PROTECTIVE DEVICE FOR AN OPTOCHEMICAL SENSOR, AND CORRESPONDING OPTOCHEMICAL SENSOR

Abstract

The present disclosure relates to a protective device for a sensor unit of an optochemical sensor for determining or monitoring at least one analyte present in a medium, including at least one protective substance for protecting the sensor unit against a physical and/or chemical alteration caused by at least one substance contained in the medium, and an at least partially media-permeable functional layer, where the protective device, in a region facing towards the medium, can be attached to the sensor unit or applied to the sensor unit. The present disclosure further relates to an optochemical sensor having a protective device according to the present disclosure.

Claims

1. A protective device for a sensor unit of an optochemical sensor for determining or monitoring at least one analyte present in a medium, the protective device comprising: at least one protective substance for protecting the sensor unit against a physical and/or chemical alteration caused by at least one substance contained in the medium; and an at least partially media-permeable functional layer, wherein the protective device, in a region facing towards the medium, is embodied to be attached to the sensor unit or applied to the sensor unit.

2. The protective device of claim 1, wherein the at least one protective substance is: a buffer, including a pH buffer polymer, a pH buffer solution, a redox buffer, and/or a redox buffer polymer; an adsorbent; a radical scavenger; a reducing agent; a catalyst; or a polymer.

3. The protective device of claim 2, wherein the polymer of the at least one protective substance is an acrylamide or an acrylamide with at least one imidazole unit.

4. The protective device of claim 1, wherein the functional layer is embodied: in the form of a diaphragm, including a ceramic diaphragm, a fiber diaphragm or a ground diaphragm; in the form of an annular gap; in the form of an organic or inorganic membrane; in the form of a gel; or in the form of a dispersion.

5. The protective device of claim 1, wherein the protective device is embodied in the form of a cap or capsule releasably connectable with the sensor unit.

6. The protective device of claim 1, further comprising a releasable attachment unit structured to enable attachment of the protective device to the sensor unit. The protective device of claim 1, wherein: the protective substance is included in the functional layer; the protective substance is contained in a protective layer attached to the functional layer on a side opposite the medium; or the protective substance is part of an aqueous solution that is at least partially surrounded by the functional layer.

8. The protective device of claim 1, wherein: the protective device is embodied to be fastened to the sensor unit such that a region of the protective device adjacent the medium, and/or a transition region between the protective device and the sensor unit, is substantially gapless and/or without clearance; and/or a surface of the protective device adjacent the medium has a surface region shaped to optimize flow.

9. The protective device of claim 1, comprising a first functional layer and a second functional layer, wherein at least the protective substance is located between the first functional layer and the second functional layer.

10. The protective device of claim 9, wherein the first functional layer or the second functional layer includes inorganic fibers adapted to absorb liquid.

11. The protective device of claim 1, wherein at least the protective substance is present in an inlay which is at least partially surrounded by the functional layer.

12. The protective device of claim 1, further comprising at least one analyte-permeable, diffusion-inhibiting component.

13. The protective device of claim 12, wherein the diffusion-inhibiting component is contained in a diffusion barrier layer disposed on a side of the protective device adjacent the sensor unit.

14. The protective device of claim 1, further comprising at least one indicator component formulated to signal replacement of the protective device.

15. The protective device of claim 1, further comprising a substance for reducing a surface tension of at least one component of the protective device, wherein the substance is an alcohol or surfactant.

16. An optochemical sensor for determining and/or monitoring at least one analyte present in a process medium, the senor comprising: a sensor unit including a substrate to which an indicator is applied; a protective device attached to the sensor unit, the protective device including: at least one protective substance for protecting the sensor unit against a physical and/or chemical alteration caused by at least one substance contained in the medium; and an at least partially media-permeable functional layer, wherein the protective device, in a region facing towards the medium, is embodied to be attached to the sensor unit or applied to the sensor unit; a light source adapted to transmit measuring radiation, thereby exciting the indicator to emit luminescence radiation; a detection unit adapted to detect the correspondingly generated luminescence radiation; and an electronics unit configured to determine the concentration or the partial pressure of the at least one analyte in the process medium based on a quenching of the luminescence radiation of the indicator.

17. The optochemical sensor of claim 16, wherein the at least one protective substance is: a buffer, including a pH buffer polymer, a pH buffer solution, a redox buffer, and/or a redox buffer polymer; an adsorbent; a radical scavenger; a reducing agent; a catalyst; or a polymer.

