WO2007045440A1

WO2007045440A1 - Sensor and method for optically detecting a chemical substance

Info

Publication number: WO2007045440A1
Application number: PCT/EP2006/010011
Authority: WO
Inventors: Hilmar Franke; Davor Kosanic
Original assignee: Universität Duisburg-Essen
Priority date: 2005-10-17
Filing date: 2006-10-17
Publication date: 2007-04-26
Also published as: DE102005055288A1

Abstract

The invention relates to a sensor (1) and to a method for optically detecting a chemical substance, in particular, a polar gas. Said sensor (1) comprises only one connection (5) for an optical wave guide (6) for the inlet and outlet of, preferably, broadband light or white light. A sensor element (3) of the sensor (1) forms an optical resonance system which works based on the combination of tunnelling modes and surface plasmon resonance and which is radiated twice by the light prior to the detection thereof. Said sensor (1) can be used universally, for example, as an alcohol tester or as a contactless switch.

Description

Sensor and method for the optical detection of a chemical substance

The present invention relates to a sensor for optical detection of a chemical substance according to the preamble of claim 1, a method for optically detecting in particular polar gases and uses of the sensor or method.

The present invention is concerned with the optical detection of chemicals, in particular gases. The term "detection" or "detecting" is here in particular not only the determination of the presence of the respective substance, but also the (possible) determination of the absolute content, the relative proportion and / or the distinction between different substances To understand isomers or the like.

The article "Selective optical detection of aromatic vapors" by Robert P. Podgorsek et al., Published in "Applied Optics", Vol. 41, No. 4, pp. 601-608, of Feb. 1, 2002, which is the starting point of the present Invention discloses a sensor for the optical detection of aromatic vapors. The sensor has a prism in the form of a right-angled triangle, which has a sensor element on one side of the catheter and is mirrored on the other side of the catheter. The sensor element forms an optical resonance system and consists of an intermediate layer of silver and a polymer film of Teflon. The polymer layer is sufficiently porous so that aromatic gases, such as xylenes, can diffuse into it. The gas front of the gas molecules diffusing into the polymer layer is optically detectable. Polarized laser light is introduced into the prism via the hypotenuse and falls obliquely onto the sensor element, from which it is reflected or deflected onto the mirrored side of the catheter and from there to a detection system. The reflection at the sensor element depends on the wavelength and on the gas front or gas concentration in the polymer layer with corresponding polarization of the light due to leak modes and surface plasma resonances. Thus, a very selective optical detection of aromatic gases or vapors is possible. Further, in particular theoretical details for the optical determination of molecular diffusion coefficients in polymer films and for optimized leak-mode spectroscopy can be found in the articles "Optical Determination of Molecule Diffusion coefficients in Polymer Films" by RP Podgorsek et al., Published in "Applied Physics Letters", Vol 73, no. 20, pages 2887 to 2889, 16 November 1998, and "Optimized leaky mode spectroscopy with a single planar film" by M. Leitz et al., Published in "Applied Physics Letters", Vol. 77, No. 17, pages 2674 to 2676, of October 23, 2000.

No. 5,815,278 A discloses an optical sensor for surface plasmon spectroscopy with broadband light or white light. The light is coupled into a waveguide via one half of a spherical collimator and reflected at the end of the waveguide. The reflected light is directed across the other half of the collimator on a receiver for spatial resolution of the reflected light. A sensor element is arranged laterally on the waveguide for interaction with the light in the waveguide. Accordingly, only the surface plasmon resonance is utilized here.

WO 97/15820 A1 relates to a surface plasmon resonance sensor. Only one metal layer (50 nm gold) is used to obtain a plasmone. All arrangements require two optical connections, namely an input and an output.

US 5,640,234 A discloses a sensor for the detection of chemical substances. Light is passed through a planar layer. For coupling and decoupling two optical connections are required. It uses the so-called cut-off principle, which consists of a critical change in the thickness of the conductor material. This change in thickness is achieved by swelling the conductor material in the presence of a gas to be measured or a liquid to be measured.

