Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
MICROFLUIDIC SYSTEM WITH ACTUATORS
Document Type and Number:
WIPO Patent Application WO/2008/125927
Kind Code:
A3
Abstract:
The invention relates to microfluidic system (100), particularly a biosensor, for manipulating a sample in a sample chamber (1). The device comprises at least one actuator (10) that reversibly changes its spatial configuration if it is heated and/or cooled. The actuator (10) may particularly be arranged adjacent to an associated heating element (20) of a 5 heating array that is used to establish a predetermined spatial and/or temporal temperature profile in the sample chamber (1). The configuration change of the actuator (10) can be used to move the sample fluid or to control its passage through fluid channels. A plurality of actuators (10) may optionally be provided that undergo their configuration changes at different temperatures, particularly temperatures within a range that is passed during a 10 reaction like PCR.

Inventors:
GILLIES MURRAY F (NL)
DEN TOONDER JACOB M J (NL)
PONJEE MARC W G (NL)
JOHNSON MARK T (NL)
Application Number:
PCT/IB2007/055104
Publication Date:
January 29, 2009
Filing Date:
December 14, 2007
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
KONINKL PHILIPS ELECTRONICS NV (NL)
GILLIES MURRAY F (NL)
DEN TOONDER JACOB M J (NL)
PONJEE MARC W G (NL)
JOHNSON MARK T (NL)
International Classes:
F04B19/00; B01L3/00
Domestic Patent References:
WO2006087655A12006-08-24
Foreign References:
US20030156991A12003-08-21
US20060069425A12006-03-30
Other References:
ANQUETIL P A ET AL: "Artificial Muscle Technology: Physical Principles and Naval Prospects", IEEE JOURNAL OF OCEANIC ENGINEERING, IEEE SERVICE CENTER, PISCATAWAY, NJ, US, vol. 29, no. 3, 1 July 2004 (2004-07-01), pages 706 - 728, XP011121556, ISSN: 0364-9059
Attorney, Agent or Firm:
SCHOUTEN, Marcus, M. et al. (AE Eindhoven, NL)
Download PDF:
Claims:
CLAIMS:

1. A micro fluidic system (100) for manipulating a sample, comprising a sample chamber (1); a heating device (20) that is adapted to establish a predetermined spatial and/or temporal temperature profile in the sample chamber (1); - at least one heat-sensitive actuator (10) that is disposed in the sample chamber (1) and that can reversibly change its spatial configuration upon a temperature change under predetermined operating conditions.

2. The micro fluidic system (100) according to claim 1, wherein the actuator (10) can move a surrounding sample fluid and/or block or free a fluid channel by its configuration change.

3. The micro fluidic system (100) according to claim 1, wherein the actuator (10) has the form of a strip (11) that can be changed between a rolled up and an extended spatial configuration.

4. The micro fluidic system (100) according to claim 1, wherein the actuator (10) comprises liquid crystals.

5. The micro fluidic system (100) according to claim 4, wherein the liquid crystals are embedded in an elastomer.

6. The microfluidic system (100) according to claim 4, wherein the liquid crystals contain molecules that undergo isomerization under the influence of light and/or heat.

7. The microfluidic system (100) according to claim 1, wherein the actuator (10) comprises materials with different thermal expansion coefficients.

8. The micro fluidic system (100) according to claim 1, wherein it comprises a plurality of such actuators (10) arranged in an actuator array.

9. The micro fluidic system (100) according to claim 8, wherein at least some of the actuators (10) have different transition characteristics.

10. The micro fluidic system (100) according to claim 1, wherein the actuator (10) changes its configuration at a transition temperature that is passed during a reaction taking place in the sample chamber (1).

11. The micro fluidic system (100) according to claim 1, wherein at least one heating element (20) is disposed adjacent to the actuator (10).

12. The micro fluidic system (100) according to claim 11, wherein the heating element (20) is adapted to operate in a pulsed mode.

13. The micro fluidic system (100) according to claim 1, wherein it comprises a plurality of heating elements (20) which have different heating characteristics, particularly different thermal resistances between the heating element (20) and an associated actuator (10).

14. The micro fluidic device (100) according to claim 1, wherein at least one light emitter is disposed adjacent to the actuator.

