pH SENSOR, METHOD FOR MANUFACTURING SUCH A SENSOR AND METHOD FOR MEASURING pH USING SUCH A SENSOR

Abstract

The invention relates to a pH sensor comprising: a substrate (1); a semiconductor layer (2); a hydrogen ion-sensitive layer (2a) covering the semiconductor layer; a source electrode (3) and a drain electrode (4) in ohmic contact with the semiconductor layer (2); characterized in that the hydrogen ion-sensitive layer (2a) is made up of molecules comprising groups capable of donating and / or accepting hydrogen ions, the molecules being linked by non-covalent interactions to the semiconductor layer (2) so as to form a molecular assembly. Figure 1

Description

Title of the invention: PH SENSOR, METHOD FOR MANUFACTURING SUCH A SENSOR AND METHOD FOR MEASURING PH USING SUCH A SENSOR Technical field

[0001] The invention relates to the improvement of ion-sensitive field effect transistors (ISFETs) as a pH sensor, as well as a method of manufacturing such a sensor. The invention also relates to a method of measuring the pH of a solution using such a sensor. STATE OF THE ART

[0002] There are many applications requiring the measurement of the pH of an aqueous solution.

[0003] Different sensors have been developed to implement such a measurement.

[0004] Electrochemical probes comprise a reference electrode whose electrical potential is known and a measuring electrode whose electrical potential depends on the pH, intended to be brought into contact with the solution to be analyzed. The pH measurement is based on the measurement of the potential difference between the two electrodes. However, these probes require complex electronics and are relatively fragile.

[0005] There are also ISFET type pH sensors. An ISFET sensor is a field effect transistor that is used to measure ion concentrations in a liquid or solution. An ISFET sensor generally comprises an ion-sensitive layer whose surface is in contact with the solution and whose opposite surface is in contact with a channel arranged between two drain and source electrodes and a reference electrode (or a gate electrode) in contact with the solution. When the concentration of H+ or OH- ions in the solution changes, the current flowing in the channel changes accordingly. BRIEF DESCRIPTION OF THE INVENTION

[0006] The aim of the invention is to improve the performance of ISFET type pH sensors by a method which is easy to implement and which makes it possible to increase the sensitivity and stability of the sensor, while giving it as linear a behavior as possible over a wide pH range.

[0007] To this end, the invention proposes a pH sensor comprising: - a substrate; - a semiconductor layer; - a hydrogen ion sensitive layer covering the semiconductor layer- driver; - a source electrode and a drain electrode in ohmic contact with the semiconductor layer;

[0008] characterized in that the layer sensitive to hydrogen ions is made up of molecules comprising groups capable of giving up and / or capturing hydrogen ions, the molecules being linked by non-covalent interactions to the semiconductor layer so as to form a molecular assembly.

[0009] In particular, the hydrogen ion sensitive layer is a self-assembled layer by ir-ir stacking. It makes it possible to obtain a stable assembly with the semiconductor layer without requiring structural modifications of the latter and making it possible to preserve the intrinsic properties of the semiconductor layer.

[0010] Furthermore, the nature of the hydrogen ion sensitive layer can be easily modulated to vary the linearity region depending on the desired pH range for the sensor.

[0011] According to other advantageous but optional characteristics of the sensor:

[0012] - molecules comprising groups capable of yielding and / or capturing ions hydrogen comprise at least two different groups capable of giving up and / or capturing hydrogen ions, the pKa of the groups being separated by at least 1 pH unit from each other, preferably by 2 to 6 pH units from each other;

[0013] - the different groups capable of giving up and / or capturing hydrogen ions are carried by the same molecule or are carried by distinct molecules;

[0014] - the sensor further comprises a grid electrode electrically insulated from of the sensitive layer and having a free surface suitable for being in contact with a solution to be analyzed;

[0015] - the gate electrode is arranged on the substrate at a distance from the sensitive layer, such that the semiconductor layer, the source, drain and gate electrodes together form a liquid gate field effect transistor, the semiconductor layer forming a channel of said transistor;

[0016] - the grid electrode is covered with a layer sensitive to hydrogen ions consisting of molecules comprising groups capable of yielding and / or capturing hydrogen ions, the molecules being linked by non-covalent interactions to the grid electrode so as to form a molecular assembly;

[0017] - the semiconductor layer comprises one or more graphene monolayers stacked graphene monolayers;

[0018] - the semiconductor layer comprises one or more monolayers of disulfide of molybdenum;

[0019] - molecules comprising groups capable of yielding and / or capturing ions hydrogen are monocyclic aromatic molecules, aromatic molecules polycyclic, monocyclic heteroaromatic molecules, polycyclic heteroaromatic molecules or mixtures thereof;

[0020] - the groups capable of giving up and / or capturing hydrogen ions are selected selected from the group consisting of carboxylic acids, boronic acids, sulfonic acids, pyridines, amines and mixtures thereof;

[0021] - molecules comprising groups capable of yielding and / or capturing ions hydrogens are selected from the group consisting of anilines, porphines, porphyrins, pyrene-l-boronic acid, 1-pyrenebutyric acid, 1-aminopyrene, phthalocyanines and mixtures thereof;

[0022] - the sensor further comprises a dialysis membrane arranged opposite the layer sensitive to hydrogen concentration so as to protect said layer from fouling by a film of proteins or microorganisms;

[0023] - the sensor further comprises an absorbent pad arranged on one side of the layer semiconductor opposite the hydrogen ion sensitive layer and orifices formed in the semiconductor layer so as to circulate by capillarity in the absorbent pad a solution to be analyzed in contact with the hydrogen ion sensitive layer.

[0024] Another aspect of the invention relates to a method of manufacturing said sensor. Said method comprises: - the formation of a molecular assembly between a semiconductor layer and molecules comprising groups capable of yielding and / or capturing hydrogen ions, the molecules being linked by non-covalent interactions to the semiconductor layer, so as to form a layer sensitive to hydrogen ions on the semiconductor layer;

[0025] - the formation of two electrically conductive tracks distant from each other in ohmic contact with the semiconductor layer, so as to form a source electrode and a drain electrode.

[0026] The method may further comprise forming a gate electrode electrically insulated from the semiconductor layer, said gate electrode having a free surface adapted to be in contact with the solution to be analyzed.

