SENSOR MEMBRANE, MEMBRANE CAP AND OPTOCHEMICAL SENSOR

Abstract

The present disclosure relates to a sensor membrane for an optochemical sensor for determining a measurand correlating with a concentration of an analyte in a measuring fluid, comprising: a functional layer comprising a first polymer matrix doped with a luminescent dye whose emissivity after excitation with electromagnetic radiation can be changed by the analyte; and a second polymer matrix in which the functional layer is at least partially encapsulated and which is permeable to the analyte at least in a subregion facing the measuring fluid and adjacent to the functional layer, wherein the sensor membrane comprises an optically detectable substance, different from the luminescent dye, for marking the sensor membrane. The present disclosure further relates to a membrane cap having such a sensor membrane and an optochemical sensor.

Claims

1. A sensor membrane for an optochemical sensor for determining a measurand correlating with a concentration of an analyte in a measuring fluid, the sensor membrane comprising: a functional layer comprising a first polymer matrix doped with a luminescent dye whose emissivity after excitation with electromagnetic radiation can be changed by the analyte; a second polymer matrix in which the functional layer is at least partially encapsulated and which is permeable to the analyte at least in a subregion adjacent the measuring fluid and adjacent to the functional layer; and an optically detectable substance, different from the luminescent dye, for marking the sensor membrane.

2. The sensor membrane of claim 1, wherein the functional layer is a layer having one or more island-shaped functional layer elements.

3. The sensor membrane of claim 1, wherein the second polymer matrix includes a same polymer material as the first polymer matrix.

4. The sensor membrane of claim 1, wherein the sensor membrane comprises a layer stack with a front-side exterior surface intended for contact with the measuring fluid and a back-side exterior surface connected to a substrate.

5. The sensor membrane of claim 1, wherein the second polymer matrix encapsulates the functional layer such that a first layer of the second polymer matrix covers the functional layer and a second layer of the second polymer matrix is disposed between the functional layer and the substrate, and wherein the first layer and the second layer of the second polymer matrix are chemically and/or physically connected to one another in a region surrounding the functional layer.

6. The sensor membrane of claim 5, wherein the first layer and/or the second layer of the second polymer matrix are/is doped with the optically detectable substance to mark the sensor membrane.

7. The sensor membrane claim 1, wherein, in addition to being doped with the luminescent dye, the first polymer matrix of the functional layer is further doped with the optically detectable substance to mark the sensor membrane.

8. The sensor membrane claim 1, wherein the optically detectable substance is selected from the group consisting of organometallic compounds, metal porphyrin complexes, polyaza annulene dyes, polyaza[18]annulene dyes, azaborone dipyrromethenes (Aza-BODIPY), boron dipyrromethenes (BODIPY) and metallophthalocyanine complexes.

9. The sensor membrane claim 1, wherein the optically detectable substance is an upconversion material.

10. The sensor membrane claim 1, wherein the optically detectable substance comprises one or more inorganic luminescent pigments that consist of an inorganic solid, which itself exhibits donor acceptor luminescence or charge transfer luminescence, or is doped with one or more luminescent ions, the one or more luminescent ions being selected from the group consisting of In.sup.+, Sn.sup.2+, Pb.sup.2+, Sb.sup.3+, Bi.sup.3+, Ce.sup.3+, Ce.sup.4+, Pr.sup.3+, Nd.sup.3+, Sm.sup.2+, Sm.sup.3+, Eu.sup.2+, Eu.sup.3+, Gd.sup.3+, Tb.sup.3+, Dy.sup.3+, Ho.sup.3+, Er.sup.3+, Tm.sup.2+, Tm.sup.3+, Yb.sup.2+, Yb.sup.3+, Ti.sup.3+, V.sup.2+, V.sup.3+, V.sup.4+, Mn.sup.2+, Mn.sup.3+, Mn.sup.4+, Fe.sup.3+, Fe.sup.4+, Fe.sup.5+, Co.sup.3+, Co.sup.4+, Ni.sup.2+, Cu.sup.+, Ru.sup.2+, Ru.sup.3+, Pd.sup.2+, Ag.sup.+, Ir.sup.3+, Pt.sup.2+ and Au.sup.+.

