OPTOCHEMICAL SENSOR

Abstract

A sensor (202) uses an optical-sensing technique for determining more than one parameter in a measurement medium (204). The sensor has an optochemical sensitive element (208) with a first sensing layer (228) and a second sensing layer (230). Each of the sensing layers is arranged on a substrate (222). The first sensing layer has a first indicator (236) that determines a first parameter and the second sensing layer has a second indicator (238) that determines a second parameter in the measurement medium.

Claims

1. An optochemical sensitive element for determining at least two parameters in a measurement medium, the element comprising: a substrate comprising a first surface and a second surface, the first and second surfaces being on opposite sides of the substrate; at least one first sensing layer arranged on the first surface of the substrate, each of the first sensing layers comprising a first indicator for determining a first parameter, immobilized in a first polymer matrix; and at least one second sensing layer arranged on the second surface of the substrate, each of the second sensing layers comprising a temperature sensitive indicator for determining a temperature of the measurement medium, immobilized in a second polymer matrix.

2. The optochemical sensitive element of claim 1, wherein the first parameter is a concentration of a dissolved gas in the measurement medium.

3. The optochemical sensitive element of claim 2, wherein the first indicator is adapted for determining oxygen concentration and comprises a substance selected from the group consisting of: metal-organic complex comprising polycyclic aromatic hydrocarbon, such as pyrene and/or its derivatives, oxygen sensitive transitional metal polypyridil complex in particular [Ru(bpy).sub.3].sup.2+ or metalloporphyrin complex comprising in particular platinum or palladium, derivatives thereof and combinations thereof.

4. The optochemical sensitive element of claim 2, wherein the first indicator is adapted for determining carbon dioxide concentration and comprises 8-hydroxypyrene-1,3,6-trisulfonic acid.

5. The optochemical sensitive element of claim 1, wherein the temperature sensitive indicator comprises a substance selected from the group consisting of: rhodamine complex, temperature sensitive metal ligand complex in particular [Ru(bpy).sub.3].sup.2+ or lanthanide-doped bulk materials, in particular doped Al.sub.2O.sub.3 or YAB doped with chromium ions, derivatives thereof and combinations thereof.

6. The optochemical sensitive element of claim 1, wherein at least one of the first and second polymer matrices comprises a substance selected from the group consisting of: polystyrene film, cyclic olefin copolymer, poly (n-methyl methacrylimide) and combinations thereof.

7. The optochemical sensitive element of claim 1, wherein the respective first and second polymer matrices are different in composition.

8. The optochemical sensitive element of claim 1, wherein the first sensing layer comprises a second indicator for determining the pH of the measurement medium.

9. The optochemical sensitive element of claim 1, wherein the substrate comprises a material selected from the group consisting of glass, polyester, amorphous polyamide, partially crystalline polyamide, acrylate, polycarbonate, ethylene-norbornene copolymer (cyclic olefin copolymer) and combinations thereof.

10. The optochemical sensitive element of claim 1, wherein the first sensing layer covers the first surface of the substrate.

11. The optochemical sensitive element of claim 1, wherein the second sensing layer covers at least a portion of the second surface of the substrate.

12. The optochemical sensitive element of claim 11, wherein the second sensing layer is arranged on the second surface of the substrate as any of the following shapes: a disc or an annular ring.

13. An optochemical sensor comprising: an optochemical sensitive element, according to claim 1, for determining, in a measurement medium, at least two parameters thereof; and a sensor housing comprising: at least one light source, and at least one detection unit, wherein the optochemical sensitive element is arranged in a light path between the light source and detection unit.

14. A method for producing an optochemical sensitive element for determining at least two parameters in a measurement medium, the method comprising the steps of: providing a substrate having a first surface and a second surface; applying a first sensing layer on the first surface using a first application technique, wherein the first sensing layer comprises a first indicator for determining a first parameter in the measurement medium, immobilized in a first polymer matrix; applying a second sensing layer on the second surface using a second application technique, wherein the second sensing layer comprises a temperature sensitive indicator for determining a temperature of the measurement medium, immobilized in a second polymer matrix; wherein the first sensing layer applied to the first surface of the substrate is configured to be opposite to the second sensing layer applied to the second surface of the substrate.

15. The method of claim 14, wherein at least one of the first and second application techniques is chosen from the group consisting of: spin coating, blade coating, dip coating and screen printing.

16. The optochemical sensitive element of claim 2, wherein the first parameter is the concentration of ozone in the measurement medium.