[0027] Another aspect of the invention relates to a method for measuring the pH of a solution using a sensor as described above. Said method comprises: - bringing the solution into contact with the free surface of the sensitive layer of the sensor, - applying an electric potential difference between the source electrode and the drain electrode so as to cause an electric current to flow in the semiconductor layer, - the measurement of a variation in an electrical property of the semiconductor layer- driver, - the determination of the pH of the solution from said variation in electrical property.

[0028] In some embodiments, said property is a conductance of the semiconductor layer.

[0029] In other embodiments, said electrical property is a shift, on a curve of variation of the conductance of the sensitive semiconductor layer as a function of the gate voltage, of the gate voltage for which the conductance is minimal.

[0030] An application of the invention relates to a flexible patch incorporating a sensor as described above. Said patch comprises a polymer film having an inner face adapted to be in contact with a food, the skin or a cellular tissue. The pH sensor is arranged on the inner face so that the free surface of the layer sensitive to the hydrogen ion concentration is in contact with said food, skin or cellular tissue to measure the pH of said food, skin or cellular tissue.

[0031] Another application of the invention relates to a device for monitoring the pH in a tank or a water circuit integrating a sensor as described above. Brief description of the drawings

[0032] Other characteristics and advantages of the invention will emerge from the detailed description which follows, with reference to the appended drawings, in which:

[0033] - [Fig.l] is a sectional schematic diagram of a pH sensor according to a first embodiment;

[0034] - [Fig.2] is a sectional schematic diagram of a pH sensor according to a second embodiment;

[0035] - [Fig.3] is a sectional schematic diagram of a pH sensor according to a third embodiment;

[0036] - [Fig.4] illustrates a sectional view of the sensor of [Fig.3] at the layer level sensitive to hydrogen ions, protected by a dialysis membrane;

[0037] - [Fig.5] is a graph illustrating the variation in conductance of the semi- sensitive conductive of the sensor, according to a first principle of pH measurement,

[0038] - [Fig.6] illustrates an example of measurement of variation of the resistance of the layer semiconductor as a function of time,

[0039] - [Fig.7] is a graph illustrating the shift, on a variation curve of the conductance of the sensitive semiconductor layer as a function of the gate voltage (field effect curve), the charge neutrality point, i.e. the gate voltage for which the conductance is minimal,

[0040] - [Fig.8] is a sectional view of the sensor incorporating an absorbent pad;

[0041] - [Fig.9] is a graph illustrating the shift of the charge neutrality point in pH function for a graphene layer functionalized by PB Al (not in accordance with the invention),

[0042] - [Fig. 10] is a graph illustrating the shift of the charge neutrality point in pH function for a graphene layer functionalized with PBA2 (not in accordance with the invention),

[0043] - [Fig.l 1] is a graph illustrating the shift of the charge neutrality point in pH function for a functionalized graphene layer according to the invention,

[0044] - Figures 12A, 12B, 12C and 12D are graphs illustrating the shift of the point of charge neutrality as a function of pH in the presence and absence of bovine serum albumin (BSA) in the solution to be analyzed, with and without dialysis membrane.

[0045] For reasons of readability of the figures, the drawings are not necessarily made to scale. DETAILED DESCRIPTION OF EMBODIMENTS Sensor structure

[0046] The sensor comprises a layer of a semiconductor material supported by a substrate, a pH sensing layer, sensitive to hydrogen ions, self-assembled on the semiconductor material and intended to be exposed to a solution to be analyzed, and electrical contacts at opposite ends of the layer of semiconductor material to allow the flow of an electric current in the semiconductor layer. The sensor is thus in the form of an ISFET transistor. Substrate

[0047] The substrate fulfills a role of mechanical support for the ISFET transistor.

[0048] In preferred embodiments, the substrate is in the form of a thin, flexible film, capable of being deformed in order to adapt to the geometry of a medium whose pH is to be measured. By "flexible" is meant in the present text that the substrate can be bent in at least two orthogonal directions without breaking or being damaged. The flexibility of the substrate is advantageously chosen according to the nature of the electrical contacts of the transistor, so as not to subject these contacts to bending or torsional stresses likely to damage them.

[0049] Particularly advantageously, the substrate may thus be formed from one of the following materials: parylene (poly(para-xylylene)), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide, polyamide-imide (PAI), poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole, or an elastomer such as a thermoplastic polyurethane (TPU).

[0050] The substrate may typically have a thickness of about 1 to 125 micrometers, making it particularly well suited to a sensor manufacturing process in Roll-to-Roll lamination process, as described below.

[0051] In other embodiments, particularly when no flexibility of the sensor is desired, the substrate may be in the form of a rigid layer, which may be relatively thick. In this case, the substrate may be formed from one of the following materials: alumina, sapphire, silicon nitride, silicon carbide, silicon, quartz or glass.

[0052] An intermediate layer may be arranged between the substrate and the semiconductor layer. Particularly advantageously, the intermediate layer is a flexible conformal coating, such as poly(para-xylylene) or a copolymer thereof comprising a chlorine substitution on the benzene ring or CF2 linking units between each benzene ring, a polyimide, a polyamide, a polyamide-imide, a silicone polymer, an acrylic, an epoxy, a polyurethane or a styrene-rubber copolymer. Semiconductor layer

[0053] According to a preferred embodiment, the semiconductor layer comprises or is made of graphene. The semiconductor layer may comprise a single monolayer of graphene or several stacked monolayers of graphene, in other words a multilayer consisting of a stack of several monolayers of graphene, typically a stack comprising from 2 to 7 layers of graphene.

[0054] Graphene is an advantageous material due to its electronic properties, in particular its high charge carrier mobility, its stable crystalline structure (without native oxide on the surface) and the thickness of its ultra-thin layer. Furthermore, due to its biocompatibility and transparency, it is particularly advantageous for applications in the fields of health, cosmetics or agri-food.

[0055] In another embodiment, the semiconductor layer comprises or is made of molybdenum disulfide (MoS2). Like graphene, molybdenum disulfide has a two-dimensional structure. The semiconductor layer may comprise one or more monolayers of molybdenum disulfide.

