Preparation method and application of self-powered sensor for lactic acid detection

Abstract

The invention relates to the technical field of sensor analysis and detection, in particular to a preparation method and application of a self-powered sensor for lactic acid detection, polystyrene spheres (PS spheres) are introduced into a copper-iron co-doped zeolite imidazole framework 8 (CoFe-ZIF-8) to prepare a precursor, and the precursor is carbonized to obtain a catalyst PS-Co1-Fe1-NC. The catalyst shows oxygen reduction (ORR) performance higher than that of commercial Pt / C under alkaline and neutral conditions, and when the catalyst is used for an alkaline zinc-air battery (ZAB) and neutral ZAB, the performance of the catalyst is better than that of a commercial Pt / C + RuO2 battery. A self-energized sensing platform is constructed by a biological cathode modified by PS (at) Co1-Fe1-NC and lactate oxidase (LOx) and a zinc sheet and is used for lactic acid detection. When lactic acid exists, LOx catalyzes lactic acid to decompose and consume oxygen and reacts with ORR to form an oxygen consumption competitive relationship, so that the open-circuit voltage is reduced, and the purpose of detecting lactic acid is achieved. The application of the self-energized sensor in lactic acid detection is widened, and the self-energized sensor has a wide linear range, high sensitivity and low detection limit for lactic acid detection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sensor analysis and detection, and particularly relates to a preparation method and application of a self-powered sensor for lactic acid detection. BACKGROUND

[0002] Lactic acid is a key substance involved in energy metabolism in living organisms, and its dynamic changes have attracted much attention. In clinical medicine, accurate detection of lactic acid level is crucial for early diagnosis, disease monitoring and prognosis evaluation. For example, in shock and sepsis, abnormal blood lactic acid concentration can guide treatment. In the field of sports science, monitoring the lactic acid accumulation of athletes is beneficial to optimize training and improve performance. Lactic acid detection can provide a basis for clinical diagnosis and promote the optimization of scientific exercise programs. Therefore, it is of great significance to construct a convenient and sensitive detection method for lactic acid.

[0003] Currently, the detection methods of lactic acid mainly cover instrument analysis, chemical analysis and electrochemical sensing. Instrument analysis mainly includes high performance liquid chromatography, liquid chromatography-mass spectrometry and other laboratory equipment offline determination of lactic acid. However, the complex sample pretreatment, expensive equipment, long analysis time and high operation requirement make it difficult to apply to on-site rapid detection. Titration analysis is often used in lactic acid detection in chemical analysis, but the sample processing process is complex, the operation is tedious, time-consuming and labor-intensive, and there must be a suitable means to indicate the end point, such as an indicator, a potentiometer, etc. However, the existing electrochemical technology still faces many challenges in realizing efficient and accurate detection. For example, the traditional electrochemical detection method depends on the electrochemical workstation, which limits the outdoor and real-time monitoring of the detection, so it is very important to develop a small and integrated sensor.

[0004] Self-powered electrochemical sensors have attracted widespread attention due to their simple construction, small size, fast response speed and low cost. However, the low and unstable output signal is a problem faced by current self-powered electrochemical sensors. SUMMARY

[0005] In view of the above research background, the purpose of the present application is to provide a preparation method and application of a self-powered sensor for lactic acid detection. The present application replaces noble metals with PS@Co1-Fe1-NC as the cathode material of zinc-air battery, reduces the cost, and designs a self-powered electrochemical sensor based on the coupling of PS@Co1-Fe1-NC cathode catalyst and LOx, to realize sensitive detection of lactic acid.

[0006] To solve the above technical problems, the present application adopts the following technical solutions: A preparation method of a self-powered sensor, comprising the following steps: (1) Preparation of solution A: the polystyrene nanospheres (PS spheres) are added to a polyvinylpyrrolidone (PVP) methanol solution as a surface stabilizer, growth modifier, nanoparticle dispersant, and reducing agent, and solution A is obtained by stirring and ultrasonic treatment.

[0007] (2) Preparation of PS@Co1-Fe1-NC: a soluble zinc salt is dissolved in methanol, denoted as ①; 2-methylimidazole (2-Meln) is dissolved in methanol, denoted as ②, and ① is sequentially added to A, and then ② is added to A and stirred. A soluble cobalt salt and a soluble iron salt are dissolved in methanol, denoted as ③; 2-methylimidazole is dissolved in methanol, denoted as ④, and ③ is sequentially added to A and stirred, and then ④ is added to A and stirred, and PS@Co1-Fe1-ZIF is obtained after treatment. The PS@Co1-Fe1-ZIF is calcined and carbonized under a protective atmosphere to obtain PS@Co1-Fe1-NC.

