stateof the microfluidic well, the system can comprise optical means for providing a fluorescencesignal. The fluorescence signal can then represent one or more pictures of the plurality ofaliquots and / or of the fluid stored in the storage section, wherein at least one picture can showone or more of the plurality of aliquots and / or the fluid stored in the storage section in afluorescent state. Irrespective of this, the optical means for providing the fluorescence signaland the optical means for enabling the analysis of the present filling state can simply be thesame. However, this does not necessarily have to be the case. Alternatively or additionally,the optical means for providing the fluorescence signal can be connected to a control unit,preferably the control unit mentioned above. The control unit can then be configured to control,for example stop, the amplification of the plurality of aliquots and / or the fluid stored in thestorage section based on the fluorescence signal.According to a third aspect of the invention, a method for providing a molecular analysis of afluid sample, in particular for providing a digital polymerase chain reaction analysis, is provided.The method comprising the stepsproviding an analysis apparatus and a microfluidic device with at least one microfluidic wellconfigured to receive the fluid sample;- providing the fluid sample to the at least one microfluidic well via a respective inlet end of thismicrofluidic well;insertion of the microfluidic device into the analysis apparatus; andfilling a microfluidic circuit of the microfluidic device at least partially, preferably at leastsubstantially, with fluid of the fluid sample, wherein fluid that does not reach and / or flowsbeyond microchambers of the microfluidic well during that filling process is stored in amicrofluidic storage circuit of the microfluidic device.The method of the third aspect of the invention shares the advantages described in the contextof the system according to the second aspect of the invention. In particular, the method allowsa storing of surplus fluid of the fluid sample in the microfluidic storage circuit. The pressure ispreferably applied at a predetermined time of the molecular analysis.The steps of the method according to the third aspect are preferably performed in thepresented order.In the following, embodiments of the method according to the third aspect of the invention willbe described.In a preferred embodiment, a pressure is applied to the fluid sample in order to push the fluidsample into the microfluidic circuit, wherein fluid that does not reach and / or flows beyond themicrochambers during the application of the pressure is stored in the microfluidic storagecircuit. In this way, the microfluidic circuit can be easily and reliably filled with the fluid sample.The pressure can for example be applied to the fluid sample by means of one or more pistons.The at least one piston can then be pushed into the at least one inlet end after the fluid samplehas been filled into the at least one inlet end. In order to prevent a contamination of the fluidsample and a release of the fluid sample from the microfluidic device, the at least one inlet endcan be covered with an elastic layer after the fluid sample has been filled into the at least oneinlet end. Then, the at least one piston can be pushed into the elastic layer, thereby deformingthe elastic layer into the inlet end and applying the pressure to the fluid sample. As analternative to the application of the pressure by means of the at least one piston, the pressurecan also be applied to the fluid sample by means of a, in particular controlled, gas flow. Thegas flow can then be applied to the fluid sample via the at least one inlet end. In order toprevent a contamination of the fluid sample and a release of the fluid sample from themicrofluidic device, the at least one inlet end can then be covered with a, preferably semi-permeable, membrane after the fluid sample has been filled into the at least one inlet end.Then, the gas flow can be applied to the fluid sample through the membrane. Irrespective ofthis, for the sake of simplicity, the gas of the gas flow can be air.As an alternative or in addition to the application of a pressure to the fluid sample, themicrofluidic circuit and / or the microfluidic storage circuit can be filled with the fluid sample atleast partially, for example at least substantially, due to capillary forces. Then, an applicationof pressure to the fluid sample can be dispensed with. This can be advantageous with respectto the technical effort, will, however, typically be less reliable than a filling by means of anapplication of a pressure to the fluid sample.In a further preferred embodiment, the method comprises the step of fluidly separating themicrochambers from each other, in particular after the microchambers have been at leastpartially filled with the fluid sample. This prevents the exchange of fluid between themicrochambers. In principle, the application of the pressure on the fluid sample can be stoppedbefore the microchambers are fluidly separated from each other. However, with respect to acontrolled filling of the microchambers with the fluid sample, it can be useful to maintain thepressure on the fluid sample at least partially until the microchambers are fluidly separatedfrom each other. Irrespective of this, the fluidic separation of the microchambers can beachieved easily and reliably by deforming a sealing layer into channel segments of at least onemicrofluidic channel that fluidly couple the microchambers. The sealing layer can cover themicrofluidic circuit at least partially, preferably at least