[0056] The semiconductor layer can be encapsulated by a single monolayer of hexagonal boron nitride (h-BN) or by a stack of several layers of hexagonal boron nitride. Hexagonal boron nitride is in fact a material whose structure is close to that of graphene, which has a smooth surface and is free of electrical charges. Furthermore, this material is biocompatible. It therefore protects and preserves the properties of the sensor and, as a result, improves its performance.

[0057] In another embodiment, the semiconductor layer comprises or is made of silicon covered with a layer of hexagonal boron nitride.

[0058] Other semiconductor materials may be used, provided that they can bond by ir-ir stacking to the hydrogen ion concentration-sensitive layer. Hydrogen ion sensitive layer

[0059] The hydrogen ion-sensitive layer is made up of molecules comprising groups capable of releasing and / or capturing hydrogen ions. The hydrogen ion-sensitive layer is therefore sensitive to the hydrogen ion concentration in the medium in which the sensor is intended to operate.

[0060] The molecules comprising groups capable of yielding and / or capturing hydrogen ions are linked by non-covalent interactions to the semiconductor layer, thus forming a molecular assembly. The hydrogen ion-sensitive layer formed from molecules comprising groups capable of yielding and / or capturing hydrogen ions is therefore arranged on the surface of the semiconductor layer and linked to it non-covalently. In other words, the semiconductor layer can be said to be functionalized non-covalently by molecules comprising groups capable of yielding and / or capturing hydrogen ions.

[0061] The non-covalent interactions are typically ir-ir stacking, commonly called "pi-stacking" according to English terminology. Thus, the layer sensitive to the hydrogen ion concentration is typically formed from a molecular assembly by ir-ir stacking on the surface of the semiconductor layer.

[0062] Since semiconductor materials are not intrinsically sensitive to the concentration of hydrogen ions, the molecular assembly makes it possible to provide sensitivity to pH, more precisely to pH variations, thus varying the electrical charge on the surface of the semiconductor layer.

[0063] The molecules comprising groups capable of yielding and / or capturing hydrogen ions are generally monocyclic aromatic molecules, polycyclic aromatic molecules, monocyclic heteroaromatic molecules, polycyclic heteroaromatic molecules or mixtures thereof. It is understood that these molecules may be natural molecules carrying groups capable of yielding and / or capturing hydrogen ions or they may be functionalized by groups capable of yielding and / or capturing hydrogen ions.

[0064] The polycyclic molecules may comprise two, three, four, five, six or even more aromatic rings, for example from 2 to 10 aromatic rings, the rings being able to be fused or not. The polycyclic molecules may further comprise non-aromatic rings.

[0065] Polycyclic aromatic molecules generally comprise from 10 to 40 carbon atoms, or even from 14 to 32 carbon atoms.

[0066] The aromatic molecules preferably comprise 1, 2, 3, 4, 5, 6 or 10 rings aromatic.

[0067] The heteroaromatic molecules comprise one or more aromatic rings comprising, in addition to carbon atoms, at least one heteroatom, preferably from 1 to 4 heteroatoms, such as, for example, one or more sulfur, oxygen, nitrogen atoms or mixtures thereof.

[0068] The aromatic molecules are typically selected from the group consisting of benzene, naphthalene, anthracene, phenathrene, chrysene, pyrene, tetracene, triphenylene, pentacene, benzopypyrene, corannulene, coronene, ovalene and mixtures thereof.

[0069] The polycyclic heteroaromatic molecules can be selected from the group consisting of porphins, porphyrins and their mixtures.

[0070] The groups capable of giving up or capturing hydrogen ions can be selected from the group consisting of carboxylic acids, boronic acids, sulfonic acids, pyridines, amines and mixtures thereof.

[0071] The molecules comprising groups capable of giving up and / or capturing hydrogen ions are generally selected from the group consisting of anilines, porphines, porphyrins, pyrene-1-boronic acid, 1-pyrenebutyric acid, 1-aminopyrene, phthalocyanines and mixtures thereof.

[0072] The molecules comprising groups capable of yielding and / or capturing hydrogen ions generally comprise at least two different groups capable of yielding and / or capturing hydrogen ions, the pKa of the groups being separated by at least 1 pH unit from each other, preferably by 2 to 6 pH units from each other. The different groups capable of yielding and / or capturing hydrogen ions can be carried by the same molecule or by separate molecules.

[0073] Thus, in certain embodiments, the molecular assembly comprises (or the molecules comprising groups capable of donating and / or capturing hydrogen ions comprise) at least one first molecule comprising a group capable of donating or capturing hydrogen ions and at least one second molecule comprising a group capable of donating or capturing hydrogen ions, the pKa of the groups of the first and second molecules being separated by at least 1 pH unit from each other, preferably by 2 to 6 pH units from each other.

[0074] In certain embodiments, when the groups capable of donating and / or capturing hydrogen ions are carried by the same molecule, the molecular assembly comprises (or the molecules comprising groups capable of donating and / or capturing hydrogen ions comprise) at least one (first) molecule comprising at least two groups capable of donating or capturing hydrogen ions, the pKa of the groups of the (first) molecule being separated by at least 1 pH unit from each other, preferably by 2 to 6 pH units from each other. In these embodiments, the molecular assembly may further comprise a second molecule comprising at least one group capable of donating or capturing hydrogen ions, or even further comprise two or three distinct molecules comprising at least one group capable of donating or capturing hydrogen ions. In these embodiments, the pKa of the different groups capable of donating or capturing hydrogen ions is separated by at least 1 pH unit from each other, preferably by 2 to 6 pH units from each other. Electrodes

[0075] The sensor further comprises two electrically conductive tracks in ohmic contact with the semiconductor layer. The two tracks are arranged at the two opposite ends of the semiconductor layer and form a source electrode and a drain electrode.

[0076] The source and drain electrodes may be formed from a solidified electrically conductive ink, which may typically comprise carbon in one or more forms, such as carbon black or graphene, silver, gold, copper, platinum, palladium, or an alloy of these metals, in an organic binder. An advantage of such an ink is that it adheres well to the substrate and accommodates some bending and / or torsional deformation, thereby enabling the use of a flexible substrate.

[0077] Said electrodes are connected to an electrical power supply, for example a cell or a battery (not shown), allowing, when a sufficient electrical potential difference is applied between the source electrode and the drain electrode, an electrical current to flow in the semiconductor layer.