[0008] (3) Construction of a self-powered sensor: the PS@Co1-Fe1-NC is dispersed in ethanol containing a perfluorosulfonic acid resin solution to obtain PS@Co1-Fe1-NC ink; the PS@Co1-Fe1-NC ink is added dropwise to the surface of a glassy carbon electrode to obtain PS@Co1-Fe1-NC / GCE; a lactic acid oxidase solution is added dropwise to the surface of the PS@Co1-Fe1-NC / GCE to obtain LOx / PS@Co1-Fe1-NC / GCE; and a self-powered sensor is constructed with the LOx / PS@Co1-Fe1-NC / GCE as a cathode and a zinc sheet as an anode.

[0009] (4) Lactic acid detection: PBS solutions containing different concentrations of lactic acid are prepared, and the concentrations are tested in order from low to high; due to the presence of lactic acid, the lactic acid oxidase at the cathode interface catalyzes the decomposition of lactic acid to consume oxygen, and competes with the ORR reaction at the cathode to form oxygen, which reduces the open-circuit voltage of the zinc-air battery, and the greater the increase in lactic acid concentration, the greater the decrease in open-circuit voltage signal, thereby achieving the purpose of detecting lactic acid.

[0010] The sensor of the application is composed of PS@Co1-Fe1-NC / LOx as a cathode and a zinc sheet as an anode. In the absence of lactic acid, O2 in the electrolyte solution is reduced under the catalysis of the cathode PS@Co1-Fe1-NC, and the anode zinc sheet is oxidized at the same time, which forms an electron path and generates a potential difference. In the presence of lactic acid, part of the O2 in the electrolyte solution participates in the LOx catalytic reaction of lactic acid to produce H2O2. This establishes an O2 consumption competition model in the ZAB, resulting in a decrease in the open-circuit potential (E0) of the zinc-air battery. E OCPThe application widens the application of the self-powered sensor in lactic acid detection, and the constructed sensor has a wide linear range, high sensitivity and low detection limit for lactic acid detection.

[0011] In the preferred embodiment of the application, the ratio of the use amount of the PS balls to the methanol is 0.05g-1.5g:0.1mL-0.3mL.

[0012] In the preferred embodiment of the application, the ratio of the use amount of the soluble zinc salt to the methanol is 0.6g-2.4g:20mL-80mL, the ratio of the use amount of the 2-methyl imidazole to the methanol is 0.7-2.8g:20-80mL, and the mass ratio of the soluble cobalt salt to the soluble iron salt is 0.0587g-0.2348g:0.0815g-0.2360g.

[0013] In the preferred embodiment of the application, the calcination carbonization temperature is 900 DEG C-950 DEG C, and the calcination carbonization time is 2 hours-3 hours.

[0014] In the preferred embodiment of the application, the ratio of the use amount of the PS@Co1-Fe1-NC catalyst to the ethanol is 1mg-3mg:0.5mL-1mL, the ratio of the use amount of the PS@Co1-Fe1-NC to the perfluorosulfonic acid resin solution is 1mg-3mg:5ul-10ul, and the mass concentration of the perfluorosulfonic acid resin solution is 0.25%.

[0015] In the preferred embodiment of the application, the concentration of the lactic acid oxidase solution is 100U / mL-300U / mL.

[0016] In the preferred embodiment of the application, the polystyrene nanospheres are prepared by the following method: mixing deionized water and polyvinylpyrrolidone, carrying out oil bath reaction, adding styrene and then adding K2S2O8 aqueous solution as an initiator, and post-treating the reaction product to obtain polystyrene nanospheres.

[0017] In the preferred embodiment of the application, the ratio of the use amount of the deionized water to the polyvinylpyrrolidone is 100mL:0.25-1g, the ratio of the use amount of the styrene to the K2S2O8 aqueous solution is 6.5mL-13mL:10mL-20mL, the oil bath reaction temperature is 60 DEG C-80 DEG C, and the oil bath reaction time is 20 hours-24 hours.

[0018] Another object of the application is to provide a self-powered sensor prepared by the preparation method.

[0019] A third object of the application is to provide an application of the self-powered sensor in lactic acid detection.

