EP2165753A2 - Micro-device for analysing liquid samples - Google Patents

Abstract

The device has an excitation electrode (20) for generating a radial and oscillating electric field around a symmetrical axis under the effect of electrical control such that the electric field generates axisymmetric surface waves of fluid droplet (F1) in presence of the droplet provided on the electrode. The fluid droplet includes a symmetrical axis coinciding with the symmetrical axis. The field induces an electrowetting voltage difference between the excitation electrode and the droplet, where the difference has amplitude comprised between 1 volt to 100 volts. Independent claims are also included for the following: (1) a liquid droplet analyzing device comprising analyzing units (2) a method for forming surface waves at an interface of liquid droplet by electrowetting (3) a method for analyzing liquid droplet.

Description

TECHNICAL AREA

The present invention relates to the general field of the analysis of liquid samples, in particular for the detection of constituents possibly present in the sample.

It also relates to the field of discrete microfluidics insofar as the liquid sample to be analyzed can be in the form of a drop. The term "drop" here includes substantially hemispherical drops, puddles or capillary bridges.

The invention particularly relates to a device for forming surface waves at the interface of a drop of liquid by electrowetting.

The proposed invention finds many applications in the concentration and detection of biological or chemical targets, the rheological characterization of fluid samples, or even the transmission of microfluidic movements.

STATE OF THE PRIOR ART

In many fields, it is sought to detect constituents possibly present in a drop of liquid.

This may be the case, for example, for establishing a biological or medical diagnosis, or in the field of genetic or agri-food engineering. It can be sought to detect or assay in particular macromolecules, cells, analytes, organelles, pathogens, intercalants.

This is also the case in the field of the nuclear power industry, where it is essential to be able to detect the radioactive elements present in the liquid effluents, in particular the actinides which form with plutonium the most dangerous waste.

Environmental detection, more broadly, seeks to determine the concentration including pathogens, metals, solid particles, colloids in liquids of interest.

In most of these areas, one seeks to analyze small volume liquid samples in a reduced time in the simplest and least intrusive manner possible.

The discrete microfluidic (or digital) allows the manipulation and the displacement of drops of very small volume. It plays an increasing role in the development of new micro-systems such as lab-on-a-chip, and allows to carry out numerous analysis steps in chains.

It differs from continuous microfluidics (in channels) in particular by the possibility of eliminating pumps, valves, walls necessary for the containment of the flow ... The physicochemical contaminations parietal can thus be minimized, or even discarded.

By way of illustration, mention may be made of the biochips which constitute, in the field of molecular biology, nucleic acid hybridization analysis systems (DNA and / or RNA), or antigen / type interaction. antibody, protein / ligand, protein / protein, enzyme / substrate, etc. We then seek to obtain kinetic parameters or equilibrium constants associated with these chemical interactions.

The detection of biological molecules can be carried out using PCR or ELISA techniques known to those skilled in the art. These techniques usually use the grafting of a labeled probe molecule of a fluorescent compound. The level of fluorescence emitted is then measured by optical means to thus quantify the hybridization process.

These detection techniques are generally preceded by a preparation of the liquid sample to be analyzed. The preparation may consist of mixing or mixing the liquid of the sample and then the concentration of the biological molecules in a determined zone, for example at the fluid interface of the liquid sample.

An example device for carrying out these preparation operations, to then detect the biological molecules present in a drop, is described in the patent application. WO2008 / 068229 filed in the name of the plaintiff.

This device makes it possible to generate a circulating flow, or vortex, inside the drop by electrohydrodynamics without inducing deformation interfacial nor overall displacement of the drop. This vortex then makes a mixture of the liquid of the drop, by stirring or centrifugation, which makes it possible to accelerate the hybridization kinetics while being compatible with the constraints of miniaturization. It also makes it possible to concentrate the constituents at the interface of the drop under the effect of a centrifugal force, for a more sensitive detection.

To generate this vortex, the drop is disposed on a dielectric layer covering two electrodes having zigzag-shaped edges facing one another. The application of a potential difference between these two electrodes gives rise to an oblique electric field with respect to the interface of the drop, because of the shape of the edges and the position of the drop. The tangential component of the electric field then causes the displacement of the electrical charges accumulated at the interface, which induces by viscosity a flow of the liquid inside the drop.

This device thus makes it possible to mix the liquid of the drop and to concentrate the constituents at the interface of the drop, thus making it possible to carry out purification, extraction or even more precise detection.

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

The intensity of the vortex generated depends on that of the electric field. However, it decreases sharply as one moves away from the electrodes. Also, the vortex is noticeably located near electrodes. The mixture made in the drop is not homogeneous, and the constituents are more concentrated near the electrodes and the triple line.

However, it can be sought to obtain a significant concentration away from the contact line and the plane of the electrodes, for example at the apex of the drop, to thereby avoid disturbances due to boundary conditions (triple line) and to the walls, and allow a subsequent detection easier, which the device according to the prior art does not allow.

Moreover, the vortex does not make it possible to give by itself the information sought on the constituents possibly present in the drop, as their concentration or the kinetic parameters of chemical or biological interactions, except by implementing heavy speed field visualization techniques, such as micro-PIV (Particle Image Velocimetry). It is then necessary to use detection techniques (PCR, ELISA, etc.) which involve the labeling of probe molecules, and which entail a high cost and a high processing time.

STATEMENT OF THE INVENTION

The object of the present invention is to provide a device for ensuring the mixing of the liquid of a drop and a significant concentration of constituents possibly present at the interface in an area of the interface substantially distant from the triple line of the drop.

To do this, the invention firstly relates to a wave forming device at the interface of a liquid drop by electrowetting.

According to the invention, said device comprises at least one excitation electrode adapted to generate an oscillating and radial electric field around a first axis of symmetry, under the effect of an electric control, so that in the presence of a drop of liquid disposed on said excitation electrode and having an axis of symmetry substantially coinciding with said first axis of symmetry, said electric field generates waves at the interface of said drop, said generated waves being substantially axisymmetric.

By substantially axisymmetric waves is meant mainly or even exclusively axisymmetric waves.

Thus, these axisymmetric waves generated by electrowetting at the triple line propagate uniformly over the entire interface of the drop and cause a substantially homogeneous micromixing of the liquid of the drop.

The axisymmetric nature of the waves makes it possible to obtain a resonant mode in a determined zone remote from the triple line and from the excitation electrode. It is then possible to obtain a potentially significant concentration in this zone of constituents possibly present at the interface, in particular of larger components. AT As an illustration, in the case of a semi-spherical droplet, the resonant mode is obtained substantially at the apex (top) of the drop.

In addition, the concentration of constituents at the interface may be substantially homogeneous or increase as one moves away from the wetting plan containing the triple line of the drop, depending on whether these axisymmetric waves are substantially stationary or progressive.

Advantageously, said formed waves exhibit a substantially linear behavior.

