A specific electrochemical sensor based on metal oxides and its construction method and application

Abstract

The present invention provides an electrochemical sensor based on metal oxides and a construction method and application thereof. The electrochemical sensor of the present invention comprises a working electrode, a reference electrode and a counter electrode; the working electrode is obtained by modifying a conductive substrate with a metal oxide, and is also loaded with an oxidase and a cross-linking agent. By detecting hydrogen peroxide, a product of an oxidase-catalyzed reaction, through the electroreduction of the metal oxide, electrochemical sensors for glucose, uric acid, lactic acid, creatine, etc. are further constructed, which avoids interference from interfering substances during the detection process and has strong detection specificity and high sensitivity.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical sensors, and in particular refers to a specific electrochemical sensor based on metal oxides and a construction method and application thereof. Background Art

[0002] Electrochemical sensors constructed with oxidase as the recognition module are widely used in environmental monitoring, medical diagnosis and other fields. When oxygen is present, oxidase reacts with the analyte to generate hydrogen peroxide. Therefore, by detecting the concentration of hydrogen peroxide, the concentration of the analyte can be indirectly obtained. At present, such electrochemical sensors are usually based on the principle of electrochemical oxidation of hydrogen peroxide, and the catalysts used are mostly precious metals, such as platinum, rhodium, gold, and their alloys. Problems with existing electrochemical sensors: On the one hand, the precious metals used are expensive, which increases the production cost of the sensor. On the other hand, in order to achieve higher detection sensitivity, a higher potential needs to be applied during detection of oxidative sensors, which also causes endogenous and exogenous interfering substances such as ascorbic acid, uric acid, acetaminophen, dopamine, etc. to be oxidized at the same time, generating interference current and affecting the accuracy of the sensor.

[0003] In order to improve the anti-interference performance, reduction sensors based on the principle of electrochemical reduction of hydrogen peroxide have gradually come into the market. However, the commonly used precious metal catalysts will not only reduce hydrogen peroxide, but also reduce oxygen at the same potential. Therefore, the final output current of this type of sensor is the sum of the reduction currents of hydrogen peroxide and oxygen. From the thermodynamic point of view of the reaction, oxygen reduction even occurs more preferentially than hydrogen peroxide reduction. The oxygen concentration is easily affected by various factors in the environment, such as temperature, air pressure, etc. When the oxygen concentration fluctuates, the oxygen reduction current fluctuates accordingly, and the final output current also fluctuates, affecting the accuracy of the detection.

[0004] At present, hydrogen peroxide electroreduction catalysts with resistance to oxygen interference have been discovered, such as Prussian blue. Prussian blue is a hexacyanoferrate with unique structure and electrochemical properties. Prussian blue has a zeolite structure that allows low molecular weight molecules, such as hydrogen peroxide, to pass through. Although Prussian blue can be used to achieve highly selective detection of hydrogen peroxide and avoid interference from oxygen reduction and various interfering substances, its instability severely limits its application in practical processes. When the pH value of the test solution is greater than 6.4, hydroxide ions react with iron ions, causing the crystal structure to dissolve and affecting stability; in addition, changes in potassium ion concentration during the detection process will also seriously affect stability.

[0005] In order to solve the above problems, metal oxides with excellent stability are gradually used. An article reported the use of metal oxide-modified carbon paste electrodes to detect hydrogen peroxide concentration by electroreduction method. However, 1) ordinary metal oxides have poor conductivity, and electrons diffuse slowly at the electrolyte-metal oxide interface and in the bulk phase, and cannot be directly used for electrochemical detection. Therefore, metal oxides often need to be combined with highly conductive substances, such as carbon materials, to increase the electron transfer rate. The addition of carbon materials will also cause oxygen to be reduced synchronously during the hydrogen peroxide reduction process, and hydrogen peroxide cannot be accurately detected; 2) common metal oxides will also reduce oxygen while catalyzing the reduction of hydrogen peroxide, affecting the reduction current of hydrogen peroxide. It can be seen that the introduction of ordinary metal oxides cannot simultaneously solve the two problems of current reduction sensors: electrode stability and detection selectivity. Therefore, it is urgent to develop a specific electrochemical sensor with high selectivity.

