Phosphate ion detection sensor, pretreatment method thereof, and use method thereof

Abstract

To provide a phosphate ion detection sensor suitable for use in a phosphate buffer system in a living body.SOLUTION: An electrochemical sensor comprises a working electrode 30 made of a Zr-based material, and a reference electrode 40 selected from any one of an Ag / AgCl electrode, a calomel electrode, a Hg / HgO electrode, a lead electrode, a precious metal, and a standard hydrogen electrode, where the working electrode 30 is brought into contact with a phosphate buffer solution containing phosphate ions, the surface of the working electrode 30 that comes into contact with an electrolyte solution to be measured has a coating layer formed of a zirconium phosphate layer, and the sensor is configured to measure change in an equilibrium reaction between zirconium and zirconium phosphate, which forms the working electrode 30, as change in natural potential.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a phosphate ion detection sensor suitable for use in a phosphate buffer system in a living body. The present invention also relates to a pretreatment method for a phosphate ion detection sensor suitable for use in a phosphate buffer system in a living body, and a method for using the same. [Background technology]

[0002] Phosphate detection sensors are used, for example, to detect eutrophication, which is a water pollution problem, and in the phosphate buffer system in living organisms, but are also used in metal plating applications. "Eutrophication," a typical water pollution problem in lakes and ponds, is a state in which nutrients such as nitrogen and phosphorus accumulate more than necessary and their concentrations become high. As eutrophication progresses, phytoplankton and other organisms that use nitrogen and phosphorus as nutrients proliferate abnormally, causing not only mass outbreaks of blue-green algae and mass deaths of fish and shellfish, but also having a major impact on water use, such as on drinking water, agricultural and industrial water, and fishery resources. Therefore, eutrophication countermeasures have been adopted to reduce the amount of nitrogen and phosphorus discharged into rivers that flow into closed water bodies such as lakes, bays, etc. By installing a device equipped with a sensor that can measure changes in phosphate ion concentration in closed water bodies such as lakes, bays, etc., it is expected that the state of water pollution can be continuously monitored on a daily basis.

[0003] On the other hand, almost all biological processes are pH-dependent. Even a slight change in pH can cause metabolic acidosis or alkalosis, resulting in metabolic failure. Therefore, the buffer system in the body plays an important role in maintaining the pH within an extremely narrow range and functioning as a resistance system that minimizes pH changes caused by intracellular and extracellular influences, thereby allowing metabolism to proceed normally. Among the buffer systems in the body, the phosphate buffer system is extremely important because the phosphate concentration inside the cells is kept higher than outside the cells. Therefore, the main molecule that exerts a buffering effect "inside the cells" is the "phosphate ion." The phosphate concentration in living cells is typically 1 to 50 mM. In contrast, the environmental standards (for lakes and marshes) for the conservation of the living environment set by the Ministry of the Environment stipulate that total phosphorus should be 0.1 mg / L or less for environmental conservation purposes. In other words, when considering the measurement range as a phosphate ion detection sensor, the phosphate concentration in living organisms is 1,000 to 100,000 times higher than that of phosphate concentration sensors used for red tide countermeasures.

[0004] To date, methods such as absorptiometry, volumetric methods, atomic absorption spectrometry, gravimetry, and biosensor methods have been proposed for measuring the concentration of phosphate ions in phosphate buffer solutions (see, for example, Patent Documents 1 and 2). However, the above-mentioned conventional methods used for detecting eutrophication have the following problems. (a) Although the sensitivity of phosphate ion concentration measurement is high, the phosphate ion concentration in the body (1 to 50 mM) is outside the measurement range. (i) The measured phosphate ion concentration changes depending on the presence of other ions in the body (e.g. chloride ions and various metal ions). (c) A large device is required to analyze the measured phosphate ion concentration, and the device cannot be incorporated into the living body (it is difficult to continuously obtain information from within the living body).