substantially. Alternatively oradditionally, it can be particularly preferred with respect to an easy and reliable fluidicseparation of the microchambers if the deformation of the sealing layer into the channelsegments is achieved by applying a compressive force to the sealing layer, preferably in adirection at least partially, in particular at least substantially, perpendicular to the sealing layer.Irrespective of the direction, the compressive force can for example be applied to the sealinglayer by means of a roll and / or a clamping plate.In a further embodiment, the method further comprises the amplification of the fluid within themicrochambers and within the microfluidic storage circuit by applying a thermal treatment tothat fluid, preferably after the fluidic separation of the microchambers. Details of such anamplification depend on the applied analysis and are well-known in the art. In particular, thethermal treatment for the digital polymerase chain reaction analysis is well-known. During theamplification, the fluid within the microfluidic storage circuit can be, preferably optically,analyzed. In this way, the result of the molecular analysis can be further improved.In a further embodiment of the method according to the third aspect of the invention, themethod comprises, preferably as a last step, the retrieval of the fluid stored in the microfluidicstorage circuit. This additional step allows a further analysis of the retrieved fluid. The retrievalof the fluid stored in the microfluidic storage circuit is preferably performed after theamplification of the fluid within the microchambers and within the microfluidic storage circuit.Irrespective of this, the fluid stored in the microfluidic storage circuit can be easily andexpediently retrieved through a storage opening structure of the microfluidic device. For thesame reason, it can be even more preferred if the fluid stored in the microfluidic storage circuitis retrieved by means of a syringe through the storage opening structure.Preferably, a plurality of storage sections for a respective plurality of microfluidic wells isprovided by the microfluidic device and a further step of the method comprises a selection ofthe storage sections whose stored fluid appears to be interesting for a further analysis afterthe amplification. This selection is preferable based on results of an analysis provided by theanalysis apparatus after the amplification and / or during the amplification of the fluid.It shall be understood that the microfluidic device of the first aspect of the invention, the systemfor providing a molecular analysis of a fluid sample of the second aspect of the invention, andthe method for providing a molecular analysis of a fluid sample of the third aspect of theinvention have similar or identical embodiments.These and other aspects of the invention will be apparent from and elucidated with referenceto the embodiments described hereinafter.BRIEF DESCRIPTION OF THE DRAWINGSIn the following drawings:Fig. 1 shows a first embodiment of a microfluidic device according to a first aspect ofthe invention;Fig. 2 shows a second embodiment of the microfluidic device according to the firstaspect of the invention;Fig. 3 shows a cross-section of an embodiment of storage opening structure of themicrofluidic device according to the first aspect of the invention;Figs. 4A-D show details of the first embodiment of the microfluidic device shown inFig. 1;Fig. 5 shows an embodiment of a system according to a second aspect of the invention;Fig. 6 shows a flow diagram of an embodiment of a method according to a third aspectof the invention;Fig. 7 shows a third embodiment of the microfluidic device according to the first aspectof the invention.DETAILED DESCRIPTION OF EMBODIMENTSFig. 1 shows an embodiment of a microfluidic device 100 according to a first aspect of theinvention. The microfluidic device 100 is configured to receive a fluid sample and to divide itinto a plurality of aliquots. One microfluidic well 105 of the microfluidic device 100 is shown inFig. 1. In a preferred variant of this embodiment, the microfluidic device 100 comprises at leastone further microfluidic well.The microfluidic well 105 comprises a microfluidic circuit 110 with a plurality of microchambers112, which provide a respective reaction space for an aliquot of the plurality of aliquots. Themicrofluidic well 105 further comprises an inlet end 120 coupled to the microfluidic circuit 110via at least one microfluidic channel 130, 130', 130'', 130''' and an outlet end 125 coupled tothe microfluidic circuit 110 via the at least one microfluidic channel 130, 130' 130'', 130'''The plurality of microchambers 112 is arranged such that each microchamber 112 is at leastindirectly via further microchambers 112 fluidly coupled with the inlet end 120 and with theoutlet end 125. In the present embodiment, four microfluidic channels 130, 130', 130'', 130'''are arranged parallel to each other and each connect five microchambers 112 in a row. Theconnections between two respective microchambers 112 are formed by the respectivemicrofluidic channel 130, 130', 130'', 130'''. As a consequence of this microfluidic structureeach microchamber 112 is configured to receive fluid from the inlet end 120 via the at leastone microfluidic channel 130, 130', 130'', 130''' and to provide gas displaced by the fluiddownstream to the outlet end 125. Possible structures of such microchambers 112 are knownin the art and are therefore not described in detail in the following. As a non-limiting example,US 2021 / 0379593 A1 describes an embodiment of such microchambers.In the shown embodiment, the microfluidic well 105 comprises a filling