17. The optochemical sensitive element of claim 2, wherein the first sensing layer comprises a second indicator for determining the concentration of a second dissolved gas, different from the first dissolved gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Other features and advantages disclosed herein will become more apparent from the following detailed description of exemplary embodiments when read in conjunction with the following figures. The figures show:

[0044] FIG. 1 is a schematic of an optochemical sensor;

[0045] FIG. 2 is a longitudinal cross sectional view of an optochemical sensitive element housed within an optochemical sensor immersed in a measurement medium;

[0046] FIG. 3 is a schematic cross sectional view of an embodiment of an optochemical sensitive element for measuring the temperature and two other parameters in a measurement medium;

[0047] FIG. 4 is a schematic cross sectional view of another embodiment of an optochemical sensitive element for measuring the temperature and three other parameters in a measurement medium;

[0048] FIG. 5A is a schematic cross sectional view of an embodiment showing an arrangement of a second sensing layer of an optochemical sensitive element;

[0049] FIG. 5B is a schematic top view of embodiment shown in FIG. 5a showing the arrangement of the second sensing layer of the optochemical sensitive element;

[0050] FIG. 6A is a schematic cross sectional view of an embodiment showing an arrangement of a second sensing layer of an optochemical sensitive element;

[0051] FIB 6B is a schematic top view of embodiment shown in FIG. 6a showing the arrangement of the second sensing layer of the optochemical sensitive element;

[0052] FIG. 7A is a schematic cross sectional view of an embodiment showing an arrangement of a second sensing layer of an optochemical sensitive element;

[0053] FIG. 7B is a schematic top view of embodiment shown in FIG. 7a showing the arrangement of the second sensing layer of the optochemical sensitive element; and

[0054] FIG. 8 is a schematic cross sectional view of an embodiment of an optochemical sensitive element comprising various layers.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0055] FIG. 1 shows a schematic cross sectional view of an optochemical sensor 2 immersed in a measurement medium 4. The optochemical sensor 2 has two ends, a distal end that is immersed in the measurement medium 4 and a proximal end having a sensor head 7, which is connected via a wire or wireless connection to a control unit 20. An optochemical sensitive element 8 is arranged at the distal end of the optochemical sensor 2 that is immersed in the measurement medium 4.

[0056] Further, the optochemical sensor 2 comprises a light source 12, a detection unit 14 and optical elements 16 housed within a sensor housing 6. Further, the optochemical sensor can comprise more than one light source and/or more than one detector respectively within the sensor housing 6.

[0057] During measurement operation of the optochemical sensor 2 based on the principle of photoluminescence, excitation light is emitted by the light source 12 and is directed by optical elements 16, such as filters, mirrors or lenses, towards the optochemical sensitive element 8 such that the emitted light interacts with the optochemical sensitive element 8. A light path is indicated by arrows 18. The optochemical sensitive element 8 is arranged in the light path 18 between the light source 12 and detection unit 14, as seen in FIG. 1. A photoluminescence response signal, in particular a fluorescence or phosphorescence response signal that is emitted after excitation interacts with the optochemical sensitive element 8 and is detected by the detection unit 14. As previously described, in optochemical sensors based on photoluminescence a reduction in the photoluminescence caused by an analyte in the measurement medium is detected. The detection unit 14 comprises at least one detector, for example a photodiode. Depending on the number of parameters in the measurement medium to be measured, the detection unit 14 can further comprise corresponding detectors for one or more of the parameters. The detection unit 14 further comprises optical filters that are positioned in front of the detectors. These optical filters help in separating signals that are received from the optochemical sensitive element 8. The sensor further comprises optical fibers to direct the light to and/or emit the light from the optochemical sensitive element 8.

[0058] The response signal received by the detection unit 14 is amplified and processed by the control unit 20. The control unit 20 is connected via a wired or wireless connection to the sensor head 7 and it can also function as a regulation unit. The control unit 20 can further be connected to a terminal which in turn can be connected to a display, a process control system, a transmitter or a further processing unit and/or similar devices. The control unit 20 is arranged either as an external unit or also entirely or in part inside the sensor housing 6. In this embodiment, the control unit 20 has a wire-bound or wireless connection to the sensor head 7 of the optochemical sensor 2. The state of the art includes different variants of the control unit 20 and the latter is therefore only symbolically illustrated. The optochemical sensitive element 8 is releasably connected to the sensor housing 6 so that the optochemical sensitive element 8 can be easily replaced.

