Elementary electrode, electrode and electrochemical detection device comprising such an electrode

Abstract

The invention relates to elementary electrodes (1) of which at least two characteristic dimensions are less than 1 μm or than 2.5 μm, comprising a reactive surface (3), the characteristic dimensions of which are less than 1 μm or than 2.5 μm, a thin catalyst layer (4), a portion of the surface of which is comprised in the reactive surface, a thin carbon layer (5), in an allotropic form of the carbon chosen from boron-doped diamond and nitrogen-doped non-hydrogenated amorphous carbon, in contact with said thin catalyst layer and of which one portion of the surface (6) is comprised in the reactive surface (3), a support (7), in contact with at least one of the thin layers, enabling electrical measurements to be carried out. The invention also relates to electrodes, in particular working electrodes (9), comprising a plurality of such elementary electrodes (1), to a method for preparing same, and to electrochemical detection devices (2), for detecting at least one electroactive species, comprising these electrodes.

Description

[0001] ELEMENTARY ELECTRODE, ELECTRODE AND ELECTROCHEMICAL DETECTION DEVICE COMPRISING SUCH AN ELECTRODE

[0002] Current environmental considerations are leading to growing public concern about the integrity and sustainability of the environments they come into contact with. Consequently, the population has obvious needs for safety and quality control of these environments.

[0003] Water is an essential environment for life, however the increase in industrial, agricultural, domestic and urban activities and more generally economic activities leads to a degradation of supply sources which is not without consequences on the uses (e.g. food, leisure, industrial, etc.) which are made of this liquid. In order to ensure the adequacy between the quality of water and its use, it is essential to have in situ analysis tools and methods capable of continuously monitoring in real time the evolution of the composition of aqueous environments.

[0004] The analysis tools and methods used today are generally based on chemical, optical, electrochemical, or biological measurement principles. Sensors generally have a sensitive surface allowing recognition of the species with which it interacts, as well as a transducer system transforming the interaction into an electrical signal. Sensors are generally coupled to an electronic system for acquiring, processing, and transmitting the electrical signal. This electronic system is generally referred to as a "reading system."

[0005] Electrochemical sensors allow the detection of ionic species in liquid solution. Species described as electroactive generally correspond to species that dissociate in ionic form in liquid media, particularly in aqueous media. This family of compounds includes inorganic salts, such as heavy metal salts, acids and bases, and dissolved gases.

[0006] The main expectations surrounding sensors relate in particular to their sensitivity and their detection limit, which must be consistent with the desired concentration level of the species of interest, as well as their precision. Other desirable characteristics include a small footprint, low energy consumption, the lowest consumption of resources linked to their production and a relatively short response time for the application concerned. When such specifications are met, the sensor is a truly useful instrument for carrying out in situ measurements or monitoring online processes.

[0007] When the sensor is permanently immersed in an aqueous medium, it will be subject to both strong mechanical and chemical constraints, and it will be subject to progressive fouling of mineral or biological origin. These operating constraints will impact the accuracy of the measurements and the lifespan of the sensor.

[0008] Electrochemical sensors are classified into different categories depending on the detection mode on which they are based: in particular, we distinguish between potentiometric, amperometric, and conductivity sensors.

[0009] Potentiometric and amperometric sensors generally use several electrodes in contact with the solution of interest:

[0010] • A so-called “working” electrode: o It is used to qualify the presence of at least one electroactive species; o Historically, working electrodes have often been made from a solid, “noble” metal plate (i.e. resistant to oxidation), such as gold or platinum for example; o The invention mainly concerns the structure and manufacture of this type of electrode;

[0011] • A so-called “reference” electrode: o It must have an invariable electrical potential regardless of the composition of the medium in which it is immersed. By convention, in water, the potential scale originates from the potential of the “normal hydrogen electrode”, an electrode generally using a platinum electrode; o For simpler (less expensive) and more compact designs, a silver-silver chloride electrode is generally used. However, the stability and lifetime of a silver-silver chloride electrode are not optimal when the electrode is immersed in a medium with a variable chloride content;

[0012] • A possible “auxiliary” electrode: o It is also called “counter electrode”; o It is used in the case of amperometric sensors to collect in the form of electric current the signal generated on the surface of the working electrode; o It is typically made of metal, and in particular of noble metal.

[0013] Conductivity sensors use combinations of two or four electrodes.

[0014] It is observed that electrochemical sensors using a working electrode made of a single material are generally sensitive to many chemical species. While reading techniques sometimes allow preferential detection of certain chemical species, for example for voltage scanning techniques where current peaks appear at voltage values ​​associated with certain compounds, species with similar responses and present in the same solution to be analyzed disrupt the measurement.

[0015] It has been shown that the addition of catalysts, particularly in the form of nanoparticles on the surface of a working electrode, can improve the analytical performance of a sensor in terms of specificity, selectivity and sensitivity. For example, the publication "Nanoparticles in electrochemical sensors for environmental monitoring" (Trends in Analytical Chemistry, Volume 30, Issue 11, 2011, Pages 1704-1715, https: / / doi.Org / 10.1016 / j.trac.2011.05.009) provides a partial assessment of the effectiveness of catalysts, particularly for the use of metal-type nanoparticles or their oxides.

[0016] The deposition of nanoparticles on the surface of the working electrode can be carried out by electrodeposition methods. However, the adhesion of the nanoparticles is generally insufficient to obtain a sufficiently long electrode lifetime, in particular for environmental monitoring applications. In addition, the development of the deposition conditions depending on the catalyst can be difficult. The invention aims in particular to address the problems encountered in the field of electrochemical devices and associated solution and media analysis methods, by proposing an electrode structure using catalysts. Such a structure is easily adapted to the nature of each catalyst. The nature of the materials and the structure are defined to extend the lifetime of immersed sensors and maintain measurement accuracy continuously in a wide variety of aqueous media.

[0017] To this end, the invention relates to an elementary electrode, at least two characteristic dimensions of which are less than 1 pm or 2.5 pm, comprising:

[0018] • A reactive surface, whose characteristic dimensions are less than 1 pm or 2.5 pm,

[0019] • A thin layer of catalyst, part of the surface of which is included in the reactive surface,

[0020] • A thin layer of carbon in an allotropic form of carbon chosen from boron-doped diamond and nitrogen-doped non-hydrogenated amorphous carbon, in contact with said thin layer of catalyst and part of the surface of which is included in the reactive surface,

[0021] • A support, in contact with at least one of the thin layers, allowing the creation of an electrical contact.

[0022] Advantageously, a thin intermediate layer is present between the support and a thin layer of carbon or catalyst.

[0023] Advantageously, the reactive surface is only constituted by a part of the surface of the thin carbon layer and a part of the surface of the thin catalyst layer.

[0024] Advantageously, the surface area of ​​the thin layer of catalyst included in the reactive surface represents 20 to 50% of the reactive surface.

[0025] Advantageously, the reactive surface has a non-statistical morphology.

[0026] Advantageously, each point on the surface of the thin layer of catalyst included in the reactive surface is at a distance of less than 250 nm or 400 nm or 1000 nm from at least one point on the surface of the thin layer of carbon included in the reactive surface. Advantageously, the thin layer of carbon is in the form of boron-doped diamond whose boron concentration is between 10 18 and 3.10 21 atoms. cm -3 .

[0027] Advantageously, the thin carbon layer is in the form of non-hydrogenated amorphous carbon doped with nitrogen of the ta-C:N type.

[0028] The invention also relates to an electrode, comprising a plurality of elementary electrodes according to the invention.

[0029] Advantageously, elementary electrodes are present on 60 to 100% of the reactive surface of the working electrode.

[0030] A particular embodiment relates to an electrode comprising a plurality of elementary electrodes each having at least two characteristic dimensions less than 1 μm or 2.5 μm, said elementary electrodes each having:

[0031] • A reactive surface, whose characteristic dimensions are less than 1 pm or 2.5 pm,

[0032] • A thin layer of catalyst, part of the surface of which is included in the reactive surface,

[0033] • A thin layer of carbon, in an allotropic form of carbon chosen from boron-doped diamond and nitrogen-doped non-hydrogenated amorphous carbon, in contact with said thin layer of catalyst and part of the surface of which is included in the reactive surface,

[0034] • A support, in contact with at least one of the thin layers, allowing the creation of an electrical contact, the reactive surface having a non-statistical morphology, the support being common to the elementary electrodes and the reactive surface of the electrode being made up of the reactive surfaces of the elementary electrodes.

[0035] Advantageously, each point on the surface of the thin layer of catalyst included in the reactive surface is at a distance less than or equal to 400 nm or 1000 nm from at least one point on the surface of the thin layer of carbon included in the reactive electrode surface.

[0036] Advantageously, the reactive surface has a three-dimensional structuring obtained by a specific abrasion step of an upper layer to allow a lower layer to be in contact with the medium of interest. Advantageously, the thin layer of catalyst and the thin layer of carbon are superimposed.

[0037] Advantageously, the surface area of ​​the thin layer of catalyst included in the reactive surface represents 10 to 65% of the reactive surface area or 20 to 50% of the reactive surface area.

[0038] Advantageously, the thin layer of catalyst is above the thin layer of carbon, the reactive surface comprising central pads, connected to their nearest neighbors by walls, of round, polygonal or square shape, and of characteristic dimension between 50 and 1600 nm, for example between 50 nm and 100 nm, obtained by etching the thin layer of catalyst.

[0039] Advantageously, the electrode comprises an electrically insulating layer, for example made of oxide or nitride, delimiting a closed frame surrounding and delimiting the reactive electrode surface.

[0040] Advantageously, the insulating layer is deposited on a layer taken from among the thin carbon layer and the thin catalyst layer and an intermediate thin layer and on the support so as to be in direct physical contact with the layer and the support.

[0041] The invention also relates to a printed circuit assembly comprising a printed circuit comprising a printed circuit comprising at least one electrode according to any one of the preceding claims and a polymer protective layer, the electrode being fixed on one face of the printed circuit, the insulating layer separating the protective layer from the reactive surface.

[0042] The invention also relates to a device for the electrochemical detection of at least one electroactive species in a liquid medium comprising:

[0043] • At least one working electrode being an electrode according to the invention,

[0044] • At least one reference electrode,

[0045] • An electrochemical measuring system capable of being connected to the working electrode and the reference electrode.

[0046] Advantageously, the electrochemical detection device comprises:

[0047] • A first printed circuit comprising or on which are fixed:

[0048] (a) the working electrode, (b) the reference electrode,

[0049] • A second printed circuit comprising an electrochemical measurement system capable of being connected to said electrodes.

[0050] Advantageously, the first and second printed circuits form a single printed circuit on a first face of which the different electrodes are grouped and on the second face of which the electrochemical measurement system is grouped, and where appropriate the electronic system for controlling and reading the non-electrochemical sensor is arranged.

[0051] The invention also relates to a network of electrochemical detection devices according to the invention in which the electrochemical measurement system of each of the devices is capable of communicating with a central measurement system.

[0052] The invention also relates to a method for preparing an electrode according to the invention, on a support, comprising:

[0053] • A step of depositing a thin layer of catalyst,

[0054] • A step of depositing a thin layer of carbon in an allotropic form of carbon chosen from boron-doped diamond and nitrogen-doped non-hydrogenated amorphous carbon,

[0055] • At least one step of depositing a photosensitive resin,

[0056] • At least one step of selective exposure of the photosensitive resin,

[0057] • At least one step of partial elimination of the photosensitive resin,

[0058] • At least one etching step of the upper thin layer not protected by the residual photosensitive resin,

[0059] • At least one step of removing residual photosensitive resin.

