WO2008149282A2

WO2008149282A2 - Microfluidic device and method of operating a microfluidic device

Info

Publication number: WO2008149282A2
Application number: PCT/IB2008/052152
Authority: WO
Inventors: Marc W. G. Ponjee; Clemens J. M. Lasance; Murray F. Gillies; Mark T. Johnson; Stefano Cattaneo
Original assignee: Koninklijke Philips Electronics N. V.
Priority date: 2007-06-06
Filing date: 2008-06-03
Publication date: 2008-12-11

Description

Micro fluidic device and method of operating a micro fluidic device

FIELD OF THE INVENTION

The invention relates to a micro fluidic device. Moreover, the invention relates to a method of operating a micro fluidic device.

BACKGROUND OF THE INVENTION

Micro-fluidic devices are at the heart of many biochip technologies, being used for both the preparation of fluidic (for instance blood based) samples and their subsequent analysis.

A biosensor is an example of a micro fluidic device and may be used for the detection of an analyte that combines a biological component with a physicochemical or physical detector component.

A sample solution may comprise any number of components, including, but not limited to, bodily fluids (for instance blood, urine, serum, lymph, saliva, anal and vaginal secretions, perspiration and semen) of virtually any organism, with mammalian samples being preferred and human samples particularly preferred; environmental samples (for instance air, agricultural, water and soil samples); biological warfare agent samples; research samples (that is in the case of nucleic acids, the sample may be the products of an amplification reaction, including both target and signal amplification); purified samples, such as purified genomic DNA, RNA, proteins, etc.; raw samples (bacteria, virus, genomic DNA, etc.). Virtually any experimental manipulation may have been done on the sample.

Integrated devices comprising biosensors and micro-fluidic devices are generally known. Such devices generally comprise small volume wells or reactors, in which chemical or biochemical reactions are performed and the results examined, and may regulate, transport, mix and store minute quantities of fluids rapidly and reliably to carry out desired (bio)chemical reactions and analysis in large numbers. By carrying out assays in small volumes, significant savings can be achieved in time and the costs of targets, com- pounds and reagents. The market for nucleic acid detection for medical, environmental, food and forensic applications is growing rapidly.

Temperature control is often of vital importance in biotechnology applications, where controlled heating provides functional capabilities, such as mixing, dissolution of solid reagents, thermal denaturation of proteins and nucleic acids, enhanced diffusion rates of molecules in the sample, and modification of surface binding coefficients. A number of reactions, including DNA amplification techniques, ligand binding, enzymatic reactions, extension, transcription and hybridization reactions are generally carried out at optimized, controlled temperatures. Furthermore, temperature control may be necessary to operate micro fluidic pumps and reversible/irreversible valves that are thermally actuated.

A prime example of a biochemical process that requires reproducible and accurate temperature control is high-efficiency thermal cycling for DNA amplification using polymerase chain reaction (PCR). PCR is a temperature controlled and enzyme-mediated amplification technique for nucleic acid molecules, usually including periodical repetition of three reaction steps: a denaturing step at 92-96 ⁰C, an annealing step at 37-65 ⁰C and an extending step at ~72 ⁰C. PCR can produce millions of identical copies of a specific DNA target sequence within a short time, thus has become a routinely used procedure in many diagnostic, environmental, and forensic laboratories to identify and detect a specific gene sequence.

Conventional arrays of temperature control elements have been described, for instance consisting of individually controlled elements (US 2004/0053290 Al) or based on CMOS technology (WO 2005/037433 Al). In an active matrix approach, individual heaters may be addressed line-at-a- time. An active matrix array may be fabricated from one of the well-known large area electronics technologies, such as a-Si, LTPS (low-temperature polysilicon) or organic technologies. Besides a TFT (thin film transistor) as a switch, also diodes or MIM (metal- insulator-metal) diodes/switches can be used as active elements. US 6,692,700 B2 discloses a system for preventing or reducing unwanted heat in one region of a micro fluidic device while generating heat in other selected regions of the device. In one example, current is supplied to a heating element through electric leads, wherein the leads are designed so that the current density in the leads is substantially lower than the current density in the heating element. This may be accomplished using conductive leads which have a cross-sectional area which is substantially greater than the cross- sectional area of the heating element. In another example, unwanted heat in the micro fluidic complex is reduced by thermally insulating the electric leads from the microfluidic complex. This may be accomplished by running each lead directly away from the microfluidic complex, through a thermally insulating substrate. After the leads pass through the thermally insulating substrate, they are then routed to the current source. Thus, the thermally insulating substrate substantially blocks the transfer of heat from the leads to the microfluidic complex. In another example, unwanted heat is removed from selected regions of the microfluidic complex using one or more cooling devices. Such cooling devices (e.g., Peltier elements) may be attached to a substrate to remove heat generated by heating elements and/or other electronic circuitry.

The described solutions above in particular solve the temperature non- uniformity that may occur laterally (i.e. parallel to the substrate via which the sample is heated). However, for accurate temperature control of a biosensor dealing with the lateral non-uniformity is often not sufficient, and solutions are needed to improve the temperature uniformity in the vertical direction (i.e. along the direction perpendicular to the top and bottom substrates).

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the invention to provide a sample analysis system with an efficient temperature management.

In order to achieve the object defined above, a microfluidic device and a method of operating a microfluidic device according to the independent claims are provided. - A -

According to an exemplary embodiment of the invention, a microfluidic device for analysing a fluidic sample is provided, the microfluidic device comprising a casing enclosing a sample chamber, and a thermal barrier supply mechanism adapted for providing a thermal barrier in an upper portion of the sample chamber (particularly for filling an upper portion of the sample chamber with a material providing thermal insulation) to thermally decouple an upper portion of the casing from the fluidic sample located in a lower portion of the sample chamber.

According to another exemplary embodiment of the invention, a method of operating a microfluidic device having the above mentioned features is provided, the method comprising filling the fluidic sample in a lower portion of the sample chamber, and providing a thermal barrier in an upper portion of the sample chamber (particularly filling the upper portion of the sample chamber with a material providing thermal insulation) to thermally decouple the upper portion of the casing from the fluidic sample located in a lower portion of the sample chamber. In the context of this application, the term "sample" may particularly denote any solid, liquid or gaseous substance to be analysed, or a combination thereof. For instance, the substance may be a liquid or suspension, furthermore particularly a biological substance. Such a substance may comprise proteins, polypeptides, nucleic acids, lipids, carbohydrates or full cells, etc. The "substrate(s)" and/or the "casing" may be made of any suitable material, like glass, plastics, or a semiconductor. According to an exemplary embodiment, it may be advantageous to provide a substrate which is partially or (essentially) entirely transmissive for an electromagnetic radiation beam such as a light beam for reading out a sensor surface. For example, when using a light beam, a glass substrate may be an appropriate choice. The term "substrate" may be thus used to define generally the elements for layers that underlie and/or overlie a layer or portions of interest. Also, the "substrate" may be any other base on which a layer is formed, for example a glass or metal layer.