18. The optochemical sensor of claim 16, wherein the functional layer is embodied: in the form of a diaphragm, including a ceramic diaphragm, a fiber diaphragm or a ground diaphragm; in the form of an annular gap; in the form of an organic or inorganic membrane; in the form of a gel; or in the form of a dispersion.

19. The optochemical sensor of claim 16, wherein the protective device is embodied in the form of a cap or capsule releasably connectable with the sensor unit.

20. The optochemical sensor of claim 16, wherein: the protective substance is included in the functional layer; the protective substance is contained in a protective layer attached to the functional layer on a side opposite the medium; or the protective substance is part of an aqueous solution that is at least partially surrounded by the functional layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The present disclosure is explained in greater detail with reference to the following figures. Shown are:

[0048] FIG. 1A is a longitudinal section of a sensor cap known from the prior art;

[0049] FIG. 1B is a detail view of the sensor cap of FIG. 1A;

[0050] FIGS. 2A-2C show various embodiments of a protective device according to the present disclosure in the form of a layer structure;

[0051] FIGS. 3A-3D show various embodiments of the protective device according to the present disclosure, with a functional layer;

[0052] FIGS. 4A-4M show various embodiments of the protective device according to the present disclosure, with two functional layers; and

[0053] FIGS. 5A-5C show an embodiment of the protective device according to the present disclosure, in which the protective substance is introduced into an inlay.

[0054] In the description, identical elements are provided with the same reference characters.

DETAILED DESCRIPTION

[0055] FIGS. 1A and 1B show a longitudinal section through an optochemical sensor cap 102, known from the prior art, of an optochemical sensor 1 (not shown). The sensor cap 102 consists of a cylindrical housing, frequently also termed a spot housing, that consists of a sleeve-shaped outer component 6 and a plug-in component 5. The components 5, 6, 7 are connected to each other in a region of the sensor shaft by means a threaded joint 8.

[0056] The sensor cap 102 seals an end region of the cylindrical housing facing towards the medium 4 and comprises a matrix 11 for determining the analyte. The analytes to be determined or monitored are any ions or gases that are present in the medium 4. The analyte-sensitive matrix 11 may consist of several functional layers. One of the functional layers 12 contains the analyte-sensitive substance.

[0057] In the known solution, a round, flat, transparent glass substrate, on whose surface facing the medium 4 the analyte-sensitive matrix 11 is applied, is used as an optical component 7 or optical element. The end region of the sleeve-shaped outer component 6, said end region facing towards the medium 4, has an annular recess 9 into which an O-ring 10 is inserted as a seal. By means of the O-ring 10, the sleeve-shaped outer component 6 in the connecting region 10 is sealed axially and gap-free against the analyte-sensitive matrix 11 or membrane.

[0058] A protective device 13 according to the present disclosure, as presented by way of example in different embodiments in FIGS. 2, 3 and FIG. 4, serves to protect the sensor unit 3, in particular, the matrix 11, against premature aging.

[0059] Depending upon the application, the protective device 13 may have a different design in the event that a protection against aggressive substances in typical disinfectants is sought, for example, as they occur in the foodstuffs industry. Typical disinfectants which the capsule according to the present disclosure is to protect against are ozone, hypobromides which contain free bromine, hypochlorites which contain free chlorine, hydrogen peroxide, peracetic acid, or also chlorine dioxide. In many instances, a basic buffering in combination with reducing materials or radical scavengers and/or absorbers is, for example, suitable for rendering the respective disinfectant ineffective. The disinfectant contains ozone, but acid buffers are also conceivable, sincefor example, given ozonethe half-time of exchange is starkly increased, and thus un-decomposed ozone may react with reducing agents or absorbers. However, acid buffers are unsuitable for chlorinated disinfectants.

[0060] The following possible reactions, which may proceed within the protective device 13 in order to render the disinfectant ineffective, are indicated by way of example for chlorine and ozone:

[0061] Chlorine:

[0062] Cl.sub.2+2OH.sup.->Cl.sup.+OCl.sup.+H.sub.2O

[0063] Ozone:

[0064] 1 O.sub.3+OH.sup..fwdarw.HO.sub.2.sup.+O.sub.2

[0065] 2 O.sub.3+HO.sub.2.sup..fwdarw..sup.OH+O.sub.2.sup.+O.sub.2

[0066] Depending upon the desired usage, the protective substance may, for example, be a bufferin particular, a pH buffer polymer, a pH buffer solution, a redox buffer, a redox buffer polymer; an adsorbent; a radical scavenger; a reducing agent; a catalyst; or a polymerin particular, an acrylamide, such as an acrylamide with at least one imidazole unit. A listing of a few examples of suitable protective substances is given in the following. However, it is to be noted that this list is in no way exhaustive.

