Abstract
A sensor element for an optochemical sensor includes: a luminescence indicator, whose luminescence can be quenched with oxygen; and scavenger units to deactivate singlet oxygen, forming a chemical reaction product by reacting with singlet oxygen, wherein the scavenger units are selected to be recovered by a decomposition reaction induced thermally, photochemically or by a pressure increase of the chemical reaction product formed by the reaction with singlet oxygen.
Claims
1. A sensor element for an optochemical sensor, the sensor element comprising: a luminescence indicator, whose luminescence can be quenched with oxygen; and scavenger units configured to deactivate singlet oxygen via forming a chemical reaction product by reacting with singlet oxygen, wherein the scavenger units are selected to be recovered by a decomposition reaction, which decomposition reaction is induced thermally, photochemically, or by a pressure increase of the chemical reaction product formed by the reaction with singlet oxygen.
2. The sensor element according to claim 1, further comprising a polymer matrix in which the luminescence indicator is present in the form of a mixture or bound to the polymer matrix or encapsulated in micelles or core-shell structures contained in the polymer matrix.
3. The sensor membrane according to claim 2, wherein the scavenger units are bound to the polymer matrix.
4. The sensor element according to claim 1, wherein the scavenger units are bound to the luminescence indicator.
5. The sensor element according to claim 1, wherein: the sensor element includes micelles in which the luminescence indicator is encapsulated; and the scavenger units are bonded to a material comprising the micelles or to the luminescence indicator.
6. The sensor element according to claim 1, wherein: the sensor element includes core-shell particles in which the luminescence indicator is encapsulated; and the scavenger units are bonded to a material comprising a shell of the core-shell particles or to the luminescence indicator.
7. The sensor element according to claim 6, wherein the scavenger units are bonded to a polymer forming the shell of the core-shell particles.
8. The sensor element according to claim 1, wherein: the sensor element includes a self-assembled monolayer (SAM) of surface-active molecules; and the scavenger units are bound to at least a portion of the surface-active molecules comprising the SAM or to the luminescence indicator.
9. The sensor element according to claim 1, wherein the scavenger units bind singlet oxygen as endoperoxide.
10. The sensor element according to claim 9, wherein the scavenger units are selected from: substituted benzene derivatives, naphthalene, naphthalene derivatives, acenes, substituted acenes, acene derivatives.
11. The sensor element according to claim 10, wherein the scavenger units are acenes selected from: anthracene, tetracene, pentacene and hexacene.
12. The sensor element according to claim 10, wherein the scavenger units are acene derivatives with methyl, phenyl, pyridinyl, alkynyl, or tetramethylsilane as substituents.
13. The sensor element according to claim 1, wherein the luminescence indicator is a metal-porphyrin complex, or an iodinated BODIPY, a metal-phthalocyanine, a halo(iodo)triangulenium complex, a platinum-organic complex, ruthenium phenanthroline, difluoroboron and aluminum chelate of 9-hydroxyphenalenone or a benzannelized derivative of 6-hydroxybenz[de]anthracen-7-one.
14. An optochemical sensor for measuring a measured variable representing the concentration of oxygen or a reactive oxygen-containing species in a measuring medium, the optochemical sensor comprising: a sensor element according to claim 1; a radiation source configured to excite the luminescence indicator to emit luminescence radiation; and a detector configured to record at least one optical property of the luminescence indicator.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] In the following, the present disclosure is explained on the basis of the exemplary embodiments shown in the figures. The same reference signs refer to the same components of the components shown in the figures. In the figures:
[0028] FIG. 1 shows a schematic representation of an optochemical sensor with a sensor membrane;
[0029] FIG. 2 shows a schematic representation of possible chemical reaction pathways for photochemically induced aging of a luminescence indicator;
[0030] FIG. 3 shows an example of reversible binding of singlet oxygen by scavenger units bound to a luminescence indicator;
[0031] FIG. 4 shows further examples of scavenger units for binding to a luminescence indicator with scavenger units;
[0032] FIG. 5 shows a first example of a polymer matrix modified with scavenger units for reversible binding of singlet oxygen;
[0033] FIG. 6 shows a second example of a polymer matrix modified with scavenger units for reversible binding of singlet oxygen;
[0034] FIG. 7 shows examples of micelle materials modified with scavenger units for reversible binding of singlet oxygen;
[0035] FIG. 8 shows examples of SAM units modified with scavenger units for reversible binding of singlet oxygen; and
[0036] FIGS. 9a and 9b each show a schematic representation of the insertion of scavenger units into luminescence-indicator-containing pigment capsules (beads).