The term "sample chamber" may particularly denote a three-dimensional volume which is provided to accommodate a sample. The term "temperature controller" may particularly denote any entity for measuring, adjusting, regulating, manipulating or influencing a temperature of the fluidic sample in the sample space. This may include heating, cooling or simply controlling.

The term "thermal barrier supply mechanism" may particularly denote any apparatus, entity or procedure provided for supplying a thermal barrier in a volume between an upper level of the fluidic sample and a lower surface of an upper portion of the casing/housing. Such a thermal barrier may provide thermal insulation between the fluidic sample and the upper portion of the casing to avoid heating energy or cooling energy losses. A thermal barrier may also be formed by employing a thermal 'switch', for example consisting of a memory metal or a bimetal, or anything that causes thermal coupling/decoupling.

The terms "upper portion" and "lower portion" may particularly relate to an arrangement of the microfluidic device which is appropriate for using the microfluidic device for detecting particles in a fluidic sample. Therefore, "low" and "upper" may be defined by the vector of the gravitational force and may relate to a lab coordinate system in which the device is operated.

According to an exemplary embodiment of the invention, an apparatus may be provided in which a closed or sealed sample chamber accommodating a sample is intentionally provided with a low thermal conductivity substance to bridge a space between an upper level of the fluidic sample on the one hand and the bottom surface of an upper portion of the casing enclosing the sample space on the other hand. This technical teaching may particularly allow improving the heating/cooling efficiency or the transfer of thermal energy from/to heating and/or cooling elements which may be provided in a lower portion of the casing and the fluidic sample. This may allow for a faster thermodynamic equilibrium between the fluidic sample and a lower portion of the housing, and therefore an accelerated sensor procedure. Further, a sufficient flexibility or compressibility of the (for instance gaseous) thermal barrier may allow the expansion of the fluidic sample under the influence of heat to be compensated. Provisions may be optionally taken to improve the homogeneity of the thermal barrier, for instance to keep a gaseous thermal barrier homogeneously distributed above a liquid surface of the fluidic sample.

The density of the thermal barrier may be (significantly) smaller than the density of the fluidic sample. Thus, the influence of the gravitational force acting on the thermal barrier and on the sample in combination with the arrangement of the heatable/coolable component of the temperature controller in a lower portion of the casing may automatically result in a desired arrangement of thermally coupled and thermally uncoupled components.

In microfluidic devices for molecular diagnostics, the temperature of compartments containing fluid may be controlled at elevated temperatures. An example of this is the thermal cycling in PCR. The temperature control should be fast, accurate and uniform.

According to an exemplary embodiment of the invention, it is possible to incorporate a layer of gas in a compartment, which is to be thermally cycled, and methods of how to generate such a gas layer may be provided. This may be advantageous as the gas layer may have excellent thermal insulation properties, which enhance the heating rate and improve the temperature uniformity in a compartment. In contrast to non-compressible liquids (for instance aqueous solution) which may be used in bio-assays, the gas layer is compressible and, therefore, will allow the expansion of the liquid even upon (fast) temperature increase without the build up of high pressures. This may be advantageous as it may prevent leakage from the compartments (for instance by de-lamination) due to pressure build-up.

According to an exemplary embodiment of the invention, methods to obtain a homogeneous layer of gas on top of a liquid within a micro fabricated (bio)chemical reaction chamber on a micro-fluidic device may be provided. This may be beneficial for the case that accurate temperature control (for instance thermal cycling) of a liquid is required and where the thermal homogeneity of the liquid is important for the (bio)chemical reaction. This is the case for the polymerase chain reaction (PCR) often used for DNA amplification. According to an exemplary embodiment of the invention, methods are provided of how to generate the homogeneous gas layer within a micro-fabricated reaction well. These methods may be based on electrolysis, with gas containing structures and/or in combination with a hydrophobic layer.

In the following, further exemplary embodiments of the micro fluidic device will be explained. However, these embodiments also apply to the method, and vice versa.

The casing of the micro fluidic device may be completely closable or completely closed. In such a completely closed condition, the sample may be entirely decoupled from influences of the environment, and may be sealed against the environment. In such a scenario, it may be advantageous that such an insulated sample is provided with a proper thermal barrier simultaneously allowing expansion or compression of the sample within the sample chamber.

The device may comprise a temperature controller located in a lower portion of the casing and adapted for controlling a temperature of the fluidic sample located in the sample chamber. Such a temperature controller may selectively influence the sample temperature with marginal heat losses by thermal equilibration procedures between the sample and the upper casing portion which is suppressed or eliminated by the thermal barrier.

The temperature controller may comprise a heater, particularly a resistive heater such as an ohmic heater, a capacitive heater or an inductive heater. However, other heating procedures are possible, for instance a Peltier heater, an electromagnetic radiation based heater, etc. The temperature controller may also comprise a cooler, for instance a Peltier cooler. This may allow to perform a temperature adjustment or even complex temperature cycles.

The temperature controller may be embedded (exclusively) in a first substrate forming the lower portion of the casing. Such an integrated implementation of the temperature controller may allow providing a large sample space and a homogeneous heating of the sample.

The thermal barrier supply mechanism may be adapted for filling the upper portion of the sample chamber with gas, particularly air, or a liquid having a low thermal conductivity. It is also possible to use massive or hollow particles in the portion of the sample space provided for the thermal barrier. Differences in the density between such material and material of the fluidic sample may then automatically make these materials accumulate above the liquid surface of the fluidic sample, thereby serving as a proper thermal barrier. The particles may be gas filled. They can also be made of a thermally insulating material, for instance with a density lower than water.

The thermal barrier supply mechanism may be adapted for generating a gas as the thermal barrier by electrolysis. For this purpose, one or more electrode structures may be provided within the sample space and may be activated for generating the gas by electrolysis. Advantageously, the electrode structure(s) may be provided on the upper portion of the casing, thereby generating the gas at a position where it shall be located on the long term. Such embodiments may allow for a cost-efficient production of the device, since in many (bio-)sensors, electrode structures may be present anyway (for instance for moving electrically charged molecules of a sample under the influence of an electric force generated by applying an electric voltage to the electrodes). Thus, such electrodes may contribute synergistically to both sample transport and thermally insulating gas generation by electrolysis.