channel 132 and acollecting channel 134. Via the filling channel 132, the inlet end 120 is fluidly coupled to themicrofluidic channels 130, 130', 130'', 130'''. And via the collecting channel 134, themicrofluidic channels 130, 130', 130'', 130''' are fluidly coupled to the outlet end 125.The microfluidic device 100 according to the first aspect of the invention further comprises astorage section 140 with a microfluidic storage circuit 142 that is arranged between themicrofluidic circuit 110 and the outlet end 125 in order to store fluid that flows beyond themicrochambers 112 of the microfluidic well 105 during a filling process of the microfluidicdevice 100. The stored fluid can therefore not be provided at the intended reaction space. Inthe shown embodiment, every microfluidic well 105 comprises a separate storage section 140.For reasons of clarity just one microfluidic well is depicted in Fig. 1.As an alternative or in addition to the storage section 140 arranged between the microfluidiccircuit 110 and the outlet end 125, the microfluidic device 100 could comprise a storage sectionwith a microfluidic storage circuit that is arranged between the inlet end 120 and the microfluidiccircuit 110 in order to store fluid that does not reach the microchambers 112 during the fillingprocess of the microfluidic device 100 and can therefore not be provided at the intendedreaction space. The microfluidic storage circuit of this storage section could for example bedesigned as a large distribution channel.The microfluidic well 105 shown in Fig. 1 is just one of at least four microfluidic wells of themicrofluidic device 100. In a preferred embodiment, the microfluidic device comprises at least10 microfluidic wells, preferably at least 20 microfluidic wells. In a further preferredembodiment, each microfluidic well of the microfluidic device comprises at least 50microchambers, in particular at least 200 microchambers. The different microfluidic wells donot share a fluidic connection. Therefore, each inlet end 120 has to be filled with the fluidsample separately and provides a respective storage section 140. In a not shown embodiment,there is at least one microfluidic well that does not provide a respective storage section.Providing certain microfluidic wells without the storage section might be necessary due tostructural reasons and / or to simplify a manufacturing of the microfluidic device.In the embodiment shown in Fig. 1, a storage opening structure 144 is provided in the storagesection 140 to allow a retrieval of the stored fluid. The storage opening structure 144 ispreferably closed by a layer, a cap or the like. A possible structure of this storage openingstructure 144 is shown in Fig. 3. The providing of the storage section allows an easy accessto amplified fluid that is free from contamination. Thereby, a further analysis, especially aspecific analysis, of certain parts of the fluid sample is enabled.In a not shown embodiment, every microfluidic channel of the microfluidic circuit is fluidlyconnected to a separate storage section with a separate microfluidic storage circuit. Suchseparate storage section might be connected to separate outlet ends or to a combined outletend of the respective microfluidic well.The microfluidic storage circuit 142 of the shown embodiment has a larger cross section thanthe microfluidic channels 130, 130', 130'', 130''', respectively. Thereby, capillary forces thatmight press fluid at least partly into the microfluidic channels 130, 130', 130'', 130''', forexample during an unintended pre-wetting of the microfluid well 105, cannot cause a flow offluid into the storage section 140.The microfluidic device 100 according to the first aspect of the invention is particularlyadvantageous for handling a fluid sample within the scope of a polymerase chain reactionanalysis, especially within the scope of a digital polymerase chain reaction (dPCR) analysis.This is the case since a large number of aliquots has to be applied to a thermal treatment fora reasonable interpretation of the final analysis. The provided microfluidic device 100 allows afurther analysis, such as for example a sequencing of stored fluid. If the fluid of a certainmicrofluidic well 105 appears to be of special interest, the stored fluid of the respective storagesection 140 can be retrieved to provide further analysis.Fig. 2 shows a second embodiment of the microfluidic device 200 according to the first aspectof the invention.The microfluidic device 200 differs from the microfluidic device 100 shown in Fig. 1 in view ofthe structure of the storage section 240. The microfluidic storage circuit 242 comprises ameander-like structure. Such a structure allows a large volume of stored fluid allocated at alittle space of the microfluidic device 200 while a small cross section of the microfluidic storagecircuit 242 avoids gas bubbles or the like during the retrieval of stored fluid. In a not shownembodiment, such a meander-like structure can also have channels with a larger cross sectionthan the microfluidic channels of the microfluidic circuit in order to avoid an unintended flow offluid into the storage section due to capillary forces.The meander-like structure of the embodiment shown in Fig. 2 has a spiralled configuration.The spiralled configuration comprises a plurality of circuit sections wherein these circuitsections respectively comprise a linear channel and the circuit sections of the storage circuit242 are arranged such that the linear channels are at least partially parallel to each other. Twosuccessive circuit sections of the spiralled configuration are connected to each other via arespective turning point that redirects