The invention relates to a microfluidic system and a method for delivery of a sample of body fluid to an analysing system with the use of the microfluidic system. The invention relates especially to biochemical analyses of blood.

Various blood tests have nowadays become primary and widespread medical tests. A blood sample is collected from a patient, then blood cells are separated from the blood plasma (or serum) and finally appropriate biochemical testing is performed on serum/plasma samples.

Blood collection from patients is mostly performed using standard syringes with needles or - at present mostly - special vacuum vessels (ampoules), made of glass or plastic, with tight stopper and fitted component comprising needle. The needle is inserted into a blood vessel and the initially empty ampoule fills with blood in a short time. Subsequently, the ampoule is disconnected from the needle, resulting in a blood containing ampoule tightly closed with the stopper. Another empty ampoule can then be connected to the needle if needed. Usually, both components described here are single-use, thus guarantying necessary sterility. Said ampoules with needles have been disclosed, for instance, in publications US 2010323437 Al, KR 20080025050 A or JP 2000189406 A. Typical ampoule lengths are in the order of a few centimetres with typical volumes ranging from a few hundred microliters to a few mililiters. It is also possible to collect a drop of capillary blood from a patient's finger to a capillary wetted by blood. In such a procedure, blood is collected to the capillary and fills appropriately prepared ampoule connected to the capillary. The ampoule is disconnected after the collection is completed.

Blood cells are usually separated from blood plasma/serum by centrifugation of blood contained in a vessel (e.g., in the ampoule mentioned in the paragraph above) in a centrifuge. As a result of centrifugation, blood cells are deposited at the bottom of the ampoule, with plasma (or serum) above. The ampoules so prepared are placed in stands, essentially in vertical position, and analysed in biochemistry analysers.

Biochemistry analysers are advanced automated devices used to examine chemical composition of blood. For instance, contents of glucose, lipids (e.g. cholesterol, triglycerides), enzymes or ions in blood are assayed this way. Using a set of needles and a specially designed mechanism, an analyser collects from an ampoule a serum (or plasma) sample, mixes it with appropriately selected reagents in a small cuvette, as a result of which the concentration of components of interest in blood can be determined, for example by means of a photometrical analysis of the products of chemical reaction.

Biochemistry analysers so constructed and capable of carrying out the above- described test procedure are commercially available (e.g., Flexor XL analysers manufactured by ELITech), and disclosed in numerous patents and patent applications (e.g., publications JP 8211072 A, JP 10132735 A, JP 201033924 A, US 20040185549 Al, US20050014274 Al, US 4808380, US 6162399 or US20070065945 Al).

A separate group of analysers are instruments operated with disposable discs (e.g., commercially available Abaxis Piccolo ^® Xpress and Samsung IVD-A10A models), containing reagents that are necessary to carry out diagnostic reactions (existing instruments use reagents in a freeze-dried form) and allowing for the use of the necessary biological material. These instruments require transferring of the biological material, previously collected from a patient, with an external dispensing device (pipette), which increases the number of operations required to complete the procedure and elongates the time needed to complete the test. The range of analyses that can be carried out using the disc-based instruments is limited by availability of reagents which retain their activity after freeze- drying. Dispensing in these devices is performed with the use of centrifugal force which is supposed to assure uniform spreading out of biological material and solvent to places where the freeze-dried reagents are stored and reactions take place. The fundamental limitations of the accuracy of measurements performed with the disc technology-based analysers are related to reproducibility of manufacture of small portions of reagents in the freeze-dried form and reproducibility of dispensing.

As follows from the above description, the process of obtaining blood serum (or blood plasma) needed for medical tests and subsequent delivery of the serum (or plasma) to an analyser is complex, quite invasive for a patient and requires many operations, including filling an ampoule, ampoule centrifugation, and finally multiple collections of serum (or plasma) from the ampoule for consecutive assays. In particular, the presently existing procedures require performing several operations related to transporting of blood and serum (or plasma) samples between different vessels and/or hydraulic tubing, often involving manual or mechanical operations needed to make hydraulic connections between these vessels and/or tubing. Reduction of the number of operations on blood and serum (or blood plasma) samples would be extremely advantageous in view of simplification of the procedure and minimisation of possibility of errors and contaminations. Simplification of the procedure of transfer of blood plasma (or serum) to the analyser results also in shortening of time from blood collection from the patient to appropriate analysis.