[0067] pH Buffer: [0068] inorganic and organic buffers from the range of carbonate buffers, phosphate buffers, borate buffers, or phthalates, [0069] buffers which contain trisodium citrate, magnesium citrate, sodium lactate, sodium acetate, potassium acetate, sodium tetraborate, potassium or sodium tartrate, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, ammonium malate, disodium malate, monosodium malate, monopotassium malate, alkali monophosphates, potassium/sodium/lithium salt, calcium monohydrogen phosphate, magnesium monohydrogen phosphate, or mixtures of at least two of the cited substances, [0070] buffers in which the primary and/or side chain polymer has with an imidazole unit, e.g., a polyacrylamide copolymer with imidazoles which form low-viscosity gels, [0071] Nafion, [0072] silicones with buffering groups such as imidazole, or [0073] exines

[0074] Redox Buffer: [0075] inorganic substances, [0076] polymers with redox properties, such as ferrocene units, metalloporphyrin units, metallophthalocyanin units, or [0077] polymers with quinoid units

[0078] Absorbents: [0079] graphite, [0080] carbon nanotubes, [0081] activated charcoal, [0082] graphenes/graphene oxide, carbon nanotubes (CNT), and derivatives, [0083] zeolites, [0084] metal organic frameworks (MOF), [0085] zeolitic imidazolate frameworks (ZIF), [0086] high-fiber materials such as polyimidesfor example, FDA-DAM, [0087] copolymers consisting of dianhydride 5,5[2,2,2 trifluoromethyl-1-(trifluoromethyl) ethylindene] bis-1,3-isobenzofurandione and diamine 2,4,6-trimethyl 1,3-phenylendiamine, or [0088] an aerosol, or [0089] exines (for example, Lycopodium Clavatum)

[0090] Reducing Agent: [0091] unsaturated hydrocarbons, [0092] alkenes, [0093] alkines, [0094] thiols, [0095] disulfides, [0096] substances (for example, polymers or oligomers) with amine or thiol groups, [0097] polymers with amine or thiol groups, [0098] substances with unsaturated alkyl groups, or

[0099] Catalyst: [0100] metals such as finely-powdered platinum, gold, or silver, or [0101] subgroup metallic oxidesfor example, titanium oxide, silicon oxide, aluminum oxide, zirconium oxides, zeolites, MOF's, or ZIF's

[0102] Polymers: [0103] analyte-permeable polymers, [0104] acrylamides, [0105] acrylamides with imidazole units which are preferably attached in the 2,4,5 position, [0106] polymers with sulfonic acid groupsfor example, PAMPS, [0107] polymers containing amine, [0108] exines, unmodified or modifiedfor example, with a pH buffer or a redox buffer unit, [0109] polymers with redox buffer units or pH buffer units

[0110] The at least one functional layer may, for example, be embodied in the form of a diaphragmin particular, a ceramic diaphragm, a fiber diaphragm, or a ground diaphragm; in the form of an annular gap; in the form of anin particular, organic or inorganicmembrane; in the form of a gel; or in the form of a dispersion.

[0111] If the functional layer is a membrane, all analyte-permeable polymers, for example, are thus conceivable for forming the membrane sealed, in particular, at the medium side. Common polymers are often comprised of porous and non-porous tetrafluoroethylene (e.g., Teflon); fluorinated cross-linked and cross-linked primary and side chain polymers; silicones; fluorinated silicones; or combinations of these. Moreover, softeners are optionally used.

[0112] The functional layer may be designed to be both water-impermeable and water-permeable. Water-permeable functional layers, in particular, lend themselves to combination with a bubble-repellent surface geometry.

[0113] In the event that the protective device has an analyte-permeable, diffusion-inhibiting component, the latter may be: a gelin particular, a gel having at least one functional group or at least one filler; a polymerin particular, a polymer blend or a block polymer having at least one hydrophilic and/or hydrophobic unit, an adsorbent (in particular, activated charcoal or graphene oxide), a reducing agent, a catalyst (in particular, a metal oxide), a redox agent; an unsaturated substance; water; or an ionic fluid.

[0114] The diffusion-inhibiting component may, for example, be of such a design that it is not permeable to various reactive substances, for example, to free chlorine or ozone. Alternatively, however, the diffusion-inhibiting component may also be such that it binds corresponding substances or also converts them into less-reactive substances. However, the diffusion-inhibiting component is in every instance permeable to the analyte.