[0078] Said electrodes can be isolated from the external environment of the sensor, and in particular from the solution to be analyzed, by insulating varnishes such as epoxy varnishes, polyurethane varnishes, or silicone varnishes.

[0079] Particularly advantageously, the electrodes may be isolated from the external environment by an encapsulating film which may be formed from one of the following materials: polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide, polyamide-imide (PAI), poly-2,2'-(m-phenylene)-5,5'-bibenzimidazole, or an elastomer such as a thermoplastic polyurethane (TPU). The encapsulating film may typically have a thickness of about 25 to 125 micrometers, which makes it particularly well suited to a sensor manufacturing process by lamination, as described below.

[0080] The encapsulation film is advantageously covered, on its surface facing the substrate, with a hot melt adhesive. Said hot melt adhesive may be ethylene vinyl acetate (EVA), a silicone-based elastomer or a reactive polyurethane (PUR).

[0081] Advantageously but optionally, the sensor further comprises a reference electrode having a free surface adapted to come into contact with the solution to be analyzed and arranged at a distance from the semiconductor channel. The reference electrode is configured to apply a reference voltage to the solution to be analyzed.

[0082] The reference electrode may be arranged on the same substrate as the semiconductor layer, and therefore extend in the same plane.

[0083] Alternatively, the reference electrode may extend in a plane parallel to that of the semiconductor layer. For example, the reference electrode may be arranged opposite the semiconductor layer and separated from said layer by a thickness of solution to be analyzed. The reference electrode and the semiconductor layer may thus be integrated into a fluidic channel in which a sample of the solution to be analyzed circulates.

[0084] In other configurations, the reference electrode may be separate from the sensor and placed in the solution to be analyzed in the vicinity of the hydrogen ion-sensitive layer. Thanks to said electrode, a liquid gate is thus formed on the transistor channel.

[0085] The reference electrode may be formed from a metal layer, a conductive ink, one or more graphene monolayers, or a combination of these materials.

[0086] In some embodiments, the free surface of the reference electrode may have the same functionalization as the semiconductor layer.

[0087] Optionally, the sensor further comprises a back gate electrode (not shown) arranged between the substrate and the semiconductor layer and electrically insulated from the semiconductor layer by an electrically insulating layer. The main utility of a back gate in the transistor is the modulation of the conductivity of the semiconductor layer and the possibility of placing said transistor at the optimal operating point for which the variation of conductivity with the gate potential is maximum without disturbing the liquid gate potential.

[0088] The sensor then constitutes a field effect transistor which can be used to measure the concentrations of H+ or OH- ions in a solution. When the concentration of H+ or OH- ions in the solution changes, the current flowing in the channel changes accordingly.

[0089] Figures 1 to 3 illustrate different non-limiting configurations of the pH sensor.

[0090] [Fig. 1] is a cross-sectional schematic diagram of a pH sensor according to a first embodiment.

[0091] The sensor comprises a substrate 1, on which is arranged a semicon- conductive layer 2 covered with a layer 2a sensitive to the hydrogen ion concentration. As indicated above, an intermediate layer (not shown) can be arranged between the semiconductor layer and the substrate.

[0092] Two electrically conductive tracks 3, 4 in ohmic contact with the semiconductor layer 2 respectively form a source electrode and a drain electrode.

[0093] The electrodes are isolated from the environment outside the sensor by an encapsulation film 5. Said film has at least one opening 5a exposing at least part of the free surface 2a of the sensitive layer, so that the free surface 2a can thus be brought into contact with a solution S to be analyzed, without said solution coming into contact with the source and drain electrodes.

[0094] [Fig. 2] is a sectional schematic diagram of a pH sensor according to a second embodiment. The elements designated by the same reference signs as in [Fig. 1] are identical or perform the same function.

[0095] Compared to the sensor of [Fig.l], the sensor of [Fig.2] further comprises a gate electrode 6 arranged on the substrate at a distance from the sensitive semiconductor layer 2. The gate electrode is partially encapsulated in the encapsulation layer, which however comprises an opening 5b, distinct from the opening 5a formed opposite the sensitive layer 2, exposing the free surface 6a of the gate electrode. Thus, both the hydrogen ion sensitive layer and the gate electrode (which also forms a reference electrode) are in contact with the solution S to be analyzed.

[0096] [Fig. 3] is a sectional schematic diagram of a pH sensor according to a third embodiment. The elements designated by the same reference signs as in Figures 1 and 2 are identical or perform the same function.

[0097] Compared to the sensor of [Fig.2], the sensor of [Fig.3] further comprises a layer 6a sensitive to hydrogen ions covering the gate electrode 6. This functionalization of the gate electrode makes it possible to amplify the response signal of the sensor.

[0098] Furthermore, the layer 2a sensitive to hydrogen ions is covered with a dialysis membrane 7, the advantages of which will be detailed below. Sensor manufacturing method

[0099] The pH sensor according to the invention can be obtained by a manufacturing method comprising the following steps: - formation of a layer sensitive to hydrogen ions on one of the surfaces of a semiconductor layer by bringing the surface into contact with molecules comprising groups capable of giving up and / or capturing hydrogen ions; - placing, on a substrate, the semiconductor layer covered with the sensitive layer, so that the sensitive layer is opposite the substrate, - formation of two electrically conductive tracks distant from each other in ohmic contact with the sensitive layer, so as to form the source electrode and the drain electrode, - optionally, formation of a third electrically conductive track on the substrate, so as to form the gate electrode, - optionally, before placing the semiconductor layer on the substrate, forming a fourth electrically conductive track on the substrate, so as to form the rear gate electrode, an electrically insulating layer being interposed between the fourth electrically conductive track and the sensitive semiconductor layer, - optionally, deposition on the hydrogen ion-sensitive layer of a protective layer, such as a dialysis membrane, - placing the encapsulation layer on the substrate so as to completely encompass the source and drain electrodes; as indicated above, the encapsulation layer has at least one opening facing the semiconductor layer so as to expose the free surface of said sensitive layer and, where appropriate, an opening facing the gate electrode so as to expose its free surface.

