FIELD OF THE INVENTION

The invention relates to a voltammetric sensor, and, more specifically, to a voltammetric sensor for detecting analyte in a solution. The invention also relates to a method for detecting analyte in a solution.

BACKGROUND OF THE INVENTION

Voltammetric experiments are used for detecting analyte in a solution. Most voltammetric experiments control the potential of an electrode in contact with the analyte while measuring the resulting current. Normally, to conduct such an experiment, three electrodes are required: a working electrode, an auxiliary electrode and a reference electrode. The working electrode makes contact with the analyte, applies the desired potential in a controlled way and facilitates the transfer of charge to and from the analyte. The auxiliary electrode, along with the working electrode, provides a circuit over which the current is either applied or measured. The potential of the auxiliary electrode is usually not measured and is adjusted to balance the reaction occurring at the working electrode. The reference electrode is an electrode which has a stable and known electrode potential. Its only role is to act as a reference in measuring and controlling the working electrode's potential and at no point does it pass any current.

Figure 1 is a schematic view of a three-electrode voltammetric sensor. As shown in Fig.l, in such a three-electrode voltammetric sensor, the applied potential is set up between the working electrode and the reference electrode. And, due to the electrochemical reaction, it generates a current between the working electrode and the auxiliary electrode.

In all voltammetric measurements, the reactions of interest occur at the surface of the working electrode. Therefore, it is interesting to control the potential drop across the interface between the surface of the working electrode and the solution (i.e. the interfacial potential). However, it is impossible to control or measure this interfacial potential without placing another electrode in the solution. Thus, two interfacial potentials must be considered, neither of which can be measured independently. Hence, one requirement for the auxiliary electrode is that its interfacial potential remains constant, so that any changes in cell potential produce identical changes in the interfacial potential of the working electrode. But currently, the potential of the auxiliary electrode varies with the current due to the polarization of the auxiliary electrode. So the reference electrode is adopted to ensure that the potential between the working electrode and the reference electrode is controlled while the current passes between the working electrode and the auxiliary electrode.

Currently, the widely-used reference electrodes are aqueous reference electrodes like saturated calomel electrode, Ag/AgCl electrode, etc. Figure 2 shows structures of a saturated calomel electrode and an Ag/AgCl electrode used as reference electrode in a three-electrode voltammetric sensor. As shown in Figure 2, these electrodes contain a certain saturated solution in them and the contact surfaces are made of glass. Due to the potential leakage problem, it is very difficult to apply a three-electrode system comprising such a reference electrode into high- safety-required applications, such as food processing, drink water industry, and domestic applications. Moreover, the reference electrode requires professional maintenance, which inevitably increases the cost.

SUMMARY OF THE INVENTION

It would be desirable to obviate or mitigate at least some of the above disadvantages and provide an improved solution for detecting analyte in a solution on the basis of a voltammetric mechanism.

To better address one or more of these concerns, a voltammetric sensor for detecting analyte in a solution is proposed in a first aspect of the invention. The voltammetric sensor comprises only two electrodes. One of the two electrodes is a working electrode and the other of the two electrodes is a counter electrode. The ratio of the active area of the counter electrode to the active area of the working electrode is equal to or larger than 20.

Herein, the active area of an electrode can be considered as the area of the part of the electrode which contacts the analyte and also takes part in the electrochemical reaction.

In the proposed voltammetric sensor, the relatively large active area ratio of the counter electrode with respect to the working electrode can reduce the potential variation on the counter electrode significantly, which ensures that the potential of the counter electrode keeps stable when the current passes through. Consequently, no reference electrode is needed, thereby providing a safer way for detecting analyte in a solution. Moreover, the voltammetric sensor costs less due to the removal of the reference electrode.

In one embodiment, the ratio of the active area of the counter electrode to the active area of the working electrode is larger than 100.

In another embodiment, at least part of the working electrode and/or at least part of the counter electrode can be covered with an insulating material.

In another embodiment, the voltammetric sensor can further comprise a first conductor that is electrically connected with the working electrode and/or a second conductor electrically connected with the counter electrode. In a further embodiment, at least part of the first conductor and/or at least part of the second conductor can be covered with an insulating material.

