pH sensor

Abstract

The invention relates to a pH sensor. A pH sensor (3) for determining and / or monitoring a pH value of a medium (4) has a sensor unit (5) having a wall (6), wherein the wall (6) is in contact with the medium (4), at least one pH-sensitive material (8) having at least one spin state which changes as a function of the pH value, wherein the at least one pH-sensitive material (8) is arranged in or on a region of the wall (6) such that the at least one spin state is subjected to a change in the pH value of the medium (4), a spin-sensitive unit (9) which is configured to detect a variable associated with the at least one spin state, wherein the spin-sensitive unit (9) is arranged in an environment of the at least one pH-sensitive material (8) such that the spin-sensitive unit (9) is subjected to a change in the spin state of the at least one pH-sensitive material (8), and an evaluation unit (10).

Description

Technical Field

[0001] This invention relates to a pH sensor for determining and / or monitoring the pH value of a medium. Background Technology

[0002] pH is a critical measurement and influencing variable in environmental technologies and virtually all industrial processes involving water treatment, as it affects the thermodynamics and kinetics of almost all chemical reactions involving water. For example, this involves target reactions involving water, separation processes in water systems, corrosion on and within reactor and piping systems, the solubility of environmentally reactive substances, or the survival conditions of organisms. Therefore, determining (especially through real-time sensor measurements of pH) is a vital task in environmental and process measurement technologies.

[0003] pH glass electrodes have been established as the most important sensors for measuring the pH of a medium; they can measure pH with low cross-sensitivity over a wide measurement range, are chemically stable and robust, and provide an electrical measurement signal from the outset. Essentially, a typical pH single-rod measuring cell (also known as a pH sensor, or in many cases a pH electrode) consists of two electrochemical half-cells that are in contact with the measurement medium in different ways, and the voltage across the measurement medium is measured between the electrodes of the half-cells. The second half-cell serves as a reference half-cell. A challenge in pH measurement using glass electrodes is the low conductivity of the glass membrane used for the measurement, resulting in a high impedance for the entire sensor ranging from 50 MΩ to 1 GΩ at 25 °C.

[0004] Recent developments in sensor technology are exemplified by so-called quantum sensors, which utilize various quantum effects to determine a wide range of physical and / or chemical measurement variables. This approach is attracting significant attention in industrial process automation, particularly in efforts to increase miniaturization while simultaneously improving the performance of the corresponding sensors.

[0005] Quantum sensors are based on the fact that certain quantum states of individual atoms can be controlled and read out with great precision. In this way, for example, precise and low-noise measurements of electric and / or magnetic fields, as well as gravitational fields with resolution in the nanometer range, can be made. Various spin-based sensor arrangements are known in this context, where atomic transitions in a crystal body are used to detect changes in motion, electric and / or magnetic fields, or even gravitational fields. Furthermore, different systems based on quantum optical effects are known, such as quantum gravimeters, NMR gyroscopes, or optically pumped magnetometers, with the latter, in particular, being based especially on gas cells.

[0006] For example, in the field of spin-based quantum sensors, various devices utilizing atomic transitions, such as in various crystals, are known to detect minute changes in motion, electric and / or magnetic fields, or even gravitational fields. Typically, diamond with at least one silicon vacancy center or at least one nitrogen vacancy center, silicon carbide with at least one silicon vacancy, or hexagonal boron nitride with at least one vacancy color center are used as crystals. Crystals can, in principle, have one or more vacancies.

[0007] A sensor device is known from DE 10 2017 205 099 A1, comprising: a crystal having at least one vacancy; a light source; a high-frequency device for applying a high-frequency signal to the crystal; and a detection unit for detecting a fluorescence signal dependent on a magnetic field. The light source is arranged on a first substrate, and the detection device is arranged on a second substrate, while the high-frequency device and the crystal can be arranged on two interconnected substrates. An external magnetic field, current, temperature, mechanical stress, or pressure is suitable as a measurement variable. A similar device is known from DE 10 2017 205 265 A1.

[0008] DE 10 2014 219 550 A1 describes a combined sensor for detecting pressure, temperature and / or magnetic field, wherein the sensor element has a diamond structure having at least one nitrogen vacancy center.

