Sensor for detecting an analyte concentration

Abstract

A sensor for detecting analyte concentration includes: – a case; – a sensor element arranged inside the housing, which has a front surface pressed against a housing wall of the housing, wherein the housing wall has an opening leaving an analyte-sensitive area of ​​the front surface free, and wherein the sensor element has at least one contact element for electrical contacting; – an internal electrolyte contained within the housing, which is in contact with a medium surrounding the housing via an electrochemical transfer arranged in a housing wall; and – a reference electrode immersed in the internal electrolyte, wherein a flexible circuit board is arranged within the housing, comprising at least a first conductor track which is connected to the at least one contact element of the sensor element, and at least a second conductor track which serves as a potential derivation of the reference electrode.

Description

[0001] The invention relates to a sensor for detecting an analyte concentration in a measuring medium.

[0002] Determining the concentration of an analyte in a measuring medium plays a crucial role in many industrial applications, such as chemical and pharmaceutical engineering, food technology, and biotechnology, as well as in non-industrial analytical applications, such as environmental measurement technology. Sensors with an analyte-sensitive component are frequently used in laboratories and industrial process plants to determine ion concentrations. One example of a suitable analyte-sensitive component is an analyte-sensitive membrane. For instance, the glass membrane of the well-known pH glass electrode is sensitive to the concentration of hydrogen. + or H3O + -ions in a measuring medium.

[0003] Alternatively, a semiconductor element can also serve as the analyte-sensitive component, such as a device comprising an EIS structure, like an ion-sensitive field-effect transistor (ISFET) or a capacitor with an EIS structure whose capacitance depends on the concentration of the substance to be measured. The acronym "EIS" stands for "electrolyte-insulator-semiconductor," meaning the sensor comprises a layered structure with at least one insulating coating applied to a semiconductor layer or substrate, which, during measurement operation, is in contact with an electrolyte, namely the measurement medium. A voltage drop occurs at the interface between the insulating layer and the measurement medium.By appropriately selecting the insulator coating, in particular by providing an analyte-sensitive coating on or as a component of the insulator coating, the sensitivity of the sensor can be adjusted so that the voltage drop can serve as a measure of the analyte concentration. For example, the voltage drop at the interface between a tantalum(V) oxide (Ta₂O₅) layer and an aqueous sample solution depends essentially on the pH value of the sample solution. By using other layer structures, EIS sensor elements can be formed that are similarly sensitive to other ions. By immobilizing suitable detector structures, which can include enzymes, for example, on the EIS structure, it is also possible to measure concentrations of nonionic substances, such as glucose or penicillin, using such a sensor.

[0004] The previously mentioned ion-sensitive field-effect transistor (ISFET) also incorporates such an EIS structure. In a pH-sensitive ISFET, for example, the transistor gate is formed by a pH-sensitive insulator coating, which may comprise Ta₂O₅. The charge carrier density in the semiconductor channel between the source and drain of the ISFET then depends accordingly on the pH value of the medium in contact with the gate. For example, German patent DE 198 57 953 A1 describes a sensor for measuring ion concentrations or the pH value of a liquid using an ISFET.

[0005] Such sensor elements with an analyte-sensitive component, particularly semiconductor-based, are often designed as a plate or disc, for example as a chip or chip array, with front or back contact elements for electrically connecting the analyte-sensitive component. Sensors with such sensor elements are frequently designed as rod-shaped measuring probes that comprise a housing immersible in a medium, in which the sensor element is arranged so that its analyte-sensitive component comes into contact with the measuring medium. The contact elements for electrically connecting the analyte-sensitive component, via which the sensor element is connected to sensor electronics, and the sensor electronics themselves are protected within the housing. The measuring probe can be connected to a higher-level unit, such as a transmitter or a bus coupler, via a cable or wirelessly.The higher-level unit can supply the measuring probe with energy, receive and process measurement signals output by the sensor electronics, or output signals to the sensor electronics. Examples of such sensors can be found in US 6,117,292, US 6,153,070, or EP 1 396 718 A1.