In a further embodiment, at least one of the working electrodes and the counter electrode form a two-dimensional surface contact for contacting with the solution.

The voltammetric sensors as described above can be used in one or more of the following areas: domestic appliances; food industry; and drinking water industry.

In a second aspect of the invention, a method for detecting analyte in a solution by means of the voltammetric sensor as described above is proposed. The method comprises: applying a voltage to the working electrode and the counter electrode, which is at least partially in contact with the solution; and measuring a response current flowing through the working electrode and the counter electrode so as to detect the analyte in the solution.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

The proposed voltammetric sensor and method for detecting analyte in a solution will be described in the following by way of examples and with reference to the accompanying drawings without limiting the scope of protection as defined by the claims. In the Figures:

Figure 1 is a schematic view of a three-electrode voltammetric sensor;

Figure 2 shows structures of a saturated calomel electrode and an Ag/AgCl electrode used as reference electrode in a three-electrode voltammetric sensor;

Figure 3 is a schematic view of a voltammetric sensor for detecting analyte in a solution according to an embodiment of the present invention;

Figure 4 schematically shows the equivalent circuit of the voltammetric sensor according to the embodiment of the present invention;

Figures 5A-5D schematically show some examples of the voltammetric sensor according to the embodiment of the present invention;

Figures 6A-6D schematically show other examples of the voltammetric sensor according to the embodiment of the present invention;

Figures 7A-7B schematically show other examples of the voltammetric sensor according to the embodiment of the present invention; and

Figures 8A-8B schematically show other examples of the voltammetric sensor according to the embodiment of the present invention.

The use of the same reference numbers in different figures indicates similar or identical elements.

DETAILED DESCRIPTION OF EMBODIMENTS

Whereas the invention covers various modifications and alternative constructions, the embodiments of the invention are shown in the drawings and will hereinafter be described in detail. However, it should be understood that the specific description and drawings are not intended to limit the invention to the specific forms disclosed. On the contrary, it is intended that the scope of the claimed invention includes all modifications and alternative constructions thereof falling within the scope of the invention as expressed in the appended claims.

Figure 3 is a schematic view of a voltammetric sensor for detecting analyte in a solution according to an embodiment of the present invention.

As shown in Figure 3, a voltammetric sensor 100 for detecting analyte in a solution comprises only two electrodes. One of the two electrodes is a working electrode 101 and the other one is a counter electrode (which can also be referred to as an auxiliary electrode) 102. The ratio of the active area of the counter electrode 102 to the active area of the working electrode 101 is equal to or larger than 20. In another embodiment, the ratio of the active area of the counter electrode to the active area of the working electrode can be larger than 100. Herein, the active area of an electrode can be considered as the area of the part of the electrode that contacts the analyte and also takes part in the electrochemical reaction.

As described above, in the existing voltammetric sensor, the potential of the auxiliary electrode varies with the current and that's why a reference electrode is needed. In the voltammetric sensor according to the embodiment of the present invention, however, the relatively large active area ratio of the counter electrode with respect to the working electrode can reduce the potential variation on the counter electrode significantly, which ensures that the potential of the counter electrode is kept stable when the current passes through. Consequently, no reference electrode is needed, thereby providing a safer way for detecting analyte in a solution. Moreover, the voltammetric sensor costs less due to the removal of the reference electrode.

When the voltammetric sensor 100 is used for detecting analyte in a solution, the working electrode 101 and the counter electrode 102 are at least partially brought into contact with the solution. Then a voltage is applied to the working electrode 101 and the counter electrode 102. A response current flowing through these two electrodes is measured so as to detect the analyte in the solution.

The voltammetric sensor 100 can be used to detect any analyte that has a reactivity in voltammetric measurement, such as Pb ²⁺ , H ⁺ , caffeine, tannin (major flavour compounds in coffee, tea), catechins (major antioxidants in tea), etc.

In some embodiments, at least one of the working electrodes and the counter electrode form a two-dimensional surface contact for the contact with the solution. The two- dimensional surface contact (instead of the conventional body contact) can easily get the electrode fully immersed with sufficient active area in the targeted solution to keep a complete and fast electron transfer on the electrode. Besides that, the two-dimensional surface contact makes it easier to control the active area ratio between the counter electrode and the working.