[0020] (1) In the present invention, polystyrene nanospheres (PS spheres) and polyvinylpyrrolidone (PVP) are first dissolved in methanol to obtain solution A; a soluble zinc salt is dissolved in methanol, denoted as ①; 2-methylimidazole (2-Meln) is dissolved in methanol, denoted as ②, ① is added to A in sequence, and ② is added to A and stirred. A soluble cobalt salt and a soluble iron salt are dissolved in methanol, denoted as ③; 2-methylimidazole is dissolved in methanol, denoted as ④, ③ is added to A in sequence, and stirred, and ④ is added to A and stirred. After treatment, PS@Co1-Fe1-ZIF is obtained. The PS@Co1-Fe1-ZIF is calcined and carbonized under a protective atmosphere to obtain a PS@Co1-Fe1-NC catalyst; the PS@Co1-Fe1-NC catalyst is dispersed in ethanol containing a perfluorosulfonic acid resin solution to obtain a PS@Co1-Fe1-NC ink; the PS@Co1-Fe1-NC ink is dripped onto the surface of a glassy carbon electrode to obtain a PS@Co1-Fe1-NC / GCE; a lactate oxidase solution is dripped onto the surface of the PS@PS@Co1-Fe1-NC / GCE to obtain a LOx / PS@Co1-Fe1-NC / GCE; LOx / PS@PS@Co1-Fe1-NC / GCE is used as the cathode and a Zn sheet is used as the anode to construct a self-powered sensor for lactic acid detection. The present invention constructs a novel self-powered sensor for lactic acid detection by assembling a Zn sheet anode and a LOx / PS@Co1-Fe1-NC / GCE cathode, with the PS@Co1-Fe1-NC / LOx cathode and the zinc sheet anode. In the absence of lactic acid, O2 in the electrolyte solution is reduced under the catalytic action of the cathode PS@Co1-Fe1-NC, and the anode zinc sheet is simultaneously oxidized, forming an electron path and generating a potential difference. In the presence of lactic acid, part of the O2 in the electrolyte solution participates in the LOx catalytic reaction of lactic acid, thereby producing H2O2. This establishes an O2 consumption competition model within the ZAB, resulting in an open circuit potential ( E OCP ) decreases, thereby realizing the detection of lactic acid. The present invention broadens the application of self-powered sensors in lactic acid detection. The constructed sensor has a wide linear range, high sensitivity and low detection limit for lactic acid detection.

[0021] (2) The present invention uses PS balls prepared by oil bath and solvent methods to regulate CoFe-doped porous carbon catalysts, which are used as cathodes for zinc-air batteries. The zinc-air batteries constructed using this catalyst show excellent power density, energy density, and durability, and outperform commercial Pt / C catalysts. At the same time, the biocathode modified with PS@Co1-Fe1-NC and lactate oxidase (LOx) catalyzes the decomposition of lactic acid in the presence of lactic acid, consuming O2, and competing with the cathode ORR reaction to form O2, causing voltage changes, thereby achieving the purpose of detecting lactic acid.

[0022] (3) Compared with the traditional detection mode, the electrochemical detection method used in the application has the characteristics of simple and flexible operation, simple instrument and equipment, high sensitivity, low detection cost, wide linear range and low detection limit. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Figure 2 is a working mode diagram of a self-powered sensor composed of a cathode LOx / PS@Co1-Fe1-NC / GCE and an anode Zn sheet in the application.

[0024] Figure 2 Figure 3 is a scanning electron microscope image of PS@Co1-Fe1-ZIF and PS@Co1-Fe1-NC prepared in Example 1 of the application.

[0025] Figure 3 Figure 4 is a CV curve of PS@Co1-Fe1-NC, Co1-Fe1-NC, PS@NC and 20wt% Pt / C in 0.1M PBS solution, and ORR performance in 0.1M PBS solution.

[0026] Figure 4 Figure 5 is (a) full-speed ORR performance of PS@Co1-Fe1-NC measured in 0.1M PBS solution, and (b) electron transfer number and hydrogen peroxide yield performance measured in 0.1M PBS solution.

[0027] Figure 5 Figure 6 is (a) specific capacity, (b) polarization curve, (c) power density and (d) durability test results of zinc-air batteries assembled in a neutral environment.

[0028] Figure 6 Figure 7 is the open circuit voltage in the preparation process of GCE, PS@Co1-Fe1-NC, PS@Co1-Fe1-NC+LOx and PS@Co1-Fe1-NC+LOx+lactate electrodes.

[0029] Figure 7 Figure 8 is the open circuit voltage of different concentrations of lactic acid, wherein the concentration of lactic acid is 1μM-100mM.

[0030] Figure 8 Figure 9 is the relationship between the open circuit voltage after adding lactic acid and the concentration of lactic acid, and the inset in the figure is a linear relationship diagram of the open circuit voltage and the logarithmic value of the concentration of lactic acid.