[0009] DE 10 2018 214 617 A1 discloses a sensor device that also has a crystal with multiple color centers, wherein different filter elements are used to improve efficiency and miniaturization.

[0010] A sensor device is known from German patent application number 10 2020 123 993.9 (not yet published) that uses the fluorescence signal of a crystal with at least one vacancy to evaluate process variables of a medium. Furthermore, state monitoring of each process is performed based on variables characterized by magnetic fields (such as permeability or susceptibility). Additionally, a limit level sensor is known from German patent application number 10 2021 100223.0 (not yet published) in which a statement about a limit level is determined based on fluorescence.

[0011] Another subfield within quantum sensors involves gas pools, in which atomic transitions and spin states, particularly for determining magnetic and / or electrical properties, can be visually queried. Typically, gaseous alkali metals and buffer gases are present in the gas pool. The magnetic properties of the surrounding medium can be determined by the Rydberg states generated within the gas pool.

[0012] For example, gas pools are used in quantum-based standards, providing highly accurate physical variables. Therefore, they have long been used in frequency standards or atomic clocks, as known from EP 0 550 240B1.

[0013] US 10 184 796 B2 further discloses a chip-sized atomic gyroscope in which a gas cell is used to determine the magnetic field. A gas cell-based optically pumped magnetometer is known from US 9 329 152 B2. By manipulating the atomic states in the gas cell, further applications of gas cells can be inferred. Therefore, JP 4066804 A2 describes the use of a gas cell to determine absolute path length. Furthermore, gas cells are also used as the starting point for microwave sources, as described in EP 1 224 709 B1.

[0014] The first method for a pH sensor based on quantum effects has been known from the scientific literature. Wrachtrup et al. described the determination of pH using diamond with nitrogen-vacancy centers, whose surface was functionalized with a paramagnetic Gd complex (Nature Communications 2017, 8, 14701). A chemi-switch was used as the link between the diamond surface and the Gd complex, which released the Gd complex in a controlled and irreversible manner under the influence of pH. The resulting pH measurement accuracy was approximately 0.7 pH units. After release, the Gd complex remained in the medium and could not be reattached to the diamond surface.

[0015] Kapanidis et al. demonstrated the dependence of the lifetime of various charge states on the NV centers of nanodiamonds at different pH values ​​(Nanoscale 2020, 12, 21821). However, the lifetime of the charge states was not stable over several measurement cycles, which, according to the authors, may be due to changes on the nanodiamond surface.

[0016] Cigler et al. described nanodiamonds with pH- and temperature-sensitive polymer shells (Nanoscale, 2019, 11, 18537). Increased pH leads to an increase in negative charge within the polymer shell, resulting in its expansion, which in turn causes changes in the fluorescence spectrum of the NV centers. Under process conditions, the expansion and contraction of the polymer shell may be influenced by other molecules in the medium. Summary of the Invention

[0017] Therefore, the object of the present invention is to specify a pH sensor that represents an alternative to previous pH sensors.

[0018] According to the present invention, this objective is achieved by a pH sensor for determining and / or monitoring the pH value of a medium, the pH sensor having

[0019] - A sensor unit having a wall, wherein the wall is in contact with a medium.

[0020] - At least one pH-sensitive material having at least one spin state that changes according to pH value, wherein the at least one pH-sensitive material is disposed in or on a region of a wall such that the at least one spin state is subjected to changes in the pH value of the medium.

[0021] - A spin-sensitive unit configured to detect a variable associated with at least one spin state, wherein the spin-sensitive unit is arranged in an environment of at least one pH-sensitive material, such that the spin-sensitive unit is subjected to changes in the spin state of the at least one pH-sensitive material, and

[0022] - An evaluation unit that determines the pH value of the medium based on a variable detected by a spin-sensitive unit and associated with at least one spin state.

[0023] Compared to a pH glass electrode, the pH sensor according to the present invention does not require a reference electrode. The pH-sensitive material changes at least one of its spin states depending on the pH of the medium; typically, the pH-sensitive material is at least partially in contact with the medium. The pH of the medium can be determined by reading out the variable associated with at least one spin state using a spin-sensitive element. A defined distance exists between the spin-sensitive element and the pH-sensitive material. The spin-sensitive element and / or the pH-sensitive material are not consumed when determining the pH; the pH is not determined using an irreversible process. The pH sensor according to the present invention is chemically stable and does not release ions or molecules into the medium. In addition to a single pH-sensitive material, several different pH-sensitive materials can be used to extend the measurement range regarding pH.

