EP1141687A1 - Measuring probe and method for measuring the concentration of agents in gases and/or liquids - Google Patents

Measuring probe and method for measuring the concentration of agents in gases and/or liquids

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Publication number
EP1141687A1
EP1141687A1 EP99959234A EP99959234A EP1141687A1 EP 1141687 A1 EP1141687 A1 EP 1141687A1 EP 99959234 A EP99959234 A EP 99959234A EP 99959234 A EP99959234 A EP 99959234A EP 1141687 A1 EP1141687 A1 EP 1141687A1
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EP
European Patent Office
Prior art keywords
measuring
measuring probe
agents
concentration
gases
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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EP99959234A
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German (de)
French (fr)
Inventor
Gerlinde Bischoff
Robert Bischoff
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Individual
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Individual
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Publication of EP1141687A1 publication Critical patent/EP1141687A1/en
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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T436/00—Chemistry: analytical and immunological testing
    • Y10T436/11—Automated chemical analysis

Definitions

  • the invention relates to a measuring probe of a measuring device and an associated measuring method for measuring the concentration of agents in gases and / or liquids.
  • the measuring device uses the change in electrical properties.
  • the substances to be examined are brought into contact with the surface of the measuring device.
  • the substance applied changes the conductivity of the surface of the measuring device as a function of its concentration.
  • G01N 27/00 the analysis of substances using electrical methods.
  • G01N 27/12 specifically considers resistance tests that change the resistance of a solid body depending on the absorption of a liquid. For this purpose, measuring probes with electrodes are used, which are considered in G01N 27/07.
  • such measuring probes of the measuring devices consist of two suitably shaped electrodes, which are fastened on a carrier, and the conductivity of a suitable substance between them is determined as an indirect measured variable for determining the concentration of the agents to be examined.
  • various, mostly specially optimized, substances are used, to which the substances to be adsorbing agents.
  • the substance itself has a certain electrical conductivity, which changes as a result of the absorption and physical binding of the agents serving as adsorbents.
  • Suitable substances are organic and inorganic semiconducting substances whose relative change in conductivity due to the adsorption of these agents is sufficiently large.
  • both narrow-band and broad-band selectively acting substances are known.
  • the change in the electrical conductivity is used to determine the concentration, since in the measuring range used there is a monotonous relationship with the concentration. It is possible to use an alternating field to measure the change in electrical conductivity and its other characteristic values, e.g. specific complex loss angle to be used in addition for the evaluation.
  • the usable conductivity range can be represented in a suitable conductivity of the measuring probe by a suitable design of the electrodes.
  • the proportionate influence of the adsorption on the part of the substance used for the measurement can be changed by a suitable design of the surface, for example pores, between the electrodes.
  • the adsorption time is determined in particular by the type of substance layer and the substance temperature.
  • a large number of such measuring probes for determining the concentration of various agents in gases are produced on ceramic carriers using organic semiconducting substances, preferably polymers. Due to the high air humidity and the high surface tension of water the substances of such measuring probes are provided with a thin film of water in a standard atmosphere. Because of its own conductivity, this results in an overall conductivity of the measuring device which is approximately an order of magnitude higher than that of the substances used. In order not to falsify the measurement result due to the absorption of moisture, such measuring probes are provided with a heating element or a separate temperature control, which heat the substance in such a way that the moisture film evaporates completely. As a result, these measuring probes necessarily work with the
  • the usable measuring range extends with respect to the
  • EP 0 328 108 A3 describes an electrochemical sensor for measuring the concentration of a chemical substance in a solution, two field effect transistors and a reference electrode on a substrate are arranged. A hydrogel is arranged as an "electrode" over the area of the channel of one of the two FETs and the reference electrode. Enzymes are used for substance detection which control the FET by changing the conductivity in the electrode. The detection of the type and concentration of the substance in the solution is done by evaluating the signal from the FET.
  • This sensor is only suitable for the determination of relatively high concentrations in the range of a few ppm of substances in solutions. Agents in gases cannot therefore be adequately determined. Concentrations of only a few, selected substances can be determined.
  • the hydrogel of the sensor can easily be irreversibly contaminated with interfering substances, which makes the sensor unusable. Due to the microstructures, complex microelectronic technologies are required to manufacture the sensor.
  • the object of the invention is to develop a measuring probe and an associated measuring method which, while overcoming the above disadvantages, realizes a sensitive measuring probe for the detection of agents and their concentration in gases and / or liquids, these under different real measuring conditions without additional effort can be used and no heating element is required.
  • the essence of the invention lies in the fact that a measuring probe in the form of a two-pole system is used to determine the electrical resistance of a sensor-active layer, in which a cover film is specifically formed from a liquid, for example water, which is formed over the substance of the sensor-active layer. is included in the active zone of the measuring probe.
  • the cover film thus provides a combination of different partial conductivities, in particular the substance, the cover film and the active surface which forms between the two.
  • molecules of the cover film are available as adsorbate for the agent of a gas or a liquid to be determined. With the targeted selection of the liquid for the Cover film, the adsorption properties can be optimized for certain agents.
  • the measuring method according to the invention is specially designed for the measuring probe according to the invention. This is basically operated in saturation with regard to the adsorption of the liquid in the diffusion layer. In the basic state (0% agent + liquid in saturation) there is a comparatively high conductivity. In the presence of certain agents, depending on the type, these cause a hindrance / promotion of the movable load carriers or reduce / increase the number of movable load carriers. In this way, even the slightest traces of the gas to be detected have a potentiated influence on the electrical conductivity of the measuring probe and drastically reduce / increase the conductivity; the effect of reversible doping occurs on the surface of the measuring probe. This effect is effective even at relatively low concentrations of the agents to be determined and increases with increasing concentration of the agent.