[0006] EP 1 396 718 A1 describes a sensor with an ISFET as the sensing element. A pressure plate presses the ISFET, with its rear surface facing away from its ion-sensitive area, against an end face of a sensor housing. The pressure plate has a central opening that leaves the ion-sensitive area of ​​the ISFET exposed, while the source and drain terminals of the ISFET are located in an internal area of ​​the sensor, protected against ingress of the measuring medium. The pressure plate is connected to the sensor housing by a medium-tight, circumferential ultrasonic weld. The interior of the sensor housing is divided into a sensor chamber and a sensor space by an internal tube running within the housing. The sensor space serves as the reference electrode chamber; that is, it contains a reference electrolyte into which a reference electrode is immersed.Connecting wires, linked to the front or rear contact elements of the ISFET, are routed through the sensor's interior to connect the ISFET's source and drain. These wires connect the ISFET to a sensor indicator. The sensor's interior is filled from the inner tube to the rear surface of the ISFET with a potting compound, such as an epoxy adhesive, which provides mechanical support for the ISFET.

[0007] The patent in EP 1 396 718 A1 exemplifies the principle, consistently applied in the prior art, of separating a sensor interior, which serves for contacting and guiding the sensor element's leads, from an electrolyte-filled space in which the reference electrode, typically designed as a second-order reference electrode, is located. Manufacturing sensors based on this principle, as known from the prior art, requires numerous individual work steps and is therefore very complex and costly.

[0008] Furthermore, the sensor housing of such sensors often contains a sensor circuit, frequently electronic, also known as sensor electronics, connected to the leads. This circuitry performs initial processing, particularly amplification and, if necessary, digitization of the measurement signal. Moisture ingress into the sensor electronics can lead to sensor failure. Therefore, considerable effort must be made to ensure the tightness of the electrolyte-filled reference electrode chamber from the sensor electronics, which are also typically housed within the sensor casing.

[0009] It is therefore the object of the present invention to provide an electrochemical sensor of the type mentioned above which overcomes the aforementioned disadvantages. In particular, the sensor should be easier to manufacture and ensure improved sealing of the area of ​​the sensor housing containing the sensor circuitry against the internal electrolyte contained within the housing.

[0010] This problem is solved according to the invention by a sensor according to claim 1.

[0011] The sensor according to the invention for detecting an analyte concentration comprises: – a case; – a sensor element arranged inside the housing, which has a front surface pressed against a housing wall of the housing, wherein the housing wall has an opening leaving an analyte-sensitive area of ​​the front surface free, and wherein the sensor element has at least one contact element for electrical contacting; – an internal electrolyte contained within the housing, which is in contact with a medium surrounding the housing via an electrochemical transfer arranged in a housing wall; and – a reference electrode immersed in the internal electrolyte, wherein a flexible circuit board is arranged inside the housing, comprising at least a first conductor track which is connected to the at least one contact element of the sensor element and at least a second conductor track which serves as a potential lead of the reference electrode.

[0012] Integrating both the lead of the sensor element's at least one contact element and the reference electrode's potential lead into a single flexible circuit board eliminates the need for the previously established separation between a sensor interior, through which the sensor element's connecting wires are routed, and a separate sensor space containing an internal electrolyte, such as a reference electrode chamber containing the reference electrode immersed in the electrolyte. The flexible circuit board can be located directly within the conductive reference electrolyte, thus eliminating the need for a watertight separation between the space containing the connecting wires and the space containing the internal electrolyte. This simplifies sensor manufacturing, as the complex inner tube assembly required to create a watertight separation from the internal electrolyte is no longer necessary.Furthermore, eliminating the inner tube frees up more space inside the housing. This makes it possible to accommodate a flexible circuit board whose length significantly exceeds the axial length of the housing. This simplifies the production of different sensor types with varying housing lengths, as it eliminates the need to stock different circuit board variants of varying lengths to connect the sensor element's contact elements to the sensor circuit.

[0013] If multiple contact elements of the sensor element are present, all necessary connecting lines can be implemented as conductor tracks of the flexible circuit board.

[0014] A suitable base material for the flexible circuit board is a plastic film, for example a polyimide film. The conductor tracks serving as connecting leads for the sensor element and / or the conductor track serving as the potential conductor for the reference electrode can run within the electrically insulating base material or be covered by an additional plastic coating so that they do not come into contact with the internal electrolyte.