[0100] The protective layer makes it possible to isolate the hydrogen ion-sensitive layer from any macromolecules or enzymes that may react with this layer. The dialysis membrane may be made of cellulose acetate, polysulfone, polyethersulfone, polyacrilonitrile, Nafion™, or porous parylene.

[0101] [Fig.4] illustrates a sectional view of the sensor of [Fig.3] at the level of window 5a. The semiconducting layer 2 extends over an intermediate layer 2b, for example made of parylene, which provides the connection between the semiconducting layer and the substrate.

[0102] A dialysis membrane 7 is arranged on the hydrogen ion-sensitive layer 2a, being separated therefrom by a thin layer of liquid or a hydrogel. For this purpose, the membrane is placed in deionized water to moisten.

[0103] As demonstrated in Example 5, said dialysis membrane prevents fouling of the hydrogen ion-sensitive layer by a film of proteins or microorganisms by allowing ionic equilibrium of the liquid in the immediate vicinity of the sensor while protecting it from adsorption of proteins or microorganisms.

[0104] A lamination process is particularly suitable for assembling the sensor. For this purpose, the encapsulation layer is advantageously coated with a thermal adhesive. mofusible which flows during lamination and ensures a fluid seal between the free surface of the semiconductor layer and the source and drain electrodes. However, any other assembly process can be implemented.

[0105] Typically, the formation of the hydrogen ion sensitive layer on one of the surfaces of the semiconductor layer by molecular assembly can be carried out according to the following steps: - bringing one of the surfaces of the semiconductor layer into contact with a solution containing molecules comprising groups capable of yielding and / or capturing hydrogen ions; - rinsing with the solution solvent; - rinsing with deionized water.

[0106] The molecules comprising groups capable of giving up and / or capturing hydrogen ions are as described previously.

[0107] The solvent used to prepare the contacting solution may be any polar solvent capable of solubilizing molecules comprising groups capable of yielding and / or capturing hydrogen ions. For example, the solvent may be dimethylformamide, dimethylsulfoxide or mixtures thereof. pH measurement method

[0108] The general principle of measuring pH using the sensor is the measurement of a variation of an electrical property of the semiconductor layer which is affected by the pH. For this purpose, a potential difference is applied between the source electrode and the drain electrode to cause an electric current to flow between the source electrode and the drain electrode.

[0109] The electrical property considered may vary depending on the structure of the sensor and its control mode.

[0110] When the sensor does not have a gate electrode (as in [Fig. 1]), the electrical property is the conductance of the semiconductor layer, which corresponds to the ratio between the intensity of the electric current flowing between the source and the drain (generally noted Ids) and the potential difference applied between the source and the drain.

[0111] The sensor can therefore be used as a chemoresistor.

[0112] [Fig.5] illustrates the principle of measuring the conductance of the semiconductor layer as a function of time (chronoamperometry), which shows a variation in the conductance when the solution to be analyzed is brought into contact with said layer.

[0113] [Fig.6] illustrates an example of measurement of variation R (expressed in %) of the resistance of the semiconductor layer as a function of time t (expressed in s). The corresponding pH value has been plotted at different locations on the curve. sensors were initially rinsed with deionized water and then with pH6 buffer.

[0114] 500pL of this pH6 buffer was added to each window and 400pL was removed, leaving 100pL to ensure the electrical measurement.

[0115] After 300 seconds (i.e. 5 minutes, pH6a measurement), 400 pL of a pH7 buffer was added and the mixture was homogenized then 400 pL was removed, leaving 100 pL to ensure the electrical measurement.

[0116] After 300 seconds (pH7a measurement), 400pL of a pH8 buffer was added and the mixture was homogenized and then 400pL was removed, leaving 100pL to ensure the electrical measurement.

[0117] After 300 seconds (pH8 measurement), 400pL of pH7 buffer was added and the mixture was homogenized then 400pL was removed, leaving 100pL to ensure the electrical measurement.

[0118] After 300 seconds (Ph7b measurement), 400pL of the pH6 buffer was added and the mixture was homogenized then 400pL was removed, leaving 100pL to ensure the electrical measurement (pH6b).

[0119] The resistance variations of pH6a and pH6b are the same. The same applies to those of pH7a and pH7b.

[0120] This measuring principle can also be used when the sensor comprises a back grid electrode, said electrode being subjected to a constant voltage.

[0121] When a grid electrode is present, the field effect can be used to measure the pH of a solution to be analyzed.

[0122] Indeed, it is possible to influence the flow of electric current in the semiconductor layer by applying an electric voltage to the gate electrode, even if said electrode is distant from the semiconductor layer.

[0123] As discussed above, the free surface of the semiconductor layer and the free surface of the gate electrode are both exposed to the solution to be analyzed through the openings formed in the encapsulation layer.

[0124] A double electrolytic layer is then formed, that is to say an accumulation of charged particles at the interface between the grid electrode and the analyzed solution, which is an electrolytic solution. The ions of the solution are in fact attracted by the free surface of the grid electrode, forming a layer of positive and negative charges.

[0125] When a positive voltage is applied to the gate electrode, the positive charges of the electrolytic double layer are attracted to said electrode, which causes a depletion of the charge carriers in the channel. This reduces the electrical conductivity and turns off the transistor, preventing the flow of current.

[0126] Conversely, applying a negative voltage to the gate electrode attracts negative charges, creating a buildup of charge carriers in the channel. This increases electrical conductivity and activates the transistor, allowing electric current to flow.

[0127] Thus, the electrolytic double layer acts as a switch that controls the conductivity of the channel: by changing the charge distribution in the electrolytic double layer by applying a voltage to the gate electrode, the transistor can be turned on or off, thereby regulating the electric current.

[0128] The curve of the electric current between the source and the drain as a function of the voltage applied to the gate electrode (denoted Vg) has a minimum for a voltage (denoted VD) also called the charge neutrality point or Dirac point (called "Dirac shift" in English). A voltage lower than the charge neutrality point promotes the conduction of holes in the channel, while a voltage higher than the charge neutrality point promotes conduction of electrons in the channel.

[0129] It has been demonstrated that the charge neutrality point depends on the pH of the solution to be analyzed. A measurement of the shift in the charge neutrality point under the effect of contact with the solution to be analyzed therefore makes it possible to determine the pH of said solution.