In some embodiments, at least part of the working electrode and/or at least part of the counter electrode can be covered with an insulating material. The insulating material can provide a better electrical isolation between the unreacted portions of the working electrode and the counter electrode. In some embodiments, the insulating material enables at least one of the working electrodes and the counter electrode to form a two-dimensional surface contact for the contact with the solution and therefore makes it easier to control the active area ratio between the counter electrode and the working electrode.

In some embodiments, the voltammetric sensor further comprises a first conductor that is electrically connected with the working electrode and/or a second conductor that is electrically connected with the counter electrode. Optionally, at least part of the first conductor and/or at least part of the second conductor is covered with an insulating material, which can be used for electrically insulating the first conductor and/or the second conductor from the solution. The conductors can be used for electrically connecting the counter electrode and the working electrode with external electronics, such as a voltmeter, an ammeter, etc. In some embodiments, the conductors can be made of material(s) less expensive than the materials of the electrodes, thereby lowering the cost of producing the voltammetric sensor. Figure 4 schematically shows the equivalent circuit of the voltammetric sensor

100.

Due to the designed layout of the voltammetric sensor 100, no capacity effect and reaction resistance on the counter electrode need to be considered. So the basic equivalent circuit can be simplified as shown in Figure 4. RL is the resistance of the solution. Ca is the equivalent capacitance of the working electrode surface. R _R is the reaction resistance on the working electrode, i is the current response between the working electrode and the counter electrode, which is also the sum of i _c and i _r . i _c is the current response of C _d and i _r is the current response of R _R .

In the following part, some examples of the voltammetric sensor are described in detail. It should be noted that these examples are to be considered illustrative or exemplary and not restrictive. The voltammetric sensor according to the present invention is not limited to these examples.

Figures 5A-5D schematically show some examples of the voltammetric sensor according to the embodiment of the present invention.

In the voltammetric sensors as shown in Figures 5A-5D, the working electrode and the counter electrode are formed separately.

Figure 5A schematically shows one example of the voltammetric sensor by means of a front view and a bottom view. As shown in Figure 5A, the voltammetric sensor 200 comprises a working electrode 201 and a counter electrode 202, which are shaped as cylinders. In Figure 5A, the hatchings denote the active areas of the working electrode 201 and the counter electrode 202. The ratio of the active area of the counter electrode 202 to the active area of the working electrode 201 is equal to or larger than 20, more preferably, larger than 100. Here, the active area of each electrode is the sum of the area of the immersed portion of the circumferential surface of the electrode and the area of the bottom surface of the electrode.

On the outer surface of each electrode, it is possible to use a mark to indicate the active area of the electrode. For example, a range is denoted by two marked lines formed on the circumferential surface of each electrode. When the two electrodes are at least partially immersed into the solution to detect analyte in the solution, the active area ratio between the counter electrode and the working electrode, which is at least equal to or larger than 20 between the counter electrode and the working electrode can be fulfilled as long as the liquid surface of the solution is within the range. It should be noted that, such a mark is not necessary in some cases. For example,when the diameter of the counter electrode is large enough, i.e. the ratio of the diameter of the counter electrode to the diameter of the working electrode is at least equal to or larger than 20, the active area ratio between the counter electrode and the working electrode, which is at least equal to or larger than 20 between the counter electrode and the working electrode can certainly be fulfilled as long as the height of the immersed portion of the counter electrode is equal to or higher than that of the working electrode.

Although the working electrode and the counter electrode as shown in Figure 5A are shaped as cylinders, the shapes of the electrodes are not limited to the shape of a cylinder. The working electrode and the counter electrode can be formed in different shapes according to the application of the voltammetric sensor and/or specific requirements.

As an example, the material of the working electrode can be Pt, W, Ag, etc., and the material of the counter electrode can be Pt, Au, stainless steel, etc. It should be noted that there is no limitation on the selection of material for the working electrode and the counter electrode. Suitable materials of the electrodes can be selected on the basis of the application of the voltammetric sensor and/or specific requirements.