[0060] Advantageously, the method is a method for collectively preparing a plurality of electrodes of the invention, in which the support is common to the electrodes.

[0061] Other characteristics and advantages of the invention will emerge on reading the detailed description which follows, with reference to the appended figures, which illustrate:

[0062] Figure 1 a: Schematic illustration of a printed circuit comprising or on which are fixed a working electrode, according to the invention, a protective layer as well as an intermediate layer, in which the periphery of the working electrode is physically isolated from the printed circuit by an intermediate layer,

[0063] Figure 1 b: Schematic illustration of a printed circuit comprising or on which are fixed a working electrode, according to the invention, a protective layer as well as an intermediate layer, in which the periphery of the working electrode is physically isolated from the printed circuit by a protective layer,

[0064] Figure 1 c: Schematic illustration of a printed circuit comprising or on which are fixed a working electrode, according to the invention, a protective layer as well as an intermediate layer, in which the periphery of the working electrode is physically isolated from the printed circuit by an intermediate layer,

[0065] Figure 2: Schematic illustration of the use of a network of devices for the continuous analysis of the quality of river water used by an industrial plant,

[0066] Figure 3: Schematic illustration of mask configurations used to make electrodes,

[0067] Figure 4a: Schematic illustration of a mask opposite an electrode in which the thin carbon layer is under the thin catalyst layer,

[0068] Figure 4b: Schematic illustration of a mask opposite an electrode in which the thin layer of catalyst is under the thin layer of carbon,

[0069] Figure 5a: Schematic illustration of the arrangement of electrodes on a rectangular printed circuit board,

[0070] Figure 5b: Schematic illustration of the arrangement of electrodes on a circular printed circuit board,

[0071] Figure 6: Schematic illustration of an exploded view of an electrochemical detection device,

[0072] Figure 7: a schematic representation of a sectional view of an example of an electrode according to the invention,

[0073] Figure 8a: a schematic representation of a top view of the active surface of the electrode of Figure 7 and the plane P along which the section of Figure 7 is made, Figure 8b: a schematic representation of a top view of an active surface of another example of electrode according to the invention,

[0074] Figure 9: A schematic representation of a section of an assembly comprising a printed circuit on which electrodes of Figure 7 are arranged.

[0075] Elementary electrode

[0076] The invention relates in particular to an elementary electrode 1, two examples of which are shown in Figures 4a and 4b.

[0077] More specifically, the invention relates to an elementary electrode 1, at least two characteristic dimensions of which are less than 1 pm or 2.5 pm, characterized in that it comprises:

[0078] • A reactive surface 3, whose characteristic dimensions are less than 1 pm or 2.5 pm,

[0079] • A thin layer of catalyst 4, part of the surface of which is included in the reactive surface 3,

[0080] • A thin layer of carbon 5, in an allotropic form of carbon chosen from boron-doped diamond and nitrogen-doped non-hydrogenated amorphous carbon, in contact with said thin layer of catalyst 4 and part of the surface of which is included in the reactive surface 3,

[0081] • A support, in contact with at least one of the thin layers, allowing the creation of an electrical contact.

[0082] This support is advantageously a part of the support referenced 7 in figures 4a and 4b common to several elementary electrodes in the non-limiting example shown in these figures.

[0083] In other words, the elementary electrode 1 comprises a stack of a plurality of layers along a stacking axis z.

[0084] The stacking axis z is therefore defined as the axis along which the layers are stacked.

[0085] The stacking axis z is shown in dotted lines in Figures 4a and 4b.

[0086] The plurality of layers comprises a support on which the thin layer of catalyst 4 and the thin layer of carbon 5 are stacked or deposited so that: • the characteristic dimensions of the reactive surface 3 are less than 1 pm or 2.5 pm,

[0087] • part of the surface of the thin layer of catalyst 4 is included in the reactive surface 3,

[0088] • part of the thin carbon layer 5 is included in the reactive surface 3.

[0089] Advantageously, as in the non-limiting examples of FIGS. 4a to 4c, the thin layer of catalyst 4 and the thin layer of carbon 5 are stacked on top of each other.

[0090] In other words, the thin layer of catalyst 4 and the thin layer of carbon 5 are advantageously superimposed.

[0091] In other words, a single layer taken from the thin layer of catalyst 4 and the thin layer of carbon 5 is attached to the support 7 or to an intermediate layer 8 separating the thin layer of carbon 5 and the thin layer of catalyst 4 from the support 7.

[0092] This single layer is interposed between the support 7 or the intermediate layer 8, separating the single layer of the support 7, and the other layer taken from the thin layer of catalyst 4 and the thin layer of carbon 5.

[0093] By characteristic dimensions of an elementary electrode, we advantageously mean the dimensions of the elementary electrode. Optionally:

[0094] • The contact between the thin carbon layer 5 and the thin catalyst layer 4 is achieved by an intermediate thin layer 8, and / or

[0095] • At least one intermediate thin layer 8 is present between the support 7 and a thin layer of carbon 5 or catalyst 3.

[0096] In other words, the elementary electrode 1 comprises a first intermediate thin layer 8 interposed between the thin carbon layer 5 and the thin catalyst layer 4 along the z axis and in direct physical contact with the thin carbon layer 5 and the thin catalyst layer 4 and / or a second intermediate thin layer 8 interposed, along the z axis, between the thin carbon layer 5 and the support 7 and in direct physical contact with the thin carbon layer 5 and the support 7 and / or a third intermediate thin layer 8 interposed, along the z axis, between the thin catalyst layer 4 and the support 7 and in direct physical contact with the thin catalyst layer 4 and the support 7. By two layers in direct physical contact with each other is meant two layers joined to each other.

[0097] Advantageously, the elementary electrode 1 has a non-statistical morphology, that is to say that it is not possible to obtain such an elementary electrode 1 in series by using a statistical manufacturing process.

[0098] In particular, this involves a specific morphology of top-down manufacturing processes and in particular a regular and reproducible morphology using manufacturing processes including a photolithography etching step.

[0099] In other words, the elementary electrode 1 is advantageously obtained by a manufacturing process comprising a photolithographic etching step.

[0100] The manufacturing process comprising the photolithography etching step is advantageously top-down (also called “top-down” in English terminology).

[0101] Advantageously, the reactive surface of the elementary electrode has a non-statistical morphology.

[0102] Advantageously, the reactive surface of the elementary electrode is obtained by a manufacturing process comprising a photolithographic etching step.

[0103] Advantageously, the photolithography etching step makes it possible to form a three-dimensional structuring of the reactive surface.

[0104] Advantageously, the elementary electrode is an elementary working electrode.

[0105] Reactive surface

[0106] The reactive surface 3 of an electrode, in particular of an elementary electrode 1, corresponds to the surface of the electrode intended to be in contact with the solution or the medium of interest, and on all or part of which at least one electrochemical reaction is likely to occur.

[0107] According to a specific embodiment, the reactive surface is only constituted by a part of the surface of the thin carbon layer and a part of the surface of the thin catalyst layer. Alternatively, a part of at least one intermediate layer 8 is included in the reactive surface 3 as in the examples of figures 4a, and 4b.

[0108] Preferably, the surface area of ​​the thin catalyst layer 4 included in the reactive surface 3 represents between 10% and 65%, preferably 20 to 50% of it. This ensures good measurement performance and efficient, low-energy cleaning of the entire reactive surface of the electrode.

[0109] Advantageously, the reactive surface of the elementary electrode falls within the perimeter of a square whose sides have a length less than 2.5 pm or 1 pm.

[0110] According to a specific embodiment, the reactive surface of the elementary electrode is inscribed within the perimeter of a square whose sides measure from 10 to 1000 nm, preferably from 50 to 200 nm.

[0111] This square is advantageously taken in a plane perpendicular to the z axis.

[0112] By the characteristic dimensions of the reactive surface 3 of the electrode 1 is advantageously meant the dimensions of a rectangular parallelepiped, in which the reactive surface is inscribed. This rectangular parallelepiped is for example square-based.

[0113] In a specific embodiment, the length of each of the sides is between 10 nm and a length less than 2500 nm or 1000 nm, preferably between 50 and 200 nm.

[0114] Advantageously, the reactive surface of the elementary electrode has a three-dimensional structure, i.e. it is not uniformly flat.

[0115] According to this specific embodiment, the thin layers of catalyst and carbon are superimposed and the three-dimensional structuring is then typically obtained by specific abrasion, for example using a photolithography etching process, of the upper layer to allow the lower layer to be in contact with the medium of interest.

[0116] The lower layer and the upper layer are advantageously taken from the thin layer of catalyst and the thin layer of carbon. The upper layer is the layer that is etched to release the lower layer so as to allow it to be in direct physical contact with the external environment.

[0117] Therefore, the surface of the upper layer is partly free for carrying out the specific abrasion and the lower layer is covered by the upper layer.

[0118] The upper layer is advantageously separated from the support 7 by the lower layer.

[0119] The morphology of the dug structure can be a furrow or a plot of substantially round, square or hexagonal section

[0120] In other words, the hollow has the shape of a furrow or a well with a round, square or hexagonal section.

[0121] The hollow being made by specific abrasion, it opens on the surface of the upper layer which is opposite the support.

[0122] The width of a groove or the diameter of a pad are of the order of 10 nm to 1200 nm or 500 nm, preferably from 50 nm to 200 nm, advantageously between 70 nm and 100 nm.

[0123] The height of the furrow or well allowing a plot to be exposed is significantly greater than the height of the thin layer.

[0124] This last thin layer is advantageously the upper etched thin layer.

[0125] Advantageously, the reactive surface 3 comprises at least one three-dimensional structure, and this is preferably a pad or a well. Advantageously, the reactive surface 3 also comprises a substantially planar surface attached to the three-dimensional structure.

[0126] For example, the reactive surface 3 comprises a pad or a well attached to a peripheral surface.

[0127] This peripheral surface is advantageously a surface from which the hollow is dug or from which the stud protrudes.

[0128] Advantageously, the peripheral surface is a surface of the lower layer when it is attached to a pad.

[0129] Advantageously, the peripheral surface is a surface of the upper layer when it is attached to a hollow.

[0130] Advantageously, the peripheral surface is substantially planar. Advantageously, the peripheral surface is substantially perpendicular to the z axis.

[0131] Advantageously, the height of the hollow is less than the dimensions of the hollow in the plane perpendicular to the z axis. The height is taken along the z axis.

[0132] Support

[0133] For the purposes of the invention, the support allowing the production of an electrical contact is composed of at least one layer of conductive or semi-conductive material.

[0134] The use of such a material makes it possible either to polarize the reactive surface or to detect the electrical signal generated by the redox reactions at the reactive surface.

[0135] According to a specific embodiment, the support comprises a single layer of material, preferably of conductive or semiconductive material.

[0136] The thickness of the support is generally chosen so that its handling, in particular during the manufacture of electrodes or a device as defined, is easy and that it does not break due to mechanical stresses linked to mass production. According to a specific embodiment, the support has a thickness of between 200 and 3000 pm, preferably between 250 pm and 2000 pm, preferably between 500 pm and 800 pm or 1000 pm.

[0137] Alternatively, the support comprises several layers of materials.

[0138] Thin layer

[0139] Advantageously, by thin layer is meant a layer having a thickness of between 0.01 pm and 2 pm.