[0115] For example, the diffusion-inhibiting component may be part of a diffusion barrier layer which has a pH value >7, preferably >8, and in particular preferably >9. For example, at a pH value >9, free chlorine is typically no longer present. The diffusion barrier layer may also act as a buffer layer, for example. However, the diffusion barrier layer may also be composed of different sub-layers having different pH values, which sub-layers are arranged following one another. For example, one sub-layer may be designed as a neutral buffer layer.

[0116] Examples of different possible embodiments for a protective device 13 having a first functional layer 14 are shown in FIG. 2. Shown in FIG. 2a are a sensor cap 2 in simplified presentation and two similar embodiments of protective device 13 and 13, which respectively have a bubble-repelling geometry in a surface region O or O facing towards the medium. Shown on the right side is the protective device 13 in a state attached to the sensor cap 2 containing the sensor unit 3 (not shown). The protective device 13 has a functional layer 14 (not separately designated here) which is provided essentially on the region facing towards the medium 4 and containing the polymer matrix 11, whereas, in the case of the protective device, a cylindrical sleeve 15 is, moreover, provided which at least partially covers a side wall S of the sensor cap 2 in the installed state on the sensor unit 3.

[0117] In the present instance according to FIG. 2a, the surface regions O and O of the protective devices 13 or 13 that face towards the medium 4 are of conical design, and thus have a bubble-repelling geometry. However, this is not mandatory, as, for example, is evident using the protective device 13 from FIG. 2b. As in the case of FIG. 2a, in FIG. 2b, the protective device 13 is depicted, on the left, as a separate unit and, on the right, in the state in which it is installed at the sensor cap 2.

[0118] For attachment to the sensor unit 3, the protective devices 13 from FIGS. 2a-2c may, for example, respectively be pulled over the sensor cap 2 or be plugged onto the sensor cap 2. However, numerous other possibilities are also alternatively conceivable which fall under the present disclosure. For example, an attachment unit (not depicted) may be provided for the protective device 13.

[0119] Various possibilities are conceivable for the arrangement of the at least one protective substance 16 within the protective device 13, which possibilities are drawn by way of example in FIGS. 3a-3d, for the case of a protective device 13 with a functional layer 14. The functional layer 14 is depicted as a flat layer without special bubble-repelling geometry in the surface region O facing towards the medium. Other embodiments may, naturally, comprise surface-repelling geometries.

[0120] In the instance depicted in FIG. 3a, the protective substance 16 is introduced into the functional layer 14. Alternatively, however, as depicted in FIG. 3b, the protective substance 16 may also be contained in a protective layer 17, which is arranged following the functional layer 14 on a side facing away from the medium 4. Moreover, if the protective device 13 contains a diffusion-inhibiting component 18, this may, on the one hand, be the functional layer 14, or be arranged in a separate diffusion barrier layer 19 which is arranged on the side of the functional layer 14 facing away from the medium 4, into which is, in turn, integrated the protective substance 16, as shown in FIG. 3c. Alternatively, the functional layer 14, a protective layer 16, and a diffusion barrier layer 19 may also be arranged one atop the other, as illustrated in FIG. 3d.

[0121] In addition to a layer structure for the protective device 13, as indicated in FIGS. 3b-3d, many additional possibilities are still conceivable which, altogether, fall under the present disclosure. For example, the protective substance and/or the diffusion-inhibiting component may also be part of a solution, for example, an aqueous solution, which is at least partially surrounded by the at least one functional layer 14.

[0122] In the event that the functional layer 14, the protective layer 16, and/or the diffusion barrier layer 19 is or are comprised of a gel, the protective device 13 may also be attached to the sensor unit 3 by means of a covalent bond. In this regard, a protective device 13 is preferably in the form of a gel layer sequence with various pH buffer gels. A pH-neutral gel (pH 5-9) is arranged facing towards the sensor unit 3 and serves as a diffusion barrier layer 19. Following this, and thus facing towards the medium 4, is at least one additional gel layer serving as a protective layer 16, e.g., with a pH buffering in the acid or alkaline pH range (pH<5 or pH>9). However, multiple gel layers with different pH bufferings, for example, graduated pH bufferings, serving as a protective layer 16, are also conceivable.

