EP2143948A2 - Microfluidic system for displacement of a fluid - Google Patents

Abstract

The device has an opening (11B) located at a level of an end (12B) of a microchannel (10). Electrically conducting liquid (F1) partially fills the microchannel in a longitudinal direction, and electrically insulating fluid (F2) e.g. air, forms an interface (I1) with the fluid (F1). Fluid (F3) e.g. medicine or radioactive tracer, forms an interface (I3) with the insulating fluid. Displacement units displace the fluid (F1) to induce displacement of the insulating fluid through the opening, and have a dielectric layer (40) directly covered with a hydrophobic layer. The conducting fluid is constituted by aqueous solution charged with ions.

Description

TECHNICAL AREA

The present invention relates to the general field of microfluidics and relates to a microchannel liquid displacement device.

The invention applies in particular to the injection of liquid out of the device provided for this purpose, for the purpose of performing biochemical, chemical or biological analyzes, or for therapeutic purposes.

STATE OF THE PRIOR ART

Microfluidics has been a field of research that has been booming for the past ten years, mainly because of the development and development of chemical or biological analysis systems, called lab-on-chips .

Indeed, microfluidics can effectively handle small volumes of liquid. It is then possible to perform on the same support all the steps of analysis of a liquid sample, in a relatively short time and using small volumes of sample and reagents.

Depending on the application, handling small volumes of liquid sometimes requires an injection of a defined volume of liquid in a given area.

For example in the medical field, an application may require injecting a defined volume of liquid into the body of a patient for the purpose of treatment or for the purpose of establishing a diagnosis. The liquid can then be a drug, a radioactive tracer, or any other suitable substance.

For this, a liquid displacement device for injecting it into a medium outside the device is necessary. It is essential that the displacement device presents no risk, in terms of safety, for the body or the area intended to receive the liquid to be injected. In addition, it is essential to control both the amount of liquid injected and the injection rate.

The document US-A1-2003 / 006140 discloses a liquid spray device in the form of droplets by variable dielectric pumping, whose operating principle is based on the phenomenon of dielectrophoresis.

The operation is as follows, with reference to figure 1 which schematically represents the device according to the prior art in a longitudinal section.

A microchannel A10 comprises an inner wall whose lower and upper faces each comprise a flat electrode A31, A32 extending along the longitudinal axis of the microchannel and disposed facing one another.

An insulating liquid plug AF ₁ is located between these electrodes, surrounded upstream and downstream along the longitudinal axis by an insulating surrounding fluid AF ₂ . We call a liquid droplet a big drop length contained in a channel or tube. The terms upstream and downstream are defined with reference to the X direction parallel to the axis of the microchannel A10.

The AF ₁ liquid plug has a higher permittivity value than the surrounding fluid AF ₂ .

An electric field is generated between the two electrodes A31 and A32, which has a gradient along the longitudinal axis of the microchannel. For this, a potential difference is applied to the ends of the electrode A31 while the potential of the electrode A32 is fixed.

The displacement of the liquid plug AF ₁ along the longitudinal axis of the microchannel A10 is then obtained by dielectrophoresis. More precisely, the displacement results from the appearance of a so-called dielectrophoretic force resulting from the difference in permittivity between the liquid plug AF1 and the surrounding fluid AF ₂ , and the electric field gradient resulting from the applied voltages. The dielectrophoretic force tends to attract the high permittivity liquid, here the liquid AF ₁ , to the high intensity areas of the electric field.

The variation of the applied voltages makes it possible to control the displacement of the liquid plug AF ₁ , and consequently of the surrounding fluid AF ₂ , along the longitudinal axis of the channel A10.

The microchannel A10 further has at one end A12B an opening A11B for ejection by spraying a liquid AF ₃ . The spray liquid AF ₃ is placed between the AF fluid ₂ and the opening A11B.

Thus, the displacement of the liquid plug AF ₁ towards the end A12B of the microchannel A10 causes a displacement of the liquid AF ₃ in the same direction and the spraying thereof in the form of droplets through the opening A11B.

The liquid ejection device according to the prior art, however, has a number of disadvantages.

Dielectric pumping by dielectrophoresis requires the use of high electrical voltages, which may be limiting depending on the applications of the ejection device. Thus, for a medical application in which the device is used near a surface to be treated sensitive to electric fields, such as the body of a patient, the device according to the prior art obviously has a security problem.

In addition, the dielectrophoretic force depends on the height d of the dielectric at (d ^-1 ) , that is the height of the insulating liquid plug AF1 between the electrodes A31 and A32. In the case of the use of a high microchannel, for example a few hundred micrometers, it is necessary to substantially increase the intensity of the applied electric field to obtain a force of sufficient intensity, which, d on the one hand increases the risks for the surface to be treated, and on the other hand complicates the control electronics and requires bulky batteries.

In addition, the power consumption is important to produce a high intensity electric field.

Moreover, the operating principle of the dielectric pump makes the device according to the prior art limited to the use of two dielectric liquids AF ₁ and AF ₂ and excludes any electrically conductive liquid.

Finally, the arrangement of the electrodes A31 and A32 forms the air gap of a planar capacitor. The device is then limited to a microchannel of rectangular cross section. A square cross section would show edge effects of the electric field that would penalize the dielectrophoretic force and therefore the operation of the device according to the prior art. In addition, the arrangement of the electrodes A31 and A32 in a microtube, that is to say a microchannel with circular cross section, is not feasible in a simple manner.

One solution to avoid these drawbacks could be the use of a mechanical piston disposed inside the microchannel and exerting a pressing force on the liquid to be sprayed. However, there are significant risks of leaks between the piston and the walls of the microchannel that can render inoperative the liquid displacement device.

STATEMENT OF THE INVENTION

The object of the present invention is to remedy at least in part the aforementioned drawbacks and to provide in particular a liquid displacement device whose displacement is obtained by the generation of a low intensity electric field.

To do this, the invention relates to a liquid displacement device, comprising at least one substrate comprising a microchannel, said microchannel having a first end and a second end, substantially opposite one another in the longitudinal direction. the microchannel, an opening on the surrounding medium being located substantially at said second end.

• un premier liquide remplissant partiellement le microcanal dans le sens longitudinal du microcanal,
• un fluide situé en aval dudit premier liquide en direction de la seconde extrémité et formant avec le premier liquide une première interface, ladite première interface étant située dans une portion de contrôle du microcanal, et
• un second liquide situé en aval dudit fluide en direction de la seconde extrémité et formant avec le fluide une seconde interface.

Said device comprises:

• a first liquid partially filling the microchannel in the longitudinal direction of the microchannel,
• a fluid located downstream of said first liquid towards the second end and forming with the first liquid a first interface, said first interface being located in a control portion of the microchannel, and
• a second fluid located downstream of said fluid towards the second end and forming with the fluid a second interface.

According to the invention, the device comprises means for moving the first liquid by electrowetting, the first liquid being electrically conductive and the electrically insulating fluid, the displacement of the first liquid inducing the displacement of the second liquid, via the fluid, through said opening.

• au moins un premier moyen électriquement conducteur,
• une couche d'un matériau diélectrique recouvrant directement le premier moyen conducteur, ladite couche diélectrique étant au moins partiellement mouillée par ledit premier liquide,
• au moins un second moyen électriquement conducteur formant contre-électrode, en contact avec le premier liquide, et
• un premier générateur de tension pour appliquer une différence de potentiel entre lesdits premier et second moyens conducteurs.

Said means for moving the first liquid by electrowetting can comprise:

• at least one first electrically conductive means,
• a layer of a dielectric material directly covering the first conductive means, said dielectric layer being at least partially wetted by said first liquid,
• at least a second electrically conductive means forming a counter electrode, in contact with the first liquid, and
• a first voltage generator for applying a potential difference between said first and second conductive means.

According to one embodiment of the invention, the substrate comprising the control portion being electrically conductive, the first electrically conductive means comprises the conductive substrate.

Preferably, the microchannel comprises an injection portion extending substantially from the opening towards the control portion, said second interface being located in the injection portion. In this case, a stack of a first layer of a dielectric material, an electrically conductive means that can be brought to a determined potential, and a second layer of a dielectric material is disposed on the inner wall of the injection portion so as to electrically isolate the second liquid from the conductive substrate. Each element of said stack has a substantially equal length in the longitudinal direction of the injection portion.

According to one embodiment of the invention, said first electrically conductive means comprises at least one at least one electrode disposed on at least a portion of the wall in the longitudinal direction of the microchannel and located in the control portion.

Advantageously, said first electrically conductive means comprises an electrode extending over the entire length of the control portion.

Preferably, the liquid displacement device comprises a reservoir communicating with the microchannel through an opening located at the first end and containing said first conductive liquid.

Said first electrically conductive means may comprise an array of electrodes extending over the entire length of the control portion.

Advantageously, the first liquid forms a liquid plug surrounded by fluid so as to form a rear interface and a front interface, the two interfaces being located in the control portion.