[0140] Thin layer of carbon

[0141] According to a particular embodiment, the allotropic form of the carbon of the thin layer is non-hydrogenated amorphous carbon doped with nitrogen or diamond-like carbon or “DLC”, and the thickness of the layer is between 0.01 μm and 1 μm or 2 μm. Advantageously, the thin layer of non-hydrogenated amorphous carbon doped with nitrogen or diamond-like carbon or “DLC” has a thickness of less than 1 μm, typically it is between 30 and 100 nm, preferably between 50 and 70 nm.

[0142] According to another particular embodiment, the allotropic form of the carbon of the thin layer is boron-doped diamond or “BDD” and the thickness of the layer is here between 0.01 pm and 2 pm, preferably between 0.1 pm and 2 pm, preferably between 0.5 to 1.5 pm.

[0143] Thin layer of catalyst

[0144] Typically, the thin layer of catalyst 4 has a thickness of between 10 nm and 1000 nm, preferably from 20 nm to 500 nm, advantageously between 50 nm and 200 nm.

[0145] According to a particular structuring method, each point on the surface of the thin layer of catalyst included in the reactive surface is at a distance less than or equal to 1000 nm from at least one point on the surface of the thin layer of carbon included in the reactive surface, preferably less than or equal to 500 nm, advantageously less than 250, preferably less than 200 nm, preferably between 50 and 100 nm.

[0146] This feature has the surprising advantage of allowing efficient self-cleaning of the entire reactive surface by excitation, i.e. by polarization of the elementary electrode by an electrical signal when the reactive surface is in contact with an aqueous solution.

[0147] Intermediate thin layer

[0148] Typically, each intermediate thin layer 8 has a thickness less than or equal to 200 nm.

[0149] Advantageously, each intermediate thin layer 8 has a thickness of between 5 nm and 50 nm, preferably between 5 nm and 20 nm.

[0150] The intermediate thin layer likely to be present between the support and a thin layer (of carbon or catalyst), or between each thin layer, i.e. separating thin layers stacked on top of each other, is sometimes referred to as a thin bonding layer insofar as its composition is chosen in such a way that it promotes adhesion between the different elements.

[0151] Its thickness is generally around a hundred or ten nanometers. When it is composed of the same materials as the layers it separates, it is typically less than 20 nm.

[0152] Electrode

[0153] The invention also relates to an electrode characterized in that it comprises:

[0154] • A reactive surface having a three-dimensional structure of which at least two characteristic dimensions are less than 1 pm or 2.5 pm,

[0155] • A thin layer of catalyst, part of the surface of which is included in the reactive surface,

[0156] • A thin layer of carbon, in an allotropic form of carbon chosen from boron-doped diamond and nitrogen-doped non-hydrogenated amorphous carbon, in contact with said thin layer of catalyst and part of the surface of which is included in the reactive surface,

[0157] A support, in contact with at least one of the thin layers, allowing electrical measurements to be carried out.

[0158] The invention also relates to an electrode characterized in that it comprises a plurality of elementary electrodes EE as previously described.

[0159] An example of such an electrode is shown in Figures 7 and 8a.

[0160] In Figure 7, dotted lines delimit elementary electrodes EE included in the electrode E comprising a plurality of elementary electrodes EE sharing the same support S.

[0161] Each elementary electrode EE is advantageously an elementary electrode as defined previously comprising:

[0162] • reactive surface sr, whose characteristic dimensions, as defined previously, are less than 1 pm or 2.5 pm,

[0163] • A thin layer of catalyst 4, part of the surface of which is included in the reactive surface sr,

[0164] • A thin layer of carbon 5, in an allotropic form of carbon chosen from boron-doped diamond and nitrogen-doped non-hydrogenated amorphous carbon, in contact with said thin layer of catalyst and part of the surface of which is included in the reactive surface,

[0165] • An s7 support, in contact with at least one of the thin layers, allowing the creation of an electrical contact.

[0166] In the example of Figure 7, the thin layers of carbon and catalyst are joined together, just like the thin layer of carbon and the support. Alternatively, as previously specified, the elementary electrode comprises at least one intermediate thin layer separating two of these layers.

[0167] Advantageously, the reactive surface has a non-statistical morphology.

[0168] The elementary electrodes of an electrode may be identical. Alternatively, the electrode may comprise at least two distinct elementary electrodes.

[0169] The electrode E advantageously comprises a stack of layers along a stacking axis z.

[0170] In the non-limiting example of Figure 7, the thin carbon layer 5 and the thin catalyst layer 4 are stacked on the support s7 along the z axis.

[0171] Preferably, the elementary electrodes EE share the same support S and / or the same composition and / or the same organization or morphology.

[0172] In the example of figures 7 and 8a, the elementary electrodes EE of electrode E share the same support S.

[0173] Since the support is electrically conductive, the elementary surfaces of the electrodes are all at the same electrical potential.

[0174] In other words, the support s7 of each elementary electrode EE is a portion of the support S which is continuous. This makes it possible to produce the elementary electrodes collectively to manufacture the electrode.

[0175] Advantageously, the elementary electrodes EE share the same thin layer of carbon 5E and / or the same thin layer of catalyst 4E. In the non-limiting example of FIGS. 7 and 8a, the thin layer of catalyst 4 of each of the elementary electrodes EE is deposited on the thin layer of carbon 5, itself deposited on the support s7.

[0176] In other words, the thin layer of carbon 5 is interposed between the thin layer of catalyst 4 and the support s7.

[0177] In this example, the elementary electrodes EE of electrode E share the same thin layer of carbon 5E. In other words, the thin layer of carbon 5 of each of the elementary electrodes EE is a part of the continuous thin layer of carbon 5E of electrode E.

[0178] According to one embodiment of the invention, the electrode E is obtained by juxtaposition of elementary electrodes of the same composition.

[0179] The reactive surface SR of the electrode E is advantageously made up of the sum of the reactive surfaces sr of the elementary electrodes EE.

[0180] In other words, the reactive surface SR of the electrode E is made up of all the reactive surfaces sr of the elementary electrodes EE.

[0181] Where appropriate, this reactive surface SR of the electrode may have the same characteristics as these, in particular with regard to: the different three-dimensional structures, as well as the distance between each point on the surface of the thin layer of catalyst included in the reactive surface and at least one point on the surface of the thin layer of carbon included in the reactive surface.

[0182] Thus, in the non-limiting example of figures 7 and 8a, the elementary electrodes are contiguous.

[0183] Figure 8a represents the reactive surface SR of the electrode E in top view. Figure 7 is a section of the electrode E along the plane P shown in dotted lines in Figure 8a, this plane is perpendicular to the z axis.

[0184] Figure 8b is a top view of the reactive surface SR' of an electrode which is a variant of the electrode of Figures 7 and 8a. This reactive surface SR' is composed of reactive surfaces of elementary electrodes.

[0185] The reactive surface sr, sr' of an elementary electrode is delimited by a bold line in figures 8a and 8b.

[0186] In the non-limiting examples of Figures 8a and 8b, the surface sr, sr' is a unitary three-dimensional pattern of the reactive surface SR, SR' of the electrode. Each of the reactive surfaces SR, SR' comprises the repetition of the same elementary pattern sr, sr' so as to form a continuous surface composed of the same reactive surfaces sr, sr' of the elementary electrodes. This continuous surface forms a central part of the reactive surface SR, SR', the periphery of the reactive surface is composed of portions of this elementary pattern.

[0187] In other words, the peripheral elementary electrodes have a three-dimensional reactive surface which is a portion of the reactive surface sr, sr'.

[0188] In the example of figures 7 and 8a, the catalyst layer 4E is made up of catalyst pads PL spaced apart from each other, each catalyst pad PL belonging to only one of the elementary electrodes EE.

[0189] Therefore, the 4E catalyst layer is discontinuous.

[0190] Thus, the reactive surface SR of the electrode E consists of the free surface of the catalyst PL pads and the free surface of the thin carbon layer 5E on which the PL pads are deposited, the latter free surface having a grid shape surrounding the pads.

[0191] Thus, the reactive surface sr of each elementary electrode comprises at least a part of a surface of a catalyst pad PL and a surface of a portion 5 of the thin carbon layer 5E on which the pad PL is deposited. This pad is the catalyst layer 4 of the elementary electrode.

[0192] In the variant shown in Figure 8b, the electrode differs from that of Figure 8a in that the thin catalyst layer 4E' of the electrode is a layer pierced with wells so as to allow the surface of the thin carbon layer 5 to be in direct physical contact with the surrounding medium. This configuration makes it possible to obtain a catalyst layer 4E' having better mechanical strength.

[0193] Thus, the reactive surface SR' of the electrode differs from that of Figure 7 in that it is made up of the free surface of the catalyst grid 4E' and the free surface of the thin carbon layer 5E' on which the catalyst grid 4E' is deposited, the latter free surface being discontinuous and composed of elementary surfaces surrounded and delimited by the catalyst grid 4E'.

[0194] Thus, the reactive surface sr' of each elementary electrode comprises at least a part of a surface of a well drilled in a portion 4' of the catalyst grid 4E' and of a surface of a portion 5 of the thin carbon layer 5E onto which the well opens.

[0195] Alternatively, the wells or studs are replaced by furrows.

[0196] Advantageously, the three-dimensional structuring of the reactive surface is obtained by specific abrasion.

[0197] Advantageously, the catalyst PL pads or PU wells or grooves are formed by a specific abrasion step of an initial thin layer of catalyst deposited on the thin layer of 5E carbon so as to release a surface of 5E carbon layer.

[0198] Therefore, the morphology of the reactive surface sr, sr' of each of the elementary electrodes is non-statistical.

[0199] The specific abrasion step includes, for example, a photolithography etching process.

[0200] The invention also applies to the configurations of figures 7, 8a and 8b in which the thin layers of carbon and catalyst are interchanged.

[0201] In this variant, the reactive surface comprises surfaces of carbon pads separated by a surface of the catalyst layer or wells piercing the thin carbon layer separated by a surface of the thin carbon layer.

[0202] In this variant, the wells or studs can also be replaced by furrows.

[0203] Advantageously, the three-dimensional structuring of the reactive surface is obtained by specific abrasion.

[0204] Advantageously, the carbon pads or the wells or grooves piercing the thin carbon layer are advantageously produced by a specific abrasion step of an initial thin layer of catalyst deposited on the thin carbon layer so as to release the thin layer of catalyst.

[0205] Therefore, the morphology of the reactive surface of each of the elementary electrodes is non-statistical.

[0206] The specific abrasion step comprises, for example, a photolithographic etching process. Of course, the arrangements of elementary electrodes in Figures 8a and 8b are not limiting, the contiguous elementary electrodes may have identical or different reactive surfaces.

[0207] According to one embodiment of the invention, the elementary electrodes EE are present on 1 to 100%, preferably between 60 and 100%, of the reactive surface of the electrode.

[0208] Typically the electrode is in the form of a multi-layer plate.

[0209] In general, its length and width are between 1 and 20 mm, in particular or for example 5x5 mm or 7x7 mm; it can be substantially circular with a diameter between 1 and 20 mm, and in particular 3 to 10 mm.

[0210] Preferably the electrode is a working electrode.

[0211] The thickness of the electrode typically corresponds to that of an elementary electrode.

[0212] Advantageously, as in the non-limiting example of Figure 7, the electrode E comprises an electrically insulating layer Cl forming a closed frame surrounding and delimiting the reactive surface SR and being deposited on the thin carbon layer 5E, the insulating layer Cl also being deposited on the support S so as to form a closed frame surrounding and delimiting the thin carbon layer 5E.