[0015] The internal electrolyte can be contained in a first chamber formed within the housing, wherein the housing has a second chamber sealed against the first chamber, in which a sensor circuit, in particular an electronic one, is housed, and wherein the first chamber is sealed against the second chamber, in particular by means of at least one seal through which the flexible printed circuit board passes. The seal can in particular be made of an elastic material. The first chamber can be formed in a front region of the housing, i.e., on the sensor element side. The second chamber can be formed in a rear region of the housing, i.e., on the connection side.

[0016] The seal can, for example, comprise two or more sealing elements that are clamped against each other by bearing against the inner wall of the sensor housing. The flexible circuit board can be routed between the sealing elements from the first chamber to the second chamber.

[0017] The first and second conductor tracks can be electrically connected to the sensor circuit, the sensor circuit being designed to detect one or more electrical measurements via the conductor tracks and process them into one or more, possibly digital, measurement signals and output them to a higher-level unit connected to the sensor.

[0018] The sensor circuit can be arranged on a circuit board located within the second chamber, which is coupled to the flexible circuit board such that the first and second conductor tracks are electrically connected to the sensor circuit. The circuit board containing the sensor circuit can, for example, be designed as a rigid board. The connection layouts of the flexible circuit board and the circuit board carrying the sensor circuit can be matched, further reducing manufacturing effort.

[0019] Suitable materials for the rigid circuit board include common circuit board materials, e.g. based on phenol or epoxy resin, such as FR2, FR3, FR4, FR5, or polyimide.

[0020] In another advantageous embodiment, the sensor circuit is arranged on a section of the flexible circuit board located within the second chamber.

[0021] In one embodiment, the housing can comprise a sensor body and an electronics housing part that is permanently connected to the sensor body. wherein the sensor body has a sensor shaft that is at least partially tubular and an end section adjoining the sensor shaft at the front, which comprises the housing wall against which the front surface of the sensor element is pressed, and the rear end of the sensor shaft is closed by the electronics housing part.

[0022] The electronic housing component can be attached to the sensor shaft, for example, by adhesive bonding, and fitted like a cap. The sensor body can be made of glass or a plastic, such as PEEK, suitable for immersion in the measuring medium. The electronic housing component is not intended for immersion in the measuring medium and can therefore be made of any plastic.

[0023] The aforementioned seal can be arranged in the rear region of the sensor shaft, sealing the first electrolyte-filled chamber of the housing against the second chamber containing the sensor circuitry. The seal can comprise at least two, in particular elastic, plastic sealing elements that bear against the inner wall of the tubular sensor shaft and have two sealing surfaces that are in tension against each other. The flexible circuit board is clamped between these surfaces, ensuring a liquid-tight seal between the circuit board and the second chamber.The clamping seal formed in this way is particularly easy to handle during the manufacture of the sensor and allows a significantly more secure sealing of the front, electrolyte-filled first chamber against the rear second chamber, in which the sensor circuitry is housed, compared to conventional sensors, in which the inner tube described above and the potential derivation of the reference electrode must be guided through a sealing plug arranged in the sensor shaft.

[0024] The electronic housing component can include an interface for connection to a higher-level unit. This interface can comprise a mechanical interface, such as a plug-in connector that can be detachably connected to a complementary socket on a cable connected to the higher-level unit, or an electrical or electronic interface. This electrical or electronic interface allows the sensor circuit to exchange energy and data with the higher-level unit when the mechanical interface is connected to the complementary interface of the higher-level unit or the cable connected to it. For this purpose, the sensor circuit includes circuit components that provide signals at the interface. The interface can, for example, have galvanic contacts or be designed as a contactless, capacitively or inductively coupled interface.

[0025] The reference electrode can comprise a silver wire, at least partially chlorided, which is electrically connected to the second conductor track, for example by a soldered connection. This silver wire is arranged within the first chamber of the housing and immersed in the internal electrolyte, which serves as the reference electrolyte. The internal electrolyte can be a 3 molar KCl solution. This solution is in electrolytic contact with the medium surrounding the housing via the electrochemical transition arranged in the housing wall, which can be designed, for example, as a simple bore or as a porous plastic or ceramic diaphragm.