15. A method for manipulating a sample in a sample chamber (1), wherein the temperature inside the sample chamber (1) is controlled and wherein the spatial configuration of a heat-sensitive actuator (10) is changed by changing its temperature.

16. Use of the micro fluidic system (10) according to any of the claims 1 to 14 for molecular diagnostics, biological sample analysis, or chemical sample analysis, food analysis, and/or forensic analysis.

Description:

Micro fluidic system with actuators

FIELD OF THE INVENTION

The invention relates to a micro fluidic system for manipulating a sample comprising at least one actuator, the use of such a device, and to a method for manipulating a sample.

BACKGROUND OF THE INVENTION

From the US 2005/0152808 Al, a microfluidic device for the investigation of fluids is known which comprises actuators serving as pumps or valves that are controlled by heating elements. The actuators comprise a wax plug that can be molten and then be moved by expanding gas bubbles. Said actuators are rather complicated and need several heating elements for melting and moving the wax plug.

Based on this situation it was an object of the present invention to provide means for manipulating a sample that can be integrated in a cost effective way into usual microfluidic systems.

SUMMARY OF THE INVENTION

This objective is achieved by a microfluidic system according to claim 1, a method according to claim 18, and a use according to claim 19. Preferred embodiments are disposed in the dependent claims. The microfluidic system according to the present invention is intended for the manipulation of a sample, particularly a liquid or gaseous chemical substance like a biological body fluid which may contain particles. The term "manipulation" shall denote any interaction with said sample, for example measuring characteristic quantities of the sample, investigating its properties, transporting it, processing it mechanically or chemically or the like. The microfluidic system comprises the following components, of which at least some belong to a microfluidic device:

A sample chamber in which the sample to be manipulated can be provided. The sample chamber is typically an empty cavity or a cavity filled with some substance like a gel that may absorb a sample substance; it may be an open cavity, a closed cavity, or a cavity

connected to other cavities by fluid connection channels. The sample chamber is typically a part of a microfluidic device.

A heating device that is adapted to establish a predetermined spatial and/or temporal temperature profile in the sample chamber. The heating device may be integrated into a microfluidic device or be an external device with respect to the microfluidic device. At least one heat-sensitive actuator that is disposed in said sample chamber and that can controlledly change its spatial configuration upon a temperature change under predetermined operating conditions. In this context, the "change of a configuration" shall imply a transition between two different shapes that are not simply related to each other by a scaling of their sizes; such a configuration change is therefore different from the usual expansion or shrinking that all homogeneous materials experience if temperature changes. Moreover, it should be noted that the actuator changes its configuration only if predetermined operating conditions prevail, for example a certain transition temperature, wherein said operating conditions may of course also comprise a continuous interval of values. The actuator is typically a solid, structured object composed of different materials. Particular examples of actuators will be described in connection with preferred embodiments of the invention. The temperature change may for example be effected by heating, cooling or illuminating the actuator.

The described microfluidic system has the advantage that a simple change of temperature suffices to control the actuator, wherein said temperature change can be achieved with the help of the heating device that is typically already present for other purposes. The configuration change of the actuator can be used for many different purposes, e.g. for moving objects (cells, particles etc.) or fluid in the sample chamber. Preferably, the actuator is designed such that it can move a surrounding sample fluid and/or block or free a fluid channel. The actuator can thus serve as a pump or a valve in the microfluidic system.

According to a preferred embodiment of the invention, the actuator has the form of a strip that can be changed between a rolled up and an extended spatial configuration. Such an actuator can be produced comparatively easily, for example by generating layered structures with methods known from microelectronics.

There are various possibilities to design an actuator that changes its configuration if heat or light (generating heat by absorbance) are applied, e.g. by using memory materials. According to a preferred embodiment, the actuator comprises liquid crystals that crystallize or melt, respectively, under the influence of heat, light, electrical

fields etc. Detailed information about liquid crystals and particular materials that can be applied in connection with the present invention can be found in the literature (for example: Dirk J. Broer, Henk van Houten, Martin Ouwerkerk, Jaap M.J. den Toonder, Paul van der Sluis, Stephen I. Klink, Rifat A.M. Hikmet, Ruud Balkenende, "Smart Materials", Chapter 4 in "True Visions: Tales on the Realization of Ambient Intelligence", ed. by Emile Aarts and Jose Encarnacao, Springer Verlag, 2006, which is incorporated into the present application by reference).