Preferably, said waves have an amplitude-to-wavelength ratio of between 10 ^-5 and 1.

Preferably, said waves have an amplitude ratio on wavelength between 10 ^-5 and 10 ^-1.

Preferably, said waves have an amplitude-to-wavelength ratio of between 10 ^-4 and 10 ^-2 .

Preferably, said waves have an amplitude-to-wavelength ratio of the order of 10 ^-3 .

Preferably, said waves have a drop radius amplitude ratio of less than or equal to 10 ^-1 , preferably less than or equal to 10 ^-2 , preferably of the order of 10 ^-3 .

By ray of the drop, we mean the radius of a half-sphere modeling the drop disposed on said excitation electrode in the absence of waves at the interface, or the radius, said equivalent radius, of a sphere having a volume equal to that of said drop.

According to a first embodiment of the invention, the device comprises a single excitation electrode having substantially a disk shape.

According to one variant, the device comprises a single substantially annular excitation electrode.

According to a second embodiment of the invention, the device comprises a first substantially annular excitation electrode and a second counter electrode excitation electrode having substantially a disc shape surrounded by said first excitation electrode.

According to one variant, the device comprises a first excitation electrode and a second counter-electrode excitation electrode, each having substantially a half-annular shape arranged facing one another.

According to a variant, the device comprises a first excitation electrode and a second excitation electrode forming a counter-electrode, each having substantially a half-disc shape arranged facing one another.

The excitation electrode or electrodes may comprise an inner edge defining a substantially circular inner edge, the triple line of said drop being preferably substantially opposite said inner edge.

The excitation electrode or electrodes may also comprise an outer edge defining a substantially circular outer edge, the triple line of said drop being preferably substantially opposite said outer edge.

In the first embodiment of the invention, the device may comprise a voltage generator for applying an electric potential to said excitation electrode different from that of said drop.

In the second embodiment of the invention, the device may comprise a voltage generator for applying a potential difference between the first excitation electrode and the counter-electrode.

Preferably, said electric field induces a difference in electrowetting potential between the excitation electrode and said drop having a frequency of between 10 Hz and 150 Hz.

Said difference in electrowetting potential may have an amplitude of between 1V and 100V.

Preferably, said electrowetting potential difference has an amplitude of between 1V and 50V.

Advantageously, the excitation electrode or electrodes are covered with a layer of a dielectric material.

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

Advantageously, said dielectric layer is hydrophobic.

The device may comprise means for trapping the triple line of said drop.

The wave forming device may further comprise at least one excitation electrode secondary electrode, located opposite, parallel to said excitation electrode, adapted to generate an oscillating and radial electric field around a third axis of symmetry substantially coinciding with said first axis of symmetry, under the effect of said electric control.

In this case, said drop may be a capillary bridge formed between said excitation electrode and said secondary excitation electrode.

• un dispositif de formation d'ondes selon l'une quelconque des caractéristiques décrites précédemment,
• des moyens de caractérisation géométrique des ondes formées, et
• des moyens d'analyse, connectés auxdits moyens de caractérisation géométrique, pour analyser, à partir de la caractérisation géométrique des ondes formées, les propriétés physiques et/ou chimiques de ladite goutte.

The invention also relates to a device for analyzing a drop of liquid comprising:

• a wave forming device according to any one of the features described above,
• means for geometrically characterizing the waves formed, and
• analysis means, connected to said geometric characterization means, for analyzing, from the geometrical characterization of the waves formed, the physical and / or chemical properties of said drop.

According to one variant, the geometric characterization means are means for measuring the amplitude of the waves formed.

The means for measuring the amplitude of the waves formed may be measuring means by light absorption and / or interferometry.

According to another variant, the geometric characterization means are means for measuring the slope of the waves formed along a line of the interface.

The means for measuring the slope of the waves formed may be measuring means by refractometry.

The geometric characterization means may be both means for measuring the amplitude of the waves formed and means for measuring the slope of the waves formed along a line of the interface.

• un dispositif de formation d'ondes selon l'une quelconque des caractéristiques décrites précédemment,
• des moyens de caractérisation cinématique des ondes formées, et
• des moyens d'analyse, connectés auxdits moyens de caractérisation cinématique, pour analyser, à partir de la caractérisation cinématique des ondes formées, les propriétés physiques et/ou chimiques de ladite goutte.

According to another embodiment, the device for analyzing a drop of liquid comprises:

• a wave forming device according to any one of the features described above,
• means for kinematic characterization of the waves formed, and
• analysis means, connected to said kinematic characterization means, for analyzing, from the kinematic characterization of the waves formed, the physical and / or chemical properties of said drop.

The kinematic characterization means may be means for measuring the normal speed of the waves formed.

In the case of the rheological analysis of the drop of liquid, the characterization of geometric or kinematic waves makes it possible to determine the physicochemical properties of the liquid, in particular its interfacial properties. In the case of the detection of the constituents present, the amplitude or the slope of the waves informs about the present constituents, and makes it possible to obtain the kinetic parameters or equilibrium constants associated with possible chemical interactions.

Thus, unlike the prior art, it is possible to dispense with any optical or fluorescent probe grafting which can disturb the interactions or the physicochemical properties of the liquid.

In addition, the detection techniques are simpler to implement than in the prior art, while ensuring high accuracy. Optical techniques (refractometry, light absorption, interferometry, ellipsometry) can be used to perform the geometric or kinematic characterization of waves. In addition, the axisymmetric nature of the waves makes it possible to obtain a resonance phenomenon in an area of the interface remote from the triple line. The analysis means, based on the geometric or kinematic characterization of the waves, preferably in this zone, make it possible to calculate the mechanical or physicochemical properties of the liquid, in particular the interfacial properties.

It is thus possible to perform a real-time, rapid diagnosis in that the mixing, concentration and analysis steps can be performed simultaneously.

The analysis technique is non-intrusive, so there is no risk of physicochemical denaturation of the liquid sample or disturbance of the possible molecular organization at the interface.

Thus, the device for analyzing a drop of liquid can perform the analysis of the chemical properties of the drop without labeling biological or chemical targets contained in the drop.

However, the device for analyzing a drop of liquid may further comprise measuring means, at the interface of said drop, of the concentration of marked biological or chemical targets. Thus, the analysis has increased accuracy because of the use of several methods of chemical analysis.

According to another embodiment, the device for analyzing a drop of liquid comprises a wave-forming device according to any one of the characteristics described above, and measuring means, at the interface of said drop, concentration of marked biological or chemical targets.

Said targets may be labeled with a fluorescent or radioactive compound.

• disposer une goutte de liquide sur au moins une électrode d'excitation présentant un premier axe de symétrie, de sorte que l'axe de symétrie de ladite goutte coïncide sensiblement avec ledit premier axe de symétrie, et
• générer un champ électrique oscillant et radial autour dudit premier axe de symétrie, de manière à former des ondes essentiellement axisymétriques à l'interface de ladite goutte.