[0006] Oxygen defects refer to defects formed when an oxygen atom is removed from the lattice oxygen of metal oxides. The introduction of oxygen defects can change the thermodynamic and kinetic properties of metal oxides during the reaction process. Therefore, by adjusting the concentration of oxygen defects, the conductivity of metal oxides and the adsorption properties of reactants (hydrogen peroxide and oxygen) can be adjusted, thereby changing the catalytic selectivity of metal oxides for their substrates. Through this strategy, it is expected to obtain a catalyst that only adsorbs and reduces hydrogen peroxide but not oxygen, and to construct a specific electrochemical sensor. Summary of the invention

[0007] To solve the above technical problems, the present invention provides a specific electrochemical sensor based on metal oxides and a construction method and application thereof, and constructs an electrochemical sensor that avoids interference from oxygen and other interfering substances during the electro-oxidation process.

[0008] The first object of the present invention is to provide an electrochemical sensor based on metal oxides, comprising a working electrode, a reference electrode and a counter electrode; the working electrode is obtained by modifying a conductive substrate with metal oxides.

[0009] In one embodiment of the present invention, the metal oxide is selected from metal oxides composed of metal elements with variable valence states.

[0010] In one embodiment of the present invention, the metal oxide is selected from one or more of tin oxide, iron oxide, manganese oxide, cerium oxide, cobalt oxide, tungsten oxide, vanadium oxide and nickel oxide; the valence of tin in the tin oxide is a mixture of divalent and tetravalent, the valence of iron in the iron oxide is a mixture of divalent and trivalent; the valence of manganese in the manganese oxide is a mixture of trivalent and tetravalent; the valence of cerium in the cerium oxide is a mixture of trivalent and tetravalent; the valence of cobalt in the cobalt oxide is divalent and trivalent; the valence of tungsten in the tungsten oxide is tetravalent and hexavalent; the valence of vanadium in the vanadium oxide is trivalent and pentavalent; the valence of nickel in the nickel oxide is divalent and tetravalent. The oxygen defect concentration in the tin oxide or iron oxide is 0%-35.0%; further, the oxygen defect concentration of the tin oxide is 5.3%-35%.

[0011] In one embodiment of the present invention, the tin oxide is prepared by the following method:

[0012] 1) Add ammonia water to the tin dichloride solution until it becomes alkaline, and separate the solid and liquid to obtain stannous hydroxide after the reaction is completed;

[0013] 2) Drying the stannous hydroxide in step 1);

[0014] 3) grinding the stannous hydroxide in step 2) and calcining to obtain the tin oxide;

[0015] In one embodiment of the present invention, the alkaline pH is 8-12.

[0016] In one embodiment of the present invention, in step 1), the concentration of the tin dichloride solution is 0.01 mol / L-0.5 mol / L.

[0017] In one embodiment of the present invention, in step 2), the drying temperature is 40° C.-120° C., and the drying time is 12 h-48 h.

[0018] In one embodiment of the present invention, in step 3), the calcination atmosphere is oxygen, inert gas and a mixture of oxygen and inert gas, the volume ratio of oxygen to inert gas is (0.1-1): (0.1-0.5), the calcination temperature is 400°C-600°C, and the time is 2h-12h.

[0019] In one embodiment of the present invention, the working electrode is also loaded with an oxidase and an enzyme cross-linking agent.

[0020] In one embodiment of the present invention, the oxidase is selected from one or more of glucose oxidase, choline oxidase, sarcosine oxidase, α-glycerophosphate oxidase, cholesterol oxidase, lactate oxidase, bilirubin oxidase, ascorbic acid oxidase, uricase, collagenase, uronidase, protease and proteolytic enzyme.

