WO2001057243A1

WO2001057243A1 - Biological microsensor

Info

Publication number: WO2001057243A1
Application number: PCT/DK2001/000063
Authority: WO
Inventors: Ulrik Bruhn; Niels Them Kjaer
Original assignee: Danfoss A/S
Priority date: 2000-02-03
Filing date: 2001-01-27
Publication date: 2001-08-09
Also published as: AU2001228324A1; DE10004642A1; DE10004642C2

Abstract

The invention relates to a biological microsensor comprising a housing (2) in which an electrode system with an electrolyte reservoir, a storage space for bacterial nutrient and a reaction chamber (8) are arranged, whereby the reaction chamber (8) is closed on the outer wall of the housing (2) by a first membrane and is connected to the storage space. The aim of the invention is to produce an unsusceptible microsensor. To this end, a heating device (14) is arranged in the vicinity of the reaction chamber (8).

Description

Biological microsensor

The invention relates to a biological microsensor with a housing in which an electrode arrangement with an electrolyte supply, a storage space for bacterial nutrient and a reaction chamber are arranged, the reaction chamber being closed off on the outer wall of the housing with a first membrane and with the storage space in Connection is established.

Such a microsensor is known from WO 98/21309 AI. Such sensors can be used, for example, to examine water for certain ingredients, such as nitrates or the like. Such microsensors are used, for example, in sewage treatment plants to control the air supply to the water as a function of the nitrate load in the water, or in groundwater testing. Bacteria are used for the analysis, which are matched to the substance to be examined. For example, you can choose bacteria that metabolize nitrates to N ₂ O (laughing gas) in a biological way. This laughing gas can then be detected more easily than the nitrates themselves. The bacteria reproduce themselves. Because of the relatively large bacterial nutrient supply in the storage room, such sensors have a relatively long service life. A biological equilibrium is established practically automatically in the reaction chamber, ie one can assume on average that the same amount of bacteria is always present, so that one can reliably rely on the secondary product generated by the bacteria (here: laughing gas) Amount of the primary product "processed" by the bacteria (here: nitrate). Such sensors work reliably in a wide range and with reproducible values. However, it has been found that a change in measured values can be observed, especially at low temperatures. In the known case, this is avoided by using microorganisms which display the desired activity even at low temperatures. In any case, there is a risk that the microorganisms will die if the temperature is too low.

EP 0 351 516 A2 describes a precalibrated disposable electrochemical sensor, in particular for examining blood, which has a temperature compensator in order to improve the accuracy of the measurement in cases where the calibration temperature and the temperature of the sample differ. In other words, the temperature compensator calculates temperature-related deviations between the output signal of the electrochemical sensor and the "true" concentration of the substance.

WO 95/14962 AI shows a potentiometric biosensor in which a Peltier element is provided which keeps the entire sensor at a desired temperature. For this purpose, the Peltier element is arranged between a heat sink and an aluminum plate that receives the reaction chamber. However, this sensor can only be used under controlled environmental conditions. In particular, its use under water or floating in water is not possible because the surroundings would then remove too much heat.

US 5 160 604 describes a system for detecting toxic substances with the help of immobilized microorganisms. This system is used in the case of water To operate quality assurance. Here the reaction chamber and the electrode arrangement are arranged in a hot water bath which has a constant temperature. In addition, heat exchangers are arranged in the hot water bath, through which liquid to be analyzed and, if appropriate, analysis liquids are passed in order to enter the reaction chamber at a predetermined temperature.

DE 39 42 664 C2 describes a sensor arrangement for determining the moisture content of gases, in which the gas is heated by heating elements before it can enter a reaction chamber. The heating elements are controlled with the help of a temperature sensor, which determines the temperature of the gas. This makes it possible to keep the sensor at a constant temperature of around 450 ° C.

The invention has for its object to provide a micro sensor that is relatively insensitive.

With a biological microsensor of the type mentioned at the outset, this object is achieved in that a heating device is arranged in the region of the reaction chamber.