[0213] Thus the thin layer of carbon 5E is distant from the edge of the support in the x, y plane, this makes it possible to facilitate a cutting step intended to separate collectively manufactured electrodes.

[0214] Advantageously, the method for manufacturing the electrode comprises a step of depositing the thin layer of carbon 5E on the support and a step of etching by photolithography intended to remove a portion of the thin layer of carbon 5E so that the insulating layer Cl can be deposited on the support and form the closed frame surrounding the thin layer of carbon 5E.

[0215] Advantageously, the insulating layer Cl is in direct physical contact with the thin carbon layer 5 and the support S.

[0216] Alternatively, the electrode comprises an intermediate thin layer interposed between the insulating layer and the carbon thin layer to facilitate adhesion between the insulating layer and the carbon layer. Thus, the insulating layer Cl is in direct physical contact with the intermediate thin layer and the support S.

[0217] In a variant, particularly applicable to the configuration of figure 8 or to any configuration in which the thin carbon layer is interposed between the support and the thin catalyst layer, the electrically insulating layer forms a closed frame surrounding and delimiting the reactive surface and is deposited on the thin catalyst layer.

[0218] Advantageously, the insulating layer is also deposited on the support so as to form a closed frame surrounding and delimiting the thin layer of catalyst.

[0219] Advantageously, the insulating layer is in direct physical contact with the thin catalyst layer and the support.

[0220] Thus, the insulating layer Cl is in direct physical contact with the intermediate thin layer and the support.

[0221] Alternatively, the electrode comprises an intermediate thin layer 8 interposed between the insulating layer and the thin catalyst layer to facilitate adhesion between the insulating layer and the thin catalyst layer.

[0222] The insulating layer is then in direct physical contact with the thin catalyst layer and the support.

[0223] Advantageously, the insulating layer Cl is stacked on the support S without surrounding the support S in a plane perpendicular to the z axis.

[0224] This is also the case in particular in figure 1 b when layer 18 is an electrically insulating layer.

[0225] The manufacture of an electrode having such a configuration is easy, the Cl layer being deposited on the support.

[0226] In the case of a collective manufacturing process of the electrodes, the latter can be separated by a simple cutting step.

[0227] Alternatively, the insulating layer Cl surrounds the support S. This is particularly the case in figure 1a when the layer 18 is an electrically insulating layer.

[0228] Each of the examples of electrode according to the invention may have an insulating layer as described previously.

[0229] The insulating layer Cl is, for example, an electrically insulating metal oxide, for example SiO, SiO2, or alumina, ... or an electrically insulating nitride, for example a silicon nitride for example SisN4.

[0230] These materials provide qualities of adhesion, sealing, electrical insulation and chemical inertia.

[0231] The nitride insulating layers, in particular, are resistant to hydroxyl ions, which helps to avoid or limit the risks of deterioration of the electrochemical detection device during self-cleaning of the electrode.

[0232] The invention relates to a printed circuit assembly EC, a non-limiting example of which is shown in Figure 9, comprising a printed circuit 12 and at least one electrode according to the invention, for example several as in the example of Figure 9.

[0233] The electrode according to the invention is an electrode according to any one of the embodiments described in the present application. The electrode is, for example, an electrode E of Figure 7 as shown in Figure 9.

[0234] Advantageously, as in the example of figure 9, the electrode E is fixed on a face F1 of the printed circuit 12.

[0235] Electrode E is, for example, glued, soldered or welded to the printed circuit board.

[0236] Advantageously, the printed circuit assembly EC is configured so that the only electrically conductive surface of the electrode E intended to be in direct physical contact with the aqueous medium is the surface of the reagent SR.

[0237] Advantageously, the entire reactive surface SR of the electrode E is intended to be in physical contact with the water.

[0238] Advantageously, the printed circuit assembly comprises a protective layer 17 covering the insulating layer C1 of each electrode E and, in the case of the presence of several electrodes, separating the electrodes deposited on the printed circuit 12.

[0239] Advantageously, the protective layer 17 completely covers the free parts of the face F1 of the printed circuit separating the electrodes (in the case of the presence of several electrodes) or surrounding the electrode or each of the electrodes.

[0240] Advantageously, the protective layer 17 is in direct physical contact with the printed circuit 12. The protective layer 17 is, for example, fixed to the printed circuit 12, by a screw-nut system.

[0241] Advantageously, the protective layer 17 is separated from the reactive surface SR of the electrode by the insulating layer Cl.

[0242] In other words, the protective layer 17 is distant from the reactive surface.

[0243] This arrangement is applicable to the fixing of any electrode of the invention on a printed circuit 12.

[0244] The insulating layer thus makes it possible to limit the risks of deterioration of a protective layer by hydroxyl free radicals likely to be generated by the surface of the thin carbon layer 5.

[0245] The protective layer can be injected around the electrode(s) after protecting the reactive surface of each electrode or can be previously injected into a mold so as to form a part which is positioned on the electrodes and the first face F1 of the printed circuit, for example by a screw-nut system.

[0246] When the part is previously injected into a mold, it is advantageously elastically deformable so that it is elastically deformed to position it on the electrodes and the first face of the printed circuit.

[0247] Electrodes can be manufactured collectively using a common support which will be larger than the support of a single electrode. This could for example be a disc of 100 to 300 mm in diameter.

[0248] They are then advantageously separated, for example by cutting, then transferred to a printed circuit like a classic electronic component.

[0249] The invention is particularly suitable for liquid media, in particular predominantly aqueous media. A medium of interest may thus correspond in particular to water used in human and animal food, swimming pool water, wastewater from pipes, water described as natural (e.g. rivers, lakes), water used in crops (e.g. fish farming, agriculture), aqueous solutions for bioreactors. The invention is also suitable for liquid media with a high alcohol composition such as alcoholic beverages or alcoholic media in the food industry.

[0250] Specific use of elementary electrodes and electrodes

[0251] The invention also relates to the use of at least one elementary electrode or at least one electrode, according to the invention, in an electrochemical system as a working electrode, reference electrode or auxiliary electrode.

[0252] The invention relates to the production of elementary electrodes and electrodes, according to the structures and compositions described and the use of such electrodes in an electrochemical measuring device. The structures and compositions of electrodes described can be used to produce a range of working electrodes and depending on the nature of the thin layer of catalyst - and in particular in the case of platinum - such electrode structures can also be used to produce reference electrodes and / or auxiliary electrodes.

[0253] Electrochemical detection device in liquid medium

[0254] The invention also relates to an electrochemical detection device DD, an example of which is shown in Figure 6 in exploded view, of at least one electroactive species in a liquid medium, characterized in that it comprises:

[0255] - At least one working electrode 9 as previously defined,

[0256] - At least one reference electrode 10,

[0257] - An electrochemical measuring system capable of being connected to said electrodes 9, 10.

[0258] The working electrode is an electrode according to any of the embodiments or variations described in the patent application.

[0259] Preferably the electrochemical detection device DD comprises:

[0260] • A first printed circuit 12, comprising or to which are attached: o At least one working electrode 9 as previously defined, o At least one reference electrode 10, • A second printed circuit 13 comprising or to which is attached an electrochemical measurement system connected to the first printed circuit 12 by an electrical connector 20.

[0261] In the non-limiting embodiment of Figure 6, the device comprises several working electrodes 9 which are electrodes according to the invention, several reference electrodes 10 and several auxiliary electrodes 14 on a first printed circuit 12 associated with a second printed circuit 13n, protected by O-rings 20 and arranged in a circular plastic housing in two parts 15a, 15b. Advantageously, the electrochemical detection device DD comprises a printed circuit assembly EC as defined previously.

[0262] The printed circuit 12 of the electrochemical detection device DD is advantageously the first printed circuit of the electrochemical detection device.

[0263] Advantageously, the printed circuit assembly comprises: o At least one electrode according to the invention which is a working electrode, o At least one reference electrode 10.

[0264] The electrochemical detection device DD is advantageously configured so that the only electrically conductive surface of the electrode intended to be in contact with the aqueous medium is the surface of the reagent.

[0265] Advantageously, the entire reactive surface of the electrode is intended to be in physical contact with the water.

[0266] According to a particular embodiment, the first printed circuit further comprises or is further attached to:

[0267] • At least one auxiliary electrode, and / or,

[0268] At least one non-electrochemical sensor, and preferably several sensors of different nature, such as in particular a temperature sensor, a turbidity sensor or a pressure sensor. According to another embodiment, the second printed circuit further comprises or is further fixed to:

[0269] • At least one potentiometric, amperometric or conductometric type measurement system, and / or,

[0270] • An electronic system for controlling and reading non-electrochemical sensors, and / or

[0271] • At least one means of monitoring and self-checking the status of the device, and / or

[0272] At least one means for activating the self-cleaning properties of the surface of the thin carbon layer, by causing the generation of hydroxyl radicals in an aqueous medium. Optionally, the first and second printed circuits form a single printed circuit on a first face of which the different electrodes are grouped and on the second face of which the electrochemical measurement system, and where appropriate the electronic system for controlling and reading the non-electrochemical sensor, is arranged.

[0273] Preferably the DD device also includes:

[0274] • A main body 15a, 15b, within which the previously mentioned elements 12, 13, 9, 10 are arranged,

[0275] • Electrical power supply means connected to the electrochemical measurement system, such as an electrical network or an autonomous means, such as a battery or cell.

[0276] The main body 15a, 15b is typically chosen such that it provides mechanical stability to all of the elements, including the electrical power supply means.

[0277] Printed circuit board grouping the electrodes

[0278] According to a particular embodiment, the device comprises a plurality of working electrodes as previously defined, in particular between 2 and 20, preferably between 3 and 8.

[0279] It is advantageous if the working electrodes are of different natures, they can in particular differ in the type of thin catalyst layer. Alternatively, they are identical.

[0280] Preferably, the device, for each working electrode, comprises a reference electrode and optionally an auxiliary electrode, depending on the reading method chosen. Thus, to carry out potentiometric measurements, a working electrode and a reference electrode are associated; for an amperometric measurement, an auxiliary electrode is additionally associated. To carry out analyses sequentially, it is possible to use the same reference electrode and, where appropriate, the same auxiliary electrode. Electrodes, beyond the detection of species, can thus be used for several purposes, in particular to measure the conductivity of the medium of interest, for example in a reading system dedicated to 2 or 4 electrodes.

[0281] According to different embodiments, the device is:

[0282] • A pH and conductivity measuring device,

[0283] • A device for measuring pH and conductivity, as well as nitrate, phosphate,

[0284] • A device for measuring pH and conductivity, as well as dissolved oxygen,

[0285] • A device for measuring pH and conductivity, as well as chlorine.

[0286] Protective layer

[0287] According to a particular embodiment, examples of which are shown in figures 1 a to 1 c and 9, a protective layer 17 is present on at least part of the surface of the first printed circuit 12.

[0288] Such a protective layer 17 makes it possible in particular to protect the surface of the printed circuit 12 during prolonged immersion in a medium of interest and also to preserve the reliability of the measurements, in particular by avoiding the appearance of short circuits between the medium to be analyzed and the different layers of the electrodes.

[0289] The thickness of the protective layer is typically 0.1 and 1000 pm.

[0290] According to a specific embodiment, the protective layer partially covers the reactive surface of the electrode(s) present on the surface of the printed circuit.