  • the result is a differential conductance of the measuring probe which decreases / rises with respect to the basic state.
  • this can be used after a previous calibration to calculate the concentration of the specific agents.
  • an equivalent circuit diagram of this sensor is advantageously used, which represents this as an electrical two-pole connection.
  • the complex substitute sizes required for the description in the measurement window preferably correlate with the resistances and the thicknesses of the individual layers.
  • the advantages of the invention consist in particular in the fact that the sensitivity of the measuring method is higher by at least two powers of ten compared to measuring probes without a cover film over the substance, the detection limit for agents to be determined is thus in the ppt (parts per trillion) range of the concentration of the agent. It is possible to carry out measurements under real conditions without additional effort, for example at room temperature in a normal atmosphere or inside the body of living beings. Long-term measurements for the continuous monitoring of concentrations of certain agents can be carried out without complicated equipment.
  • measuring probes can be combined with other measuring probes in order to be able to take into account the influence of these parameters in the calculation in the method according to the invention, for example by determining the temperature and / or the humidity.
  • measuring probes can be combined, for example, in an array with different structural dimensions and / or substances in order to include the selective properties of the substances with respect to certain agents in the analysis.
  • sensors of this type are integrated on the carrier directly into the circuit of a controllable semiconductor element, such as, for example, the base or gate circuit. Further possibilities for using the measurement results of concentrations of certain agents arise when they are passed on to IT recipients via IT networks or telecommunications equipment to authorized recipients.
  • FIG. 1 as a basic structure of the measuring probe.
  • FIG. 2 as an equivalent circuit diagram of the measuring probe.
  • a measuring probe 1 for agents in gases consists of a pair of electrodes 2, which are partially applied to a carrier 3, which can be designed as a surface elevation.
  • a suitable solid substance 4 in particular an organic semiconductor in the form of a polymer, which reacts to the adsorption of certain agents 5 with a sufficient change in the conductivity, is located in a layered manner above this surface structure.
  • the agents 5 to be analyzed are in a gas phase 6, which as the surroundings of the measuring probe spreads over the surface of the measuring probe 1.
  • a cover film 7 made of water, which is formed by the finite atmospheric humidity of the gas phase 6.
  • an equivalent circuit diagram for the individual layers and thicknesses of the measuring probe can be adopted in the form of a resistance network, which maps the measuring probe as an electrical two-pole connection in the permissible measuring window.
  • Such an equivalent circuit diagram is preferably used as the basis for the calibration of the measuring probe 1 and the determination of the concentration of the agents 5 to be analyzed based thereon. This enables, in particular, non-linear imaging on essentially independent basic values that strongly correlate with the geometric design of the measuring probe. By using complex substitute variables in the form of resistors, the behavior in the alternating electrical field is also described.
  • a parallel connection between an active and a reactance in each case characterizes the sheet resistances for the carrier 3, the substance 4, the active surface 8, the cover film 7 made of water and the gas phase 6 as well as a replacement resistor I 9, essentially depending on the thicknesses of the Electrodes 2 and the substance 4, an equivalent resistor II 10, essentially dependent on the thickness of the active surface 8 and an equivalent resistor III 11, essentially dependent on properties of the cover film 7.
  • the thickness of the cover film 7, for example of water, is essentially dependent on the Temperature dependent.
  • the individual sheet resistors are each connected in parallel, the equivalent resistors [9, 10, 11] being arranged on both sides between the sheet resistances of substance 4, active surface 8, cover film 7 and gas phase 6.
  • the change in the overall conductivity of the sensor is registered via lines from the electrodes 2 and recorded and evaluated to determine the concentration of the agent.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
  • Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)

Abstract

The invention relates to a sensitive measuring probe (1) and an associated measuring method for detecting agents and the concentration thereof in gases and/or liquids. The inventive measuring probe can be used in a wide range of different real measuring conditions without any additional measures, and no heating element is required. To this end, a liquid cover film (7) is provided over the sensor-active layer of a measuring probe (1). Said cover film is integrated into the active area of the measuring probe (1) and the combination of different partial conductance values, especially the substance (4), the cover film (7) and the active surface (8) which forms between the two is used to establish the overall conductance value without compensation.

Description

Meßsonde und Verfahren zur Messung der Konzentration von Agenzien in Gasen und/oder FlüssigkeitenMeasuring probe and method for measuring the concentration of agents in gases and / or liquids
Die Erfindung bezeichnet eine Meßsonde einer Meßvorrichtung und ein zugehöriges Meßverfahren zur Messung der Konzentra- tion von Agenzien in Gasen und/oder Flüssigkeiten. Dabei nutzt die Meßvorrichtung die Veränderung von elektrischen Eigenschaften. Zur Messung werden die zu untersuchenden Substanzen mit der Oberfläche der Meßvorrichtung in Verbindung gebracht . Die aufgebrachte Substanz verändert in Ab- hängigkeit ihrer Konzentration die Leitfähigkeit der Oberfläche der Meßvorrichtung.The invention relates to a measuring probe of a measuring device and an associated measuring method for measuring the concentration of agents in gases and / or liquids. The measuring device uses the change in electrical properties. For the measurement, the substances to be examined are brought into contact with the surface of the measuring device. The substance applied changes the conductivity of the surface of the measuring device as a function of its concentration.