[0021] In one embodiment of the present invention, the conductive substrate is selected from glassy carbon electrode, carbon cloth, carbon paper, graphite, silicon wafer, conductive glass, metal substrate, conductive ceramic or conductive polymer.

[0022] The second object of the present invention is to provide a method for constructing the electrochemical sensor, comprising the following steps: loading a metal oxide on the surface of a conductive substrate to obtain a working electrode, and assembling the working electrode with a reference electrode and a counter electrode to obtain the electrochemical sensor.

[0023] In one embodiment of the present invention, it also includes modifying the surface of the working electrode with an oxidase and a cross-linking agent, and assembling the working electrode with a reference electrode and a counter electrode to obtain the electrochemical sensor.

[0024] In one embodiment of the present invention, the concentration of the oxidase is 2 mg / mL-500 mg / mL.

[0025] In one embodiment of the present invention, the cross-linking agent is glutaraldehyde, N,N-thiocarbonyldiimidazole, genipin, acetic anhydride, diglycidyl ethyl ether, methyl succinimidyl ester, etc.

[0026] In one embodiment of the present invention, the mass ratio of the cross-linking agent to water is (1-100): (100:10000).

[0027] In one embodiment of the present invention, the tin oxide solution further comprises perfluorosulfonic acid resin (Nafion); wherein the mass ratio of the tin oxide to Nafion is (0.5-2):(100-5000).

[0028] The third object of the present invention is to provide the use of the electrochemical sensor in detecting hydrogen peroxide, glucose, sucrose, lactose, uric acid, creatinine, urea, lactic acid, acetylcholine, ethanol, sarcosine, ascorbic acid, triglycerides or cholesterol.

[0029] The present invention improves the conductivity of the metal oxide and reduces the transmission impedance of electrons from hydrogen peroxide to the metal oxide surface by introducing oxygen vacancies on the metal oxide surface. At the same time, low concentrations of oxygen vacancies will not increase the metal oxide's ability to adsorb oxygen. This allows the metal oxide to have the performance of electrically reducing hydrogen peroxide, but not reducing oxygen and other interfering substances in the electro-oxidation process. On this basis, an anti-interference hydrogen peroxide sensor is constructed. By detecting the hydrogen peroxide, a product of the oxidase catalytic reaction, through the electro-reduction of the tin oxide, an electrochemical sensor for glucose, uric acid, lactic acid, sarcosine, etc. is further constructed, and the interference of interfering substances is avoided during the detection process. In addition, the price of tin oxide is lower than that of the currently used precious metals, which is conducive to reducing the production cost of the sensor.

[0030] The above technical solution of the present invention has the following advantages compared with the prior art:

[0031] 1. The present invention adjusts the surface oxygen vacancy concentration of metal oxides so that the metal oxides can electro-reduce hydrogen peroxide without reducing oxygen and interfering substances in the electro-oxidation process, thereby preparing anti-interference sensors for hydrogen peroxide, glucose, lactic acid, uric acid, creatine, etc.

[0032] 2. The specially prepared metal oxide of the present invention is used to replace precious metals, thereby reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein

[0034] Figure 1 This is a schematic diagram of the principle that the metal oxide in the hydrogen peroxide sensor described in Example 1 of the present invention reduces hydrogen peroxide but does not reduce oxygen.

[0035] Figure 2 ac are the current-potential curves of three tin oxide-glassy carbon electrodes in different PBS buffer solutions.

[0036] Figure 3 The current-potential curves of the conductive substrate loaded with iron oxide in different PBS buffer solutions.

[0037] Figure 4 The current-oxygen concentration curve of the hydrogen peroxide sensor described in Example 1 of the present invention in PBS buffer solutions containing different concentrations of oxygen and hydrogen peroxide.

[0038] Figure 5 1 is the current-concentration curve of the hydrogen peroxide sensor described in Example 1 of the present invention in PBS buffer solutions containing different concentrations of hydrogen peroxide.

[0039] Figure 6 This is a test diagram of the anti-interference performance of the hydrogen peroxide sensor described in Example 1 of the present invention in a PBS buffer solution containing hydrogen peroxide.