DE 33 44 019 A1 discloses arrangements for the optical measurement of

Concentrations. The actual measuring chambers are irradiated by the measuring light, so that the measurement of the effective light path in the measuring chamber depends. Various constructions are proposed, each requiring an optical input and an optical output.

The present invention has for its object to provide a sensor for optical detection of a chemical substance, a method for optically detecting a particular polar gas and uses of the sensor or method, with a simple, inexpensive construction and low cost a very fast, sensitive and / or selective

Detection of chemical substances, especially gases, most preferably polar gases, such as humidity, is possible.

The above object is achieved by a sensor according to claim 1, a method according to claim 20 or a use according to claim 25 or 26. Advantageous developments are the subject of the dependent claims.

According to the proposal, the sensor element forming an optical resonance system is irradiated twice by the light before its detection. This is a very high sensitivity or selectivity beneficial and very easy to implement.

The double irradiation results in particular from the fact that in a direction of incidence obliquely directed to the sensor element light is reflected by this and then reflected back to the sensor element, to then be reflected back into the direction of incidence of the sensor element. Accordingly, this "dual irradiation" is also particularly well suited for combination with only a single terminal and optical fiber for the supply and discharge of light.

Another aspect of the present invention is to provide the sensor with only a single terminal for a light guide for the supply and dissipation of light, in particular broadband light or white light. This allows a very simple, inexpensive and compact design.

Accordingly, the sensor can be made very compact and simple. Another aspect of the present invention is to use broadband light or white light, which is then reflected to different degrees depending on the wavelength or wavenumber due to the combination of leakage modes and Oberflächenplamononenresonanz of the optical resonance system formed by the sensor element. In a simplest variant, preferably only the detection of the reflectivity (intensity) takes place only in a narrow frequency bank with a fixed angle of incidence of the light on the sensor element or the detection layer and, moreover, the detection of a chemical substance, in particular one into the sensor element or its detection layer diffusing gas, such as humidity.

The combination of the double irradiation with the use of broadband light or white light is likewise very advantageous since this combination leads to a very high sensitivity or selectivity with little effort.

Another aspect of the present invention is to use an ionomer such as Nafion (trademark of DuPont) or polyimide as a detection layer for detection of polar chemicals, especially polar gases. Experiments have shown that especially water, propanol and / or ethanol or their gases or vapors can be detected very quickly with high sensitivity or selectivity.

Compared with the prior art, in the present invention, the measuring spot and thereby also the sensor can be decisively miniaturized, a very compact design can be realized with only one optical connector, a local change of an optical resonator layer can be detected, an amplification of the leakage wave resonance by a metal film can be achieved in an adjacent layer of a dialectic and / or a very narrow spectral width in the range of a resonance and thus a high selectivity can be achieved.

Further aspects, features, properties and advantages of the present invention will become apparent from the following description of preferred exemplary embodiments with reference to the drawing. It shows: 1 is a schematic representation of a proposed sensor according to a first embodiment with an associated evaluation device;

FIG. 2 is a schematic sectional view of the sensor with a sensor element; FIG. and

Fig. 3 is a schematic representation of a proposed sensor according to a second embodiment with an associated

Evaluation.

In the figures, the same reference numerals are used for the same or similar parts, even if a repeated description is omitted for simplicity reasons.

1 shows a schematic representation of a proposed sensor 1 according to a first embodiment with an associated device 2 for the supply of light and evaluation.

The sensor 1 is used for the optical detection of a chemical substance, in particular a gas, more preferably a polar gas or polar gas molecules, for example of water, propanol, ethanol or the like and in particular of water vapor, humidity, alcohol vapors, ethanol vapors or the like.

In the illustrated example, the sensor 1 and the device 2 are formed as separate parts. This allows in particular an optimal miniaturization of the sensor 1. However, it is also possible to integrate the device 2 in the sensor 1.

The sensor 1 has a sensor element 3, which lies in a light path 4 or is irradiated by light. In particular, the light is supplied only via a single connection 5 and a light conductor 6 connected or connectable thereto. The sensor 2 is preferably operable with white light or broadband light, which can be generated as required by an LED. Alternatively, however, also relatively or very narrow-band light, for example, by an LED, in particular with about ± 20 nm, or laser light can be used.