Advantageously, the displacement of the first interface towards the first end of the microchannel causes aspiration of the second liquid through the opening towards the first end.

Said electrode may comprise two parts parallel to each other.

Preferably, said electrode extends over the entire perimeter of the control portion. Thus, said electrode comprises only a part whose circumferential surface is substantially continuous.

Advantageously, said layer of dielectric material is covered directly with a layer of hydrophobic material.

The microchannel may have a convex polygonal cross section.

Alternatively, the microchannel may have a substantially circular cross section.

According to one embodiment of the invention, the microchannel has a plurality of control portions arranged in series, each control portion being partially filled with the first liquid and fluid.

According to another embodiment of the invention, the microchannel has a plurality of control portions arranged in parallel, each control portion being partially filled with the first liquid and fluid.

The longitudinal axis of the control portions may be substantially perpendicular to the longitudinal axis of the injection portion.

According to one embodiment of the invention, the height of the injection portion is substantially greater than the height of the control portion.

Advantageously, the height of the injection portion is between substantially 10 and 50 times the height of the control portion.

A connecting portion may connect the control portion to the injection portion, the connector portion being filled with fluid only.

According to one embodiment of the invention, the microchannel comprises an injection portion extending substantially from the opening towards the control portion, said second interface being located in the injection portion. A second liquid filling system is then connected to the microchannel at the injection portion, and comprises a reservoir filled with a second liquid communicating with the injection portion via a valve.

This can be a three-way valve.

• un premier état dit de remplissage, dans lequel le réservoir communique avec la partie de stockage,
• un second état dit d'injection, dans lequel l'écoulement de second liquide provenant du réservoir est bloqué, la partie de stockage communiquant avec la partie d'injection.

Said valve may be arranged to share the injection portion in a storage portion communicating with the control portion and in which the second interface is located, and an injection portion communicating with the opening of the second end, and can be adapted to occupy alternately two states:

• a first so-called filling state, in which the reservoir communicates with the storage part,
• a second so-called injection state, wherein the flow of second liquid from the reservoir is blocked, the storage portion communicating with the injection portion.

• une partie de stockage propre à chaque microcanal, communiquant avec chaque portion de contrôle, dans laquelle est située la seconde interface, et
• une partie d'injection commune aux deux microcanaux communiquant avec l'ouverture de la seconde extrémité,

According to one variant, two microchannels are arranged in parallel and interconnected so as to have in common the second end provided with the opening, each microchannel comprising an injection portion extending substantially from the opening towards the respective control portion, said second interface being located in the injection portion. A second filling system liquid is connected to the microchannels so as to share each injection portion in:

• a storage portion specific to each microchannel, communicating with each control portion, in which the second interface is located, and
• an injection portion common to both microchannels communicating with the opening of the second end,

said filling system comprising a tank filled with second liquid communicating with the microchannels via a valve.

Said valve may be a four-way valve.

• un premier état, dans lequel le réservoir communique avec la partie de stockage d'un premier microcanal alors que la partie de stockage du second microcanal communique avec la partie d'injection,
• un second état, dans lequel le réservoir communique avec la partie de stockage du second microcanal alors que la partie de stockage du premier microcanal communique avec la partie d'injection.

It can be adapted to occupy alternately two states:

• a first state, in which the reservoir communicates with the storage part of a first microchannel while the storage part of the second microchannel communicates with the injection part,
• a second state, wherein the reservoir communicates with the storage portion of the second microchannel while the storage portion of the first microchannel communicates with the injection portion.

The flow of second liquid through the opening may be constant.

Advantageously, the liquid displacement device comprises a system for controlling the displacement of the first liquid as a function of the position of the first interface or the second fluid interface located in the microchannel, said system for controlling the displacement of the first liquid comprising a capacitive measuring device for controlling the displacement of the first liquid as a function of the value of the measured capacitance.

• ladite électrode de contrôle formant électrode de détection,
• ladite contre-électrode de contrôle formant contre-électrode de détection,
• un second générateur de tension pour appliquer une différence de potentiel entre ladite électrode de détection et ladite contre-électrode de détection,
• des moyens de mesure de la capacité formée entre ladite électrode de détection et ladite contre-électrode de détection.

According to one embodiment, the capacitive measuring device is adapted to determine the position of the first interface, and comprises:

• said sensing electrode control electrode,
• said counter-control electrode forming a counterelectrode of detection,
• a second voltage generator for applying a potential difference between said sensing electrode and said sensing counter-electrode,
• means for measuring the capacitance formed between said detection electrode and said counterelectrode of detection.

• au moins une électrode de détection disposée sur au moins une partie de la paroi du microcanal définissant une portion de détection située en aval de ladite portion de contrôle, ladite seconde interface étant située dans ladite portion de détection,
• un moyen électriquement conducteur formant contre-électrode de détection, en contact avec le second liquide,
• un second générateur de tension pour appliquer une différence de potentiel entre ladite électrode de détection et ladite contre-électrode de détection,
• des moyens de mesure de la capacité formée entre ladite électrode de détection et ladite contre-électrode de détection.

According to a variant, the capacitive measuring device is adapted to determine the position of the second interface, and comprises:

• at least one detection electrode disposed on at least a portion of the wall of the microchannel defining a detection portion located downstream of said control portion, said second interface being located in said detection portion,
• an electrically conductive means forming a counterelectrode of detection, in contact with the second liquid,
• a second voltage generator for applying a potential difference between said sensing electrode and said sensing counter-electrode,
• means for measuring the capacitance formed between said detection electrode and said counterelectrode of detection.

The capacitive measuring device may comprise calculation means, connected to the measurement means, for determining the position of the interface as a function of the value of the measured capacitance.

The capacitive measuring device may comprise control means, connected to the calculation means and to the first voltage generator, for controlling the value of the potential difference applied by the latter.

According to one embodiment, the second liquid being electrically conductive, a layer of a dielectric material covers the detection means.

According to one variant, the second liquid is dielectric, whose value of the permittivity is different from that of the fluid.

Preferably, the measuring means comprise a capacitor connected in series with the detection means, and a voltmeter for measuring the voltage across said capacitor.

Alternatively, the measuring means comprise an impedance analyzer.

Said detection means may comprise a plurality of elementary detection electrodes.

In this case, said substrate can be brought to a potential determined by an electrically conductive means. This advantageously comprises an electrode disposed on an outer face of the substrate and extending over the entire length of the detection means.

Other advantages and features of the invention will become apparent in the detailed non-limiting description below.

BRIEF DESCRIPTION OF THE DRAWINGS

• La figure 1, déjà décrite, est une représentation schématique en coupe longitudinale d'un dispositif de pulvérisation de liquide selon l'art antérieur ;
• Les figures 2A à 2C représentent le principe de fonctionnement de déplacement de gouttes par électromouillage ;
• La figure 3 représente le principe de fonctionnement de déplacement de liquide par électromouillage, dans une configuration fermée de dispositif de déplacement de liquide ;
• Les figures 4A et 4B sont des représentations schématiques en coupe longitudinale d'un dispositif de déplacement de liquide selon le premier mode de réalisation préféré de l'invention, pour deux étapes du fonctionnement ;
• La figure 5 est une représentation schématique en coupe longitudinale d'un dispositif de déplacement de liquide selon une variante du premier mode de réalisation préféré de l'invention, dans laquelle une matrice d'électrodes de contrôle est prévue ;
• La figure 6 est une représentation schématique en coupe longitudinale d'un dispositif de déplacement de liquide selon le second mode de réalisation préféré de l'invention ;
• La figure 7 est une représentation schématique en coupe longitudinale d'un dispositif de déplacement de liquide selon un troisième mode de réalisation de l'invention, dans lequel une pluralité de portions de contrôle disposées en série est prévue ;
• La figure 8 est une représentation schématique en coupe longitudinale d'un dispositif de déplacement de liquide selon un quatrième mode de réalisation de l'invention, dans lequel une pluralité de portions de contrôle disposées en parallèle est prévue ;
• La figure 9 est une représentation schématique en coupe longitudinale d'une partie du microcanal du dispositif de déplacement de liquide selon un cinquième mode de réalisation de l'invention, permettant de diminuer les effets de l'hystérésis de l'angle de contact ;
• Les figures 10A et 10B sont des représentations schématiques en coupe longitudinale d'un dispositif de déplacement de liquide selon un sixième mode de réalisation de l'invention, pour deux étapes du fonctionnement ;
• Les figures 11A et 11B sont des représentations schématiques en coupe longitudinale d'un dispositif de déplacement de liquide selon une variante du sixième mode de réalisation de l'invention, pour deux étapes du fonctionnement ;
• Les figures 12A, 12B, 13A et 13B sont des représentations schématiques en coupe longitudinale d'un dispositif de déplacement de liquide selon un septième mode de réalisation de l'invention, muni d'un système d'asservissement du déplacement du liquide piston. Les figures 13A et 13B montrent des variantes du septième mode de réalisation représenté dans les figures 12A et 12B.