11. The sensor membrane claim 1, wherein the optically detectable substance comprises an electrochromic material.

12. The sensor membrane claim 1, wherein the functional layer is covered with a protective supporting and/or insulating layer that is permeable to the analyte.

13. The sensor membrane claim 12, wherein the protective, supporting and/or insulating layer is at least partially embedded in the second polymer matrix covering the functional layer.

14. The sensor membrane claim 12, wherein the protective, supporting and/or insulating layer is formed from a polymer doped with a pigment.

15. A membrane cap for an optochemical sensor, the membrane cap comprising: a sensor membrane comprising: a functional layer comprising a first polymer matrix doped with a luminescent dye whose emissivity after excitation with electromagnetic radiation can be changed by the analyte; a second polymer matrix in which the functional layer is at least partially encapsulated and which is permeable to the analyte at least in a subregion adjacent the measuring fluid and adjacent to the functional layer; and an optically detectable substance, different from the luminescent dye, for marking the sensor membrane; and a housing, wherein the sensor membrane is disposed on a front side of the housing.

16. The membrane cap of claim 15, wherein the housing is configured to be detachably connected to a sensor body on a side of the housing opposite the front side.

17. An optochemical sensor for determining a measurand correlating with a concentration of an analyte in a measuring fluid, the sensor comprising: a sensor membrane comprising: a functional layer comprising a first polymer matrix doped with a luminescent dye whose emissivity after excitation with electromagnetic radiation can be changed by the analyte; a second polymer matrix in which the functional layer is at least partially encapsulated and which is permeable to the analyte at least in a subregion adjacent the measuring fluid and adjacent to the functional layer; and an optically detectable substance, different from the luminescent dye, for marking the sensor membrane; a probe housing including at least one immersion region adapted for immersion into the measuring fluid, wherein the sensor membrane is disposed in the immersion region of the probe housing; a radiation source disposed in the probe housing and configured to irradiate excitation radiation into the sensor membrane; a radiation receiver disposed in the probe housing and configured to receive radiation emitted by the luminescent dye and/or the optically detectable substance; and a sensor circuit disposed in the probe housing and configured to control the radiation source, to receive signals from the radiation receiver and to generate and output signals based on the received signals from the radiation receiver.

18. A method for testing and/or identifying a sensor membrane of an optochemical sensor, which includes a functional layer that has a first polymer matrix doped with a luminescent dye whose emissivity after excitation with electromagnetic radiation can be changed by an analyte, and includes a second polymer matrix in which the functional layer is at least partially encapsulated and which is permeable to the analyte at least in a subregion facing the measuring fluid and adjacent to the functional layer, the method comprising: testing whether the sensor membrane contains an optically detectable substance that differs from the luminescent dye using an optical detection method.

19. The method of claim 18, wherein the testing comprises: exciting the optically detectable substance to emit electromagnetic radiation; detecting a signal using a radiation receiver configured to receive emission radiation of the optically detectable substance contained in the sensor membrane and convert the emission radiation into an electrical signal; and determining whether the sensor membrane contains the optically detectable substance based on the electrical signal.

20. The method of claim 19, further comprising testing whether the sensor membrane contains the optically detectable substance using another optical or chemical method.

21. The method of claim 18, further comprising identifying the optically detectable substance.

22. The method of claim 21, wherein the testing and the identifying is performed using the optochemical sensor including a radiation source, a radiation receiver and a sensor circuit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The present disclosure is explained in further detail below on the basis of the exemplary embodiments shown in the figures, as follows:

[0064] FIG. 1 shows an optochemical sensor according to a first exemplary embodiment;

[0065] FIG. 2 shows an optochemical sensor according to a second exemplary embodiment;

[0066] FIG. 3 shows a first exemplary embodiment of a sensor membrane for an optochemical sensor;

[0067] FIG. 4 shows a second exemplary embodiment of a sensor membrane for an optochemical sensor;

[0068] FIG. 5 shows a third exemplary embodiment of a sensor membrane for an optochemical sensor; and

[0069] FIG. 6 shows a fourth exemplary embodiment of a sensor membrane for an optochemical sensor.