respective fluid from a first linear channel of a first circuitsection to a second linear channel of a second circuit section. The depicted storage circuit 242comprises 7 turning points. All linear channels between respective turning points show a similarlength in the depicted embodiment. In a not shown embodiment, the meander-like structurehas another number of turning points, preferably between 3 and 12 turning points, especiallybetween 5 and 10 turning points, in particular at least 6 turning points. It is obvious for a personskilled in the art that other structures of the storage section, such as a circular structure, a loop-shaped structure, a coiled structure, an angular structure or the like, can also be used for amicrofluidic device according to the first aspect of the invention. In that sense, the depictedstorage sections form non-limiting examples of the storage section according to the first aspectof the invention.In the depicted embodiment, a depth of the microfluidic storage circuit 242 is essentially equalto a depth of the microchambers 112. Similar depths of microfluid storage circuit 242 andmicrochambers 112 of the respective microfluidic well ensure a similar thermal treatmentduring the activation of the sample fluid.The microfluidic storage circuit 242 is configured to store at least 5 µL, preferably at least 10µL of the fluid sample. This amount of stored fluid is usually enough for further analysispurposes. For example, this amount of stored fluid usually allows a further sequencinganalysis.Furthermore, the microfluidic channels 130, 130' 130'', 130''' of the microfluidic circuit 110comprise at least one fluidic delay structure 250 that is in the depicted embodiment a fluidicstop structure 250, which is configured to inhibit a fluid flow until a predefined fluid pressure isreached. In the shown embodiment, the respective fluidic stop structure 250 is arrangedbetween the plurality of microchambers 112 and the microfluidic storage circuit 242. The fluidicstop structure 250 allows at the provided position a control of the flow of fluid into the storagesection 240. Only after the predefined fluid pressure is reached, the fluid can flow into themicrofluidic storage circuit 242. Thereby, an unintended filling of the storage section 240 isavoided. In a not shown embodiment, further fluidic delay structures, preferably fluidic stopstructures, are arranged within the microfluidic circuit 110 and / or in the microfluidic storagecircuit 242. Further fluidic delay structures, in particular fluidic stop structures, mayadvantageously allow a detailed control of a filling process for the microfluidic device. Thereby,an unintended filling of areas of the circuit and / or a trapping of gas might be avoided. Possibledesigns for fluidic stop structures are well known in the art and therefore not described in thefollowing. In general, stop structures provide a flow resistance due to capillary forces and / ordue to flow turbulences.Fig. 3 shows a cross-section of an embodiment of a storage opening structure 344 of themicrofluidic device according to the first aspect of the invention.The storage opening structure 344 is configured to stay closed during the filling process of theplurality of microchambers and to allow a retrieval of a storage sample of the stored fluid 360by an external device 370 which pierces the storage opening structure 344. The externaldevice 370 is in the depicted embodiment a syringe.In the shown embodiment, the storage opening structure 344 stays closed due to a cover layer365 arranged at the storage opening structure 344. In the shown embodiment, the cover layer365 itself has multiple layers. The cover layer 365 comprises a glue layer 366 configured toattach the cover layer 365 at the microfluidic storage circuit 342. Furthermore, the cover layer365 comprises a carrier layer 367 which carries in this embodiment the pressure sensitiveadhesive (PSA). Using a PSA carrier allows the simply piercing of the carrier with the externaldevice 370, in particular with the syringe.Preferably, the cover layer 365 is arranged to hold the storage opening structure 344 closedduring the filling process. Thereby, a contamination of the stored fluid can be reliably avoided.Figs. 4A-D show details of the microfluidic device 100 shown in Fig. 1 in a sectional view alonga section plane along the microfluidic channel 130 in the region of two of the microchambers112 (Figs. 4A, 4C) and in a sectional view along a section perpendicular to the microfluidicchannel 130 in a region between the two microchambers 112 (Figs. 4B, 4D). As far as shownin Figs. 4A-D, the microfluidic device 200 shown in Fig. 2 can have at least substantially thesame structure.The microfluidic device 100 comprises an adhesive sealing layer 480, for example in the formof an adhesive plastic film, that is glued to the microfluidic well 105 and covers themicrochambers 112. In the depicted embodiment, the sealing layer 480 and the cover layer365 (cf. Fig. 3) are arranged on opposite sides of the microfluidic device 100 and are differentlayers. However, in an alternative embodiment, the sealing layer 480 and the cover layer 365could be arranged on the same side of the microfluidic device 100 and could be the samelayer.In Figs. 4A, 4B, the sealing layer 480 is arranged at least substantially outside the microfluidicchannel 130, thus allowing fluid flow through the microfluidic channel 130. In this way, fluid ofthe fluid sample can flow from one microchamber 112 to another microchamber 112 via themicrofluidic channel 130 during a filling process of the microfluidic device 100. In order to fluidlyseparate the microchambers 112 from each other after