Electrochemical sensor

Abstract

Electrochemical sensor (10) having at least three elements (18, 20, 22, 24, 28), the at least three elements (18, 20, 22, 24, 26, 28) being chosen from a group of elements, the electrochemical sensor (10) comprising a transducer element (20) and a membrane element (22) that is selective for at least one target species, wherein the membrane element (22) and another element (18, 20, 24, 28) of the electrochemical sensor (10) chosen from the group of elements are in direct contact and bonded together by covalent chemical bonds at an interface between them and wherein at least two elements (18, 20, 24, 28) chosen from the group of elements other than the membrane element (22) are in direct contact and bonded together by covalent chemical bonds at an interface between them.

Description

[0001] Electrochemical Sensor

[0002] The invention relates to an electrochemical sensor.

[0003] Common electrochemical sensors, for example ion selective electrodes, comprise a membrane element that is selective for at least one target species and a transducer element that converts the presence of the target species (also referred to as analyte) into an electric signal, in particular the concentration into an electric potential or current.

[0004] Such electrochemical sensors can be applied for many different purposes, for example to detect ions, molecules, proteins, bacteria, enzymes or other species for clinical, biological pharmaceutical or similar uses.

[0005] However, the lifetime of these sensors is typically limited. In particular, the functionality of the sensor can deteriorate over time due to layer delamination and / or water accumulation at the sensor’s elements interfaces.

[0006] The object of the invention is to provide an electrochemical sensor with improved lifetime and durability.

[0007] The object of the invention is solved by an electrochemical sensor having at least three elements being chosen from a group of elements comprising a conductor element, a transducer element, a membrane element, a hydrophilic element, a housing and a substrate, the electrochemical sensor comprising the transducer element that converts the presence of at least one target species into an electrical signal and the membrane element that is selective for the at least one target species. The membrane element and another element of the electrochemical sensor chosen from the group of elements are in direct contact and bonded together by covalent chemical bonds at an interface between them. Furthermore, at least two elements chosen from the group of elements other than the membrane element are in direct contact and bonded together by covalent chemical bonds at an interface between them.

[0008] The invention is based on the recognition that covalent chemical bonds can improve the contact and adhesion between the individual elements, in particular layers of the electrochemical sensors. In other words, the layers can be grafted together to improve the robustness of the electrochemical sensor. It was found that besides lifetime also the temperature resistance of electrochemical sensors can be significantly improved when not only bonding the ion selective membrane, but also other elements of the electrochemical sensor together by covalent chemical bonds. Furthermore, the signal and / or charge transport properties across the individual elements can be improved by the interface bonding.

[0009] It should be clear that the expression “two elements being bonded together by covalent chemical bonds at an interface between them” means that the two elements which are bonded together by covalent chemical bonds are covalently bound to each other over the full area defined by the interface between them or only over parts of the area defined by the interface.

[0010] The transducer element converts the presence of at least one target species into an electrical signal, i.e. the transducer element is configured to convert the presence of the at least one target species into an electrical signal. E.g., the transducer element may be configured to convert the concentration of the at least one target species into an electric potential or current.

[0011] The electrochemical sensor can further comprise the conductor element.

[0012] In one variant, the electrochemical sensor comprises the conductor element, wherein the conductor element is in direct contact with and bonded to the transducer element by covalent chemical bonds at an interface between both elements, i.e. at an interface between the conductor element and the transducer element. In particular, the conductor or ion-to-electron transducer elements can be a conductive or semiconductive material. Materials such as metal or metalloid and their derivatives (e.g. oxidated or halogenated forms), or materials doped intrinsically by chemical elements to affect their electrical conductivity can be applied, for example an electrode in platinum (Pt), gold (Au), carbon (C), indium tin oxide (ITO), silver I silver chloride (Ag / AgCI), tantalum oxide (Ta2Os), iridium oxide (lrOx), n-type or p-type silicon. The ion-to-electron transducer element can also comprise structures like nanoscale collections of single molecules, or polymers that are intrinsically electrically conducting or semi-conducting. It may include organic conductive polymers and their copolymers, for example polyacetylene (PAC), polyphenylene vinylene (PPV), polypyrrole (PPY), polyaniline (PANI), polyphenylene sulfide (PPS), polythiophene (PT), their respective derivatives and / or mixtures, such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The transducer element and the conductor element are examples of two elements other than the membrane element that can be bonded together to increase the overall sensor stability and lifetime.