In the aforementioned case, the liquid crystals are preferably incorporated in an elastomer network, e.g. in polysiloxane. Changes of size or shape of the liquid crystals can then induce corresponding movements of the elastomer, for example in a way similar to the action of muscles at the joints of an arm.

The liquid crystals mentioned above preferably contain molecules that undergo isomerization under the influence of light and/or heat, wherein said molecules may particularly comprise azo-benzene groups. In another preferred embodiment, the actuator is a heterogeneous system and comprises materials with a different thermal expansion coefficient, such that upon temperature increase of the actuator the shape of the actuator configuration changes. The temperature increase may be due to applying heat from an external source to the actuator or by internal heat generation in the actuator (e.g. infrared radiation absorption). While the microfluidic system may in principle comprise just one single actuator of the kind described above, it is preferred that it comprises a plurality of such actuators that are arranged in an "actuator array". In the most general sense, the term "array" shall in the context of the present invention denote an arbitrary three-dimensional arrangement of a plurality of elements (e.g. actuators). Typically such an array is two- dimensional and preferably also planar, and the elements are arranged in a regular pattern, for example a grid or matrix pattern.

In the aforementioned case, at least some of the actuators may optionally have different characteristics of the transition of their configuration, for example different transition temperatures at which they change their spatial configuration. Such a spread of transition characteristics has the advantage that, if the sample chamber is uniformly heated, the actuators do not all change their configuration simultaneously. In this way there are always some actuators during e.g. the heating of a sample chamber that change their configuration and thus guarantee a continuous mixing of the sample.

In a further development of the aforementioned embodiment, the actuators with different transition characteristics are distributed in a regular or in a random pattern across the actuator array to provide a spatially uniform and/or coordinated effect.

The at least one heat-sensitive actuator preferably changes its configuration at a transition temperature that is passed during a (physical, chemical or biochemical) reaction taking place in the sample chamber, particularly during a temperature controlled DNA amplification process such as polymerase chain reaction (PCR). The activity of the actuator(s) is then immediately linked to the processes that take place in the sample chamber, which is beneficial as no extra measures are needed to control it. In a preferred embodiment of the invention, a heating element is disposed adjacent to the at least one heat-sensitive actuator, wherein said heating element is by definition able to exchange heat with the actuator, i.e. to heat or to cool it. By selectively controlling the heating element, configuration changes of the actuator can then be induced as desired. Such a control of the actuator may be the only purpose of the heating element. Typically, the heating element has, however, the additional (or even primary) function of exchanging heat with a sample in the sample chamber, and it may be a component of the heating device mentioned above.

The micro fluidic system may particularly comprise a plurality of such heating elements which are arranged in a heating array. If the micro fluidic system further comprises an actuator array, the heating elements and the actuators are preferably aligned with respect to each other. Each actuator may for example have one heating element in its vicinity.

In a further development of the embodiment with at least one heating element, said heating element is preferably adapted to operate in a pulsed mode. The resulting pulsation of the heat exchange with the associated actuator allows to effect repeated configuration changes of the actuator. Preferably, the pulsed operation of the heating element is designed such that the pulses average out in the sample chamber. In this case, a constant temperature can be maintained in the sample chamber while the actuator in the immediate vicinity of the heating element experiences temperature fluctuations.

If the micro fluidic system comprises a plurality of actuators and associated heating elements, said heating elements are preferably adapted to generate a temporal and/or spatial coordination of the actuators. The heating elements may for example be activated such that a spatial wave of activation sweeps across the array of actuators. If the heating elements are operated in the aforementioned pulsed mode, the pulses in neighboring heating elements

may be shifted with respect to each other to assist the averaging of temperatures in the sample chamber.