the microchambers 112 have been atleast partially filled with the fluid sample, a compressive force F can be applied to the sealinglayer 480 in the direction of the microfluidic well 105.In Figs. 4C, 4D, a compressive force F has been applied to the sealing layer 480 in a directionat least substantially perpendicular to the sealing layer 480, for example by means of a rolland / or a clamping plate. As a result of the application of the compressive force F, the sealinglayer 480 is deformed into channel segments of the microfluidic channel 130 that fluidly couplethe microchambers 112 such that the channel segments are sealed by the sealing layer 480.In this way, the microchambers 112 are fluidly separated from each other. The sealing layer480 is also deformed into the microchambers 112. However, due to the greater depth of themicrochambers 112 compared to the depth of the channel segments of the microfluidic channel130, a volume for the fluid sample remains in each microchamber 112.Fig. 5 shows an embodiment of a system 500 according to a second aspect of the invention.The system 500 is arranged and configured for providing a molecular analysis of a fluid sample,in particular for providing a digital polymerase chain reaction analysis. The system 500comprises the microfluidic device 100 according to at least one of the preceding embodimentsand an analysis apparatus 590.As an example, the microfluidic device 100 comprises eight microfluidic wells 105 as depictedin Fig. 1. The microfluidic device 100 is shown in an inserted state, where it is inserted into theanalysis apparatus 590 by using a holding structure 592 of the analysis apparatus 590.The analysis apparatus 590 is configured to receive the microfluidic device 100 and to amplifythe plurality of aliquots within the plurality of microchambers by providing a predefined thermaltreatment. For that reason, the analysis apparatus 590 comprises a heating unit 594 that iscontrolled by a control unit 595 of the analysis apparatus 590. The microfluidic storage circuitis arranged such that the fluid stored in the storage section is also amplified by the analysisapparatus 590.In a not shown embodiment, the analysis apparatus is configured to receive the microfluidicdevice via the holding structure and to analyze a surface of the microfluidic device with opticalmeans. The optical means are preferably formed by a camera. The optical means can forexample enable an analysis of a present filling state of the microfluidic wells 105. Then, thecontrol unit 595 can control the filling of the microfluidic device 100 based on data provided bythe optical means. Alternatively or additionally, the optical means can provide a fluorescencesignal representing one or more pictures of the plurality of aliquots and / or the fluid stored inthe storage section, wherein in at least one picture at least one of the aliquots and / or the fluidstored in the storage section is in a fluorescent state. Then, the control unit 595 can control,for example stop, the amplification based on the fluorescence signal.Furthermore, the analysis apparatus 590 comprises pressuring means 596 that are formed bya plate with a series of pistons 598, which are arranged to be pressed inside the respectiveinlet end in order to provide a fluid pressure of the inserted sample fluid. Preferably, the appliedfluid pressure enables a flow of fluid through the microfluidic circuit of the microfluidic device100. In the shown embodiment, an elastic layer 599 is provided at the microfluidic device 100in order to prevent a contamination of the sample fluid in the analysis apparatus 590. The layer599 is elastic in order to enable the pistons 598 of the pressuring means 596 to press into theinlet end through the layer 599 without damaging that layer 599. In a preferred variant of thisembodiment, the elastic layer is also adhesive. Thereby a reliable sealing of the inlet end isprovided. In a not shown embodiment, no layer is used in order to seal the inlet end. In suchan embodiment, other precautionary measures might ensure that the fluid sample is notcontaminated.As an alternative or in addition to the plate with the pistons 598, the analysis apparatus 590could also comprise means for providing a gas flow into the respective inlet end in order toapply a pressure to the sample fluid within the microfluidic device 100 and cause a flow of fluidthrough the microfluidic circuit of the microfluidic device 100. Then, instead of the elastic layer599, a semi-permeable membrane could be provided such that the gas flow can be appliedthrough the membrane to the fluid within the microfluidic device 100 and, at the same time, thefluid cannot escape from the microfluidic device 100.The elastic layer 599 is preferably configured to allow a piercing of that layer by an externaldevice, such as a syringe, in order to retrieve sample fluid through the elastic layer 599 andthe storage opening structure. In that way, the elastic layer 599 may form an additional layercompared to the storage opening structure. Alternatively, the elastic layer may form the onlyclosure for the storage opening structure according to the first aspect of the invention.Preferably, the sample fluid is brought into the inlet end of the microfluidic device 100 prior tothe insertion of this microfluidic device 100 into the analysis apparatus 590. After the fluidsample is brought into the respective inlet ends, the elastic layer 599 is brought onto themicrofluidic device 100 in order to seal the inlet end and afterwards the microfluidic device 100is brought into the holding structure 592, formed for example as sliding rails.In order to fluidly separate the microchambers from