[0005] Representative metallic materials that are implanted in living bodies include pure Ti and Ti alloys, stainless steel, and precious metals. Of these, stainless steel is less corrosion resistant than Ti-based materials and precious metals, and therefore is not suitable as a bioexposed material for sensors that are placed in living bodies for long periods of time. Another problem is that precious metals, such as gold, platinum, and palladium, are expensive. Ti-based materials are highly biocompatible and have excellent corrosion resistance, but they react with calcium ions and phosphate ions in body fluids to precipitate calcium phosphate on the surface, which means that another reaction may be mixed into the equilibrium reaction of metal / metal phosphate, potentially affecting the natural potential.

[0006] On the other hand, Non-Patent Document 1 examines the difference in surface properties between titanium and zirconium in the calcium phosphate formation ability in simulated biological fluids. The surface oxide film of titanium is not completely oxidized and is relatively reactive. On the other hand, the surface oxide film of zirconium is more passive and protective than the surface oxide film of titanium. Neither calcium nor phosphate exists stably alone on titanium, and calcium phosphate is formed naturally, and the calcium phosphate formed on titanium is stable and has a protective effect. On the other hand, calcium is not incorporated on zirconium, but zirconium phosphate is easily formed on zirconium, so it has excellent stability and protection. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6799236 [Patent Document 2] Patent No. 4686885 [Non-patent literature]

[0008] [Non-Patent Document 1] Y. Tsutsumi, D. Nishimura, H. Doi, N. Nomura, T. Hanawa, Materials Science and Engineering C, 29 1702-1708 (2009) Summary of the Invention [Problem to be solved by the invention]

[0009] Here, the requirements for the electrode material used in the phosphate ion detection sensor are that the change in the measured potential must be influenced only by the change in the phosphate ion concentration, in other words, that no other electrochemical reactions occur on the electrode surface. Possible chemical reactions on the electrode surface include the dissolution of metal due to corrosion reactions and the formation of calcium phosphate due to the reaction of calcium ions and phosphate ions in body fluids. As a general-purpose metal material for medical use, stainless steel has concerns about its corrosion resistance, and Ti-based materials have the problem of accelerating the formation of calcium phosphate. In addition, precious metals other than Pt have issues with corrosion resistance, the formation of calcium phosphate cannot be suppressed, and they are expensive.

[0010] The present invention has been made to solve the above-mentioned problems of the prior art, and has an object to provide a phosphate ion detection sensor suitable for use in a phosphate buffer system in a living body. [Means for solving the problem]

[0011] The inventors of the present invention thought that a Zr-based material that has excellent biocompatibility and corrosion resistance, is not as expensive as precious metals, and does not form calcium phosphate on the surface could be used as an electrode, and came up with the present invention. That is, Zr (zirconium) belongs to the 4th group like Ti, and forms a passivation film, which is a dense oxide film, on the surface, and therefore exhibits extremely good corrosion resistance. In addition, unlike Ti, Zr hardly forms calcium phosphate on the Zr surface, so it is suitable as a metal material to be embedded in a living body. Furthermore, Zr has excellent biocompatibility and is not as expensive as precious metals.

[0012] [1] As shown in FIG. 1, the phosphate ion detection sensor of the present invention is an electrochemical sensor including a working electrode 30 made of a Zr-based material and a reference electrode 40 selected from any one of an Ag / AgCl electrode, a calomel electrode, an Hg / HgO electrode, a lead electrode, a noble metal electrode, and a standard hydrogen electrode, The surface of the working electrode 30, which comes into contact with the electrolyte solution to be measured, has a coating layer formed of a zirconium phosphate layer, and is configured to measure changes in the equilibrium reaction between zirconium and zirconium phosphate that form the working electrode 30 as changes in natural potential. [2] In the phosphate ion detection sensor [1] of the present invention, the Zr-based material is preferably selected from pure zirconium, a binary alloy selected from one or more of Zr-Cu, Zr-Ni, Zr-Fe, Zr-Al, Zr-Cr, Zr-Ti, Zr-Sn, Zr-Bi, Zr-Sb, Zr-Mo, or Zr-Nb, or a ternary or higher alloy selected from two or more of Zr and Cu, Ni, Fe, Al, Cr, Ti, Sn, Bi, Sb, Mo, or Nb. [3] In the phosphate ion detection sensor [1] of the present invention, the precious metal is preferably selected from the group consisting of Ag (silver), Au (gold), Pt (platinum), Pd (palladium), Rh (rhodium), Ru (ruthenium), Os (osmium), Ir (iridium), and alloys thereof. [4] In the phosphate ion detection sensor [1] of the present invention, the coating layer preferably covers the surface of the working electrode in contact with the electrolyte solution to be measured, with a thickness of 1 nm to 50 nm, more preferably 1 nm to 10 nm.