In the illustrated embodiment, the generation of the light takes place in the device 2, for example with a light-emitting diode, to which the light guide 6 is connected for supplying the light to the sensor 2.

The light guide 6 is preferably separable from the sensor 1. However, the light guide 6 may also form part of the sensor 1, in particular be structurally fixed thereto.

The sensor 1 has a light-guiding body 7, in particular made of glass or another suitable transparent material.

In the first embodiment, the light guide body 7 is formed as an angle prism, in particular in the form of a right-angled triangular prism. However, it may also be in particular a different isosceles triangle prism.

The supply and discharge of light via a side of the catheter or a side of the two legs of equal length. The sensor element 3 is arranged on the hypotenuse side or on the side connecting the two legs of equal length.

The supplied or incident light passes from the terminal 5 within the optical waveguide 7 to the hypotenuse where it meets the sensor element 3 at an angle of incidence α. The structure, the function and the operation of the sensor element 3 will be explained later with reference to FIG. 2 in detail.

The light is reflected after interaction with the sensor element 3 of this again, and indeed at the corresponding angle α to the other side of the catheter or leg side of the light guide 7. At least in this area, the light guide 7 is mirrored or another mirror arranged so that the light from there back to the sensor element 3 again. is valid. The light thus strikes again or for the second time on the sensor element 3, in particular in the region of the light impinging on the sensor element 3 from the connection 5, that is to say of the incident light. This rear reflection or the second impingement of the light on the sensor element 3 is referred to in the present invention as "second irradiation" or "twice irradiated" and is particularly preferred. The second irradiation causes the light to interact again with the sensor element 3 and thus a particularly high sensitivity or selectivity can be achieved.

The light is then reflected back from the sensor element 3 to the terminal 5 and passed through the terminal 5 and the light guide 6 to the device 2, in which a receiver, not shown, is arranged.

2 shows, in a schematic, fragmentary section, the light guide body 7 with the sensor element 3 arranged directly on the hypotenuse side. The sensor element 3 forms, in particular, an optical resonance system.

The sensor element 3 is preferably formed as a layer system, which is particularly preferably coated directly on the light guide 7. This allows a simple and inexpensive production. However, any other coupling of the sensor element 3 to the light is possible.

The sensor element 3 has a detection layer 8, which is preferably porous. A chemical substance 9 to be detected can diffuse into the detection layer 8, as indicated schematically by arrows in FIG. 2. The substance 9 is present in particular in gaseous form. However, in principle it is also possible for the detection layer 8 to be in direct contact with a liquid phase which diffuses into the detection layer 8.

Due to the change in the optical properties of the sensor element 3 or the detection layer 8 that accompanies the diffusion, a determination of the diffusion coefficient and / or other parameters is possible. Due to these diffusion coefficients or parameters, a detection of a specific substance can take place. This is not only true when diffusing into the Detection layer 8, but also during the out-diffusion from the diffusion layer. 8

The detection layer 8 is preferably made of an ionomer, in particular of the polymer material available under the trade name Nafion from DuPont, or of polyimide.

A very uniform detection layer 8 with the desired thickness of preferably 0.1 to 10 .mu.m, in particular 1 to 5 .mu.m, is achieved according to a particularly preferred embodiment by so-called spin coating.

The sensor element 3 further has an intermediate layer 10, which in particular serves to adapt the refractive index. The intermediate layer 10 preferably contains or consists of metal, in particular gold, silver and / or aluminum. The thickness of the intermediate layer 10 is preferably 5 to 100 nm, in particular 10 to 70 nm.

The sensor element 3 interacts with the incident light in the form of leakage modes in combination with Oberflächenplasmonenresonanzen. Accordingly, the reflectivity varies depending on both the wavelength or wavenumber and on the chemical substance to be detected or its diffusion within the detection layer 8. For details and possibilities, also with regard to the evaluation or detection and detection in the aforementioned sense is referred to as supplementary disclosure to the aforementioned articles, which are hereby incorporated by reference. These items are also to be found in more detail, for example, with regard to the polarization of the light.