This makes it possible to always provide the bacteria or microorganisms in the reaction chamber with an ambient temperature in which these microorganisms feel comfortable, ie a temperature at which the microorganisms develop the desired activity. The fact that the heating device is arranged in the region of the reaction chamber eliminates the need to heat the entire sensor or at least the housing. This not only saves energy, but also minimizes also reduces the risk of heat dissipation with the associated drop in temperature. It is therefore easier to keep the temperature in the reaction chamber constant at the desired value. The temperature that should be in the reaction chamber need not be excessively high. Temperatures of 15 ° C are quite sufficient for many microorganisms. At these low temperatures, the risk that the heating device must heat up further and larger parts of the housing and thus the outer surfaces is relatively low. The energy consumption also remains low.

The heating device is preferably designed as an ohmic resistor or as an induction heating device. An ohmic resistor generates heat when current flows through it. An induction heater generates heat due to magnetic excitation that can be generated by a current in an insulated conductor. The current flow can be regulated easily and in a known manner. Because of the low energy consumption, the sensor can also be operated with a battery, so that it can work relatively independently of supply facilities and can accordingly also be used off-road or in open water.

The ohmic resistor is preferably designed as a conductor track which bears against a wall of a part delimiting the reaction chamber. The heating device thus requires practically no or only very little

Installation space so that the sensor can be optimized for the desired response.

It is preferred here that the ohmic resistance is evaporated. By vapor deposition, a rela- tiv small thickness, which in turn leads to a desired high ohmic resistance value.

In an alternative embodiment, the ohmic resistance can be designed as a film. In this case too, the installation space required is small and the ohmic resistance value is high.

The ohmic resistance is preferably designed in the form of a spiral. The conductor track is thus arranged in a spiral, possibly also as a double spiral. This allows a relatively long conduction path, which not only results in a higher ohmic resistance value, but also concentrates the heat generation on a relatively small area.

The electrolyte supply is preferably arranged in an electrolyte compartment which is separated from the storage compartment by a conical insert, the tip of which is adjacent to the reaction chamber. The conical insert has several advantages. Firstly, the assembly of the sensor is simplified. You can fill the housing, which also limits the storage space for the bacterial nutrient, with a certain amount of this nutrient and then insert it. The conical shape of the insert means that the nutrient supply can be easily pushed aside. The insertion can therefore take place at a relatively high speed, for example with the aid of an automatic handling machine. On the other hand, an electrolyte space that expands from the tip of the cone can be realized in this way. Since the tip of the cone is arranged adjacent to the reaction chamber, the electrochemical reactions which are detected with the electrode arrangement will also take place there should be. There will always be enough electrolyte there. Finally, if the housing is correspondingly more conically expanded, it can also be ensured that the storage space for the bacterial nutrient undergoes an expansion pointing away from the reaction chamber. This makes it possible to limit the multiplication of the microorganisms in the storage room. The microorganisms can rather be kept in the reaction chamber.

The heating device is preferably arranged on the insert. On the one hand, the insert is sufficiently close to the reaction chamber. On the other hand, the insert is easy to handle and replace.

It is preferred that the heating device is arranged on the inside of the insert. In order for the heating device to give off the necessary heat, its temperature must be higher than that of its surroundings. By making the heater by using the

Separates the reaction chamber, it is avoided that the microorganisms come into contact with the possibly relatively hot heating device and are damaged.

An opening closed by a second membrane is preferably arranged at the tip of the insert. The second membrane serves to allow the secondary product, which is generated by the microorganisms, to enter the electrolyte space.

The insert and the second membrane are preferably formed in one piece. This can be achieved relatively easily, in particular, if one chooses silicone or a comparable material for the use. In this case you just have to use it Dilute the tip sufficiently to form the second membrane.

The insert preferably lies against the inner wall of the housing in which the reaction chamber is arranged, grooves being provided in this inner wall of the housing which connect the reaction chamber to the storage space. With the help of the insert, the reaction chamber is almost completely closed. This creates defined relationships for the microorganisms. Channels are only made available via the grooves, with the aid of which the reaction chamber is connected to the storage space. Sufficient nutrients for the microorganisms can thus be added via these grooves so that the microorganisms, more precisely the microorganism culture, are given a sufficient lifespan.