[0013] [5] In the pretreatment method of the phosphate ion detection sensor [1] to [4] of the present invention, in which the surface of the working electrode that comes into contact with the electrolyte solution to be measured is covered with a zirconium phosphate layer, the solution to be brought into contact with the surface of the working electrode 30 is a phosphate buffer solution containing 0.1 mM to 100 mM phosphate ions, the pretreatment temperature is from 0°C to 100°C, and the pretreatment time is from 0.1 h to 100 h. [6] In the pretreatment method [5] for the phosphate ion detection sensor of the present invention, preferably, the solution to be brought into contact with the working electrode 30 is a phosphate buffer solution containing 1 mM to 50 mM phosphate ions, the pretreatment temperature is 30°C or higher and 60°C or lower, and the pretreatment time is 1 hour or higher and 48 hours or lower. [7] A method for using the phosphate ion detection sensor of the present invention is such that the measurement range of the phosphate ion sensor according to any one of [1] to [4] is 0.1 mM to 20 mM. [8] In the method [7] for using the phosphate ion detection sensor of the present invention, the measurement range of the phosphate ion sensor is preferably 1 mM to 4 mM, which is the range of phosphate ion concentrations in a living body. Effect of the Invention

[0014] According to the phosphate ion detection sensor and method for using the same of the present invention, since a Zr-based material is used as the working electrode, the sensor is sensitive to changes in phosphate ion concentration in the range of 1 to 50 mM, is less susceptible to the influence of other factors in the body (such as salinity, pH, and temperature), and can measure changes in potential by exposing only a small portion of the electrode, making it possible to install the sensor in a very small device. According to the pretreatment method for the phosphate ion detection sensor of the present invention, as a pretreatment for immersing a Zr-based material in the environment to be measured, zirconium phosphate is formed in advance on the electrode surface to stabilize the electrode surface, thereby preventing a large change in potential when the electrode is immersed in a solution. [Brief description of the drawings]

[0015] [Figure 1] 1 is an overall configuration diagram of a phosphate ion detection sensor showing one embodiment of the present invention. [Diagram 2] FIG. 1 is a diagram showing a main part of a phosphate ion detection sensor according to one embodiment of the present invention, in which (A) is a schematic diagram and (B) is an external view. [Figure 3A] FIG. 1 shows the change in spontaneous potential of pure Zr immersed in 10 mM PBS for 48 hours. [Figure 3B] FIG. 1 shows the change in spontaneous potential of pure Zr immersed in PBS at 50° C. [Figure 4] FIG. 1 is an explanatory diagram showing the case where pure Zr is immersed in PBS of different concentrations, (A) showing the procedure for the ascending order test, and (B) showing the procedure for the descending order test. [Diagram 5] FIG. 1 shows the potential changes in ascending order tests of samples immersed in 10 mM PBS at each temperature for 48 hours. [Figure 6] This shows the potential change in ascending order tests of samples immersed in PBS of each concentration at 50° C. for 48 hours. [Figure 7] This is a graph showing potential changes in a descending test of samples immersed in 10 mM PBS at each temperature for 48 hours. [Figure 8] This shows the potential change in a descending test of samples immersed in PBS of each concentration at 50°C for 48 hours. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] <Detection principle of the phosphate ion detection sensor of the present invention> The detection principle of the phosphate ion detection sensor of the present invention uses an electrochemical method. The electrochemical detection principle is a measurement principle that replaces measurement methods such as absorptiometry, volumetric method, atomic absorption spectrometry, gravimetry, and biosensor method. In other words, in the electrochemical detection principle, if a metal is an oxidant (Ox) and a metal phosphate compound is a reductant (Red), the following equilibrium reaction occurs between the oxidant Ox and the reductant Red.