The purpose of the present invention is to provide a microfluidic system allowing for delivery of a sample to an analyser with a minimum number of operations to perform. Another purpose of the invention is to provide a method for delivery of a sample to an analyser using the said microfluidic system.

According to the present invention, a microfluidic system for delivery of a sample of body fluid, in particular blood, to an analysing system, comprising the first chamber connected to the first opening and the second chamber, whereas the chambers are interconnected and connected to the third channel having the third opening, and in addition the first chamber is connected to the fourth channel and the fifth channel, having the fourth and the fifth openings, while the second chamber is connected to the second channel having the second opening, is characterized in that the connection between the first chamber and the second chamber is a constriction.

Preferably, the constriction between the first chamber and the second chamber is a microfluidic channel.

Preferably, the third channel is connected to the constriction, preferably to a microfluidic channel, between the first chamber and the second chamber.

Preferably, the second, third, and fourth openings are arranged so that after placing correctly the microfluidic system in a centrifuge rotor, they are closer to the axis of rotation of the centrifuge rotor than the first opening.

Preferably, after placing correctly the microfluidic system in the centrifuge rotor, the connection between the fourth and the fifth channels is closer to the centrifugation axis than the first opening.

Preferably, the third and the fourth channels connect to the first chamber or to the constriction at an acute angle with respect to the direction of the centrifugal force F _cen tr, which centrifugal force appears when the microfluidic system is placed correctly in a centrifuge rotor and centrifuged.

Preferably, the widths of the second, third, fourth, fifth, and microfluidic channels are from 0.4 mm to 1 mm, preferably 1 mm.

Preferably, the cross-sections of the second, third, fourth, fifth, and microfluidic channels have the shape of a closed figure, preferably a trapezium, square, rectangle, circle or ellipse.

Preferably, the first chamber and the second chamber are arranged so that after placing correctly the microfluidic system in the centrifuge rotor, the first chamber is closer to the rotation axis, and the second chamber is further away from the rotation axis.

Preferably, the ratio of the volume of the first chamber to that of the second chamber is 2:1, 3:2, 1:1, 2:3, or 1:2. The chamber volume ratio may be set arbitrarily, depending on the population's biological variability and the intended yield.

Preferably, the second, third, fourth, fifth, and microfluidic channels comprise internal surfaces coated with substances which interact with a blood component, preferably selected from the group including: EDTA (salt of the ethylenediaminetetraacetic acid), trisodium citrate, heparinates (preferably in the form of sodium, lithium or ammonium salt), heparin, hirudin, potassium oxalate, sodium fluoride, iodoacetate, thrombin inhibitors (preferably ppack or agratroban), silica, kaolin, glass particles, diatomaceous earth, thrombin-based agents, and ellagic acid.

Furthermore, the present invention relates also to a method for delivery of a body fluid sample to an analysing system, with the use of the microfluidic system described above, the method characterised in that it comprises the following steps: a) body fluid is collected to the first chamber and the second chamber of the microfluidic system, b) optionally the body fluid is centrifuged in the microfluidic system, which results in its separation into constituents, and c) a constituent is pushed out through an opening in a centrifuge rotor to an analyser by pumping oil through the microfluidic system.

Preferably, in the method according to the invention the above-described microfluidic system is used which has a volume from 50 μΙ to 150 μΙ, preferably 50 μΙ, 100 μΙ or 150 μΙ.

Preferably, in the method according to the invention in step b) the centrifugation speed ranges from 3000 to 6000 rpm, preferably 3000, 4000 or 6000 rpm.

Preferably, in the method according to the invention in step b) the centrifugation lasts from 30 to 90 seconds, preferably 30, 60 or 90 seconds.

It is to be noted that the volume ratio of both chambers can be changed arbitrarily depending on patient's sex and age (hematocrit varies with age and sex).