[0291] According to a specific embodiment, an intermediate layer can be interposed between the working electrode, according to the invention, included in the first printed circuit and the protective layer in order in particular to reinforce the adhesion between the layers.

[0292] This configuration makes it possible in particular to avoid the effects linked to poor adhesion which are likely to cause detachment of the protective layer and consequently a loss of sealing. According to another embodiment of the device, this intermediate layer between the working electrode, according to the invention, and the protective layer, may in particular be made of a material which is substantially inert to the electrolytic activity of the electrode and capable of ensuring sealing and electrical insulation between the working electrode and the protective layer.

[0293] Figures 1 a, 1 b and 1 c schematically illustrate a sectional view of a printed circuit 12 comprising or to which are fixed, a working electrode 9, according to the invention, a protective layer 17 as well as an intermediate layer 18 according to different implementations of the invention: the periphery of the working electrode 9, is physically isolated from the printed circuit 12 by a protective layer 17 and / or an intermediate layer 18 according to the configuration.

[0294] By the periphery of the electrode is physically isolated from the printed circuit 12 by a protective layer 17 and / or an intermediate layer 18, it is meant that the protective layer 17 and / or the intermediate layer 18 is interposed between the printed circuit 12 and the periphery of the electrode over the entire periphery of the electrode.

[0295] Second circuit board

[0296] According to a specific embodiment, this second printed circuit 13 comprises or supports the components making it possible to:

[0297] • Receive and respond to commands from external application software,

[0298] • Select and request the electrodes capable of constituting a defined sensor and reading the raw measurement values,

[0299] • Calculate the concentrations of the chemical species to be analyzed from the raw values ​​and / or self-corrections (e.g. temperature variation, presence of multiple species, etc.),

[0300] • Check that the device is working correctly and in particular carry out a self-diagnosis.

[0301] Preferably, the electrochemical detection device is a multi-parametric measurement system, which may, if necessary, constitute an “electronic tongue”.

[0302] Main body of the device The main body 15a, 15b may comprise several parts, typically a part arranged to allow contact between at least one working electrode 9, according to the invention, and the medium or solution of interest and a complementary part capable of being arranged to allow electrical connections.

[0303] The main body 15a, 15b may in particular be in the form of a hollow housing, such as a box of parallelepipedal, circular or elliptical section, with an upper part 15b arranged to position the measuring system arranged on the second printed circuit 13 and a lower part 15a arranged to position the electrochemical measuring system.

[0304] The device generally comprises physical insulation means 21 making it possible to avoid contact between the electrochemical measurement system and the medium or liquid solution of interest. This may be, for example, a coating of polymer or suitable insulating material or a seal such as an O-ring or several O-rings 21, in particular or for example made of elastomer such as rubber, polysiloxane, polyurethane.

[0305] Network of devices

[0306] The invention also relates to a network of electrochemical detection devices according to the invention 2a, 2b, 2c, 2d characterized in that the measurement system of each of the devices 2a, 2b, 2c, 2d is capable of communicating with a central measurement system 19b. Communication with the latter can be done in particular by wire and preferably by telecommunication (e.g. radio, WiFi, Bluetooth). Typically the central measurement system 19a is a computer, a tablet or a smartphone. An illustrative diagram, applied to the case of the continuous analysis of the quality of the waters of a river which are used by an industrial plant, is presented in Figure 2: it represents a set of independent devices 2a, 2b, 2c, 2d in interaction, by telecommunication, with a central measurement system 19b which allows them to be controlled.A first device 2a is placed upstream of the plant, the second 2b in the water sampling area, the third 2c in the plant discharge area and the fourth 2d further downstream of the plant U in order to check dilutions and possible changes in pollution. As shown, the user UT can directly control the devices 2a, 2b, 2c, 2d via his smartphone 19a, he is in particular able to calibrate them, to ensure their operation as well as the type of measurement that will be carried out, which is itself in interaction with a remote or central system 19b allowing the storage and processing of data. The work is presented in Mohammad Salah Uddin Chowdury et al. / Procedia Computer Science 155 (2019) 161-168 with additional illustrations of device networks.

[0307] Materials - thin carbon layer

[0308] The properties of natural diamond are particularly interesting for applications requiring a long service life, as this material is not easily altered and its surface becomes less dirty than that of other materials. Materials containing a high proportion of "diamond" are preferred for elementary electrodes and the electrodes according to the invention: boron-doped diamond (BDD) and diamond-like carbon (DLC).

[0309] Boron-doped diamond (BDD)

[0310] Since the use of natural diamond is not feasible for producing electrodes using fewer resources, various synthesis methods have been developed, in particular CVD ("chemical vapor deposition"), with two variants: MWCVD (microwave CVD) or HFCVD (hot filament CVD).

[0311] Depending on the synthesis conditions, diamond is obtained in the form of a single crystal, or in the form of polycrystals whose grain size can be modulated from a few micrometers to a few nanometers. The thickness of the layers obtained is mainly a function of the duration of the synthesis. In practice, thicknesses of less than 5 pm are sufficient for use in a sensor.

[0312] However, diamond is an insulating material. To make it usable as an electrode (i.e., to lower its resistivity to values ​​approaching that of a metal), this material can be doped during its synthesis by introducing atoms with a structure close to that of carbon. Boron doping is the method best mastered industrially. It is generally accepted that from a concentration of 3x10 20 atom / cm 3 , we enter the zone where boron-doped diamond has metallic behavior.

[0313] In the context of the invention, it is preferable, when the allotropic form of carbon chosen is boron-doped diamond, that the boron concentration is between 10 18 and 3.10 21 atoms. cm -3 .

[0314] Example of using boron-doped diamond (BDD)

[0315] Examples of preparation and use of BDD layers for sensors are presented in patent WO2017037094A1 which describes a device for electrochemical detection by amperometry of at least one electroactive species in a liquid medium from boron-doped diamond electrodes. This device is presented as an "electronic tongue". It uses several working electrodes, which react to different compounds, because their surface has been covered with different metal catalysts.

[0316] The deposition of a catalyst in the form of islands a few nanometers in diameter is obtained here by depositing a thin layer and then by dewetting leading to random fragmentation. The size and position of the islands are therefore themselves random. However, the manufacturing parameters make it possible to modulate the average size.

[0317] The methods for producing nanostructures are based on a so-called bottom-up approach, which takes advantage of the specific properties of certain materials which, once deposited on a substrate, demonstrate a capacity for morphological organization of a statistical nature - this is referred to as a statistical preparation process. This is linked to the existence of interaction dynamics between the substrate and the deposited material, the elasticity of the material as well as the temperature which lead to phenomena of coalescence or dewetting of the material to lead to a statistical distribution of the material on the surface of the substrate.From a practical point of view, in the electronics industry, a thin film formed outside thermodynamic equilibrium is generally heated to a temperature high enough to activate surface diffusion or evaporation: the thin film will return to an equilibrium state and spontaneously transform into a set of three-dimensional islands of a shape characteristic of the phenomenon, thus undergoing a morphological transition called dewetting. Usually, dewetting proceeds by recoil of the edge of the thin film or by formation of holes in it. For reasons of mass conservation, the thin film, during its recoil, forms a characteristic ridge whose height varies with the dewetting rate and therefore the surface diffusion kinetics of the atoms that compose it. For the thinnest films, fractal or spinodal dewetting processes may exist.Furthermore, this type of phenomenon, given its statistical nature, leads to nanostructures whose dimensions are not significantly homogeneous and whose locations are unevenly distributed: the heights as well as the extent of the nanostructure on the substrate are significantly variable over the same observation zone.

[0318] The electronic language reading system uses the measurements on the different working electrodes to calculate the concentration of a compound of interest for which there is no satisfactory direct measurement (due to lack of specificity of the catalysts or lack of sensitivity).

[0319] Diamond-like carbon (DLC)

[0320] There are a large number of allotropic forms of carbon and carbon structures, each with its own characteristics and properties, as well as specific preparation methods for each. In these structures, atoms are classified by their degrees of atomic hybridization:

[0321] • sp3: configuration in which the four valence electrons of carbon are assigned to identical hybrid orbitals oriented towards the vertices of a tetrahedron and where each of the valence electrons establishes an o bond (strong bond); this is the configuration of diamond itself,

[0322] • sp2: this configuration corresponds to an assignment of three valence electrons to hybrid orbitals oriented towards the vertices of a right triangle to establish an o bond (strong bond), the last electron is able to form a TT bond (weak bond),

[0323] • sp: this configuration corresponds to an assignment of two valence electrons to diametrically opposite orbitals which form strong bonds (o bond) and to the other two electrons to non-hybridized py and pz orbitals (orthogonal to the hybridized orbitals) which constitute IT bonds (weak bond).

[0324] Hydrocarbon compounds, consisting in particular of covalently bonded carbon and hydrogen atoms, present a great diversity of structures: hydrocarbons, graphite, etc. Among these, we distinguish the family of amorphous materials based on carbon and hydrogen, synthesizable in the form of a thin layer, which is generally designated by the term diamond-like carbon (DLC) film.According to the International Union of Pure and Applied Chemistry (IUPAC), diamond-like carbon (DLC) films are hard, amorphous films with a significant fraction of sp3 hybridized carbon atoms and may contain a significant amount of hydrogen. Depending on the deposition conditions that lead to their formation, these films may be entirely amorphous or contain diamond crystallites. They are not called "diamond" unless a complete three-dimensional diamond crystal lattice is proven (IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A.D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). Online version (2019-) created by S.J. Chalk. ISBN 0-9678550-9-8. https: / / doi.Org / 10.1351 / goldbook).

[0325] Within the DLC family, we can consider four large sub-families determined according to the presence or absence of hydrogen as well as the sp3 / sp2 hybridization ratio:

[0326] • DLC “aC”: non-hydrogenated amorphous carbon containing mainly sp2 hybridized carbon,

[0327] • DLC “aC: H”: hydrogenated amorphous carbon containing mainly sp2 hybridized carbon,

[0328] • DLC “ta-C”: non-hydrogenated amorphous carbon containing mainly sp3 hybridized carbon,

[0329] • DLC “ta-C: H”: hydrogenated amorphous carbon containing mainly sp3 hybridized carbon.

[0330] Even if the resistivity of DLC is more favorable than that of "pure" diamond, it is advisable - as with BDD - to introduce a dopant to lower it. In practice, nitrogen doping is generally preferred.

[0331] In the context of the invention, it is preferable, when the allotropic form of carbon chosen is non-hydrogenated amorphous carbon doped with nitrogen, that it be of the “ta-C:N” type, the thin layer of carbon may in particular have the following characteristics:

[0332] • It contains at least 30%, preferably 50%, of sp3 hybridized carbon, preferably at least 75% and advantageously at most 90%.

[0333] • Nitrogen doping is less than 5 atomic%, preferably between 2 and 4 atomic%.

[0334] Example of using diamond-like carbon (DLC)

[0335] The use of DLC to make electrodes has also been explored; the following references illustrating the preparation and use of DLC layers can be mentioned:

[0336] • US Patent 6,423,193 describes an electrode comprising nitrogen-doped DLC (ta-C:N) structures for electroanalytical and electrosynthetic applications. o The ta-C:N layer is obtained at room temperature by vacuum deposition of carbon and nitrogen ions on a substrate which can be of variable nature, and can in particular correspond to a silicon wafer. o A masking process is used during deposition, so that an array of electrodes is obtained.