DETAILED DESCRIPTION

[0070] FIG. 1 schematically shows a longitudinal view of an optochemical sensor 1 according to a first exemplary embodiment. In the present exemplary embodiment, sensor 1 is designed to determine a concentration of a gas dissolved in a measuring liquid, for example, dissolved oxygen. The sensor 1 has a probe housing 2 which, in the exemplary embodiment shown here, has a substantially cylindrical design. The probe housing 2 is closed by a sensor membrane 3 at its front end region intended for contact with a measuring medium. The sensor membrane 3 comprises, inter alia, a luminescent dye embedded in a polymer matrix, the luminescence of which is quenched by the analyte, for example oxygen. Alternatively, the luminescent dye may also have the property that its luminescence is enhanced by the analyte. This is the case, for example, in optical pH detection with luminophores on the basis of the photoinduced electron transfer (PET) effect. The sensor membrane 3 may comprise a stabilizing substrate and a plurality of layers applied to the substrate. Their detailed construction is explained in more detail below with reference to FIGS. 3 to 6.

[0071] A radiation source 4 which may comprise one or more LEDs, for example, is arranged in the probe housing 2. Furthermore, a radiation receiver 5 which may comprise one or more photodiodes, for example, is also arranged in the probe housing 2. The probe housing 2 also contains a light guide 6 that conducts radiation emitted by the radiation source 4 to the sensor membrane 3 and conducts luminescence radiation emitted by the luminescent dye embedded in the sensor membrane 3 to the radiation receiver 5. The light guide 6 may comprise one or more optical fibers. In the exemplary embodiment shown here, the light guide 6 is formed by a fiber bundle which has a first arm 6.1 that connects the radiation source 4 to the sensor membrane 3 and which has a second arm 6.2 that connects the radiation receiver 5 to the sensor membrane 3. The radiation source 4 and the radiation receiver 5 are electrically connected to a sensor circuit 7. The sensor circuit 7 is designed to excite the radiation source 4 to emit radiation and to control said radiation source. Furthermore, the sensor circuit 7 is designed to receive and process signals of the radiation receiver 5 which represent the luminescence radiation received by the radiation receiver 5. The processed signals serve as measurement signals of the sensor 1 and can be output by the sensor circuit 7 to a superordinate unit, for example a measurement transmitter, a controller, a computer or an operating device, via an interface 8. The interface 8 may be a cable connection fixedly connected to the sensor circuit 7, a detachable plug connection with galvanic contacts or else a galvanically separated, for example, inductively coupling, plug connection. Via the cable 9 connected to the interface 8, the sensor circuit 7 can be supplied with energy, also for operating the radiation source 4. Furthermore, the sensor circuit 7 can transmit signals, for example, data, to the superordinate unit via the cable 9 and, optionally, receive signals, for example, data, from the superordinate unit.

[0072] The detection of measured values and the evaluation of the signals of the radiation receiver 5 for determining a measured value can be divided between the sensor circuit 7 and the superordinate unit. For example, the sensor circuit 7 itself can be designed to control the radiation source 4. For this purpose, it can comprise a microcontroller that executes a computer program which is stored in a memory of the sensor circuit 7 and serves to control the radiation source 4 in order to detect measured values. Alternatively, at least part of the functions of the control may also be carried out by the superordinate unit, which then sends corresponding control signals for actuating the radiation source 4 to the sensor circuit 7. Accordingly, in order to process the signals detected by the radiation receiver 5, the microcontroller can execute a computer program which is stored in a memory of the sensor circuit 7 and which serves to evaluate the signals in order to determine measured values. The correspondingly processed signals can be output as measurement signals representing the measured values to the superordinate unit via the interface 8.

[0073] In contact with the measuring liquid containing the analyte of a specific concentration, the analyte penetrates into the polymer matrix and interacts with the luminescent dye. If the luminescent dye is excited by radiation of the radiation source 4 to emit luminescence radiation, the luminescence is quenched as a function of the concentration of the analyte, for example in the case of oxygen detection in the polymer matrix. Conversely, an increase in the fluorescence or phosphorescence is however also possible (for example in the case of an optical pH measurement). The sensor circuit 7 detects characteristic parameters by means of the radiation receiver 5 such as, for example, the luminescence intensity, the phase shift of the luminescence signal or also the decay time of the luminescence and determines a measured value of the analyte concentration present in the measuring medium by comparison with a calibration function.