The invention also relates to a method of forming waves at the interface of a liquid drop by electrowetting, comprising the steps of:

• disposing a drop of liquid on at least one excitation electrode having a first axis of symmetry, so that the axis of symmetry of said drop coincides substantially with said first axis of symmetry, and
• generating an oscillating and radial electric field around said first axis of symmetry, so as to form substantially axisymmetric waves at the interface of said drop.

Said waves may have an amplitude-to-wavelength ratio of between 10 ^-5 and 1, preferably between 10 ^-5 and 10 ^-1 , preferably between 10 ^-4 and 10 ^-2 , preferably of the order of 10 ^{-5. -3} .

Said waves may also have an amplitude to radius ratio of the lower drop or equal to 10 ^-1 , preferably less than or equal to 10 ^-2 , preferably of the order of 10 ^-3 .

The invention also relates to a method for analyzing a drop of liquid, comprising the implementation of a wave forming method according to any one of the characteristics described above, a step of geometric characterization of said formed waves. then a step of analyzing the physical and / or chemical properties of said drop, from the geometrical characterization of said formed waves.

The geometric characterization step can be a measure of the amplitude of the waves formed.

Preferably, the measurement of the amplitude of said waves is carried out in a determined zone of the interface substantially remote from the triple line of the drop.

Alternatively, the geometric characterization step is a measurement of the slope of the waves formed along a line of the interface.

The invention also relates to a method for analyzing a drop of liquid, comprising the implementation of a wave forming method according to any one of the preceding characteristics, a step of kinematic characterization of said formed waves, then a step of analyzing the physical and / or chemical properties of said drop, from the kinematic characterization of said formed waves.

The kinematic characterization step may be a measure of the normal velocity of the formed waves.

The invention also relates to a method for analyzing a drop of liquid according to one of any of the previously described features, further comprising a step of measuring, at the interface of said drop, the concentration of labeled biological or chemical targets.

The invention relates to a method for analyzing a drop of liquid, comprising the implementation of a wave forming method according to any one of the preceding characteristics, and a measurement step, at the interface of said drop, of the concentration of marked biological or chemical targets.

The invention finally relates to the use of a wave forming device according to any one of the preceding characteristics, or to an analysis device according to any one of the preceding features, said drop of liquid being a drop of blood.

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

BRIEF DESCRIPTION OF THE DRAWINGS

• Les figures 1A et 1B sont des représentations schématiques en coupe longitudinale d'un dispositif illustrant le principe d'excitation d'une goutte de liquide par électromouillage ;
• La figure 2 est une représentation schématique en coupe longitudinale d'un dispositif de formation d'ondes selon un premier mode de réalisation de l'invention comportant une unique électrode d'excitation ;
• Les figures 3A et 3B montrent en vue de dessus différentes formes de l'électrode d'excitation selon le premier mode de réalisation ;
• La figure 4 est une représentation schématique en coupe longitudinale d'un dispositif de formation d'ondes selon un second mode de réalisation de l'invention comportant une électrode d'excitation et une contre-électrode planaire ;
• Les figures 5A à 5C montrent en vue de dessus différentes formes d'électrode d'excitation et de contre-électrode planaire ;
• Le figure 6 est une représentation schématique en coupe longitudinale d'un dispositif de formation d'ondes selon un troisième mode de réalisation préféré de l'invention comprenant un pont capillaire ; et
• La figure 7 est une représentation schématique en coupe longitudinale d'un dispositif d'analyse d'une goutte liquide, dans le cas de la mesure de l'amplitude des ondes formées.

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

• The Figures 1A and 1B are diagrammatic representations in longitudinal section of a device illustrating the principle of excitation of a drop of liquid by electrowetting;
• The figure 2 is a schematic representation in longitudinal section of a training device waveform according to a first embodiment of the invention comprising a single excitation electrode;
• The Figures 3A and 3B show in top view different forms of the excitation electrode according to the first embodiment;
• The figure 4 is a schematic representation in longitudinal section of a wave forming device according to a second embodiment of the invention comprising an excitation electrode and a planar counterelectrode;
• The FIGS. 5A to 5C show in plan view different forms of planar electrode and counter electrode;
• The figure 6 is a schematic representation in longitudinal section of a wave forming device according to a third preferred embodiment of the invention comprising a capillary bridge; and
• The figure 7 is a schematic representation in longitudinal section of a device for analyzing a liquid drop, in the case of measuring the amplitude of the waves formed.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A device according to the invention implements a device for exciting a drop of liquid by electrowetting, or more precisely, by electrowetting on a dielectric.

The principle of electrowetting on dielectric used in the context of the invention can be illustrated using Figures 1A and 1B as part of an open type device.

A drop of an electrically conductive liquid F1 rests on an excitation electrode 20, from which it is isolated by a dielectric layer 12 and a hydrophobic layer 13. There is therefore a hydrophobic and insulating stack.

The hydrophobic nature of this layer 13 means that the drop F1 has a contact angle, on this layer, greater than 90 °.

It is surrounded by a dielectric fluid F2, and forms with this fluid an interface I.

The excitation electrode 20 is formed on the surface of a substrate 11, or integrated therewith.

A counter electrode 30, here in the form of a catenary wire, maintains an electrical contact with the drop F1. This counterelectrode 30 may also be a buried wire or a planar electrode in the hood of a confined system. However, she may also not be present.

The excitation electrode 20 and the counter electrode 30 are connected to a voltage source 50 for applying an electrowetting voltage U between the electrodes.

When the excitation electrode 20 is activated, that is to say when there is electrical contact between this electrode 20 and the voltage source 50 via a conducting wire, the drop assembly F1, dielectric layer 12 and activated electrode 20 acts as a capacitance.

où e est l'épaisseur de la couche diélectrique 12, 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 angle of contact of the interface of the drop F1 then decreases according to the relation: $${\cos }^{\left(U\right)}={\mathrm{<figure-callout\; id="0"\; label="cos"\; filenames="imgf0001.png,imgf0004.png"\; state="\{\{state\}\}">cos</figure-callout>}}^{\left(0\right)}+\frac{1}{2}\frac{{\mathrm{\epsilon }}_r}{e\mathrm{\sigma }}{U}^2$$

where e is the thickness of the dielectric layer 12, ε _r the permittivity of this layer and σ the surface tension of the interface of the drop.

When the electrowetting voltage is alternating, the liquid behaves like a conductor insofar as the frequency of the bias voltage is substantially lower than a cutoff frequency. This depends in particular on the electrical conductivity of the liquid, and is typically of the order of 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 may be substantially greater than the hydrodynamic response frequency of the liquid F1, 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 the order of a few hundred hertz. The response of the drop F1 thus 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 , it appears an electrostatic pressure acting on the interface I, close to the line of contact. The interface is deformed so as to respect the contact angle imposed by electrowetting ( Figure 1B ).