[0337] • Zeng et al. "Diamond-like carbon (DLC) films as electrochemical electrodes." Diamond and Related Materials 43 (2014): 12-22, describes experiments conducted around the use of DLC in electrodes.

[0338] • Patent application US2011 / 0308942 describes microelectrode arrays for detecting heavy metals in aqueous solutions. These arrays are designed on silicon supports by depositing a doped DLC layer and a patterning layer to form a multitude of electrodes. Materials - thin catalyst layer

[0339] A catalyst is a material whose presence makes it possible to cause a reaction (electrochemical oxidation-reduction) of interest for the measurement of an ionic compound in a particular analysis medium.

[0340] For the purposes of the invention, the thin catalyst layer may consist of a metal, which may in particular be chosen from platinum, tungsten, titanium, copper, nickel, aluminum or even gold, silver, rhodium, osmium, palladium and ruthenium, or a metal alloy comprising, for example, at least one metal chosen from the list set out.

[0341] Advantageously, the metal or metal alloy is chosen by those of them which are likely to oxidize naturally by being exposed to ambient air or at the place of analysis or under an oxygen plasma flow. In this case, an oxide layer is created with a typical thickness between a few nanometers and a few tens of nanometers. The thin layer of catalyst included in the reactive surface is then all or partly an oxide layer.

[0342] Example of catalyst use

[0343] The publication “Detection of Nitrate / Nitrite Using BDD Electrodes Coated with Metal Nano-Catalysts” (ZRIBI, B. and SCORSONE, E. Multidisciplinary Digital Publishing Institute Proceedings, 2017, vol. 1, no. 4, p. 452) illustrates the comparative performances of several catalysts that are likely to be used in the context of the invention.

[0344] As an example, we can also cite some thin layers of catalyst depending on the species we wish to detect:

[0345] • Dissolved oxygen: TiO2, Pt, Au-Pd, Cu-Pd, Au-Cu,

[0346] • Nitrate: CuO, Au-Pt, Au-Ru,

[0347] • Phosphate: NiOOH,

[0348] • pH (H+): TiO2, WO3, IrOx.

[0349] The choice of catalyst is made with both performance and cost considerations. The same catalyst can be used to target different chemical species.

[0350] Materials - support Among the semiconductor materials that can be used for the support, we can notably cite silicon.

[0351] Conductive materials include conductive metals and metal alloys, including niobium, tungsten, titanium, copper, steel, aluminum, gold, or silver.

[0352] According to a specific embodiment, the support comprises a single layer of material, preferably of conductive material.

[0353] The use of an S support makes it possible to limit the quantity of carbon 5 or catalyst 4 used. This consequently makes it possible to obtain a cheap electrode by very significantly limiting the quantities of the most expensive materials.

[0354] In the embodiment of Figure 9, the support S comprises a single layer of material.

[0355] Alternatively, the support comprises several layers of conductive materials stacked along the z axis.

[0356] Materials - intermediate thin layer

[0357] The intermediate thin layer is generally made of a material which does not significantly affect the electrical conductivity between the support S and the thin layer with which it is in contact.

[0358] This may include a metal such as titanium and its alloys, copper and its alloys, tungsten, iron alloys, niobium, etc.

[0359] Mainly to promote adhesion between the different thin layers, a specific thin layer can be inserted between two functional layers (among carbon layer, catalyst layer and support).

[0360] The intermediate thin layer can be an independent material or a mixture of the materials surrounding the intermediate layer.

[0361] For example, we can cite:

[0362] • Titanium is often used as a thin layer to bond DLC carbon,

[0363] • Niobium is the preferred material as a support for the growth of BDD carbon.

[0364] Materials - protective layer The protective layer can be chosen from waterproof materials, known to be unalterable and having strong adhesion to the surface of the electrodes.

[0365] This may include a polymer resin, for example a polyurethane, silicone, epoxy resin, etc., or an injectable thermoplastic resin.

[0366] Such a protective layer protects the printed circuit from damage by the aqueous solution and prevents short circuits that may occur between the different layers of the electrode in the event of infiltration.

[0367] An intermediate layer between the protective layer and the working electrode may also be present, it is then chosen for its resistance properties with respect to the electrolytic activity of the electrode.

[0368] Advantageously, metal oxides (SiO2, Alumina, etc.) or nitrides, which can provide adhesion, sealing, electrical insulation and chemical inertia, will be chosen for this protective layer. The oxide or nitride protective layer can be produced by PVD or a sol-gel process.

[0369] Preparation process - working electrode

[0370] The invention also relates to a method for preparing an electrode as previously defined, on a support, characterized in that it comprises:

[0371] A step of depositing a thin layer of catalyst,

[0372] A step of depositing a thin layer of carbon in an allotropic form of carbon chosen from boron-doped diamond and nitrogen-doped non-hydrogenated amorphous carbon,

[0373] At least one step of depositing a photosensitive resin,

[0374] At least one step of selective exposure of the photosensitive resin, At least one step of partial elimination of the photosensitive resin, At least one step of etching the upper thin layer not protected by the residual photosensitive resin,

[0375] At least one step of removing residual photosensitive resin.

[0376] The sequence of steps from resin deposition to residual resin removal is an example of specific abrasion. The thin carbon layer and the thin catalyst layer are deposited on the support.

[0377] Advantageously, during the process the thin layer of catalyst and the thin layer of carbon are stacked on top of each other.

[0378] In other words, the thin carbon layer and the thin catalyst layer are deposited so that the thin carbon layer is interposed between the thin catalyst layer and the support or vice versa. The thin layer separated from the support by the other thin layer is the upper layer.

[0379] The photosensitive resin is deposited on the top layer

[0380] The resin is then exposed through a mask to achieve selective exposure and then partially eliminated.

[0381] The selective exposure step creates, by exposure to light radiation, reactions within the photosensitive resin and causes chemical modifications, the irradiated areas will see their solubility evolve according to the type of resin - positive or negative. The specific solvents contained in the developer used during the elimination step will make it possible to eliminate the exposed or unexposed resin according to its solubility and thus, by retaining areas of residual resin, to expose the upper thin layer present on the support. Exposure is selective, because it uses a mask, formed of opaque and transparent areas to the applied light radiation and generally placed on the exposure device, which makes it possible to define the pattern that one wishes to reproduce during the etching step.

[0382] At the end of the step of partial elimination of the photosensitive resin, the part of the resin remaining, i.e. not eliminated, is the residual photosensitive resin.

[0383] The step of etching the upper thin layer not protected by the residual photosensitive resin makes it possible to achieve a three-dimensional structuring of the reactive surface of the electrode, according to the dimensional characteristics previously mentioned.

[0384] The residual photosensitive resin is then removed.

[0385] At the end of this last step the entire reactive surface is formed.

[0386] Thus, during the etching step, the upper layer taken from these two layers is etched down to the lower layer taken from these two layers, so that a surface of the lower layer is part of the reactive surface.

[0387] In other words, part of the surface of the lower layer is free. It is therefore intended to be in contact with the medium of interest.

[0388] Thus, the etching step makes it possible to form a three-dimensional structuring of the reactive surface sr of each of the elementary electrodes EE so as to form the three-dimensional structuring of the reactive surface SR of the electrode E and to obtain the reactive surface SR after the elimination of the residual photosensitive resin following the etching step.

[0389] In other words, during this process, the final shape of the thin carbon layer and the thin catalyst layer of the electrode is obtained.

[0390] Advantageously, the reactive surface of the electrode comprises the reactive surfaces of the elementary electrodes or consists of the reactive surfaces of the elementary electrodes.

[0391] Therefore, in general, the method comprises a specific abrasion step to form the three-dimensional structuring of the reactive surface of the electrode.

[0392] After removal of the residual photoresist, the reactive surface of the electrode is free.

[0393] Preferably the electrode is a working electrode.

[0394] The method preferably comprises a step of polishing the support, to obtain a surface roughness of less than 50 nm, or is carried out with a support whose surface roughness is less than 50 nm.

[0395] Advantageously, during the method according to the invention, several electrodes according to the invention are manufactured collectively.

[0396] For this purpose, the support is common to the different electrodes.

[0397] Preparation process - thin carbon layer

[0398] The deposition of the thin carbon layer can be carried out by the processes conventionally used in industry, some of which have been mentioned previously.

[0399] DLC deposition by PVD (physical vapor deposition) has been explored for several decades, mainly along two axes: control of the sp3 / sp2 ratio and the inclusion of various dopants to promote certain properties.

[0400] With a view to using DLC ​​as a sensitive layer in an electrochemical sensor, we will seek to maximize the sp3 / sp2 ratio and include nitrogen doping to reduce the resistivity of the material.

[0401] High-power pulsed magnetron-assisted plasma generation (HiPIMS) techniques have emerged to maximize the sp3 / sp2 ratio. Numerous publications have presented successive improvements. Examples include:

[0402] • « Recent progress on high power impulse magnetron sputtering

[0403] (HiPIMS)” ; AIP Advances 9, 035242 (2019); https: / / doi.Org / 10.1063 / 1 .5084031 ;

[0404] • « High power impulse magnetron sputtering of diamond-like carbon coatings” ; J. Vac. Sci. Technol. A 38(4) Jul / Aug 2020; doi: https: / / doi.Org / 10.1116 / 6.0000070 ;

[0405] • “Optimization of HiPIMS discharges: The selection of pulse power, pulse length, gas pressure, and magnetic field strength” ; Journal of Vacuum Science & Technology A 38, 033008 (2020); https: / / doi.Org / 10.1116 / 6.0000079 ;

[0406] • “From pulsed-DCMS and HiPIMS to microwave plasma-assisted sputtering: Their influence on the properties of diamond-like carbon films” ; Surface and Coatings Technology, Volume 432, 2022,127928, https: / / doi.Org / 10.1016 / j.surfcoat.2021 .127928.

[0407] In the context of the present invention, it is advantageous to optimize the process according to the characteristics sought for a set of sensors, but the invention is not dependent on a particular implementation of the process.

[0408] The previously mentioned patent WO2017037094A1 contains a detailed description of methods for manufacturing BDDs. The particular embodiments within the meaning of the invention may incorporate these conditions.

[0409] Preparation process - thin catalyst layer

[0410] The deposition of the thin layer of catalyst, for example of a few tens of nanometers, can also be carried out by the processes conventionally used in industry, some of which have been recalled previously and in particular in patent W02017037094A1.

[0411] Preparation process - etching and mask

[0412] Etching is generally carried out by a photolithographic process, on the external layer of the electrode being manufactured, as traditionally used in the microelectronics industry.

[0413] Typically, the process involves a step of depositing a photosensitive resin, then using a mask reproducing the patterns that one wishes to give to the reactive surface of the electrodes, i.e. their three-dimensional structure as previously exposed. This is followed by exposure to insolation or light radiation, then removal of the mask. Depending on the type of resin, the exposed part (or the spared part) becomes soluble in a chemical developer. This results in a thin layer (of carbon or catalyst) partially covered with resin. The actual etching of the upper thin layer is then carried out, for example using an oxygen ion plasma.

[0414] The mask may in particular be chosen from materials used in new generation lithography, in particular lithography techniques applicable to scales below 2.5 micrometers, for example below 1 micrometer, for example at 800 nm or 500 nm, preferably 200 nm, advantageously below 50 nm. Typically it is a mask used with microelectronics lithography techniques.