The electrode arrangement is preferably arranged on a support part which is connected to the housing via a

Snap connection is connected, wherein the insert has a flange which is clamped between the carrier part and the housing. With this configuration, an easily manufactured microsensor is obtained. The insert is placed in the housing, if necessary after the nutrient supply for the microorganisms has been filled in, and the carrier part is put on. This means that all required parts are automatically positioned in the correct position. If the carrier part and the housing are now locked together, a manageable unit is created in which all required parts are fixed in the correct position at the same time.

The heating device preferably has flat-shaped connections which extend into the clamping area between the housing and carrier part are sufficient. The electrical energy required to operate the heating device can be introduced with great "target certainty" at the flat connections. Because the connections extend into or protrude into the clamping area, they are automatically fixed when the support part and housing are locked.

It is particularly preferred here that contacts are arranged on the carrier part, which are located at the connections

Apply pressure. With the assembly, the electrical contact to the connections of the heating device is also formed at the same time

The carrier part and the housing or the insert preferably have an asymmetry and can only be connected to one another in one or two angular positions. It is therefore possible to assign a clear function to the contacts on the carrier part. For example, two contacts can be assigned the function of transmitting the electrical heating power, while other contacts on the carrier part are connected to the electrodes of the electrode arrangement.

Preferably, only a single angular position of the carrier part and housing or insert will be permitted. If necessary, it is also permitted to use an angular position offset by 180 °.

A part of a temperature control device is preferably arranged on the carrier part. This can be, for example, a temperature sensor or a PtlOO or a PtlOOO resistor or a thermal coupler (two metals that differ in a voltage series). It is not necessary that the entire temperature control device is arranged on the carrier part. However, if you place the "sensitive" parts here, then you will get the information you need without any additional construction work, exactly where it is created.

An evaluation and control device is preferably provided, which operates the heating device below a predetermined outside temperature and, above this outside temperature, arithmetically corrects the values determined with the aid of the electrode arrangement. This takes into account the fact that the microorganisms reduce their activity below predetermined temperatures or even stop them altogether. In this case, the heat supply helps with the heating device. If, on the other hand, the ambient temperature is higher than the specified temperature, cooling is not used because the microorganisms are still active at higher values. However, since there may be changes in the output signal here, these changes are compensated for depending on the temperature.

The invention is described in more detail below on the basis of a preferred exemplary embodiment in conjunction with the drawing. Show here:

1 shows a biological microsensor in an exploded view,

2 shows a cross section through the microsensor,

3 shows an enlarged detail III according to FIG. 2,

4 shows a first external view of the microsensor, 5 shows a second external view of the microsensor and

6 shows an enlarged top view of the microsensor without a carrier part.

1 shows a microsensor 1 with three essential components, namely a housing 2, an insert 3 and a carrier part 4. The housing 2 and the carrier part 4 consist of a harder plastic. They can also consist of different plastics, preferably those that are injection moldable. The insert 3 consists of a softer plastic, for example silicone.

As can be seen from FIG. 2, in the assembled microsensor 1, the housing 2, the insert 3 and the carrier part 4 are axially assembled in such a way that the insert 3 in the housing 2 separates a storage space 5 for bacteria nutrient from an electrolyte space 6. The insert 3 has an essentially conical shape, so that the electrolyte space 6 widens from the top of the insert 3 towards the bottom. The housing 2 has a recess 7 on its bottom, which widens more than the cone of the insert 3, so that the storage space 5 also widens with increasing height, at least at its lower end.

A reaction chamber 8 is arranged in the wall of the housing 2 at the lower end of the recess 7 (based in each case on the representations of FIGS. 2 and 3), ie where the wall of the housing 2 is cheapest. The reaction chamber 8 is covered on the outside by a first membrane 9. The first membrane 9 can be formed from the same material as the housing 2 be and if necessary be integrally formed with the housing 2.

The top of the reaction chamber, which in this embodiment is the only side that is not delimited by the housing 2, is covered by the insert 3. For this purpose, the insert 3 has a second membrane 10 at its tip.