[0026] The electrically conductive connection between the reference electrode and the flexible circuit board can be located in a front-side, i.e., sensor-element-side, area of ​​the flexible circuit board, preferably near the sensor element. By contacting the reference electrode with the flexible circuit board in the front end region of the sensor, the requirement, found in prior art sensors, for an additional potential trace from the reference electrode to the sensor circuit located in the rear electronic housing is eliminated. This additional trace would have to run almost the entire length of the sensor. The front end region of the sensor housing, in which the sensor element and the connection between the reference electrode and the circuit board are located, can be filled with a potting compound, for example, an epoxy-based one. This potting compound serves to improve the insulation of the connections, particularly soldered joints, between the contact elements.the reference electrode and the first conductor tracks or the second conductor track of the flexible circuit board.

[0027] Instead of a wire soldered onto the flexible circuit board, a layered system arranged on the circuit board can also serve as a reference electrode. In this embodiment, the reference electrode can comprise a silver layer arranged on the flexible circuit board, in electrical contact with the second conductor track, which is at least partially covered by an AgCl layer.

[0028] To improve signal quality, the flexible circuit board can include an additional shielding layer.

[0029] The flexible circuit board can be equipped with a temperature sensor in the area of ​​the sensor element, which is connected to a third conductor track on the flexible circuit board. This third conductor track can be connected to the sensor circuit, which in this configuration is also designed to process signals provided by the temperature sensor. Like the potential lead of the reference electrode and the connecting leads of the sensor element, the third conductor track can also be embedded in the electrically insulating base material of the circuit board or covered by an additional plastic coating, so that it is not in electrical contact with the internal electrolyte.The temperature sensor and any other SMD components present on the flexible circuit board are preferably arranged in a front end area of ​​the housing near the sensor element, similar to the connection point of the reference electrode with the circuit board, and may additionally contain a potting compound.

[0030] The sensor element can comprise an EIS structure. In particular, the sensor element can comprise an ion-sensitive field-effect transistor, which, in addition to the analyte-sensitive area located on the front surface and serving as a gate, has a source terminal located on the front surface or on a rear surface facing away from the front surface of the sensor element and serving as a contact element, and a drain terminal located on the front surface or on the rear surface of the sensor element and serving as a further contact element. In this case, the flexible circuit board has two first conductor tracks, one of which is electrically connected to the source terminal and the other to the drain terminal.The flexible circuit board can be equipped with a temperature sensor, particularly an SMD component, located near the sensor element. As mentioned previously, this temperature sensor is conductively connected to a third conductor track on the flexible circuit board. The first two conductor tracks and the third conductor track are connected, as described above, to a sensor circuit located in a second chamber that is liquid-tight from the first chamber of the sensor housing, which contains the internal electrolyte. The sensor circuit serves to detect and further process signals provided via the contact elements of the sensor element and / or by the temperature sensor.

[0031] The invention will be explained in more detail below with reference to the embodiment shown in the figures. The figures show:

[0032] Fig. 1. An overall view of an electrochemical sensor, partly in longitudinal section;

[0033] Fig. 2 an enlarged longitudinal section view of the front end section of the in Fig. 1 of the sensor shown;

[0034] Fig. 3 a detailed representation of one in which in Fig. 1. Flexible circuit board containing sensor shown, with a sealing arrangement in a first position;

[0035] Fig. 4 a detailed presentation of the in Fig. 3 shown circuit board with the sealing arrangement in a second position.

[0036] Fig. Figure 1 shows a schematic longitudinal section view of an electrochemical sensor. 1 For measuring the pH value of a sample medium. As an analyte-sensitive sensor element. 2The sensor shown here comprises an ion-sensitive field-effect transistor. Although the invention is described below using a pH sensor with a pH-sensitive ISFET as the sensor element, the invention is of course transferable to sensors with other sensor elements, in particular sensor elements comprising ISFETs or ChemFETs or other EIS structures, as well as with ion- or analyte-sensitive membranes that provide a signal dependent on the concentration of an analyte in a measuring medium.

[0037] The sensor 1 includes a housing 3 , which essentially consists of a sensor body 4 and one firmly attached to the sensor body 4 connected electronics housing part 5 is formed. The sensor body 4 It can be made of a non-electrically conductive material, such as glass or plastic. In the present example, the sensor body consists of 4Made of polyetheretherketone (PEEK). The sensor body 4 includes a tubular sensor shaft, the front end section of which ( Fig. 2) is designed to be immersed in a measuring medium for measuring the pH value. The sensor shaft of the sensor body is located on the back. 4 firmly attached to the electronics housing part 5 connected, in the manner of a cap on the back of the sensor shaft 4 is attached and closes it. The electronics housing part 5 It consists of a non-electrically conductive plastic.