The thermal barrier supply mechanism may comprise an inlet via which material forming the thermal barrier and/or the fluidic sample is tillable in the sample space. This inlet may be coupled or decoupled to the environment using a valve or the like.

The thermal barrier supply mechanism may comprise a thermally insulating liquid, gel- like or solid structure provided on the upper portion of the casing. Such a solid structure may allow for a stable and reproducible thermal barrier function. It may include the provision of a gel, a foam, an aerogel etc. The upper portion of the casing may be free of a temperature controller. In other words, according to the described embodiment, no heating/cooling components of the temperature controller are provided in the upper portion of the casing. In this scenario it may be desirable to thermally decouple the upper portion of the casing from the fluidic sample, since the upper portion of the casing does not contribute to the temperature control function. This thermal decoupling (or weak coupling) may be obtained by the thermal barrier.

A sensor-active structure may be located at a surface of the lower portion of the casing. Such a sensor-active structure may comprise capture molecules, a magnetic sensor area, an electric sensor area, a chemical sensor surface, etc. A sensor-active structure comprising capture molecules may be read out optically, magnetically or electrically.

A thermal barrier support unit may be provided and adapted for supporting the thermal barrier to remain essentially homogeneously located in the upper portion of the sample chamber. Such a thermal barrier support unit may support the thermal barrier at an upper portion of the sample space. Particularly, the thermal barrier support unit may comprise one or more protrusions extending from the upper portion of the casing into the sample chamber. If these protrusions are made of a (for instance hydrophilic) material for pinning the thermal barrier at the upper portion of the casing, it may be ensured that even a gaseous thermal barrier reliably and essentially homogeneously remains at an upper portion of the sample space.

The thermal barrier support unit may also comprise a hydrophobic layer. When the upper portion of the casing is made from such a hydrophobic material, no liquid portion of the fluidic sample will accumulate at the upper portion of the casing to disturb the thermal insulation functionality. The thermal barrier support unit may comprise a hydrophilic lateral (wall) portion of the casing. This may further promote that the fluidic sample remains at a lower part of the sample chamber.

The casing may enclose a plurality of separate sample chambers. In other words, the microfluidic device may be a sensor assay for high throughput analysis applications. For instance, the individual sample chambers may be arranged in an essentially matrix-like manner.

The microfluidic device may be a sensor device, a biosensor device, a biochip, a lab-on-chip, an electrophoresis device, a sample transport device, a sample mix device, a cell lysing device, a sample washing device, a sample purification device, a polymerase chain reaction (PCR) device, or a hybridization analysis device. Particularly, the microfluidic device may be implemented in any kind of life science apparatus.

At least a part of an electronic circuitry of the microfluidic device may be realized in low-temperature polysilicon (LTPS) technology. Thus, LTPS may be used for an electrical connection to electrodes and/or local current sources.

At least a part of the components of the microfluidic device may be integrated in the casing. This may allow to integrate not only sensors and heaters but also control electronics to form real time feedback.

The aspects defined above and further aspects of the invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to these examples of embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited.

Fig. 1 illustrates a sensor device according to an exemplary embodiment of the invention. Fig. 2 is a schematic illustration of a compartment according to an exemplary embodiment of the invention comprising a gas layer which is not present between the fluid of interest and the heating elements, wherein the thickness of the gas layer needs not to be as uniform as indicated in Fig. 2.

Fig. 3 and Fig. 4 show temperature simulations of compartments filled with water at t=25s after ramp up of the heaters from 20⁰C to 95°C, wherein in Fig. 3 a 20 μl compartment is completely filled with water, and in Fig. 4 a 22.5 μl compartment is filled with 20 μl water and 2.5 μl air such that the air layer has a uniform thickness and is present between the top substrate and the water.

Fig. 5 and Fig. 6 show flipping of a microfluidic device/compartment according to an exemplary embodiment of the invention comprising a gas layer, which is used for bio-particle detection using immobilized capture probes, wherein in Fig. 5 it is shown that before flipping the gas layer is present between the fluid and the substrate opposite to the substrate comprising the immobilized capture spots, and wherein it is shown in Fig. 6 that after flipping the gas layer is present between the fluid and the substrate comprising the immobilized capture spots, wherein the device may optionally incorporate a heating element and/or sensing element.

Fig. 7 to Fig. 10 show schematics of the generation of a gas layer in a micro fluidic compartment using electrolysis according to an exemplary embodiment of the invention, wherein Fig. 7 shows starting to fill the compartment, Fig. 8 shows a compartment completely filled, Fig. 9 shows the generation of gas based on electrolysis using electrodes on top of the substrate, and Fig. 10 shows stopping the generation of gas and closing valves.

Fig. 11 and Fig. 12 show flipping of a microfluidic device/compartment according to an exemplary embodiment of the invention comprising a layer of particles comprising gas or a thermally insulting liquid/solid having a sufficiently small density to float on the sample, which is used for bio-particle detection using immobilized capture probes, wherein Fig. 11 shows the situation before flipping the particle layer being present between the fluid and the substrate opposite to the substrate comprising the immobilized capture spots, and Fig. 12 shows the scenario after flipping in which the particle layer is present between the fluid and the substrate comprising the immobilized capture spots, wherein the device may optionally incorporate a heating element and/or sensing element. Fig. 13 and Fig. 14 show a microfluidic device according to an exemplary embodiment of the invention in which a gas layer is incorporated using particles which are charged (for instance positive) and filled with gas, wherein the particles can be manipulated using electrical fields to a specific location, wherein Fig. 13 shows a scenario with the particles being in between the fluid and the top substrate, and Fig. 14 shows a scenario with the particles being in between the fluid and bottom substrate.

Fig. 15 and Fig. 16 show a microfluidic device according to an exemplary embodiment of the invention in which a compliant layer with a relatively low thermal conductivity is incorporated using an aerogel (Fig. 15) and a film with gas pockets (Fig. 16), wherein the thickness of the compliant layer needs not to be as uniform as indicated in Fig. 15 and Fig. 16. Fig. 17 shows an ideal situation in a sensor device according to an exemplary embodiment of the invention.

Fig. 18 shows a sensor device under undesired circumstances according to an exemplary embodiment of the invention.