[0040] Figure 7 a is the current-concentration curve of the glucose sensor in Example 2 of the present invention in PBS buffer solutions containing different concentrations of glucose, Figure 7 b is a test diagram of the anti-interference performance of the glucose sensor.

[0041] Figure 8 This is a test diagram of the anti-interference performance of the lactic acid sensor described in Example 3 of the present invention.

[0042] Fig. 9 a is the current-concentration curve of the uric acid sensor described in Example 4 of the present invention in PBS buffer solutions containing different concentrations of uric acid, Fig. 9 b is a test diagram of the anti-interference performance of the uric acid sensor described in Example 4 of the present invention.

[0043] Fig.10 This is a test diagram of the anti-interference performance of the sarcosine sensor described in Example 5 of the present invention. DETAILED DESCRIPTION

[0044] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0045] The preparation method of the metal oxide used in the present invention:

[0046] 1. The tin oxide of the present invention is prepared according to the following method, and the specific steps are as follows:

[0047] 1) Dissolve 0.01mol / L-0.5mol / L tin dichloride in water, and add 5mL-50mL ammonia water while stirring the solution until the pH is 8-12.

[0048] 2) After the reaction is completed, centrifuge to obtain stannous hydroxide solid, and dry the solid product at 40°C-120°C for 12h-48h.

[0049] 3) Grinding the product and calcining it to obtain tin oxide; wherein the calcination atmosphere is oxygen, inert gas, or a mixture of oxygen and inert gas, the volume ratio of oxygen to inert gas is (0.1-1): (0.1-0.5), the calcination temperature is 400°C-600°C, and the time is 2h-12h.

[0050] 4) By regulating the calcination atmosphere, temperature and time in step 3, the concentration of oxygen defects on the surface of tin oxide can be regulated. When the calcination atmosphere is oxygen, the temperature is 600°C, and the time is 6h, the obtained tin oxide has no oxygen defects, the defect concentration is 0%, and the valence of the tin element is +4; when the calcination atmosphere is a mixed gas of oxygen and argon, the volume ratio of oxygen and argon is 1:0.1, the temperature is 450°C, and the time is 2h, the obtained tin oxide has oxygen defects, the defect concentration is 5.3%, the ratio of tetravalent tin to divalent tin is 89.2:10.8, and the comprehensive valence of the tin element is +3.78; when the calcination atmosphere is argon, the temperature is 450°C, and the time is 2h, the obtained tin oxide has oxygen defects, the defect concentration is 35.0%, the ratio of tetravalent tin to divalent tin is 65.1:34.9, and the comprehensive valence of the tin element is +3.30. This is because during the calcination of stannous hydroxide, the different atmospheres, temperatures and times cause the divalent tin ions in the stannous hydroxide to be oxidized to tetravalent tin oxides to different degrees. When argon or oxygen is used as the calcination atmosphere at low temperatures, the divalent tin ions are not completely oxidized, and the valence of the tin in the resulting tin oxide is a mixture of divalent and tetravalent tin, which generates oxygen defects.

[0051] 5) The tin oxides with defect concentrations of 0%, 5.3% and 35.0% were loaded on glassy carbon electrodes with Nafion, respectively, and placed in argon-saturated PBS electrolyte, normal PBS electrolyte, and argon-saturated PBS electrolyte containing 1 mM hydrogen peroxide, and cyclic voltammetry tests were performed. The experimental results are as follows: Figure 2 ac shown. Figure 2 The curves of 0% tin oxide in a measured in the three solutions overlap, indicating that the tin oxide reduces neither oxygen nor hydrogen peroxide; Figure 2 The curves of 5.3% tin oxide in b measured in argon-saturated PBS electrolyte and normal PBS electrolyte overlap, while the current of the curve measured in argon-saturated PBS electrolyte containing 1 mM hydrogen peroxide increases, indicating that the tin oxide does not reduce oxygen, but reduces hydrogen peroxide; Figure 2 The two curves of 35.0% tin oxide in c measured in normal PBS electrolyte and argon-saturated PBS electrolyte containing 1mM hydrogen peroxide both have increased current compared to argon-saturated PBS electrolyte, indicating that the tin oxide reduces both oxygen and hydrogen peroxide. The above results show that changes in the oxygen defect concentration on the surface of tin oxide can change the reduction performance of oxygen and hydrogen peroxide. Changes in the defect concentration affect the charge transfer performance of tin oxide and the adsorption performance of oxygen on the surface of tin oxide. When the defect concentration of tin oxide is 5.3%, specific detection of hydrogen peroxide can be achieved to avoid oxygen interference.