[0038] As in Fig. 2 is recognizable in detail, the sensor element 2 with its front surface 6 via an elastic sealing element 7 against a front wall 8 of the sensor body 4 pressed against the wall 8 has an opening 9 on, which has a pH-sensitive surface area of ​​the sensor element 2leaves this area free, so that it remains open when the sensor is immersed. 1 into a measuring medium with which it comes into contact.

[0039] The sensor element 2 is achieved by means of a pressure part attacking its back side facing away from the pH-sensitive surface area. 10 against the elastic sealing element 7 pressed down. The pressure part 10 It can, for example, consist of an elastomer, so that the sensor element is sandwiched between the elastic sealing element. 7 and the pressure part 10 is jammed. The pressure part 10 rests against a wall of the housing 3 connected counterpart 11 away.

[0040] While the pH-sensitive surface area of ​​the sensor element designed as an ISFET 2 forming transistor gate with which the housing 3The source and drain of the ISFET are in contact with the surrounding medium by means of the sealing element. 7 medium-tight from the environment of the housing 3 enclosed area of ​​the front surface 6 of the sensor element 2 arranged. Contact elements serving as source and drain connections can be located either on the front surface, as in the example shown here. 6 of the sensor element 2 or on one of the front surfaces 6 be arranged on the rear surface facing away from the road.

[0041] The contact elements are electrically conductive via a soldered connection to the conductor tracks of a flexible circuit board. 12 connected, running axially through the sensor body 4 The conductor tracks run within the flexible circuit board. In the example shown here, the conductor tracks run inside the flexible circuit board. 12 They run along the entire length of the flexible circuit board. 12and are connected to one in the connection housing part 5 arranged sensor circuit 13 connected. In the front end area of ​​the sensor body. 4 is on the flexible circuit board 12 a reference electrode 14 The wire is arranged and consists of a silver wire partially sheathed in PEEK. At one end, advantageously its sensor element-side end, the silver wire is conductively connected, for example by means of a soldered connection, to another conductor track of the flexible circuit board, which is also connected to the sensor circuit. 13 is connected. At its other end, the silver wire has an AgCl coating, which is inserted into a housing within the sensor body. 4 contained internal electrolytes 15 immerses. In the present example, the internal electrolyte comprises 15 an aqueous 3molar KCl solution. The internal electrolyte can also be a gel electrolyte, which may consist of a polymer with embedded KCl solution. Via a [missing information] in the housing wall of the sensor body. 4 arranged microporous diaphragm 16 , for example made of ceramic, the internal electrolyte 15 with the front end area of ​​the sensor 1 surrounding medium in electrolytic contact, so that charge transport between the inner electrolyte 15 and the surrounding medium.

[0042] The case 3 in its front end area approximately to the height of the counterpart 11 potted with a potting material, for example an epoxy resin, so that in particular the sensor element-side end of the reference electrode connected to the flexible circuit board is also potted 14as well as its connection point with the conductor track serving as a potential conductor opposite the internal electrolyte 15 is isolated.

[0043] The ladder map 12 It therefore serves to connect both the sensor element and the sensor element. 2 as well as the reference electrode 14 with the sensor circuit. As explained at the beginning, the conventional division of the housing into an inner chamber containing the connecting wires of the sensor element and a further chamber containing the internal electrolyte is dispensed with, which, among other things, simplifies the manufacturing of the sensor. 1 It simplifies things and also results in more space being available inside the sensor.

[0044] In the front potted area of ​​the housing 3 , preferably as close as possible to the sensor element 2 , is on the flexible circuit board 12 additionally a temperature sensor 22arranged, which is connected to another conductor track of the flexible circuit board 12 is connected. The other conductor track is like the potential-dissipating conductor track of the reference electrode. 14 and those with the sensor element 2 connected conductor tracks with the sensor circuit 13 connected, which is connected to the temperature sensor 22 The provided signals are captured and processed.