Fig. 19 shows a photo of a real sample according to an exemplary embo diment o f the invention.

Fig. 20 and Fig. 21 show a schematic of a top substrate according to an exemplary embodiment of the invention vertically flipped (Fig. 20) and a cross-sectional view (Fig. 21) thereof.

Fig. 22 to Fig. 24 show a sample before electrolysis (Fig. 22), upon electrolysis (Fig. 23), and five seconds after electrolysis (Fig. 24).

Fig. 25 shows a gas formation pattern structures on bottom of a chamber.

Fig. 26 and Fig. 27 show schematics of a gas in a compartment without a hydrophobic layer (Fig. 26) and with a hydrophobic layer (Fig. 27).

DESCRIPTION OF EMBODIMENTS

The illustration in the drawings is schematical. In different drawings, similar or identical elements are provided with the same reference signs.

In the following, referring to Fig. 1, a micro fluidic device, namely a sensor device 100 for analyzing a fluidic sample 101 according to an exemplary embodiment of the invention will be explained.

The sensor device 100 comprises a casing having components 102 to 104 enclosing a sample chamber 105. The casing is formed of the lower substrate 102, an upper substrate 103 and a lateral wall 104. Furthermore, ohmic heating elements 111 of a temperature controller 106 are located in the lower portion 102 of the casing 102 to 104 for controlling a temperature of the fluidic sample 101 located in the sample chamber 105. The upper portion 103 of the casing 102 to 104 is free of a temperature controller which is only provided in the lower casing portion 102. The temperature controller 106 may comprise

(i) the resistive heater 111,

(ii) temperature sensing element(s) and

(iii) integrated electronics for feedback control embedded in the first substrate 102 forming the lower portion of the casing 102 to 104. Moreover, a thermal barrier supply mechanism 107 is adapted for filling an upper portion 108 of the sample chamber 105 with a thermal barrier 109 to thermally decouple an upper portion 103 of the casing 102 to 104 from the fluidic sample 101 located in a lower portion 110 of the sample chamber 105. The thermal barrier supply mechanism 107 may fill the upper portion 108 of the sample chamber 105 with gas by electrolysis, using the electrodes 112. The electrodes 112 are provided on the upper portion 103 of the casing 102 to 104.

Fig. 1 shows a direction 130 of the gravitational force defining the terms "upper" and "lower" as used herein.

The device 100 comprises a control unit 140 such as a CPU or a microprocessor. The CPU 140 controls the entire system 100. Furthermore, an optional input/output device 150 is provided which allows a human user to control or supervise the function of the device 100. Such an input/output device 150 may comprise a display unit like a cathode ray tube, an LCD device, a TFT device, etc. It may also comprise input elements like a keypad, a joystick, a trackball or even a microphone of a voice recognition system.

As can be taken from Fig. 1, the CPU 140 controls a switch 141 of the thermal barrier supply mechanism 107. When the switch 141 is closed, a voltage supply unit 142 provides electrical energy to electrodes 112 which generate, by electrolysis, a gas 109 forming the thermal barrier. Control electronics may be integrated for instance on a substrate/glass in the form of LTPS, or a-Si structures.

Furthermore, the CPU 140 controls a switch 145 of the temperature controller 106. When the switch 145 is closed, a current supply unit 146 supplies energy to the buried or integrated heating element 111 structure provided in (or on an inner surface of) the lower substrate 102. This may allow heating the sample 101 and to thereby influence an interaction between the sample 101 and capture molecules 114 provided on an inner surface of the lower substrate 102. The sensor-active structure 114 is located at the inner surface of the lower portion 102 of the casing 102 to 104.

Furthermore, a temperature sensor 148 is provided on or in the lower substrate 102 to measure the temperature of the fluidic sample 110 and to provide the CPU 140 with corresponding temperature data so that the CPU 140 may control or regulate the temperature, by providing corresponding control signals to the switch 145.

A sample may be supplied from a reservoir 168 through the selectively openable or closable valve 113 into the sample space 110. In a similar manner, at an outlet of the sample space 110, a valve 149 is provided via which the sample may be collected in a reservoir 165 after the analysis. The casing 102 to 104 is completely sealable against the environment by a corresponding control of the valves 113, 149.

In the following, aspects of embodiments of the invention will be explained in detail. Generally, in a micro total analysis system (μ-TAS), for instance lab-on-a- chip, the sample (for instance blood) to be analyzed may be present in an enclosed volume. On a lab-on-a-chip, several processing steps may be carried out that may use elevate temperatures, such as PCR and hybridisation on a biosensor (for instance melting curves).

To enhance the speed of a bio-assay that includes thermal processing steps, both the temperature uniformity (<1 ⁰C) of a compartment as well as the heating rate (at a given power dissipation) may be desired to be high. This may give improved control of the temperature in a compartment and moreover may reduce the time needed in the event that multiple thermal cycles are required, as for instance for PCR. In view of costs, electronic elements (for instance heaters, sensors, switches) are preferably located only on a single side of a (disposable) lab-on-a-chip. When heating a compartment from a single side (for instance bottom substrate), a good thermal insulator may be advantageous on the opposite side to prevent heat leakage and to realize a low thermal gradient in the compartment.

Upon (fast) temperature increase, the non-compressible liquids (for instance aqueous solution) often used in bio-assays needs to expand, which in the case of an enclosed volume will lead to the build-up of pressures and may lead to breakdown of the compartment (for instance fluid leakage due to de-lamination). When considering a lab-on- a-chip comprising an array of compartments filled with fluids, leakage of one or more compartments as a consequence of the pressure build up is unacceptable. The volume expansion ΔFof a fluid as a function of temperature T at constant pressure p is described by the cubic thermal expansion coefficient γ:

The volume compression of a fluid as a function of pressure at constant temperature is described by the compressibility coefficient K.

From these equations it is possible to derive that the pressure build up of a fluid as a function of temperature at constant volume is described by:

( dp λ ₌ γ {dτ )_r K

The table below lists values of γ and K for air and water. In addition, the table shows the desired volume expansion of air and water at constant pressure, as well as the pressure build up as a function of temperature in an enclosed volume. These latter numbers are based on the values of γ and K at 20 ⁰C.

p = 1 atm, T = 293 K T: 20 ⁰C => 95 ⁰C γ (K^"1) K (Pa^"1) AV_xJV (%) Δp_y (Bar)

Air 3.411-10^"3 9.9-10^"6 25.6 0.26

Water 0.206- 10^"3 0.459- 10^"9 1.55 337

When considering a cell comprising a bottom and top glass substrate with in between SU-8 walls to define the compartment, the volume of the cell is not exactly constant as the temperature is varied. Due to the larger thermal expansion of SU-8 with respect to glass, the cell volume will decrease thereby causing an even higher pressure build up.