Figure 5B schematically shows another example of the voltammetric sensor by means of a front view and a bottom view. In this example, at least part of the working electrode 201 is covered with an insulating material 203 and at least part of the counter electrode 202 is covered with an insulating material 204. The insulating material 203 surrounds part of the circumferential surface of the working electrode 201 with the bottom surface and the upper portion of the working electrode exposed. Similarly, the insulating material 204 surrounds part of the circumferential surface of the counter electrode 202 with the bottom surface and the upper portion of the counter electrode exposed. The insulating materials 203 and 204 can be of the same material or of different materials. The insulating materials 203 and 204 enable the working electrode 201 and the counter electrode 202 to form a two-dimensional surface contact for the contact with the solution. As described above, such a two-dimensional surface contact can easily get the electrode fully immersed with sufficient active area in the solution to keep a complete and fast electron transfer.

As an example, the insulating materials 203 and 204 can be PTFE (polytetrafluoroethylene). But there is no limitation on the selection of material for the insulating materials 203 and 204. In theory, all non-electrical-conductive materials can be used as insulating material. Suitable materials can be selected on the basis of the application of the voltammetric sensor and/or specific requirements.

Similar to Figure 5A, the hatchings in Figure 5B denote the active areas of the working electrode 201 and the counter electrode 202. The ratio of the active area of the counter electrode 202 to the active area of the working electrode 201 is equal to or larger than 20, but more preferably larger than 100. Here, the active area of each electrode is the area of the bottom surface of the electrode. Therefore, the active area ratio between the counter electrode and the working electrode, which is at least equal to or larger than 20 between the counter electrode and the working electrode can be fulfilled as long as the ratio of the area of the bottom surface of the counter electrode to that of the working electrode is at least equal to or larger than 20. In other words, the two-dimensional surface contact makes it easier to control the active area ratio between the counter electrode and the working electrode.

Although the working electrode and the counter electrode as shown in Figure 5B are shaped as cylinders, the shapes of the electrodes are not limited to the shape of a cylinder. The working electrode and the counter electrode can be formed in different shapes according to the applications of the voltammetric sensor and/or specific requirements.

As an example, the material of the working electrode can be Pt, W, Ag, etc., and the material of the counter electrode can be Pt, Au, stainless steel, etc. But there is no limitation on the selection of material for the working electrode and the counter electrode. Suitable materials of the electrodes can be selected on the basis of the application of the voltammetric sensor and/or specific requirements. It should be noted that, although both the working electrode and the counter electrode are covered with insulating materials in Figure 5B, it is also possible to cover only one of the electrodes with an insulating material, as long as the active area ratio between the counter electrode and the working electrode stays at least equal to or larger than 20. In other words, at least part of the working electrode and/or at least part of the counter electrode can be covered with an insulating material.

Figure 5C schematically shows another example of the voltammetric sensor by means of a front view and a bottom view. In this example, the voltammetric sensor 200 further comprises a first conductor 205 that is electrically connected with the working electrode 201 and a second conductor 206 that is electrically connected with the counter electrode 202. The conductors 205 and 206 are used for electrically connecting the working electrode 201 and the counter electrode 202 with external electronics, such as a voltmeter, an ammeter, etc. The first and the second conductors 205 and 206 are formed by materials that have no reactivity in the voltammetric measurement; and the first conductor 205 can be of a similar or of a different material as the material of the second conductor 206. The materials of the conductors 205 and 206 can furthermore be selected in such a way that the are less expensive than the materials of the electrodes, thereby lowering the cost of producing the voltammetric sensor. Although the first and the second conductors 205 and 206 as shown in Figure 5C have the same diameters as the working electrode 201 and the counter electrode 202, respectively, the first and the second conductors 205 and 206 can also be formed with different diameters from the working electrode 201 and the counter electrode 202, respectively.

Similar to Figure 5A, the hatchings in Figure 5C denote the active areas of the working electrode 201 and the counter electrode 202. The ratio of the active area of the counter electrode 202 to the active area of the working electrode 201 is equal to or larger than

20, but more preferably larger than 100. Here, the active area of each electrode is the sum of the area of the circumferential surface of the electrode and the area of the bottom surface of the electrode.

Although the electrodes and the conductors as shown in Figure 5C are shaped as cylinders, the shapes of the electrodes and the conductors are not limited to the shape of a cylinder. The electrodes and the conductors can be formed in different shapes according to the application of the voltammetric sensor and/or specific requirements.