The advantages of the invention are as follows:

• minimisation of manual and mechanical operations/actions consisting in making hydraulic connections between containers and tubing used for collecting and transferring samples of blood and serum (or plasma) that must be performed on a sample which is to be collected, separated using centrifugal force, and deposited/transferred (in an easy way) directly to the place where the sample will be used, i.e. for example to the place where it will be analysed;

• minimisation of the physical path a blood sample must pass (by flow) from the moment it is collected to the moment it is used in the form of serum (or plasma) - it contributes to a reduction of the material lost from the blood sample and to increase of safety in the case of dangerous (e.g., infectious) blood samples, and also, if needed, minimisation of the surface area of vessels and tubing that are in contact with blood sample;

• reduction of the amount of single-use materials to be disposed in the process of collection, separation and further use of a blood sample;

• easy handling of small volume samples, minimisation of possible user errors, and simplification of construction of devices required for automation of performed operations;

• minimisation of time between the collection of blood needed for analysis and the delivery of separated plasma (or serum) to an analyser.

The invention will now be described in more detail in preferred embodiments, with reference to the accompanying figures, wherein:

Fig. 1 shows schematically a microfluidic system (chip) with the volume of 50 μΙ, according to the invention in a preferred embodiment;

Fig. 2 shows schematically the upper layer of the microfluidic system shown in Fig. 1;

Fig. 3 shows schematically the lower layer of the microfluidic system shown in Fig. 1;

Fig. 4 shows a scheme of the microfluidic system from Fig. 1 filled with a blood sample;

Fig. 5 shows a scheme of the microfluidic system from Fig. 4 after completed centrifugation and separation of the blood cells from serum;

Fig. 6 shows schematically a microfluidic system with the volume of 100 μΙ, according to the invention in a preferred embodiment;

Fig. 7 shows a scheme of the microfluidic system from Fig. 6 filled with a blood sample;

Fig. 8 shows a scheme of the microfluidic system from Fig. 7 after completed centrifugation and separation of the blood cells from serum;

Fig. 9 shows schematically a microfluidic system with the volume of 150 μΙ, according to the invention in a preferred embodiment;

Fig. 10 shows a scheme of the microfluidic system from Fig. 9 filled with a blood sample; Fig. 11 shows a scheme of the microfluidic system from Fig. 10 after completed centrifugation and separation of the blood cells from serum.

The following labelling is used in the Figures: an arrow indicates the direction of action of the centrifugal force F _centr , 01 - the first opening used for introducing blood into the system, 02, 03- the third and fourth (venting) openings used also for introducing the fluid which pushes out the serum (or plasma) from the first chamber, 05 - the fifth opening for delivering serum (or plasma) to an analyser, 04 - the second opening venting the chambers, Zl- the first chamber, Z2- the second chamber, Kl- the first channel, connecting the first opening 01 with the first chamber Zl, K3- the third channel, connecting the first and the second chamber with the third opening, K4 - the fourth channel, connecting the first chamber with the fifth channel, K5- the fifth channel, connecting the fourth channel with the fourth and fifth openings, K6 - the second channel, connecting the second opening with the second chamber, K2- the microfluidic channel connecting the first chamber with the second chamber.

Preferred embodiments of the invention

Example 1 - sample delivery using a microfluidic system (chip) with a volume of 50 μΙ

A two-layer microfluidic chip shown in Fig. 1 - 5 has been manufactured, with the lower layer comprising a channel draining the blood plasma (serum) from the system to an analyser through the fifth opening 05, other channels and chambers - the first chamber Zl and the second chamber Z2 - for blood sample. The upper plate comprises four openings: the first 01, the third 02, the fourth 03, and the second 04, including the first opening 01 allowing for the supplying of blood sample directly from a patient's finger. Optionally, the first opening 01 can be adapted to install capillaries or a funnel to make blood collection easier. The fifth opening 05, used to supply plasma (or serum) to an analyser, can optionally be adapted to install capillaries to facilitate the process of fluid transfer. It is obvious for persons skilled in the art that each of the openings (the third 02 or the second 04) can be used for blood sample collection, in addition each of the openings can be arranged both in the upper and the lower plate, as well as at the external edge formed by joined plates. It is important that the third opening 02, together with the third channel K3, are used after centrifugation is completed to push out the serum (or plasma) obtained in centrifugation, and that the fifth opening 05, together with the fifth channel K5, are used to supply the serum to an analyser - at that time the first opening 01 and the second opening 04 should remain closed. It is noteworthy that the inlet of the microfluidic channel K2 to the second chamber Z2 should take into account biological variability of the material being collected so that after separation the blood cells are below that inlet. Both layers of the said system have been joined permanently so as to maintain the necessary tightness of the entire microfluidic system. The volume of the microfluidic system in the discussed embodiment is about 50 μΙ, and the third K3, fourth K4, fifth K5, second K6 and microfluidic K2 channels inside the chip are 1 mm wide. It is to be noted, however, that channels with the widths of 0.9 mm, as well as 0.8 mm, as well as 0.7 mm, as well as 0.6 mm, as well as 0.5 mm, and also 0.4 mm will fulfil their roles in the system. The channels' cross sections can have the shape of any closed figure, and in particular of a trapezium, square, rectangle, circle, ellipse, etc.