[0013] Additionally or alternatively, the conductor element can be in direct contact with and bonded to the membrane element by covalent chemical bonds at an interface between both elements.

[0014] It is also possible that the transducer and the conductor element consist of the same material, for example conductive platinum or carbon based materials. This facilitates fabrication of the sensor because the transducer element and the conductor element can be manufactured in a single processing step.

[0015] It is also conceivable that the electrochemical sensor comprises an insulating substrate, wherein the conductor element, the transducer element and / or the selective membrane element partially cover(s) the substrate. In an area of the substrate that is not covered by the conductor element, the substrate is in direct contact with and bonded to another element, in particular the membrane element or the transducer element or the hydrophilic element, by covalent chemical bonds at an interface between the substrate and the directly contacting element.

[0016] The substrate serves as a support for the electrochemical sensor. The covalent chemical bonds between the substrate and other contacting elements further increase the mechanical stability and lifetime of the sensor.

[0017] Additionally, the substrate can serve as an electrical insulator. It may consist of an inorganic material, for example a ceramic or glass material (e.g. quartz, mica, porcelain, SiC>2, AI2O3, AIN, SisN^ or composite material, for example printed circuit board material made from fiberglass and epoxy plastic (e.g. FR-4). These materials present different interesting combinations between chemical inertness, robustness and / or excellent electrical insulation properties, thus preventing unwanted interferences to the detection signal.

[0018] In one advantageous variant, the conductor element and / or the transducer element comprise(s) a structured, in particular randomly or specifically organized, electrically conductive or semiconductive material. Materials such as aggregated dendritic or self-assembled crystalline particles, nanotubes, -sheets, -flakes, -cubes, -rods, -wires, or any compounds in a specific morphology with a high specific surface area (e.g. porous or nanoflower shape) can be applied. Of course, the aforementioned materials, composites or also mixtures are possible.

[0019] By applying a structured material, the contacting interface to other elements can be increased. In addition, charge transport and electrical properties can be improved.

[0020] In another preferred embodiment, the conductor element consists of a solid electrical conductive material with a functionalized, in particular silanized, interface to a neighboring element. The conductor element and / or the transducer element can be for example a solid plain contact made from graphite, graphene, doped or glassy carbon (C), gold (Au), platinum (Pt), copper (Cu) or silver (Ag). The functionalization, in particular silanization, is technically easy to implement and enables and / or improves formation of covalent chemical bonds between the conductor element and directly contacting layers.

[0021] Optionally, every element, in particular layer, of the electrochemical sensor is in direct contact with and bonded to at least another element of the electrochemical sensor by covalent chemical bonds at (an) interface(s) between the directly contacting elements. This configuration provides highest thermal and mechanical stability of the sensor.

[0022] In a further embodiment, the membrane element comprises a polymer matrix. The polymer matrix may be insulating, hydrophobic and / or based on a repetitive structure of the same monomers or a mix of different monomers and comonomers. Materials composing the polymer matrix and based on organic hydrophobic polymers, for example epoxies, polyethylenes, polystyrenes, poly(vinyl chlorides), polysiloxanes, polyesters, polyurethanes, poly([meth]acrylates), polyethers or fluorocarbon polymers and derivatives, can be applied. It can also contain cross-linkers, plasticizers, detergents or several of them in order to adapt the hardness of the membrane and to control the transport of the target species.

[0023] Alternatively, the monomers and co-monomers can have an alkyl group (e.g. derivatives of acrylate or methacrylate) to replace the use of plasticizer. It is also conceivable that at least some of the alkyl groups can be replaced by other functionalized groups containing halogen elements or atoms, such as chloride or fluoride. This improves the hydrophobicity of the membrane element and avoids water permeation and accumulation at the interfaces.

[0024] In a further embodiment, the membrane element comprises a polymer matrix and at least one chemical selective agent, in particular an ionophore for the recognition of the target species and / or at least one neutral carrier for improving the transport properties of the target species through the selective membrane element. This improves the selectivity of the sensor for the target species.

[0025] In order to avoid depletion of the membrane constituents, at least one of the selective agent(s) and / or neutral carrier(s) can be covalently bonded to the polymer matrix.

[0026] In a technically simple arrangement, the polymer matrix is made of polymerized monomers and co-monomers, wherein the polymerized co-monomers or part of the polymerized co-monomers are the selective agent.