As an example, the material of the working electrode can be Pt, W, Ag, etc., and the material of the counter electrode can be Pt, Au, stainless steel, etc. But there is no limitation on the selection of material for the working electrode and the counter electrode. Suitable materials of the electrodes can be selected on the basis of the application of the voltammetric sensor and/or specific requirements.

It should be noted that, although both the working electrode and the counter electrode are electrically connected with the conductors in Figure 5C, it is also possible to form an assembly of only one conductor that is electrically connected with one of the two electrodes, as long as the active area ratio between the counter electrode and the working electrode stays at least equal to or larger than 20. In other words, the voltammetric sensor can comprise a first conductor that is electrically connected with the working electrode and/or a second conductor that is electrically connected with the counter electrode.

Figure 5D schematically shows another example of the voltammetric sensor by means of a front view and a bottom view. The voltammetric sensor as shown in Figure 5D has a similar structure to that of the voltammetric sensor as shown in Figure 5C, except that at least part of the first conductor 205 and at least part of the second conductor 206 are covered with insulating materials 203 and 204, respectively. The insulating materials 203 and 204 can be of the same material or of different materials.

Optionally, the insulating materials 203 and 204 can be formed to further cover at least parts of the circumferential surfaces of the working electrode 201 and the counter electrode 202. For example, the insulating materials 203 and 204 can be formed to further cover the entire circumferential surfaces of the working electrode 201 and the counter electrode 202 with the bottom surfaces of the electrodes exposed, so as to enable the working electrode 201 and the counter electrode 202 to form a two-dimensional surface contact for the contact with the solution.

It should be noted that, although both the first conductor and the second conductor are covered with insulating materials in Figure 5D, it is also possible to cover only one of the conductors with an insulating material. In other words, at least part of the first conductor and/or at least part of the second conductor can be covered with an insulating material.

Figures 6A-6D schematically show other examples of the voltammetric sensor according to the embodiment of the present invention.

In the voltammetric sensors as shown in Figures 6A-6D, the working electrode 201 and the counter electrode 202 are also formed separately. Compared with the voltammetric sensors as shown in Figures 5A-5D, the counter electrodes of the voltammetric sensors in these examples form at least part of a container for holding a solution that contains the analyte to be detected.

As shown in Figure 6A, the voltammetric sensor 300 comprises a working electrode 301 shaped as a rod and a counter electrode 302 forming at least part of a container for holding the solution. As an example, the counter electrode 302 can form the bottom and one of the sidewalls of the container. In Figure 6A, the hatchings denote the active areas of the working electrode 301 and the counter electrode 302. The ratio of the active area of the counter electrode 302 to the active area of the working electrode 301 is equal to or larger than 20, but more preferably larger than 100. Here, the active area of the working electrode is the sum of the area of the immersed portion of the circumferential surface and the area of the bottom surface of the working electrode, whereas the active area of the counter electrode is the sum of the area of the portion of the sidewall of the container, which is in contact with the solution, and the area of the bottom surface of the container.

Similar to the voltammetric sensor as shown in Figure 6A, on the surfaces of the electrodes of the voltammetric sensor 300, it is possible to use mark(s) to indicate the active areas of the electrodes. For example, there is a range denoted by two marked lines formed on the circumferential surface of the working electrode 301 and/or there is another range denoted by two marked lines formed on the surface of the portion of the counter electrode 302 forming the sidewall of the container. The active area ratio between the counter electrode and the working electrode, which is at least equal to or larger than 20, between the counter electrode and the working electrode can be fulfilled when the liquid surface of the solution is within the range(s). It should be noted that such a mark is not necessary in some cases.

Figure 6B schematically shows another example of the voltammetric sensor. In this example, at least part of the working electrode 301 is covered with an insulating material 303 and at least part of the counter electrode 302 is covered with an insulating material 304.

The insulating material 303 surrounds part of the circumferential surface of the working electrode 301 with the bottom surface and the upper portion of the working electrode exposed. And the insulating material 304 partially covers the portion of the counter electrode 302 that forms the sidewall of the container and is formed down to the bottom of the container. The insulating materials 303 and 304 can be of the same material or of different materials.