Channels of the chip may comprise internal surfaces coated with substances which are desirable in view of the final outcome of the blood separation. These substances may be used to counteract blood coagulation and they include, by way of example and in a non- limiting manner: EDTA (salt of the ethylenediaminetetraacetic acid), trisodium citrate, heparinates (sodium, lithium or ammonium salt of heparin), hirudin, potassium oxalate, sodium fluoride, iodoacetate or thrombin inhibitors, (e.g., ppack or agratroban). The substances may also be used to activate blood coagulation, for instance they may be: silica, kaolin, glass particles, diatomaceous earth, thrombin-based agents or ellagic acid.

The microfluidic system - according to the invention - is used as follows:

A patient puts their pricked finger to the first opening 01 on the surface of the chip. Blood is aspirated into the system, and in particular to the first chamber Zl and the second chamber Z2, spontaneously, due to capillary forces. The system discussed here can be filled by an adult person in about 30 seconds, whereas the amount of blood so collected and sufficient for performing analyses is as little as 50 μΙ, i.e. about ten times less than for traditional syringes or blood collection ampoules mentioned in the introduction. After filling the chip with blood it is placed in a rotor especially designed for that purpose. The centrifuge rotor comprises a well that is adapted to the size and shape of the chip. The rotor is made of aluminium (or other suitable material - e.g., ABS, polyacetal (POM), polystyrene or polyamide 66 with glass fibre filler). After centrifugation, the blood separates into plasma or serum, and blood cells, whereas the plasma/serum is located closer to the axis of rotation in the first chamber Zl with the volume of 20 μΙ, and the blood cells - further away from the axis of rotation in the second chamber Z2 with the volume of 30 μΙ. The direction of the centrifugal force during centrifugation is indicated with an arrow in Fig. 1 - 3. It is to be noted that the ratio of the chambers' volumes can be changed arbitrarily, depending on patient's sex and age (the hematocrit varies depending on age and sex). In addition, the rotor and the chip comprise openings allowing for the supplying of oil through a hydraulic system that is used for dispensing plasma portions to an analysing system. Pumping oil into the microfluidic system (e.g., through the third opening 02 or the fourth opening 03) results in pushing out a portion of plasma therefrom. The plasma flows out through an opening in the rotor.

Centrifugation should be performed setting appropriate time and rotational speed values. Centrifugation parameters - time and rotational speed, e.g., 3 minutes at 8000 RPM (revolutions per minute) - are known to persons skilled in the art of diagnostic testing.

For the microfluidic system presented above, a series of tests for fixed rotational speed and variable centrifugation time has been carried out. The results of these experiments are shown below:

It is obvious to a person skilled in the art that specific plasma yield (for an adult it ranges from 35% to 60% on average) can be assured by using other rotational speeds and centrifugation times than those listed here, in particular higher rotational speeds and shorter centrifugation times. For the system under study, the ratio of the volume of the first chamber Zl to that of the second chamber Z2 is 2:3. This results from the biological variability in a population. Persons skilled in the analytics know that blood composition varies significantly depending on age and sex. That's why the chambers' volume ratio can be especially adapted to a specific social group (women, men, children, elderly people, etc.) and be 2:1, 3:2, 1:1, 2:3, 1:2, etc. As shown in the Table above, the condition was met already after centrifugation time of 90 seconds.