[0027] It is also conceivable that the electrochemical sensor comprises the hydrophilic element, the hydrophilic element being located between the transducer element and the membrane element. The hydrophilic element can be in direct contact with and bonded to the transducer element by covalent chemical bonds at an interface between both elements, i.e. an interface between the hydrophilic element and the transducer element, and / or in direct contact with and bonded to the membrane element by covalent chemical bonds at an interface between both elements, i.e. an interface between the hydrophilic element and the membrane element.

[0028] The hydrophilic element may comprise at least a hydrophilic polymer matrix with favorable interactions with a polar solvent leading to solubility or swelling capability (e.g. hydrogel), and an internal electrolyte including a polar solvent (e.g. water), soluble salts used to increase the electrical conductivity (e.g. KCI, NaCI), interfered salts used as potential-determining ions, a known amount of the target species, a free chemical dopant (e.g. one or both forms of a redox couple), a chelating agent (e.g. ethylenediaminetetraacetic acid, EDTA) and / or chemicals to buffer the internal pH, or several of them. Materials composing the hydrophilic polymer matrix and based on organic hydrophilic polymers, for example those from natural compounds such as polysaccharides (e.g. dextran, alginate, chitosan, agarose, and pullulan) and / or proteins (e.g. albumin, gelatin, collagen, lectin, legumine, and viciline), and / or from synthetic compounds such as polyacrylamides, poly([alkyl] acrylic acids), poly([meth]acrylates), poly(ethylene glycols), poly(ethylene oxide)s, poly(styrene sulfonic acids), poly(vinyl amides), poly(vinyl amines), poly(vinyl azines), poly(N-vinyl imidazoles), poly(vinyl pyridines), poly(ethylene imines), poly(L-histidines), poly(methyl vinyl ethers), poly(oxymethylenes), poly(L-prolines), polyfurans or poly(vinyl alcohols), their respective derivatives and / or mixtures, can be applied.

[0029] In general, the hydrophilic layer can be applied to achieve a fixed target species and / or interferent(s) concentration(s) at the transducer and / or membrane interface(s). It can thus improve the sensitivity, the limit of detection and / or the selectivity of the sensor.

[0030] In another embodiment, the transducer element comprises chemical groups and / or contains chemicals, in particular cross-linkers, which form covalent chemical bonds at the interface to directly contacting neighboring elements. Chemical bonds may be formed with the membrane element, the conductor element, or both. This reduces the risk of layer delamination and water accumulation at the interfaces.

[0031] It is also conceivable that the chemical groups and / or chemicals form covalent chemical bonds within the transducer element. This improves the thermal and chemical stability of the transducer element and prevents possible depletion of constituents.

[0032] In another variant, the transducer element may comprise a conductive polymer, in particular with a chemical dopant (for example an electroactive and / or redox species). The dopant can for example improve the conductivity of the transducer element and / or increase the sensor sensitivity or response time to changes in the target species concentration.

[0033] In another preferred embodiment, the transducer element and / or the hydrophilic element comprise(s) a chelating agent. By applying the chelating agent (e.g. EDTA), the amount of target species at said layers and / or layer interfaces can be fixed. This improves in particular the lower detection limit of the sensor.

[0034] It is furthermore conceivable, that the electrochemical sensor comprises the substrate, the substrate consisting of insulating material with a functionalized, in particular silanized, interface to a neighboring element. The surface modification of a material brings physical, chemical and / or biological characteristics different from the initial material’s surface ones. For example, the process of functionalizing the substrate results in the formation of a monolayer, which acts as a coupling agent between the substrate and the neighboring element(s), thereby improving their adherence at the interface. The functionalization includes the addition of small functional groups, moieties, oligomers and / or polymers onto the surface or interface, in particular by oxidation or grafting processing methods using, for example plasma, flame or corona treatments. The functionalization added part may be an integrating part of or used to bond to, for example by a further chemical reaction, at least one of the neighboring element(s) components, for example as a copolymer of a neighboring polymeric matrix. The functionalization provides a simple and yet very effective way to achieve covalent chemical bonds between the substrate and neighboring element(s).

[0035] In another variant, the substrate is partially covered with the aforementioned conductor and / or transducer element(s). To facilitate the manufacturing process of the electrochemical sensor, the substrate, the conductor and / or the transducer element(s) can be functionalized together in one processing step.