The device 2 preferably has a fiber spectrometer, not shown, in order to evaluate the information. Alternatively, the device 2 may comprise a photodiode for detecting the information, in particular when exciting in a small wavelength range or working with narrow-band light or laser light. The light guide 6 preferably terminates in the device 2 in the form of a Y-type optical fiber. Light, for example a halogen lamp or a light-emitting diode, is coupled into the fiber via one end of a fiber and conducted to the sensor 1. After the measurement information has been recorded in the light spectrum, the light is returned to the device 2 and preferably via the other fiber to the fiber spectrometer, not shown, or any other suitable measuring device in the device 2, where the information is evaluated in the illustrated sense , In principle, an intensity meter can also be sufficient for the evaluation.

For collimating, the sensor 1 preferably has a collimator 11, which is integrated into the connection 5, for example.

For the polarization of the light in the desired manner - in Fig. 1 perpendicular to the plane - the sensor 1 has a preferably foil-like polarizer 12, which is arranged in the representation example between the terminal 5 and light guide 6 on the one hand and the sensor element 3 or the Lichtleitkörper 7 on the other , This allows a simple, compact and inexpensive construction.

In the first embodiment of the sensor 1, the angle of incidence α of the light is fixed. It is chosen so that the desired detection is possible. Using white light or very broadband light eliminates the need to tune the wavelength of the light.

Experiments have shown that, in particular with the particularly preferred Nafion or polyimide and with the structure described, a very high sensitivity or selectivity can be achieved with a high reaction rate.

The sensor 1 and the method can detect, for example, water vapor with high sensitivity and selectivity. The sensor 1 and the method described allow such a high sensitivity and rapid response that, for example, the increased humidity upon approach of a person, in particular a hand or a finger, can be detected. Accordingly, the sensor 1 or the described method according to a special ders preferred variant for a proximity sensor, proximity switch, other non-contact switch, such as a threshold, or the like used. Thus, for example, the approach of a person or an animal to the sensor element 3 can be detected in a very simple, inexpensive and effective manner.

But it is also possible to detect the skin moisture when touching the sensor element 3 by means of the sensor 1 and the method. This can then be evaluated, for example, to detect a touch or used for other purposes.

According to another preferred variant, the sensor 1 or the method can also be used for an alcohol test. Namely, if the sensor 1 or the method is suitably matched, it is possible to detect alcohol fumes, in particular ethanol gases, in the respiratory air or possibly even from the skin of a person, in particular in order to determine the alcohol content in the blood.

In the following, a second embodiment of the proposed sensor 1 will be explained with reference to FIG. 3, wherein only essential differences from the first embodiment will be discussed. The statements and explanations to the first embodiment therefore apply correspondingly or in addition.

In the second embodiment, the light guide 7 preferably has the shape of a half-cylinder prism. The terminal 5 is movable relative to the light guide 7 on a circular path, as indicated by the double arrow. Accordingly, the incident angle α is adjustable in the second embodiment. Thus, a suitable angle for a given material configuration can be found in a very simple way.

Optionally, a diaphragm 13 is provided in order to block off beam portions which arise due to reflection or refraction on the curved prism surface.

Claims

claims:

A sensor (1) for optically detecting a chemical substance, in particular a gas, comprising a sensor element (3) which lies in a light path (4) and forms an optical resonance system, the detection being based on leak modes and surface plasmon resonance or detection of the reflectivity of the sensor element (3), characterized in that the sensor element (3) can be irradiated twice by the light before its detection.

2. Sensor according to claim 1, characterized in that the sensor element (3) is irradiated twice in the same area or at the same location from the light.

3. Sensor according to claim 1 or 2, characterized in that the sensor (1) has only a single terminal (5) for a light guide (6) for the supply and discharge of light.

4. Sensor according to claim 3, characterized in that the sensor (1) is designed such that in particular via the terminal (5) or light guide (6) supplied light obliquely in a direction of incidence on the sensor element (3), from this is reflected and then reflected back to the sensor element (3) for the second irradiation, to be reflected again in the direction of incidence and in particular via the terminal (5) or light guide (6) to be derived.