The insulating materials 303 and 304 enable the working electrode 301 and the counter electrode 302 to form a two-dimensional surface contact for the contact with the solution. As described above, such a two-dimensional surface contact can easily get the electrode fully immersed with sufficient active area in the solution to keep a complete and fast electron transfer.

As an example, the insulating materials 303 and 304 can be PTFE (polytetrafluoroethylene). But there is no limitation on the selection of material for the insulating materials 303 and 304. In theory, all non-electrical-conductive materials can be used as insulating material. Suitable materials can be selected on the basis of the application of the voltammetric sensor and/or specific requirements.

In the voltammetric sensor as shown in Figure 6B, the ratio of the active area of the counter electrode 302 to the active area of the working electrode 301 is equal to or larger than 20, but more preferably larger than 100. Here, the active area of the working electrode is the area of the bottom surface of the electrode, whereas the active area of the counter electrode can be regarded as the area of the portion of the counter electrode that forms the bottom surface of the container. Therefore, the active area ratio between the counter electrode and the working electrode, which is at least equal to or larger than 20, between the counter electrode and the working electrode can be fulfilled as long as the active area ratio between these two bottom surfaces is at least equal to or larger than 20. In other words, the two- dimensional surface contact makes it easier to control the active area ratio between the counter electrode and the working electrode.

It should be noted that, although both of the working electrode and the counter electrode are covered with insulating materials in Figure 6B, it is also possible to cover only one of the electrodes with an insulating material, as long as the active area ratio between the counter electrode and the working electrode stays at least equal to or larger than 20. In other words, at least part of the working electrode and/or at least part of the counter electrode can be covered with an insulating material.

Figure 6C schematically shows another example of the voltammetric sensor. In this example, the voltammetric sensor 300 further comprises a first conductor 305 that is electrically connected with the working electrode 301 and a second conductor 306 that is electrically connected with the counter electrode 302, which forms the bottom of the container. The conductors 305 and 306 are used for electrically connecting the working electrode 301 and the counter electrode 302 with external electronics, such as a voltmeter, an ammeter, etc. The first and the second conductors 305 and 306 are formed by materials that have no reactivity in the voltammetric measurement, and the material of the first conductor 305 can be of the same material or of different material compared to the material of the second conductor 306. Furthermore, it is possible to select materials that are less expensive for the conductors 305 and 306 than the materials of the electrodes, which thereby lowers the cost of producing the voltammetric sensor. Although the first conductor 305 as shown in Figure 6C has the same diameter as the working electrode 301, the first conductor 305 can also be formed with a different diameter than the one of the working electrode 301.

In the voltammetric sensor as shown in Figure 6C, the ratio of the active area of the counter electrode 302 to the active area of the working electrode 301 is equal to or larger than 20, but more preferably larger than 100. Here, the active area of the working electrode

301 is the sum of the area of the circumferential surface of the electrode and the area of the bottom surface of the electrode, whereas the active area of the counter electrode is the area of the counter electrode 302 forming the bottom of the container.

It should be noted that, although both the working electrode and the counter electrode are electrically connected with conductors in Figure 6C, it is also possible to form only one conductor that is electrically connected with one of the two electrodes as long as the active area ratio between the counter electrode and the working electrode stays at least equal to or larger than 20. In other words, the voltammetric sensor can comprise a first conductor that is electrically connected with the working electrode and/or a second conductor that is electrically connected with the counter electrode.

Figure 6D schematically shows another example of the voltammetric sensor. The voltammetric sensor as shown in Figure 6D has a similar structure to that of the voltammetric sensor as shown in Figure 6C, except that at least part of the first conductor 305 and at least part of the second conductor 306 are covered with insulating materials 303 and 304, respectively. The insulating materials 303 and 304 can be of the same material or of different materials.

Optionally, the insulating material 303 can be formed to further cover at least part of the circumferential surface of the working electrode 301. For example, the insulating material 303 can be formed to further cover the entire circumferential surface of the working electrode 301 with the bottom surface of the electrode exposed; while the insulating material 304 can be formed down to the bottom of the container, so the working electrode 301 and the counter electrode 302 can form a two-dimensional surface contact for the contact with the solution.