According to an exemplary embodiment of the invention, it is possible to in- corporate a gas layer in the compartment. This gas layer has a beneficial effect on the temperature uniformity during thermal cycling, as well as solving the thermal expansion problem. Moreover, methods to generate a defined gas layer are provided, such that an array of compartments can still be simply filled with a defined volume of liquid, and the thermal contact between heaters and fluid is defined. According to an exemplary embodiment of the invention, the incorporation of a layer of gas in a compartment or an array of compartments on a micro-fluidic device (for instance micro total analysis system, lab-on-a-chip) may be performed, such that the gas is not present between the fluid of interest (for instance bio-liquid) and the substrate on the side from which the compartment(s) is heated. Such a system 200 is shown in Fig. 2.

Fig. 2 is a schematic illustration of a compartment 200 according to an exemplary embodiment of the invention comprising a gas layer 109 which is not present between the fluid of interest 101 and the heating elements 111.

The thermal conductivity of the gas layer 109 should be lower than that of the fluid of interest 101 in order to improve the thermal properties (for instance heating rate, temperature uniformity). The compressibility of the gas layer 109 should be high with respect to that of the fluid of interest 101 in order to reduce the pressure build-up during thermal cycling. The gas layer 109 may be a fluid (such a fluid is a general term for a gas or a liquid) of which the thermal conductivity is lower and the compressibility is higher than that of the sample fluid of interest 101. Only partially filling the compartments 200 is not trivial considering that the compartments 200 are distributed in an array on a microfluidic device that is already capped and have to be filled automatically with a defined volume. An easy method of filling a compartment 200 with a defined volume of liquid 101 is to fill the compartment 200 with tailored dimensions completely. More severely, in case of a lab-on-a-chip for molecular diagnostics with integrated electronics, the use of heater elements 111 and sensor elements (not shown in Fig. 2) on a single side only is a characteristic of exemplary embodiments of the invention. Therefore, the compartment 200 should be filled such that the fluid 101 is in good thermal contact with the heaters 111, i.e., no gas (for instance air) should be present in between the fluid 101 and the heaters 111.

In addition, methods are disclosed herein to incorporate/generate a defined gas layer 109 in a compartment 200, such that the compartment 200 can be filled with a defined volume of liquid 101 using the volume 105 defined by the compartment 200, and such that the thermal contact between heaters 111 and fluid 101 is defined (i.e., no gas 109 should be present in between the fluid 101 and the heaters 111).

According to an exemplary embodiment of the invention, electrolysis may be used to generate a gas layer. According to another exemplary embodiment of the invention, it is possible to incorporate hollow particles, which are filled with gas, into the sample fluid. The incorporation of the gas layer 109 may be advantageous as it may solve the problems described above. Below the advantages of embodiments of the invention are illustrated.

Temperature simulations of a typical compartment that can be used for PCR (for instance glass substrates, SU-8 walls, resistive heaters, 7x7 mm² base area, height 400 μm, bottom substrate in contact with temperature reference plate) may illustrate the effect of a gas layer 109 (for instance air) on the temperature uniformity during thermal cycling.

This is illustrated in a diagram 300 shown in Fig. 3 and in a diagram 400 shown in Fig. 4. Fig. 3 shows a compartment that is completely filled, whereas Fig. 4 shows a standard cell with a 50 μm thick air layer. Clearly, the air layer increases the temperature uniformity. Moreover, the leakage of heat through the top substrate to the surroundings is significantly reduced, which reduces the time needed to ramp up the temperature of a compartment to a specific set point. Finally, the power needed to heat the cell is reduced. The effect as described above is believed to occur in general due to the low thermal conductivity of gas (air: 30 mW/mK @95 ⁰C) with respect to that of fluid (water: 677 mW/mK @95 ⁰C).

Next, pressure build-up during thermal cycling will be explained.

Due to the compressibility of a gas layer (for instance air) the liquid (for in- stance water) with extremely low compressibility can expand upon temperature increase, thereby compressing the gas layer. As a consequence, the high pressure build-up (for instance >300 bar) estimated above in the absence of a gas layer is replaced by a relatively low pressure build-up when the gas layer is present. The low pressure build-up can be estimated using the ideal gas equation. As an estimate, for a 50 μm thick air layer and a liquid volume expansion of 1.5% (see table above), the pressure of the air layer rises from 1 bar (20 ⁰C) to 1.3 bar (95 ⁰C)

Hence, the gas layer will allow the expansion of the liquid upon (fast) temperature increase without the build up of high pressures. This may be advantageous as it may prevent leakage of the cells (for instance by de-lamination) due to pressure build-up. According to an exemplary embodiment of the invention, a micro-fluidic device comprising a compartment for thermal cycling (for instance for PCR) with a gas layer may be provided.

According to such an embodiment, it is possible to incorporate a layer of gas 109 in a compartment 200 on a micro-fluidic device of which the temperature may vary (see Fig. 2). The layer of gas 109 may be incorporated, whilst the top substrate 102 and the bottom substrate 103 are already present and attached to one another before filling the compartment 200. This may distinguish an embodiment of the invention from a situation on a micro fluidic device in which a compartment is filled with a volume of fluid smaller than the volume of the compartment and subsequently sealing the compartment.

According to an embodiment of the invention, the thermal conductivity of the gas layer 109 may be lower than that of the fluid of interest 101 in order to improve the thermal properties (for instance heating rate, temperature uniformity). In addition, the compressibility of the gas layer 109 should be high with respect to that of the fluid of interest 101 in order to reduce the pressure build-up during thermal cycling. In general, both conditions may be fulfilled when a gas is used. Gases that may be used, but not limited to this list, are; air, nitrogen, oxygen, water vapour, noble gases or mixtures of gases.

The compartment 200 may be used to perform chemical and/or biochemical reactions, or may regulate, transport, mix and store minute quantities of fluids rapidly and reliably to carry out desired (bio)chemical reactions and analysis in large numbers. For example, the compartment 200 may be used for DNA amplification based on PCR, which may require thermal cycling. Other examples include the use of the compartment 200 for DNA analysis based on micro-array technologies (for instance hybridisation of DNA target molecules with complementary oligonucleotide probe sequences), or thermal cell lysing. The compartment 200 may be connected to at least one channel to be able to fill and remove a fluid 101. In addition, the compartment 200 may contain one or more valves and/or one or more pumps.