[0024] Changes in the spin state of pH-sensitive materials can be caused by alterations in energy levels, spin reversal, and / or changes in the spin energy of the pH-sensitive material. Specifically, changes in spin state can lead to a change in pH-sensitive material from diamagnetic to paramagnetic, and vice versa. Typically, the spin state of a pH-sensitive material is defined by the spin of electrons, each possessing a magnetic dipole moment and interacting with any external magnetic field that may be present.

[0025] In one possible embodiment, a magnetic field device is provided that generates a magnetic field at least in the region of the pH-sensitive material. For example, the magnetic field causes energy state splitting (Zeeman splitting) in the pH-sensitive material. Furthermore, the magnetic field can amplify changes in the magnetic field caused by spin state changes, making these changes more easily read out by the spin-sensitive unit based on variables associated with the spin state, or even smaller spin state changes. However, depending on the measurement location, a weak magnetic field may already be present in the environment, sufficient to determine the spin state or spin state changes by means of the spin-sensitive unit based on variables associated with at least one spin state.

[0026] In one possible embodiment, the spin-sensitive unit is a crystal or gas cell with at least one vacancy. Crystals and gas cells with at least one vacancy exhibit a fluorescence signal upon appropriate photoexcitation, which is particularly dependent on the magnetic field applied to the crystal or gas cell. The spin state of the pH-sensitive material influences the applied magnetic field, allowing the spin state to be read out based on the fluorescence signal. The fluorescence signal is a variable associated with at least one spin state. Optionally, the crystal is also excited by a high-frequency or microwave signal. Crystals and gas cells with at least one vacancy center lead to improved measurement accuracy of spin state detection and thus pH value detection due to their high sensitivity to magnetic fields. Furthermore, statements regarding magnetic flux density, magnetic susceptibility, magnetic permeability, or another variable associated with at least one of these variables can be determined based on the fluorescence signal.

[0027] Preferably, the crystal is diamond having at least one silicon vacancy center or at least one nitrogen vacancy center, silicon carbide having at least one silicon vacancy, or hexagonal boron nitride having at least one vacancy color center.

[0028] Advantageously, a gas cell is a cell containing at least one gaseous alkali metal.

[0029] In another embodiment, the spin-sensitive unit has an excitation unit for photoexcitation of the crystal or gas cell and a detection unit for detecting the fluorescence signal of the crystal or gas cell. Optionally, filters, mirrors, and other optical elements may be used to guide the excitation light to the crystal or gas cell and / or to direct the fluorescence signal to the detection unit.

[0030] In one possible embodiment, at least one pH-sensitive material and a spin-sensitive unit are embedded in the wall of the sensor unit. The pH-sensitive material is at least partially in contact with the medium. For example, the spin-sensitive unit may be sintered into a glass together with the pH-sensitive material.

[0031] In an alternative embodiment, the spin-sensitive unit is configured as a first layer applied to the surface of the wall facing away from the medium, wherein at least one pH-sensitive material is embedded in the wall of the sensor unit. The spin-sensitive unit can be applied to the wall of the sensor unit by means of known methods such as chemical / physical vapor deposition.

[0032] In another alternative embodiment, at least one pH-sensitive material is configured as a second layer applied to the medium-facing surface of the wall, wherein a spin-sensitive unit is configured as a third layer disposed between the second layer and the wall or disposed on the medium-averse surface of the wall.

[0033] At least one pH-sensitive material preferably comprises an oxide or nitride. In the context of this application, "substance" is understood to mean an ion, molecule, or compound. The environment of a pH-sensitive material can change depending on the pH of the medium, for example, by exchanging ligands bound to the substance, resulting in a change in the spin state of the pH-sensitive material. Relevant ligands include protons, hydrated hydrogen ions, and hydroxide ions.

[0034] Advantageously, at least one pH-sensitive material contains Ti(III) ions. Depending on the pH of the medium, Ti(III) ions alternate between a low-spin state with low spin energy (low spin) and a high-spin state with higher energy (high spin). If appropriate, Ti(III) ions can be oxidized to Ti(IV) ions at high pH values ​​by the influence of oxygen-containing ligands.