Es ist bekannt, daß mit Hilfe von Widerstandsmessung die Konzentration verschiedener Agenzien bestimmt werden. So wird bsw. in der IPC (Internationale Patentklassifikation) G01N 27/00 die Analyse von Stoffen durch Anwendung elektrischer Methoden beschrieben. Unter G01N 27/12 werden speziell Widerstandsuntersuchungen betrachtet, die den Widerstand eines festen Körpers in Abhängigkeit der Absorption einer Flüssigkeit verändern. Verwendet werden dazu Meßson- den mit Elektroden, die in G01N 27/07 betrachtet werden.It is known that the concentration of various agents can be determined with the aid of resistance measurement. So bsw. described in the IPC (International Patent Classification) G01N 27/00 the analysis of substances using electrical methods. G01N 27/12 specifically considers resistance tests that change the resistance of a solid body depending on the absorption of a liquid. For this purpose, measuring probes with electrodes are used, which are considered in G01N 27/07.
Es ist weiter bekannt, daß derartige Meßsonden der Meßvorrichtungen aus zwei geeignet geformten Elektroden, die auf einem Träger befestigt sind, bestehen und die Leitf higkeit einer geeigneten Substanz zwischen diesen als mittelbare Meßgröße zur Bestimmung der Konzentration der zu untersuchenden Agenzien bestimmt wird. Abhängig von den zu untersuchenden Agenzien werden verschiedene, meist speziell optimierte, Substanzen verwendet, an welche sich die zu un- tersuchenden Agenzien adsorbieren. Dabei weist die Substanz selbst eine gewisse elektrische Leitfähigkeit auf, die sich durch die Aufnahme und physikalische Bindung der als Adsor- bat dienenden Agenzien verändert . Geeignete Substanzen stellen dabei organische und anorganische halbleitende Stoffe dar, deren relative Änderung der Leitfähigkeit durch Adsorption dieser Agenzien hinreichend groß ist. Bezüglich unterschiedlicher Agenzien sind sowohl schmalbandig als auch breitbandig selektiv wirkende Substanzen bekannt . Die Veränderung der elektrischen Leitfähigkeit dient zur Bestimmung der Konzentration, da im verwendeten Meßbereich ein monotoner Zusammenhang dieser mit der Konzentration gegeben ist. Es ist möglich, zur Messung der Veränderung der elektrischen Leitfähigkeit ein Wechselfeld zu benutzen und deren weitere Kennwerte, bsw. spezifischer komplexer Verlustwinkel, zusätzlich zur Auswertung heranzuziehen.It is also known that such measuring probes of the measuring devices consist of two suitably shaped electrodes, which are fastened on a carrier, and the conductivity of a suitable substance between them is determined as an indirect measured variable for determining the concentration of the agents to be examined. Depending on the agents to be investigated, various, mostly specially optimized, substances are used, to which the substances to be adsorbing agents. The substance itself has a certain electrical conductivity, which changes as a result of the absorption and physical binding of the agents serving as adsorbents. Suitable substances are organic and inorganic semiconducting substances whose relative change in conductivity due to the adsorption of these agents is sufficiently large. With regard to different agents, both narrow-band and broad-band selectively acting substances are known. The change in the electrical conductivity is used to determine the concentration, since in the measuring range used there is a monotonous relationship with the concentration. It is possible to use an alternating field to measure the change in electrical conductivity and its other characteristic values, e.g. specific complex loss angle to be used in addition for the evaluation.
Durch eine geeignete Gestaltung der Elektroden läßt sich der nutzbare Leitfähigkeitsbereich in einem geeigneten Leitwert der Meßsonde abbilden. Durch eine geeignete Ge- staltung der Oberfläche, beispielsweise Poren, zwischen den Elektroden läßt sich der anteilige Einfluß der Adsorption auf dem zur Messung genutzten Teil der Substanz verändern. Die Adsorptionszeit wird insbesondere durch die Art der Substanzschicht und der Substanztemperatur bestimmt.The usable conductivity range can be represented in a suitable conductivity of the measuring probe by a suitable design of the electrodes. The proportionate influence of the adsorption on the part of the substance used for the measurement can be changed by a suitable design of the surface, for example pores, between the electrodes. The adsorption time is determined in particular by the type of substance layer and the substance temperature.