The temperature of the compartment 200 may be varied using at least one heating element 111. According to an embodiment of the invention, the compartment 200 may be heated exclusively from a single side. The heating element 111 may be present on the outside of the compartment 200, but is preferably integrated in the compartment 200 (as illustrated in Fig. 2). The integrated heater element 111 may be covered with a layer or a stack of layers, for instance for electrical insulator properties or improved biocompatibility. Multiple heater segments 111 may be present per compartment 200 for improved temperature control. Moreover, for many applications (for instance PCR) an array of compartments 200 may be used. The temperature of the compartments 200 may be controlled using a single heater 111 , or using an array of heating elements 111. The control of the heaters 111 may be based on active matrix principles. In addition, the compartment 200 may comprise a temperature sensor 148 (not shown in Fig. 2). According to an embodiment of the invention, the temperature sensor 148 may be present on the substrate 102 comprising the heating element(s) 111.

In order to control the location of the air layer 109 (that is in between the fluid of interest 101 and the substrate 103 from which side the fluid 101 is not heated), the device 200 may be oriented such that the side of the device 200 from which the compartment is heated is located closer to the earth's center of gravity (or the center of gravity of the planet on which the device is being used) than the side of the device 200 from which the compartment is not heated. This may be advantageous as in general, the density of the gas 109 is lower than the density of the fluid of interest 101. This is true for gravity forces in general, including centrifugal forces.

According to an exemplary embodiment of the invention, a gas layer 109 may be incorporated in a micro-fluidic device comprising a hybridization array with surface sensitive read-out (see Fig. 1).

Particularly, it is possible to incorporate a gas layer 109 in a compartment 100 on a micro-fluidic device comprising a DNA hybridisation spot or array of spots 114. Generally, the temperature of such a compartment 200 may be controlled in order to define the hybridisation process and with that the analysis of DNA fragments present in the sample fluid 101. For example, temperature control may be advantageous to monitor melting curves. Incorporation of a gas layer 109 may be advantageous as it may increase amongst others the temperature uniformity and may allow for the thermal expansion of the fluid 101. In addition, the incorporated gas layer 109 can be used to enhance the detection sensitivity. Numerous techniques may be applied to read-out a hybridization array with increased sensitivity using surface-specific sensing. For example, it is possible to optically detect fluorescent labels excited by evanescent waves of light passing through a light-guide directly underneath the surface comprising immobilized capture sites. This approach may be advantageous as only fluorescent labels in proximity of the surface are excited. Another example is the electrical detection of hybridised molecules for instance by measuring a change in capacitance or TFT characteristics.

The sensitivity of such methods can be further enhanced by removing non- covalently bonded molecules before detection. This may be achieved by incorporating a gas layer 109 between the fluid of interest 101 and the substrate 103 opposite to the substrate 102 comprising the hybridisation capture sites 114 Such a scenario is illustrated in Fig. 5 and Fig. 6 on the example of a sensor device 500.

This situation is maintained during hybridisation and temperature control periods. Prior to analysis, the micro-fluidic device 500 may be flipped over such that the gas layer 109 becomes located in between the hybridisation array 114 and the fluid of interest 101 (see Fig. 5). This will happen due to the gravity force 130 and the differences in density between gas 109 and liquid 101. Hence, due to the flipping, the fluid 101 containing non- covalently bonded target molecules is removed from the close vicinity of the surface comprising the immobilized capture spots 114. As a consequence the background signal is lowered (for instance fluorescent dyes in the fluid 101 that are not bonded to the capture spots 114 cannot be excited by the optical evanescent field), and the signal to background ratio is increased, and with that the detection sensitivity. This may also be relevant for measuring the capacitance via TFTs where the fluid should be removed before measurement. Embodiments of the invention can be applied in general to a bio-sensor based on surface immobilized capture spots (for instance a protein sensor).

According to an embodiment of the invention, a method to generate a gas layer in situ-electrolysis may be provided. In this embodiment it is possible to generate a gas layer in situ using electrolysis.

Fig. 7 to Fig. 10 illustrates the process for a compartment 700 with an inlet 701, an outlet 702, an inlet valve 113 and an outlet valve 149.

The scenario of the process is as follows: At the start of the process, see Fig. 7, the valves 113, 149 of the compartment 700 are opened and fluid 101 is entered into the compartment 700 via the inlet 701. The air present in the compartment 700 can leave via a second valve 149. This valve 149 is suited to vent air and may also be suited to act as a valve of the fluid 101.

The compartment 700 is completely filled, see Fig. 8, such that the volume of fluid 101 enclosed is defined by the volume of the compartment 700.

While at least one valve 113, 149 is open, which is suited to vent fluid 101, gas 109 generation is started using electrolysis, see Fig. 9. For instance, opposite voltages are applied to neighbouring electrodes 112. The voltage needed to exceed the threshold for electrolysis is theoretically 1.2 V in ultra-pure water though in practise a voltage of 2-3 V may be necessary due to, e.g., resistance in the electrical circuit or slow electron transfer at the electrode interface. Closely spaced electrodes 112 may be used in order to generate a large number of small bubbles which can coalesce. The electrodes 112 may be controlled using integrated electronics, for instance based on crystalline Si, LTPS, microcrystalline Si or amorphous silicon. Electronic circuits may be used to control the bubble formation. When the gas layer 109 has been generated, see Fig. 10, the electrolysis is stopped and the compartment 700 is sealed by closing the valve(s) 113, 149. Now the compartment 700 is ready to start processing, for instance thermal cycling for PCR.

According to an embodiment of the invention, a method to incorporate a gas layer or a layer of gas filled particles may be provided. In such embodiments, see Fig. 11 to Fig. 14, it is possible to incorporate a gas layer 109 in a compartment 1100 by including hollow particles 1101 filled with gas in the fluid 101. These particles 1101 may be included in the fluid 101 before filling the compartment 1100 or when the fluid 101 is already present in the compartment 1100. Alternatively a correct dosage of these particles 1101 can be placed in the compartments 1100 during the manufacturing process, for instance prior to filling the compartment 1100 with sample fluid 101. These particles 1101 may be hollow spheres that are filled with air, including nanoparticles for which the diameter is (much) less than the mean free path of the gas, for example 65 nm for nitrogen. This may be advantageous as the thermal conductivity is reduced even further.

