FR3061303A1 - ELECTROCHEMICAL CELL DEVICE AND ELECTROCHEMICAL MEASUREMENT SYSTEM COMPRISING SUCH A DEVICE - Google Patents

Abstract

The present invention relates to a device (51) of electrochemical cells (C (i, j)), characterized in that it comprises: - a superposition of three electrode layers (1, 2, 3) with their reports of tracks relays (12, 22, 32), said reference electrode layer layers (2), counter electrode layer (3) and working electrode layer (1), the electrodes of these three layers being at least in part superimposed, and a plurality of orifices (40) passing through the superimposed electrodes (21, 31) of the reference electrode layer (2) and the counter-electrode layer (3), these orifices ( 40) being closed by the working electrode layer (1) and thus constituting a volume (43) forming said electrochemical cells (C (i, j)) whose working electrodes (11) are the bottom (44), said electrochemical cells (C (i, j)) being arranged in a pattern comprising N lines of index i and M columns of index j of cells, av ec N an integer greater than or equal to 1 and M an integer greater than or equal to 1, such that if N is equal to 1, then M is greater than or equal to 2, and if M is equal to 1, then N is greater than or equal to 2, in which: - the cells (C (i, j)) of a line i comprise a common working electrode which electrically connects said cells of the line i, - the cells (C (i, j)) of a column j comprise a common reference electrode and a common counter electrode which electrically connect said cells of the column j.

Description

(® Agent (s): REGIMBEAU.

® ELECTROCHEMICAL CELL DEVICE AND ELECTROCHEMICAL MEASUREMENT SYSTEM COMPRISING SUCH A DEVICE.

FR 3 061 303 - A1

The present invention relates to a device (51) of electrochemical cells (C (i, j)), characterized in that it comprises:

- a superposition of three layers of electrodes (1,2, 3) with their relative tracks transfers (12, 22, 32), these layers forming layer of reference electrodes (2), layer of counter-electrodes (3 ) and layer of working electrodes (1), the electrodes of these three layers being at least partially superimposed, and,

- A plurality of orifices (40) passing through the superposed electrodes (21,31) of the reference electrode layer (2) and of the counterelectrode layer (3), these orifices (40) being closed by the layer d working electrodes (1) and thus constituting a volume (43) forming said electrochemical cells (C (i, j)) of which the working electrodes (11) are the bottom (44), said electrochemical cells (C (i, j)) being arranged according to a pattern comprising N rows of index i and M columns of index j of cells, with N an integer greater than or equal to 1 and M an integer greater than or equal to 1, such as if N is equal to 1 then M is greater than or equal to 2, and if M is equal to 1 then N is greater than or equal to 2, in which:

the cells (C (i, j)) of a line i comprise a common working electrode which electrically connects said cells of line i,

the cells (C (i, j)) of a column j comprise a common reference electrode and a common counter electrode which electrically connect said cells of column j.

i

ELECTROCHEMICAL CELL DEVICE AND ELECTROCHEMICAL MEASUREMENT SYSTEM COMPRISING SUCH A DEVICE

FIELD OF THE INVENTION

The present invention relates to an electrochemical cell device for detecting or even quantifying, electrochemically, chemical or biochemical species in solutions previously introduced into the electrochemical cells of the device. Such a device is particularly suitable for carrying out, or in addition to, methods for assaying biological molecules such as immunoenzymatic methods, also called immunoassays, or “immunoassay”, according to English terminology, such as the technique ELISA (from the English term: Enzyme Linked Immunosorbent Assay) or else such as quantitative polymerase chain reaction (PCR) based on in vitro DNA amplification.

STATE OF THE ART

An electrochemical cell device generally includes a plurality of electrochemical cells, each of which is composed of a working electrode, a reference electrode, and a counter electrode also called an auxiliary electrode. The cells are produced on a suitable support by various techniques such as screen printing or photolithography.

This is particularly the case for the electrochemical device described in the scientific publication Anal. Chem. 2002, 74, 3321-3329, Aguilar et al. in which the cells are composed of gold electrodes formed by physical gas deposition or by plasma assisted chemical vapor deposition. In each case, the wells of the electrochemical cells are produced by photolithography of a polyimide layer.

The manufacture of the electrochemical device of this document requires the use of sophisticated and complex manufacturing processes to be implemented, in addition to imposing particular constraints, such as the need to use them in clean rooms.

The scientific publication Electrochimica Acta 52 (2007) 7248-7253, Rawson et al., Describes an electrochemical device in which the electrodes constituting the electrochemical cells are serigraphed in the form of tubular carbon and silver microstrips. In particular, the electrodes are screen printed on either side of a polyester support and then are covered by a dielectric layer. The cell is then formed by mechanical drilling of a well with a diameter of the order of 1 mm through the electrode support.

In each of the two previous publications, the electrochemical cells obtained comprise annular electrodes resulting from the production of the corresponding wells, whether the latter are produced by photolithography or by mechanical drilling. However, making a well through the various electrodes previously made on a support may have the consequence of degrading the working electrode and in particular its measurement surface, which results in erroneous current measurements at the cell output and inconclusive results for the associated assay method.

Among the different techniques used for the production of electrodes, screen printing is widely used since it is both quick to implement and has a relatively low financial cost compared to other techniques.

Conventionally, the three electrodes are on the same flat support, and are associated with their runway reports. The runway reports constitute electrical connections making it possible to electrically connect the electrodes of the different electrochemical cells to an electrical connection device, the latter electrically connecting the electrochemical device to a potentiostat which applies an electrical potential to the cells of the device.

In other words, each electrochemical cell includes a working electrode, a reference electrode, and a counter electrode associated with as many carryovers, i.e. a carryover for the working electrode, a carryover for the 'reference electrode, and a track report for the counter electrode. This substantial number of carryovers leads to a bulk of the device, which is particularly problematic in the case where it is desired to have a device whose cells have a very small volume and having a high cell density.

The miniaturization of electrochemical devices is indeed a recurring problem in the field of electrochemical analysis, it involves a high density of electrochemical cells of very small volume.

However, due to the space generated by the number of carryovers of the electrodes of each cell, the decrease in the volume of the cells cannot be accompanied by a proportional decrease in the surface occupied by said cells with their carryovers.

It therefore appears necessary to reach this minimum level of miniaturization imposed by the very design of the electrochemical cells and their associated runway reports.