DETAILED DESCRIPTION
[0037] In FIG. 1, an optochemical sensor 1 for determining the concentration of an analyte in a measuring fluid, for example, dissolved oxygen in the measuring fluid, is shown schematically in a longitudinal sectional view. The sensor 1 comprises a radiation source 2 and a detector 3, along with a sensor element 7 comprising a sensitive layer 4. The sensitive layer 4 contains a luminescence indicator for detecting oxygen. For example, the sensitive layer 4 can have a matrix, such as a polymer matrix, in which the luminescence indicator is included, for example, in the form of a mixture with the polymer matrix or chemically bonded to the polymer matrix. The luminescence indicator can be excited to luminescence, for example, fluorescence, by radiation emitted from the radiation source 2. For this purpose, a wavelength of the radiation emitted by the radiation source 2 is selected to match the absorption spectrum of the luminescence indicator to excite it. The detector 3 is configured to record luminescence radiation emitted by the luminescence indicator and convert it into an electrical measurement signal. In the present example, the sensor element 7 comprises an optical insulating layer 5 and a transparent support 6 in addition to the sensitive layer 4. In alternative embodiments, the sensitive layer 4 and the optical insulating layer 5 can be designed as a membrane (sensor spot) arranged on a transparent support or as a self-supporting membrane or as a layer system on an end face of an optical fiber or a light guide. The sensor element 7 can have further layers, and/or the sensor element 7 can be a component of a replaceable housing cap of the optochemical sensor.
[0038] In the present example, radiation from the radiation source 2 is radiated to the sensor element 7 via a first branch of a light guide 8. Luminescence radiation emitted from the luminescence indicator reaches the detector 3 via a second branch of the light guide 8. The sensor 1 includes a sensor circuit 9 that is configured to control the light source 2 and to receive and process the electrical measurement signals from the detector 3. It can be connected via a cable connection 12 or wirelessly for communication with a higher-level unit, in order to output to it the measurement signals or values or signals derived from the measurement signals. In the present example, the sensor element 7, the optical fiber 8, the radiation source 2, the detector 3 and the sensor circuit 9 are housed in a probe housing 10.
[0039] In a measuring mode of the sensor 1, the sensor element 7 is brought into contact with a measuring medium, for example, with a measuring fluid containing oxygen. The luminescence indicator is excited to luminescence by excitation radiation from radiation source 2, which is quenched by oxygen in a concentration-dependent manner. The luminescence radiation is recorded in the detector 3 as an electrical measurement signal, for example, in the form of a decay time, an intensity or a phase angle. The oxygen concentration in the measuring fluid is determined from the recorded measuring signal. This can be performed in the sensor circuit 9 or in the higher-level unit connected to the sensor circuit 9, for example, a transducer or other electronic display or operating device. For the decay time or phase shift measurements, a radiation source 2 with temporal modulation of the intensity (e.g., pulse, sinusoidal or square-wave modulation) and a time-resolved or sensitivity-modulated detector 3 can be used.
[0040] During the excitation of the luminescence indicator, highly reactive singlet oxygen can be formed by transferring energy from the luminescence indicator to oxygen molecules present in the sensitive layer 4. This can react directly or indirectly via intermediates with the luminescence indicator or with other substances in the sensitive layer 4, for example, with the polymer matrix containing the luminescence indicator. As a result, optical properties of the luminescence indicator or sensitive layer 4 also change and thus a decay time or an intensity or a phase angle recorded by the detector 3 can also change.
[0041] FIG. 2 shows possible reaction pathways that can lead to degenerative aging of the luminescence indicator. In the present example, the luminescence indicator is a platinum-porphyrin complex A, whose luminescence can be doused by oxygen. Singlet oxygen can react directly with functional groups of the luminescence indicator. As shown in FIG. 2, however, singlet oxygen can also react with solvent molecules present in the sensitive layer 4 of the sensor element 7, in this case, for example, water or components of the sensitive layer, for example, a polymer matrix containing the luminescence indicator, to form highly reactive intermediates, for example, hydroxide, oxygen or benzyl radicals. Such radicals can in turn react with porphyrin complex A and be bound to the complex as additional functional groups. The modified porphyrin complex B formed in this way has different optical properties than the original porphyrin complex A. The more frequently such reactions occur in the sensitive layer 4 of the sensor 1, the more the measurement signal recorded by the detector is distorted, which ultimately leads to a drift of the sensor signal.