Eine Vielzahl von derartigen Meßsonden zur Bestimmung der Konzentration verschiedener Agenzien in Gasen werden mit organisch halbleitenden Substanzen, vorzugsweise Polymeren, auf Keramikträgern gefertigt. Bedingt durch die hohe Luftfeuchtigkeit und die hohe Oberflächenspannung von Wasser sind die Substanzen derartiger Meßsonden im Normklima mit einem dünnen Wasserfilm versehen. Daraus resultiert aufgrund seiner eigenen Leitfähigkeit eine Gesamtleitfähigkeit der Meßvorrichtung, die ca. eine Größenordnung über jener der verwendeten Substanzen liegt. Um das Meßergebnis nicht durch die Feuchtigkeitsaufnahme zu verfälschen, sind derartige Meßsonden mit einem Heizelement oder einer separaten Temperierung versehen, welche die Substanz derart aufheizen, daß der Feuchtigkeitsfilm vollständig verdunstet. Die- se Meßsonden arbeiten dadurch notwendig bei gegenüber derA large number of such measuring probes for determining the concentration of various agents in gases are produced on ceramic carriers using organic semiconducting substances, preferably polymers. Due to the high air humidity and the high surface tension of water the substances of such measuring probes are provided with a thin film of water in a standard atmosphere. Because of its own conductivity, this results in an overall conductivity of the measuring device which is approximately an order of magnitude higher than that of the substances used. In order not to falsify the measurement result due to the absorption of moisture, such measuring probes are provided with a heating element or a separate temperature control, which heat the substance in such a way that the moisture film evaporates completely. As a result, these measuring probes necessarily work with the
Umgebung höheren Temperaturen, vorzugsweise oberhalb vonEnvironment higher temperatures, preferably above
150°C. Der nutzbare Meßbereich erstreckt sich bezüglich der150 ° C. The usable measuring range extends with respect to the
Konzentration der Agenzien zumeist von mindestens 1 ppmConcentration of the agents mostly of at least 1 ppm
(parts per million) bis zu einer Sättigungskonzentration des bestimmten Agens. In diesem Meßbereich liegt mit zunehmender Konzentration ein monoton wachsender Leitwert der Meßsonde vor, welcher durch eine vorherige Eichung in die Konzentration des zu bestimmenden Agens umrechenbar ist. Der Nachteil derartiger Sensoren ist einerseits die relativ geringe Empfindlichkeit gegenüber nachzuweisenden geringsten Konzentrationen bestimmter Agenzien in Gasen und andererseits die Notwendigkeit der Aufheizung. Dadurch werden derartige Meßsonden komplexer und teurer in der Herstellung sowie im Betrieb. Des weiteren ist der Einsatz im Umge- bungstemperaturbereich, beispielsweise bei Normklima, nur eingeschränkt möglich.(parts per million) up to a saturation concentration of the specific agent. In this measuring range, with increasing concentration, there is a monotonically increasing conductivity of the measuring probe, which can be converted into the concentration of the agent to be determined by prior calibration. The disadvantage of such sensors is on the one hand the relatively low sensitivity to the lowest concentrations of certain agents in gases to be detected and on the other hand the need for heating. This makes such probes more complex and expensive to manufacture and operate. Furthermore, use in the ambient temperature range, for example in a standard climate, is only possible to a limited extent.
Die Druckschrift EP 0 328 108 A3 beschreibt einen elektrochemischen Sensor zur Messung der Konzentration einer chemischen Substanz in einer Lösung, wobei auf einem Substrat zwei Feldeffekttransistoren sowie eine Referenzelektrode angeordnet sind. Über dem Bereich des Kanals eines der beiden FET und der Referenzelektrode ist ein Hydrogel als „Elektrode" angeordnet, zur Stoffdetektion werden Enzyme genutzt, die den FET durch Veränderung der Leitfähigkeit in der Elektrode ansteuern. Die Detektion der Art und Konzentration der Substanz in der Lösung erfolgt mittels Auswertung des Signals vom FET.EP 0 328 108 A3 describes an electrochemical sensor for measuring the concentration of a chemical substance in a solution, two field effect transistors and a reference electrode on a substrate are arranged. A hydrogel is arranged as an "electrode" over the area of the channel of one of the two FETs and the reference electrode. Enzymes are used for substance detection which control the FET by changing the conductivity in the electrode. The detection of the type and concentration of the substance in the solution is done by evaluating the signal from the FET.
Dieser Sensor ist nur zur Bestimmung relativ hoher Konzentrationen im Bereich von einigen ppm von Substanzen in Lö- sungen geeignet, Agenzien in Gasen sind damit nicht hinreichend bestimmbar. Es lassen sich Konzentrationen nur weniger, ausgewählter Stoffe bestimmen. Zudem ist das Hydrogel des Sensors mit störenden Substanzen leicht irreversibel kontaminierbar, wodurch der Sensor unbrauchbar wird. Zur Herstellung des Sensors sind aufgrund der Mikrostruktu- ren aufwendige Technologien der Mikroelektronik erforderlich.This sensor is only suitable for the determination of relatively high concentrations in the range of a few ppm of substances in solutions. Agents in gases cannot therefore be adequately determined. Concentrations of only a few, selected substances can be determined. In addition, the hydrogel of the sensor can easily be irreversibly contaminated with interfering substances, which makes the sensor unusable. Due to the microstructures, complex microelectronic technologies are required to manufacture the sensor.
In der Bekanntmachung der PCT-Anmeldung mit der Nummer WO 89/08713 wird eine Methode und ein Apparat zur Bestimmung der Konzentration von bestimmten Körperflüssigkeiten offenbart. Eine Flüssigkeitsprobe wird in eine Probenzelle mit zwei Elektroden eingebracht und mit einem Oxidantium sowie einem Puffer als Redox-System, gemischt und anschließend die Leitfähigkeit amperometrisch ausgelesen sowie mittels einer Auswerteeinheit und Anzeigeeinheit die Konzentration der bestimmten Substanz der Körperflüssigkeit angezeigt. Die Leitfähigkeit der Probenflüssigkeit wird außerdem zum Einschalten des Meßgeräts genutzt. Nachteilig an dieser Lösung ist die Anwendbarkeit nur für Flüssigkeiten, die rela- tive Unempfindlichkeit mit einer unteren Nachweisgrenze im Konzentrationsbereich von ppm sowie die Anordnung einer Referenzelektrode in der Probenzelle. Es handelt sich um eine weiterentwickelte Meßanordnung zur Bestimmung der Leitfähigkeit von Flüssigkeiten.In the publication of PCT application number WO 89/08713, a method and an apparatus for determining the concentration of certain body fluids is disclosed. A liquid sample is introduced into a sample cell with two electrodes and mixed with an oxidant and a buffer as a redox system, then the conductivity is read out amperometrically and the concentration of the specific substance of the body fluid is displayed by means of an evaluation unit and display unit. The conductivity of the sample liquid is also used to switch on the measuring device. The disadvantage of this solution is the applicability only for liquids, the relative insensitivity with a lower detection limit in Concentration range of ppm and the arrangement of a reference electrode in the sample cell. It is a further developed measuring arrangement for determining the conductivity of liquids.