There are several methods to manipulate the gas particles 1101 into the correct location.

- Due to gravity forces, the gas filled particles 1101, which in general have a lower density than the fluid of interest 101 in bio-assays (for instance aqueous solution), will float on top of the fluid 101 (see Fig. 11). Hence, depending on the orientation of the microfluidic device 1100 (see Fig. 12), the gas filled particles 1101 can be located in between the fluid 101 and the top substrate 103, opposite to the bottom substrate 102 from which the compartment 1100 is heated. Or the gas filled particles 1101 can be located in between the fluid 101 and the bottom substrate 102. - Electrical fields may be used to manipulate the particles 1101 to the desired location (see Fig. 13 and Fig. 14). For this purpose, a voltage supply unit 1300 and electrodes 1301 may be provided. In case particles 1101 are used with functionalized coatings, the particles 1101 may be charged, so that DC electrical fields (electrophoresis) may be used to manipulate the particles 1101 either towards the bottom substrate 102 or top substrate 103. In case the particles 1101 have no permanent charge, dielectrophoresis (with AC or DC electrical fields) may be used to manipulate the particles 1101. For this electrical field manipulation, electrodes 1301 may be used to apply the desired electrical fields to the particles 1101. The electrodes 1101 may be integrated in the microfluidic device 1100. The electrodes 1301 may be located on the side of the top substrate 103 facing the fluid 101 such that high electrical fields can be generated using relatively low voltages. In a further embodiment, application of the voltages on the electrode structures 1310 may be based on large area electronics using active matrix technology.

- Magnetic fields may be used to manipulate magnetic particles, for instance hollow nanoparticles of a magnetic material such as Ni, to the desired location. This includes hollow particles that have been functionalized with magnetic labels. These labels may contain a permanent magnetic moment or be paramagnetic. The magnetic fields may be applied from outside of the device. The magnetic field may be applied from inside the device 1100, for instance by applying currents through electrode structures 1301. The electrode structure 1301 may be present on top substrate 103 and/or bottom substrate 102. In a further embodiment, driving of the current through the electrode structures 1301 is based on large area electronics using active matrix technology.

According to an embodiment of the invention, a device 1500, 1600 comprising a compliant layer with low thermal conductivity may be provided. Such an embodiment is shown in Fig. 15 and in Fig. 16.

In such embodiments it is possible to incorporate a compliant layer 1501, 1601, 1602 in a compartment 1500, 1600 on a micro-fluidic device of which the temperature may vary, such that it is situated between the sample fluid 101 and the top substrate 103. The compliant layer 1501, 1601, 1602 should have a low thermal conductivity and can consist of a single material or may comprise multiple of materials and layers. As an example of a single layer of a single material, an aerogel 1501 may be present between the sample fluid 101 and top substrate 103 (see Fig. 15).

In another example, a porous membrane may be present between the sample fluid 101 and the top substrate 103. In a further example, a film (for instance foil) 1601 comprising gas pockets

1602 (for instance sandwiched) may be present between the sample fluid 101 and the top substrate 103 (see Fig. 16). Besides having a low thermal conductivity, the above embodiments may be beneficial in the sense that the compliant layer allows for sample fluid expansion without the build up of high pressures.

The problem(s) of (a) pressure build-up in a closed volume of liquid when thermally cycling and (b) poor temperature homogeneity for performing PCR may include the introduction of an air (or another gas) layer on top of the solution. The gas allows the expansion of the liquid and provided that it is homogeneous also improves the temperature profile of the liquid in the chamber. This gas can be introduced by completely filling the chamber and then performing electrolysis or by introducing small air filled particles. When a free gas layer is created in a small reaction chamber, the gas does not remain as a layer of gas but instead minimizes its surface energy and forms a bubble extending from top to bottom of the chamber.

The intended situation is shown schematically in Fig. 17 and what may actually happen under undesired circumstances in Fig. 18. Fig. 19 shows the situation in a real sample.

While such a situation does not have any consequence for allowing the expansion of the liquid 101 it does not result in a homogeneous thermal profile. In fact the thermal profile is significantly worse than the case where no gas is enclosed. The gas layer 109 should be present between the liquid 101 and the (glass) substrate 103 opposite to the (glass) substrate 102 via which the liquid 101 is heated/cooled.

Methods according to exemplary embodiments of the invention for avoiding the formation of large gas bubbles 1800 will be explained in the following.

It is possible to create a gas layer 109 by electrolysis of the liquid sample 101 via planar electrodes 112 situated on the inner- side of the top substrate 103 of the reaction chamber 105 (when the liquid 101 is heated/cooled via the bottom substrate 102). Although it is possible to structure the surface with nucleation sites where bubbles form, and thus initially form a reasonably homogenous layer of gas 109, this situation is not stable as the small bubbles eventually coalesce into a few much larger bubbles. To avoid this problem it is possible to create structures on the inner-side of the top substrate 103 that act to pin the gas bubbles near the point of nucleation and so prevent them from coalescing into larger bubbles.

An example of such a structure 2000, 2100 is shown schematically in Fig. 20 and Fig. 21. The view 2000 shown in Fig. 20 is the top substrate 103 facing upwards rather than downwards as would be the case in the actual sample.

Fig. 20 and Fig. 21 show SU-8 structures 2001 avoiding the formation of large bubbles.

The structure shown in Fig. 20 and Fig. 21 was fabricated using standard photolithography and micro-fabrication technologies. This can also be created using other technologies, for instance injection molding technology, Si micro -machining, embossing, printing or sandblasting.

A photograph of this structure is shown in Fig. 22 where the sample is illuminated from behind and the electrodes (made from Al) appear as dark horizontal lines. In this context, a voltage of 10V is applied between the two electrodes for a period of 2s. The voltage can, however, be anything above the threshold voltage required for electrolysis, 1.2V (though the pulse length would need to be adjusted to create the correct amount of gas).

For a voltage of 10 V and a pulse length of 2s, significant gas was created from a high density of nucleation sites, see Fig. 23.

After the 5 s period an image was taken and this is shown in Fig. 24. In this figure, it is clear that the periodicity of the gas bubbles roughly corresponds to the periodicity of the (pinning) wall structures. What is more, the position of bubbles is constant and after a period of 5 minutes no coalescence was observed. Upon repeating this experiment with the device vertically flipped then the pinning structures on the lower substrate are much less effective. This is shown in Fig. 25 and is simply due to the difference in density of water and gas, which causes the gas to float away from the lower substrate 102 on which the pinning structures 2001 are located. Optical methods (for instance, fluorescence) may be used to monitor reactions in micro fluidic devices. The index of refraction of the material used for the wall structures can be chosen to match that of the upper substrate to avoid any disturbance to the optical read-out from the chamber. Alternatively the structures can be purposely not index matched in order to allow alignment of the detector and sample for optical read-out.