each other, channel segments of themicrofluidic channel that are arranged between microchambers are closed, before a thermaltreatment or the like starts. The channel segments are closed by applying a compressive forceto the sealing layer as described above with regard to Figs. 4A-D. Further details about theclosing of the microfluidic channel are for example described in US 2021 / 0379593 A1. In orderto provide a reliable structural support against the external pressure it can be advantageousto provide the microfluidic storage circuit with a small width of the respective channels in adirection perpendicular to the external pressure. Thereby the structure of the microfluidicdevice can be particularly robust.After the sample fluid is pressed inside the microchambers, the analysis apparatus 590 isfurther configured to apply a certain predefined analysis of the fluid sample in the differentmicrochambers, in particular to apply a predefined thermal treatment of the sample fluid viathe heating unit 594. The control unit 595 is configured to control the heating unit 594 and thepressuring means 596 meaning that the filling process can be completed before the heatingvia the heating unit 594 starts. In the shown embodiment, the retrieval of sample fluid can bedone manually with an external device after the microfluidic device 100 is removed from theanalysis apparatus 590. In a not shown embodiment, the analysis apparatus is configured toretrieve a fluid sample out of the respective storage opening structure.Fig. 6 shows a flow diagram of an embodiment of a method 600 according to a third aspect ofthe invention.The method 600 is configured for providing a molecular analysis of a fluid sample, in particularfor providing a digital polymerase chain reaction analysis. The method 600 comprising stepsas given in the following.A first step 610 comprises a providing of an analysis apparatus and of a microfluidic devicewith at least one microfluidic well configured to receive the fluid sample.A second step 620 comprises a providing of the fluid sample to the at least one microfluidicwell via a respective inlet end of this microfluidic well.A further step 630 comprises an insertion of the microfluidic device into the analysis apparatus.A last step 640 comprises a filling of a microfluidic circuit of the microfluidic device at leastpartially, preferably at least substantially, with fluid of the fluid sample, wherein fluid that doesnot reach and / or flows beyond microchambers of the microfluidic well during that filling processis stored in a microfluidic storage circuit of the microfluidic device. In order to fill the microfluidiccircuit at least partially with the fluid, preferably a pressure is applied to the fluid sample, forexample by means of at least one piston or a gas flow, thereby pushing the fluid sample intothe microfluidic circuit.The steps 610, 620, 630, 640 of the method 600 according to the third aspect of the inventionare preferably performed in the given order.Usually, after the method 600, the molecular analysis is provided by further steps of theparticular analysis method.In an embodiment, the method comprises a fluidic separation of the microchambers from eachother, preferably by deforming a sealing layer into channel segments of at least one microfluidicchannel fluidly coupling the microchambers, in particular by applying a compressive force tothe sealing layer. This step is preferably provided after the application of the pressure on thefluid sample. Then, it can be further preferred if the pressure on the fluid sample is at leastpartially maintained until the microchambers are fluidly separated from each other.The analysis method preferably comprises an amplification of the fluid within themicrochambers and within the microfluidic storage circuit by applying a thermal treatment tothat fluid. This step is preferably provided after the fluidic separation of the microchambers.In a preferred embodiment, the method comprises an additional step, preferably provided atthe end of the method, namely a retrieval of the fluid stored in the microfluidic storage circuit,preferably through a storage opening structure of the microfluidic device. This retrieved fluidmight also be further analyzed according to a particular analysis method.Fig. 7 shows a third embodiment of the microfluidic device 700 according to the first aspect ofthe invention.The microfluidic device 700 differs from the microfluidic device 100 shown in Fig. 1 in view ofthe structure of the storage section 740. The microfluidic storage circuit 742 comprises areceiving space 701 for the fluid to be stored in the microfluidic storage circuit 742. In thereceiving space 701, a plurality of spacers 703 in the form of cylindrical pillars 703 arearranged. The spacers 703 support the cover layer, which covers in the depicted embodimentthe entire microfluidic storage circuit 742 including the storage opening structure 144, so thatthe cover layer does not hang into the receiving space 701.LIST OF REFERENCE SIGNS100, 200, 700microfluidic device105microfluidic well110microfluidic circuit112microchamber120inlet end125outlet end130, 130', 130", 130"microfluidic channel132filling channel134collecting channel140, 240, 740storage section142, 242, 342, 742microfluidic storage circuit144, 344storage opening structure250fluidic delay structure, fluidic stop structure360stored fluid365cover layer366glue layer367carrier layer370external device480sealing layer500system590analysis apparatus592holding structure594heating unit595control unit596pressuring means598piston599elastic layer600method610, 620, 630, 640steps of the method701receiving space703spacerFcompressive force