Embodiments of the invention will now be described, by way of nonlimiting examples, with reference to the accompanying drawings, in which:

• The figure 1 , already described, is a schematic representation in longitudinal section of a liquid spray device according to the prior art;
• The FIGS. 2A to 2C represent the operating principle of displacement of drops by electrowetting;
• The figure 3 represents the operating principle of fluid displacement by electrowetting, in a closed configuration of liquid displacement device;
• The Figures 4A and 4B are diagrammatic representations in longitudinal section of a liquid displacement device according to the first preferred embodiment of the invention, for two stages of operation;
• The figure 5 is a schematic representation in longitudinal section of a liquid displacement device according to a variant of the first preferred embodiment of the invention, wherein a matrix of control electrodes is provided;
• The figure 6 is a schematic representation in longitudinal section of a device for displacing liquid according to the second preferred embodiment of the invention;
• The figure 7 is a schematic representation in longitudinal section of a liquid displacement device according to a third embodiment of the invention, in which a plurality of control portions arranged in series is provided;
• The figure 8 is a schematic representation in longitudinal section of a liquid displacement device according to a fourth embodiment of the invention, in which a plurality of control portions arranged in parallel is provided;
• The figure 9 is a schematic representation in longitudinal section of a portion of the microchannel of the liquid displacement device according to a fifth embodiment of the invention, to reduce the effects of the hysteresis of the contact angle;
• The Figures 10A and 10B are diagrammatic representations in longitudinal section of a liquid displacement device according to a sixth embodiment of the invention, for two stages of operation;
• The Figures 11A and 11B are diagrammatic representations in longitudinal section of a liquid displacement device according to a variant of the sixth embodiment of the invention, for two stages of operation;
• The Figures 12A, 12B , 13A and 13B are schematic representations in longitudinal section of a liquid displacement device according to a seventh embodiment of the invention, provided with a system for controlling the displacement of the piston liquid. The Figures 13A and 13B show variants of the seventh embodiment shown in Figures 12A and 12B .

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A device according to the invention implements a liquid displacement device, by electrowetting, or more precisely by electrowetting on dielectric.

The principle of electrowetting on dielectric implemented in the context of the invention can be illustrated using the Figures 2A - 2C as part of an open type device.

A drop of an electrically conductive liquid F ₁ rests on an array of electrodes 30, from which it is isolated by a dielectric layer 40 and a hydrophobic layer 50 ( Figure 2A ). There is therefore a hydrophobic and insulating stack.

The hydrophobic nature of this layer means that the drop has a contact angle, on this layer, greater than 90 °.

It is surrounded by a dielectric fluid F ₂ , and forms with this fluid an interface I ₁ .

The electrodes 30 are themselves formed on the surface of a substrate 20.

A counter electrode 70, here in the form of a catenary wire, maintains an electrical contact with the drop F ₁ . This counter-electrode can also be a buried wire or a planar electrode in the hood of a confined system.

The electrodes 30 and the counter electrode 70 are connected to a voltage source 80 for applying a voltage U between the electrodes.

When the electrode 30 (1) located near the drop F ₁ is activated, using switching means 81 whose closure makes contact between this electrode and the voltage source 80 via a common conductor 82, voltage drop assembly F ₁ , dielectric layer 40 and activated electrode 30 (1) acts as a capacitance.

où e est l'épaisseur de la couche diélectrique 40, ε_r la permittivité de cette couche et σ la tension de surface de l'interface de la goutte.As described in the article of Berge entitled "Electrocapillarity and wetting of insulating films by water", CR Acad. Sci., 317, Series 2, 1993, 157-163 the contact angle of the interface of the drop F ₁ facing the activated electrode 30 (1) then decreases according to the relation: $$\cos {\mathrm{\theta }}_1^{\left(U\right)}=\cos {\mathrm{\theta }}_1^{\left(0\right)}+\frac{1}{2}\frac{{\mathrm{\epsilon }}_r}{e\mathrm{\sigma }}{\mathrm{<figure-callout\; id="2"\; label="U"\; filenames="imgf0004.png,imgf0005.png"\; state="\{\{state\}\}">U</figure-callout>}}^2$$

where e is the thickness of the dielectric layer 40, ε _r the permittivity of this layer and σ the surface tension of the interface of the drop.

When the bias voltage is alternating, the liquid behaves like a conductor when the frequency of the bias voltage is substantially lower than a cutoff frequency, the latter, depending in particular on the electrical conductivity of the liquid, is typically of the order a few tens of kilohertz (see for example the article of Mugele and Baret entitled "Electrowetting: from basics to applications", J. Phys. Condens. Matter, 17 (2005), R705-R774 ). On the other hand, the frequency is substantially greater than the frequency allowing to exceed the hydrodynamic response time of the liquid F ₁ , which depends on the physical parameters of the drop such as the surface tension, the viscosity or the size of the drop, and which is of the order of a few hundred Hertz.

The response of the drop F ₁ then depends on the rms value of the voltage, since the contact angle depends on the voltage U ² .

According to the article Bavaria et al. entitled "Dynamics of droplet transport induced by electrowetting actuation", Microfluid Nanofluid, 4, 2008, 287-294 , there appears an electrostatic pressure acting on the interface I ₁ , near the contact line. If this electrostatic pressure is applied asymmetrically, the drop F ₁ can then be moved. In the Figure 2A the activation of the electrode 30 (1) causes the drop to move in the X direction.

The drop can thus be eventually displaced step by step ( Figures 2B and 2C ), on the hydrophobic surface 50, by successive activation of the electrodes 30 (1), 30 (2), etc., along the catenary 70.

It is therefore possible to move liquids, but also to mix them (by bringing drops of different liquids near), and to perform complex protocols.

The figure 3 illustrates the phenomenon of displacement of a liquid by electrowetting in a closed or confined type device comprising a microchannel.

In this figure, the numerical references identical to those of Figures 2A - 2C designate the same elements.

The microchannel 10 is partially filled with the conducting liquid F ₁ forming an interface I ₁ with the dielectric fluid F ₂ .

In this example, the electrode array 30 is replaced by a single electrode 30.

When the electrode 30 is not activated, the interface I ₁ is static, the liquid F ₁ and the fluid F ₂ are at rest.

When the electrode 30 is activated, the pressure of electrostatic origin appears and acts on the interface I ₁ , which puts the liquid F ₁ in motion in the direction X.

The liquid F ₁ can thus be displaced on the hydrophobic surface 50 by activation of the electrode 30. The fluid F ₂ is then "pushed" by the liquid F ₁ .

Examples of devices implementing this principle are described in the article of Pollack et al. entitled "Electro-wetting-based actuation of droplets for integrated microfluidics", Lab Chip, 2002, 2, 96-101 .

A first preferred embodiment of the invention is shown on the Figures 4A and 4B which show, in longitudinal section, a microfluidic liquid displacement device.

In this figure, the numerical references identical to those of the figure 3 designate the same elements.

With reference to the Figure 4A , the microchannel 10 has a first end 12A comprising a first opening 11A and a second end 12B opposite the first end 12A in the longitudinal direction of the microchannel 10 and comprising a second opening 11B.

The microchannel 10 may have a convex polygonal cross section, for example square, rectangular, hexagonal. It is considered here that a square section is a special case of the more general rectangular shape. It can also have a circular cross section.

The term microchannel is taken in a general sense and includes in particular the particular case of the microtube whose section is circular.

Throughout the following description, the terms height and length refer to the size of the microchannel 10 or a portion of the microchannel 10 in the transverse and longitudinal directions, respectively. Thus, for a microchannel of rectangular section, the height corresponds to the distance between the lower and upper walls of the microchannel, and for a microchannel of circular section, the height designates the diameter thereof.

In addition, note that the verbs "to cover", "to be located on" and "to be disposed of" may not imply direct contact. Thus, a material may be disposed on a wall without there being direct contact between the material and the wall. Similarly, a liquid can cover a wall without direct contact. In these two examples, a material intermediary may be present. Direct contact is assured when the qualifier "directly" is used with the verbs mentioned above.

A control electrode 30 is disposed directly on at least one face of the inner wall 15 of the substrate 20, and extends in the longitudinal direction of the microchannel 10. It is said buried. The electrode 30 extends over part or all of the perimeter of the microchannel 10.

The insulating layer 40 and the hydrophobic layer (not shown) which cover the electrode 30 may be a single layer combining these two functions, for example a parylene layer.

In the example shown, the counter-electrode 70 is introduced into the liquid F ₁ at the reservoir 60, in the form of one or more points of electrical contact with the conducting liquid F1. It can also be a catenary in the form of an electrically conductive wire, for example Au (shown in FIG. figure 5 ).

The voltage source 80, preferably an alternating voltage, is connected to the electrode 30 and the counter-electrode 70. The frequency is preferably between 100 Hz and 10 kHz, preferably of the order of 1 kHz.