Although both the first conductor and the second conductor are covered with insulating materials in Figure 6D, it is also possible to cover only one of the conductors with an insulating material. In other words, at least part of the first conductor and/or at least part of the second conductor can be covered with an insulating material.

It should be noted that the shapes of the electrodes and the conductors are not limited to those shown in Figures 6A-6D. The electrodes and the conductors can be formed in different shapes according to the application of the voltammetric sensor and/or specific requirements. As an example, the material of the working electrode can be Pt, W, Ag, etc., and the material of the counter electrode can be Pt, Au, stainless steel, etc. But there is no limitation on the selection of material for the working electrode and the counter electrode. Suitable materials of the electrodes can be selected on the basis of the application of the voltammetric sensor and/or specific requirements.

Figures 7A-7B schematically show other examples of the voltammetric sensor according to the embodiment of the present invention.

The voltammetric sensors as shown in Figures 7A-7B are formed as integrated sensors.

Figure 7A schematically shows one example of the voltammetric sensor by means of a front view and a top view. As shown in Figure 7A, the voltammetric sensor 400 comprises a working electrode and a counter electrode. The working electrode comprises a first portion 401a to be immersed in the solution and a second portion 401b connected with the first portion 401a and used for electrically connecting the first portion 401a with external electronics, such as a voltmeter, an ammeter, etc. The counter electrode also comprises a first portion 402a to be immersed in the solution and a second portion 402b connected with the first portion 402a and used for electrically connecting the first portion 402a with external electronics. The outer surface of the second portion 401b of the working electrode is partially surrounded by an insulating material 403 and the first portion 402a of the counter electrode is formed to partially surround the outer surface of the insulating material 403 and to be separated from the first portion 401a of the working electrode. The outer surface of the second portion 402b of the counter electrode is also partially surrounded by the insulating material 403.

In Figure 7A, the dashed lines show that the portion 401b is embedded in the insulating material 403 and passes through it at one end. The hatchings denote the active areas of the working electrode and the counter electrode. The ratio of the active area of the counter electrode connected to the active area of the working electrode is equal to or larger than 20, but more preferably larger than 100. Here, the active area of the working electrode can be regarded as the sum of the areas of the circumferential surface and the bottom surface of the first portion 401a of the working electrode, whereas the active area of the counter electrode can be regarded as the area of the circumferential surface of the first portion 402a of the counter electrode. Figure 7B schematically shows another example of the voltammetric sensor. The voltammetric sensor as shown in Figure 7B has a similar structure to that of the voltammetric sensor as shown in Figure 7 A, except that the second portion 401b of the working electrode and the second portion 402b of the counter electrode are replaced by a first conductor 405 and a second conductor 406, respectively. The conductors 405 and 406 are used for electrically connecting the working electrode 401 and the counter electrode 402 with external electronics, such as a voltmeter, an ammeter, etc. Thefirst conductor 405 can be of a similar or different a material asthe material of the second conductor 406. The materials of the conductors 405 and 406 can be selected to be less expensive than the materials of the electrodes, thereby lowering the cost of the voltammetric sensor.

It should be noted that, although the voltammetric sensors as shown in Figures 7A and 7B are shaped as cylinders, the shape of the voltammetric sensor is not limited to the shape of a cylinder. The voltammetric sensor can be formed in different shapes according to applications of the voltammetric sensor and/or specific requirements. For example, the cross section of the voltammetric sensor can be in the shape of triangle, square, ellipse, polygon, etc.

As an example, the material of the working electrode can be Pt, W, Ag, etc., and the material of the counter electrode can be Pt, Au, stainless steel, etc.; the insulating material can be PTFE (polytetrafluoroethylene); and the material of the conductors can be Cu, Ag, etc. But there is no limitation on the selection of material for the electrodes, the conductors and the insulating material. Suitable materials can be selected according to applications of the voltammetric sensor and/or specific requirements.

Figures 8A-8B schematically shows other examples of the voltammetric sensor according to the embodiment of the present invention.

The voltammetric sensors as shown in Figures 8A-8B are also formed as integrated sensors.