It should be noted that, in a manner known to those skilled in the art, the application of this electrostatic pressure asymmetrically, using a network of excitation electrodes, causes the displacement of the drop F1. The drop can thus be optionally displaced step by step on the hydrophobic surface, by successive activation of the excitation electrodes. It is therefore possible to move liquids and perform complex protocols.

A wave forming device at the fluid interface of a drop of liquid according to the first preferred embodiment of the invention is shown schematically on the figure 2 , in longitudinal section.

The device comprises an excitation electrode 20 forming a plane and integrated in a first substrate 11.

According to the first embodiment of the invention, the device comprises a single excitation electrode 20 in substantially disk form ( figure 3A ). A substantially annular shape is also possible, as described later with reference to the figure 3B .

The plane containing the excitation electrode substantially parallel to the plane (i, j) of the direct orthonormal coordinate system ( i , j , k ) is called the median plane of the electrode.

Preferably, the excitation electrode 20 is covered with a layer of a dielectric material 12. Advantageously, said dielectric layer 12 is covered with a layer of a hydrophobic material 13 (not shown).

The wave forming device comprises a drop of liquid F1 in contact with the hydrophobic layer so as to at least partially cover the excitation electrode 20.

As has been mentioned above, the term "drop" can designate a substantially semispherical droplet, a puddle, or even a capillary bridge. In the example shown on the figure 2 , the drop F1 is substantially semi-spherical, more precisely hemispherical.

In the description that follows, the verbs "cover", "be arranged on" do not necessarily imply direct contact with the excitation electrode. As will be described later, the drop may cover, or be arranged on the excitation electrode 20, without being in direct contact with it, for example when a hydrophobic layer 13 and / or a dielectric layer 12 covers said electrode 20.

The interface I of the drop is the fluid interface formed between the liquid of the drop F1 and a surrounding fluid F2.

The line of the drop in contact with the hydrophobic layer and belonging to the drop interface is called triple line. The triple line is preferably substantially circular.

The interface forms an angle of contact with the plane of the triple line, this angle being conventionally measured in the liquid of the drop. When the drop is in contact with the hydrophobic layer, and in the absence of any electrostatic stress, the contact angle is substantially greater than 90 °.

The drop may contain constituents in the volume and at the interface. The generic term "constituents" denotes all the species that may be present in the drop (macromolecules: DNA, RNA, proteins, cells, organelles, actinides, colloids or solid particles, etc.). We can also talk about biological or chemical targets.

According to the invention, the excitation electrode 20 has a first axis of symmetry and the drop F1 has a second axis of symmetry which coincides substantially with the first axis. The first and second axes of symmetry are preferably substantially perpendicular to the median plane.

In the example of the figure 2 , and with reference to the figure 3A the excitation electrode 20 has an edge 22 forming an outer edge. The outer edge is substantially circular, because of the axis of symmetry of the electrode.

As shown in figure 3A which is a top view of the excitation electrode, the droplet is preferably arranged so as to at least partially cover the excitation electrode 20. The triple line is preferably located substantially opposite the edge exterior.

The excitation electrode 20 is adapted to generate an oscillating and radial electric field around the first axis of symmetry. For this, it can be connected to a voltage generator 50 which applies a potential to the electrode 20 substantially different from that of the drop F1. A so-called electrowetting potential difference is then generated between the excitation electrode 20 and the drop F1.

The electrowetting voltage generated by the voltage generator 50 can comprise a first V component or high frequency, and a so-called excitation voltage modulation v.

The excitation modulation is noted v (ω) and has a frequency ω substantially less than the hydrodynamic response frequency of the drop. The frequency ω can be between 10 Hz and 500 Hz, and preferably between 10 Hz and 150 Hz. The amplitude A _v can be between 1V and 100V, and preferably between 1V and 50V.

The low frequency modulation v (ω) makes it possible to harmonically modulate the contact angle. Because the frequency is less than the hydrodynamic response frequency, the variation of the contact angle substantially follows the amplitude and frequency of the modulation v . We can then talk about oscillatory electro-jetting.

The first component is denoted V and can be continuous, between 1V and a few hundred volts, for example 200V. Preferably, it is of the order of a few tens of volts. It can also be a high frequency alternating voltage V (Ω) of frequency Ω, substantially greater than the hydrodynamic response frequency, for example between 500 Hz and 10 kHz, preferably of the order of 1 kHz. This component is then seen by the drop as a DC voltage equal to the effective value of the voltage V, since the contact angle depends on the voltage V ² , according to the relationship given above. The rms value can vary between 1V and a few hundred volts, for example 200V. Preferably, it is of the order of a few tens of volts.

This component V makes it possible to impose a determined contact angle at the interface of the drop and thus to adjust the general shape thereof.

According to another embodiment, the voltage generator 50 can also generate a low-frequency electrowetting voltage, which does not include a V- component or a high-frequency component. In this case, the amplitude and the frequency correspond to the values described for the excitation modulation v.

The excitation electrode 20 may be produced by depositing a thin layer of a metal chosen from Au, Al, ITO, Pt, Cu, Cr ... or an Al-Si alloy ... conventional microtechnologies of microelectronics, for example by photolithography. The electrode 20 is then etched in a suitable pattern, for example by wet etching.

The thickness of the electrode 20 may be between 10 nm and 1 μm, preferably 300 nm. Its size depends on the size of the F1 drop to be excited. She will be preferentially commensurable with the size of the drop.

A dielectric layer 12 may cover the excitation electrode 20. It may be made of Si ₃ N ₄ , SiO ₂ , SiN, barium strontium titanate (EST) or other high-permittivity materials such as HFO ₂ , Al ₂ O ₃ , Ta ₂ O ₅ [29], Ta ₂ O ₅ -TiO ₂ , SrTiO ₃ or Ba _1-x Sr _x TiO ₃ . The thickness of this layer 12 may be between 100 nm and 3 μm, generally between 100 nm and 1 μm, preferably 300 nm. The dielectric layer 12 of SiO ₂ can be obtained by thermal oxidation. A plasma enhanced chemical vapor deposition (PECVD) process is preferred to the low pressure vapor deposition (LPCVD) process for thermal reasons. Indeed, the temperature of the substrate is only brought between 150 ° C and 350 ° C (depending on the desired properties) against 750 ° C for LPCVD deposit.

Finally, a hydrophobic layer 13 may be deposited on the dielectric layer 12. For this, a Teflon deposit by dipping, by spin coating , or by spray, or plasma-deposited SiOC can be carried out. Hydrophobic silane deposition in the vapor or liquid phase can be carried out. Its thickness is between 100 nm and 5 μm, preferably 1 μm. This layer 13 makes it possible in particular to reduce or even to avoid the effects of hysteresis of the wetting angle.

The liquid of the drop F1 is electrically conductive and may be an aqueous solution charged with ions, such as Cl ^-, K ^+, Na ^+, Ca ^2+, Mg ^2+, Zn ^2+, Mn ^2+, other. The liquid can also be mercury, Gallium, eutectic Gallium, or ionic liquids of the type bmim PF ₆ , bmim BF ₄ or tmba NTf ₂ .