Finally, in order to perform electrochemical measurements such as methods for assaying biological molecules, the electrodes of the different cells are connected to a potentiostat. However, each cell is connected to the potentiostat independently of the other cells, so that the measurement of the electric current at the output of the cells is carried out on one cell at a time. Consequently, the installation of the various electrical connectors connecting the carry-over tracks of the device to the potentiostat is long and laborious, and the measurement of the current is just as much so, in particular when the device comprises a large number of cells.

STATEMENT OF THE INVENTION

The aim of the invention is therefore to remedy the drawbacks of the prior art by proposing an electrochemical device in which the density of the cells, and possibly the number of cells, are greater than the existing devices.

The invention also aims to provide an electrochemical device in which the cells each have a reduced number of carryovers compared to existing devices, in order to reduce the bulk caused by the cells and their carryovers.

The invention aims to provide an electrochemical device the structure of which makes it possible to adapt, and in particular to decrease, the volume of the electrochemical cells which it comprises, to a value lower than that of the existing devices, preferably to a value less than 10 pL, and more preferably at a value of the order of or less than 1 pL.

Another object of the invention is to provide an electrochemical device in which the working electrode of the electrochemical cells retains its structural integrity during the manufacture of the device, has increased efficiency, and in which the surface of the working electrode is maximized in relation to the volume of the electrochemical cell. It is specified that the volume of the electrochemical cell corresponds to the volume of the well of the cell receiving a chemical solution.

Another object of the invention is therefore to provide an architecture of electrochemical cells which is particularly suitable for being implemented in the device mentioned.

The invention also aims to propose a method for manufacturing such an electrochemical device having the characteristics described above.

Finally, the invention aims to propose an electrochemical measurement system comprising this electrochemical device. In particular, the system includes a reduced number of electrical connectors compared to the state of the art.

To this end, according to a first aspect, the invention proposes an electrochemical cell device, characterized in that it comprises:

A superimposition of three layers of electrodes with their relative tracks transfers, these layers forming reference electrode layer, layer of counterelectrodes and layer of working electrodes, the electrodes of these three layers being at least partly superimposed, and, • a plurality of orifices passing through the superposed electrodes of the reference electrode layer and of the counter-electrode layer, these orifices being closed by the layer of working electrodes and thus constituting a volume forming said electrochemical cells of which the working electrodes are the bottom, said electrochemical cells being arranged in a pattern comprising N rows of index i and M columns of index j of cells, with N an integer greater than or equal to 1 and M an integer greater than or equal to 1, such that if N is equal to 1 then M is greater than or equal to 2, and if M is equal to 1 then N is greater than or equal to 2, da ns which:

• the cells of a line i comprise a common working electrode which electrically connects said cells of line i, • the cells of a column j include a common reference electrode and a common counter electrode which electrically connect said cells of column j.

The indices i and j make it possible to designate respectively the rows and the columns of the device. Thus, i is an integer which varies between 1 and N, and j is an integer which varies between 1 and M.

According to other aspects, the proposed device has the following different characteristics taken alone or according to their technically possible combinations:

at least one of the layers of reference electrodes, counter-electrodes, and working electrodes is produced with its runway reports by screen printing;

each of the reference electrodes, counter electrodes, and working electrodes of the corresponding electrode layers comprises a single track transfer;

the device also comprises at least one electrically insulating layer comprising a plurality of orifices corresponding to the orifices passing through the layer of reference electrodes and the layer of counter electrodes, the thickness of said electrically insulating layer being chosen so as to adapt the volume of electrochemical cells;

said at least one electrically insulating layer is arranged above the device or at the interface of at least two of the electrode layers;

the device further comprises at least one adhesive layer arranged at the interface of at least two of the electrode layers, making it possible to connect said electrode layers and to keep them in position relative to one another;

the electrochemical cells have a volume less than or equal to 10 μΙ_, and preferably between 1nL and 1 μΙ_;

the device comprises a density of electrochemical cells greater than or equal to one cell per square centimeter, preferably greater than or equal to ten cells per square centimeter, and more preferably greater than or equal to one hundred cells per square centimeter.

According to a second aspect, the invention provides an electrochemical cell with three electrodes connected to runway reports, said cell being characterized in that it comprises:

• a working electrode which occupies the entire surface of the bottom of the volume formed by said cell, • a counter-electrode and a reference electrode situated in the walls of said cell, said electrodes and their relative tracks being located in planes different in said cell.

Optionally, the reference electrode and the counter-electrode are annular.

According to a third aspect, the invention proposes a method for manufacturing an electrochemical cell device, in which the following steps are implemented:

a) production of at least three layers of electrodes and their track transfers, these layers being intended to form a layer of reference electrodes, a layer of counter-electrodes and a layer of working electrodes, the electrodes of these three layers being configured to be at least partially superimposable one above the other,

b) superposition of the layer intended to form the layer of reference electrodes and of that intended to form the layer of counter-electrodes, then production of a plurality of orifices in the electrodes of the two layers thus superimposed,

c) assembly by superposition of the assembly obtained in step b) on the layer intended to form a layer of working electrodes, the latter closing the orifices at one of their ends, the orifices thus closed constituting volumes forming the electrochemical cells of which the working electrodes are the bottom, said assembly being carried out so as to obtain a pattern of electrochemical cells of the device described above.

According to other aspects, the proposed manufacturing process has the following different characteristics taken alone or according to their technically possible combinations:

step b) is as follows: production of a plurality of orifices in the electrodes of the layer intended to form the reference electrode layer and separately in the electrodes from that intended to form the layer of counter electrodes, then superimposition of the electrode layers thus pierced so as to make the orifices of each of the electrode layers correspond;

at least one of said layers of electrodes is produced with its run tracks by screen printing;

one or more of steps b) and c) are carried out by prior deposition of at least one adhesive layer on at least one of the electrode layers in order to connect said layers and to keep them in position relative to one another to the other ;

one or more of steps b) and c) are carried out by the addition, prior to the production of the orifices, of at least one electrically insulating layer on at least one of the electrode layers.

According to a fourth aspect, the invention proposes an electrochemical measurement system comprising:

• an electrochemical cell device as described above, • a potentiostat electrically connected to the electrochemical cell device, making it possible to impose a difference in electrical potential at the input of the electrochemical cells, and to measure an electric current intensity at the output of said electrochemical cells , • an electrical connection device able to selectively connect electrically, one or more of the reference electrodes and counterelectrodes of the device via their track transfers, with the potentiostat.