[0035] In one possible embodiment, Ti(III) ions can be generated by an excess of Ti(IV) ions in a glass containing TiO2. The Ti(III) ions are generated during a so-called self-doping process in titanium dioxide. This can occur by means of an excess of Ti(IV) ions binding a reducing agent.

[0036] Advantageously, the walls of the sensor unit are made of glass.

[0037] In other embodiments, the evaluation unit is configured to determine and / or monitor the temperature of the medium based on variables associated with at least one spin state. For example, a crystal with at least one vacancy exhibits temperature-dependent zero-field splitting. The fluorescence signal of the crystal is a measure of both at least one spin state of the pH-sensitive material and the temperature of the medium. Different evaluation algorithms are required in each case to determine the temperature and pH value based on the fluorescence signal.

[0038] In an alternative embodiment, a temperature sensor is arranged in the region of the sensor unit such that the temperature sensor determines and / or monitors the temperature of the medium. For example, the temperature sensor is a platinum resistance thermometer. Attached Figure Description

[0039] The following is for reference. Figures 1 to 5b The invention will be explained in more detail below:

[0040] Figure 1 A simplified energy scheme for negatively charged NV centers in diamond.

[0041] Figure 2 The first embodiment of the pH sensor according to the present invention.

[0042] Figure 3 The second embodiment of the pH sensor according to the present invention.

[0043] Figure 4 The third embodiment of the pH sensor according to the present invention.

[0044] Figure 5a , Figure 5b The fourth embodiment of the pH sensor according to the present invention. Detailed Implementation

[0045] Figure 1 A simplified energy scheme for negatively charged nitrogen-vacancy centers (NV centers) in diamond is shown to illustrate the excitation and fluorescence of vacancies in crystals. The following considerations can be transferred to other crystals with corresponding vacancies.

[0046] In diamond, each carbon atom is typically covalently bonded to four other carbon atoms. Nitrogen vacancy centers (NV centers) consist of vacancies (i.e., unoccupied lattice space) in the diamond lattice and a nitrogen atom that is one of four adjacent atoms. In particular, negatively charged NV centers are crucial for the excitation and evaluation of fluorescence signals. In the energy schemes of negatively charged NV centers, besides the triplet ground state… 3 Besides A, there is also the excited triplet state. 3 E, each of them has three magnetic substates m s =0, ±1. In addition, two metastable singlet states... 1 A and 1 E is in the ground state. 3 A and excited state 3 Between E. In the absence of an external magnetic field, the two states m s =+ / -1 is transferred from the ground state m s =0 splitting, which is called zero field splitting Δ(T) and it depends on the temperature T.

[0047] Excitation light 1 from the green region of the visible spectrum (i.e., excitation light 1 with a wavelength of 532 nm) causes electrons to be released from the ground state. 3 A is excited to the excited state. 3The vibrational state of E, which recovers to the ground state while emitting a fluorescent photon 2 with a wavelength of 630 nm. 3 A. The fluorescence signal is a measure of the zero-field splitting Δ(T) and can be used to determine and / or monitor the temperature T.

[0048] The applied magnetic field of strength B causes the splitting of magnetic substates (Zeeman splitting), resulting in the ground state consisting of three energy-separated substates, each of which can be excited. However, the intensity of the fluorescence signal depends on the corresponding magnetic substate that excited it, making the magnetic field strength B calculated, for example, using the Zeeman formula based on the distance between fluorescence minimums. The magnetic field strength B is altered or generated by at least one spin state of the pH-sensitive material 8.

[0049] In the context of this invention, other possibilities for evaluating fluorescence signals are provided, such as the evaluation of fluorescence intensity, which is also proportional to the applied magnetic field. Furthermore, for example, an electrical evaluation can be performed via magnetic resonance photocurrent detection (PDMR). Besides these examples of fluorescence signal evaluation, other possibilities also fall under the scope of this invention.