[0074] During operation of the sensor 1, the sensor membrane 3 may be subject to aging, especially, if it is subjected during its operating time to sterilization or cleaning processes in which it is subjected to high temperatures and optionally also aggressive cleaning media, for example hot sodium hydroxide solution. This may even result in damage to the sensor membrane 3 which makes any further use of the sensor 1 no longer seem reasonable. In this case, the sensor membrane 3 can be replaced by a new sensor membrane 3. To this end, the sensor 1 must optionally be taken out of operation for a longer period, since the probe housing 2 must be opened in order to replace the sensor membrane 3.

[0075] FIG. 2 shows a schematic longitudinal sectional view of a second exemplary embodiment of an optochemical sensor 10. The sensor 10 of the second exemplary embodiment is constructed substantially identically to the sensor 1 of the first exemplary embodiment (FIG. 1), but replacement of the sensor membrane 3 with this sensor 10 is less complex. Identically designed components of the sensors 1, 10 according to the first exemplary embodiment (FIG. 1) and according to the second exemplary embodiment (FIG. 2) are denoted by identical reference signs.

[0076] The sensor 10 has a sensor membrane 3 with a luminescent dye, a radiation source 4, a radiation receiver 5 and a light guide 6 designed as a fiber bundle and connects the radiation source 4 and the radiation receiver 5 to the sensor membrane 3 so that excitation light from the radiation source 4 impinges on the sensor membrane 3 and luminescence radiation emitted by the luminescent dye in the sensor membrane 3 reaches the radiation receiver 5. It also comprises a sensor circuit 7 which is electrically connected to the radiation source 4 and the radiation receiver 5 and which can be connected to a superordinate unit via an interface 8. A power supply of the sensor circuit 7 and the transmission of data from the sensor circuit 7 to the superordinate unit takes place via a cable 9. The sensor circuit 7 can be designed analogously to the sensor circuit 7 of the sensor 1 according to the first exemplary embodiment and provides identical functions.

[0077] The sensor 10 shown in FIG. 2 differs from the sensor 1 of the first exemplary embodiment substantially in that its probe housing 11 is constructed in two parts. It comprises a first cylindrical housing part which forms a sensor body 12. This sensor body 12 comprises the components of the sensor 10 that have a long service life, such as the sensor circuit 7 and the optical components, i.e. the radiation source 4 and the radiation receiver 5 as well as the light guide 6. At its front end, the sensor body 12 may be open or have a window that is transparent to the excitation radiation and the luminescence radiation.

[0078] The probe housing 11 comprises a second housing part which forms a membrane cap 13. Said membrane cap can be detachably connected to the sensor body 12. In the present exemplary embodiment, the connection is realized by a screw connection 14. The membrane cap 13 has a cylindrical housing which has the sensor membrane 3 at its front end. On the rear side, the membrane cap has a thread 15 which cooperates with a complementary thread 16 of the sensor body 12 to form the screw connection 14.

[0079] This construction allows a simple replacement of the sensor membrane 3 in that the membrane cap 13 can be replaced by a new, structurally identical membrane cap 13. In this way, the replacement of the sensor membrane 3 does not require any prolonged period of shutdown of the sensor 10.

[0080] The structure of the sensor membrane 3 is now described in more detail with reference to FIGS. 3 to 6. FIG. 3 shows a first possible embodiment of the sensor membrane 3 in a schematic longitudinal sectional view. The sensor membrane 3 comprises a substrate 20 and a layer stack of functional and encapsulation layers arranged on the substrate 20. The substrate 20 may consist of a material that is transparent to the excitation radiation and luminescence radiation, for example of glass, ceramic, a polymer, an organometallic compound or zeolite. The substrate material may also be of a hybrid structure and be composed of at least two materials selected from the aforementioned materials. This includes, for example, the use of a hybrid material of two or more polymers or of two or more different ceramics or glasses.

[0081] The sensor membrane 3 further comprises a first functional layer 23 composed of one or more island-shaped layer elements (in FIGS. 3 to 6, only one such island-shaped layer element is shown in each case). The first functional layer 23 consists of a first polymer matrix in which a luminescent dye 24 is embedded. The luminescent dye 24 serves as a specific indicator for an analyte to be detected by means of the optochemical sensor 1 or 10. The first polymer matrix may be formed from a polymer or a polymer blend which on the one hand is permeable to the analyte and on the other hand can be doped with the luminescent dye 24. Suitable examples include silicone, porous or non-porous PVDF, PVF, Teflon AF, Hyflon AD, Nafion, a copolymer or terpolymer or n-polymer with a polystyrene unit, e.g., polystyrene co-vinylpyridine, polystyrene co-vinylpyridine co-divinylbenzene, or a blend of several of the polymers mentioned.