Die Aufgabe der Erfindung besteht darin, eine Meßsonde und ein zugeordnetes Meßverfahren zu entwickeln, welches bei Überwindung obiger Nachteile eine empfindliche Meßsonde zur Detektion von Agenzien und deren Konzentration in Gasen und/oder Flüssigkeiten realisiert, wobei diese unter ver- schiedensten realen Meßbedingungen ohne zusätzlichen Aufwand einsetzbar ist und kein Heizelement benötigt.The object of the invention is to develop a measuring probe and an associated measuring method which, while overcoming the above disadvantages, realizes a sensitive measuring probe for the detection of agents and their concentration in gases and / or liquids, these under different real measuring conditions without additional effort can be used and no heating element is required.
Die Aufgabe wird durch die im Patentanspruch 1 und im Patentanspruch 7 aufgeführten Merkmale gelöst. Bevorzugte Weiterbildungen ergeben sich aus den Unteransprüchen.The object is achieved by the features listed in claim 1 and in claim 7. Preferred further developments result from the subclaims.
Das Wesen der Erfindung liegt darin begründet, daß eine Meßsonde in Form eines Zweipols zur Ermittlung des elektrischen Widerstands einer sensoraktiven Schicht verwendet wird, bei der gezielt ein Deckfilm aus einer Flüssigkeit, beispielsweise Wasser, der über der Substanz der sensorak- tiven Schicht ausbildet wird, in die aktive Zone der Meßsonde einbezogen wird. Durch den Deckfilm liegt somit eine Kombination verschiedener Teilleitwerte vor, insbesondere der Substanz, des Deckfilms und der sich zwischen beiden ausbildenden aktiven Oberfläche. Moleküle des Deckfilms stehen zusätzlich zur Substanz als Adsorbat für das zu bestimmende Agens eines Gases oder einer Flüssigkeit zur Verfügung. Mit der gezielten Auswahl der Flüssigkeit für den Deckfilm sind die Adsorbtionseigenschaften für bestimmte Agenzien optimierbar.The essence of the invention lies in the fact that a measuring probe in the form of a two-pole system is used to determine the electrical resistance of a sensor-active layer, in which a cover film is specifically formed from a liquid, for example water, which is formed over the substance of the sensor-active layer. is included in the active zone of the measuring probe. The cover film thus provides a combination of different partial conductivities, in particular the substance, the cover film and the active surface which forms between the two. In addition to the substance, molecules of the cover film are available as adsorbate for the agent of a gas or a liquid to be determined. With the targeted selection of the liquid for the Cover film, the adsorption properties can be optimized for certain agents.
Das erfindungsgemäße Meßverfahren ist speziell für die erfindungsgemäße Meßsonde ausgelegt. Diese wird grundsätzlich bezüglich der Adsorption der Flüssigkeit in der Diffusionsschicht in Sättigung betrieben. Im Grundzustand (0% Agens + Flüssigkeit in Sättigung) liegt ein vergleichsweise hoher Leitwert vor. Bei Anwesenheit bestimmter Agenzien bewirken diese je nach Art eine Behinderung/Förderung der bewegli- chen Ladungsträger, bzw. reduzieren/erhöhen die Zahl der beweglichen Ladungsträger. Auf diese Weise haben auch geringste Spuren des zu detektierenden Gases einen potenzierten Einfluß auf die elektrische Leitf higkeit der Meßsonde und reduzieren/erhöhen die Leitfähigkeit drastisch, es tritt der Effekt einer reversiblen Dotierung an der Oberfläche der Meßsonde auf. Dieser Effekt wirkt bereits bei relativ geringen Konzentrationen der zu bestimmenden Agenzien und verstärkt sich mit zunehmender Konzentration des Agens. Das Resultat ist bei zunehmender Konzentration der bestimmten Agenzien ein bezüglich des Grundzustandes fallender/steigender differentieller Leitwert des Meßsonde. Dieser kann erfindungsgemäß nach einer vorhergehenden Eichung zur Berechnung der Konzentration der bestimmten Agenzien verwendet werden. Dazu wird vorteilhaft ein Ersatz- Schaltbild dieses Sensors verwendet, welches diesen als elektrischen Zweipol darstellt. Die zur Beschreibung im Meßfenster benötigten komplexen Ersatzgrößen korrelieren vorzugsweise mit den Widerständen und den Dicken der einzelnen Schichten. Die Vorteile der Erfindung bestehen insbesondere in der gegenüber Meßsonden ohne Deckfilm über der Substanz höheren Empfindlichkeit des Meßverfahrens um mindestens zwei Zehnerpotenzen, die Nachweisgrenze für zu bestimmende Agenzien liegt damit im ppt (parts per trillion) Bereich der Konzentration des Agens. Es besteht die Möglichkeit Messungen unter realen Bedingungen ohne zusätzlichen Aufwand, beispielsweise bei Raumtemperatur in üblicher Atmosphäre oder auch im Körperinneren von Lebewesen durchzuführen. Lang- Zeitmessungen zur kontinuierlichen Überwachung von Konzentrationen bestimmter Agenzien sind ohne komplizierten apparativen Aufwand realisierbar.The measuring method according to the invention is specially designed for the measuring probe according to the invention. This is basically operated in saturation with regard to the adsorption of the liquid in the diffusion layer. In the basic state (0% agent + liquid in saturation) there is a comparatively high conductivity. In the presence of certain agents, depending on the type, these cause a hindrance / promotion of the movable load carriers or reduce / increase the number of movable load carriers. In this way, even the slightest traces of the gas to be detected have a potentiated influence on the electrical conductivity of the measuring probe and drastically reduce / increase the conductivity; the effect of reversible doping occurs on the surface of the measuring probe. This effect is effective even at relatively low concentrations of the agents to be determined and increases with increasing concentration of the agent. As the concentration of the particular agents increases, the result is a differential conductance of the measuring probe which decreases / rises with respect to the basic state. According to the invention, this can be used