[0050] Figure 2 A first embodiment of a pH sensor 3 for determining and / or monitoring the pH value of a medium 4 according to the present invention is shown. The pH sensor 3 includes a sensor unit 5 having a wall 6 that isolates the sensor unit 5 from the medium 4. Thus, the wall 6 is at least partially in contact with the medium 4, which is, for example, located in a container 7. Alternatively, the medium 4 may be present in a tube. Located in the region of the sensor unit 5 are at least one pH-sensitive material 8 and a spin-sensitive unit 9. An evaluation unit 10, which determines the pH value of the medium 4 based on a variable read from the spin-sensitive unit and associated with at least one spin state, may be arranged in the region of the sensor unit 5 or another unit. Figure 1 In this configuration, the evaluation unit 10 is, for example, arranged within a housing 17 connected to the sensor unit 5. Other electronic devices, as well as connectors and devices for power supply and / or data transmission, may optionally be located within the housing 17. The evaluation unit 10 may also be arranged separately from the sensor unit.

[0051] At least one pH-sensitive material 8, having at least one spin state that changes according to pH value, may also be arranged in the region of the wall 6. Therefore, the pH-sensitive material 8 is arranged such that at least one spin state is subjected to changes in the pH value of the medium 4. A spin-sensitive unit 9 is configured to detect variables associated with at least one spin state and is thus arranged in the region of the at least one pH-sensitive material 8, such that the spin-sensitive unit 9 is subjected to changes in its spin state.

[0052] The following attached figures ( Figures 3 to 5bDifferent embodiments of a pH sensor are shown, and in particular the arrangement of the pH-sensitive material 8 and the spin-sensitive unit 9. Figure 3 In this structure, both the pH-sensitive material 8 and the spin-sensitive unit 9 are embedded in the wall 6. For example, the spin-sensitive unit 9 is a crystal with at least one vacancy (such as diamond with at least one silicon vacancy center or at least one nitrogen vacancy center), silicon carbide with at least one silicon vacancy, or hexagonal boron nitride with at least one vacancy color center. Alternatively, the spin-sensitive unit 9 may also be a gas pool, for example, a pool enclosed with at least one gaseous alkali metal.

[0053] The wall 6 is made of glass, for example, and the pH-sensitive material 8 may optionally contain oxides or nitrides or Ti(III) ions, which may be generated, for example, from an excess of Ti(IV) ions in a glass containing TiO2. Therefore, Figure 3 The example shown could be a glass wall 6 in which diamond with at least one silicon or nitrogen vacancy center and Ti(III) ions is embedded.

[0054] Specifically, the crystal or gas cell can be optically read out, such that the spin-sensitive unit 9 also has an excitation unit 11 for photoexcitation of the crystal or gas cell and a detection unit for detecting the spin-dependent fluorescence signal of the crystal or gas cell. The excitation unit 11 and the detection unit 12 can, for example, be arranged in the region of the sensor unit. Alternatively, they can also be spaced apart from the wall 6, and an optical guide can be used to conduct excitation light and fluorescence between the spin-sensitive unit 9 and the excitation unit 11 and the detection unit 12.

[0055] Optionally, the pH sensor 3 may have a magnetic field device 19 (e.g., a coil or a permanent magnet) that generates a magnetic field at least in the region of the pH-sensitive material 8.

[0056] Figure 4 A third embodiment of the pH sensor 3 according to the invention is shown, wherein a wall 6 terminates at a container wall 18. A pH-sensitive material 8 is embedded in the wall 6 as an example, while a spin-sensitive unit is applied as a first layer 13 to the surface of the wall 6 facing away from the medium 4. Optionally, a temperature sensor 16 may be configured to determine and / or monitor the temperature of the medium 4 in the region of the sensor unit 5. For example, the temperature sensor 16 is a Pt resistance thermometer. Alternatively, the evaluation unit 10 is designed to determine and / or monitor the temperature of the medium 4 based on a variable associated with at least one spin state.

[0057] Alternatively, both the pH-sensitive material 8 and the spin-sensitive unit 9 are configured as layers, such as Figure 5a and Figure 5bAs shown. pH-sensitive material 8, as a second layer 14, is applied to the surface of wall 6 facing the medium 4. Spin-sensitive unit 9, as a third layer 15, is applied to the surface of wall 6 facing away from the medium 4. Figure 5a ) or between the second layer 14 and wall 6 ( Figure 5b ).