The radius of the drop F1 may for example be between 10 microns and centimeter, and preferably be 1mm.

The surrounding fluid F2 is preferably insulating and may be air, a mineral oil or silicone, a perfluorinated solvent, such as FC-40 or FC-70, or an alkane.

The surrounding fluid F2 is immiscible with the conductive liquid F1 of the drop.

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

The voltage generator 50 applies a potential to the excitation electrode 20 substantially different from that of the drop F1. An electrowetting voltage U is then generated between the excitation electrode 20 and the drop F1. Due to the common symmetry of the excitation electrode 20 and the drop F1, the associated electric field is substantially normal to the triple line, in the plane thereof.

The electric field therefore has substantially no tangential component, which avoids any electrohydrodynamic or electrokinetic phenomenon of vortex formation, such as, for example, in the device according to the prior art for example.

Voltage modulation v induces a substantially isotropic contact angle variation along the triple line. The drop F1 does not undergo substantially any displacement, in particular in the wetting plane. The electric field is thus oscillating and radial about the axis of symmetry of the drop F1 and the excitation electrode 20.

The electric field then causes a variation of the contact angle and possibly an oscillating and radial displacement of the triple line around an equilibrium position.

The harmonic variation of the contact angle then generates a network of axisymmetric waves at the interface I of the drop F1, from the triple line.

The waves propagate uniformly at the interface, thus achieving a micro-mixing of the liquid of the drop F1 substantially homogeneous.

By the axisymmetric character of the waves, a resonant mode is obtained at the apex 41 of the drop, that is to say in the zone substantially furthest from the drop. The amplitude is then maximum at the apex 41 and has a defined frequency.

Preferably, the waves have an amplitude preferably between 10 nm and 100 μm, preferably 1 μm.

The wavelength may be such that the amplitude to wavelength ratio is between 10 ^-5 and 1, preferably between 10 ^-4 and 10 ^-2 , preferably of the order of 10 ^-3 .

In the case where the drop contains target constituents in the solubilized state, the interface I of the drop F1 can be functionalized in order to selectively capture these constituents. The device according to the invention then makes it possible to concentrate the constituents from the volume of the drop at its interface.

The concentration is significant at the apex 41 of the F1 drop, and thus eliminates the disturbances due to the boundary conditions (triple line, wall of the hydrophobic layer).

The progressive component of the wave array can allow a selective concentration of the adsorbed components at the interface I of the drop F1. It can transport the constituents to the apex 41 of the drop, differentially depending on the extent of their molecular section. Here again, the concentration at the apex 41 is made significant.

Constituents not transported by the waves are likely to remain in the vicinity of the triple line. In this case, there is a device for separating or purifying these constituents. Specific extraction by ejection of droplets under electric field or by formation and breaking of a capillary bridge can allow to form two or more drops containing the separated constituents.

A variant of the first embodiment of the invention relates to the shape of the excitation electrode 20.

So, as shown in figure 3B the excitation electrode 20 may have an annular shape whose axis of symmetry substantially coincides with that of the drop F1.

In this case, the triple line can be located, in the absence of electrostatic stress, substantially opposite the inner border, or the outer border, or between the two borders.

The fact that the triple line is, out of electrostatic stress, substantially opposite the inner edge makes it possible to easily control the spreading of the drop under the effect of the electrowetting voltage.

Furthermore, the fact that the triple line is, out of electrostatic stress, substantially opposite the outer edge allows to use it as a trapping line of the triple line.

A second embodiment of the invention is shown on the figure 4 wherein the device comprises a first excitation electrode 20, and a second excitation electrode 30 forming a counter-electrode.

Preferably, the counter-electrode 30 is planar, integrated in said substrate 11, and included in the median plane of the first excitation electrode 20.

The figure 4 is a schematic representation in longitudinal section of a device comprising an annular excitation electrode 20 surrounding the disk-shaped counterelectrode 30. The two electrodes 20, 30 have an axis of symmetry substantially coinciding with that of the drop.

The Figure 5A is a top view of said electrodes. The spacing between the electrodes can be between 1 .mu.m and 10 .mu.m.

To generate an oscillating and radial electric field around the first axis of symmetry, a generator The voltage difference 50 can apply a potential difference to the electrodes 20, 30. This potential difference makes it possible to generate a potential difference, referred to as electrowetting, between the electrodes 20, 30 and the drop F1.

The electrowetting voltage has the same characteristics as in the first embodiment and is therefore not described again here. The waves formed at the interface are also identical to what has been described previously.

The triple line of the drop is, out of electrostatic stress, preferably located substantially opposite the outer edge of the counter electrode 30, of the inner or outer edge of the excitation electrode 20.

If the annular electrode 20 has an outer edge 22 sufficiently remote from the drop, the geometry of this border 22 may be arbitrary, for example polygonal, since the electric field at the triple line remains radial.

The Figures 5B and 5C are top views of the first excitation electrode 20 and the second excitation electrode 30 forming a counter-electrode.

The Figure 5B illustrates half annular electrodes 20, 30 and the Figure 5C electrodes 20, 30 in the form of a half-disc. Each electrode is arranged facing one another, so that the electrical activation of the electrodes 20, 30 by the voltage generator 50 makes it possible to generate a radial electric field around the first axis of symmetry. The minimum spacing between the electrodes can be between 1 .mu.m and 10 .mu.m.

The operation and embodiment of the device according to the second embodiment are identical to what has been described previously.

The advantage of using a second electrode electrode 30 against the electrode is to set the potential of the drop to a substantially equidistant value of the potentials of the two electrodes 20, 30. The electrowetting voltage is thus better defined in the first embodiment in which the drop F1 has a floating potential.

It should be noted that the dielectric layer 12 is not essential to the phenomenon of electrowetting. Indeed, in the absence of a dielectric layer 12, the drop F1 is then in electrical contact with the excitation electrode 20. During the activation of the electrode 20, an electric double layer is formed in the droplet. the surface of the electrode 20 and forms a dielectric layer whose thickness is of the order of magnitude of the Debye distance (a few tens of nanometers). The electrowetting voltage applied remains advantageously low in order to avoid electrochemical phenomena such as the electrolysis of water.

Moreover, it is advantageous to increase the hydrophobicity of the solid layer on which the drop rests, to promote the sliding of the triple line and limit the viscous dissipation. For this, thiols can be grafted onto the solid layer in question.

It may be advantageous, on the contrary, to trap the triple line to limit its displacement and associated viscous dissipation. For this, the triple line can be trapped by a ring-shaped roughness etched in the solid substrate. In this case, the waves are not formed by the oscillating and radial displacement of the triple line but by the harmonic variation of the contact angle.