Example 2 - sample delivery using a microfluidic system (chip) with the volume of 100 μΙ

A two-layer microfluidic chip shown in Fig. 6 - 8 has been manufactured, with the lower layer comprising a channel draining the blood plasma (serum) from the system to an analyser through the fifth opening 05, other channels and chambers - the first chamber Zl and the second chamber Z2 - for blood sample. The upper plate comprises four openings (the first 01, the third 02, the fourth 03, and the second 04), including the first opening 01 allowing for the supplying of blood sample directly from a patient's finger. Optionally, the first opening 01 can be adapted to install capillaries or a funnel to make blood collection easier. The fifth opening 05, used to supply plasma (or serum) to an analyser, can optionally be adapted to install capillaries to facilitate the process of fluid transfer. It is obvious for persons skilled in the art that each of the openings: the third 02 or the second 04, can be used for blood sample collection, in addition each of the openings can be arranged both in the upper and the lower plate, as well as at the external edge formed by joined plates. It is important that the third opening 02, together with the third channel K3, are used after centrifugation is completed to push out the serum (or plasma) obtained in centrifugation, and that the fifth opening 05, together with the fifth channel K5, are used to supply the serum to an analyser - at that time the first opening 01 and the second opening 04 should remain closed. It is noteworthy that the inlet of the microfluidic channel K2 to the second chamber Z2 should take into account biological variability of the material being collected so that after separation the blood cells are below that inlet. Both layers of the said system have been joined permanently so as to maintain the necessary tightness of the entire microfluidic system. The volume of the microfluidic system in the discussed embodiment is 100 μΙ, and the third K3, fourth K4, fifth K5, second K6 and microfluidic K2 channels inside the chip are 1 mm wide. It is to be noted, however, that channels with the widths of 0.9 mm, as well as 0.8 mm, as well as 0.7 mm, as well as 0.6 mm, as well as 0.5 mm, and also 0.4 mm will fulfil their roles in the system. The channels' cross sections can have the shape of any closed figure, and in particular of a trapezium, square, rectangle, circle, ellipse, etc.

Channels of the chip may comprise internal surfaces coated with substances which are desirable in view of the final outcome of the blood separation. These substances may be used to counteract blood coagulation and they include, by way of example: EDTA (salt of the ethylenediaminetetraacetic acid), trisodium citrate, heparinates (sodium, lithium or ammonium salt of heparin), hirudin, potassium oxalate, sodium fluoride, iodoacetate or thrombin inhibitors, (e.g., ppack or agratroban). The substances may also be used to activate blood coagulation, for instance they may be: silica, kaolin, glass particles, diatomaceous earth, thrombin-based agents or ellagic acid.

The microfluidic system - according to the invention - is used as follows:

A patient puts their pricked finger to the opening 01 on the surface of the chip. Blood is aspirated into the system, and in particular to the first chamber Zl and the second chamber Z2, spontaneously, due to capillary forces. The system discussed here can be filled by an adult person in about 30 seconds, whereas the amount of blood so collected and sufficient for performing analyses is as little as 100 μΙ, i.e., several times less than for traditional syringes or blood collection ampoules mentioned in the introduction. After filling the chip with blood it is placed in a rotor especially designed for that purpose. The centrifuge rotor comprises a well that is adapted to the size and shape of the chip. The rotor is made of aluminium (or other suitable material - e.g., ABS, polyacetal (POM), polystyrene or polyamide 66 with glass fibre filler). After centrifugation, the blood separates into plasma or serum, and blood cells, whereas the plasma/serum is located closer to the axis of rotation in the first chamber Zl with the volume of 40 μΙ, and the blood cells - further away from the axis of rotation in the second chamber Z2 with the volume of 60 μΙ. The direction of the centrifugal force during centrifugation is indicated with an arrow in Fig. 6. It is to be noted that the ratio of the chambers' volumes can be changed arbitrarily, depending on patient's sex and age (the hematocrit varies depending on age and sex). In addition, the rotor and the chip have openings allowing for the supplying of oil through a hydraulic system that is used for dispensing plasma portions to an analysing system. Pumping oil into the microfluidic system (e.g., through the third opening 02 or the fourth opening 03) results in pushing out a portion of plasma therefrom. The plasma flows out through an opening in the rotor.

Centrifugation should be performed setting appropriate time and rotational speed values. Centrifugation parameters - time and rotational speed, e.g., 5 minutes at 6000 RPM - are known to persons skilled in the art of diagnostic testing.