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[0017] At this time, the equilibrium potential E of this reaction system is expressed by the following equation (Nernst equation):

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[0018] In other words, in the phosphate ion detection sensor of the present invention, a metal material containing Zr as a main component (Zr-based material) is used as the electrode substrate of the working electrode. When the Zr-based material is immersed in a phosphate buffer solution containing phosphate ions, zirconium phosphate is formed on the Zr surface in the material. In the present invention, the change in the equilibrium reaction between zirconium and zirconium phosphate is measured as a change in natural potential. EXAMPLES

[0019] FIG. 1 is a diagram showing the overall configuration of a phosphate ion detection sensor according to one embodiment of the present invention. In the figure, a beaker 10 is filled with a phosphate buffer solution 20 as an electrolyte solution, and a working electrode 30 and a reference electrode 40 are immersed in the phosphate buffer solution 20. The working electrode 30 is provided with a resin 32 that limits the area in contact with the phosphate buffer solution 20, and a conductor (reference electrode side) 34. The reference electrode 40 is provided with a conductor (reference electrode side) 44 that is connected to a potentiostat 50. The potentiostat 50 measures the potential difference between the working electrode 30 and the reference electrode 40. A potentiostat is a device that generally controls a three-electrode cell consisting of a working electrode, a counter electrode, and a reference electrode, and controls the potential level of the electrodes as desired, regardless of the state of the electrolyte. A galvanostat is a device that has a very high internal resistance and thus accurately controls the current flowing through the electrodes, and a galvanostat may be used instead of a potentiostat. The reference electrode 40 may be a hydrogen electrode, a calomel electrode, a silver-silver chloride electrode (Ag / AgCl electrode), a mercury-mercury oxide electrode (Hg / HgO electrode), a mercury-mercury sulfate electrode, or the like.

[0020] FIG. 2 is a diagram showing a main part of a phosphate ion detection sensor according to one embodiment of the present invention, where (A) is a schematic diagram and (B) is an external view. In the figure, the main parts of the phosphate ion detection sensor are a working electrode 30, a resin 32, and a conducting wire 34. The working electrode 30 is made of a Zr-based material such as a pure zirconium disk. Zr-based materials include binary alloys such as Zr-Cu, Zr-Ni, Zr-Fe, Zr-Al, Zr-Cr, Zr-Ti, Zr-Sn, Zr-Bi, Zr-Sb, Zr-Mo, and Zr-Nb (see Aoki Shigeo and Taro Yoshinori, "Mechanical Properties, Heat Treatability, and High-Temperature Oxidation of Zr-Based Binary Alloys," Journal of the Japan Institute of Metals, Vol. 26, pp. 215-219 (1962)). The resin 32 is an insulating plastic, and covers the area of ​​the working electrode 30 except for the electrode surface. Various plastics such as epoxy resin, polyurethane, phenolic resin, tetrafluoroethylene resin, polyacetal, polyvinyl chloride, ABS resin, polyethylene, polypropylene, polystyrene, etc. are used for the resin 32. The lead wire 34 connects the working electrode 30 and the potentiostat 50 so that the potential change of the working electrode 30 can be measured, and for example, a coated copper wire is used.