[0123] A preferred embodiment for a protective device 13 includes that the diffusion-inhibiting component 18 be a neutral gel, for example, the gel indicated in the following structural formula:

##STR00001##

[0124] It is, in this case, a neutral gel in the form of an acrylamide with imidazole units at the 2, 4, and 5 positions. This neutral gel is preferably combined with a protective substance in the form of an acid gel, e.g., the poly(2-acrylamide-2-metyl-propane sulfonic acid) and polyacrylamide, PAMPS-PDAAAm, indicated in the following structural formula:

##STR00002##

[0125] By contrast, if a basic protective substance 16 is desired, a polyamine, polyacrylamide with a pyridine unit, or tertiary and quaternary amine units, an ammonium compound such as diallyldimethylammonium chloride (DADMAC), or also a, for example modified, cellulose, an exine, or a polystyrene with a diethylaminoethyl group may be used. A preferred example of a modified cellulose is given in the following structural form:

[0126] The neutral gel and the acid or base gel are thereby preferably arranged in successive layers, similarly as in FIG. 3d.

[0127] An additional embodiment of the present disclosure includes that the protective device 13 comprise multiple functional layers. Shown in FIGS. 4a-4m by way of example are various preferred variants of a protective device 13 which, in addition to a first functional layer 14 facing towards the medium 4, moreover has: a second layer 20 which, for example, may contain a filler material (in particular, in the form of inorganic fibers), a gel, the diffusion-inhibiting component 18, or also the protective substance 16; and a second functional layer 21 which faces towards the sensor unit 3. The first functional layer 14 and second functional layer 21 may thereby be of identical or different designs.

[0128] The functional layers 14 and 21, as well as the layer 20, may be designed to be both media-permeable, for example gas-permeable or fluid-permeable, or media-impermeable. However, in every case, it is permeable to the analyte. This is illustrated by way of example using FIGS. 4a-4d. In FIG. 4a, both functional layers 14 and 21 are designed to be media-permeable; in FIG. 4b, the second functional layer 21 is media-impermeable; in FIG. 4c, the first functional layer 14 is media-impermeable; and, finally, in FIG. 4d, both functional layers 14 and 21 are designed to be media-impermeable.

[0129] Furthermore, the first functional layer 14 may have a bubble-repelling geometry, as illustrated by way of example for various variants using FIGS. 4e-4m. Furthermore, in FIG. 4k, the first functional layer is designed such that it is impermeable to a medium 4 in the form of a gas.

[0130] In the following, various variants for protective devices 13 are indicated by way of example, corresponding to one of the embodiments from FIGS. 3a-3d or FIGS. 4a-4m.

[0131] Variant 1:

[0132] The functional layers 14 and 21 are designed to be media-permeable, and the layer 20 contains inorganic fiber bundles, e.g., polyaluminosilicates or polysilicic acids, which exhibit strong capillary forces, as well as a protective substance 16 in the form of a water-insoluble buffer substance, which ensures a pH buffering with approximately pH 7-pH 10. The first functional layer 14 is, for example, designed to be tapered in form by means of single pore, or in the form of a hydrophilic, and thus water-absorbing, membrane. For example, cross-linked polyvinyl alcohols or a superhydrophilic porous PVDF are to be considered in this regard.

[0133] Variant 2:

[0134] In an embodiment similar to variant 1, activated charcoal as an adsorbent is used as a protective substance 16, which is contained in the layer 20. The activated charcoals may be further oxidized for a better wetting capability. Alternatively, zeolites, MOF, ZIF, or polyimides may also be added as adsorbents.

[0135] Variant 3:

[0136] The layer 20 contains fiber bundles to which metal oxides are added as a protective substance 16.

[0137] Variant 4:

[0138] A basic buffer, e.g., a carbonate buffer, or a natural substance such as an exine and/or microporous glass, is used as a protective substance 16. With regard to the use of natural substances to encapsulate a luminescent dye, plant spores or fungal spores may be used, e.g., Lycopodium clavatum, from which may, in particular, be extracted labile, fluorescent materials, for example, proteins, lipids, nucleic acids, or carbohydrates.

[0139] One possibility for production includes suspending Lycopodium clavatum spores (250 g) in acetone and boiling under reflux for approximately 4 hours. The dispersion is then centrifuged, and the excess decanted. Following this, the defatted spores are stirred overnight under reflux in 4% potassium hydroxide solution (vol %); filtered; neutrally washed with hot water; and then washed with ethanol until colorless. The base hydrolyzed sporopollenins are then dried overnight in a desiccator on phosphorus pentoxide. 150 g of the product so obtained is subsequently suspended in orthophosphate (85%, 600 ml) and stirred for one week under reflux. The degreased and base-hydrolyzed and acid-hydrolyzed sporopollenins (exines) are finally filtered, neutrally washed with water, and washed and refluxed again for 1 h with hydrochloric acid (200 ml), acetone (200 ml), and ethanol, filtered, and, at the end, dried with phosphorus pentoxide in a desiccator.