According to other aspects, the proposed electrochemical measurement system has the following different characteristics taken alone or according to their technically possible combinations:

the system is such that:

• the electrochemical cells of the electrochemical cell device are arranged according to the pattern described above, • the potentiostat comprises:

a voltage control device able to be electrically connected to the reference electrodes and the counter electrodes of the M columns of the electrochemical cell device, and selectively to a reference electrode and a counter electrode of a column j of the electrochemical cell device, for applying a setpoint potential to the reference electrode and to the counter-electrode of column j, at least one device for applying an electrical potential to a working electrode of a line i of the electrochemical cell device and of measuring the intensity of the electric current at said working electrode.

The electrical connection device includes:

• a first electrical distributor making it possible to selectively electrically connect the voltage control device with a reference electrode of a column j, and, • a second electrical distributor, making it possible to selectively electrically connect the application device d an electrical potential with a counter electrode of said column j, in order to impose a set electrical potential on said reference electrode controlled by means of said counter electrode.

The invention finally proposes a method for measuring an electric current intensity at the output of the electrochemical cells of an electrochemical cell device, by the implementation of an electrochemical measurement system described above, characterized in that it includes the following steps:

• for a measurement of an intensity of the electric current leaving the electrochemical cells of a column j of the electrochemical cell device:

a) imposing a set electrical potential on the reference electrode and on the counter electrode of a column j, said reference electrode and said counter electrode being selectively connected to the device for applying an electrical potential, the other reference electrodes and counter electrodes being disconnected,

b) imposing an electrical potential on the N working electrodes of the cells of column j, so as to generate a potential difference between the potential of the working electrodes and the setpoint potential of the reference electrodes and counter electrodes,

c) measure an intensity of electric current leaving the cells of column j at the working electrodes, the working electrodes being connected to the devices for measuring an electric current, • repeat steps a) to c) to measure an intensity of the electrical current at the outlet of the electrochemical cells (C (i, j)) of column j + 1 of the electrochemical cell device.

DESCRIPTION OF THE FIGURES

Other advantages and characteristics of the invention will appear on reading the following description given by way of illustrative and nonlimiting example, with reference to the appended figures which represent:

Figures 1A and 1B, a diagram of the layers of working electrodes, reference electrodes, and counter electrodes;

Figure 1C, a diagram of a device of one hundred electrochemical cells resulting from the assembly of the electrode layers of Figures 1A and 1B;

Figure 2, an embodiment of the electrode layers in which the electrodes are screen printed on screen printing films;

Figure 3, a diagram of an electrochemical cell of the device of Figure 1C;

Figure 4, a diagram of an electrochemical measurement system comprising the electrochemical cell device of Figure 1C;

Figure 5, a detailed representation of a system comprising a sixteen-cell electrochemical device;

Figure 6, an electrical diagram equivalent to a column of cells of the representation of Figure 5.

DETAILED DESCRIPTION OF THE INVENTION

The electrochemical cell device is represented in FIG. 1C under the reference 51 and is obtained from three layers of electrodes superposed one on the other represented in FIGS. 1A and 1B, in which are provided orifices which constitute the volume of the electrochemical cells, the volume as illustrated corresponding to the wells of said cells.

With reference to FIGS. 1A and 1B, the electrode layers comprise a first electrode layer intended to form a working electrode layer 1, a second electrode layer intended to form a reference electrode layer 2, and a third layer of electrodes intended to form a layer of counter-electrodes 3.

The electrodes 11, 21, 31 of these layers 1, 2, 3 are configured to be at least partially superimposable one above the other. On the other hand, the carryovers of tracks 12, 22, 32 may possibly be superimposable one above the other, but are preferably configured not to be so, so that all the carryovers of tracks of the different layers of electrodes are visible by an operator on the electrochemical device 51. This also offers ergonomic advantages since facilitating the electrical connection of the runway reports 12, 22, 32 to the electrical connection device and to the potentiostat. This aspect will be better understood on reading the description made in support of FIGS. 1C and of FIG. 4.

In the example of the Figures, the electrodes 11, 21, 31 are in the form of strips of electrodes connected to the runway reports. In particular, an electrode is associated with a carry-over.

The carryovers of tracks 12, 22, 32 make it possible to electrically connect, or connect, the electrodes 11,21,31 of the layers of electrodes 1,2, 3 to an electrical connection device 52, the latter being in turn electrically connected to a potentiostat 53. The potentiostat is suitable for imposing a difference in electrical potential on the cells, bearing the reference C (i, j), of the electrochemical device and for measuring an intensity of an electric current at the output of the cells. This last aspect will be developed in more detail later in this text.

The electrode layers are preferably produced by methods of applying a conductive material on a suitable support, such as screen printing, inkjet printing, vaporization, or even stamping. Particular preference will be given to screen printing. The resolution limit of the screen printing being approximately 30 μm, this leads to electrodes of approximately 100 μm in diameter, which is particularly advantageous compared to the cells of conventional devices which generally have a volume (corresponding to the volume of the cell well) between 20 pl_ and 100 μΙ_. To further reduce this volume, it is necessary to reduce the height of the wells formed by the cells, as will be described later.

The electrode support is preferably a plastic support, in particular polyethylene terephthalate (PET), polypropylene (PP), polycarbonate (PC), polyethylene (PE), or a cyclic olefin copolymer (according to English terminology: cyclic olefin copolymer, COC), or a ceramic support. According to a preferred embodiment of the invention, when the electrode layers are produced by a method of applying a conductive ink on a support, the reference electrodes 21 are produced in silver, and the working electrodes 11 as well as the counter electrodes 31 are made of carbon. Where applicable, since the carbon ink is not an efficient electronic conductor (R _s s 20 Ω / sq, Ω / sq denoting ohms per square or “ohm per square” according to English terminology), it is it is necessary to add a track 13, 33 in silver under the electrodes 11 and 31 in carbon in order to allow the passage of current at all the cells of the electrodes concerned, in particular to the cells furthest from the carryovers of tracks. Thus, the track transfers 12, 22, 32 extend from one end of the highly conductive reference electrodes 21, and over the entire length of the working electrodes 11 and weakly conductive counter electrodes 31, extending from one end of said working electrodes and counter electrodes.

According to a particular embodiment of the invention, at least one of the electrode layers is made of indium oxide doped with tin. Such an electrode is produced by one of the vapor deposition techniques well known to those skilled in the art. Since indium oxide doped with tin is transparent and conductive, in an even more particular embodiment, at least the layer of working electrodes is made of this material, thus allowing optical measurements to be taken in addition to electrochemical measurements.