[0059] FIG. 2 shows a longitudinal cross sectional view of an optochemical sensitive element 208 housed within an optochemical sensor 202. The optochemical sensitive element 208 is shown to be arranged at a distal end of an optochemical sensor 202 that is immersed in a measurement medium 204. The optochemical sensitive element 208 comprises at least two sensing layers i.e. a first sensing layer 228 and a second sensing layer 230 arranged on a substrate 222. The first sensing layer 228 is arranged on a first surface 224 of the substrate 222. The second sensing layer 230 is arranged on a second surface 226 of the substrate 222. The substrate 222 is arranged within a sensor housing 206 such that first surface 224 of the substrate 222 is arranged to face towards the measurement medium 204 while the second surface 226 of the substrate 222 is arranged to face away from the measurement medium 204.

[0060] Example shapes or geometries of substrates include but are not limited to rectangular, hexagonal, circular, triangular, square-formed or polygonal substrates. The substrate 222 is optically transparent to an excitation light emitted from a light source (see FIG. 1). Preferably, the substrate 222 is made of glass. It can also be made from any of the following materials: polyester, amorphous or partially crystalline polyamide, acrylate, polycarbonate, ethylene-norbornene copolymer (cyclic olefin copolymer) or combinations of these materials thereby being a hybrid substrate.

[0061] The first sensing layer 228 arranged on the first surface 224 of the substrate 222 determines a first parameter in the measurement medium 204. The second sensing layer 230 arranged on the second surface 226 of the substrate 222 determines the temperature of the measurement medium 204.

[0062] In a preferred embodiment, the first sensing layer 228 is configured to determine the first parameter, such as the concentration of a dissolved gas, in the measurement medium 204. The first sensing layer 228 comprises a first indicator 236 immobilized in a first polymer matrix 232. The second sensing layer 230 comprises a temperature sensitive indicator 238 immobilized in a second polymer matrix 234.

[0063] Examples of polymers that can be used to form optically transparent polymer matrices of the respective sensing layers are: polystyrene film, cyclic olefin copolymers such as ethylene-norbornene copolymer, cyclic olefin polymer (COP) and poly(n-methyl methacrylimide) (PMMI) or mixtures thereof. Alternatively, the second sensing layer can employ silicone polymers for its polymer matrix composition. Moreover to better suit each indicator, the first polymer matrix 232 and second polymer matrix 234 can be made from different polymers. Further, it is also possible that the indicators are immobilized in the same polymer matrix material.

[0064] Polymer matrices provide a considerable amount of good mechanical stability and thus immobilizing indicators in them becomes advantageous. Additionally, these matrices are also known to withstand the acidic and/or basic cleaning processes, which are, for example used in chemical process environments, and this in turn provides an optochemical sensitive element with a longer service life.

[0065] A suitable indicator to detect an analyte of interest in a measurement medium is selected based on the basis of the type of analyte to be determined, its solubility in a polymer matrix as well as its photoluminescence lifetimes and the dependency of the photoluminescence quenching from the parameter being measured.

[0066] In an exemplary embodiment where the optochemical sensitive element 208 is used to determine the temperature-compensated oxygen concentration in the measurement medium 204, a suitable indicator is chosen for the measurement of oxygen concentration in the measurement medium. Subsequently, the second sensing layer 230 takes into account temperature changes in the measurement medium 204 during said measurement of the said first parameter by compensating for temperature changes thereby providing the temperature compensated measurement of the oxygen concentration in the measurement medium 204.

[0067] Examples of suitable indicators for the measurement of oxygen are metal-organic complexes comprising polycyclic aromatic hydrocarbons such as pyrene and/or pyrene derivatives, oxygen sensitive transitional metal polypyridil complex, in particular [Ru(bpy).sub.3].sup.2+ or metalloporphyrin complex comprising in particular platinum or palladium. Additionally, there are numerous commercially available indicators that may be used in the measurement of oxygen.

[0068] In a further exemplary embodiment, the optochemical sensitive element 208 is configured for determining the first parameter, in particular the concentration of a dissolved gas, such as carbon dioxide or ozone, in the measurement medium 204. The measurement of this parameter is temperature compensated by correspondingly measuring the temperature of the measurement medium 204 utilizing the temperature sensitive indicator 238 of the second sensing layer 230. A suitable indicator for the measurement of dissolved carbon dioxide is 8-hydroxypyrene-1,3,6-trisulfonic acid.

[0069] Providing a temperature sensitive indicator 238 in the second sensing layer 230 facing away from the measurement medium 204 offers an advantage that it allows the temperature sensitive indicator to be protected from the measurement medium, specifically as protection from corrosive measurement media.

[0070] Preferably, the temperature sensitive indicator is chosen from any of rhodamine complex or its derivatives, metal ligand complex, in particular [Ru(bpy).sub.3].sup.2+ or lanthanide-doped bulk material, in particular doped Al.sub.2O.sub.3 or YAB doped with chromium ions.