In another embodiment of the invention, the micro fluidic system comprises a plurality of heating elements that have different heating characteristics. The heating elements may in particular have differently tight thermal couplings to associated actuators and/or to the sample chamber. Even if all these heating elements are driven identically, e.g. with the same current, or even if the sample chamber is homogeneously heated, the resulting temperature increases in the associated actuators will be different. This guarantees that the activation of actuators (with identical transition temperatures) is spread in time during a heating process. The heating elements may particularly comprise a resistive strip, a transparent electrode, a Peltier element, a radio frequency heating electrode, or a radiative heating (IR) element. All these elements can convert electrical energy into heat, wherein the Peltier element can additionally absorb heat and thus provide a cooling function.

In another embodiment of the invention, the micro fluidic device comprises at least one light emitter, for example a Light Emitting Diode (LED) that is disposed adjacent to the actuator. In this case, a selective control of the light emitter can be used to induce configuration changes of the associated actuator.

The invention further relates to a method for the manipulation of a sample in a sample chamber, wherein the temperature inside the sample chamber is controlled and wherein the spatial configuration of a heat-sensitive actuator is changed by changing its temperature (e.g. by heating, cooling, or illuminating said actuator).

The method comprises in general from the steps that can be executed with a microfluidic system of the kind described above. Therefore, reference is made to the preceding description for more information on the details, advantages and improvements of that method.

The invention further relates to the use of the microfluidic systems described above for molecular diagnostics, biological sample analysis, chemical sample analysis, food analysis, and/or forensic analysis. Molecular diagnostics may for example be accomplished with the help of magnetic beads that are directly or indirectly attached to target molecules.

BRIEF DESCRIPTION OF THE FIGURES

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. These embodiments will be described by way of example with the help of the accompanying drawings in which:

Fig. 1 schematically shows a planar view (left) and a cross section (right) of a microfluidic system according to the present invention;

Fig. 2 schematically shows an actuator and an associated heating element of the microfluidic system of Fig. 1; Fig. 3 shows a typical temperature variation as a function of time for a PCR;

Fig. 4 shows a DC current supply (top) and a pulsed current supply (bottom) to the heating element of Fig. 2;

Figs. 5 and 6 show a cross section and a planar view, respectively, of an actuator that is used to induce pressure waves at a hydrophilic or hydrophobic stop. Like reference numbers in the Figures refer to identical or similar components.

DETAILED DESCRIPTION

Biochips for (bio)chemical analysis, such as molecular diagnostics, will become an important tool for a variety of medical, forensic and food applications. In general, biochips comprise a biosensor in most of which target molecules (e.g. proteins, DNA) are immobilized on biochemical surfaces with capturing molecules and subsequently detected using for instance optical, magnetic or electrical detection schemes. Examples of magnetic biochips are described in the WO 2003/054566, WO 2003/054523, WO 2005/010542 A2, WO 2005/010543 Al, and WO 2005/038911 Al, which are incorporated into the present application by reference.

In many of the assays that can be carried out on such "lab-on-a-chip" devices, environment processing steps involving heating of the sample are essential. An example of this is a thermal controlled DNA amplification process, such as the polymerase chain reaction (PCR), which is an enzymatic method to amplify DNA by repeating a series of thermally controlled reaction steps. In the PCR the number of amplified DNA molecules is

(theoretically) doubled during each cycle. Typically, the thermocycling consists of three steps: melting of the double stranded DNA (denaturisation) to separate complementary strands, binding of the specific primers to the target site (annealing), and extension of the primers by a thermostable enzyme such as Taq polymerase (extension). Typical temperatures for the denaturisation, annealing and extension steps are 94°, 40-72°, and 72°C, respectively. While PCR has been applied for many years in biochemistry labs around the world it is only recently, with the advent of lab-on-a-chip technology, that PCR has been performed on small volumes of material (typically 0.01-50 μl).

Moreover, the specificity of a biosensor is improved by accurate control of the temperature. Temperature control is used during a hybridization assay to regulate stringency of the binding of a target biomolecule to a functionalized surface, e.g. the binding of a DNA strand to its complementary strand. A high stringency, and therefore accurate temperature control, is required when for instance single point mutations are of interest.

Besides being of high importance for PCR and related methods, and hybridization assays, temperature control on a biochip (lab-on-a-chip) is needed in general. For example because many bio molecules are stable in a small temperature window (usually around 37°C), or become de-activated when temperatures are outside of this temperature window.