An electrode layer 1, 2, 3 comprises one or more electrodes 11, 21, 31, the latter corresponding to electrode areas or electrode patterns. For reasons of simplification, the zones or patterns of electrodes will be assimilated to the electrodes.

The electrodes of each layer of electrodes 1, 2, 3 and their transfer tracks 12, 22, are produced on supports 10, 20, 30 distinct from each other.

More particularly, when the electrode layers are produced by screen printing, the electrodes are screen printed on screen printing films, shown in FIG. 2.

A first film 100 is then obtained on which the working electrodes 11 are screen printed, a second film 200 on which the reference electrodes 21 are screen printed, and a third film 300 on which the counter electrodes 31 are screen printed. An insulating layer 400 can also be assembled on the preceding electrode films, as will be described below.

Ports 40 are then produced in the reference electrode layer 2 and in the counter-electrode layer 3, at their electrodes 21, 31. Then the electrode layers thus pierced are superimposed so that the orifices 40 of the reference electrode layers and the orifices of the counter-electrode layers are in correspondence. The orifices 40 of the two layers are thus aligned and form continuous orifices which pass through both the layers of reference electrodes 2 and the layers of counter electrodes 3.

Alternatively, in order to simplify the embodiment, it is also possible to start by superimposing the reference electrode layer 2 and the counterelectrode layer 3, then make orifices 40 in the electrode layers thus superimposed. The orifices 40 are then produced simultaneously in the two superimposed layers, making the process simpler and quicker to execute.

It is preferable to make the orifices 40 by a laser method, in order to obtain orifices having a number of defects and roughness reduced compared to mechanical drilling methods such as blade drilling for example.

When the electrode supports are screen printing films 100, 200, 300, the latter conventionally comprise screen-printed targets 42 facilitating the alignment of the films. In order for the films to be aligned, it suffices to ensure that all of the test patterns of these films are themselves aligned.

To return to the assembly of the layers of reference electrodes 2 and of counter-electrodes 3, said layers of electrodes are arranged then superimposed so that the reference electrodes 21 and the counter-electrodes 31 are parallel to each other.

Finally, the layers of reference electrodes 2 and of counter electrodes 3 thus pierced and assembled are themselves assembled on the layer of working electrodes 1, in order to obtain a device 51 of electrochemical cells as shown in the Figure 1C. The electrode layers are superimposed in different planes, and the working electrode layer 1 forms the bottom 44 of the electrochemical cells C (i, j) of the device.

As regards the assembly of the layer of working electrodes 1, it is superimposed on the layers of reference electrodes and counter-electrodes so that the working electrodes are orthogonal to the reference electrodes 21 and to the counter-electrodes 31. The working electrodes are thus partially superimposed on the reference electrodes and the counter electrodes.

In doing so, a pattern of “crossed electrodes” is produced, the arrangement of the various elements of which makes it possible to obtain an electrochemical device 51 of reduced size in comparison with devices of the state of the art. We will come back to this aspect later.

Furthermore, one or more adhesive layers are preferably used, referenced in 5, 6, 7 in FIG. 3, which are positioned at the interface of two neighboring electrode layers (1,2, 3), in order to to connect them and keep them in position relative to each other.

The adhesive layer may for example comprise a double-sided adhesive, an adhesive such as a screen-printing adhesive activatable under ultraviolet (UV) radiation or a two-component screen-printing adhesive for example. It is also possible to use methods of bonding or assembling such layers, chosen according to the materials of the layers to be assembled, such as the firing of ceramic or the melting of plastic at low temperature for example.

In addition, optionally, an electrically insulating layer, which bears the reference 4 in FIG. 3, can be superimposed on one or more of the electrode layers. It is for example possible to position an insulating layer 4 on one or the other of the layers of reference electrodes 2 and of counter electrodes 3, in order to assemble them. It is also possible to plan to deposit a plurality of insulating layers 4 between different layers of electrodes. In particular, when the electrode layers are bonded together by adhesive layers 5, 6, 7, the insulating layers 4 are adjacent to said adhesive layers. Adding an insulating layer and adjusting its thickness allows the height and, therefore, the volume of the electrochemical cells to be adjusted.

The electrically insulating layer can be made for example of plastic material, in particular of polyethylene terephthalate (PET), polypropylene (PP), polycarbonate (PC), polyethylene (PE) type, or also of cyclic olefin copolymer type (according to Anglo-Saxon terminology: cyclic olefin copolymer, COC), or in ceramic material.

Figure 1C illustrates an electrochemical cell device 51 capable of being obtained following the completion of the steps of the manufacturing process described above. According to this embodiment, the electrochemical device comprises a hundred cells C (i, j) distributed according to a pattern comprising ten rows of cells, of index i, and ten columns of cells, of index j, with i a whole number included. between 1 and 10, and j an integer between 1 and 10. The rows i of cells and the columns j of cells are orthogonal. It will be understood that, depending on the orientation of the device in space, the lines can be columns and vice versa.

Each working electrode 11 is common to, that is to say electrically connected to, all the cells C (i, j) of a line i, that is to say to the ten cells of a line i .

Each reference electrode 21 is common to all the cells C (i, j) of a column j, that is to say to the ten cells of a column j.

Similarly to the reference electrodes 21, each counter electrode 31 is common to all the cells C (i, j) of a column j, therefore to the ten cells of a column j.

The counter-electrodes and the reference electrodes are thus arranged two by two along the columns j.

According to this pattern of crossed electrodes, the transfer tracks 12, 22, 32 advantageously extend from different parts of the device 51. The transfer tracks 12 of the working electrodes 11 extend from the lateral part (to the left ) of the device, the track transfers 22 of the reference electrodes 21 extend from the lower part (downwards) of the device, and the track transfers 32 of the counter-electrodes 31 extend from the upper part (towards the top) of the device. This offers the ergonomic advantages described above since facilitating the electrical connection of the runway reports 12, 22, 32 to the electrical connection device and to the potentiostat. For the same purpose, the runways reports 12, 22, 32 are also arranged so as to meet, without coming into contact with each other, in a determined zone of the device. In FIG. 1C, this zone is situated substantially in the extension of the left lateral part of the device 51, from which extend the runways 12 of the lines of working electrodes

11.