[0052] 2. The iron oxide used in the present invention is prepared according to the following method, and the specific steps are as follows:

[0053] 1) dissolving 0.1-2.0 mol / L ferrous chloride in anhydrous ethanol to obtain a clear solution;

[0054] 2) dropping 1-50 μl of the clear solution onto a conductive substrate and drying in an oven at 40-120° C. for 5-20 min;

[0055] 3) calcining the conductive substrate on which the solution has been dropped to obtain a conductive substrate loaded with iron oxide; wherein the calcination atmosphere is a mixture of oxygen and inert gas, the volume ratio of oxygen to inert gas is (0.1-1): (0.01-0.5), the calcination temperature is 400° C.-600° C., and the time is 2 h-12 h;

[0056] 4) By regulating the calcination atmosphere, temperature and time in step 3), the concentration of oxygen defects on the surface of the iron oxide can be regulated. When the volume ratio of oxygen to argon is 1:0.01, the calcination temperature is 450°C, and the time is 3 hours, the iron element in the obtained iron oxide cannot be completely oxidized, the iron element has both divalent and trivalent iron elements, and a suitable concentration of oxygen defects is generated.

[0057] 5) The conductive substrate loaded with iron oxide was used as a working electrode and placed in argon-saturated PBS electrolyte, normal PBS electrolyte, and argon-saturated PBS electrolyte containing 1 mM hydrogen peroxide, and cyclic voltammetry was performed. The experimental results are as follows: Figure 3 The curves measured in the argon-saturated PBS electrolyte and the normal PBS electrolyte overlap, while the current of the curve measured in the argon-saturated PBS electrolyte containing 1 mM hydrogen peroxide increases, indicating that the iron oxide does not reduce oxygen, but reduces hydrogen peroxide.

[0058] Example 1

[0059] This embodiment provides a hydrogen peroxide sensor and a construction method thereof, which are specifically as follows:

[0060] 1) Disperse tin oxide in a perfluorosulfonic acid resin (Nafion) aqueous solution, drop it on the surface of a glassy carbon electrode, and place it at 25°C for 1 hour to dry, thereby obtaining a tin oxide-modified glassy carbon electrode; wherein the mass ratio of tin oxide to the Nafion aqueous solution is 2.5:1000, and the volume ratio of the solution to water is 1:99.

[0061] 2) The dried glassy carbon electrode is used as a working electrode and assembled with a reference electrode and a counter electrode to obtain a hydrogen peroxide sensor.

[0062] 3) The hydrogen peroxide sensor was placed in PBS electrolyte, PBS electrolyte containing 0.1 mM hydrogen peroxide, and PBS electrolyte containing 0.5 mM hydrogen peroxide, respectively, and the concentration of dissolved oxygen in the electrolyte was changed (by passing argon gas into the solution to reduce the oxygen concentration in the solution, and passing oxygen gas into the solution to increase the oxygen concentration in the solution), and a constant potential electrochemical test was performed at a potential of -0.25 V. The experimental results are shown in FIG. Figure 4 As shown, the sensor detection current does not change, indicating that the sensor has the performance of resisting oxygen interference and can accurately detect hydrogen peroxide when the oxygen concentration fluctuates.