[0045] In the tubular section of the sensor body that forms the sensor shaft 4 is a seal 17 arranged, which places the sensor housing into a first chamber 18 and a second chamber 19 subdivided. The first chamber 18 is located in the sensor body 4 and contains the reference electrolyte 15 The second chamber 19 is formed by the rear end section of the sensor body 4 and the electronic housing part attached to it 5formed in this second chamber 19 is the sensor circuit 13 arranged. The seal 17 In the example shown here, this is achieved by two elastic sealing elements that abut each other. 23 , 24 formed, which fill the cross-section of the sensor shaft and are supported against its inner wall, so that the space between the sealing elements 23 , 24 ladder map leading from the first to the second chamber 12 between two adjacent sealing surfaces of the sealing elements 23 , 24 is clamped in place. In this way, the sensor circuit is 13 containing second chamber 19 opposite the first electrolyte-filled chamber 18 It is sealed liquid-tight, so that no internal electrolyte can enter. 15 into the second chamber 19 can penetrate.

[0046] The seal 17 is in the Fig. 3 and Fig. 4 shown in detail. The sealing elements 23 , 24 In the example shown here, this can lead to a rotationally symmetrical, plug-like seal. 17 to be assembled. A first sealing element 23 exhibits an axial symmetry symmetry with respect to the rotational axis of the seal 17 ongoing cut 25 up, into which the second sealing element 24 , as in Fig. 3 can be seen, it is retractable. The flexible circuit board 12 can be used against one within the incision 25 arranged surface of the first sealing element 23 to be applied and will be used when the seal is joined. 17 between this surface and an adjacent surface of the second sealing element 24 Pressed in. With their outer surfaces 26 , 27 the sealing elements are supported 23 , 24 against the inner wall of the tubular sensor shaft, thus sealing the first chamber18 liquid-tight from the second chamber 19 .

[0047] Additionally, the area between the seal can 17 and the end of the sensor body that is open towards the back of the sensor 3 be filled with a potting compound.

[0048] The flexible circuit board indicates within the first chamber 18 a curved path, so that the length of the flexible circuit board between the sensor element 2 and the seal 17 is greater than the distance between the seal 17 and the sensor element 2 This serves, firstly, to relieve strain on the flexible circuit board. 12 Secondly, it is due to the space saved within the sensor body. 4As a result of dispensing with an additional inner tube, it is possible to manufacture different sensor types of different lengths using flexible circuit boards of the same length, whereby the circuit board 12 may be folded once or multiple times, depending on the sensor body 4 significantly shorter than the circuit board 12 is.

[0049] In the example shown here, the sensor circuit 13 on a rigid ladder board 20 arranged. The contact elements of the sensor element. 2 and the reference electrode 14 connected conductor tracks of the flexible circuit board 12 are with associated connections of the sensor circuit 13 connected. To further simplify the manufacturing of the sensor. 1 These are the connection diagrams of the flexible circuit board 12 and the rigid ladder map 20 coordinated.

[0050] The second chamber19 It can be filled with a potting compound, e.g., an epoxy resin. In particular, the sensor circuit can be 13 to be spilled.

[0051] The sensor circuit 13 In addition to means for further processing the measurement signals, in particular for their amplification and digitization, it includes a memory for storing sensor data and / or measured values. Furthermore, the circuit in the example shown here includes an inductive interface integrated into a mechanical sensor connector. 21 This interface 21 can be connected to a (not shown) complementary socket to connect the sensor 1 to connect to a higher-level unit, such as a transmitter, a conventional computer, or a bus coupler. Data, especially measured values, and power can be transmitted via the inductive interface. QUOTES INCLUDED IN THE DESCRIPTION

[0052] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0053] DE 19857953 A1

[0004] US 6117292

[0005] US 6153070

[0005] EP 1396718 A1 [0005, 0006, 0007]