[0058] List of reference numerals

[0059] 1. Excitation light

[0060] 2. Fluorescence

[0061] 3 pH sensors

[0062] 4. Medium

[0063] 5 sensor units

[0064] 6 walls

[0065] 7 Containers

[0066] 8 pH-sensitive materials

[0067] 9 Spin Sensing Units

[0068] 10 Evaluation Units

[0069] 11 Excitation Unit

[0070] 12 detection units

[0071] 13 First Layer

[0072] 14 Second Layer

[0073] 15 Third Floor

[0074] 16 Temperature Sensors

[0075] 17. Casing

[0076] 18 container wall

[0077] 19 Magnetic field device

Claims

1. A pH sensor (3) for determining and / or monitoring the pH value of a medium (4), said pH sensor having: - Sensor unit (5), the sensor unit having a wall (6), wherein, The wall (6) is in contact with the medium (4). - At least one pH-sensitive material (8), said at least one pH-sensitive material having at least one spin state that changes according to pH value, wherein said at least one pH-sensitive material (8) is disposed in a region of said wall (6) or on said wall (6) such that said at least one spin state is subjected to changes in pH value of said medium (4). - A spin-sensitive unit (9), the spin-sensitive unit being configured to detect a variable associated with the at least one spin state, wherein the spin-sensitive unit (9) is disposed in the environment of the at least one pH-sensitive material (8) such that the spin-sensitive unit (9) is subjected to changes in the spin state of the at least one pH-sensitive material (8), and - Evaluation unit (10) determines the pH value of the medium (4) based on a variable detected by the spin-sensitive unit (9) and associated with the at least one spin state, wherein the at least one pH-sensitive material (8) contains Ti(III) ions, and wherein the at least one pH-sensitive material (8) and the spin-sensitive unit (9) are embedded in the wall (6) of the sensor unit (5), wherein the pH-sensitive material (8) is embedded in the wall (6), and the spin-sensitive unit is applied as a first layer (13) on the surface of the wall (6) facing away from the medium (4).

2. The pH sensor according to claim 1, in, The spin-sensitive unit (9) is a crystal with at least one vacancy or a gas pool.

3. The pH sensor according to claim 2, in, The crystal is diamond having at least one silicon vacancy center or at least one nitrogen vacancy center, silicon carbide having at least one silicon vacancy, or hexagonal boron nitride having at least one vacancy color center.

4. The pH sensor according to claim 2, in, The gas pool is a pool that encloses at least one gaseous alkali metal.

5. The pH sensor according to claim 2, in, The spin-sensitive unit (9) has an excitation unit (11) for photoexcitation of the crystal or the gas cell and a detection unit (12) for detecting spin-dependent fluorescence signals of the crystal or the gas cell.

6. The pH sensor according to any one of claims 1 to 5, in, The spin-sensitive unit (9) is configured as a first layer (13), which is applied to the surface of the wall (6) facing the medium (4), wherein at least one pH-sensitive material (8) is embedded in the wall (6) of the sensor unit (5).

7. The pH sensor according to any one of claims 1 to 5, in, The at least one pH-sensitive material (8) is configured as a second layer (14), which is disposed on the surface of the wall (6) facing the medium (4), wherein the spin-sensitive unit (9) is configured as a third layer (15), which is disposed between the second layer (14) and the wall (6) or on the surface of the wall (6) facing away from the medium (4).

8. The pH sensor according to any one of claims 1 to 5, in, The at least one pH-sensitive material (8) includes oxides or nitrides.

9. The pH sensor according to claim 1, in, The Ti(III) ions can be generated by an excess of Ti(IV) ions in a glass containing TiO2.

10. The pH sensor according to any one of claims 1 to 5, in, The wall (6) of the sensor unit (5) is made of glass.

11. The pH sensor according to any one of claims 1 to 5, in, A temperature sensor (16) is arranged in the region of the sensor unit (5) such that the temperature sensor (16) determines and / or monitors the temperature of the medium (4).

12. The pH sensor according to any one of claims 1 to 5, in, The evaluation unit (10) is configured to determine and / or monitor the temperature of the medium (4) based on variables associated with the at least one spin state.

13. The pH sensor according to any one of claims 1 to 5, in, A magnetic field device (19) is provided, which generates a magnetic field at least in the region of the pH-sensitive material (8).

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