Advantageously, each of the working electrodes 11, reference electrodes 21, and counter electrodes 31 is connected to a single track transfer 12, 22, 32, so that there is a race transfer 12 by row of cells and two carryovers of tracks 22, 32 per column of cells. This makes it possible to reduce the number of track reports of the device, and by extension the number of electrical connectors necessary for the connection of said track reports to the potentiostat, while making it possible to carry out a simple and rapid sequential measurement of the electric current at the output of the cells, as will be explained in more detail below.

FIG. 3 represents a cell C (i, j) of the electrochemical device 51. The cell comprises a well 43 which is delimited laterally by a superposition of a layer of a reference electrode 2, of a layer of counter electrode 3, and an insulating layer

4, held in a fixed position relative to one another by adhesive layers 5,

6, 7, and the bottom 44 of which is a working electrode 11 on its support 10.

The superposition of the reference electrode layer 2, the counterelectrode layer 3, and the insulating layer 4 forms the side wall 45 of the electrochemical cell C (i, j). Each of these layers is separated from the neighboring layer (s) by an adhesive layer 5, 6, 7 formed by a double-sided adhesive ensuring the bonding of said layers together.

The layer of counter-electrodes 3 comprises a support layer 30 and a counterelectrode 31 produced on the upper surface of said support 30. The layer of counterelectrode 3 is surmounted by a first adhesive layer 5 on which the insulating layer 4 rests, the upper surface of which constitutes the upper surface of the electrochemical cell. It rests on a second adhesive layer 6, itself resting on the reference electrode layer 2, at the interface between the counter-electrode layer 3 and the reference electrode layer 2.

Similarly, the reference electrode layer 2 comprises a support layer 20, and a reference electrode 21 produced on the upper surface of said support. The reference electrode layer 2 is surmounted by the second adhesive layer 6. It rests on a third adhesive layer 7 itself resting on the working electrode layer 1, at the interface between the electrode layer of reference 2 and the working electrode layer 1.

The addition of the insulating layer 4 and the adjustment of its thickness E _C p makes it possible to adjust the height H _P of the electrochemical cells of the device, and consequently the height of the device itself. This is particularly useful in the case where the thickness of the different layers of electrodes is fixed but the height of the cells needs to be modified.

It is specified that, in general, the height of the cell can be adjusted by adapting the thickness of the different electrode layers, and if necessary the thickness of the electrode supports.

The reference electrode layer 2 rests on the working electrode layer 1. The latter comprises a support layer 10 and a working electrode 11 formed on the upper surface of said support 10. The working electrode 11 is surmounted by the third adhesive layer 7.

The working electrode 11 thus occupies the entire surface of the bottom 44 of the well 43, and extends under the layers of reference electrode 2 and of counter electrode 3.

The layers of reference electrodes 2 and / or of counter electrodes 3 can either be oriented with the face carrying the electrode up or towards the bottom of the electrochemical cell, while taking care of the good electrical insulation of the electrodes between them.

Advantageously, the reference electrodes 21 and counter electrodes 31 are respectively arranged on a different face of the same support. Such an embodiment simplifies assembly by avoiding a bonding step and, if necessary, reducing the volume of the electrochemical cell.

Therefore, the surface of the working electrode 11 is maximized and is in particular greater than that of an electrochemical cell of the state of the art in which the working electrode is a side electrode arranged in the side wall. of the electrochemical cell.

In particular, in the case of a cylindrical cell, the surface Si of the bottom of the cell of radius R (equal to half the diameter D) is calculated by the following relation: Si = π * R ² (1), and the surface S ₂ of a lateral electrode of height H _E (not shown) of this same cell (the radius R is identical), is calculated by the following relation: S ₂ = 2 * π * R * H _E (2) .

Thus, Si is greater than S ₂ if and only if: R> 2 * H _E (3).

This is particularly advantageous for measuring the low currents expected in the case of small volume cells.

We prefer a device whose cells have a volume less than 10 pl_, and preferably between 1 nL and 1 μΙ_.

A device will be chosen very particularly whose cells are cylindrical, whose diameter is between 1 mm and 2 mm, whose height is between 0.5 mm and 1.5 mm, and whose volume is between 0.5 μΙ_ and 1.5 μΙ_.

It is specified that the reference electrode layer 2 and the counter-electrode layer 3 can be superimposed on each other in any order. In other words, it is possible to position the reference electrode layer 2 above or below the counter-electrode layer 3. However, it is preferable to position the reference electrode layer 2 below the layer counter-electrode 3, in order to minimize the distance between the reference electrode 21 and the working electrode 11, for purposes of precision on the difference in electric potential imposed between the working electrode 11 and the working electrode reference 21 and limitation of any electrical losses due to the resistivity of the solution between these electrodes.

In addition, the electrode layers may have the same or different thickness.

In particular, it is preferable to use a layer of counter-electrodes 3 whose thickness, and therefore the contact surface with the solution contained in the well, is large compared to that of the reference electrode 2, so that its influence on d 'possible electrical loss is negligible.

The cells are preferably of cylindrical shape, which induces layers of reference electrodes 2 and counter electrodes 3 of annular shape, concentric, and a working electrode 11 at the bottom of the disc-shaped cell. However, the cells can be of any shape suitable for the implementation of the electrochemical device 51. To adjust the shape of the well 43 and the cell electrodes, it suffices simply to adjust the shape of the orifices 40 to be drilled.

An advantage of the manufacturing process is that it makes it possible to obtain an electrochemical device 51 whose cell volume is easily adjustable, and in particular easily reducible or even miniaturizable. In fact, to obtain a device 51 whose cells have a predetermined volume, the diameter D and the height H _P of the wells 43 of the cells are adjusted accordingly when the corresponding orifices 40 are produced. The height H _P of the wells is adjusted by the choice of the thicknesses of the layers of reference electrodes 2 and of counter-electrodes 3 which delimit them, it being understood that the corresponding orifices 40 pass through said layers. In accordance with the method described above, the layers of reference electrodes 2 and of counter-electrodes 3 pierced are assembled on the layer of working electrodes 1. It is therefore not necessary to adjust the surface of the electrode beforehand. working 11, which, whatever the height of the cell, has an optimal value since it extends over the entire surface of the bottom 44 of the cell.