The first membrane 9 must be permeable to a so-called "primary product", the presence and concentration of which is to be determined. Microorganisms, for example bacteria, are arranged in the reaction chamber 8, which convert this primary product into a secondary product. The second membrane 10 must be permeable to this secondary product. For example, the primary product can be nitrate, which is transformed by bacteria into N ₂ 0 (laughing gas) as a secondary product. Accordingly, the nitrates must be able to pass through the first membrane, while the second membrane 10 must be permeable to nitrous oxide. The second membrane 10 can be formed in one piece with the insert 3, for example likewise in that the insert 3 has been thinned to the required extent at its tip.

The carrier part 4 has a working electrode 11 and a reference electrode 12, both of which are connected to the electrolyte located in the electrolyte space 6. The working electrode 11 is adjacent to the second membrane 10, which in turn covers the reaction chamber 8, so that the secondary product generated in the reaction chamber 8 enters an intermediate space between the working electrode 11 and the second membrane and an electrochemical reaction can take place there. The electrode arrangement 11, 12 with the electrolyte here corresponds to a conventional electrochemical measuring cell which is known per se and therefore does not need to be explained further.

On the inside of insert 3, i.e. On the side facing the electrolyte chamber 6, a heating device 14 is applied to the insert 3. The heating device 14 is a flat ohmic resistor which can be produced, for example, by vapor deposition or printing or by applying a film. You can also use an electrically conductive or metallizable plastic. The resistance value can be, for example, 150 Ω. The exact value depends on the power supply. As can be seen from FIG. 6, the heating device 14 has the shape of a double spiral in plan view, the conductor track having a relatively long length and a relatively small width in order to achieve the desired ohmic resistance value. The conductor track can be formed from copper or aluminum, for example.

The conductor track of the heating device 14 has connections 15, 16, which are drawn over a flange 17 of the insert 3 and rest on the surface of this flange 17. The housing 2 has a few pins 18 onto which the insert 3 with its flange 17 and the carrier part 4 with a plate 19 are attached.

Here, the carrier part 4 on the edge of the plate 19th

Locking hooks 20, which can engage behind corresponding projections 21 on the housing 2 when the three parts housing 2, insert 3 and carrier part 4 are plugged together. Here, the housing 2, as can be seen, for example, from FIG. hen that the carrier part 4 and the housing can only be assembled in a single angular position. For example, webs 22 which are missing on a fourth side 23 can be provided on three sides.

The carrier part 4 has a series of electrical connections 24-28. These connections 24-28 can be designed, for example, as electrically conductive pins which penetrate the plate 19 of the carrier part 4. The middle connection 28 is in electrical connection with the working electrode 11. A further connection 27 is connected with the reference electrode 12. A third connection 26 is connected to a Pt100 resistor 29, which is arranged in the shaft 30 of the carrier part 4 , in which the working electrode 11 is also arranged. The PtlOOO resistor forms part of a temperature control device, i.e. it is part of a circuit that controls the flow of current through the heater 14.

The two connections 24, 25 serve to establish the electrical connection to the heating device 14. The corresponding pins are passed through the plate 19, as can be seen, for example, in FIG. 1. If the carrier part 4 and the housing 2 are now snapped together with the connections 15, 16 of the heating device 14 with the interposition of the flange 17, then the connections 24, 25 press on the connections 15, 16 and thus provide an electrical connection between the connections 24, 25 and the

Heater 14 ago. Since the individual parts can only be assembled in a predetermined angular position, it is ensured that the corresponding contacts 24, 25 are only connected to the heating device 14. can occur, but not with the working electrode 12 or the Pt100 resistor 29.

As stated above, the second membrane 10 covers the reaction chamber 8. The reaction chamber 8 is filled with microorganisms, for example bacteria, which can transform nitrate into N ₂ O. In order to ensure the survival of these bacteria, 7 channels 31 are provided in the wall of the recess, which ensure a connection between the reaction chamber 8 and the storage space 5 for the bacterial nutrient. This makes it possible for the nutrient in the reaction chamber 8 to be continuously supplemented.