[0415] The process can also take advantage of nanoimprinting techniques, for example block copolymers, in the form of thin films, such as the poly(styrene-b-methylmethacrylate) (PS-b-PMMA) system or polystyrene-block-polydimethylsiloxane (PS-b-PDMS) which can be used with UV radiation. These masks are widely explored in the literature (see in particular: Javier Arias Zapata. Advanced lithography by self-assembly of PS-b-PDMS and associated plasma ething: application to the fabrication of functional graphene nanoribbons arrays. Micro and nanotechnologies / Microelectronics. Université Grenoble Alpes, 2018. English. NNT: 2018GREAT011. Tel-02281286 and Karim Aissou. Study of the self-organization of thin films of diblock copolymers for applications in microelectronics. Materials. Université Joseph-Fourier - Grenoble I, 2008. French. Tel-00267271).This type of technique is particularly suitable if you want to achieve very high precision in structuring.

[0416] Preparation process - electrodes on printed circuit board

[0417] As with other components, particularly bare chips, electrodes of the same composition can be grouped either in blister packs or on reels. Pick and place robots, used in the electronics industry, are able to automatically position each electrode on the printed circuit board. The electrodes can be glued or soldered to the contacts on the printed circuit board provided for this purpose.

[0418] Preparation process - protective layer

[0419] The application of a protective layer, particularly on a printed circuit board, is generally done by placing the first printed circuit board, or device, in a mold and placing insulation pads on the electrodes, then coating the surface of the first printed circuit board, on which an intermediate layer may have been previously placed, with the chosen material using a PVD or sol-gel process. After coating and drying, the mold is removed.

[0420] ADVANTAGES OF THE INVENTION

[0421] The manufacturing process used for the electrodes and devices according to the invention is very simple to implement, thanks in particular to the deposition of solid layers and the use of masks to define the size and distribution of the catalyst surfaces included in the reactive surface.

[0422] The use of intermediate thin layers makes it possible to consolidate the adhesion between the elements and to associate thin carbon layers with a wider range of thin catalyst layers. The process is not statistical in nature: the specific adjustments and fine-tuning are controlled directly by the user by the simple use of a mask without it being necessary to determine fine adjustments of the deposition and / or dewetting parameters as in statistical deposition processes. The presence of a thin catalyst layer makes it possible to reinforce the specificity of the electrochemical measurements carried out with the electrodes according to the invention when they are used as working electrodes. In addition, the electrode manufacturing process makes it possible to easily adjust the proportion of catalyst in the reactive surface.

[0423] Thanks to the mechanical resistance properties, and in particular its surface hardness, of carbon, in the allotropic forms used, the working electrodes have a significantly longer service life than other known electrodes.

[0424] Furthermore, the surface of the thin carbon layer is naturally extremely smooth - its roughness is on the order of a few nanometers - compared to metal electrodes, for example. Surprisingly, it has been found that this type of surface is less prone to fouling - particularly of biological origin - than rougher surfaces. In the case where the starting support is smooth, as is the case for silicon or a polished metal support, this effect is significantly increased.

[0425] Furthermore, surprisingly, particularly in the distance configurations described and particularly with the previously proposed structuring, the self-cleaning properties of the carbon surface in the allotropic forms described, particularly boron-doped diamond, make it possible to generate sufficient hydroxyl radicals, by applying an electric current, to decompose the organic or mineral compounds likely to have been deposited on the reactive surface, including the surface occupied by the thin catalyst layer. This makes it possible in particular to maintain the sensitivity of the sensors while extending their lifetime. Self-cleaning is also energy-efficient and is effective when the aqueous solution moves at low speed relative to the reactive surface.

[0426] The preparation processes also make it possible to design and obtain reference electrodes as well as auxiliary electrodes.

[0427] The use of a plurality of working electrodes allows the detection device to benefit from the electrochemical specificity of each of the working electrodes. The networking of electrochemical measurement devices using these electrodes, and in particular within a detection module, makes it easy, in the case of a multiparametric analysis, to obtain a particularly fine response on the quality of the medium or solution of interest using the device. Thus, by grouping and processing the signals coming from each of the working electrodes, it is possible to obtain a precise signal, which is called a chemical fingerprint. The device has, in such a configuration, the characteristics of what is usually referred to as an electronic "tongue" or "nose".

[0428] The proposed devices comprise a modular part, the first printed circuit or detection module, which:

[0429] • Can be easily replaced in the device, this saves materials in use, and,

[0430] • Allows the device to be easily adapted to the type of measurement the user wishes to perform by changing the detection module.

[0431] The invention, through its flexibility, makes it possible to develop measuring devices and networks of measuring devices capable of meeting the specific requirements of various fields.

[0432] EXAMPLES OF ACHIEVEMENT

[0433] The following preparation examples are intended to illustrate the invention, in particular the preparation of elementary electrodes, working electrodes and sensors, in a non-limiting manner.

[0434] Preparation of electrodes

[0435] In order to prepare a sensor that meets the expectations of the application for which it is intended (see below) it is useful to consider the structuring of the reactive surface of the elementary electrodes and the working electrodes.

[0436] When the thin catalyst layer is below the thin carbon layer, basic reactive surfaces generally comprising a central well, of round, polygonal or square shape, and of characteristic dimensions between 50 nm and 1600 nm, for example between 800 nm and 1600 nm or between 100 nm and 800 nm or between 50 nm and 100 nm have been produced by etching the thin carbon layer using different masks during their preparation. These dimensions and shapes are applicable to the elementary electrodes described previously.

[0437] By thin layer of catalyst under or below the thin layer of carbon, it is meant that the thin layer of catalyst is interposed between the thin layer of carbon and the support.

[0438] When the thin catalyst layer is above the thin carbon layer, basic reactive surfaces comprising central pads, possibly connected to their nearest neighbors by walls, of round, polygonal or square shape, and of characteristic dimension between 50 nm and 1600 nm, for example between 800 nm and 1600 nm or between 100 and 800 nm or between 50 nm and 100 nm were produced by etching the thin catalyst layer using different masks during their preparation. The walls connecting the pads stiffened the structure. It is worth noting that the presence of the walls makes it possible to increase the relative surface area occupied by the catalyst within the electrode.

[0439] The characteristic dimension of a plot is the side of a square in which the plot fits.

[0440] This dimension is taken in a plane perpendicular to the z axis.

[0441] These dimensions and shapes are applicable to the elementary electrodes described previously

[0442] The basic embodiment of the reactive surface of an electrode according to the invention, in particular a working electrode, is obtained by the juxtaposition of wells or catalyst pads inserted into the carbon surface (or matrix).

[0443] For example, a surface comprising wells or pads (of round, square, polygonal section) of characteristic dimension between 50 nm and 1600 nm, for example between 800 and 1600 nm or between 100 and 800 nm or between 50 and 100 nm, for example of approximately 100 nanometers of characteristic dimension, spaced at the same distance can be prepared. This gives a density of wells or pads close to 25% of the total surface. The density of pads can easily be modulated by intercalating other pads in a staggered manner, and a density close to 45% is then obtained, or on the contrary by separating the pads by two elementary spaces (approximately 200 nm in the present case) and a density slightly greater than 10% is then obtained. The characteristic dimension of a pad is the side of a square in which the pad is inscribed.

[0444] This dimension is taken in a plane perpendicular to the z axis.

[0445] These dimensions and shapes are applicable to the elementary electrodes described previously

[0446] Figure 3 schematically illustrates examples of mask configurations M1, M2, M3, M4 used to produce electrodes according to the invention having varied three-dimensional structures: the light (white) zones correspond to the spaces cleared of the masks in the case where the catalyst layer is located under the carbon, the black zones correspond to the spaces cleared of the masks in the case where the catalyst layer is located above the carbon.

[0447] Preparation of working electrodes with simple structures

[0448] Working electrodes consisting of a metal support, the surface of which exhibits catalytic properties, and a thin carbon layer were prepared.

[0449] Figures 4a and 4b schematically illustrate the correspondence between the type of mask adopted and the electrode structures E1, E2 seen in section that can be obtained using a mask.

[0450] The white areas of the MM1 and MM2 masks are areas preventing the passage of the radiation used during the insolation step while the black areas of these masks are areas allowing the passage of the radiation used during the insolation step. In other words, the light areas are the clear areas of the MM1 mask.

[0451] In the exemplary embodiments shown in these figures, each of the electrodes E1, E2 comprises a stack of layers comprising a support 7, on which are stacked a thin layer of carbon 5 and the thin layer of catalyst 4 stacked one on the other.

[0452] Figure 4a shows the configuration in which the thin carbon layer 5 is under the thin catalyst layer 4. In other words, the thin carbon layer 5 is interposed between the support 7 and the thin catalyst layer 4. In the non-limiting example of Figure 4a, the stack E1 comprises two intermediate layers, one being interposed between the thin carbon layer 5 and the thin catalyst layer 4, the other being interposed between the thin carbon layer 5 and the support 7. Figure 4b represents the preferred configuration in which the thin catalyst layer 4 is under the thin carbon layer 5. In other words, the thin carbon layer 5 is interposed between the support 7 and the thin catalyst layer 4.

[0453] An advantage of this embodiment is to limit the risks of separation of the thin carbon layer 5 from the support 7, which makes it possible to preserve the self-cleaning properties of the electrode over time.

[0454] In the non-limiting example of figure 4b, the stack E2 comprises an intermediate layer 8 interposed between the thin carbon layer 5 and the thin catalyst layer 4.

[0455] Advantageously, the intermediate layer 8 is contiguous to the thin carbon layer 5 and to the thin catalyst layer 4.

[0456] The advantage of structure 4a is easier production of etching patterns because the catalyst layer is thinner than the diamond layer. The advantage of structure 4b is to obtain a more mechanically resistant catalyst layer because it is inserted between the carbon layer and the support 7.

[0457] Electrodes were made from tungsten, copper, and titanium supports. As mentioned earlier, these catalytic supports can be advantageously used for the selective detection of pH, nitrate, or dissolved oxygen, for example, without prejudice to their usefulness for other measurements.

[0458] In the case of titanium, the spontaneous formation of an intermediate TiC layer a few nanometers thick (about 5 nm) was noted when a BDD layer was grown on such a support.

[0459] From a practical point of view, the use of such structures, incorporating a massive support with catalytic properties, proves to be resource-efficient, as it does not require the additional preparation of a thin layer of catalyst.

[0460] In other words, in this case, the support is the catalyst layer. Preparation of working electrodes with complex structures

[0461] This structure has the advantage of being easily adaptable to the characteristics of many catalysts that can be used. To reduce the amount of resources required for production, the aim is generally to reduce the number of layers to be deposited. The choice of layer stacking remains mainly dictated by the adhesion properties of the different layers.

[0462] During the preparation of the thin layer of catalyst located under the thin layer of carbon, it was observed that:

[0463] • The adhesion between a metallic catalyst and a metallic support is often very good; if necessary, a thin intermediate layer between the two metals could be used.

[0464] • Oxygen plasma etching is easier and faster through a thin layer of carbon than through a thin layer of catalyst.

[0465] • The thin carbon layer is naturally harder than the thin catalyst layer, it resists abrasion better, for example when the medium to be analyzed contains suspended particles.

[0466] Generally speaking, titanium also allows for a good intermediate thin layer to be produced with the carbon layer, whether it is of the DLC or BDD type. It has also been observed that:

[0467] • The catalytic properties of titanium oxide can be used, for example, for the measurement of dissolved oxygen.

[0468] • In the case of DLC, good performance was observed for both titanium and chromium.