Another advantage of the manufacturing process comes from the fact that the working electrodes 11 of the electrochemical device 51 retain their structural integrity throughout the implementation of the process. In other words, the surface of the working electrodes 11 is neither modified nor altered during the carrying out of the process. In particular, they undergo no chemical treatment and no mechanical treatment. The orifices 40 provided in the layers of reference electrodes 2 and of counter electrodes 3 are in fact produced before the assembly of said layers on the layer of working electrodes 1, the latter not therefore being pierced. Thus, the physicochemical properties of the working electrodes are optimal, as are the electrochemical measurements carried out with their use.

Figures 4, 5, and 6 show diagrams of an electrochemical measurement system 50. The elements of the system 50 shown in Figure 4 have already been briefly described above. It is recalled, however, that the system 50 as illustrated comprises the device of FIG. 1C, an electrical connection device 52, as well as a potentiostat 53.

The electrical connection device 52 makes it possible to electrically connect the electrodes

11, 21, 31 at the potentiostat 53. For this, the track transfers 12, 22, 32 of the electrodes are connected to the electrical connection device 52, and the latter is in turn connected to the potentiostat 53, and is capable of receiving control instructions for potentiostat 53, or even to dialogue with it. It makes it possible in particular to electrically and selectively connect one or more electrodes 11, 21, 31 of the device with the potentiostat 53, according to the control instructions of the latter.

The operation of the electrochemical system 50 will now be described with reference to Figures 5 and 6.

The potentiostat 53 comprises a voltage control device 60 shown diagrammatically by an operational amplifier, and a plurality of current measurement devices 64, 65, 66, 67. The electrical connection device 52 comprises meanwhile the distributors 61, 62.

The electrochemical system 50 comprises sixteen cells C (i, j) distributed in 4 rows i and 4 columns j. Each reference electrode 21.1, 21.2, 21.3, 21.4 is common to the four cells C (i, j) of a column j, and, similarly, each counter electrode 31.1, 31.2, 31.3, 31.4 is common to the four cells C (i, j) of a column j. The reference electrodes and the counter electrodes are electrically connected to the common voltage control device 60, which makes it possible to impose a set electrical potential U _c on the reference electrodes and the counter electrodes of the electrochemical cells (the means of application of a potential to the working electrodes are not shown).

The reference electrodes 21 and the counter electrodes 31 are electrically connected to the voltage control device 60 via their respective distributor 61, 62. These distributors make it possible to electrically and selectively connect a reference electrode 21 or a counter electrode 31 of a column j to the voltage control device 60, in order to impose the setpoint potential U _c on the cells of the column j. More precisely, the distributors 61, 62 are configured to selectively connect a reference electrode 21 and a counter-electrode 31 of the same column j by selecting the channels 63 of the corresponding track reports, in order to impose a setpoint potential U _c to all the cells of column j, for carrying out a measurement of the cells of column j Each working electrode 11.1, 11.2, 11.3, 11.4 is common to the four cells C (i, j) of a line i, and is electrically connected to an electrical current measuring device 64, 65, 66, 67. The latter makes it possible to apply a potential U (not shown) to the corresponding working electrode, and to measure the intensity l _or t of the electric current at the output of a cell, at said working electrode, resulting from the potential difference UU _c at the terminals of the cell between the potential U and the setpoint potential U _c .

The electrical current measuring devices 64, 65, 66, 67 are advantageously configured to simultaneously measure the currents at the output of all the cells of the same column, for carrying out a measurement of the cells of column j.

With regard to the measurement of the electric currents at the outlet of the cells, this is carried out according to a sequence comprising a number M of measurements. A measurement corresponds to the measurement of the current at the output of the cells of a column j connected by the same counter electrode and reference electrode

For measurement 1 for example, the reference electrode 21.1 and the counter electrode 31.1 of column 1 are connected to the voltage control device 60 via their respective distributor 61, 62, and the reference electrodes 21.2, 21.3, 21.4 and the counterelectrodes 31.1, 31.2, 31.3 of the other columns 2, 3, and 4 are disconnected. The working electrodes 11.1, 11.2, 11.3, 11.4 of the four lines of the device are all connected to their respective electric current measuring device 64, 65, 66, 67 which measure the values of intensity of the electric currents at the output of the cells. column 1 at the working electrodes. In other words, the intensity values of the electric currents at the output of the four cells in column 1 are simultaneously measured.

Once the measurement of the intensities of the electric currents is complete for column 1, this marking the end of measurement 1, the reference electrode 21.1 and the counter electrode 31.1 of column 1 are disconnected. Then, the reference electrode 21.2 and the counterelectrode 31.2 of column 2 are in turn connected, via distributors 61, 62 which switch from one channel 63 to another, this marking the start of measurement 2 in which the measurement steps are identical to those of measurement 1, for column 2.

These steps are similar for all the measurements corresponding to the M columns of cells of the device.

To measure the intensity values of the currents at the output of all the cells C (i, j) of the device, a sequence of measurements is therefore carried out comprising as many measurements as there are columns. In the example illustrated in Figure 5, four measurements are made to measure the intensity values of the currents at the output of the sixteen cells of the device.

Obviously, it is possible to carry out several sequences of measurements similar to that described above, in particular with a view to examining the repeatability of the results obtained.

A sequential current measurement is thus carried out, comprising one or more measurement sequences, in which a measurement sequence corresponds to the column by column measurement of the values of intensity of the currents at the output of all the cells of the electrochemical device.

It is specified that the potentiostat, which imposes an electrical potential difference UU _c on the cells, is configured to vary this potential difference during a measurement, in order to scan a range of potential between two extreme potential values. Thus, the potentiostat allows on the one hand to control throughout a measurement the potential difference between the working electrode and the reference electrode while varying this potential difference, and on the other hand to measure the intensity values of the currents leaving the cells.

The intensity values of the currents output from the cells of the corresponding column are measured continuously when the potential applied to the cells varies during a measurement. It is thus possible to obtain curves translating for example the evolution of the intensity values of the currents leaving the cells as a function of the variation of the potential applied to said cells during the measurement time.

Preferably, the speed of scanning in electrical potential during a measurement is between 100 mV.s ' ¹ and 500 mV.s' ¹ . For a scanning speed between 100 mV.s ' ¹ and 500 mV.s' ¹ , it takes approximately one minute to measure the electric currents at the output of the hundred cells of the device illustrated in Figure 4.