Thus, the response of the liquid F ₁ depends on the effective value of the applied voltage since the contact angle depends on the voltage U ² , according to the relationship given above. The rms value can vary between 0V and a few hundred volts, for example 200V. Preferably, it is of the order of a few tens of volts.

The length of the electrode 30 in the longitudinal direction of the microchannel 10 defines a control portion 16.

The control portion 16 includes a first end 16A towards the first end 12A of the microchannel 10 and a second end 16B towards the second end 12B in the longitudinal direction of the microchannel 10.

Injection portion 17 is the portion of the microchannel 10 extending from the second end 12B of the microchannel 10 towards the control portion 16.

A reservoir 60 that can contain the liquid F1 can be connected to the microchannel 10 via the opening 11A of the end 12A, and is intended to supply the microchannel 10 with a piston liquid F ₁ .

The interface I ₁ is located in the control portion 16. The triple line of the interface I ₁ is contained in a plane substantially transverse to the microchannel 10.

The microchannel 10 also comprises a second liquid F ₃ , called the liquid of interest, which partially fills the channel from substantially the second end 12B. The second liquid F ₃ is in contact with the fluid F ₂ . The interface between these two fluids forms an interface I ₃ .

The interface I ₃ is in contact with the inner wall 15 of the microchannel 10. The connection line between the interface I ₃ and the wall 15 defines a triple line and a contact angle θ ₃ can be measured in the liquid F ₃ . The triple line of the interface I ₃ is contained in a substantially transverse plane of the microchannel 10.

The interface I ₃ is located in the injection portion 17, therefore outside the control portion 16.

The piston liquid F ₁ is electrically conductive and may be an aqueous solution loaded with ions, for example Cl ^- , K ⁺ , Na ⁺ , Ca ²⁺ , Mg ²⁺ , Zn ²⁺ , Mn ²⁺ , others. The piston liquid F ₁ can also be mercury, gallium, eutectic gallium, or ionic liquids of the type bmim PF6, bmim BF4 or tmba NTf2.

The liquid of interest F ₃ can be a liquid suitable for a chemical, biological or medical application. In the latter case, the liquid F ₃ may in particular be a medicinal liquid or a liquid containing active agents, molecules or a radioactive tracer.

The fluid F ₂ is electrically insulating. It may be a gas, for example air, or a liquid such as an alkane, for example hexadecane or undecane, or a silicone or mineral oil, or fluorinated solvents, for example FC-40 ® or the FC-70®. In the case of the silicone oil, the dynamic viscosity is preferably substantially less than about 10cp. Preferably, the fluid F ₂ is biologically compatible with the liquid F ₃ .

The fluid F ₂ is immiscible with the piston liquid F ₁ and with the liquid of interest F ₃ .

The microchannel has a length of between 100 μm and 500 mm, preferably between 500 μm and 100 mm.

The height or the diameter of the microchannel 10 is typically between a few nanometers and 200 μm, and preferably between 1 μm and 100 μm.

The reservoir can have a capacity of between a few nanoliters and 1ml.

The substrate 20 may be silicon or glass, polycarbonate, polymer, ceramic. In the case of a silicon substrate, it is preferable to provide an insulating layer on the surface, this insulating layer may be deposited or result from thermal oxidation. The electrode 30 is obtained by depositing a thin layer of a metal chosen from Au, Al, ITO, Pt, Cu, Cr ... or an Al-Si alloy ... using conventional microtechnologies of the microelectronics, for example by photolithography.

The thickness of the electrode is between 10 nm and 1 μm, preferably 300 nm. The length of the electrode 30 is from a few micrometers to a few millimeters.

The electrode 30 is covered with a dielectric layer made of Si ₃ N ₄ , SiO ₂ ... having a thickness of between 100 nm and 3 μm, preferably between 300 nm and 1 μm. The dielectric layer of SiO ₂ can be obtained by thermal oxidation.

Finally, a hydrophobic layer may be deposited on the substrate. For this, a Teflon deposit by dipping or spray or SiOC deposited by plasma can be achieved. Hydrophobic silane deposition in the vapor or liquid phase can be carried out. Its thickness will be between 100 nm and 3 μm, preferably between 300 nm and 1 μm

The operating principle is as follows, with reference to Figures 4A and 4B .

As shown in Figure 4A , the interface I ₁ is located in the control portion 16. Initially, it is preferably located near the first end 16A of this portion.

The activation of the electrode 30 by the voltage source 80 causes the liquid F ₁ to move towards the second end 16B of the control portion 16.

As a result, the liquid F ₁ "pushes" the fluid F ₂ in the same direction, that is to say towards the second end 12B of the microchannel 10, and at the same time, "pushes" the liquid of F interest ₃ .

From the moment when the liquid F ₃ reaches the second opening 11B, an amount of liquid F ₃ is injected outside the displacement device corresponding to the amount of liquid F ₃ displaced.

When the interface I ₁ reaches the second end 16B of the control portion 16, the liquid F ₁ substantially covers the electrode 30 in its entirety. The triple line is then no longer subject to the electrowetting force. The contact angle θ ₁ increases to its value corresponding to the absence of imposed electric field and the liquid F ₁ stops.

As a result, the liquid F ₁ no longer causes the displacement of the fluid F ₂ which comes to rest, as well as the liquid of interest F ₃ which is then no longer injected.

The device according to the invention has a certain number of advantages.

The separating fluid F _{2 also} makes it possible to avoid mixing between the piston liquid F ₁ and the liquid of interest F ₃ , which could denature the physical, chemical or biological properties of the liquid of interest F ₃ .

The dielectric separating fluid F ₂ allows the use of any type of liquid of interest F ₃ , whatever the chemical composition and the electrical conductivity of the latter.

Moreover, the control electrode 30 can occupy only a part of the perimeter of the control portion 16.

Thus, in the case of a microchannel 10 of section for example rectangular, the electrode 30 may comprise an upper part 31 ( Figure 4A ) disposed directly on an upper wall 15S of the microchannel 10, and a lower portion 32 disposed directly on a lower wall 15I of the microchannel 10, the two parts 31 and 32 being parallel to each other. This arrangement is particularly suitable for a rectangular section since the side walls have a surface substantially smaller than that of the upper and lower walls 15S and 15I. The edge effects of the electric field are thus minimized.

Nevertheless, the electrode 30 may also be disposed over the entire perimeter of the control portion 16. The electrode 30 is then disposed on the set of upper walls 15S, lower 15I and lateral, or in the case of a circular section, over the entire periphery of the control portion 16.

This arrangement has the advantage of applying the electrowetting force over the entire triple line of the interface I ₁ . The curvature of the interface I ₁ is then uniformly modified, which makes the capillary pressure at the interface between the two fluids F ₁ and F ₂ uniform.

Indeed, the triple line of the interface I ₁ remains substantially contained in a transverse plane of the control portion 16.

The displacement of the interface I ₁ is then more efficient, which allows to obtain a control of the injection rate and the injected volume of the liquid F ₃ more accurate.

If the electrowetting force was not uniform along the triple line, the plane containing the triple line of the interface I ₁ would no longer be substantially transversal to the control portion 16. The liquid F ₁ could move by example in the direction of the second end 12B of the channel 10 and the fluid F ₂ move in the opposite direction, which is to be avoided.

According to a variant of the first embodiment of the invention represented in the figure 5 an array of independent electrodes 30 is disposed directly on at least one side of the substrate 20, as described above with reference to FIGS. 2A to 2C .

As previously, a control portion 16 of the microchannel 10 is defined as the portion extending in the longitudinal direction of the microchannel 10 and which comprises the matrix of electrodes 30.

The spacing between adjacent electrodes can be substantially between a few micrometers and a few tens of micrometers.

In this variant and in accordance with the embodiment of FIGS. 2A to 2C , it is advantageous that the liquid F ₁ is in the form of a liquid stopper entirely placed in the control portion 16. The liquid can thus be displaced step by step, on the hydrophobic layer 50 of the control portion 16 by successive activation of the electrodes 30 (1), 30 (2) ... of the electrode matrix.

An advantage of this embodiment is that it is possible to control the displacement of the drop of liquid F ₁ along the two directions X and -X, depending on the activation of the electrodes 30.

It is thus possible to perform not only the injection of the liquid F ₃ out of the device, but also the suction of the liquid F ₃ , that is to say the displacement of the liquid F ₃ towards the control portion 16 .

The suction of the liquid F ₃ may allow the filling of the microchannel 10 F ₃ liquid, for example from a liquid tank F ₃ , for subsequent use of the device according to the invention.

It is also possible to suck another liquid than the liquid F ₃ , after injection thereof. For example, a sample of liquid, after injection of the liquid F ₃ , for the purpose of analyzing it later.

A second preferred embodiment will now be described in detail with reference to the figure 6 , which shows a schematic representation in longitudinal section of the displacement device, in which the control electrode 30 is replaced by the advantageously polarized substrate 20.