It should also be noted that the device according to the invention has the advantage of not requiring a counter-electrode arranged in direct electrical contact with the drop, for example in the form of a suspended wire. Thus, the electric field remains normal to the triple line. The waves formed are therefore axisymmetric, thus avoiding any disturbance of the axis of symmetry due to the presence of the counter-electrode. This also allows for greater ease of implementation and integration into existing on-chip labs. In addition, a counter-electrode in direct contact with the drop, for example in the form of suspended wire, can disturb the concentration of the constituents at the interface.

The figure 6 is a schematic representation in longitudinal section of the device according to a third embodiment of the invention.

The device no longer comprises a single plane substrate 11, but also a second substrate 11-1, disposed opposite the first 11 and substantially parallel thereto.

The second substrate 11-1 also comprises at least one excitation electrode 20-1, 30-1, opposite the that 20, 30 of the first substrate. A hydrophobic layer and a dielectric layer 12-1 can also be provided.

A drop F1 can be sandwiched between the two substrates so as to form a capillary bridge. The lower excitation electrodes 20, 30 and 20-1, 30-1 are connected to the voltage generator 50, or as shown in FIG. figure 6 to a second voltage generator 50-1 synchronous with the first 50.

Thus, the activation of the electrodes makes it possible to generate waves according to the same characteristics as previously. The resonant mode is here formed at the central section 42 of the capillary bridge.

The constituents can thus be transported to the central section 42 of the liquid bridge, differentially according to the extent of their molecular section. The device then makes it possible to concentrate the constituents of the interface at the interface line of the central section 42 of the capillary bridge.

Constituents not transported by the waves are likely to remain in the vicinity of the lower and upper triple lines. In this case, there is a device for separating or purifying these constituents. Specific breakage extraction of the capillary bridge may be practiced by relative vertical removal of the first and second substrates from each other, or by amplification of the electrowetting voltage.

The device according to the third embodiment has an operation and an embodiment substantially similar to what has been described in the first and second embodiments.

The invention also relates to an analysis device comprising a device for forming waves at the interface of a droplet according to any one of the embodiments described above.

The analysis of the drop may be performed for the purpose of rheological analysis, to measure surface tension, dynamic viscosity, interfacial viscosity and elasticity, etc. It can also detect in real time the interfacial aging and thus the concentration of target constituents.

The device for analyzing a drop of liquid, according to a first embodiment, comprises a wave forming device as described above, means for geometric characterization of the waves formed, and analysis means, connected to said Geometric characterization means for analyzing, from the geometrical characterization of the waves formed, the physical and / or chemical properties of said drop F1.

According to a first variant, the geometric characterization means are means for measuring the amplitude of the waves formed, for example, by light absorption and / or interferometry.

The measurement of the amplitude is preferably local, in the interfacial zone of the resonant mode, that is to say at the level of the apex 41 for a semi-spherical drop, and at the central section 42 of a capillary bridge.

The figure 7 gives an example of an analysis device with amplitude measurement, here at the apex of a semi-spherical drop.

The measurement of the amplitude is preferably localized in the zone of the resonant mode 41. Indeed, the resonant nature of the waves is particularly sensitive to the presence of constituents concentrated at the interface. Thus, as the interface is enriched in constituents, we can observe a shift in the resonant frequency. This behavior can be measured in real time during the interfacial aging process, or by comparison between an initial stationary chemical state of the interface and a final steady state, after concentration at the interface.

The linear behavior of the waves, that is to say having a very low wavelength amplitude ratio, of between 10 ^-5 and 1, preferably between 10 ^-4 and 10 ^-2 , or of the order of 10 ^-3 , allows to connect the resonant frequency to the rheological properties of the interface by a dispersion relation. In addition, the dynamic surface tension is dependent on the value of the concentration of components at the interface.

Also, the measurement of the amplitude at the apex 41 of the drop F1 makes it possible to obtain, using the means of analysis, the resonance frequency and thus the rheological and thus physicochemical properties of the liquid of the drop.

The light absorption technique (not shown) can also be used, which makes it possible to measure the height of the drop. In this detection mode, a light source sends a beam through the drop. This beam is reflected on the electrode 20, passes through the drop in the opposite direction, then is collected by an optical and sent to a detector. The beam can also be transmitted through the droplet and the substrate, the latter then being transparent to the incident wavelength, and then detected. The signal measured by the detector is given by Beer Lambert's law. It is therefore inversely proportional to the height of the liquid. The light source may be a laser or a light emitting diode (LED). The detector may be a photodiode, a camera or any other light sensitive device. This measurement of absorption strongly depends on the presence of biological species. It is advantageous to standardize the height measurements when the drop oscillates by the height of the drop at rest. This makes it possible to perform a more sensitive differential measurement than the absolute measurements.

It is advantageous to use the interferometry technique which makes it possible to measure in real time the amplitude of the waves of the interface at the apex 41 of the drop. It has the advantage of being easy to integrate on a lab-on-a-chip. The measurement accuracy is finer than that of other optical techniques and the measurement is faster to operate since it is a single analog signal to be processed.

The principle of the interferometric technique is presented on the figure 7 in the example of a hemispherical drop.

A part of a laser beam, delivered by the source 61, is led by a network 62, which may be a fiber network, towards the apex 41 of the drop while the other part is directed towards a photodetector 63. Partially at the interface I of the drop F1, the beam is returned to the photodetector 63 on which it interferes with the first beam. A network of interference fringes appears and when the interface of the drop is set in motion, the fringes move. The photodetector 63 translates this movement of fringes by a variation of intensity whose evolution over time generates a frequency modulated signal. The temporal evolution of the instantaneous frequency makes it possible to translate the displacement of the apex 41 of the drop (treatment of the signal of the time-frequency type or by identification of an interferometric model). The minimum threshold of movement of the apex 41 of the drop may be half a wavelength, or about 300 nm for a HeNe laser emitting in the red. By its ease of implementation, this optical technique allows easy integration in labs on a chip.

The light source 61 is preferably coherent. In one embodiment of the invention, the light source 61 is a laser diode, for reasons of compactness, cost and integration. Liquid height measurements are more accurate at short wavelengths, but lasers are less compact and more expensive. As a result, red and near-infrared wavelengths are preferred.

In the case of measurements coupled with fluorescence, the laser is selected according to the absorption wavelengths of the fluorophores present in or at the interface of the drop.

The light source 61 may optionally be thermoregulated in order to deliver the most constant power possible. Its power can also be continuously monitored and adapted to correct the effects of certain parameters that may disturb the measurement (temperature, height of the drop at rest, optical index of the fluid, etc.)