[0130] This principle is illustrated in [Fig.7], which shows the drain-source current curve Ids as a function of the voltage Vg applied to the gate electrode (also called the field effect curve) for two solutions of different pH. We observe a shift DS = VD2-VDi, where VD1 and VD2 are the minimum of each respective curve. This shift DS varies linearly with the pH.

[0131] The sensor can therefore be seen as an ISFET transistor whose channel is functionalized by an assembly ensuring measurement stability and linearity in a wide pH range. Applications

[0132] The sensor can be used in a wide variety of applications requiring the measurement of the pH of a solution.

[0133] These applications include cosmetics, health, environmental monitoring, precision agriculture, the food industry and scientific research. Patch

[0134] A particularly advantageous application of the sensor, due to its flexibility and biocompatibility, is its use in the form of a patch intended to be applied to the skin of an individual, to cellular tissue or to food to monitor its pH.

[0135] Said patch comprises at least one polymer film having an inner face and an outer face.

[0136] The inner face is intended to be applied against the medium of which it is desired measure the pH. Optionally, part of the inner face has an adhesive area allowing the patch to be stuck to the area where the pH is to be measured.

[0137] The outer face of the polymer film may be fluid-tight and have an area comprising a pressure-sensitive adhesive layer for securing the patch to the skin.

[0138] The pH sensor is arranged on the inner face of the polymer film so that the free surface of the layer sensitive to the hydrogen ion concentration is in contact with said food, skin or cellular tissue.

[0139] The patch can thus enable continuous monitoring of the pH of chronic wounds. Chronic wounds are often subject to complications and delayed healing due to local pH imbalances. The pH of the wound is in fact a particularly relevant indicator of the state of the wound. For example, a wound that becomes infected sees its pH increase.

[0140] The use of the pH sensor integrated into a patch to monitor the pH of chronic wounds therefore presents considerable advantages for healthcare professionals and patients, because real-time monitoring of the pH of these wounds allows for accurate assessment of the condition of the wound and rapid adaptation of treatment protocols.

[0141] Advantageously, the sensor can integrate an absorbent pad allowing the solution to circulate in contact with the sensor by capillarity.

[0142] [Fig.8] illustrates an embodiment of the sensor integrating such a buffer, at the window through which the hydrogen ion-sensitive layer is exposed to the solution to be analyzed.

[0143] An absorbent pad 8, for example made of cellulose, cotton or any other hydrophilic material, is arranged between the substrate 1 and the semiconductor layer 2. In the example illustrated, the semiconductor layer 2 is arranged on an intermediate layer 2b, for example parylene if the semiconductor layer is made of graphene. The absorbent pad is then interposed between the substrate 1 and the intermediate layer 2b. For purely illustrative purposes, an absorbent pad made of agarose gel may have a thickness of the order of 0.3 mm to 1 mm.

[0144] Orifices 9 pass through the semiconductor layer 2 and the intermediate layer 2b to create a fluidic connection between the free surface of the sensor (i.e. the layer 2a sensitive to hydrogen ions) and the absorbent pad 8. The orifices 9 typically have a diameter of between 50 pm and 500 pm.

[0145] The solution to be analyzed can then circulate by capillarity in the orifices 9 and the absorbent pad 8.

[0146] In the case of monitoring a wound, this circulation makes it possible to measure the pH of the exudate as it leaves the wound and thus to detect more quickly the development of the wound.

[0147] In the field of cosmetics, the patch can be applied to healthy skin in order to measure the acidity of the skin.

[0148] In the agri-food sector, the patch can be applied to a food in order to monitor its state of preservation.

[0149] Device for monitoring pH in a tank or water circuit

[0150] The pH sensor may be arranged so that the sensitive layer is in contact with the liquid medium, for example by placing the sensor on a side opening of a tank or water pipe. EXAMPLES

[0151] The following examples illustrate in a non-restrictive manner the subject of the present invention. Comparative example 1

[0152] In this example, a graphene semiconductor layer of a pH sensor is functionalized on its free surface by a molecular assembly composed solely of 1-pyrenebutyric acid (PBA1) having a pKa of 4.7.

[0153] The sensitive layer is manufactured according to the following protocol:

[0154] 1) Preparation of a solution of PBA1 in dimethylformamide (DMF) at 10 mM (mmol / L);

[0155] 2) Cleaning the free surface of a graphene layer with deionized water (DI) to remove any impurities;

[0156] 3) Deposition on the graphene surface (4.5 μL) of the PBAl(10 mM) solution;

[0157] 4) Rinsing with DMF then with a buffer solution followed by drying with pressurized air

[0158] 5) Rinse twice in DI water to remove free PB Al.

[0159] The calibration of the electrical properties of the sensitive layer thus prepared is carried out by successive immersion in buffer solutions at different pH (6, 7, 8, then return to 7 in order to evaluate a possible hysteresis). Between each measurement, the sensitive layer is rinsed with deionized water. The buffers used are PBS 1X reconstituted from the solutions of monobasic and dibasic phosphate at pH 6.0; 7.0; 0 with a conductivity of 15mS / cm. The measuring instrument is GrapLabl: a direct current and a gate voltage are applied and the voltage or resistance of the channel is measured as a function of the gate voltage.

[0160] [Fig.9] illustrates the DS shift of the charge neutrality point ("Dirac shift") (in mV) as a function of pH. A significant asymmetry is observed between acidic and basic pHs. The sensor shows a high sensitivity of the order of 80mV / pH at acidic pHs, allowing precise and responsive detection in this pH range. However, the sensitivity is very low, around 25mV / pH for basic pHs, which limits the sensor's ability to accurately detect pH variations in this range.

[0161] Consequently, functionalizing the surface of the semiconductor layer only with PB Al does not allow for a wide sensitivity zone to pH variations. Comparative example 2

[0162] In this example, a graphene semiconductor layer of a pH sensor is functionalized on its free surface by a molecular assembly composed of pyrene-l-boronic acid (PBA2) having a pKa of 8.8.

[0163] The preparation of the sensitive layer and the tests of the electrical properties are carried out in an identical manner to Example 1.

[0164] [Fig. 10] illustrates the DS shift of the charge neutrality point ("Dirac shift") (in mV) as a function of pH. A significant asymmetry is observed between acidic and basic pHs. The sensor shows a high sensitivity to basic pHs of the order of 65mV / pH allowing precise and reactive detection in this pH range. However, the sensitivity is very low for acidic pHs of the order of 35mV / pH which limits the ability of the sensor to accurately detect pH variations in this range.