[0042] FIG. 3 illustrates an example of reversible binding of singlet oxygen by scavenger units bound to a luminescence indicator according to the present disclosure; a platinum-porphyrin complex is used here as the luminescence indicator, wherein the porphyrin is functionalized with phenyl groups, to each of which scavenger units are bound via a spacer unit A. Presently, the scavenger units are each formed from a naphthalene derivative. For example, the spacer unit A can be formed by an ether group, an alkyl group, ethylene glycol or polyethylene glycol. Singlet oxygen formed upon irradiation of sensitive layer 4 with excitation radiation is bound to polycyclic aromatics via a [4+2] cycloaddition, in this case to the scavenger units formed by the substituted naphthalene groups. The endoperoxide formed is stable up to temperatures of 50? C. If the temperature is increased above 50? C., the equilibrium of the reaction equation shown in FIG. 3 is on the left side, i.e., the reactant side. Thus, when the temperature rises above this threshold, for example, during a sterilization process where temperatures of 120? C. or more are reached, the oxygen bound to the scavenger units is released again and the scavenger units are regenerated. Even if singlet oxygen is released again in this way at elevated temperatures, this occurs with a time delay and in small amounts, such that the aging effects described on the basis of FIG. 2 occur to a much lesser extent if the luminescent dye is functionalized with scavenger units as shown in FIG. 3. Advantageously, longer-chain spacer groups A are used to minimize interference of the scavenger units with the luminescence properties of the luminescence indicator.
[0043] FIG. 4 shows further examples of scavenger units that can be used to reversibly bind singlet oxygen to the luminescence indicator. The scavenger units can be, in particular, substituted polycyclic aromatics, for example, the functionalized anthracenes and anthracene derivatives or functionalized naphthalenes and naphthalene derivatives shown herein. With the examples according to FIG. 4, the scavenger units are also bound to the luminescence indicator via spacer units A, which can be selected quite analogously as described with reference to FIG. 3.
[0044] FIG. 5 shows a first example of a polymer matrix modified with scavenger units for the reversible binding of singlet oxygen. The polymer can be a polystyrene or polystyrene derivative with the scavenger units as side chain groups. Thus, in the present example, a methyl-substituted naphthalene is bound to the matrix polymer via an alkyl spacer group. Alternatively, the spacer group can be an alkyl ether or an alkyl ester group.
[0045] FIG. 6 shows a second example of a polymer matrix modified with scavenger units for the reversible binding of singlet oxygen. Here, a polycyclic aromatic compound is again selected for the reversible binding of singlet oxygen, specifically the anthracene-based dicarboxylic acid C. The scavenger units are not provided here as functional side groups of the polymer, as in the previously described example, but serve in an additional function as crosslinkers for the polymer forming the polymer matrix of the sensitive layer 4. To prepare sensitive layer 4, platinum porphyrin complex A, which serves as a luminescent dye, is added during polymerization of 2,3-epoxypropyl methacrylate and dicarboxylic acid C, which serves as a crosslinker. In this exemplary embodiment, the anthracene units linked via ester groups to the methacrylate chains of the matrix polymer thus formed serve as scavenger units and, quite analogously to the exemplary embodiment described with reference to FIG. 4, bind singlet oxygen as endoperoxide via a [4+2] cycloaddition and release it again upon an increase in temperature or pressure.
[0046] In another embodiment, the luminescence indicator can be encapsulated in micelles or core-shell structures. The scavenger units for reversible binding of singlet oxygen can be bound to the micelle material in such embodiments. Preferably, they are bound to the non-polar chain end of the molecules forming the micelles, as exemplified in FIG. 7. In this case, the scavenger units are arranged inside the micelle and thus separated by the micelle membrane from, for example, the polar measuring fluid, for example water or aqueous solutions. This reduces the risk of contamination of the measuring fluid by the scavenger units.
[0047] Alternatively, the scavenger units can be bound to SAM-forming molecules with siloxane end group or thiol end group via aliphatic chains as spacers. Such monomers can form a monolayer or a plurality of superimposed layers on a transparent substrate of the sensor element, in which the luminescence indicator is integrated. Examples of suitable SAM-forming molecules functionalized with scavenger units are shown in FIG. 8.
[0048] Alternatively, the SAM-forming molecules can be used to form core-shell structures to encapsulate the luminescence indicator, as can the monomers shown in FIG. 7.
[0049] FIGS. 9a and 9b show the formation of core-shell structures and/or micelles with luminescence indicator encapsulated therein and the additional introduction of scavenger units into such structures. Polystyrene beads, for example, can serve as the core-shell structure. The interior of the polystyrene beads is non-polar. It is therefore advantageous to functionalize polycyclic aromatics, which serve as scavenger units, in such a way that they dissolve in or mix with the non-polar matrix of the polystyrene beads. For this purpose, for example, as shown in FIG. 9a, a polycyclic aromatic, in this case anthracene, is functionalized with carboxyl groups and esterified with a longer-chain or branched alcohol by means of Steglich esterification with dicyclohexylcarbodiimide DCC and 4-dimethylaminopyridine DMAP (three examples shown in FIG. 9a).
[0050] As shown schematically in FIG. 9b, the polycyclic aromatic esters formed in this way (shown as circles 15 in FIG. 9b), but also other polycyclic aromatic scavenger units, can be introduced into a polystyrene bead 14 with a luminescence indicator encapsulated therein (shown as stars 16 in FIG. 9b). Encapsulation is advantageous to prevent leakage of the luminescence indicator or scavenger units into the measuring fluid.