[0063] 4) The hydrogen peroxide sensor described in step 2) was placed in PBS electrolyte containing 0mM, 1mM, 3mM, 5mM, 7mM, 10mM, 15mM, 20mM, 25mM, 30mM, 40mM, and 50mM hydrogen peroxide, respectively, and a constant potential electrochemical test was performed at a potential of -0.25V. The experimental results are as follows: Figure 5 As shown in the figure, with the increase of hydrogen peroxide concentration, the current gradually increases. The linear range of hydrogen peroxide detection is 0-10mM.

[0064] 5) Place the hydrogen peroxide sensor described in step 2) in PBS electrolyte, and add 0.1 mM hydrogen peroxide and 0.1 mM common electroactive interfering substances, including lactic acid, mannose, urea, acetaminophen, potassium oxalate, ascorbic acid, glucose, ethanol, methanol and dopamine in sequence. The experimental results are as follows Figure 6 As shown, current was generated after adding hydrogen peroxide, but no current was generated after adding interfering substances, indicating that the sensor has the ability to resist interference from interfering substances during the electro-oxidation method.

[0065] Example 2

[0066] This embodiment provides a glucose sensor and a method for constructing the same, as follows:

[0067] 1) Disperse tin oxide in Nafion aqueous solution, drop it on the surface of glassy carbon electrode, and place it at 25°C for 1 hour to dry, so as to obtain a tin oxide modified glassy carbon electrode; wherein the mass ratio of tin oxide to perfluorosulfonic acid resin aqueous solution is 2.5:1000, and the volume ratio of Nafion solution to water is 1:100.

[0068] 2) Mix the glucose oxidase solution with the chitosan solution and the glutaraldehyde solution, drip it onto the surface of the tin oxide modified glassy carbon electrode in step 1), place it at 25°C for 1 hour to dry, and then assemble it with the reference electrode and the counter electrode to obtain a glucose sensor; wherein the concentration of glucose oxidase is 20 mg / ml, the concentration of chitosan is 5 mg / ml, and the volume ratio of glutaraldehyde solution to aqueous solution is 1:100.

[0069] 3) The glucose sensor described in step 2) was placed in PBS electrolyte containing 0mM, 0.2mM, 0.4mM, 0.6mM, 0.8mM, 1mM, 1.2mM, and 1.5mM glucose, respectively, and a constant potential electrochemical test was performed at a potential of -0.25V. The experimental results are shown in FIG. Figure 7 As shown in a, as the glucose concentration increases, the current gradually increases. The linear range of glucose concentration for glucose detection is 0-0.8mM.

[0070] 4) Place the glucose sensor described in step 2) in PBS electrolyte, and add 0.6 mM glucose and 0.6 mM common electroactive interfering substances, including urea, citric acid, choline, potassium oxalate, sarcosine, ascorbic acid, maltose, sodium chloride, methanol, lactic acid, sucrose, mannose, xylose, galactose, ethanol and dopamine in sequence. The experimental results are as follows Figure 7 As shown in b, current was generated after adding glucose, but no current was generated after adding interfering substances, indicating that the sensor has the ability to resist interference from interfering substances during the electro-oxidation method.

[0071] Example 3

[0072] This embodiment provides a lactate sensor and a method for constructing the same, as follows:

[0073] 1) Disperse tin oxide in Nafion aqueous solution, drop it on the surface of glassy carbon electrode, and place it at 25°C for 1 hour to dry, so as to obtain a tin oxide modified glassy carbon electrode; wherein the mass ratio of tin oxide to perfluorosulfonic acid resin aqueous solution is 2.5:1000, and the volume ratio of Nafion solution to water is 1:100.

[0074] 2) Mix the lactate oxidase solution with the chitosan solution and the glutaraldehyde solution, drip it onto the surface of the tin oxide-modified glassy carbon electrode in step 1), place it at 25°C for 1 hour to dry, and then assemble it with the reference electrode and the counter electrode to obtain a lactate sensor; wherein the concentration of lactate oxidase is 10 mg / ml, the concentration of chitosan is 5 mg / ml, and the volume ratio of the glutaraldehyde solution to the aqueous solution is 1:100.