[0165] Consequently, functionalizing the surface of the semiconductor layer only with PBA2 does not allow for a wide sensitivity zone to pH variations. Example 3 according to the invention

[0166] In this example, a graphene semiconductor layer of a pH sensor according to the invention is functionalized on its free surface by a molecular assembly combining 1-pyrenebutyric acid (PBA1) and pyrene-1-boronic acid (PBA2).

[0167] The preparation of the sensitive layer and the tests of the electrical properties are carried out in an identical manner to Example 1 except that the 10 mM solution in DMF is an equimolar mixture of PB Al and PBA2.

[0168] [Fig. 11] illustrates the DS shift of the charge neutrality point ("Dirac shift") (in mV) as a function of pH. A perfect symmetry is observed between acidic and basic pHs in the results. In addition, the hysteresis observed at pH 7.0 is only 2 mV, which demonstrates high stability and accuracy of the pH sensor according to the invention.

[0169] The sensor also has good sensitivity characterized by a value of the order of 75 mV / pH, corresponding to a linear and sensitive response of the pH sensors according to the invention in this specific range.

[0170] Therefore, the double functionalization with PBA1 and PBA1 according to the invention makes it possible to obtain a sensitivity of the order of 75 ± 5 mV / pH for both acidic and basic pHs. This functionalization approach has demonstrated its effectiveness in terms of sensitivity and makes it possible to obtain linear and precise responses over the entire pH range.

[0171] Example 4: Studies of pH sensor conservation

[0172] Five pH sensors are manufactured from the same batch of graphene and functionalized according to the method described in Example 3.

[0173] The five sensors are then placed in a plastic box and stored at room temperature (i.e. between 20 and 25°C). Bi-weekly measurements are carried out. It appears that the characteristics of the sensors (sensitivity, linearity and hysteresis) do not vary significantly after six weeks of storage.

[0174] Thus, the pH sensors according to the invention demonstrate good stability at room temperature.

[0175] Example 5: Study of the resistance of the sensors according to the invention

[0176] It is important that the performance of the sensors is not hampered by the presence of proteins or microorganisms from the exudate (biofouling). However, sensitivity to these elements can vary between different types of sensors. Some sensor technologies may be more sensitive to interference caused by proteins or microorganisms.

[0177] It is therefore important to take this consideration into account when choosing and evaluating sensors for a specific application to ensure that the performance of the sensor is not impaired by the presence of undesirable proteins or microorganisms, in particular through specific pretreatments or coatings. Example 5a: Effect of fetal bovine serum (FBS)

[0178] Fetal bovine serum (FBS), also known as fetal bovine serum (FBS), is a fraction of the blood of the cow's fetus. Like all blood serum, it is the supernatant fluid obtained after coagulation and centrifugation of the blood. It is devoid of cells and coagulation proteins, but does contain a number of factors (proteins, hormones, ions) conducive to cell growth. The wide variety of proteins in FBS makes it a good candidate for studying biofouling.

[0179] The sensors are prepared according to the method described in Example 3 except that an additional layer is added before use of the sensors by applying BSA (2% by mass) for one hour.

[0180] This additional layer advantageously protects the sensors from the potential inhibitory effect of SVF proteins.

[0181] The electrical properties of the sensors are measured at different concentrations of SVF (1%, 3%, 5% and 10% by mass) in buffers of pH 6.0, 7.0, and 8.0. It should be noted that the presence of serum and its content does not significantly change the pH of the solutions.

[0182] In the concentration range of 1% to 3% of SVF, there is a slight increase in sensitivity. From 3 to 5%, a decrease in sensitivity is observed which does not affect the initial sensitivity of the sensors. Finally, from 5 to 10%, the sensitivity decreases by 8%.

[0183] Therefore, the upper limit of saturation is reached using 10% FBS, with only an 8% decrease in sensor sensitivity. Thus, FBS has a minor inhibitory effect on sensor sensitivity that does not significantly compromise the sensor's ability to accurately detect and measure pH changes.

[0184] The sensors according to the invention therefore exhibit good performance in terms of robustness and stability in conditions where the SVF is present at reasonable saturation levels.

[0185] Example 5b: Effect of bovine serum albumin (BSA)

[0186] Albumin is the major protein in blood plasma. Bovine Serum Albumin (BSA) is commonly used in cell culture protocols, particularly when the addition of an additional protein is necessary and when other serum components are undesirable. The concentration of BSA in the exudate is estimated to be 2% by mass.

[0187] Figures 12A to 12D illustrate the DS shift of the charge neutrality point (in mV) as a function of pH for different sensor configurations.

[0188] In the case of [Fig.l2A], the hydrogen ion sensitive layer is directly exposed to the solution to be analyzed, in the absence of BSA (curve a) and in the presence of BSA with a concentration of 2%. We therefore observe a significant drop in the sensitivity of the sensor, due to the fouling of the sensitive layer by the BSA (biofouling phenomenon).

[0189] In the case of [Fig.l2B], the hydrogen ion sensitive layer is protected by a dialysis membrane (Spectrum™ RC Spectra / Por™ Dialysis Membrane Tubing, molecule retention threshold 12,000 to 14,000 Da) as illustrated in [Fig.4]. It is observed that the curves are almost the same whether the BSA is absent (curve a) or present with a concentration of 2% in the solution (curve b). This shows the protective effect of the dialysis membrane against the biofouling phenomenon.

[0190] [Fig. 12C] compares the sensor response to a solution containing 2% BSA when the sensor is without a dialysis membrane (curve a) and when it is protected by the dialysis membrane (curve b). It can be deduced that the sensitivity of the sensor is improved thanks to the protection provided by the dialysis membrane against biofouling.