[0140] Variant 5:

[0141] For applications which are sensitive to carbon dioxide (i.e., high cross-sensitivity), a 0.01 N potassium hydroxide solution may be added to the layer 20.

[0142] Variant 6:

[0143] The protective device 13 has a first functional layer 14 in the form of a membrane, which has a pH buffer polymer and/or a redox buffer polymer and/or an absorbent and/or a reducing agent and/or a catalyst and/or a polymer.

[0144] Variant 7:

[0145] Finely-dispersed platinum, which, for example, is deposited onto a surface of a microporous glass of the first functional layer 14, serves as a protective substance 16. The finely-dispersed platinum has a strong hydrophilic effect and, for this, is in a position to take up water, even in the dry state, via strong capillary action.

[0146] Variant 8:

[0147] In this variant, the protective device 13 comprises a first functional layer 14 made of an elastic material permeable to the analyte, e.g., a thin silicone sleeve, which is sealed against the environment at one end. Contained in a region facing towards the sealed side is a protective layer 17 with a protective substance 16 in the form of a basic pH buffer gel with activated charcoal. Such a protective device 13 of elastic design has the advantage that the protective device 13 may first be filled with water and, subsequently, may be attached to the sensor unit 3, for example, be pulled over the sensor cap 2. The elastic material, advantageously, has a comparatively high tear strength and may be folded around the sensor cap 2 in a region of said sensor cap 2 that is applied towards the medium 4, and, in this way, may be installed on the sensor 1. However, in this regard, numerous additional installation possibilities are conceivable, depending upon the embodiment of the sensor 1, which installation possibilities likewise fall under the present disclosure.

[0148] An additional possible embodiment of the protective device according to the present disclosure is illustrated in FIGS. 5a-5c. The protective substance 16 is arranged, for example as part of an aqueous solution, in an inlay 22 which can be introduced into a cap 23. The cap 22 thereby comprises at least the first functional layer 14 which, in the present instance, is designed in the form of a membrane. The inlay 22 is introduced, involving, for example, a rotational motion, into the cap 23, as illustrated in FIG. 5a. The protective device 13 is subsequently attached, likewise involving, for example, a rotational motion, to the sensor cap 2 as illustrated in FIG. 5b. Via the attachment to the sensor cap 2, the inlay 22 is destroyed such that the protective substance 16, or the aqueous solution, remains in the cap 23. Finally, the sensor cap 2 with protective device 13 attached thereon is shown in FIG. 5c. Via the use of an inlay 22, the protective device 13 can, advantageously, be attached to the sensor unit 3 or to the sensor cap 2, without admission of gas.

[0149] The sensor cap 2 may, optionally, also has a valve 24 for discharging gases remaining in the inner space of the cap 23 upon installation. Such a valve 24 may also, alternatively, be part of the protective device 13. It is further noted that, in addition to the protective substance 16, the inlay 22 may also contain a diffusion-inhibiting component 18, as well as additional optional components.

[0150] Comparison tests of optochemical sensors 1, with and without protective device 13 according to the present disclosure, show that the protective device 13 leads to a significant increase in the mechanical stability, in the case of after long-term stressing in 5% sodium hypochlorite solution. Conventional sensor units 102 often showed cracks and stark indications of aging at transition points to the O-ring 10 after 14 days stirring in 90 C. sodium hydroxide solution. With additional mechanical loading such as mechanical wear, cracks in the membrane 11, once produced, lead, in the extreme case, to the sensor spot tearing off due to particles floating past. In a less extreme case, cracks in the membrane 11 may lead to measurement value errors, due to delayed adjustment of the partial pressures. Voids between membrane 11 and substrate 7 also lead to what are known as carry-over effects and measurement value errors, for example, due to excessive prevailing partial pressures, e.g., within the sensor unit 3. In principle, the measurement values were more stable when using a protective device 13.

[0151] In addition to this, it has, surprisingly, been shown that a lower change in measurement value of the partial pressures could be achieved after 1 day of treatment in 70 C., 3% sodium hypochlorite solution, in particular, at low partial pressures. In particular, for measurement values in a range between 0 hPa and 25 hPa, partial pressure increases due to appearance of degradation at the dye were determined by radical-generating cleaning agents.