For this, the substrate 20 is electrically conductive. It can be made of doped silicon in order to increase its electrical conductivity. The doping can correspond to 5.10 ¹⁸ atoms / cm ² in n or in p.

An electrode 33, connected to the voltage source 80, is arranged to apply to the substrate 20 and the counter-electrode 70 the determined potential difference.

A dielectric layer 40 is directly disposed on a portion of the inner wall 15 of the microchannel 10 so as to electrically isolate the piston liquid F ₁ from the polarized substrate 20. The dielectric layer 40 may be directly disposed on the inner wall 15 from the reservoir 60 to the second end 16B of the control portion 16, and the entire perimeter.

A hydrophobic layer (not shown) may be directly disposed on the dielectric layer 40.

Thus, the polarized substrate 20, the dielectric layer 40 and the polarized piston liquid F ₁ form a capacitor. Since the piston liquid F ₁ partially covers the dielectric layer 40 directly in the control portion 16, a electrowetting force applied to the triple line of the interface I ₁ can be generated.

In addition, for the purpose of electrically isolating the liquid of interest F ₃ from the polarized substrate 20, a stack 34 of a first dielectric layer 40, an electrode 17E, then a second dielectric layer 40, each having a length in the substantially equal longitudinal direction is disposed directly on the inner wall 15 of the injection portion 17.

The electrode 17E can be grounded, so as not to induce electrowetting effects at the triple line of the interface I ₃ .

A third embodiment of the invention will now be described in detail with reference to the figure 7 , which shows a schematic representation in longitudinal section of the displacement device, which comprises a plurality of control portions arranged in series.

The third embodiment is an improvement of the first preferred embodiment and has substantially the same components as in the first mode.

As shown in figure 7 two control portions 16 (1), 16 (2) are arranged in series. However, it is possible to have a number n of control portions 16 without being limited to 2 portions.

In the general case where n control portions are provided, each control portion 16 (i), where i∈ [1, n], has a first end 16A (i) and a second end 16B (i). The control portions 16 (i) are arranged in series along the microchannel 10 so that a second end 16B (i) is located near the first end 16A (i + 1) of the control portion 16 (i + 1) located downstream of the control portion 16 (i).

Each control portion 16 (i) is partially filled with piston-conducting liquid F ₁ (i), each interface I ₂ (i) being initially located between an end 16B (i-1) and 16A (i). A separating fluid F ₂ (i) fills the channel 10 between the interface I ₁ (i) and I ₂ (i + 1).

The piston liquid F ₁ (i) is in contact with the separating fluid F ₂ (i) and forms an interface I ₁ (i) according to the same characteristics as in the first embodiment. It is understood that the piston liquid F ₁ (i) fills both a portion of the control portion 16 (i) and a portion of the channel located between the control portions 16 (i-1) and 16 (i).

The control portion 16 (1) is located near the first end 12A of the microchannel 10, which communicates with a reservoir 60.

The control portion 16 (n) is located near the second end 12B of the microchannel 10. The separating fluid F ₂ (n) is also in contact with a liquid of interest F ₃ which partially fills the microchannel 10 from the second end 12B of the microchannel and towards the second end 16B (n) of the control portion 16 (n).

The control portions 16 (i) are spaced from each other by a distance of between a few micrometers and a few millimeters.

Preferably, this distance is defined so that the volume between the control portions 16 (i) is substantially equal to the volume defined by each control portion 16 (i), so that the piston liquid F ₁ (i) can fill substantially completely the control portion F ₁ (i).

Each control portion 16 (i) comprises a control electrode (i) or control electrode array (i) as described in the first embodiment.

The device comprises a counter electrode 70, intended to carry the conductive liquids F ₁ (i) to a determined potential. The counter-electrode 70 is a catenary wire, for example Au. It may be a buried wire or a plurality of planar electrodes arranged facing the electrodes 30 (i).

The control electrodes 30 (i) and the counter-electrode 70 are connected to a voltage source 80.

The electrodes 30 (i) are advantageously activated simultaneously.

The third embodiment of the invention has the advantage of increasing the injection pressure of the liquid F ₃ .

In fact, the electrowetting forces applied to the interfaces I ₁ (i) add up, which makes it possible to obtain a higher injection pressure of the liquid of interest F ₃ . In the case of control portions (I) identical in size and geometry, the injection pressure obtained is substantially equal to the number n of interfaces I ₁ (i) multiplied by the pressure obtained with a single control portion 16 (i).

Several devices obtained according to embodiments 1 to 3 can be associated in a matrix structure, each device can be used independently, in parallel. According to another association, several devices obtained according to these same embodiments can be associated according to a matrix structure limited to the control portions. In this case, the matrix of control portions may result in a single injection portion, or at least one injection portion, tanks that may be common to several or all of the control portions. This type of association can be obtained by realizing a network of channels 10 and tanks 60 in the plane and / or the thickness of the substrate. These devices can be made on different substrates and then stacked.

A fourth embodiment of the invention will now be described in detail with reference to the figure 8 .

The figure 8 is a schematic representation in longitudinal section of a liquid displacement device, having a plurality of control portions 16 in parallel.

A direct orthogonal reference (X, Y) is represented in the figure 9 , where the direction X is parallel to the longitudinal axis of the control portions 16.

Several substrates 21, 22, 23 are arranged to form a microchannel 10.

A first substrate 21 extends in the direction Y and has a thickness along X. The thickness of the substrate 21 is of the order of a few hundred microns, for example 500μm, 700μm or 1000μm.

The first substrate 21 is machined to obtain channels through the thickness of the substrate 21 thus defining control portions 16 (i). The control portions 16 (i) may be arranged in a honeycomb and have a diameter of the order of a few tens of microns. Preferably, each control portion 16 (i) has a circular cross section, hexagonal or having a shape of the same type.

A through channel 17B of large diameter is also produced and disposed near an edge of the substrate 21. The channel 17B is intended to form an injection portion 17B of the injection portion 17 of the microchannel 10.

A dielectric layer 40 is disposed on the wall of the substrate 21, more precisely on the inner wall 15 of the control portions 16 (i). The inner wall 15 of the channel 17B may also be covered with the dielectric layer 40.

A hydrophobic layer is disposed on the wall of the substrate 21.

The channels 16 (i) and 17B can be obtained by plasma etching of the RIE type of the substrate 21. The substrate 21 is for example silicon. The diameter of the control portions 16 (i) is between 1 μm and 100 μm, preferably substantially 30 μm. The diameter of the channel 17B may be of the order of a few hundred microns.

The dielectric layer may be SiO ₂ obtained by thermal oxidation.

The hydrophobic layer may be a plasma deposited SiOC layer. Hydrophobic silane deposition in the vapor or liquid phase may be used. Preferably, the lower face 21I of the substrate 21 is protected from the deposition of the hydrophobic layer so as to maintain a hydrophilic property.

A second substrate 22 is arranged to be in contact with the bottom wall 21I of the substrate 21. It has a first opening 2201 which communicates with the control portions 16 (i) and a second opening 2202 which communicates with the channel 17B.

The second substrate 22 may be a printed circuit type card, for example FR4, or ceramic, silicon, glass, or polymer such as polycarbonate.

A flexible membrane 25 is disposed at the lower face 22I of the substrate 22 so as to close the first opening 2201 at its lower end 22I. The membrane thus defines with the substrates 21 and 22 a reservoir 60 that can contain the liquid F ₁ .

The flexible membrane may be a thin film of elastomer or a bellows glued to the underside of the substrate 22.

A third substrate 23 is disposed on the upper face 21S of the substrate 21. The substrate 23 comprises one or more notches so as to form, in cooperation with the substrate 21, one or more cavities of the microchannel 10. More specifically, a first notch 23E1 of the substrate 23 is disposed substantially opposite the control portions 16 (i) so as to forming a connecting portion 18 of the microchannel 10. A second notch 23E2 is disposed substantially opposite the channel 17B so as to form a storage portion 17A.

The storage portion 17A communicates with the injection portion 17B, so as to form together the injection portion 17 of the microchannel 10.

The notches 23E1 and 23E2 have a height along Y between 100μm and a few millimeters, preferably 1mm. The notch 23E1 may have a lower height than the notch 23E2, to limit the volume of fluid F ₂ required.

The connection portion 18 and the storage portion 17A can communicate with each other via a communication conduit 18C of height between a few tens of microns and a few hundred microns, preferably 100 .mu.m.

The third substrate 23 may be silicon or glass. It can be assembled to the first substrate 21 by screen printing glue. Direct sealing can also be achieved by anodic bonding or molecular bonding.

Finally, a tube 24 comprising a microchannel may be arranged to communicate with the channel 17B of the substrate 21. The microchannel of the tube 24 is intended to extend the channel 17B to facilitate the injection of the liquid in an area to be treated. The component 24 may also be a catheter, a needle comprising a microchannel, or a connection between the channel 17B and a needle or catheter.

The liquids F ₁ , F ₃ and the fluid F ₂ fill the microchannel 10 in the following manner.