[0071] Known temperature sensitive indicators are less efficient photoluminescent emitters compared to indicators sensitive for dissolved gases, such as oxygen, carbon dioxide or ozone. Therefore, this is compensated by separating the temperature sensing layer 230 comprising the temperature sensitive indicator 238 from the at least first sensing layer 228 comprising the at least first indicator 236 and thus bringing it closer to the optical detection unit (see FIG. 1) in the sensor housing 206 of the optochemical sensor 202. This arrangement also allows the temperature sensing layer 230 to be disposed as a thin layer on the substrate 222 thereby leading to a faster response time of the optochemical sensitive element 208.

[0072] The excitation range for exciting the first sensing layer 228 comprising the first indicator 236, preferably adapted of an optochemical sensor for measuring dissolved oxygen, lies preferably in the range of 390 to 570 nm. The excitation range for exciting the second sensing layer 230 comprising the temperature sensitive indicator 238 lies preferably in the range of 390 to 670 nm. The excitation ranges are chosen based on spectral range or the photoluminescence answer from the respective indicator and/or sensing layer.

[0073] The light detection range for the first indicator 236, in particular the oxygen sensitive indicator, lies in the range of 600 to 870 nm whereas that for the temperature sensitive indicator 238 lies in the range of 630 to 800 nm.

[0074] FIG. 3 shows a schematic cross sectional view of an embodiment of an optochemical sensitive element 308 for measuring the temperature and two parameters in a measurement medium. A first sensing layer 328 and a second sensing layer 330 are applied to a first surface 324 and second surface 326 of a substrate 322 respectively. The first sensing layer 328 comprises a first indicator 336 immobilized in a first polymer matrix 332 and a second indicator 340 immobilized in a third polymer matrix 335. In a further embodiment, the first indicator 336 and the second indicator 340 are immobilized in the same polymer matrix.

[0075] The second sensing layer 330 comprises a temperature sensitive indicator 338 immobilized in a second polymer matrix 334. The composition of the first, second and/or third polymer matrix (332, 334, 335) can be the same or can differ. Examples of materials suitable as polymer matrices for either of the first, second or third polymer matrices are as follows: polystyrene film, cyclic olefin copolymer (COC) such as ethylene-norbornene copolymer, cyclic olefin polymer (COP) or poly(n-methyl methacrylimide) (PMMI) or a combination thereof. Alternatively, the second sensing layer 330 can employ silicone polymers for its polymer matrix composition.

[0076] The first indicator 336 present in the first sensing layer 328 is sensitive to a first parameter in a measurement medium 304 and the second indicator 340 present in the third sensing layer 335 is sensitive to a second parameter in the measurement medium 304. The temperature sensitive indicator 338 allows the measurement of the temperature in the measurement medium 304 thus allowing for temperature compensated measurements of the first and/or second parameters of interest present in the measurement medium 304.

[0077] In a further embodiment of an optochemical sensitive element 408, a first sensing layer 428 comprising three indicators for measuring three parameters is shown in FIG. 4. A first indicator 436, a second indicator 440 and a third indicator 442 are immobilized in a first polymer matrix 432. This first sensing layer 428 is applied on a first surface 424 of a substrate 422 and a second sensing layer 430 comprising a temperature sensitive indicator 438 immobilized in a second polymer matrix 434 is applied on a second surface 426 of the substrate 422.

[0078] In principle, it is possible to determine the concentration of different parameters in a measurement medium by photoluminescence quenching so long as the indicator is sensitive in regards to the parameter of interest.

[0079] FIGS. 5A and 5B show a cross sectional side view and top view respectively of an embodiment showing an arrangement of a second sensing layer 530 of an optochemical sensitive element 508. The first sensing layer 528 is arranged on a first surface 524 of a substrate 522. Preferably, the first sensing layer 528 covers the entire surface area of the first surface 524 of the substrate 522. The second sensing layer 530 is arranged on a portion of a second surface 526 of the substrate 522.

[0080] FIG. 5B provides a top view of the section of the optochemical sensitive element as shown in FIG. 5A. Preferably, the second sensing layer is arranged on half of the area of the second surface 526 of the substrate 522, as clearly depicted in FIG. 5B.

[0081] FIGS. 6A and 6B show a cross sectional side view and top view respectively of an embodiment showing an arrangement of a second sensing layer 630 of an optochemical sensitive element 608. The second sensing layer 630 of the optochemical sensitive element 608 is arranged as a particular shape to cover a portion of a second surface 626 of a substrate 622. Preferably, the second sensing layer 630 is arranged in the shape of an annular ring 630 on the surface 626 of the substrate 622 as can be clearly seen in FIG. 6B. The outer radius of the second sensing layer 630 is approximately equal to the outer radius of the substrate 622 such that the annular ring shaped second sensing layer 630 is arranged concentrically with the substrate 622.