after a previous calibration to calculate the concentration of the specific agents. For this purpose, an equivalent circuit diagram of this sensor is advantageously used, which represents this as an electrical two-pole connection. The complex substitute sizes required for the description in the measurement window preferably correlate with the resistances and the thicknesses of the individual layers. The advantages of the invention consist in particular in the fact that the sensitivity of the measuring method is higher by at least two powers of ten compared to measuring probes without a cover film over the substance, the detection limit for agents to be determined is thus in the ppt (parts per trillion) range of the concentration of the agent. It is possible to carry out measurements under real conditions without additional effort, for example at room temperature in a normal atmosphere or inside the body of living beings. Long-term measurements for the continuous monitoring of concentrations of certain agents can be carried out without complicated equipment.
Für den Sensor ist kein Heizelement erforderlich, ebenso keine Temperierung oder andere spezielle Meßbedingungen.No heating element is required for the sensor, nor is tempering or other special measuring conditions.
Es ist weiterhin vorstellbar, daß derartige Meßsonden mit anderen Meßsonden kombiniert werden, um beispielsweise durch die Bestimmung der Temperatur und/oder der Feuchtigkeit den Einfluß dieser Parameter bei der Berechnung in dem erfindungsgemäßen Verfahren berücksichtigen zu können.It is also conceivable that such measuring probes can be combined with other measuring probes in order to be able to take into account the influence of these parameters in the calculation in the method according to the invention, for example by determining the temperature and / or the humidity.
Des weiteren ist es vorstellbar, daß mehrere derartige Meßsonden zum Beispiel in einem Array mit unterschiedlichen Strukturdimensionen und/oder Substanzen kombiniert werden, um die selektiven Eigenschaften der Substanzen bezüglich bestimmter Agenzien in die Analyse mit einzubeziehen.Furthermore, it is conceivable that several such measuring probes can be combined, for example, in an array with different structural dimensions and / or substances in order to include the selective properties of the substances with respect to certain agents in the analysis.
Eine andere mögliche Weiterbildung besteht darin, daß derartige Sensoren auf dem Träger direkt in den Stromkreis eines steuerbaren Halbleiterelements, wie beispielsweise den Basis- oder Gate- Stromkreis integriert werden. Weitere Möglichkeiten zur Nutzung der Meßergebnisse von Konzentrationen bestimmter Agenzien entstehen bei Weitergabe über EDV-Netzwerke oder fernmeldetechnische Einrichtungen an autorisierte Empfänger.Another possible development is that sensors of this type are integrated on the carrier directly into the circuit of a controllable semiconductor element, such as, for example, the base or gate circuit. Further possibilities for using the measurement results of concentrations of certain agents arise when they are passed on to IT recipients via IT networks or telecommunications equipment to authorized recipients.
Die Erfindung wird als Ausführungsbeispiel an Hand von Fig. 1 als Prinzipaufbau der Meßsonde Fig. 2 als Ersatzschaltbild der Meßsonde näher erläutert.The invention is explained in more detail as an exemplary embodiment with reference to FIG. 1 as a basic structure of the measuring probe. FIG. 2 as an equivalent circuit diagram of the measuring probe.
Nach Figur 1 besteht eine Meßsonde 1 für Agenzien in Gasen aus einem Paar Elektroden 2, die partiell auf einem Träger 3 aufgebracht sind, wobei diese als eine Oberflächenüberhö- hung ausgebildet sein können. Über dieser Oberflächenstruktur befindet sich schichtförmig eine geeignete feste Substanz 4, insbesondere ein organischer Halbleiter in der Form eines Polymeren, der auf die Adsorption bestimmter Agenzien 5 mit einer hinreichenden Veränderung der Leitfähigkeit reagiert. Die zu analysierenden Agenzien 5 befinden sich in einer Gasphase 6, die sich als Umgebung der Meßsonde über der Oberfläche der Meßsonde 1 ausbreitet. Zwischen der Oberflächenstruktur der Meßsonde 1 und der Gasphase 6 befindet sich weiterhin ein Deckfilm 7 aus Wasser, der sich durch die endliche Luftfeuchtigkeit der Gasphase 6 ausbildet. Durch die gegenseitige Beeinflussung zwischen der Substanz 4 und dem Deckfilm 7 aus Wasser bildet sich eine be- züglich der Veränderung der Leitfähigkeit wirksame aktive Oberfläche 8 aus. Moleküle des zu bestimmenden Agens 5 werden an der Oberfläche der Substanz 4 sowie den Molekülen des Deckfilm 7 adsorbiert, verdrängen an diesen Stellen Wassermoleküle und verändern die Gesamtleitfähigkeit des Sensors .According to FIG. 1, a measuring probe 1 for agents in gases consists of a pair of electrodes 2, which are partially applied to a carrier 3, which can be designed as a surface elevation. A suitable solid substance 4, in particular an organic semiconductor in the form of a polymer, which reacts to the adsorption of certain agents 5 with a sufficient change in the conductivity, is located in a layered manner above this surface structure. The agents 5 to be analyzed are in a gas phase 6, which as the surroundings of the measuring probe spreads over the surface of the measuring probe 1. Between the surface structure of the measuring probe 1 and the gas phase 6 there is also a cover film 7 made of water, which is formed by the finite atmospheric humidity of the gas phase 6. As a result of the mutual influence between the substance 4 and the cover film 7 made of water, an active surface 8 which is effective with regard to the change in conductivity is formed. Molecules of the agent 5 to be determined are adsorbed on the surface of the substance 4 and the molecules of the cover film 7, displacing them at these points Water molecules and change the overall conductivity of the sensor.