For the reasons explained above, it is very important to have a means for versatile temperature control on a biochip. Fig. 1 shows in this respect an exemplary embodiment of a microfluidic system 100 that can be used for the examination of a (e.g. biological) sample in a sample chamber 1. The device 100 comprises an array of individually addressable heating elements 20, e.g. resistive strips, that are realized in the shown example on the upper side of the sample chamber 1 in a substrate 51. A further substrate 52 is arranged on the bottom side of the sample chamber 1 in which an array of sensor elements 53 is realized. With the help of said sensor elements 53, it is for example possible to detect target particles 2 (e.g. labeled biological molecules) in a sample filling the sample chamber 1. Whilst the invention is not limited to any particular type of biosensor, it can be advantageously applied to biosensors based upon optical (e.g. fluorescence), magnetic or electrical (e.g. capacitive, inductive...) sensing principles.

The heating array with its heating elements 20 can be used to either maintain a constant temperature across the entire sensor area, or alternatively to create a defined temporal temperature profile. It may optionally comprise additional elements such as temperature sensors to enable a closed-loop control of temperature. It should be noted, however, that the invention is not limited to sensor devices with such a heating array, and that any other kind of heating device could be used to achieve desired temperatures and temperature gradients in the sample chamber. Fig. 1 further shows a plurality of actuators 10 that are distributed in an actuator array across the top surface of the sample chamber 1, wherein said actuator array is in this case more sparsely occupied than the heating array. The heating elements 20 and the actuators 10 are aligned in such a way that each actuator 10 is disposed in the immediate vicinity of an associated heating element 20, particularly between the heating element 20 and

the sample chamber 1. As will be explained below, the actuators 10 are designed such that they can be activated by heat emitted by the associated heating element 20.

Fig. 2 shows in this respect a more detailed, schematic cross section through an actuator 10 and the associated heating element 20. The heating element 20 is for example realized by a resistance 21 coupled to a driving and control unit 22 that selectively provides a driving current I.

The actuator 10 consists of a film or strip 11 that is typically between 15 and 100 μm in length and made from a temperature-responsive actuating material. By incorporating liquid crystal (LC) material into an elastomeric network, a configuration system can for example be made which upon heating through a specific temperature (the nematic isotropic temperature) undergoes a transition in the backbone of the elastomer molecules and changes length. A careful control of processing conditions allows to obtain a gradient in orientation of LC molecules over the thickness of the film so that one side of the film contracts while the other expands (G.N. MoI, K.D. Harris, G.W.M. Bastiaansen, D.J. Broer, "Thermo-mechanical responses of liquid-crystal networks with a splayed molecular organization", Adv. Funct. Mater. (2005), vol. 15, 1155-1159). This creates a reversible rolling up of the film at a specific transition temperature. Fig. 2 shows a rolled up configuration in bold and an extended configuration in dotted lines. The frequency at which the actuator can be thermally actuated depends on the heater characteristics, the thermal coupling between actuator and heater, the thermal capacity of the heater, the thermal response of the actuator, the cooling rate of heater and actuator, etc.

The actuator 10 may also comprise materials that can be heated by the absorption of light.

The suggested integration of the LC-elastomer (LCE) type structures can be used to produce either mixing of a fluid as it is heated for other purposes or to produce a fluid flow via heating arrays placed under heat activated structures. Particular examples of such applications will be described in more detail in the following.

A first application relates to a chamber 1 with homogenous heater geometry as the one shown in Fig. 1, which can be used for DNA amplification, e.g. using PCR. A typical PCR temperature cycle, as it will be applied for PCR of small volumes, can be found in Fig. 3. It comprises a period during which the sample is held at 72°C, wherein the length of this period is dependent on the type of enzyme used for multiplication and the size of the DNA to be replicated. In some protocols this period may not even be necessary. For this application, it is suggested to engineer actuators 10 on top of the PCR heaters 20 that undergo the rolling

process during the temperature gradient experienced by the sample as it is heated or cooled between 50 and 100 0 C.