Claims

[1] Sensor ( 1 ) to determine an analyte concentration using: – a case ( 3 ); – one inside the housing ( 3 ) arranged sensor element ( 2 ), which is against a housing wall ( 8 ) of the housing ( 3 ) pressed-on front surface ( 6 ) has, wherein the housing wall ( 8 ) an analyte-sensitive area of ​​the anterior surface ( 6 ) releasing opening ( 9 ) exhibits, and where the sensor element ( 2 ) has at least one contact element for electrical contacting; – one inside the housing ( 3 ) absorbed internal electrolytes ( 15 ), which uses an electrochemical transition arranged in a housing wall ( 16 ) with a the case ( 3 ) surrounding medium is in contact; and – one in the internal electrolytes ( 15) immersing reference electrode ( 14 ), characterized by that inside the housing ( 3 ) a flexible circuit board ( 12 ) is arranged, which includes at least one first conductor track connected to at least one contact element of the sensor element ( 2 ) is connected, and at least one second conductor track, which serves as a potential derivative of the reference electrode ( 14 ) serves, includes. [2] Sensor ( 1 ) according to claim 1, wherein the internal electrolyte ( 15 ) in a first within the housing ( 3 ) formed chamber ( 18 ) is included and wherein the housing ( 3 ) one opposite the first chamber ( 18 ) sealed second chamber ( 19 ) has a sensor circuit, in particular an electronic one ( 13 ) is housed, and the first chamber ( 18 ) opposite the second chamber ( 19), in particular by means of at least one seal ( 17 ), is sealed, through which the flexible circuit board ( 12 ) through it. [3] Sensor ( 1 ) according to claim 2, wherein the first and second conductor tracks are connected to the sensor circuit ( 13 ) are electrically connected. [4] Sensor ( 1 ) according to claim 2 or 3, wherein the sensor circuit ( 13 ) on one within the second chamber ( 19 ) arranged circuit board ( 20 ) is arranged, which is connected to the flexible circuit board ( 12 ) is coupled in such a way that the first and second conductor tracks are electrically conductive with the sensor circuit ( 13 are connected. [5] Sensor ( 1 ) according to one of claims 2 to 4, where the housing ( 3 ) a sensor body ( 4 ) and a fixed connection to the sensor body ( 4 ) connected electronic housing part ( 5) includes, where the sensor body ( 4 ) has a sensor shaft that is at least partially tubular and an end section adjoining the sensor shaft at the front, which forms the housing wall ( 8 ), against which the front surface ( 6 ) of the sensor element ( 2 ) is pressed, includes, and the rear end of the sensor shaft is enclosed by the electronics housing part ( 5 ) is locked. [6] Sensor ( 1 ) according to claim 5, wherein in the rear region of the sensor shaft a first chamber ( 18 ) opposite the second chamber ( 19 ) sealing gasket ( 17 ) is arranged, which includes at least two plastic sealing elements clamped against each other ( 23 , 24 ) includes, between which the flexible circuit board ( 12 ) is clamped down. [7] Sensor ( 1 ) according to claim 5 or 6, wherein the electronic housing part (5 ) an interface ( 21 ) for connection to a higher-level unit. [8] Sensor ( 1 ) according to any one of claims 1 to 7, wherein the reference electrode ( 14 ) has a silver wire connected to the second conductor track, which is at least partially chlorided. [9] Sensor ( 1 ) according to one of claims 1 to 8, wherein the reference electrode comprises a silver layer arranged on the flexible circuit board and in electrical contact with the second conductor track. [10] Sensor ( 1 ) according to any one of claims 1 to 9, wherein the electrically conductive connection between the reference electrode ( 14 ) and the flexible circuit board ( 12 ) in a front area of ​​the flexible circuit board ( 12 ), preferably near the sensor element ( 2 ), is arranged. [11] Sensor ( 1) according to any one of claims 1 to 10, wherein the flexible circuit board ( 1 ) includes an additional layer of shielding. [12] Sensor ( 1 ) according to any one of claims 1 to 11, wherein the flexible circuit board ( 12 ) in the area of ​​the sensor element ( 2 ) with a temperature sensor ( 22 ) is equipped with a third conductor track of the flexible circuit board ( 12 ) is connected. [13] Sensor ( 1 ) according to claim 12, wherein the third conductor track is connected to the sensor circuit ( 13 ) is connected. [14] Sensor ( 1 ) according to any one of claims 1 to 13, wherein the sensor element ( 2 ) includes an EIS structure. [15] Sensor ( 1 ) according to any one of claims 1 to 14, wherein the sensor element ( 2 ) comprises an ion-sensitive field-effect transistor (ISFET), which, in addition to the gate-serving element, has a front surface ( 6) arranged analyte-sensitive area, one on the front surface ( 6 ) or on one of the front surfaces ( 6 ) opposite rear surface of the sensor element, serving as a contact element, and a source connection on the front surface ( 6 ) or on the back surface of the sensor element ( 2 ) arranged as a further contact element, has a drain connection.