The electrical diagram equivalent to the four cells in column 1 of the device in Figure 5 is illustrated in Figure 6. In this diagram, the four cells C (1,1), C (2,1), C (3,1 ), and C (4,1) are represented by the four dark gray rectangles which contain a resistance a resistance R ₂ , and a capacity C. The resistance Ri is the electrical equivalent of the volume of solution contained in a cell between the counterelectrode 31.1 and the reference electrode 21.1. The assembly formed by resistance R ₂ and capacitance C is the electrical equivalent of the volume of solution contained in a cell between the reference electrode 21.1 and the working electrode 11.1, 11.2, 11.3, 11.4.

The voltage control device 60 fixes the setpoint potential U _c , of a predetermined value, across the resistors Ri of the cells. The reference electrode 21.1 and the counter electrode 31.1 are subjected to the setpoint potential U _c . This setpoint potential U _c is constant during the completion of a measurement cycle.

During a measurement cycle, the potentiostat 53 imposes a potential U on the working electrodes 11.1, 11.2, 11.3, 11.4.

The resulting potential difference UU _c between the working electrodes and the reference electrode 21.1 varies over the course of the measurement time.

The intensity values of the electric currents at the output of the working electrodes are measured by the corresponding current measuring devices represented by the operational amplifiers. For each cell, the output intensity of cell l _or t (h.out for cell C (1,1), l ₂ , out for cell C (2,1), l ₃ , _O ut for the cell C (3,1), and _{4, O} ut to the cell C (4,1)) and the cell output potential V _or t (V _{1 or} t for the cell C (1,1), V _2or t for cell C (2,1), V _{3] O} ut for cell C (3,1), and V _{4] O} ut for cell C (4,1)) are linked by the following relation: V _out = - I _out * R ₃ (4), so that the measurement of V _or t makes it possible to deduce l _O ut, R3 being a characteristic of the potentiostat.

From the above, it appears that to measure the values of the intensities of the currents at the output of all the cells of the electrochemical device, the cells being distributed in N rows and M columns, we use:

N reports of working electrode tracks,

M reports of reference electrode tracks,

M carryovers of counter-electrode tracks, ie a total number of carryovers of tracks RPi within the device such as: RP! = N + (2 * M) (5).

RPi also corresponds to the number of electrodes, since an electrode is associated with a carry-over.

By way of comparison, in a conventional electrochemical device of the state of the art where each cell comprises three electrodes distinct from those of the other cells and one track transfer per electrode, a total number of track transfers RP _{2 is required} ( equal to the number of electrodes) within the device such that RP ₂ = 3 * N * M (6). RPi is therefore much lower than RP ₂ .

Taking the example of an electrochemical device comprising one hundred cells, divided into ten lines of ten cells, RP is thus necessary! = 10 + (2 * 10) = 30 carryovers of tracks and electrodes for the device of the invention, against RP ₂ = 3 * 10 * 10 = 300 carryovers of tracks and electrodes for a device of the state of the art .

In addition, a system comprising a device according to the invention comprises a number of electrical connectors reduced compared to the state of the art.

In particular, such an electrochemical system 50 comprises a single voltage control device 60 for imposing a setpoint potential U _c on all of the cells, as well as as many devices 64, 65, 66, 67 for measuring current as of cell lines.

By way of comparison, an electrochemical system provided with a conventional state-of-the-art device comprises as many voltage control devices as there are cells, and as many current measurement devices as there are cells.

The electrochemical system and device of the invention therefore comprise a number of electrodes, track transfers, and connectors (in particular voltage control devices and current measurement devices) greatly reduced compared to systems and state-of-the-art devices, due to the particular arrangement of the electrode layers and the pattern of the crossed electrodes which have just been detailed.

This makes it possible to miniaturize electrochemical devices and electrochemical systems for assaying biological molecules at very small sizes, and in particular makes it possible to densify and increase the number of cells. In addition, the particular architecture of the cells is specially adapted to this device and makes it possible to obtain cells with a volume of the order of 1 μl or less.

The electrochemical device and system described are particularly suitable for carrying out digital electrochemical measurements for the detection of biological molecules (proteins or DNA). They allow absolute quantification of the number of target molecules present in a sample by counting the positive wells (i.e. the wells in which the target is detected) and the negative wells (i.e. the wells in which the target is not present).

The digital electrochemical measurements are for example applicable to the detection of a DNA target by DNA amplification reactions which include, for example: the polymerase chain reaction (in English: Polymerase Chain Reaction, or PCR ), amplification by recombinase polymerase (in Anglo-Saxon: Recombinase Polymerase Amplification, or RPA), and isothermal amplification induced by the loop (in Anglo-Saxon: Loop-Mediated Isothermal Amplification, LAMP).

For the purpose of carrying out digital electrochemical measurements, the device can comprise a microfluidic system making it possible to circulate in the device one or more fluids bound for or leaving the cell wells.

REFERENCES

- Anal. Chem. 2002, 74, 3321-3329, Aguilar et al.

Electrochimica Acta 52 (2007) 7248-7253, Rawson et al.

Claims (19)