[0082] The first functional layer 23 is encapsulated in a second polymer matrix. In the present exemplary embodiment, this is achieved by arranging a first layer 21 of the second polymer matrix in a sandwich-like manner between the substrate 20 and the functional layer 23 and by the first functional layer 23 being completely covered by a second layer 22 of the second polymer matrix such that around the island-shaped layer element of the first functional layer 23, the first layer 21 and the second layer 22 of the second polymer matrix lie directly on top of each other and are physically and/or chemically interconnected. The second polymer matrix is designed to be permeable to the analyte at least in a subregion of the second layer 22 covering the first functional layer 23. Preferably, a polymer or a polymer blend is selected as the material of the second polymer matrix, said polymer being chemically stable with respect to the measuring medium and with respect to conventionally used cleaning media, such as sodium hydroxide solution. Ideally, in order to allow the optochemical sensor 1, 10 to be used as universally as possible, the material of the second polymer matrix is also suitable for applications in the field of food technology. Advantageously, the second polymer matrix can consist of the same material as the first polymer matrix, but the second polymer matrix is not doped with the luminescent dye 24. The thus achieved encapsulation of the first functional layer 23 or of the luminescent dye 24 contained therein extends the service life of the sensor membrane 3, since the encapsulation has a protective function for the first functional layer 23. For example, the diffusion or washing of the luminescent dye 24 out of the first functional layer 23 is delayed from the start. Even if the luminescent dye 24 diffuses from the first functional layer 23 into the second polymer matrix, the chemical environment of the luminescent dye substantially does not change so that the sensor membrane 3 does not lose its operability, at least for a time, in the sense that the evaluation of the measurement signals obtained with the sensor membrane 3 results, based on the calibration function, in measured values which still have a sufficient measurement quality. Thus, the sensor membrane 3 shown in FIG. 3 can be used for longer periods of time than conventional sensor membranes, even under rough conditions.

[0083] In the present exemplary embodiment, a second functional layer 25, which can be, for example, a protective, supporting or insulating layer, is embedded in the second layer 22 of the second polymer matrix. For example, a layer of an ambient light-absorbing material, e.g., a polymer layer containing soot, may be used as a protective layer. A mechanical support grid, for example made of metal, can be considered as the supporting layer. Of course, it is also possible to provide further functional layers which can be embedded in the second polymer matrix or arranged above or below the second polymer matrix.

[0084] In the present exemplary embodiment, the sensor membrane 3 has a final cover layer 26. Said cover layer 26 may be formed from the same polymer material as the second polymer matrix. Alternatively, it may also be formed from another polymer material. The cover layer 26 is optional, i.e. a sensor membrane according to the present disclosure can also be designed in such a way that the second polymer matrix is intended to be brought into direct contact with the measuring medium. The cover layer 26 may consist of a material which is approved for the particular application (for example in the food or pharmaceutical sector). The material of the cover layer 26 may also be optimized with regard to its resistance to chemically aggressive media or other harsh environmental conditions, for example high temperatures or strong mechanical stresses. The cover layer 26 is at least partially permeable to the analyte.

[0085] In the embodiment of the sensor membrane 3 shown in FIG. 3, an optically detectable substance 27 is contained in an edge region of the cover layer 26 which is not arranged directly above the functional layer 23.

[0086] The optically detectable substance 27 may be a stable organic or inorganic substance or a hybrid material of organic and/or inorganic substances or a mixture of organic and/or inorganic substances. Suitable materials are, for example, organometallic compounds, metal complexes, such as metal porphyrin complexes, polyaza annulene dyes, metallophthalocyanine complexes, azaborone dipyrromethenes (Aza-BODIPY), boron dipyrromethenes (BODIPY) or mixtures of these compounds. The optically detectable substance 27 is different from the luminescent dye 24, for example in that, if they are both metal complexes, it has a different central ion and/or different ligands.