• un coupleur 1 vers 2 (Y, splitter) qui divise le faisceau laser en deux voies d'amplitude respective réglable ;
• un coupleur 2 vers 1 (Y, concentrateur), qui envoie le faisceau laser vers la goutte et collecte la réflexion sur l'interface pour l'envoyer vers la dernière partie du dispositif ;
• un dispositif de focalisation délivrant la lumière du laser sur la goutte et collectant la réflexion sur la surface supérieure. Ce dispositif peut être constitué d'une tête de fibre clivée, d'une fibre lentillée, d'une microlentille, ou d'une selfoc (dans le cas où plusieurs gouttes seraient analysées simultanément) ; et
• un coupleur 2 vers 1 (Y, concentrateur), qui concentre dans une même fibre le faisceau provenant directement du laser et celui issu de la réflexion sur la goutte.

The beam splitter 62 may be composed of several elements:

• a coupler 1 to 2 (Y, splitter) which divides the laser beam into two channels of respective adjustable amplitude;
• a 2-to-1 coupler (Y, concentrator), which sends the laser beam to the drop and collects the reflection on the interface to send it to the last part of the device;
• a focusing device delivering laser light to the drop and collecting reflection on the upper surface. This device may consist of a cleaved fiber head, a lenticular fiber, a microlens, or a selfoc (in the case where several drops would be analyzed simultaneously); and
• a coupler 2 to 1 (Y, concentrator), which concentrates in the same fiber the beam coming from directly from the laser and that from the reflection on the drop.

The Y couplers mentioned above can be optical fiber couplers or microprisms.

The resulting beam is then sent to the photodetector 63.

The photodetector 63 allows the measurement of interference and can be any type of light-sensitive device (photodiode, camera, avalanche photodiode (APD) etc.). A filter transmitting only the wavelength of the laser may optionally be placed in front of the photodetector 63 in order to limit the light disturbances external to the device (ambient light). The coupling between the fiber, if there is fiber, and the photodetector 63 can be achieved by gluing, taping, or by an optical device (particularly if it is desired to place a filter in front of the photodetector).

• Une grande facilité d'intégration. Une goutte déplacée par électromouillage peut être facilement centrée sur l'un des dispositifs objet de l'invention, et disposée de sorte que son axe de symétrie vertical soit aligné avec une fibre optique à des fins de détection in situ ;
• La grande sensibilité d'un capteur interférométrique ;
• La robustesse d'une technique optique ;
• La mesure absolue sans étalonnage ; et
• La possibilité d'utiliser une détection synchrone pour augmenter le rapport signal sur bruit.

The interferometry amplitude measurement technique has a number of advantages:

• A great ease of integration. A drop ejected by electrowetting may be easily centered on one of the devices object of the invention, and arranged so that its vertical axis of symmetry is aligned with an optical fiber for in situ detection purposes ;
• The high sensitivity of an interferometric sensor;
• The robustness of an optical technique;
• Absolute measurement without calibration; and
• The ability to use synchronous detection to increase the signal-to-noise ratio.

The amplitude measuring means 60 are connected to the analysis means 70, for example arranged on a printed circuit (not shown), which make it possible to analyze the measured amplitude in order to extract the resonance frequency, and thus to to deduce the microrheological or physicochemical properties of gout.

Of course, the measuring and analysis means can be used on a drop which forms a capillary bridge. In this case, the measurement is preferably made at a point of the central section of the capillary bridge, zone of the interface of the resonant mode.

According to a second variant, the geometric characterization means are means for measuring the slope of the waves formed along a line of the interface, for example by refractometry.

The known method of refractometry (not shown) allows a slope measurement along a line of the interface, static or dynamic. It is preferable to apply this method along a line of the long interface, for example a line included in a plane passing through the center and the apex of the drop, or, in the case of a capillary bridge, in a plane passing through the central section of said capillary bridge.

Like the measurement of amplitude, the measurement of the slope makes it possible to obtain, using the means of analysis, the rheological and / or physicochemical properties of the liquid of the drop.

Of course, the geometric characterization means may comprise, at one and the same time, means for measuring the amplitude of the waves formed and means for measuring the slope of the waves formed along a line of the interface, as described above.

According to a second embodiment, the device for analyzing a drop of liquid comprises a wave forming device according to any one of the embodiments described above, means for kinematic characterization of the waves formed, and means for analysis, connected to said kinematic characterization means, for analyzing, from the kinematic characterization of the waves formed, the physical and / or chemical properties of said drop F1.

The kinematic characterization means may be means for measuring the normal speed of the waves formed, which may be similar to those for measuring the amplitude by interferometry, as described above. Indeed, the publication of Davoust et al. entitled "Detection of waves at the interface of an optical fiber" Progr. Colloid Polym. Sci. (2000), 115, 249-254 shows that these measuring means make it possible to obtain both the amplitude at the desired point and the normal speed.

The analysis of the chemical properties of the drop can thus be carried out without marking biological or chemical targets.

It may further comprise means for measuring, at the interface of said drop, the concentration of biological or chemical targets labeled with a fluorescent or radioactive compound.

These means for measuring the concentration may comprise a detector for measuring radiation, for example photon radiation. In the latter case, the photodetector may be an imager, an avalanche photodiode, a confocal microscope.

Alternatively, the device for analyzing a drop of liquid may not comprise means for characterizing the waves formed, but means for measuring, at the interface of said drop, the concentration of marked biological or chemical targets. The formation of the waves then makes it possible to mix the liquid of the drop, or even to achieve an optionally selective concentration of biological or chemical targets in a given zone of the interface, such as the apex of a drop, or the central section. a capillary bridge.

Finally, it is possible to use the wave forming device as described above, to form waves on the surface of a drop of blood.

Furthermore, the device for analyzing a drop of liquid as described above, said liquid being blood, can be advantageously used to estimate the coagulation time.

The measurement of a coagulation time is relevant for platelet disorders or haemophiliacs but also and especially for all transplant patients who receive anti-coagulant therapy.

The precise dosing of this treatment requires regular measurements which are usually performed using macroscopic facilities in the analytical laboratories.

The use of the analysis device according to the invention would then make it possible to save a lot of time and money.

Coagulation (secondary hemostasis) is triggered by a polymerization reaction following a complex cascade of coagulation factors.

This polymerization consists of a transformation of fibrinogen, a protein contained in the blood plasma, into polymerized fibrin, which creates a clot.

The typical time scale of this process is of the order of a few minutes.

The polymerization reaction gives rise to several orders of magnitude of dynamic viscosity within the drop.

Oscillations on its surface are dependent on the interfacial properties as well as the volume properties of the drop.

Continuous measurement by an optical technique for example of the amplitude of these oscillations can thus provide information on a rate of temporal damping particularly close to the coagulation time.

Thus, the device for analyzing a drop of blood makes it possible to obtain the coagulation time in a particularly rapid and inexpensive manner.

• disposer une goutte de liquide F1 sur au moins une électrode d'excitation 20 présentant un premier axe de symétrie, de sorte que l'axe de symétrie de ladite goutte F1 coïncide sensiblement avec ledit premier axe de symétrie, et
• générer un champ électrique oscillant et radial autour dudit premier axe de symétrie, de sorte que des ondes axisymétriques sont formées par électromouillage à l'interface I de ladite goutte F1.