The piston liquid F ₁ partially fills the control portions 16 (i) in the direction X.

The fluid F ₂ fills the connecting portion 18 and the communication conduit 18C. It also partially fills the control portions 16 (i) so as to form an interface I ₁ (i) in each control portion 16 (i) with the piston liquid F ₁ . It also partially fills the storage portion 17A of the injection portion 17.

The liquid of interest F ₃ partially fills the storage portion 17A of the injection portion 17 so as to form an interface I ₃ with the fluid F ₂ . The liquid of interest F ₃ also fills the injection part 17B, and at least partially the microchannel of the tube 24.

As previously described, the electrowetting force may be generated, either from the activation of electrodes 30 disposed at the control portions 16 (i), or from the activation of the biased substrate 21.

A counterelectrode electrode 70 is arranged, for example, in the tank 60 to carry the piston liquid F ₁ to a potential V0.

In the first case, each control portion 16 (i) has the inner wall 15 covered with a layer electrode metal 30. A dielectric layer 40 is deposited on the electrode 30.

The electrodes 30 (i) and the counterelectrode 70 are connected to a voltage source 80.

The electrodes 30 (i) may be connected to the voltage source 80 via a buried line (not shown) on the surface of the substrate 21 and an electrode 33 connected to the buried line and the source of the voltage.

In the second case, the first substrate 21 is electrically conductive. It can be made of silicon doped so as to increase the electrical conductivity. An electrode 33 is disposed in contact with the substrate 21 to bring it to a determined potential V1.

The dielectric layer 40 is arranged to electrically isolate the liquid F ₁ from the polarized substrate 21.

The substrate 21 and the counter-electrode 70 are connected to a voltage source 80.

The operating principle of the displacement device according to the fourth embodiment is identical to that of the first or second preferred embodiment, and is therefore not repeated here.

The device then has the advantage of being able to store a large quantity of liquid F ₃ . Indeed, the height of the storage portion 17A can be increased substantially. Thus, the sum of the liquid volumes F ₁ displaced in the control portions 16 (i) substantially equalizes the liquid volume F ₃ displaced. For the same control stroke of the interfaces I ₁ (i) in the case of a single portion of control 16 ( Figure 4A ), a larger amount of liquid F ₃ is moved and injected out of the device according to the invention.

In addition, the liquid displacement device is particularly compact and can be easily integrated in labs on a chip.

It also makes it possible to obtain a higher throughput by paralleling a large number of control portions.

A fifth embodiment of the invention will now be described in detail with reference to the figure 9 . The figure 9 is a schematic representation in longitudinal section of a portion of the microfluidic liquid displacement device, adapted to minimize the influence of the hysteresis of the contact angle.

The hysteresis of the contact angle results from surface defects, such as chemical inhomogeneities or roughness of the surface. The contact angle of a drop placed on a surface is not then unique but between two limit values called advancing angle and recoil angle. Thus, a triple line will only advance (or retreat) from the moment when the contact angle reaches the advancing (or receding) angle.

The figure 9 shows a portion of the microchannel 10. The interface I ₃ , located in the injection portion, is at rest (dashed line) and forms at the wall a contact angle θ ₃ between the recoil angle θ _{3, R} and the advancing angle θ _{3, A.} When the fluid F ₂ , under the pressure of the piston liquid F ₁ , exerts a pressure on the liquid of interest F ₃ , the interface I ₃ will gradually deform without the triple line is back, as long as the angle of contact θ ₃ remains different from the recoil angle θ _{3, R.} When θ ₃ is equal to θ _{3, R} , the triple line moves back towards the second end 12B of the microchannel 10.

This physical behavior of the interface I ₃ , due to the hysteresis of the contact angle, has several disadvantages.

On the one hand, the existence of the recoil angle θ _{3, R} introduces a kind of pressure barrier to be crossed in order to move the triple line of the interface I ₃ and then the liquid F ₃ . If the pressure force exerted by the liquid F ₁ on the liquid F ₃ via the fluid F ₂ is insufficient to exceed this pressure barrier, the hysteresis then prevents the displacement of the triple line of the liquid F ₃ , and therefore blocks the movement of the liquid F ₁ . The displacement device is then rendered inoperative.

On the other hand, as explained above, the triple line of the interface I ₃ and then the liquid F ₃ are set in motion when the contact angle θ ₃ reaches the value of the recoil angle θ _{3, R.} Thus, if, moreover, the fluid F ₂ is compressible, a delay time is introduced during which the flow rate of the liquid F ₃ through the second opening 11B is not equivalent to the flow rate of the liquid F ₁ . This can disrupt the control of the amount of liquid F ₃ injected out of the device.

In order to minimize the effect of the hysteresis of the contact angle, the height H of the injection portion 17 is made substantially larger than the height h of the control portion 16. In fact, the pressure related to hysteresis phenomena is proportional to H ^-1 . Thus, the height H can be between 5h and 50h, preferably 10h.

A connecting portion 18 of the microchannel 10 connects the control portion 16 to the injection portion 17, more precisely the second end 16B of the control portion 16 is connected to the injection portion 17. The connecting portion 18 is filled only with separating fluid F ₂ .

The pressure barrier induced by the hysteresis at the triple line of the interface I ₃ is then substantially reduced. This reduces the risk of blocking the movement of the liquid F ₁ and the delay time of setting in motion the triple line of the interface I ₃ .

A sixth embodiment of the invention will now be described in detail with reference to Figures 10A to 11B .

The Figures 10A and 10B are diagrammatic representations in longitudinal section of a microfluidic liquid displacement device for which the injection portion 17 of the microchannel can be simply filled, after dispensing liquid F ₃ , with the same liquid of interest F ₃ . The device thus adapted is then able to be used several times.

As an illustration, a liquid displacement device as described herein is considered here. in the Figure 4A . However, a device as described in Figures 5 to 9 can also be used.

The filling system 90 comprises a reservoir 91 of liquid of interest F ₃ connected to the injection portion 17 of the microchannel 10 via an L-shaped three-way valve 92. The liquid of interest F ₃ stored in the reservoir 91 is injected or aspirated by means of a pump or a syringe pump (not shown).

The three-way L-shaped valve 92 is disposed in the injection portion 17, near the second end 12B, and thus divides the injection portion into two portions, a first storage portion 17A and a second portion 17B of injection. The first storage portion 17A is the portion of the injection portion 17 between the control portion 16 and the valve 92. It comprises the interface I ₃ . The second injection portion 17B is the portion of the injection portion 17 between the valve 92 and the second end 12B of the microchannel 10. It is filled with liquid F ₃ .

The valve can occupy two different states.

A first state is a filling state in which the first storage portion 17A communicates with the reservoir 91.

A second state is an injection state in which the first storage portion 17A communicates with the second injection portion 17B.

Control means (not shown) make it possible to switch the L-shaped three-way valve in one of the two defined states.

The switching is effected according to the position of the interface I ₁ in the control portion 16. Thus, when the interface I ₁ is substantially close to the first end 16A of the control portion 16, the valve 92 switches to his injection state. When the interface I ₁ is substantially close to the second end 16B of the control portion 16, the valve 92 switches to its filling state.

The operation of the liquid displacement device according to the sixth embodiment is as follows.

As shown in figure 10A , the interface I ₁ is initially located near the first end 16A of the control portion 16. The liquid F ₃ substantially fills the first storage portion 17A of the injection portion 17 and the valve 92 is in the injection state.

When the electrode 30 is activated, an electrowetting force is applied to the triple line of the interface I ₁ and causes the liquid F ₁ to move towards the second end 16B of the control portion 16. the liquid F ₁ "pushes" the fluid F ₂ in the same direction. The liquid of interest F ₃ is then moved in the direction of the second end 12B of the microchannel 10 and injected outside the device through the second opening 11B.

When the interface I ₁ reaches the end of its run ( figure 10B ), that is to say when it arrives substantially near the second end 16B of the control portion 16, the electrode 30 is deactivated and the valve 92 switches to the filling state.

The reservoir 91 is then placed in communication with the storage portion 17A of the injection portion 17.

The liquid of interest F ₃ stored in the tank 91 then progressively fills the storage portion 17A of the injection portion 17, under the pressure force exerted on the liquid F ₃ in the tank 91.

In doing so, it moves the liquid F1 through the fluid F ₂ until the interface I ₁ is located substantially at the first end 16A of the control portion 16. The liquid displacement device is then filled.

Recall that due to the absence of an electric field, there is no electrowetting force applied to the triple line of the interface I ₁ which would induce a displacement of the liquid F ₁ towards the second end 16A of the control portion 16, and oppose the filling of the microchannel by the liquid F ₃ . Also, the liquid F ₁ can easily be displaced by the liquid of interest F ₃ of the tank 91.

To be ready for a new use, the valve 92 switches to its injection state. It then suffices to impose an electric field between the electrode 30 and the counter-electrode 70 so that, because of the displacement of the interface I ₁ , the liquid of interest F ₃ is injected out of the device.