Figure 8A schematically shows one example of the voltammetric sensor by a cross section view and a bottom view. As shown in Figure 8A, the voltammetric sensor 500 comprises a working electrode and a counter electrode. The working electrode comprises a first portion 501a to be in contact with the solution which is the active area of the working electrode and a second portion 501b connected with the first portion 501a and used for electrically connecting the first portion 501a with external electronics, such as a voltmeter, an ammeter, etc. The counter electrode also comprises a first portion 502a to be in contact with the solution which is the active area of the counter electrode and a second portion 502b connected with the first portion 502a and used for electrically connecting the first portion 502a with the external electronics. The first portion 502a (active area) of the counter electrode is formed by the bottom surface of the counter electrode in a disk shape, and the first portion 501a of the working electrode is formed to be positioned in the middle of the disk-shaped portion 502a of the counter electrode and separated from the portion 502a by an insulating material 503. As shown in Figure 8A, the bottom surfaces of the portions 501a and 502a are formed as concentric rings. The outer surface of the second portion 501b of the working electrode and the outer surface of the second portion 502b of the counter electrode are partially surrounded by the insulating material 503.

Optionally, the outer surface of the first portion 502a of the counter electrode can also be partially covered by the insulating material 503 with only the bottom surface of the portion 502a exposed, as shown in Figure 8A. In other words, the bottom surface of the working electrode and the bottom surface of the counter electrode insulated by the insulating material 503 and form a two-dimensional surface contact for contacting with the solution. Which also means the active area of the working electrode is formed by the bottom surface of the working electrode; and the active area of the counter electrode is formed by the bottom surface of the counter electrode.

In the voltammetric sensor as shown in Figure 8A, the ratio of the active area of the counter electrode to the active area of the working electrode is equal to or larger than 20, more preferably, larger than 100. Here, the active area of the working electrode is the area of the bottom surface of the first portion 501a of the working electrode and the active area of the counter electrode is the area of the bottom surface of the first portion 502a of the counter electrode. Therefore, the active area ratio at least equal to or larger than 20 between the counter electrode and the working electrode can be fulfilled as long as the area ratio between these two bottom surfaces is at least equal to or larger than 20. In other words, the two dimensional surface contact makes it easier to control the active area ratio between the counter electrode and the working electrode.

Figure 8B schematically shows another example of the voltammetric sensor. The voltammetric sensor as shown in Figure 8B has a similar structure to that of the voltammetric sensor as shown in Figure 8A, except that the second portion 501b of the working electrode and the second portion 502b of the counter electrode are replaced by a first conductor 505 and a second conductor 506, respectively. The conductors 505 and 506 are used for electrically connecting the working electrode 501 and the counter electrode 502 with external electronics, such as a voltmeter, an ammeter, etc. The first conductor 505 can be of a similar or a different material as the material of the second conductor 506. The materials of the conductors 505 and

506 can be selected to be less expensive than the materials of the electrodes, thereby lowering the cost of the voltammetric sensor.

It should be noted that, the shape of the voltammetric sensor is not limited to those as shown in Figures 8 A and 8B. The voltammetric sensor can be formed in different shapes according to the application of the voltammetric sensor and/or specific requirements.

For example, the cross section of the voltammetric sensor can be in the shape of a triangle, square, ellipse, polygon, etc. In addition to the structure of the concentric rings, the structures of the working electrode and the counter electrode can also be shaped in other non-concentric shapes.

As an example, the material of the working electrode can be Pt, W, Ag, etc., and the material of the counter electrode can be Pt, Au, stainless steel, etc.; the insulating material can be PTFE (polytetrafluoroethylene); and the material of the conductors can be Cu, Ag, etc. But there is no limitation on the selection of material for the electrodes, the conductors and the insulating material. Suitable materials can be selected according to the application of the voltammetric sensor and/or specific requirements.

The voltammetric sensors as described above can be used in one or more of the following areas: domestic appliances; food industry; and drinking water industry.

The present invention also provides a method for detecting analyte in a solution by the voltammetric sensor as describe above. The method comprises: applying a voltage to the working electrode and the counter electrode that is at least partially in contact with the solution; and measuring a response current flowing through the working electrode and the counter electrode so as to detect the analyte in the solution.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. The different embodiments described above and in the claims can also be combined. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from the study of the drawings, the disclosure and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The reference signs in the claims should not be construed as limiting the scope of these claims.