[0075] 3) Place the lactate sensor described in step 2) in PBS electrolyte, and add 0.5 mM lactate and 0.5 mM common electroactive interfering substances, including methanol, ethanol, mannose, urea, ascorbic acid, uric acid, sucrose, acetaminophen, xylose, citric acid, dopamine and glucose in sequence. The experimental results are as follows Figure 8 As shown, current was generated after adding lactic acid, but no current was generated after adding interfering substances, indicating that the sensor has the ability to resist interference from interfering substances during the electro-oxidation method.

[0076] Example 4

[0077] This embodiment provides a uric acid sensor and a construction method thereof, which are specifically as follows:

[0078] 1) Disperse tin oxide in Nafion aqueous solution, drop it on the surface of glassy carbon electrode, and place it at 25°C for 1 hour to dry, so as to obtain a tin oxide modified glassy carbon electrode; wherein the mass ratio of tin oxide to perfluorosulfonic acid resin aqueous solution is 2.5:1000, and the volume ratio of Nafion solution to water is 1:100.

[0079] 2) Mix the urate oxidase solution with the bovine serum albumin solution and the glutaraldehyde solution, drop the mixture onto the surface of the tin oxide-modified glassy carbon electrode in step 1), place the mixture at 25° C. for 1 hour to dry, and then assemble the mixture with the reference electrode and the counter electrode to obtain a uric acid sensor; wherein the concentration of urate oxidase is 5 mg / ml, the mass ratio of bovine serum albumin to water is 5:95, and the volume ratio of the glutaraldehyde solution to the aqueous solution is 1:100.

[0080] 3) Place the uric acid sensor in step 2) in a PBS electrolyte and perform a constant potential electrochemical test at a potential of -0.25 V. Then add uric acid solution to the electrolyte to make the uric acid concentration in the electrolyte 0.1 mM, 0.2 mM, 0.4 mM, 0.6 mM, 0.8 mM. The experimental results are as follows Fig. 9 As shown in a, as the concentration of uric acid increases, the current gradually increases. The linear range of uric acid detection is 0-0.6mM.

[0081] 4) Place the uric acid sensor described in step 2) in PBS electrolyte, and add 0.3 mM uric acid and 0.3 mM common electroactive interfering substances, including ascorbic acid, urea, ethanol, acetic acid, potassium oxalate, lactic acid, sucrose, mannose, acetaminophen, dopamine, citric acid, sarcosine, glucose and choline in sequence. The experimental results are as follows Fig. 9 As shown in b, current was generated after adding uric acid, but no current was generated after adding interfering substances, indicating that the sensor has the ability to resist interference from interfering substances during the electro-oxidation method.

[0082] Example 5

[0083] This embodiment provides a creatine sensor and a construction method thereof, which are specifically as follows:

[0084] 1) Disperse tin oxide in Nafion aqueous solution, drop it on the surface of glassy carbon electrode, and place it at 25°C for 1 hour to dry, so as to obtain a tin oxide modified glassy carbon electrode; wherein the mass ratio of tin oxide to perfluorosulfonic acid resin aqueous solution is 2.5:1000, and the volume ratio of Nafion solution to water is 1:100.

[0085] 2) Mix the sarcosine oxidase solution and the glutaraldehyde solution, drop them onto the surface of the tin oxide-modified glassy carbon electrode in step 1), place them at 25°C for 1 hour to dry, and then assemble them with a reference electrode and a counter electrode to obtain a sarcosine sensor; wherein the concentration of sarcosine oxidase is 20 mg / ml, and the volume ratio of the glutaraldehyde solution to the aqueous solution is 1:100.