According to a variant shown schematically in the Figures 11A and 11B , the device for moving liquid is adapted to continuously dispense the liquid of interest F ₃ .

For this, the liquid displacement device comprises two devices D1 and D2 as described in FIG. Figure 4A and a reservoir 91 containing the liquid of interest F ₃ .

A reference (X _i , Y) is represented in the figure 11A for each device Di, where i = 1.2. Each direction X _i is parallel to the longitudinal axis of the control portion 16 and oriented towards the injection portion 17.

The devices D1 and D2 and the tank 91 are connected to each other by a four-way valve 94 at 90 °. The devices D1 and D2 have, in common, downstream of the valve 94, the injection portion 17B of the injection portion 17.

Both devices D1 and D2 have a structure and operation similar to that described with reference to Figures 10A and 10B . The different features will be simply detailed here.

The valve 94 can switch to two different states.

A first state corresponds to the liquid injection F ₃ of the device D1 and to the liquid filling F ₃ of the device D2. For this, the valve 94 communicates, on the one hand the storage portion 17A of the device D1 with the injection portion 17B, and on the other hand the tank 91 with the storage portion 17A of the device D2.

The second state corresponds, on the contrary, to the liquid filling F3 of the device D1 and to the liquid injection F3 of the device D2. For that, the valve 94 communicates, on the one hand the storage portion 17A of the device D2 with the injection portion 17B, and on the other hand the tank 91 with the storage portion 17A of the device D1.

The operating principle is as follows.

With reference to the figure 11A when the device D2 is filled with the liquid F ₃ by the reservoir 91, the device D1 dispenses the liquid F ₃ from its storage portion 17A, the valve 94 then occupying the first state.

Then, when the interface I ₁ of the device D1 arrives substantially at the second end 16B of the control portion 16, the electric field of the device D1 is deactivated, the valve 94 switches to its second state ( Figure 11B ), the electric field of the device D2 is activated. The device D2 then dispenses the liquid F ₃ from its storage portion 17A while the reservoir 91 fills the liquid F ₃ the storage portion 17A of the device D1.

Thus, the liquid of interest F ₃ is dispensed out of the device according to the invention continuously and not in a jerky manner.

Of course, according to a variant not shown, several displacement devices can be connected to each other at the injection portion 17B of their respective injection portion 17. Thus, insofar as they dispense liquids of interest F ₃ of different composition and immiscible with each other, it is possible to obtain the continuous exemption of different liquid plugs of interest F ₃ .

In the case where two or more devices according to the variant of the sixth embodiment are connected to each other at the injection portion 17B of their respective injection portion 17, it is possible to obtain the continuous injection of liquids F ₃ each occupying a portion of the cross section of the injection portion 17B of the injection portion 17. The mixture between the respective liquids of interest F ₃ can possibly take place by diffusion before injection through the opening 11B of the microchannel 10.

This device makes it possible to inject liquids of interest F3 that can not be previously stored together in a tank.

A seventh embodiment of the invention will now be described in detail with reference to Figures 12A to 13B , which are schematic representations of the liquid displacement device comprising a system for controlling the displacement of the piston liquid F ₁ , in order to precisely control the quantity of liquid of interest F ₃ injected.

The Figures 12A and 12B represent the displacement device for which the displacement of the liquid F ₁ depends on the position of the interface I ₁ .

The Figures 13A and 13B show variants of the embodiments shown in the Figures 12A and 12B , for which the displacement of the liquid F ₁ depends on the position of the interface I ₃ .

With reference to Figures 12A and 12B , the servo system comprises a measuring device capacitive to determine the position of the interface I ₁ and control the movement of the liquid F ₁ .

In the first embodiment, the capacitive measurement position determining device is connected to the electrode 30 and the counter electrode 70.

It comprises an alternating voltage source 180. The frequency thereof is preferably remote from that of the voltage supplied by the voltage source 80. It is advantageously one hundred times higher. For example, it may be of the order of a few hundred kilohertz if the frequency of the voltage supplied by the voltage source 80 is of the order of a few kilohertz. The amplitude is preferably of the order of ten to one hundred times smaller than that of the voltage delivered by the voltage source 80, and is preferably of the order of about ten volts.

In order to measure the capacitance formed between the polarized liquid F ₁ and the electrode 30, a capacitance 141B is put in series with the electrode 30 to form a capacitive divider.

The value of the capacity 141B can be between 10pF and 500pF, and is preferably 100pF.

A voltmeter 141A measures the voltage across the capacitor 141B.

In addition, it is possible to replace the capacity 141B and the voltmeter 141A by an impedance analyzer.

The measured voltage is transmitted to computing means 142 of the position of the interface I ₁ .

From the measured voltage, the calculation means 142 calculate the value of the capacitance formed between the polarized liquid F ₁ and the electrode 30 and deduce from this the degree of overlap of the dielectric layer 40 by the liquid F ₁ . From the recovery rate and knowing the position of the dielectric layer 40, the calculation means 142 determine the position of the interface I ₁ in the microchannel 10.

The position of the interface I ₁ is then transmitted to control means 152. These are connected to the voltage source 80, and make it possible to vary the value of the voltage generated.

The variation of the voltage generated by the voltage source 80 makes it possible in particular to control the speed of movement of the liquid F ₁ .

The calculation means 142 and the control means 152 are for example arranged on a printed circuit (not shown).

Thus, the servo system makes it possible to control the displacement of the liquid F ₁ as a function of the position of the interface I 1 detected by capacitive measurement.

The operation of the liquid controlled displacement device according to the first embodiment of the invention is as follows.

The voltage source 80 activates the electrode 30 and allows the liquid F _{1 to move} .

The activation of the voltage source 180 makes it possible to measure the capacitance formed between the polarized liquid F ₁ and the electrode 30. For this, the voltmeter 141A of the capacitive measuring device measures the voltage at the terminals of the capacity 141B and sends the measured signal to the calculation means 142.

The calculation means 142 of the position of the interface I ₁ make it possible to obtain from the measured voltage the rate of recovery by the liquid F ₁ of the dielectric layer 40 and deduce therefrom the position of the interface I ₁ . The position of the interface I ₁ is transmitted to the control means 152.

Depending on the received signal, the control means 152 determine the value of the potential difference to be applied by the voltage source 80.

Depending on the intensity of the potential difference applied by the voltage source 80, a more or less significant electrowetting force is generated at the interface I ₁ . Its intensity makes it possible to control in particular the speed of movement of the liquid F ₁ .

The electrowetting force thus causes the displacement of the liquid F ₁ in the direction X which "pushes" in the same direction the fluid F ₂ , and thus the liquid F ₃ .

The figure 12B shows a variant of the embodiment shown in the figure 12A .

An array of electrodes 30 is disposed on one side of the microchannel 10.

The counter-electrode 70 is here an electrode formed on a part of the inner wall 15 of the microchannel 10 facing the electrode matrix 30. It may, however, be a catenary wire ( figure 2 ) or buried wire.

Switching means 121 are provided for activating an electrode 30 (i) of the electrode matrix 30. Their closure makes contact between the electrode 30 (i) and the voltage source 80. The switching means 121 are controlled by an activation driver (not shown).

When the electrode 30 (1) located near the interface I ₁ is activated, using the switching means 121, the dielectric layer 40 between this activated electrode and the liquid under tension acts as a capacitance.

The liquid F ₁ can be moved step by step on the hydrophobic surface by successive activation of the electrodes 30 (1), 30 (2), etc.

Advantageously, the substrate 20, in the case where it is slightly conductive, for example made of silicon, is brought to a determined potential. For example, it can be grounded.

For this, an electrode (not shown) in the form of a metal layer may advantageously be formed on the outer wall of the substrate 20 opposite the electrode matrix 30. It may extend over the entire length of the electrode matrix 30.

Bringing the substrate 20 to a determined potential makes it possible to avoid electrostatic disturbances between the electrodes 30 of the matrix which can noisy the signal for measuring the capacitance. The measurement of the capacity is then more precise, which improves the overall operating accuracy of the servo system.

The Figures 13A and 13B are diagrammatic representations in longitudinal section of a liquid displacement device according to a variant of the seventh embodiment of the invention, for which the detected interface is different from that subjected to the electrowetting forces.

According to this embodiment of the invention, the servo system is adapted to control the movement of the liquid F ₁ as a function of the position of an interface I ₃ . The liquid F ₃ is here electrically conductive, but it can also be dielectric, as explained below.

In the same way as in the first embodiment, the displacement of the liquid F ₁ is ensured by the activation of the electrode 30 connected to a voltage source 80.

The capacitive measuring device of the servo system comprises at least one electrode 130 formed on the inner wall 15 of the microchannel 10 and extends in the longitudinal direction of the microchannel 10. It is said buried and extends over a part or the entire perimeter of the microchannel 10.

The length of the electrode 130 defines a detection portion 160. The interface I ₃ is located in the detection portion 160.