[0021] In this specification, potential is indicated as ○V, which is based on a silver-silver chloride standard (vs. Ag / AgCl). <1. Formation of zirconium phosphate on the surface of pure Zr (sensor pretreatment)> A pure Zr rod (purity 99% or more) was used for the working electrode 30. This rod was cut into slices with a cutter (manufacturer: Heiwa Technica, model name: Finecut 31-PIN) to a thickness of about 5 mm, and a conductive wire 34 was attached to one side with a conductive adhesive (manufacturer: Kaken Tech, model name: TK Paste), and then the electrode was embedded in insulating resin 20 (manufacturer: Struers K.K., model name: Epofix) (Figure 2B). Thereafter, the surface opposite to the surface to which the conductor 34 was connected (the measurement surface) was exposed, wet-polished with SiC waterproof abrasive paper (manufacturer: Struers K.K., model name: SiC abrasive paper) up to #2000, and ultrasonically cleaned in 2-propanol (manufacturer: Fujifilm Wako Pure Chemical Industries, Ltd., model name: 2-propanol, special reagent grade) for 5 minutes.

[0022] <Immersion in phosphate buffered saline (PBS) (pretreatment)> The sample of the working electrode 30 prepared in the sensor pretreatment was immersed in a phosphate buffer solution (hereinafter referred to as PBS) to form a zirconium phosphate layer as a coating layer on the surface of the working electrode 30. The PBS was prepared by immersing phosphate buffered saline tablets (Fujifilm Wako Pure Chemical Industries, Ltd., model name: phosphate buffered saline tablets) at 10, 20, and 50 mM PO4 3- After dissolving and diluting in distilled water to - The concentration was adjusted to a constant 0.14M by adding NaCl (hereinafter, referred to as 10 mM PBS, 20 mM PBS, and 50 mM PBS, respectively). The immersion temperature was set to three levels: room temperature, 37°C, and 50°C, and the immersion time was set to three levels: 17 h, 24 h, and 48 h. Table 1 shows the number of each example, the PBS concentration, the PBS temperature, and the immersion time. [Table 1]

[0023] Figure 3A shows the change in the natural potential of samples immersed in 10 mM PBS at each temperature for 48 hours. For all samples, the natural potential rose rapidly immediately after immersion and converged to a nearly constant value after a certain amount of time had passed. The higher the PBS temperature, the faster the rate of potential increase tended to be, but no effect of temperature was observed on the convergence value. The change in potential is due to the formation of zirconium phosphate on the Zr surface, and it is believed that Zr and zirconium phosphate reached equilibrium when the natural potential became constant. In addition, when focusing on the difference in immersion time, the potential had not yet converged to a constant value in either sample after immersion for 17 hours or 24 hours, suggesting that zirconium phosphate had not yet formed sufficiently on the sample surface.

[0024] In 10 mM PBS, the potential tended to converge to about -0.2 V at all temperatures, but the values ​​varied and the effect of the immersion temperature was not significant. Figure 3B shows the spontaneous potential change of the sample immersed in 10 mM, 20 mM, and 50 mM PBS at 50°C for 48 hours. The higher the PBS concentration, the faster the potential converged to a high potential. From the above, it was found that within the range of experimental conditions in the present invention, a stable zirconium phosphate surface could be obtained by immersing in PBS of a higher concentration at a higher temperature.

[0025] <2. Measurement of spontaneous potential change in a system where the phosphate ion concentration changes (sensor response)> The change in phosphate ion concentration was measured using samples in which zirconium phosphate was formed under each condition, which was prepared by sensor pretreatment. The phosphate buffer solution used in this test was phosphate buffered saline tablets (Fujifilm Wako Pure Chemical Industries, Ltd.) at 1, 2, 5, and 10 mM PO4 3- After dissolving and diluting in distilled water to - The concentration was adjusted to a constant 0.14 M by adding NaCl (hereinafter, these are referred to as 1 mM PBS, 2 mM PBS, 5 mM PBS, and 10 mM PBS, respectively). In order to confirm the sensor response when the phosphate ion concentration in the phosphate buffer solution changes from low to high, the sample that had undergone the sensor pretreatment was immersed in 1, 2, 5, and 10 mM PBS in that order, as shown in Figure 4(A), and a test (referred to as ascending order test) was conducted to measure the spontaneous potential change at that time. Table 2 shows the number of each example in the ascending order test, the PBS concentration, PBS temperature, and the immersion time. [Table 2]