Claims

1. A microfluidic device (100,200,700) for handling a fluid sample by dividing it into aplurality of aliquots, with at least one microfluidic well (105) configured to receive thefluid sample, the at least one microfluidic well (105) comprisinga microfluidic circuit (110) with a plurality of microchambers (112), which provide arespective reaction space for an aliquot of the plurality of aliquots,an inlet end (120) coupled to the microfluidic circuit (110) via at least one microfluidicchannel (130,130', 130'',130"),an outlet end (125) coupled to the microfluidic circuit (110) via the at least onemicrofluidic channel (130, 130', 130", 130"),wherein the plurality of microchambers (112) is arranged such that each microchamber(112) is at least indirectly via further microchambers (112) fluidly coupled with the inletend (120) and the outlet end (125) such that each microchamber (112) is configured toreceive fluid from the inlet end (120) via the at least one microfluidic channel(130, 130', 130'', 130") and to provide gas displaced by the fluid downstream to theoutlet end (125),wherein a storage section (140,240,740) with a microfluidic storage circuit(142,242,342,742) is provided in order to store fluid that does not reach and / or flowsbeyond the microchambers (112) of the microfluidic well (105) during a filling processof the microfluidic device (100,200,700) and can therefore not be provided at theintended reaction space, andwherein a storage opening structure (144,344) is provided in the storage section(140,240,740).

2. The microfluidic device (100,200,700) of claim 1, wherein the storage section(140,240,740) is arranged between the inlet end (120) and the microfluidic circuit (110)and / or between the microfluidic circuit (110) and the outlet end (125) and / or whereinthe storage opening structure (144,344) is provided between the microfluidic circuit(110) and the microfluidic storage circuit (142,242,342,742).

3. The microfluidic device (100,200,700) of claim 1 or 2, wherein the storage openingstructure (144,344) is configured to stay closed during the filling process of the pluralityof microchambers (112) and to allow a retrieval of a storage sample of the stored fluid(360) by an external device (370) which pierces the storage opening structure(144,344).

4. The microfluidic device (100,200,700) of claim 3, wherein the microfluidic device(100,200,700) comprises a, preferably adhesive, cover layer (365) that is arranged tohold the storage opening structure (144,344) closed during the filling process.

5. The microfluidic device (200,700) of at least one of the preceding claims, wherein themicrofluidic storage circuit (242) comprises a meander-like structure and / or wherein themicrofluidic storage circuit (242) comprises a receiving space (701) for the fluid to bestored in which a plurality of spacers (703), preferably in the form of pillars (703), arearranged.