With the help of the heating device 14, it is now possible to always maintain a predetermined temperature in the reaction chamber 8, for example 15 ° C. The heating device 14 is indeed arranged on the side of the second membrane 10 and the insert 3 facing away from the reaction chamber 8. But since the heater 14 also in

Area of the second membrane 10 is arranged, which is relatively thin, heat transfer from the heating device 14 into the reaction chamber 8 is easily possible. There are no major losses. In particular, in this configuration it is not necessary to heat the entire microsensor 1. The storage space 5 is better thermally insulated from the heating device 14 by a thicker wall of the insert 3.

You can now operate the sensor with a control and evaluation device, not shown, so that the heating device 14 is put into operation at outside temperatures below 15 ° C. (or another preselected temperature) and the reaction chamber 8 is heated through the second membrane 10 , In this In this case, the microorganisms in the reaction chamber are kept at a temperature at which they display their greatest activity. If, on the other hand, the outside temperature rises above the preselected temperature of, for example, 15 ° C., the measurement results determined via the electrode arrangement 11, 12 are corrected arithmetically.

Claims

claims

1. Biological microsensor with a housing in which an electrode arrangement with an electrolyte supply

Storage space for bacterial nutrient and a reaction chamber are arranged, the reaction chamber on the outer wall of the housing being closed off with a first membrane and being connected to the storage space, characterized in that in the area of the reaction chamber (8) there is a heating device (14) is arranged.

2. Sensor according to claim 1, characterized in that the heating device (14) is designed as an ohmic resistor or as an induction heating device.

3. Sensor according to claim 2, characterized in that the ohmic resistance is designed as a conductor track which bears against a wall of a part (3) delimiting the reaction chamber (8).

4. Sensor according to claim 3, characterized in that the ohmic resistor (14) is evaporated.

5. Sensor according to claim 3, characterized in that the ohmic resistor (14) is designed as a film.

6. Sensor according to one of claims 3 to 5, characterized in that the ohmic resistor (14) is designed spirally.

7. Sensor according to one of claims 1 to 6, characterized in that the electrolyte supply is arranged in an electrolyte space (6) which is separated from the storage space (5) by a conical insert (3), the tip of the reaction chamber (8th ) is adjacent.

8. Sensor according to claim 7, characterized in that the heating device (14) is arranged on the insert (3).

9. Sensor according to claim 8, characterized in that the heating device (14) is arranged on the inside of the insert (3).

10. Sensor according to one of claims 7 to 9, characterized in that at the tip of the insert (3) is arranged by a second membrane (10) closed opening.

11. Sensor according to claim 10, characterized in that the insert (3) and the second membrane (10) are integrally formed.

12. Sensor according to one of claims 7 to 11, characterized in that the insert (3) rests on the inner wall of the housing in which the reaction chamber (8) is arranged, grooves (31) being provided in this inner wall of the housing which the reaction chamber ( 8) Connect to the storage room (5).

13. Sensor according to one of claims 7 to 12, characterized in that the electrode arrangement (11, 12) is arranged on a carrier part (4) which with the housing (2) is connected via a snap connection (20, 21), the insert (3) having a flange (17) which is clamped between the carrier part (4) and the housing (2).

14. Sensor according to claim 13, characterized in that the heating device (14) has flat connections (15, 16) which reach into the clamping area between the housing (2) and the carrier part (4).

15. Sensor according to claim 14, characterized in that on the carrier part (4) contacts (24, 25) are arranged which bear on the connections (15, 16) under pressure.

16. Sensor according to one of claims 13 to 15, characterized in that the carrier part (4) and the housing (2) or the insert (3) has an asymmetry and can only be connected to one another in one or two angular positions.

17. Sensor according to one of claims 11 to 16, characterized in that a part (29) of a temperature control device is arranged on the carrier part (4).

18. Sensor according to one of claims 1 to 17, characterized in that an evaluation and control device is provided which operates the heating device (14) below a predetermined outside temperature and above this outside temperature with the aid of the electrode arrangement (11, 12) determined values corrected by calculation.