1. Device (51) of electrochemical cells (C (i, j)), characterized in that it comprises: a superposition of three layers of electrodes (1,2, 3) with their relative tracks transfers (12, 22, 32), these layers forming layer of reference electrodes (2), layer of counter-electrodes (3) and working electrode layer (1), the electrodes of these three layers being at least partly superimposed, and, a plurality of orifices (40) passing through the superposed electrodes (21, 31) of the electrode layer of reference (2) and of the layer of counterelectrodes (3), these orifices (40) being closed by the layer of working electrodes (1) and thus constituting a volume (43) forming said electrochemical cells (C (i, j )) of which the working electrodes (11) are the bottom (44), said electrochemical cells (C (i, j)) being arranged in a pattern comprising N rows of index i and M columns of index j of cells, with N an integer greater than or equal to 1 and M an integer greater than or equal to 1, such that if N is equal to 1 then M e st greater than or equal to 2, and if M is equal to 1 then N is greater than or equal to 2, in which: the cells (C (i, j)) of a line i comprise a common working electrode which electrically connects said cells of the line i, the cells (C (i, j)) of a column j comprise an electrode of common reference and a common counter electrode which electrically connect said cells of column j. 2. Device according to claim 1, characterized in that at least one of the layers of reference electrodes (2), of counter-electrodes (3), and of working electrodes (1) is produced with its carry-over tracks by screen printing. 3. Device according to one of the preceding claims, characterized in that each of the reference electrodes (21), counter-electrodes (31), and working electrodes (11) of the corresponding electrode layers (2, 3 , 1) includes a single runway report (22, 32, 12). 4. Device according to one of the preceding claims, characterized in that it also comprises at least one electrically insulating layer (4) comprising a plurality of orifices corresponding to the orifices (40) passing through the layer of reference electrodes (2) and the layer of counterelectrodes (3), the thickness of said electrically insulating layer (4) being chosen so as to adapt the volume (43) of the electrochemical cells (C (i, j)). 5. Device according to claim 4, characterized in that said at least one electrically insulating layer (4) is arranged above the device or at the interface of at least two of the electrode layers (1,2, 3 ). 6. Device according to one of the preceding claims, characterized in that it further comprises at least one adhesive layer (5, 6, 7) arranged at the interface of at least two of the electrode layers (1, 2, 3), making it possible to connect said layers of electrodes and to keep them in position relative to one another. 7. Device according to one of the preceding claims, characterized in that the electrochemical cells (C (i, j)) have a volume less than or equal to 10 pl_, and preferably between 1nL and 1 μΙ_. 8. Device according to one of the preceding claims, characterized in that it comprises a density of electrochemical cells (C (i, j)) greater than or equal to one cell per square centimeter, preferably greater than or equal to ten cells per square centimeter, and more preferably greater than or equal to one hundred cells per square centimeter. 9. Electrochemical cell with three electrodes connected to runway reports, said cell being characterized in that it comprises: • a working electrode which occupies the entire surface of the bottom of the volume formed by said cell, • a counter-electrode and a reference electrode situated in the walls of said cell, said electrodes and their relative tracks being located in planes different in said cell. 10. Electrochemical cell according to claim 9, characterized in that the reference electrode and the counter electrode are annular. 11. Method for manufacturing an electrochemical cell device, in which the following steps are implemented: a) production of at least three layers of electrodes (1, 2, 3) and their runway transfers (12, 22, 33), these layers being intended to form a layer of reference electrodes (2), a layer of counter electrodes (3) and a layer of working electrodes (1), the electrodes (11, 21, 31) of these three layers being configured to be at least partially superimposable one above the other , b) superposition of the layer intended to form the layer of reference electrodes (2) and that intended to form the layer of counter-electrodes (3), then production of a plurality of orifices (40) in the electrodes of the two layers thus superimposed, c) assembly by superposition of the assembly obtained in step b) on the layer intended to form a layer of working electrodes (1), the latter closing off the orifices (40) at one of their ends, the orifices (40) thus closed constituting volumes forming the electrochemical cells (C (i, j)) of which the working electrodes (11) are the bottom (44), said assembly being produced so as to obtain a pattern of a device according to one of claims 1 to 8. 12. The method of claim 11, wherein step b) is as follows: producing a plurality of orifices (40) in the electrodes (21) of the layer intended to form the reference electrode layer ( 2) and separately in the electrodes (31) from that intended to form the layer of counter-electrodes (3), then superposition of the electrode layers (2, 3) thus pierced so as to match the orifices of each of the layers of electrodes. 13. Method according to one of claims 11 to 12, characterized in that at least one of said electrode layers (1, 2, 3) is produced with its run tracks by screen printing. 14. Method according to one of claims 11 to 13, characterized in that one or more of steps b) and c) are carried out by the prior deposition of at least one adhesive layer (5, 6, 7) on at at least one of the electrode layers (1, 2, 3) in order to connect said layers and to keep them in position relative to one another. 15. Method according to one of claims 11 to 14, characterized in that one or more of steps b) and c) are carried out by the addition, prior to the production of the orifices (40), of at least one layer electrically insulating (4) on at least one of the electrode layers (1,2, 3). 16. Electrochemical measurement system comprising: an electrochemical cell device (51) (C (i, j)) according to one of claims 1 to 8, a potentiostat (53) electrically connected to the electrochemical cell device (51), making it possible to impose a potential difference electrical input of the electrochemical cells (C (i, j)), and to measure an electric current intensity (l _or t) at the output of said electrochemical cells, an electrical connection device (52) capable of selectively connecting electrically, one or more of the reference electrodes (21) and of the counter-electrodes (31) of the device (51) via their track transfers (22, 32), with the potentiostat (53). 17. System according to claim 16, characterized in that: the electrochemical cells (C (i, j)) of the electrochemical cell device (51) are arranged according to the pattern described in claim 1, the potentiostat (53) comprises: • a voltage control device (60) capable of being electrically connected to the reference electrodes (21) and to the counterelectrodes (31) of the M columns of the electrochemical cell device (51), and selectively to a reference electrode ( 21) and to a counter-electrode (31) of a column j of the electrochemical cell device (51), making it possible to apply a setpoint potential (U _c ) to the reference electrode (21) and to the counter -electrode (31) of column j, • at least one device (64, 65, 66, 67) making it possible to apply an electrical potential to a working electrode (11) of a line i of the electrochemical cell device ( 51) and to measure the intensity of the electric current (l _or t) at said working electrode (11). 18. System according to one of claims 16 to 17, characterized in that the electrical connection device (52) comprises: a first electrical distributor (61) for selectively electrically connecting the voltage control device (60) with a reference electrode (21) of a column j, and, a second electrical distributor (63), for connecting electrically selectively the device (60) for applying an electrical potential with a counter-electrode (31) of said column j, in order to impose a set electrical potential on said reference electrode controlled by means of said counter electrode. 19. A method of measuring an electric current output from the electrochemical cells of an electrochemical cell device (51), by the implementation of an electrochemical measurement system (50) according to one of claims 16 to 18, characterized in that it comprises the following stages: for a measurement of an intensity of the electric current (l _or t) at the output of the electrochemical cells (C (i, j)) of a column j of the electrochemical cell device: a) imposing a set electrical potential (U _c ) on the reference electrode (21) and the counter electrode (31) of a column j, said reference electrode (21) and said counter electrode (31 ) being selectively connected to the device (60) for applying an electrical potential, the other reference electrodes and counter-electrodes being disconnected, b) imposing an electrical potential on the N working electrodes (11) of the cells (C (i, j)) of column j, so as to generate a potential difference between the potential of the working electrodes (11) and the potential setpoint (U _c ) of the reference electrodes (21) and of the counter-electrodes (31), c) measuring an electric current intensity (l _or t) at the outlet of the cells of column j at the working electrodes (11), the working electrodes (11) being connected to the devices (64, 65, 66, 67) of measurement of an electric current, repeat steps a) to c) to measure an intensity of the electric current leaving the electrochemical cells (C (i, j)) of column j + 1 of the device (51) of electrochemical cells.