6. The microfluidic device (100,200,700) of at least one of the preceding claims, whereinthe microfluidic storage circuit (142,242,342,742) is configured to store at least 5 μL,preferably at least 10 µL of the fluid sample, and / or wherein the volume of themicrofluidic storage circuit (142,242,342,742) is at least 50 times, preferably at least200 times, in particular at least 500 times, the volume of at least one of themicrochambers (112), preferably the volume of each of the microchambers (112).

7. The microfluidic device (200) of at least one of the preceding claims, wherein the atleast one microfluidic channel (130, 130', 130'' 130') comprises at least one fluidic delaystructure (250) configured to delay a fluid flow, and wherein, preferably, the at least onefluidic delay structure (250) comprises at least one fluidic stop structure (250)configured to inhibit a fluid flow until a predefined fluid pressure is reached.

8. The microfluidic device (200) of claim 7, wherein the at least one fluidic delay structure(250), in particular the at least one fluidic stop structure (250), is arranged between theplurality of microchambers (112) and the microfluidic storage circuit (242).

9. The microfluidic device (100,200,700) of at least one of the preceding claims, whereina cross section of the microfluidic storage circuit (142,242,342,742) is larger than across section of the at least one microfluidic channel ( 130', 130'', 130''') such thatcapillary forces do not cause a flow of fluid into the storage section (140,240,740).

10. The microfluidic device (100,200,700) of at least one of the preceding claims, whereinthe microfluidic device (100,200,700) comprises a sealing layer (480) at least partiallycovering the microfluidic circuit (110) and configured to fluidly separate themicrochambers (112) from each other, preferably by deformation into channelsegments of the at least one microfluidic channel (130, 130', 130'', 130''') fluidly couplingthe microchambers (112), in particular upon application of a compressive force (F) tothe sealing layer (480).

11. A system (500) for providing a molecular analysis of a fluid sample, in particular forproviding a digital polymerase chain reaction analysis, comprisingthe microfluidic device (100,200,700) of at least one of the preceding claims,an analysis apparatus (590) configured to receive the microfluidic device(100,200,700) and to amplify the plurality of aliquots within the plurality ofmicrochambers (112) by providing a predefined thermal treatment, andwherein the microfluidic storage circuit (142,242,342,742) is arranged such that thefluid stored in the storage section (140,240,740) is also amplified by the analysisapparatus (590).

12. The system (500) of claim 11, wherein the analysis apparatus (590) is furtherconfigured to provide the predefined fluid pressure to a fluid within the microfluidicdevice (100,200,700) in order to enable a flow of the respective fluid through themicrofluidic circuit (110) and at least partly through the microfluidic storage circuit(142,242,342,742).

13. A method (600) for providing a molecular analysis of a fluid sample, in particular forproviding a digital polymerase chain reaction analysis, comprising the stepsproviding an analysis apparatus (590) and a microfluidic device (100,200,700) with atleast one microfluidic well (105) configured to receive the fluid sample;providing the fluid sample to the at least one microfluidic well (105) via a respectiveinlet end (120) of this microfluidic well (105);insertion of the microfluidic device (100,200,700) into the analysis apparatus (590);andfilling a microfluidic circuit (110) of the microfluidic device (100,200,700) at leastpartially, preferably at least substantially, with fluid of the fluid sample, wherein fluid thatdoes not reach and / or flows beyond microchambers (112) of the microfluidic well (105)during that filling process is stored in a microfluidic storage circuit (142,242,342,742) ofthe microfluidic device (100,200,700).

14. The method (600) of claim 13, wherein a pressure is applied to the fluid sample,preferably by means of at least one piston (598) or by means of a gas flow, in order topush the fluid sample into the microfluidic circuit (110), wherein fluid that does not reachand / or flows beyond the microchambers (112) during the application of the pressure isstored in the microfluidic storage circuit (142,242,342,742).

15. The method (600) of claim 13 or 14, further comprising one or more of the followingstepsfluidly separating the microchambers (112) from each other, preferably by deforminga sealing layer (480) into channel segments of at least one microfluidic channel(130, 130', 130'' 130") fluidly coupling the microchambers (112), in particular byapplying a compressive force (F) to the sealing layer (480), and / or- amplifying the fluid within the microchambers (112) and within the microfluidic storagecircuit (142,242,342,742) by applying a thermal treatment to that fluid.

16. The method (600) of at least one of the preceding claims, further comprising the,preferably final, stepretrieval of the fluid (360) stored in the microfluidic storage circuit (142,242,342,742),preferably through a storage opening structure (144,344) of the microfluidic device(100,200,700).

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