[0082] FIGS. 7A and 7B show a cross sectional side view and top view respectively of an embodiment showing an arrangement of a second sensing layer 730 of an optochemical sensitive element 708. In this embodiment, the second sensing layer 730 is arranged as having a particular shape to cover a portion of a second surface 726 of a substrate 722. Preferably, the second sensing layer 730 is arranged in the shape of a disc 730. Therefore, in this case the outer radius of the second sensing layer 730 is lesser than the outer radius of the substrate 722, such that the disc shaped second sensing layer 730 is arranged concentrically with the substrate 722 as seen in FIG. 7B.

[0083] In a further embodiment, the shape of the second sensing layer 730 is from any of the following but not limited to these shapes or geometries: rectangular, hexagonal, circular, triangular, square-formed or polygonal.

[0084] The embodiments shown in FIGS. 5 to 7 are advantageous because an increased amount of emitted photoluminescence can be received by a detector from the first sensing layer since only a portion of a substrate of an optochemical sensitive element is covered by the temperature sensitive second sensing layer thereby resulting in higher luminescence yields and faster response times, in particular for a first indicator present in the first sensitive layer facing the measurement medium.

[0085] In a further embodiment, shown in FIG. 8, an optochemical sensitive 808 element comprises at least one cover layer that is applied over a first sensing layer 828. This embodiment of the optochemical sensitive element 808 comprises at least a first cover layer 844. The first cover layer 844 is arranged on the first sensing layer 828 and it serves as a light reflection layer. Such an arrangement is advantageous because the first cover layer 844 essentially reflects almost all excitation radiation back into the sensitive layer. This arrangement particularly helps in achieving a higher luminescence yield and provides a measuring device with shorter response times. An example of a suitable material as a light reflection layer is white silicone, preferably doped with metallic particles.

[0086] As shown in FIG. 8, the optochemical sensitive element 808 can further be covered with a second cover layer 846 that is arranged on the first cover layer 844. In this case, the second cover layer 846 serves as a stray light protection layer and is for example a black silicone layer comprising carbon. The advantageous feature of including the stray light protection layer as the second layer is that it blocks stray light that could possibly enter from the medium and interfere with the measurement results.

[0087] The first 844 and second 846 cover layers are preferably permeable to the parameter to be measured.

[0088] An optochemical sensor preferably comprises a sensitive element according to the invention, which can be releasably housed or attached to the sensor housing. This essentially allows the optochemical sensitive element to be replaced or exchanged when a parameter sensitive indicator within the optochemical sensitive element is used up or has aged.

[0089] A method to produce an optochemical sensitive element to determine at least two parameters in a measurement medium comprising the following steps: providing a substrate having at least a first surface and at least a second surface. Further, the method involves applying a first sensitive layer on the first surface of the substrate using a first application technique wherein the first sensing layer comprises a first indicator immobilized in a first polymer matrix to determine a first parameter in the measurement medium. The method further comprises the step of applying a second sensing layer on the second surface of the substrate using a second application technique wherein the second sensing layer comprises a temperature sensitive indicator immobilized in a second polymer matrix to determine temperature of the measurement medium. The optochemical sensitive element is prepared according to the above mentioned steps such that the first sensing layer applied to the first surface of the substrate is configured to be opposite to the second sensing layer applied to the second surface of the substrate.

[0090] The first sensing layer and the second sensing layer can be applied by any one of the following application techniques of spin coating, dip coating, blade coating or screen printing. In an embodiment, the application techniques of the first and the second sensing layers are different from each other. This is particularly advantageous when different application methods are better suited to the polymer matrix comprising the suitable indicator.

[0091] In another embodiment, the first sensing layer sensitive to dissolved oxygen is applied by spin coating to the first surface of the substrate. In a further preferred embodiment, the second sensing layer comprising the temperature sensitive indicator is applied by means of blade coating to the second surface of the substrate.

[0092] In a further embodiment, the first sensing layer comprises two or more indicators that are immobilized on different polymer matrices. Each sensitive region or spot can be applied individually by any one of the application techniques over the substrate, preferably by an application technique that is well suited for forming film comprising the polymer matrix and the corresponding immobilized indicator.

[0093] The method further includes a step wherein the optochemical sensitive element is arranged in an optochemical sensor such that the first sensing layer faces the measurement medium whereas the second sensing layer faces away from the measurement medium.