[0191] Finally, [Fig.l2D] compares the response of the sensor to a buffer solution not containing BSA when the sensor is without a dialysis membrane (curve a) and when it is protected by the dialysis membrane (curve b). Since curves a and b are almost the same, it can be deduced that the sensitivity of the sensor is not altered by the presence of the dialysis membrane. Example 5b: Effect of oxygen

[0192] One of the parameters that vary in the wound healing process is the oxygen level. Oxygen plays an important role at each stage of healing: tissue oxygen pressure controls fibroblast proliferation, regulates proline and lysine hydroxylation, an obligatory step in collagen synthesis, and allows the release of collagen by fibroblasts and its incorporation into the scar matrix. Apart from pH, the sensors will also face local hypoxia in the wound. It is therefore necessary to verify the effect of varying oxygen levels on the sensitivity of the sensors.

[0193] The buffers were deoxygenated using a degassing technique consisting of an ultrasonic bath and a vacuum pump. The pH does not change after deoxygenation.

[0194] For standard and deoxygenated buffers, it was observed that the sensitivity of the sensors remains constant, whether in standard buffers or in deoxygenated buffers.

[0195] The variation of the oxygen level in the buffers therefore has no significant effect on the sensitivity of the sensors. Thus the pH sensors according to the invention are robust and can provide reliable and precise measurements, independently of the composition and environmental conditions of the buffer.

Claims

Claims

1. pH sensor comprising: - a substrate (1); - a semiconductor layer (2); - a layer (2a) sensitive to hydrogen ions covering the semiconductor layer; - a source electrode (3) and a drain electrode (4) in ohmic contact with the semiconductor layer (2); characterized in that the layer (2a) sensitive to hydrogen ions is made up of molecules comprising groups capable of yielding and / or capturing hydrogen ions, the molecules being linked by non-covalent interactions to the semiconductor layer (2) so as to form a molecular assembly.

2. A pH sensor according to claim 1, wherein the molecules comprising groups capable of donating and / or capturing hydrogen ions comprise at least two different groups capable of donating and / or capturing hydrogen ions, the pKa of the groups being separated by at least 1 pH unit from each other, preferably by 2 to 6 pH units from each other.

3. pH sensor according to claim 2, in which the different groups capable of giving up and / or capturing hydrogen ions are carried by separate molecules.

4. pH sensor according to one of claims 1 to 3, further comprising a grid electrode (6) electrically insulated from the sensitive layer (2a) and having a free surface (6a) adapted to be in contact with a solution to be analyzed.

5. A pH sensor according to claim 4, wherein the gate electrode is arranged on the substrate (1) at a distance from the sensitive layer (2a), so that the semiconductor layer (2), the source (3), drain (4) and gate (6) electrodes together form a liquid gate field effect transistor, the semiconductor layer (2) forming a channel of said transistor.

6. A pH sensor according to one of claims 4 or 5, wherein the grid electrode (6) is covered with a layer (6b) sensitive to hydrogen ions consisting of molecules comprising groups capable of yielding and / or capturing hydrogen ions, the molecules being linked by non-covalent interactions to the grid electrode (6) so as to form a molecular assembly.

7. A pH sensor according to one of claims 1 to 6, wherein the semiconductor layer (2) comprises a graphene monolayer or several stacked graphene monolayers.

8. A pH sensor according to one of claims 1 to 6, wherein the semiconductor layer (2) comprises one or more monolayers of molybdenum disulfide.

9. pH sensor according to one of claims 1 to 8, in which the molecules comprising groups capable of giving up and / or capturing hydrogen ions are monocyclic aromatic molecules, polycyclic aromatic molecules, monocyclic heteroaromatic molecules, polycyclic heteroaromatic molecules or mixtures thereof.

10. pH sensor according to one of claims 1 to 9, in which the groups capable of giving up and / or capturing hydrogen ions are selected from the group consisting of carboxylic acids, boronic acids, sulfonic acids, pyridines, amines and mixtures thereof.

11. pH sensor according to one of claims 1 to 10, in which the molecules comprising groups capable of giving up and / or capturing hydrogen ions are selected from the group consisting of anilines, porphines, porphyrins, pyrene-1-boronic acid, 1-pyrenebutyric acid, 1-aminopyrene, phthalocyanines and mixtures thereof.

12. pH sensor according to one of claims 1 to 11, further comprising a dialysis membrane (7) arranged opposite the layer (2a) sensitive to the hydrogen concentration so as to protect said layer (2a) from fouling by a film of proteins or microorganisms.

13. A pH sensor according to one of claims 1 to 12, further comprising an absorbent pad (8) arranged on one side of the semiconductor layer (2) opposite the hydrogen ion-sensitive layer (2a) and orifices (9) formed in the semiconductor layer so as to circulate by capillarity in the absorbent pad (8) a solution to be analyzed in contact with the hydrogen ion-sensitive layer (2a).

14. Patch comprising a polymer film having an inner face adapted to be in contact with food, skin or tissue cellular, comprising a pH sensor according to one of claims 1 to 13 arranged on the inner face so that the free surface of the layer sensitive to the concentration of hydrogen ions is in contact with said food, skin or cellular tissue to measure the pH of said food, skin or cellular tissue.

15. A method of manufacturing a pH sensor according to one of claims 1 to 13, comprising: - the formation of a molecular assembly between a semiconductor layer (2) and molecules comprising groups capable of yielding and / or capturing hydrogen ions, the molecules being linked by non-covalent interactions to the semiconductor layer (2), so as to form a layer (2a) sensitive to hydrogen ions on the semiconductor layer; - the formation of two electrically conductive tracks distant from each other in ohmic contact with the semiconductor layer, so as to form a source electrode and a drain electrode.

16. The method of claim 15, further comprising forming a gate electrode electrically insulated from the semiconductor layer (2), said gate electrode having a free surface adapted to be in contact with the solution to be analyzed.

17. Method for measuring the pH of a solution comprising: - bringing the solution into contact with the free surface of the sensitive layer of the sensor according to one of claims 1 to 13, - applying an electrical potential difference between the source electrode and the drain electrode so as to cause an electric current to flow in the semiconductor layer, - measuring a variation in an electrical property of the semiconductor layer, - determining the pH of the solution from said variation in electrical property.

18. The method of claim 17, wherein said property is a conductance of the semiconductor layer.

19. Method according to claim 17 taken in combination with one of claims 4 to 6, in which said electrical property is an offset (DS), on a curve of variation of the conductance of the sensitive semiconductor layer as a function of the gate voltage (Vg), of the gate voltage (VDi,VD2) for which the conductance is minimal.

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