Nach Figur 2 kann ein Ersatzschaltbild für die einzelnen Schichten und Dicken der Meßsonde in Form eines Wider- Standsnetzwerks angenommen werden, welches die Meßsonde als elektrischen Zweipol im zulässigen Meßfenster abbildet. Ein derartiges Ersatzschaltbild wird vorzugsweise als Grundlage für die Eichung der Meßsonde 1 und der darauf basierenden Bestimmung der Konzentration der zu analysierenden Agenzien 5 verwendet. Dadurch wird insbesondere eine nichtlineare Abbildung auf im wesentlichen voneinander unabhängigen und stark mit der geometrischen Gestaltung der Meßsonde korre- lierenden Basiswerten ermöglicht. Durch die Verwendung komplexer Ersatzgrößen in Form von Widerständen wird zusätz- lieh das Verhalten im elektrischen Wechselfeld beschrieben. Eine Parallelschaltung zwischen jeweils einem Wirk- und einem Blindwiderstand kennzeichnet die Schichtwiderstände für den Träger 3, die Substanz 4, die aktive Oberfläche 8, den Deckfilm 7 aus Wasser und die Gasphase 6 sowie einen Er- satzwiderstand I 9, wesentlich abhängig von den Dicken der Elektroden 2 und der Substanz 4, einen Ersatzwiderstand II 10, wesentlich abhängig von der Dicke der aktiven Oberfläche 8 und einen Ersatzwiderstand III 11, wesentlich abhängig von Eigenschaften des Deckfilms 7. Die Dicke des Deck- films 7 aus beispielsweise Wasser ist im wesentlichen von der Temperatur abhängig. Die einzelnen Schichtwiderstände sind jeweils parallel geschaltet, wobei die Ersatzwiderstände [9, 10, 11] jeweils beidseitig zwischen den Schichtwiderständen der Substanz 4, der aktiven Oberfläche 8, des Deckfilms 7 und der Gasphase 6 angeordnet sind. Mittels üblicher Meß- und Auswerteeinheiten wird über Leitungen von den Elektroden 2 die Veränderung der Gesamtleit- fahigkeit des Sensors registriert und zur Bestimmung der Konzentration des Agens aufgezeichnet sowie ausgewertet. According to FIG. 2, an equivalent circuit diagram for the individual layers and thicknesses of the measuring probe can be adopted in the form of a resistance network, which maps the measuring probe as an electrical two-pole connection in the permissible measuring window. Such an equivalent circuit diagram is preferably used as the basis for the calibration of the measuring probe 1 and the determination of the concentration of the agents 5 to be analyzed based thereon. This enables, in particular, non-linear imaging on essentially independent basic values that strongly correlate with the geometric design of the measuring probe. By using complex substitute variables in the form of resistors, the behavior in the alternating electrical field is also described. A parallel connection between an active and a reactance in each case characterizes the sheet resistances for the carrier 3, the substance 4, the active surface 8, the cover film 7 made of water and the gas phase 6 as well as a replacement resistor I 9, essentially depending on the thicknesses of the Electrodes 2 and the substance 4, an equivalent resistor II 10, essentially dependent on the thickness of the active surface 8 and an equivalent resistor III 11, essentially dependent on properties of the cover film 7. The thickness of the cover film 7, for example of water, is essentially dependent on the Temperature dependent. The individual sheet resistors are each connected in parallel, the equivalent resistors [9, 10, 11] being arranged on both sides between the sheet resistances of substance 4, active surface 8, cover film 7 and gas phase 6. Using conventional measuring and evaluation units, the change in the overall conductivity of the sensor is registered via lines from the electrodes 2 and recorded and evaluated to determine the concentration of the agent.
Verwendete BezugszeichenReference symbols used
1 Meßsonde1 measuring probe
2 Elektroden2 electrodes
3 Träger 4 Substanz3 carrier 4 substance
5 Agens5 agents
6 Gasphase6 gas phase
7 Deckfilm7 cover film
8 aktive Oberfläche 9 Ersatzwiderstand I8 active surface 9 equivalent resistor I
10 Ersatzwiderstand II10 equivalent resistor II
11 Ersatzwiderstand III 11 equivalent resistor III

Claims

Patentansprüche claims
1. Meßsonde (1) mit einer sensoraktiven Schicht in Form eines elektrischen Zweipols zur Detektion von Agenzien sowie deren Konzentration in Gasen und/oder Flüssigkeiten, dadurch gekennzeichnet, daß sich über der sensoraktiven Schicht einer Meßsonde (1) ein Deckfilm (7) aus einer Flüssigkeit befindet.1. Measuring probe (1) with a sensor-active layer in the form of an electrical dipole for the detection of agents and their concentration in gases and / or liquids, characterized in that a cover film (7) from a Liquid.