[0036] Further advantages and features will become apparent from the following description of the invention and from the appended figures, which show a nonlimiting exemplary embodiment of the invention and in which:

[0037] Fig. 1 schematically shows a cross-sectional side view of a first embodiment of an electrochemical sensor according to the invention;

[0038] Fig. 2 schematically shows a cross-sectional side view of a second embodiment of an electrochemical sensor according to the invention;

[0039] Fig. 3 schematically shows a cross-sectional side view of a third embodiment of an electrochemical sensor according to the invention; Fig. 4 schematically shows a cross-sectional side view of a fourth embodiment of an electrochemical sensor according to the invention;

[0040] Fig. 5 schematically shows a cross-sectional side view of the layers and two grafted interfaces of an electrochemical sensor according to the invention;

[0041] Fig. 6 schematically shows a cross-sectional side view of the layers and three grafted interfaces of an electrochemical sensor according to the invention; and

[0042] Fig. 7 schematically shows a cross-sectional side view of the layers and three grafted interfaces as well as grafted selective agents and neutral carriers of an electrochemical sensor according to the invention.

[0043] Figure 1 schematically shows a first embodiment of an electrochemical sensor 10 according to the invention.

[0044] The sensor 10 is located in a liquid sample 12 and connected to a reference electrode 14 (for example Ag / AgCI / 3M KCI) via an electrical measurement equipment 16 (for example potentiometer).

[0045] The sensor 10 comprises a conductor element 18, a transducer element 20 and a selective membrane element 22.

[0046] In the described embodiment, the conductor element 18 is a solid contact, for example made from glassy carbon.

[0047] The transducer element 20 is a thin layer of PEDOT:PSS covering the conductor element 18.

[0048] The selective membrane element 22 consists of a polymer, for example made from polyvinyl chloride (PVC), and other chemical species and covers the transducer element 20. It is selective for at least one target species, for example calcium ions.

[0049] In this context selective means that the affinity of the membrane element 22 with the target species, due to the polymeric properties (e.g. hydrophobicity) and / or the binding efficiency from the selective and carrying agents, is better than with other species, such as interferents and / or water. In simplified terms, the mass transport of other species than the analyte is hindered through the membrane element 22 and during the transfer I exchange processes across the interfaces, for example between the membrane element 22 and the liquid sample 12.

[0050] In the described embodiment, the conductor element 18 and the transducer element 20 are in direct contact and bonded together by covalent chemical bonds at an interface between them. Furthermore, the transducer element 20 and the selective membrane 22 element are in direct contact and bonded together by covalent chemical bonds at an interface between them. The direct chemical bonds make the sensor 10 very durable and robust against high application temperatures.

[0051] The shown sensor 10 works as follows: The membrane element 22 selectively transports target species from the liquid sample 12 towards the transducer element 20. Optionally, the membrane element 22 can be charged with the target species prior to measurement in order to reduce the sensor’s commissioning. A gradient of concentration of the target species is generated between the respective interfaces of the liquid sample 12 - membrane element 22 and membrane element 22 - transducer element 20. The transducer element 20 converts the information of the analyte presence, such as its concentration, into an electric signal, in particular an electric potential or current, for example resulting from a discharge of the target species with the transducer element 20. The conductor element 18 conducts the electric signal to the electrical measurement equipment 16 where it is detected. By evaluating the detected signal, information about the interfaces’ gradient and consequently the target species in the liquid sample 12 can be obtained. For example, the potentials difference, measured by the electric equipment 16, such as a potentiometer, between the sensor 10 and the reference electrode 14 is proportional to the concentration of the target species in the liquid sample 12 according to the Nikolsky-Eisenman semiempirical model.

[0052] The given examples of the function principle and materials are of course not limiting the scope of the invention. Other types of conductor elements 18, for example from copper, graphite, graphene or doped carbon, and / or transducer elements 20, for example from Pt nanoflowers produced by electrodeposition, iridium oxides (lrOx) bonded nanoparticles or a redox conducting polymer based on a derivative of PAN I electropolymerized or chemically polymerized, and / or other types of membrane elements 22, for example an urethane acrylate based composition polymerized under UV, can be applied.