A counter-electrode 170 is formed on the inner wall 15 of the microchannel 10 facing the electrode 130. The counter-electrode 170 may also be a buried wire, or be arranged in the microchannel 10 in the form of a catenary wire, for example a wire in Au.

Preferably, the counter-electrode 170 extends in the microchannel 10 vis-à-vis the electrode 130.

The voltage source 180 is connected to the electrodes 130 and 170 to apply an alternating voltage according to the same characteristics previously described. The average value of the voltage is zero and the high frequency to avoid causing the deformation of the curvature of the interface F ₃ which would disturb the capacitive measurement.

With reference to the figure 13A the capacitive measuring device further comprises a dielectric layer 140 which directly covers the electrode 130.

When the voltage source 180 is turned on, the dielectric layer 140 between the electrode 130 and the energized liquid F3 acts as a capacitance.

The value of this capacitance can be deduced from the voltage measured across a reference capacitor 141B connected in series with the electrode 130.

The calculation means 142 make it possible to calculate the position of the interface I ₃ , from the measurement of voltage by the voltmeter 141A across the capacitors 141B.

The control means 152 control the value of the voltage generated by the voltage source 80 as a function of the position of the interface I ₃ .

Thus, the servo system makes it possible to control the displacement of the liquid F ₁ as a function of the position of the interface I ₃ determined by capacitive measurement.

With reference to the Figure 13B the electrode 130 may be replaced by an array of electrodes 130. Switching means 122 may be provided to activate the electrode 130 (i) at which the interface I ₃ is located. Their closure makes contact between the corresponding electrode 130 (i) and the voltage source 180. The switching means 122 are controlled by an activation driver (not shown).

Advantageously, as described above, the substrate 20, in the case where it is slightly conductive, for example made of silicon, is brought to a determined potential. For example, it can be grounded.

For this, an electrode (not shown) in the form of a metal layer may advantageously be formed on the outer wall of the substrate 20 vis-à-vis the matrix of electrodes 130. It may extend over the entire length of the electrode matrix 130.

In the case where the liquid F3 is dielectric and has a permittivity different from that of the fluid F ₂ , the dielectric layer 140 is no longer necessary.

Indeed, during the activation of the voltage source 180, the measurement of the voltage across the capacitance 141B makes it possible to deduce the value of the capacitance formed by the fluids F ₂ and F ₃ between the electrodes 130 and 170. The value of this capacity depends on the position of the interface I ₃ .

The servo system comprises the same components as previously described and has identical operation.

In a further embodiment of the invention not shown, the servo system can also be adapted to detect both the position of the interface I ₁ and that of the interface I ₃ , in order to obtain greater accuracy on the amount of fluid F ₃ moved. This situation is particularly suitable in the case where the fluid F ₂ has a compressibility that is important to evaluate in real time, or when the liquids F ₁ and F ₃ exhibit uncontrolled evaporation.

This detection also makes it possible to measure the injection flow rate, which makes it possible to verify that the channel is not clogged, or even to detect the presence of a leak.

Moreover, it should be noted that in all the embodiments described above, the surface of the channels, and more particularly at the level of the control portion, can be smooth, rough or micro or nano structured, so as to amplify the effects wetting and increase the capillary forces, thus the pumping pressure.

Claims (21)

A liquid displacement device comprising at least one substrate (20; 21,22,23) comprising a microchannel (10), said microchannel (10) having a first end (12A) and a second end (12B) substantially opposed to each other. one of the other in the longitudinal direction of the microchannel (10), an opening (11B) on the surrounding medium being located substantially at said second end (12B),
said device comprising: a first liquid (F ₁ ) partially filling the microchannel (10) in the longitudinal direction of the microchannel (10), a fluid (F ₂ ) located downstream of said first liquid (F ₁ ) towards the second end (12B) and forming with the first liquid (F ₁ ) a first interface (I ₁ ), said first interface (I ₁ ) being located in a control portion (16) of the microchannel (10), and a second liquid (F ₃ ) located downstream of said fluid (F ₂ ) towards the second end (12B) and forming with the fluid (F ₂ ) a second interface (I ₃ ), characterized in that
the device comprises means for moving the first liquid (F ₁ ) by electrowetting, the first liquid (F ₁ ) being electrically conductive and the fluid (F ₂ ) electrically insulating, the displacement of the first liquid (F ₁ ) inducing the displacement of the second liquid (F ₃ ), via the fluid (F ₂ ), through said opening (11B). Liquid displacement device according to claim 1, characterized in that said means for moving the first liquid (F ₁ ) by electrowetting comprise: at least one first electrically conductive means (30, 20, 21), a layer of a dielectric material (40) directly covering the first conductive means (30; 20, 21), said dielectric layer (40) being at least partially wetted by said first liquid (F ₁ ), at least a second electrically conductive means (70) forming a counter-electrode, in contact with the first liquid (F ₁ ), and a first voltage generator (80) for applying a potential difference between said first and second conductive means. Liquid displacement device according to Claim 2, characterized in that , since the substrate (20, 21) comprising the control portion (16) is electrically conductive, the first electrically conductive means (30) comprises the conductive substrate (20, 21). ). Liquid displacement device according to claim 2 or 3, characterized in that ,
the microchannel (10) comprising an injection portion (17) extending substantially from the opening (11B) towards the control portion (16), said second interface (I ₃ ) being located in the portion injection (17),
a stack (34) of a first layer of a dielectric material (40), an electrically conductive means which can be brought to a determined potential (V0 '), and a second layer of a dielectric material (40); ), each having a substantially equal length in the longitudinal direction of the injection portion (17), is disposed on the inner wall (15) of the injection portion (17) so as to electrically isolate the second liquid (F ₃ ) of the conductive substrate (20, 21). A liquid displacement device according to claim 2, characterized in that said first electrically conductive means (30) comprises at least one electrode (30) disposed on at least a portion of the wall in the longitudinal direction of the microchannel (10) and located in the control portion (16). Liquid displacement device according to claim 5, characterized in that said first electrically conductive means (30) comprises an electrode (30) extending over the entire length of the control portion (16). Liquid displacement device according to one of Claims 1 to 6, characterized in that it comprises a reservoir (60) communicating with the microchannel (10) through an opening (11A) located at the first end (12A) and containing said first conductive liquid (F _1). A liquid displacement device according to claim 5, characterized in that said first electrically conductive means (30) comprises an electrode array (30) extending the full length of the control portion (16). Liquid displacement device according to claim 8, characterized in that the first liquid (F ₁ ) forms a fluid-surrounded fluid plug (F ₂ ) so as to form a rear interface (I _{1, R} ) and a front interface (I _{1, A} ), the two interfaces (I _{1, R} , I _{1, A} ) being located in the control portion (16). Liquid displacement device according to claim 9, characterized in that the displacement of the first interface (I ₁ ) in the direction of the first end (12A) of the microchannel (10) causes suction of the second liquid (F ₃ ) through from the opening (11B) towards the first end (12A). Liquid displacement device according to any one of claims 5 to 10, characterized in that said electrode (30) comprises two parts parallel to each other. Liquid displacement device according to any one of claims 5 to 10, characterized in that said electrode (30) extends over the entire perimeter of the control portion (16). Liquid displacement device according to any one of claims 2 to 12, characterized in that said layer of dielectric material (40) is covered directly with a layer of hydrophobic material (50). Liquid displacement device according to any one of claims 1 to 13, characterized in that the microchannel has a convex polygonal cross section. Liquid displacement device according to any one of claims 1 to 13, characterized in that the microchannel has a substantially circular cross section. Liquid displacement device according to any one of claims 1 to 15, characterized in that the microchannel has a plurality of control portions arranged in series, each control portion (16 (i)) being partially filled with the first liquid ( F ₁ (i)) and fluid (F ₂ (i)). Liquid displacement device according to one of Claims 1 to 15, characterized in that the microchannel has a plurality of control portions arranged in parallel, each control portion (16 (i)) being partially filled with the first liquid (F _i (1)) and fluid (F ₂ (i)). Liquid displacement device according to one of Claims 1 to 17, characterized in that
the microchannel (10) comprising an injection portion (17) extending substantially from the opening (11B) towards the control portion (16), said second interface (I ₃ ) being located in the portion injection (17),
the longitudinal axis of the control portions (16) is substantially perpendicular to the longitudinal axis of the injection portion (17). Liquid displacement device according to one of Claims 1 to 18, characterized in that
the microchannel (10) comprising an injection portion (17) extending substantially from the opening (11B) towards the control portion (16), said second interface (I3) being located in the portion of the injection (17),
the height (H) of the injection portion (17) is substantially greater than the height (h) of the control portion (16). Liquid displacement device according to claim 19, characterized in that the height (H) the injection portion (17) is substantially between 10 and 50 times the height (h) of the control portion (16). Liquid displacement device according to claim 19 or 20, characterized in that a connecting portion (18) connects the control portion (16) to the injection portion (17), the connecting portion (18) n filled with fluid (F2).

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