The (pinning) structures 2001 may have a low thermal conductivity to avoid thermal leakage from the water 101 through the structures 2001.

In general when a thin homogeneous gas layer 109 is required in a small volume reaction well (typically 7x7x0.25 mm³ for 22 μl or smaller) then surface tension and capillary forces may prevent it from being homogenous.

The gas forms a bubble, as was illustrated in Fig. 18, or the liquid is forced along the surfaces via the capillary force, see Fig. 26.

In order to avoid this it is possible that the top glass surface 103, which interfaces with the gas 109, is covered with a layer 2701 of hydrophobic material (for example, Teflon).

This is illustrated in the sensor device 2700 shown in Fig. 27.

As a consequence of this hydrophobic layer 2701, it is energetically favourable for the liquid 101 to reduce or minimize the contact area to the top glass surface 103. The effect of the hydrophobic layer 2701 is shown schematically in Fig. 27. In order to further enhance the stability of the homogenous gas layer 109, a hydrophilic layer 2702 may be deposited on the inner-side of the lower substrate 102. This layer 2702, which can for example be created by treating the surface with an ozone-plasma, has a high affinity for the water of the sample liquid 101 and further lowers the energy of the situation shown in Fig. 27. This method may be used in combination with the above described method or sepa- rately.

When used in combination with the above described method, the surface or part of the surface of the structures 2001 may also be coated with a hydrophobic material. Alternatively the pinning structures 2001 themselves can be formed from a hydrophobic material. In both embodiments the thickness of the gas layer 109 is ultimately determined by the amount of gas produced via electrolysis. It is therefore important to accurately control the amount of current between the electrodes 112 and, consequently, the amount of gas 109 produced. The wall structures 104, 2702 should be sufficiently high to pin the gas 109 created. Nevertheless, it is important to realise that the height of the structures may be much smaller than the average thickness of the gas layer.

It should be noted that the term "comprising" does not exclude other elements or features and the "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.

Claims

1. A microfluidic device (100) for analysing a fluidic sample (101), the micro fluidic device (100) comprising a casing (102 to 104) enclosing a sample chamber (105); a thermal barrier supply mechanism (107) adapted for providing a thermal barrier (109) in an upper portion (108) of the sample chamber (105) to thermally decouple an upper portion (103) of the casing (102 to 104) from the fluidic sample (101) located in a lower portion (110) of the sample chamber (105).

2. The microfluidic device (100) of claim 1, wherein the casing (102 to 104) is completely closable or completely closed.

3. The microfluidic device (100) of claim 1, comprising a temperature controller (106), wherein the temperature controller (106) comprises a heater (111), particularly a resistive heater located in a lower portion (102) of the casing (102 to 104), particularly located exclusively in the lower portion (102) of the casing (102 to 104) formed by a first substrate (102) in which the temperature controller (106) is embedded, and adapted for controlling a temperature of the fluidic sample (101) located in the sample chamber (105).

4. The microfluidic device (100) of claim 1, wherein the thermal barrier supply mechanism (107) is adapted for filling the upper portion (108) of the sample chamber (105) with at least one of the group consisting of gas (109), air, a liquid having a low thermal conductivity, hollow particles, particles filled with a liquid, and massive particles, wherein the thermal barrier supply mechanism (107) is adapted for generating a gas (109) as the thermal barrier (109) by electrolysis, and wherein the thermal barrier supply mechanism (107) comprises at least one electrode (112) activatable for generating the gas (109) by electrolysis, and wherein the at least one electrode (112) is located on an inner surface of the upper portion (103) of the casing (102 to 104).

5. The micro fluidic device (100) of claim 1, wherein the thermal barrier supply mechanism (107) comprises an inlet (113) via which at least one of the group consisting of material forming the thermal barrier (109) and the fluidic sample (101) is tillable in the sample chamber (105), and wherein the thermal barrier supply mechanism (107) comprises a thermally insulating solid structure provided on the upper portion (103) of the casing (102 to 104).

6. The micro fluidic device (100) of claim 1, wherein the upper portion (103) of the casing (102 to 104) is free of a temperature controller.

7. The micro fluidic device (100) of claim 1, comprising a sensor-active structure (114) located at a surface of the lower portion (102) of the casing (102 to 104).

8. The micro fluidic device (2100) of claim 1, comprising a thermal barrier support unit (2001) adapted for supporting the thermal barrier (109) to remain essentially homogeneously located in the upper portion (108) of the sample chamber (105), wherein the thermal barrier support unit (2001) comprises protrusions extending from the upper portion (103) of the casing (102 to 104) into the sample chamber (105), and wherein the protrusions (2001) are made of a material for pinning the thermal barrier (109) at the upper portion (103) of the casing (102 to 104).

9. The microfluidic device (2700) of claim 8, wherein the thermal barrier support unit (2001 ) comprises a hydrophobic layer (2701 ).

10. The microfluidic device (2700) of claim 8, wherein the thermal barrier support unit comprises a hydrophilic lateral portion (2702) of the casing (102, 103, 2702).

11. The microfluidic device (100) of claim 1, wherein the casing (102 to 104) encloses a plurality of separate sample chambers (105).

12. The microfluidic device (100) of claim 1, adapted as at least one of the group consisting of a sensor device, a biosensor device, a biochip, a lab-on-chip, an electrophoresis device, a sample transport device, a sample mix device, a cell lysing device, a sample washing device, a sample purification device, a polymerase chain reaction device, and a hybridization analysis device.

13. The microfluidic device ( 100) of claim 1 , wherein at least a part of an electronic circuitry of the microfluidic device (100) is realized in low-temperature polysilicon technology.

14. The microfluidic device (100) of claim 1, wherein at least a part of the components of the microfluidic device (100) is integrated in the casing (102 to 104).

15. A method of operating a microfluidic device (100) of claim 1 , the method comprising filling the fluidic sample (101) in a lower portion (110) of the sample chamber (109); providing the upper portion (108) of the sample chamber (109) with the thermal barrier (109) to thermally decouple the upper portion (103) of the casing (102 to 104) from the fluidic sample (101) located in a lower portion (110) of the sample chamber (109).