[0087] If the optically detectable substance 27 is a luminescent substance, its luminescence is ideally not influenced, e.g., quenched or enhanced, by the analyte determinable by means of the sensor membrane 3 in order to avoid interference of the optically detectable substance 27 serving as marking of the sensor membrane 3 with the detection of measured values by means of the sensor membrane 3. However, this is not absolutely necessary since it is also possible to take into account an interaction of the analyte with the optically detectable substance 27 during the calibration of the sensor 1, 10 and to carry out a corresponding compensation when evaluating the measurement signals. Advantageously, the emission spectra of the optically detectable substance 27 and of the luminescent dye 24 have measurable differences. For example, both substances can be luminescent dyes, wherein the luminescent dye 24 contained in the first functional layer 23 emits, for example, luminescence radiation of a first wavelength, while the optically detectable substance 27 emits luminescence radiation of a second wavelength that differs from the first wavelength. A distance of at least 20 nm, preferably of at least 50 nm, should be present between the first and the second wavelength.

[0088] The optically detectable substance 27 may also comprise a high-conversion material (photon upconversion material). These materials convert low-energy to high-energy photons in an anti-Stokes scattering process. They can be, for example, organic materials, such as polycyclic aromatic hydrocarbons, or inorganic materials, such as ions of the d- or f-block elements. It is advantageous for the optically detectable substance 27 to consist of high-conversion nanoparticles (upconverting nanoparticles), e.g., quantum dots or lanthanide-doped nanoparticles, such as fluorides or oxides, e.g., NaYF.sub.4, NaGdF.sub.4, LiYF.sub.4, YF.sub.3, Gd.sub.2O.sub.3, doped with Er.sup.3+, Yb.sup.3+, Tm.sup.3+ or several of these lanthanides.

[0089] In further exemplary embodiments, the optically detectable substance 27 can be a stable inorganic material, for example an inorganic luminescence pigment from the series of solid phase substances that exhibits a donor acceptor luminescence or charge transfer luminescence. It may contain, for example, one or more ions from the following group: In.sup.+, Sn.sup.2+, Pb.sup.2+, Sb.sup.3+, Bi.sup.3+, Ce.sup.3+, Ce.sup.4+, Pr.sup.3+, Nd.sup.3+, Sm.sup.2+, Sm.sup.3+, Eu.sup.2+, Eu.sup.3+, Gd.sup.3+, Tb.sup.3+, Dy.sup.3+, Ho.sup.3+, Er.sup.3+, Tm.sup.2+, Tm.sup.3+, Yb.sup.2+, Yb.sup.3+, Ti.sup.3+, V.sup.2+, V.sup.3+, V.sup.4+, Cr.sup.3+, Mn.sup.2+, Mn.sup.3+, Mn.sup.4+, Fe.sup.3+, Fe.sup.4+, Fe.sup.5+, Co.sup.3+, Co.sup.4+, N.sub.Ni.sup.2+, Cu.sup.+, Ru.sup.2+, Ru.sup.3+, Pd.sup.2+, Ag.sup.+, Ir.sup.3+, Pt.sup.2+ and Au.sup.+. It may further comprise a binary, ternary or quaternary halide, oxide, oxyhalide, sulfide, oxysulfide, sulfate, oxysulfate, selenide, nitride, oxynitride, nitrate, oxynitrate, phosphide, phosphate, carbonate, silicate, oxysilicate, vanadate, molybdate, tungstate, germanate or oxygermanate. These may comprise cations of elements Li, Na, K, Rb, Mg, Ca, Sr, Sc, Y, La, Ti, Zr, Hf, Nb, Ta, Zn, Gd, Lu, Al, Ga and In.

[0090] The inorganic material can be present in the sensor membrane 3 as a doping or as nanoparticles embedded in the cover layer 26. The doping or the nanoparticles may form an image or text marking, for example in the form of a lettering, a number or a logo, for example in the form of a hologram.

[0091] In an alternative embodiment, the optically detectable substance 27 may also be an electrochromic material. Such materials change color as a result of an electrical pulse; examples of this are indium tin oxide (ITO), Prussian blue or Berlin blue, lithium tungsten oxide and fluorine tin oxide. In this case, the sensor membrane 3 can comprise electrodes or be in contact with electrodes via which a voltage can be applied to the sensor membrane 3 or to a layer of the sensor membrane comprising the optically detectable substance 27, said voltage being dimensioned in such a way that a color change of the optically detectable substance 27 occurs and can be detected optically.