For the microfluidic system presented above, a series of tests for fixed rotational speed and variable centrifugation time has been carried out. The results of these experiments are shown below:

It is obvious to a person skilled in the art that specific plasma yield (for an adult it ranges from 35% to 60% on average) can be assured by using other rotational speeds and centrifugation times than those listed here, in particular higher rotational speeds and shorter centrifugation times. For the system under study, the ratio of the volume of the first chamber to that of the second chamber is 2:3. This results from the biological variability in a population. Persons skilled in the analytics know that blood composition varies significantly depending on age and sex. That's why the chambers' volume ratio can be especially adapted to a specific social group (women, men, children, elderly people, etc.) and be 2:1, 3:2, 1:1, 2:3, 1:2, etc. As shown in the Table above, the condition was met already after centrifugation time of 90 seconds.

Example 3 - sample delivery using a microfluidic system (chip) with the volume of

150ul

A two-layer microfluidic chip shown in Fig. 9 - 11 has been manufactured, with the lower layer comprising a channel draining the blood plasma (serum) from the system to an analyser through the fifth opening 05, other channels and chambers - the first chamber Zl and the second chamber Z2 - for blood sample. The upper plate comprises four openings (the first 01, the third 02, the fourth 03, and the second 04), including the first opening 01 allowing for the supplying of blood sample directly from a patient's finger. Optionally, the first opening 01 can be adapted to install capillaries or a funnel to make blood collection easier. The fifth opening 05, used to supply plasma (or serum) to an analyser, can optionally be adapted to install capillaries to facilitate the process of fluid transfer. It is obvious for persons skilled in the art that each of the openings: the third 02 or the second 04, can be used for blood sample collection, in addition each of the openings can be arranged both in the upper and the lower plate, as well as at the external edge formed by joined plates. It is important that the third opening 02, together with the third channel K3, are used after centrifugation is completed to push out the serum (or plasma) obtained in centrifugation, and that the fifth opening 05, together with the fifth channel K5, are used to supply the serum to an analyser - at that time the first opening 01 and the second opening 04 should remain closed. It is noteworthy that the inlet of the microfluidic channel K2 to the second chamber Z2 should take into account biological variability of the material being collected so that after separation the blood cells are below that inlet. Both layers of the said system have been joined permanently so as to maintain the necessary tightness of the entire microfluidic system.

The volume of the microfluidic system in the discussed embodiment is 150 μΙ, and the third K3, fourth K4, fifth K5, second K6 and microfluidic K2 channels inside the chip are 1 mm wide. It is to be noted, however, that channels with the widths of 0.9 mm, as well as 0.8 mm, as well as 0.7 mm, as well as 0.6 mm, as well as 0.5 mm, and also 0.4 mm will fulfil their roles in the system. The channels' cross sections can have a shape of any closed figure, and in particular of a trapezium, square, rectangle, circle, ellipse, etc.

Channels of the chip may comprise internal surfaces coated with substances which are desirable in view of the final outcome of the blood separation. These substances may be used to counteract blood coagulation and they include, by way of example: EDTA (salt of the ethylenediaminetetraacetic acid), trisodium citrate, heparinates (sodium, lithium or ammonium salt of heparin), hirudin, potassium oxalate, sodium fluoride, iodoacetate or thrombin inhibitors, (e.g., ppack or agratroban). The substances may also be used to activate blood coagulation, for example and in a non-limiting manner they include: silica, kaolin, glass particles, diatomaceous earth, thrombin-based agents or ellagic acid.

The microfluidic system - according to the invention - is used as follows:

A patient puts their pricked finger to the opening 01 on the surface of the chip. Blood is aspirated into the system, and in particular to the first chamber Zl and the second chamber Z2, spontaneously, due of capillary forces. The system discussed here can be filled by an adult person in about 30 seconds, whereas the amount of blood so collected and sufficient for performing analyses is as little as 150 μΙ, i.e., several times less than for traditional syringes or blood collection ampoules mentioned in the introduction. After filling the chip with blood it is placed in a rotor especially designed for that purpose. The centrifuge rotor comprises a well that is adapted to the size and shape of the chip. The rotor is made of aluminium (or other suitable material - e.g., ABS, polyacetal (POM), polystyrene or polyamide 66 with glass fibre filler). After centrifugation, the blood separates into plasma or serum, and blood cells, whereas the plasma/serum is located closer to the axis of rotation in the first chamber Zl with the volume of 60 μΙ, and the blood cells - further away from the axis of rotation in the second chamber Z2 with the volume of 90 μΙ. The direction of the centrifugal force during centrifugation is indicated with an arrow in Fig. 9. It is to be noted that the ratio of the chambers' volumes can be changed arbitrarily, depending on patient's sex and age (the hematocrit varies depending on age and sex). In addition, the rotor and the chip have openings allowing for the supplying of oil through a hydraulic system that is used for dispensing plasma portions to an analysing system. Pumping oil into the microfluidic system (e.g., through the third opening 02 or the fourth opening 03) results in pushing out a portion of plasma therefrom. The plasma flows out through an opening in the rotor.