[0026] In addition, as shown in Figure 4(B), in order to confirm the response of the sensor when the phosphate ion concentration in the phosphate buffer solution changes from high to low, a test (referred to as descending sequence test) was conducted in which the sensor was immersed in 10, 5, 2, and 1 mM PBS in that order and the spontaneous potential change was measured. The immersion time in each phosphate buffer solution was 5 minutes, and the temperature of the test machine was room temperature. Table 3 shows the number of each example in the descending sequence test, the PBS concentration, PBS temperature, and the immersion time. [Table 3]

[0027] Figure 5(a)-(c) shows the potential change in ascending order test of the sample immersed in 10 mM PBS at room temperature, 37℃, and 50℃ for 48h as pretreatment conditions. As shown in formula (3), the natural potential of the sample tends to decrease as the phosphate ion concentration in the phosphate buffer solution increases. In addition, a step-like potential change was measured when the sample was moved to PBS with different phosphate ion concentrations. The step-like potential change indicates that the Zr surface has good response to the change in phosphate ion concentration in the phosphate buffer solution, and Zr-based materials are suitable as phosphate ion sensors. On the other hand, the natural potential often changes gradually while immersed in PBS of the same concentration, and especially when immersed in 10 mM PBS, the natural potential continued to change without stabilization for 5min. This tendency was remarkable when the pretreatment temperature was room temperature and 37℃, and when the pretreatment temperature was 50℃, a stable natural potential response was obtained when immersed in 1 and 2 mM PBS. This suggests that the higher the pretreatment temperature, the more stable the natural potential response.

[0028] Figures 6(a)-(c) show the spontaneous potential changes in ascending order tests when the pretreatment temperature was fixed at 50°C and the pretreatment solution was 10, 20, and 50 mM PBS. When the pretreatment solution was 20 mM or 50 mM PBS, a very stable potential response was obtained in the range of 1-10 mM, and the step-like potential change was also clearly captured when the phosphate ion concentration was changed. This suggests that using a higher concentration PBS under pretreatment conditions allows the formation of more stable zirconium phosphate on the Zr surface, demonstrating that pretreatment with a higher concentration PBS is an effective means of improving the response of phosphate ion sensors.

[0029] Figures 7(a)-(c) show the potential changes in the descending test of samples immersed in 10 mM PBS at room temperature, 37°C, and 50°C for 48 hours as pretreatment conditions. As shown by formula (3), there was a tendency for the natural potential to increase as the phosphate ion concentration decreased. As with the ascending test, the response was poor in 5 and 10 mM PBS at all pretreatment temperatures, and a large change in natural potential was observed especially in 10 mM PBS. Furthermore, compared to the ascending test, no improvement in sensor response was observed due to differences in pretreatment temperature.

[0030] Figures 8(a)-(c) show the spontaneous potential changes in a descending test when the pretreatment temperature was fixed at 50°C and the pretreatment solutions were 10, 20, and 50 mM PBS. As in Figure 7, a large potential change was observed during immersion in 10 mM PBS, but a relatively good response was obtained in 1, 2, and 5 mM PBS, and the potential change during immersion was particularly small in 20 mM and 50 mM PBS, with a clear step-like potential change.

[0031] From the above results, it became clear that Zr-based materials are useful as phosphate ion sensors, and that a more responsive surface can be obtained by pretreating the material before use as a sensor, preferably by immersing it in 50 mM PBS at 50°C for 48 hours.