[0092] As an optically detectable substance 27 can also be used a substance which changes its color under the influence of a specific influencing variable, e.g., when the pressure or temperature changes or when irradiated with electromagnetic radiation.

[0093] In order to ensure universal applicability of the sensor membrane 3, it is advantageous if all materials used are sterilizable up to a temperature of at least 140 C. and/or autoclavable up to at least 121 C. and are stable to customary cleaning and disinfecting agents, such as sodium hydroxide solution or ethylene dioxide. Advantageously, the materials used can also be selected such that they also withstand sterilization with gamma radiation at a dose of at least 5 kGy without degenerating.

[0094] The optically detectable substance 27 is also advantageously stable up to a temperature of 140 C. and chemically stable to acids, alkaline solutions and customary disinfectants, such as ethylene oxide. However, this is not strictly necessary if the optically detectable substance is to be used only as a marking of the sensor membrane 3 in order to verify its origin or its suitability for use with a specific sensor body or a specific application during a first installation of the sensor membrane 3. Later destruction of the optically detectable substance 27 when the sensor is used is then not an issue, since detection of the substance 27 is no longer necessary then.

[0095] FIG. 4 shows an alternative embodiment of the sensor membrane 3. Identically designed parts of the sensor membranes according to the exemplary embodiment shown in FIG. 3 and according to the exemplary embodiment shown in FIG. 4 are represented with identical reference signs. The sensor membrane 3 has a substrate 20 and a first functional layer 23 of a first polymer matrix with a luminescent dye 24 immobilized therein, the luminescence of which is quenched by the analyte, e.g., in the case of oxygen detection, or is enhanced by the analyte, e.g., in optical pH detection with luminophores based on the photoinduced electron transfer (PET) effect. The first functional layer 23 is encapsulated in a second polymer matrix which is applied to the substrate and the first functional layer 23 in two layers 21, 22 in a manner analogous to the exemplary embodiment as shown in FIG. 3. A second functional layer 25 with soot pigments is embedded in the second layer 22 of the second polymer matrix as a protective layer against ambient light. The sensor membrane 3 is terminated at its end intended for contact with the measuring medium by a cover layer 26 which is doped with an optically detectable substance 27 over its entire cross section. The optically detectable substance 27 can be one of the substances mentioned with reference to the exemplary embodiment of FIG. 3. In contrast to the exemplary embodiment illustrated with reference to FIG. 3, however, in the case of the sensor membrane 3 shown in FIG. 4, care must be taken to select the optically detectable substance 27 in such a way that it does not interfere with the measurement of the luminescence radiation of the luminescent dye 24.

[0096] FIG. 5 shows a schematic view of a further exemplary embodiment of the sensor membrane 3. The sensor membrane 3 is designed identically to the sensor membrane 3 shown in FIG. 3 (identical reference signs denote identically designed parts) with the only difference being that the optically detectable substance 27 is not contained in the cover layer 26 but in the first layer 21 of the second polymer matrix encapsulating the first functional layer 23 with the luminescent dye 24. In the present example, this first layer 21 of the second polymer matrix is doped with the optically detectable substance 27. The optically detectable substance 27 can be one of the substances mentioned above.

[0097] FIG. 6 schematically shows a last exemplary embodiment of the sensor membrane 3. It is also designed identically to the sensor membrane 3 shown in FIG. 3 (identical reference signs denote identically designed parts) with the only difference being that the optically detectable substance 27 is not contained in the cover layer but together with the luminescent dye 24 in the first functional layer 23. Here, too, the optically detectable substance 27 may be one of the substances mentioned above in connection with the exemplary embodiment according to FIG. 3.

[0098] Common to all these embodiments of the sensor membrane 3 is that they contain an optically detectable substance 27 which serves as a marking captively connected to the sensor membrane 3. If the sensor membrane 3 is replaced, this can serve to test whether the new sensor membrane to be used is suitable for use with the sensor 1, 10. Additionally or alternatively, the marking can also serve as protection against forgeries (product piracy) or manipulation.