[0053] For example, the conductor elements 18 and / or transducer elements 20 can comprise structured, randomly or specifically organized electrically conductive or semiconductive material to achieve an increased interface’s surface area contact and / or improved charge transport or charge transfer properties towards neighboring layers.

[0054] Further details about the individual elements, their components and their interfaces are described below with reference to Figures 5 to 7.

[0055] Figure 2 schematically shows a second embodiment of an electrochemical sensor 10 according to the invention.

[0056] The second embodiment corresponds in several essential features to the first embodiment so that only the differences will be discussed below. Identical and functionally identical parts are provided with the same reference symbols.

[0057] In contrast to the first embodiment, the sensor 10 according to the second embodiment comprises an additional hydrophilic element 24 which is located between the membrane element 22 and the transducer element 20.

[0058] The hydrophilic element 24 comprises a hydrophilic layer, in particular a hydrogel swelled with an electrolyte that improves the limit of detection and / or the selectivity of the sensor 10 by fixing the analyte concentration at the transducer interface.

[0059] Except for the additional hydrophilic element 24, the function principle is the same as described above.

[0060] In Figure 2, the hydrophilic element 24 is in direct contact with and bonded to the transducer element 20 by covalent chemical bonds at an interface between them. Furthermore, the hydrophilic element 24 is in direct contact with and bonded to the membrane element 22 by covalent chemical bonds at an interface between them.

[0061] In the second embodiment, the conductor element 18, the transducer element 20 and the membrane element 22 are located within a housing 26 with an opening that is sealed by the selective membrane element 22. The housing 26 and the selective membrane element 22 protect the hydrophilic element 24 from the liquid sample 12.

[0062] Optionally, the housing 26 is in direct contact and bonded to the selective membrane element 22 and / or the hydrophilic element 24 by covalent chemical bonds at an interface between them. The direct chemical bonding prevents delamination of the individual elements from the housing 26 even at elevated application temperatures and pressure variations of the sensor 10.

[0063] Figure 3 schematically shows a third embodiment of an electrochemical sensor 10 according to the invention.

[0064] The third embodiment corresponds in several essential features to the first embodiment, so that only the differences will be discussed below. Identical and functionally identical parts are provided with the same reference symbols.

[0065] In contrast to the first embodiment, the sensor 10 according to the third embodiment comprises a substrate 28. In the embodiment, the substrate 28 is a plain electrically and chemically inert ceramic plate, for example a thin Si / SiC>2 wafer substrate.

[0066] The conductor element 18 is a plainly deposited layer of metal partially covering the substrate 28, for example a titanium-platinum (Ti / Pt) electrode locally deposited by nanofabrication methods such as photolithography and electron-beam evaporation under vacuum processes.

[0067] Optionally, the substrate 28 and / or the conductor element 18 can be functionalized, in particular silanized.

[0068] In Figure 3, the substrate 28 and the conductor element 18 are both silanized (during manufacturing of the sensor 10, a silanization step is performed after deposition of the conductor element 18) to add, on both surfaces, functional groups used for the covalent bonding with at least one of the selective membrane 22 and / or the transducer element 20 components.

[0069] Due to the silanization, the shown sensor 10 comprises linked interfaces with direct chemical bonds between the substrate 28 and the membrane element 22 as well as between the conductor element 18 and the transducer element 20.

[0070] In a first area 30 of the substrate 28 that is not covered by the conductor element 18, nor the transducer element 20, the substrate 28 is in direct contact with and bonded to the membrane element 22 by covalent chemical bonds at an interface between them.

[0071] Additionally, in a second area 32 of the substrate 28 that is not covered by the conductor element 18, the substrate 28 is in direct contact with and bonded to the transducer element 20 by covalent chemical bonds at an interface between them.

[0072] In the embodiment, the direct chemical bonding prevents delamination of the individual elements from the substrate 28 even at elevated application temperatures and extended application times of the sensor 10.

[0073] Figure 4 schematically shows a fourth embodiment of an electrochemical sensor 10 according to the invention.

[0074] The fourth embodiment is a combination of the second and the third embodiment. Corresponding features and functionally identical parts are again provided with the same reference symbols.

[0075] In contrast to the first embodiment, the sensor 10 comprises a substrate 28 and a hydrophilic element 24.

[0076] In the fourth embodiment, every element of the electrochemical sensor 10 is in direct contact with and bonded to at least another element by covalent chemical bonds at an interface between them.