It is possible to tune the exact temperature at which the actuator experiences rolling. In the case of an LCE based actuator this may be tuned by varying the geometry of the area that is to roll. It is therefore possible to engineer different geometries to create a series of actuator structures which each roll sequentially at different temperatures between 50 and 100 0 C. The rolling of the structures will then create a chaotic mixing in the PCR chamber 1 and result in increased mixing of the fluid and a more homogeneous temperature. In the aforementioned embodiment, increased mixing of the fluid will take place during heating or cooling of the fluid. When, however, the temperature is in a plateau then the actuator will not roll or unroll and therefore no extra mixing will be achieved in these crucial periods. This can be overcome by making use of the fact that the actuators 10 are located directly on top of the heaters 20: During a period when the temperature is to be constant, it is suggested to pulse the current I supplied to the heater array instead of using a constant DC current. The pulses should be chosen to average out in the fluid but to produce a fluctuating temperature in the layer directly above the heaters 20, wherein the fluctuating temperatures should be sufficient to allow the actuators 10 to actuate the fluid. Fig. 4 shows the DC current supply to the heaters 20 for the first embodiment (upper diagram) and the pulsed current supply for the aforementioned second embodiment (lower diagram; current I in arbitrary units). Parameters of the pulse characteristics that may be used to control the heating comprise the frequency, the offset, the pulse-height, the pulse-width, etc. A single parameter or a combination of parameters may be used to create a waveform to drive the heating element. Moreover, waveforms of different heating elements may be related to one another, e.g. be in-phase or out-of-phase. This provides options to average out the pulse effect in the fluid (e.g. by pulsing out-of-phase actuators that are positioned close to one another), or to create specific manipulation (e.g. flow) patterns (e.g. line-by-line pulsing).

Alternatively or additionally to the described use of an oscillating heater current, one could also engineer the heaters 20 so that they are non-homogeneous, e.g. with different thermal resistances between them and the sample chamber/actuators. This would result in some areas of the sample warming quicker than other parts. Furthermore, the temperature gradient would result in the actuator structures 10 rolling up at different periods in time and also increase the mixing.

By the integration of different technologies, a microfluidic system can be created with a variety of functionalities, for example heater arrays for thermal processing,

micro-fluidic structures and particle manipulation electrodes/electronics. If, for example, thermal processing is integrated on a lab-on-a-chip platform then there is no extra cost in creating subsequent heaters on other areas of the glass substrate; this facilitates the suggested use of heat-sensitive actuators on top of a heater (which is only present to actuate the actuator) to allow pumping of a fluid. Alternatively an actuator structure 10 could be used to generate a pressure- wave to overcome a hydrophobic or hydrophilic stop in a micro fluidic channel. This is illustrated in a cross-sectional view in Fig. 5 and a corresponding planar view in Fig. 6. Heaters 20 cause a rolling or unrolling of the actuator structure 11, which in turn moves a droplet of sample fluid 2 through the channel. The use of heat-sensitive actuators avoids the problems of electrolysis of the water based biological fluids that occur if direct electrical actuation is used.

It should be understood that the invention is not limited to the described applications, e.g. PCR. The invention can advantageously be used in general for DNA amplification and other (bio-)chemical processes, such as DNA hybridization or bonding of proteins to anti-bodies, or DNA extraction.

In summary, it is suggested to use a thermally actuated device to pump or mix biological fluids in a lab-on-a-chip environment (i.e. molecular diagnostic device). These fluid actuators can be equipped with a heater modality specifically designed to actuate the device or can use the already existing heat sources used for instance for DNA amplification (e.g. PCR), temperature control of the biosensor and other thermal reactions on the chip. The thermally actuated mixing structures can advantageously respond to an already necessary temperature variation in a sample. An alternative is to use heat-sensitive actuators that experience a temperature change by absorption of electromagnetic radiation (e.g. infrared radiation). Finally it is pointed out that in the present application the term "comprising" does not exclude other elements or steps, that "a" or "an" does not exclude a plurality, and that a single processor or other unit may fulfill the functions of several means. The invention resides in each and every novel characteristic feature and each and every combination of characteristic features. Moreover, reference signs in the claims shall not be construed as limiting their scope.