Centrifugation should be performed setting appropriate time and rotational speed values. Centrifugation parameters - time and rotational speed, e.g., 8 minutes at 2000 RPM - are known to persons skilled in the art of diagnostic testing.

For the abovementioned microfluidic system a series of tests for fixed rotational speed and variable centrifugation time has been carried out. The results of these experiments are shown below: Chamber

Time Rotational

volume Result

[min] speed [RPM]

[μΙ]

assumed plasma yield (40%) was

150 1 3000

obtained

more than assumed plasma yield

150 2 3000

(40%) was obtained

more than assumed plasma yield

150 3 3000

(40%) was obtained

more than assumed plasma yield

150 5 3000

(40%) was obtained

It is obvious to a person skilled in the art that specific plasma yield (for an adult it ranges from 35% to 60% on average) can be assured by using other rotational speeds and centrifugation times than those listed here, in particular higher rotational speeds and shorter centrifugation times. For the system under study, the ratio of the volume of the first chamber to that of the second chamber is 2:3. This results from biological variability in a population. Persons skilled in the analytics know that blood composition varies significantly depending on age and sex. That's why the chambers' volume ratio can be especially adapted to a specific social group (women, men, children, elderly people, etc.) and be 2:1, 3:2, 1:1, 2:3, 1:2, etc. As shown in the Table above, the condition was met already after centrifugation time of 60 seconds.

It can be noticed in examples presented above that due to the use of a microfluidic channel K2, interconnecting the first chamber Zl and the second chamber Z2, and at the same time representing a constriction between the first chamber Zl and the second chamber Z2, restricting free flow between these chambers Zl and Z2, blood separation is attained at lower rotational speeds and in shorter time compared with the situation where such constriction is absent. The constriction (microfluidic channel K2) guarantees also that the separated blood cells do not spontaneously mix with the serum (plasma).

The third channel K3 allows for obtaining serum (plasma) without necessarily pushing blood cells, as it was the case in systems disclosed in the patent application publication no. WO 2013045695 A2. It allows for the maintaining of full purity of material needed for analyses. While analysing the architecture of the systems presented in examples 1-3 it should be noted that the components of the microfluidic system indicated below should be so arranged in the microfluidic system that after placing correctly the microfluidic system in the centrifuge rotor:

• the third opening 02, the fourth opening 03, and the second opening 04 are closer to the rotation axis than the first opening (01); it aims at preventing possible material leak from the system;

• the connection between the fourth channel K4 and the fifth channel K5 is closer to the centrifugation axis than the first opening 01 - to prevent filling the above- mentioned channels with non-centrifuged material.

When the microfluidic system according to the invention is in use, it is placed in a centrifuge rotor and afterwards it is centrifuged, as the result of which a centrifugal force appears. When used properly according to the present invention, the centrifugal force will extend in the direction essentially along the first Zl and second Z2 chambers and - at the same time - essentially perpendicular to the plane in which the constriction between chambers Zl and Z2 is formed. , as illustrated by arrows F _cen tr in the attached drawings. The third channel K3 and the fourth channel K4 connect to the first chamber Zl or to the constriction at an acute angle with respect to the direction of the centrifugal force. Precisely, it means that if vectors heading towards the first chamber Zl or towards the constriction are drawn along the third channel K3 and along the fourth channel K4 at their respective points of connection with the first chamber Zl or with the constriction, each of such vectors will have a positive component along F _cen tr- The purpose of the such an arrangement of the third channel K3 and the fourth channel K4 at respective points of connection is to assure that blood will flow out to the second chamber Z2 under centrifugal force during centrifugation. It allows for reduction of system losses.

The connection of the microfluidic channel K2 with the third channel K3 should always be arranged between the first chamber Zl and the second chamber Z2 - it allows for pushing serum (plasma) to an analyser without necessarily pushing blood cells through, as it was the case in systems disclosed in the patent application publication no. WO 2013045695 A2.