[0077] The sensor 10 shown in Figure 4 comprises interfaces with covalent chemical bonds between the substrate 28 and the membrane element 22 in a first area 30, between the substrate 28 and the transducer element 20 in a second area 32, and between the substrate 28 and the hydrophilic element 24 in a third area 34. It furthermore comprises interfaces with covalent chemical bonds between the conductor element 18 and the transducer element 20, between the transducer element 20 and the hydrophilic element 24, and between the hydrophilic element 24 and the selective membrane element 22.

[0078] The described embodiment is of course not limiting the scope of the invention. Similar sensors 10 are possible with less or even more chemically bound interfaces.

[0079] In the following, based on Figures 5 to 7, the individual elements of the electrochemical sensor 10 according to the invention and the interfaces are described in more detail.

[0080] Figure 5 schematically shows a side view of a section of an electrochemical sensor 10. It is conceivable, that it is the electrochemical sensor 10 according to the first and / or third embodiment (Figures 1 and / or 3).

[0081] The sensor 10 comprises a conductor element 18, a transducer element 20 and a selective membrane element 22.

[0082] The directly contacting interfaces between the conductor element 18, the transducer element 20 and the selective membrane element 22 are grafted (bound together by covalent chemical bonds). This is symbolized in Figure 5 with vertical stripe patterns 36.

[0083] In the embodiment, the transducer element 20 comprises a conductive polymer 38 with a chemical dopant, for example PEDOT:PSS.

[0084] The transducer element 20 furthermore comprises chemical coupling groups and / or contains coupling agent chemicals 40, in particular cross-linkers, which form covalent chemical bonds at the interface to directly contacting neighboring elements. The chemical coupling groups and / or coupling agent chemicals 40 furthermore form covalent chemical bonds within the transducer element 20, which results in increased stability and decreased delamination and / or water accumulation at the interface.

[0085] Furthermore, the membrane element 22 comprises at least a polymer matrix 42 and at least one chemical selective agent 44, in particular an ionophore selective to the target species, and / or at least one neutral carrier 46 for improving the transport properties of the target species through the selective membrane element 22.

[0086] Figure 6 schematically shows another side view of a section of an electrochemical sensor 10. It corresponds in several essential features to the side view of Figure 5, so that only the differences will be discussed below. Identical and functionally identical parts are provided with the same reference symbols.

[0087] Compared to the sensor 10 of Figure 5, the sensor 10 of Figure 6 has an additional hydrophilic element 24 located between the transducer element 20 and a selective membrane element 22.

[0088] It is conceivable that Figure 6 shows a section of the electrochemical sensor 10 according to the second and / or fourth embodiment (Figures 2 and / or 4).

[0089] As indicated by the vertical stripe patterns 36, the directly contacting interfaces between the conductor element 18, the transducer element 20, the hydrophilic element 24 and the selective membrane element 22 are all grafted. This makes the sensor 10 very durable.

[0090] In the described embodiment, the electrolyte contained in the hydrophilic element 24, in addition of a small amount of the target species, comprises a chelating agent 48 (for example EDTA) to improve the performance of the sensor 10, in particular the lower detection limit.

[0091] Of course, the transducer element 20 can optionally also contain chelating agent 48 and / or cross-linkers.

[0092] Figure 7 schematically shows another side view of a section of an electrochemical sensor 10. It corresponds in several essential features to the side view of Figure 6. Again only the differences will be discussed below. Identical and functionally identical parts are provided with the same reference symbols.

[0093] Compared to the sensor 10 of Figure 6, the sensor 10 of Figure 7 has a selective membrane element 22 with selective agents 44 and / or neutral carriers 46 that are grafted (covalently bonded) to the polymer matrix 42 to avoid depletion. This is indicated in Figure 7 by a spring-like tail 50 connected to the respective species. In the embodiment, the polymer matrix 42 is made of polymerized monomers and co-monomers. The polymerized co-monomers or parts of the polymerized co-monomers are the selective agents 44 and / or neutral carriers 46.