2. Meßsonde (1) mit einer sensoraktiven Schicht in Form ei- nes elektrischen Zweipols zur Detektion von Agenzien sowie deren Konzentration in Gasen und/oder Flüssigkeiten nach2. Measuring probe (1) with a sensor-active layer in the form of an electrical dipole for the detection of agents and their concentration in gases and / or liquids
Anspruch 1, dadurch gekennzeichnet, daß der Deckfilm (7) aus Wasser besteht.Claim 1, characterized in that the cover film (7) consists of water.
3. Meßsonde (1) mit einer sensoraktiven Schicht in Form ei- nes elektrischen Zweipols zur Detektion von Agenzien sowie deren Konzentration in Gasen und/oder Flüssigkeiten nach Anspruch 1 und 2, dadurch gekennzeichnet, daß der Deckfilm (7) aus der zu analysierenden Flüssigkeit besteht .3. Measuring probe (1) with a sensor-active layer in the form of an electrical dipole for the detection of agents and their concentration in gases and / or liquids according to claim 1 and 2, characterized in that the cover film (7) from the liquid to be analyzed consists .
4. Meßsonde (1) mit einer sensoraktiven Schicht in Form eines elektrischen Zweipols zur Detektion von Agenzien sowie deren Konzentration in Gasen und/oder Flüssigkeiten nach Anspruch 1 bis 3, dadurch gekennzeichnet, daß mehrere Meßsonden (1) in einem Array mit unterschiedli- chen Strukturdimensionen kombiniert sind, und daß die einzelnen Strukturen unterschiedliche Substanzen (4) aufweisen. 4. Measuring probe (1) with a sensor-active layer in the form of an electrical dipole for the detection of agents and their concentration in gases and / or liquids according to claims 1 to 3, characterized in that several measuring probes (1) in an array with different Structural dimensions are combined, and that the individual structures have different substances (4).
5. Meßsonde (1) mit einer sensoraktiven Schicht in Form eines elektrischen Zweipols zur Detektion von Agenzien sowie deren Konzentration in Gasen und/oder Flüssigkeiten nach Anspruch 1 bis 4, dadurch gekennzeichnet, daß Meßsonden (1) mit anderen Meßsonden zur Bestimmung verschiedener physikalischer Parameter kombiniert sind.5. Measuring probe (1) with a sensor-active layer in the form of an electrical dipole for the detection of agents and their concentration in gases and / or liquids according to claims 1 to 4, characterized in that measuring probes (1) with other measuring probes for determining various physical parameters are combined.
6. Meßsonde (1) mit einer sensoraktiven Schicht in Form eines elektrischen Zweipols zur Detektion von Agenzien sowie deren Konzentration in Gasen und/oder Flüssigkeiten nach Anspruch 1 bis 5, dadurch gekennzeichnet, daß die Meßsonde (1) direkt in den Steuerstromkreis eines Halbleiterbauelements implementiert ist.6. Measuring probe (1) with a sensor-active layer in the form of an electrical dipole for the detection of agents and their concentration in gases and / or liquids according to claims 1 to 5, characterized in that the measuring probe (1) implements directly in the control circuit of a semiconductor component is.
7. Meßverfahren zur Detektion von Agenzien sowie deren Konzentration in Gasen und/oder Flüssigkeiten mittels einer Meßsonde (1) nach den Ansprüchen 1 bis 6, dadurch gekennzeichnet, daß ein Deckfilm (7) aus einer Flüssigkeit, der sich über der Substanz (4) der sensoraktiven Schicht befindet, in die aktive Zone der Meßsonde (1) einbezogen wird, und daß die Kombination verschiedener Teilleitwerte, insbesondere der Substanz (4) , des Deckfilms (7) und der sich zwischen beiden ausbildenden aktiven Oberfläche (8) in die Ermittlung des Gesamtleitwertes ohne Kompensation eingehen.7. Measuring method for the detection of agents and their concentration in gases and / or liquids by means of a measuring probe (1) according to claims 1 to 6, characterized in that a cover film (7) made of a liquid which is above the substance (4) the sensor-active layer, is included in the active zone of the measuring probe (1), and that the combination of different partial conductivities, in particular the substance (4), the cover film (7) and the active surface (8) that forms between the two, is included in the determination of the total conductance without compensation.
8. Meßverfahren zur Detektion von Agenzien sowie deren Kon- zentration in Gasen und/oder Flüssigkeiten mittels einer8. Measuring method for the detection of agents and their concentration in gases and / or liquids by means of a
Meßsonde (1) nach Anspruch 7, dadurch gekennzeichnet, daß Meßwerte über EDV-Netzwerke oder/und fernmeldetech- nische Einrichtungen an autorisierte Empfänger weitergeleitet werden.Measuring probe (1) according to claim 7, characterized in that that measured values are forwarded to authorized recipients via EDP networks and / or telecommunications equipment.
HIERZU ZWEI SEITEN ZEICHNUNGEN HERE TWO SIDED DRAWINGS
EP99959234A 1998-12-10 1999-10-30 Measuring probe and method for measuring the concentration of agents in gases and/or liquids Withdrawn EP1141687A1 (en)

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