[0086] 3) Place the sarcosine sensor described in step 2) in PBS electrolyte, and add 0.8 mM sarcosine and 0.8 mM common electroactive interfering substances, including ascorbic acid, acetaminophen, dopamine, citric acid, ethanol, urea, methanol, maltose, xylose and sucrose. The experimental results are as follows: Fig.10 As shown, current was generated after adding sarcosine, but no current was generated after adding interfering substances, indicating that the sensor has the ability to resist interference from interfering substances during the electro-oxidation method.

[0087] Example 6

[0088] This embodiment provides a hydrogen peroxide sensor and a construction method thereof, which are specifically as follows:

[0089] 1) Dissolve 0.5 mol / L ferrous chloride in anhydrous ethanol to obtain a clear solution, and drop 10 μL on a graphite sheet and dry in an oven at 40°C for 10 min;

[0090] 2) calcining the graphite sheet dripped with the solution to obtain a titanium sheet loaded with iron oxide; wherein the calcination atmosphere is a mixture of oxygen and inert gas, the volume ratio of oxygen to inert gas is 1:0.01, the calcination temperature is 450°C, and the time is 3 hours;

[0091] 3) The titanium sheet loaded with iron oxide is used as a working electrode, and assembled with a reference electrode and a counter electrode to obtain a hydrogen peroxide sensor.

[0092] Example 7

[0093] This embodiment provides a glucose sensor and a method for constructing the same, as follows:

[0094] 1) Dissolve 0.5 mol / L ferrous chloride in anhydrous ethanol to obtain a clear solution, and drop 10 μL on a graphite sheet and dry in an oven at 40°C for 10 min;

[0095] 2) calcining the graphite sheet dripped with the solution to obtain a titanium sheet loaded with iron oxide; wherein the calcination atmosphere is a mixture of oxygen and inert gas, the volume ratio of oxygen to inert gas is 1:0.01, the calcination temperature is 450°C, and the time is 3 hours;

[0096] 3) Mix the glucose oxidase solution with the chitosan solution and the glutaraldehyde solution, drip it onto the surface of the titanium sheet loaded with iron oxide in step 1), place it at 25°C for 1 hour to dry, and then assemble it with the reference electrode and the counter electrode to obtain a glucose sensor; wherein the concentration of glucose oxidase is 20 mg / ml, the concentration of chitosan is 5 mg / ml, and the volume ratio of glutaraldehyde solution to aqueous solution is 1:100.

[0097] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. An electrochemical sensor based on metal oxide, characterized in that: It comprises a working electrode, a reference electrode and a counter electrode; the working electrode is obtained by modifying a conductive substrate with a metal oxide; the metal oxide is selected from metal oxides composed of metal elements with variable valence states; the metal oxide is selected from tin oxide; the valence state of tin in the tin oxide is a mixture of divalent and tetravalent tin; and the surface oxygen defect concentration of the tin oxide is 5.3%.

2. The electrochemical sensor according to claim 1, characterized in that The working electrode is also loaded with an oxidase and a cross-linking agent.

3. The electrochemical sensor according to claim 2, characterized in that The oxidase is selected from one or more of glucose oxidase, ascorbic acid oxidase, choline oxidase, sarcosine oxidase, α-glycerophosphate oxidase, cholesterol oxidase, lactate oxidase, bilirubin oxidase, uricase, collagenase, urinary tract enzyme, protease and proteolytic enzyme.

4. The electrochemical sensor according to claim 1, characterized in that The conductive substrate is selected from glassy carbon electrodes, carbon cloth, carbon paper, graphite, silicon wafers, conductive glass, metal substrates, conductive ceramics or conductive high polymers.

5. The method for constructing an electrochemical sensor according to any one of claims 1 to 4, characterized in that: The following steps are involved: The metal oxide is loaded on the surface of a conductive substrate to obtain a working electrode, which is assembled with a reference electrode and a counter electrode to obtain the electrochemical sensor.

6. Use of the electrochemical sensor according to any one of claims 1 to 4 in detecting hydrogen peroxide, glucose, sucrose, lactose, uric acid, creatinine, urea, lactic acid, acetylcholine, ethanol, sarcosine, ascorbic acid, triglycerides or cholesterol.

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