Claims

Claims1. Electrochemical sensor having at least three elements (18, 20, 22, 24, 26, 28), the at least three elements (18, 20, 22, 24, 26, 28) being chosen from a group of elements comprising a conductor element (18), a transducer element (20), a membrane element (22), a hydrophilic element (24), a housing (26) and a substrate (28), the electrochemical sensor (10) comprising the transducer element (20) that converts the presence of at least one target species into an electrical signal and the membrane element (22) that is selective for the at least one target species, wherein the membrane element (22) and another element (18, 20, 24, 26, 28) of the electrochemical sensor (10) chosen from the group of elements are in direct contact and bonded together by covalent chemical bonds at an interface between them and wherein at least two elements (18, 20, 24, 26, 28) chosen from the group of elements other than the membrane element (22) are in direct contact and bonded together by covalent chemical bonds at an interface between them.

2. Electrochemical sensor according to claim 1 , comprising the conductor element (18), wherein the conductor element (18) is in direct contact with and bonded to the transducer element (20) by covalent chemical bonds at an interface between both elements (18, 20) and / or wherein the conductor element (18) is in direct contact with and bonded to the membrane element (22) by covalent chemical bonds at an interface between both elements (18, 22).

3. Electrochemical sensor according to claim 2, comprising the substrate (28), wherein the conductor element (18) partially covers the substrate (28) and wherein in an area (30, 32, 34) of the substrate (28) that is not covered by the conductor element (18), the substrate (28) is in direct contact with and bonded to another element (20, 22, 24) chosen from the group of elements, in particular the membrane element (22) or the transducer element (20) or the hydrophilic element (24), by covalent chemical bonds at an interface between the substrate (28) and the directly contacting element (18, 20, 22, 24, 28).

4. Electrochemical sensor according to claim 3, wherein the substrate (28) consists of an inorganic material.

5. Electrochemical sensor according to one of claims 2 to 4, wherein the conductor element (18) and / or the transducer element (20) comprises a structured, in particular randomly or specifically organized, electrically conductive material.

6. Electrochemical sensor according to one of claims 2 to 5, wherein the conductor element (18) consists of a solid electrical conductive material with a functionalized, in particular silanized, interface to a neighboring element (20, 22, 24).

7. Electrochemical sensor according to any of the preceding claims, comprising the hydrophilic element (24), the hydrophilic element (24) being located between the transducer element (20) and the membrane element (22), wherein the hydrophilic element (24) is in direct contact with and bonded to the transducer element (20) by covalent chemical bonds at an interface between both elements (20, 24) and / or wherein the hydrophilic element (24) is in direct contact with and bonded to the membrane element (22) by covalent chemical bonds at an interface between both elements (22, 24).

8. Electrochemical sensor according to any of the preceding claims, wherein every element (18, 20, 22, 24, 26, 28) of the electrochemical sensor (10) is in direct contact with and bonded to at least another element (18, 20, 22, 24, 26, 28) of the electrochemical sensor (10) chosen from the group of elements by covalent chemical bonds at (an) interface(s) between the directly contacting elements (18, 20, 22, 24, 26, 28).

9. Electrochemical sensor according to any of the preceding claims, wherein the membrane element (22) comprises a polymer matrix (42) and at least one chemical selective agent (44), in particular an ionophore selective to the target species and / or at least one neutral carrier (46) for improving the transport properties of the target species through the selective membrane element (22).

10. Electrochemical sensor according to claim 9, wherein at least one of the selective agent(s) (44) and / or neutral carrier(s) (46) is / are covalently bonded to the polymer matrix (42).

11. Electrochemical sensor according to claim 9 or 10, wherein the polymer matrix (42) is made of polymerized monomers and co-monomers, wherein the polymerized co-monomers or part of the polymerized co-monomers are the selective agent(s) (44).

12. Electrochemical sensor according to any of the preceding claims, wherein the transducer element (20) comprises chemical groups and / or contains chemicals (40), in particular cross-linkers, which form covalent chemical bonds at the interface to directly contacting neighboring elements (18, 22, 24, 26, 28).

13. Electrochemical sensor according to claim 12, wherein the chemical groups and / or chemicals (40) form covalent chemical bonds within the transducer element (20).

14. Electrochemical sensor according to any of the preceding claims, wherein the transducer element (20) comprises a conductive polymer (38), in particular with a chemical dopant.

15. Electrochemical sensor according to any of the preceding claims, wherein the transducer element (20) and / or the hydrophilic element (24) comprise(s) a chelating agent (48).

16. Electrochemical sensor according to any of the preceding claims, comprising the substrate (28), the substrate (28) consisting of insulating material with a functionalized, in particular silanized, interface to a neighboring element (18, 20, 22, 24).

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