[0469] • In the case of BDD, good performances have been observed for titanium, platinum, gold, silver as well as niobium (it is preferable to add a thin layer of catalyst of a different nature for the latter).

[0470] Generally speaking, when two successive layers are deposited by PVD, it was possible to easily deposit a mixture of the two layers a few nanometers thick to form an intermediate thin layer, which reinforced the adhesion between these two layers. In order to increase the roughness of the surfaces at the nanometric scale, and facilitate the adhesion of the next layer without using an intermediate thin layer, plasma treatments were used (we speak of surface abrasion or "etching").

[0471] Preparation protocols

[0472] The deposits were made under standard conditions for each of the techniques used.

[0473] Implementation with DLC type carbon:

[0474] - Use of a 500 pm thick copper support,

[0475] - Deposition of a thin layer of tungsten by PVD with a thickness of approximately 50 nm,

[0476] - Deposition of a thin layer of titanium by PVD with a thickness of approximately 50 nm,

[0477] - Deposition of a titanium / DLC intermediate layer by PVD (increase in the quantity of DLC and reduction in the quantity of titanium), at room temperature and up to 300°C, with a thickness of 10 nm,

[0478] - Deposition of a thin layer of DLC-type carbon by PVD with a thickness of approximately 100 nm.

[0479] Implementation with BDD type carbon:

[0480] - Use of a 500 pm thick copper support,

[0481] - Deposition of a thin layer of tungsten by PVD with a thickness of approximately 50 nm,

[0482] - Optional deposition of a thin layer of titanium by PVD with a thickness of approximately 50 nm,

[0483] - Deposition of a thin layer of BDD-type carbon by CVD with a thickness of approximately 500 nm.

[0484] In terms of process it seemed simpler to start with CVD deposits and finish with the use of PVD.

[0485] Mask placement and etching were carried out in particular with mask configurations as shown in Figure 3. The unmasked surfaces allow the formation of circular cross-section pads:

[0486] - A section of approximately 100 nm, a distance between the closest wells of approximately 100 nm,

[0487] - A section of approximately 100 nm, a distance between the closest wells of approximately 20 nm,

[0488] - A section of approximately 10 nm, a distance between the closest wells of approximately 200 nm,

[0489] - A section of approximately 20 nm, a closest interwell distance of approximately 180 nm and a mesh connecting the pads with a thickness of 10 nm.

[0490] These examples are not exhaustive. Different dimensions and layouts can of course be considered.

[0491] The preparation protocols could be implemented using commercially available tools and materials:

[0492] - Commercial thin film deposition frames, for example in PVD, with characteristics such as: sputtering / vacuum evaporation with particle speed 4-10 km.s- 1 / 1 km.s-1, working pressure 5.10-3-5.10-2 mbar / 5.10-4 - 5.10-3 mbar, incident particle energy 4-50 eV / 0.2 eV;

[0493] - Commercial thin film deposition frames, for example in PVD, with characteristics such as: High Power Pulsed Magnetron Sputtering (HIPIMS);

[0494] - Pure or alloyed metal sputtering targets (binary / ternary / quaternary / +), from 99% to 99.999% or even hot-pressed targets without binder (Oxides and intermetallics).

[0495] - Thin film deposition frames using microwave plasma CVD systems, for the production of BDD-type carbon layers, with characteristics such as: 6 kW of power and pressure conditions of 10-200 Torr.

[0496] Construction of devices

[0497] Different devices were built and tested, two topologies adopted for the electrodes in these devices are illustrated in Figures 5a and 5b: on a rectangular printed circuit 12a (in Figure 5a) of (about 50 mm x 80 mm, have an area of ​​about 5 x 5 mm) with 15 electrodes and (in Figure 5b) circular 12b (about 50 mm in diameter, the electrodes have an area of ​​about 5 x 5 mm) with 8 electrodes.

[0498] The working electrodes and other electrodes were cut after preparation to have an area of ​​approximately 5x5 mm.

[0499] These configurations are particularly interesting in terms of resources required for the production of the devices, because they allow optimization of the quantity of electrodes to carry out measurements: for example, using a rectangular printed circuit, one would typically use (6x3) +4 electrodes to provide the device with 6 amperometric sensors and a conductivity measurement capacity, but here it is possible to limit the number of electrodes to 15 - i.e. 6 working electrodes (9a to 9f), 6 auxiliary electrodes (14a to 14f) and 3 reference electrodes (10a to 10c) - instead of 22, i.e. a saving of 7 electrodes.

[0500] In order to carry out potentiometric measurements, devices were tested using at least one reference electrode and one working electrode:

[0501] • Example of measurement configuration: two pairs of working electrode with reference electrode: (10a) + (9a) or (10a) + (9b) (with reference to the table below).

[0502] In order to carry out amperometric measurements, devices were tested using at least three electrodes:

[0503] • Example of measurement configuration: a working electrode, a reference electrode, an auxiliary electrode (with reference to the table below in which the working electrodes are distinguished: (10) + (9b) + (14) which presents a better performance and (10) + (9a) + (14)).

[0504] • Configurations in which the total surface area of ​​the auxiliary electrodes is greater (200%) than that of the working electrode offer improved performance; this is achieved by electrically connecting the two available auxiliary electrodes (14a + 14b). Simultaneous activation of two reference electrodes (10a + 10b) is also possible using the same methods.

[0505] In order to perform conductivity measurements, devices were tested using at least two electrodes:

[0506] • Measurements made with the reference electrodes opposite the auxiliary electrodes give good results. Measurements made with a reference electrode opposite a working electrode also give good results.

[0507] • It was observed that the presence of a metallic catalyst on the working electrode has no effect on the conductivity measurement: this type of measurement only exploits the metallic (conductive) behavior of the electrode.

[0508] • Measurements carried out with 4 aligned working electrodes give good results, this is a result consistent with the information present in the literature relating to conductivity measurements.

[0509] In evaluating the devices, it was found that the use of carbon / platinum electrodes (using the methods of the invention) as the reference electrode was particularly useful:

[0510] • Solid platinum is classically recognized and used as a reference electrode,

[0511] • Platinum is stronger / more durable than mixed structures of the Ag / AgCI type.

[0512] Although alternatives are possible, the choice of a carbon / platinum electrode for the auxiliary electrode is also functional.

[0513] Table 1 presents examples of electrode choices (composition for reference and auxiliary electrodes and detected species for working electrodes) for devices.

[0514] Table 1

[0515] For the working electrodes the following catalysts were tested

[0516] • pH: oxides of tungsten, indium, ruthenium,

[0517] • NO3: copper oxides, cobalt, or mixture,

[0518] • PO4: nickel oxides,

[0519] • Chlorine: platinum is relevant.

[0520] • Redox (oxidation-reduction potential) or mixture of any species: gold.

[0521] Conductivity could be measured thanks to the presence of several electrodes without the addition of an additional sensor. The devices could also be equipped with:

[0522] - A temperature sensor (of the medium to be analyzed) with diodes,

[0523] - A MEMS type pressure sensor,

[0524] - An optical turbidity sensor.

[0525] The electronic components that were used to build the devices correspond to commercial products.

Claims

CLAIMS 1. Electrode (1) comprising a plurality of elementary electrodes each having at least two characteristic dimensions less than 2.5 μm, said elementary electrodes each having: - A reactive surface (3), whose characteristic dimensions are less than 2.5 pm, - A thin layer of catalyst (4), part of the surface of which is included in the reactive surface, - A thin layer of carbon (5), in an allotropic form of carbon chosen from boron-doped diamond and nitrogen-doped non-hydrogenated amorphous carbon, in contact with said thin layer of catalyst and part of the surface (6) of which is included in the reactive surface (3), - A support (7), in contact with at least one of the thin layers, allowing the creation of an electrical contact, the reactive surface (3) having a non-statistical morphology, the support (7) being common to the elementary electrodes and the reactive surface of the electrode being made up of the reactive surfaces of the elementary electrodes.

2. Electrode according to the preceding claim, in which each point on the surface of the thin layer of catalyst included in the reactive surface is at a distance less than or equal to 1000 nm from at least one point on the surface of the thin layer of carbon included in the reactive electrode surface.

3. Electrode according to any one of the preceding claims, in which the reactive surface has a three-dimensional structuring obtained by a specific abrasion step of an upper layer to allow a lower layer to be in contact with the medium of interest.

4. Electrode according to the preceding claim, in which the thin layer of catalyst and the thin layer of carbon are superimposed.

5. Electrode according to any one of the preceding claims, in which the surface area of ​​the thin layer of catalyst (4) included in the reactive surface (3) represents 10 to 65% of the reactive surface or 20 to 50% of the reactive surface (3).

6. Electrode according to any one of the preceding claims, in which the thin layer of catalyst is above the thin layer of carbon, the reactive surface comprising central pads, connected to their nearest neighbors by walls, of round, polygonal or square shape, and of characteristic dimension between 50 and 1600 nm, for example between 50 nm and 100 nm obtained by etching the thin layer of catalyst.

7. Electrode according to any one of the preceding claims, comprising an electrically insulating layer, for example made of oxide or nitride, delimiting a closed frame surrounding and delimiting the reactive electrode surface.

8. Electrode according to the preceding claim, in which the insulating layer is deposited on a layer taken from among the thin carbon layer and the thin catalyst layer and an intermediate thin layer and on the support so as to be in direct physical contact with the layer and the support.

9. Printed circuit assembly comprising a printed circuit comprising a printed circuit comprising at least one electrode according to any one of the preceding claims and a polymer protective layer, the electrode being fixed on one face of the printed circuit, the insulating layer separating the protective layer from the reactive surface.

10. Device for electrochemical detection of at least one electroactive species in a liquid medium (2) comprising: - At least one working electrode (9) being an electrode according to any one of claims 1 to 8, - At least one reference electrode (10), - An electrochemical measuring system capable of being connected to the working electrode and to the reference electrode (11).

11. Device for electrochemical detection of at least one electroactive species in a liquid medium (2) according to the preceding claim, comprising: - A first printed circuit (12) comprising: (a) The working electrode (9), (b) the reference electrode (10), - A second printed circuit (13) comprising an electrochemical measurement system capable of being connected to said electrodes (11).

12. Device for electrochemical detection of at least one electroactive species in a liquid medium (2) according to claim 10 to 11, in which the first (12) and the second (13) printed circuits form a single printed circuit on a first face of which the different electrodes are grouped and on the second face of which the electrochemical measurement system (11) is grouped, and where appropriate the electronic system for controlling and reading the non-electrochemical sensor, is arranged.

13. Network of electrochemical detection devices (2) according to any one of claims 10 to 12, characterized in that the electrochemical measurement system (11) of each of the devices (2a, 2b, 2c, 2d) is capable of communicating with a central measurement system (19b).

14. Method for preparing an electrode according to any one of claims 1 to 8, on a support (7), comprising: - A step of depositing one of the thin layer of catalyst (4), - A step of depositing a thin layer of carbon (5) in an allotropic form of carbon chosen from boron-doped diamond and nitrogen-doped non-hydrogenated amorphous carbon, - At least one step of depositing a photosensitive resin, - At least one step of selective exposure of the photosensitive resin, - At least one step of partial elimination of the photosensitive resin, - At least one etching step of the upper thin layer not protected by the residual photosensitive resin, - At least one step of removing residual photosensitive resin.

15. Method according to claim 14, the method being a method of collectively preparing a plurality of electrodes according to any one of claims 1 to 8, in which the support (7) is common to the electrodes.

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