[0032] In the above embodiment, a phosphate buffered saline tablet is used as PBS, but the present invention is not limited thereto. For example, D-PBS (Dulbecco's Phosphate Buffered Saline) or Hank's balanced salt solution, which are widely used as simulated biological fluids, may be used. D-PBS is a phosphate buffered saline solution containing potassium chloride in addition to potassium-sodium phosphates and salt, and is used in the pretreatment stage for culturing tissues, organs, cells, etc., and in biochemical research. Hank's balanced salt solution is a balanced salt solution formulated with sodium bicarbonate and glucose in addition to the basic composition of D-PBS, and is used when transporting or pretreating tissues, organs, cells, etc. while maintaining their metabolic functions. [Industrial Applicability]

[0033] According to the phosphate ion detection sensor of the present invention, since a Zr-based material is used as the working electrode, it is sensitive to changes in phosphate ion concentration in the range of 1 to 50 mM, is not easily affected by other factors in the body (such as salinity, pH, and temperature), and can measure changes in potential by exposing only a small portion of the electrode, making it suitable as a phosphate ion detection sensor for implantation in the body and suitable for use in monitoring the phosphate buffer system in the body. [Explanation of symbols]

[0034] 10 Beaker 20 Phosphate Buffer Solution 30 Reference electrode 32 Resin 34 Lead wire (reference electrode side) 40 Reference electrode 44 Lead wire (reference electrode side) 50 Potentiostat

Claims

1. A working electrode made of a Zr-based material; a reference electrode selected from any one of an Ag / AgCl electrode, a calomel electrode, an Hg / HgO electrode, a lead electrode, a noble metal electrode, and a standard hydrogen electrode; An electrochemical sensor comprising: The surface of the working electrode that comes into contact with the electrolyte solution to be measured has a coating layer formed of a zirconium phosphate layer, The change in the equilibrium reaction between zirconium and zirconium phosphate forming the working electrode is measured as a change in natural potential. Phosphate ion sensor.

2. 2. The phosphate ion sensor according to claim 1, wherein the Zr-based material is selected from the group consisting of pure zirconium, a binary alloy selected from one or more of Zr-Cu, Zr-Ni, Zr-Fe, Zr-Al, Zr-Cr, Zr-Ti, Zr-Sn, Zr-Bi, Zr-Sb, Zr-Mo, and Zr-Nb, and a ternary or higher alloy selected from two or more of Zr and Cu, Ni, Fe, Al, Cr, Ti, Sn, Bi, Sb, Mo, and Nb.

3. 2. The phosphate ion sensor according to claim 1, wherein the precious metal is selected from the group consisting of Ag (silver), Au (gold), Pt (platinum), Pd (palladium), Rh (rhodium), Ru (ruthenium), Os (osmium), Ir (iridium), and alloys thereof.

4. 4. The phosphate ion sensor according to claim 1, wherein the covering layer covers the surface of the working electrode in contact with the electrolyte solution to be measured, with a thickness of 1 nm to 50 nm.

5. 5. A pretreatment method for a phosphate ion sensor according to claim 1, further comprising coating a surface of a working electrode that is in contact with an electrolyte solution to be measured with a zirconium phosphate layer, The solution to be brought into contact with the surface of the working electrode is a phosphate buffer solution containing 0.1 mM to 100 mM phosphate ions, The pretreatment temperature is 0° C. or higher and 100° C. or lower. The pretreatment time is 0.1 hours or more and 100 hours or less. A method for pretreatment of a phosphate ion sensor.

6. The solution to be brought into contact with the working electrode is a phosphate buffer solution containing 1 mM to 50 mM phosphate ions, The pretreatment temperature is 30° C. or higher and 60° C. or lower. The pretreatment time is 1 hour or more and 48 hours or less. The pretreatment method for a phosphate ion sensor according to claim 5 .

7. 5. A method for using a phosphate ion sensor according to claim 1, wherein the measurement range of the phosphate ion sensor is 0.1 mM to 20 mM.

8. 8. The method for using a phosphate ion sensor according to claim 7, wherein the measurement range of the phosphate ion sensor is 1 mM to 4 mM, which is the range of phosphate ion concentrations in a living body.

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