5. Sensor according to claim 3 or 4, characterized in that the terminal (5) or light guide (6) serves both the supply of light, in particular broadband light or white light, as well as the derivative of reflected light to its detection or evaluation ,

6. Sensor according to one of claims 3 to 5, characterized in that the connection (5) is arranged fixed or adjustable relative to the sensor element (2).

7. Sensor according to one of the preceding claims, characterized in that the angle of incidence (α) of the light on the sensor element (3) is fixed or adjustable and / or that the sensor (1) for detecting a polar or non-polar gas and / or Detection of water, propanol or ethanol is formed.

8. Sensor according to one of the preceding claims, characterized marked, that the sensor (1) with white light or broadband light is operable.

9. Sensor according to one of the preceding claims, characterized in that the sensor (1) has a light guide body (7), in particular made of glass or another transparent material, such as plastic, which is preferably designed as an angular or half cylinder prism.

10. Sensor according to claims 3 and 9, characterized in that the connection (5) is connected directly or indirectly to the light guide body (7).

11. Sensor according to claim 9 or 10, characterized in that the sensor element (3) is arranged on the light guide body (7), in particular forms a coating of the light guide body (7).

12. Sensor according to any one of claims 9 to 11, characterized in that the light guide body (7) is at least partially mirrored to reflect light back to the sensor element (3).

13. Sensor according to one of the preceding claims, characterized marked, that the sensor element (3) has a preferably porous detection layer

(8), in which a chemical substance to be detected (9), in particular gaseous, can diffuse.

14. Sensor according to claim 13, characterized in that the detection layer (8) contains or consists of a polymer, in particular Teflon, ionomer or polyimide.

15. Sensor according to claim 13 or 14, characterized in that the detection tection layer (8) has a thickness of 0.1 to 10 .mu.m, in particular 1 to 5 .mu.m.

16. Sensor according to one of the preceding claims, characterized in that the sensor element (3) has an intermediate layer (10), in particular for adjusting the refractive index.

17. Sensor according to claim 16, characterized in that the intermediate layer (10) metal, in particular gold, silver and / or aluminum, contains or consists thereof.

18. Sensor according to claim 16 or 17, characterized in that the intermediate layer (10) has a thickness of 5 to 100 nm, in particular 10 to 70 nm.

19. Sensor according to one of the preceding claims, characterized in that the sensor (1) comprises a collimator (11), a preferably foil-like polarizer (12) and / or a diaphragm (13), in particular between a connection (5). or light guide (6) and the sensor element (3) or a light guide body (7) of the sensor element (3).

20. A method for optically detecting a particular polar gas, wherein in a detection layer (8) of an ionomer or polyimide diffusing gas molecules are detected optically for the detection of a polar gas.

21. The method according to claim 20, characterized in that the detection onsschicht (8), in particular together with an associated intermediate layer (10), forms an optical resonance system, in particular for optical detection, the resonance system is irradiated twice before light of the detection.

22. The method according to claim 20 or 21, characterized in that the optical detection is based on leak modes or Oberflächenplasmonenresonanz.

23. The method according to any one of claims 20 to 22, characterized in that the detection layer (8) with light, in particular broadband light or white light, from an incident direction - optionally via an intermediate layer (10) - obliquely irradiated, wherein the light of the detection layer (8) or intermediate layer (10) is reflected and then reflected back and finally reflected back in the direction of incidence.

24. The method according to any one of claims 20 to 23, characterized in that the reflectivity of the detection layer (8) is detected as a function of the wavelength or spectroscopically and used to detect a gas.

25. The use of a sensor (1) according to any one of claims 1 to 19 and / or a method according to any one of claims 20 to 24 for a proximity sensor or non-contact switch, in particular a threshold, wherein a local increase in humidity when approaching a person or a Animal to the sensor element (3) or the skin moisture when touching the sensor element (3) by means of the sensor (1) or method detected and evaluated to detect an approach or contact.

26. Use of a sensor (1) according to any one of claims 1 to 19 and / or a method according to any one of claims 20 to 24 for an alcohol test, wherein alcohol vapor in the air or from the skin of a person by means of the sensor (1) or Detected method, in particular to determine therefrom the alcohol content in the blood.