[0099] Furthermore, the marking may also be used for monitoring a production method for sensor membranes or sensors, for example in order to avoid mix-ups of the sensor membranes during production, storage or distribution of the sensor membranes or accessories for the sensor membranes, for example membrane caps. The optically detectable substance can be used especially to allow traceability of sensor membranes which are transferred to users or of accessory parts comprising the sensor membranes. As a result, costs incurred as a result of membranes incorrectly assigned or incorrectly installed in the sensors can be avoided.

[0100] If different production batches of sensor membranes are provided with different optically detectable substances, it is possible to distinguish these production batches from one another. For example, when a defect is found in only one production batch, all the sensor membranes concerned can be identified and withdrawn from the market on the basis of the optically detectable substance marking this production batch.

[0101] The marking can also serve to automatically identify the analyte, which can be determined by means of the sensor membrane, and to adjust sensor parameters used for analyte determination in an automated manner.

[0102] The following procedure can be used to test and/or identify a sensor membrane 3: On the one hand, an optical, non-destructive detection of the optically detectable substance 27 present in the sensor membrane 3 can be carried out by means of an external device. On the other hand, an optical detection of the optically detectable substance 27 present in the sensor membrane 3 can be performed by means of the optochemical sensor in which the membrane is used. The radiation receiver 5 and the sensor circuit 7 and possibly the radiation source 4 can be used for this purpose. It is also possible for the sensor to comprise an additional radiation receiver and/or an additional radiation source which are used specifically for testing or identifying the sensor membrane 3 but not for detecting measured values of the concentration of the analyte to be determined in the measurement operation of the sensor. In FIGS. 3 to 6, arrows are drawn which symbolize the position of the test optics for the detection of the optically detectable substance: In FIGS. 3, 5 and 6, the test optics are arranged on the substrate side; here, the test can therefore, for example, take place by means of the radiation receiver 5 and/or the radiation source 4 of the sensor 1, 10 or alternatively with a separate test device. In FIG. 4, the test optics are arranged on the cover layer side; here, the test is thus carried out by means of an additional test device.

[0103] Optionally, there is also the further alternative possibility of testing the sensor membrane 3 by means of a chemical or spectroscopic method, which generally takes place by destroying the sensor membrane 3. However, the test is preferably carried out non-destructively. For particularly difficult or critical cases, destructive measurement may serve as an additional proof, for example, when testing a contiguous batch of a plurality of sensor membranes. In this case, a single one of the plurality of membranes can be examined by destroying it in order to further confirm the results of non-destructive testing of the remaining membranes.

[0104] Suitable optical methods for non-destructive measurement with an additional device or with the means of the optochemical sensor itself are, for example, depending on the type of optically detectable substance 27 used, an optical luminescence measurement, an optical absorption measurement or an x-ray measurement. Atomic absorption spectroscopy or flame emission spectroscopy may be used as destructive, especially, wet-chemical or spectroscopic, methods.

[0105] All measurement methods known to the person skilled in the art, e.g., detection of an intensity change, of a phase angle, of a decay time, of an absorption or a reflection, may be used for optical luminescence or absorption measurements. Specifically, the following measurements can be used: [0106] a) emission signal or emission spectrum when excited with one or more specific wavelength(s); [0107] b) absorption signal or absorption spectrum measured in reflection; [0108] c) polarization of radiation emitted by or converted by the optically detectable substance, measurable by means of a polarization filter; [0109] d) optical signals (e.g., absorption signal measured in reflection) as a function of the temperature, the pressure, a voltage applied to the sensor membrane; [0110] e) visual detection of discoloration upon change in temperature, pressure, application of a voltage.

[0111] Identification or testing can be carried out in a particularly reliable manner by using more than one measurement method. For example, two different non-destructive optical methods, e.g., a luminescence measurement and an absorption measurement in reflection, or two luminescence measurements in which different parameters are detected, e.g., a phase angle and a decay time, can be used for the optical detection of the optically detectable substance.

[0112] In a further advantageous variant, the optically detectable substance 27 may be irreversibly variable by ambient conditions which lead to an over-average shortening of the service life of the sensor membrane 3, such as higher temperatures than permitted by specification or other improper treatment of the sensor. In this way, testing of the optically detectable substance allows conclusions to be drawn about the remaining service life of the sensor membrane.