The invention also relates to a method for forming waves at the interface of a drop of liquid, comprising the following steps:

• disposing a drop of liquid F1 on at least one excitation electrode 20 having a first axis of symmetry, so that the axis of symmetry of said drop F1 coincides substantially with said first axis of symmetry, and
• generating an oscillating and radial electric field around said first axis of symmetry, so that axisymmetric waves are formed by electrowetting at the interface I of said drop F1.

Said waves preferably have an amplitude-to-wavelength ratio of between 10 ^-5 and 1, and advantageously equal to 10 ^-3 .

The invention also relates to a method for analyzing a drop of liquid, comprising the implementation of a wave forming method according to any one of the characteristics described above, a step of geometric characterization of said formed waves, then a step of analyzing the physical and / or chemical properties of said drop, from the geometric characterization of said formed waves.

As for the analysis device, the geometric characterization step may be a measurement of the amplitude of the waves formed, or a measurement of the slope of the waves formed along a line of the interface.

Preferably, the measurement of the amplitude of said waves is carried out in a determined zone of the interface substantially distant from the triple line of the drop, for example at the apex of a hemispherical drop, or in the central section of a capillary bridge.

The measurement of the slope can be carried out along a line contained in a plane passing through the apex and the center of a hemispherical drop, or in a plane containing the central section of a capillary bridge.

The invention also relates to a method for analyzing a drop of liquid, comprising the implementation of a wave forming method according to one of the preceding characteristics, a step of kinematic characterization of said waves formed, then a step of analyzing the physical and / or chemical properties of said drop, from the kinematic characterization of said formed waves.

The kinematic characterization step may be a measure of the normal velocity of the formed waves, as previously described.

The method of analyzing a drop of liquid may further comprise a step of measuring, at the interface of said drop, the concentration of marked biological or chemical targets.

The invention also relates to a method for analyzing a drop of liquid, comprising the implementation of a wave forming method according to any one of the preceding characteristics, and a measuring step, at the interface of said drop, the concentration of marked biological or chemical targets.

Claims (22)

Wave forming device at the interface (I) of a liquid droplet (F1) by electrowetting, characterized in that it comprises: at least one excitation electrode (20; 30) adapted to generate an oscillating and radial electric field around a first axis of symmetry, under the effect of electrical control, so that in the presence of a drop of liquid (F1) disposed on said excitation electrode (20; 30) and having an axis of symmetry substantially coinciding with said first axis of symmetry, said electric field generates waves at the interface (I) of said droplet (F1), said generated waves being essentially axisymmetric. Wave forming device according to claim 1, characterized in that said waves have an amplitude-to-wavelength ratio of between 10 ^-5 and 10 ^-1 , and / or an amplitude-to-beam ratio of the lower or equal drop at 10 ^-1 . Wave forming device according to one of Claims 1 to 2, characterized in that it comprises a single excitation electrode (20) having substantially a disc shape. Wave forming device according to one of Claims 1 to 2, characterized in that it comprises a single excitation electrode (20) substantially annular. Wave forming device according to one of Claims 1 to 2, characterized in that it comprises a first annular excitation electrode (20) and a second counter-electrode excitation electrode (30) having substantially a disk shape surrounded by said first excitation electrode (20). Wave forming device according to one of Claims 1 to 2, characterized in that it comprises a first excitation electrode (20) and a second electrode electrode (30) forming a counter-electrode, each presenting substantially a half-annular shape arranged facing one another. Wave forming device according to one of Claims 1 to 2, characterized in that it comprises a first excitation electrode (20) and a second electrode electrode (30) forming a counter-electrode, each presenting substantially a form of half-disc arranged opposite one another. Wave forming device according to one of Claims 1 to 2 or 4 to 6, characterized in that the excitation electrode or electrodes (20; 30) have an inner edge (21; 31). defining a substantially circular inner edge, the triple line of said drop being substantially opposite said inner edge. Wave forming device according to one of Claims 1 to 7, characterized in that the excitation electrode or electrodes (20; 30) comprise an outer edge (22; 32) defining a substantially circular outer edge, the triple line of said drop being substantially opposite said outer edge. Wave forming device according to any one of claims 1 to 9, characterized in that said electric field induces a difference in electrowetting potential between the excitation electrode (20) and said droplet (F1) exhibiting a frequency between 10Hz and 150Hz. Wave forming device according to claim 10, characterized in that said electrowetting potential difference has an amplitude of between 1V and 100V. Wave forming device according to any one of claims 1 to 11, characterized in that it comprises means for trapping the triple line of said droplet (F1). Wave forming device according to one of Claims 1 to 12, characterized in that it comprises, furthermore, at least one secondary excitation electrode (20-1), opposite, parallel to said driving electrode (20) adapted to generate an oscillating and radial electric field around a third axis of symmetry substantially coinciding with said first axis of symmetry, under the effect of said electric control. Wave forming device according to claim 13, characterized in that said droplet (F1) is a capillary bridge formed between said excitation electrode (20) and said secondary excitation electrode (20-1). Device for analyzing a drop of liquid, characterized in that it comprises: - a wave forming device according to any one of claims 1 to 14, means for geometric or kinematic characterization of the waves formed, and analysis means (70), connected to said characterization means, for analyzing, from the characterization of the waves formed, the physical and / or chemical properties of said droplet (F1). Device for analyzing a drop of liquid according to claim 15, characterized in that the geometric characterization means are means for measuring the amplitude (60) of the waves formed, and / or the means for measuring the slope waves formed along a line of the interface. Device for analyzing a drop of liquid according to claim 16, characterized in that the kinematic characterization means are means for measuring the normal speed of the waves formed. Device for analyzing a drop of liquid, characterized in that it comprises: - a wave forming device according to any one of claims 1 to 14, means for measuring, at the interface of said drop, the concentration of marked biological or chemical targets. A method of forming waves at the interface of a liquid drop by electrowetting, characterized in that it comprises the following steps: disposing a drop of liquid (F1) on at least one excitation electrode (20) having a first axis of symmetry, so that the axis of symmetry of said droplet (F1) substantially coincides with said first axis of symmetry, and - Generating an oscillating and radial electric field around said first axis of symmetry, so as to form substantially axisymmetric waves at the interface (I) of said droplet (F1). Waveforming method according to claim 19, characterized in that said waves have an amplitude-to-wavelength ratio between 10 ^-5 and 10 ^-1 , and / or an amplitude ratio on the radius of the drop of less than or equal to 10 ^-1 . A method of analyzing a drop of liquid, comprising the implementation of a wave forming method according to claim 19 or 20, a step of geometric or kinematic characterization of said formed waves, then a step of analyzing the physical and / or chemical properties of said drop, from the characterization of said formed waves. A method of analyzing a drop of liquid, comprising carrying out a wave forming method according to claim 19 or 20, and a step of measuring, at the interface of said drop, the concentration of marked biological or chemical targets.

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