[0031] Figure 9 Figure 10 is the anti-interference ability test of the self-powered electrochemical sensor constructed. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be described clearly and completely in the embodiments of the present application in combination with preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0033] It should be noted that all the professional terms used in the present application are only for the purpose of describing the specific embodiments, and are not intended to limit the scope of protection of the present application. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the following embodiments of the present application can be purchased from the market or prepared by the existing method.

[0034] 0.5 g of polyvinylpyrrolidone was weighed with a balance, added to 100 mL of deionized water in a three-necked flask, and nitrogen was introduced. The mixture was placed in an oil bath, stirred and heated until the temperature reached 70 ℃. After the temperature was stabilized at 70 ℃, 13 mL of styrene was added to the flask and kept at 70 ℃ for 30 min. Then 20 mL of 0.3 g K2S2O8 aqueous solution was added as an initiator, and the reaction was continued for 24 h. The mixture was centrifuged, washed with water for 3 times, and placed in a vacuum drying oven at 60 ℃ overnight to obtain polystyrene nanospheres (PS spheres). Embodiments

[0035] 1. A self-powered sensor preparation method and application for lactic acid detection, comprising the following steps: (1) Preparation of solution A 0.05 g of PS spheres and 0.2 g of PVP were dissolved in 15 mL of methanol, labeled as solution A. Then the A solution was stirred for 30 min, ultrasonicated for 30 min, and the above steps were repeated three times alternately.

[0036] (2) Preparation of PS@Co1-Fe1-NC Dissolve 0.6 g Zn(NO3)2·6H2O in 20 mL methanol, marked as ①; dissolve 0.7 g 2-methylimidazole (2-Meln) in 20 mL methanol, marked as ②, add ① to A in turn and stir for 30 min, then add ② to A and stir for 8 h. Dissolve 0.0587 g Co(NO3)2·6H2O and 0.0815 g Fe(NO3)3·9H2O in 10 mL methanol, marked as ③; dissolve 0.14 g 2-Meln in 10 mL methanol, marked as ④, add ③ to A in turn and stir for 30 min, then add ④ to A and stir for 8 h. Finally, centrifuge the A solution, wash the product with methanol for 4-6 times, and then transfer it into a vacuum drying oven and dry at 60 ℃ overnight. When the vacuum drying is completed, grind the PS@Co1-Fe1-ZIF into powder.

[0037] Place the PS@Co1-Fe1-ZIF in a porcelain boat, and heat it at a rate of 5 ℃ per minute until the temperature reaches 900 ℃ under the N2 inert atmosphere, and maintain the temperature for 2 hours, and then grind to obtain PS@Co1-Fe1-NC.

[0038] (3) Preparation of self-powered sensor Grind the obtained PS@Co1-Fe1-NC catalyst at room temperature, weigh 3.0 mg of PS@Co1-Fe1-NC with an electronic balance, disperse in 1.0 mL of ethanol, add 10 μL of 0.25wt% perfluorosulfonic acid resin solution, and ultrasonic for more than 30 minutes in an ultrasonic machine to prepare PS@Co1-Fe1-NC ink.

[0039] Drop 15 μL of PS@Co1-Fe1-NC ink on the surface of a glassy carbon electrode to obtain PS@Co1-Fe1-NC / GCE, drop 10 μL of LOx solution with a concentration of 200 U·mL -1 on the surface of PS@Co1-Fe1-NC / GCE to obtain LOx / PS@Co1-Fe1-NC / GCE, and assemble a self-powered sensor with LOx / PS@Co1-Fe1-NC / GCE as the cathode and a Zn sheet as the anode. Example

[0040] A preparation method and application of a self-powered sensor for lactic acid detection, comprising the following steps: (1) Preparation of solution A Dissolve 0.1 g of PS balls and 0.2 g of PVP in 30 mL of methanol, marked as solution A. Then stir the A solution for 30 min, and ultrasonic for 30 min, alternating three times.

[0041] (2) Preparation of PS@Co1-Fe1-NC Dissolve 1.2 g Zn(NO3)2·6H2O in 40 mL of methanol, marked as ①; dissolve 1.4 g of 2-methylimidazole (2-Meln) in 40 mL of methanol, marked as ②, and then add ① to A and stir for 30 min, and then add ② to A and stir for 8 h. Dissolve 0.1174 g of Co(NO3)2·6H2O and 0.1630 g of Fe(NO3)3·9H2O in 10 mL of methanol, marked as ③; dissolve 0.14 g of 2-Meln in 10 mL of methanol, marked as ④; add ③ to A and stir for 30 min, and then add ④ to A and stir for 8 h. Finally, centrifuge the A solution, wash the product with methanol 4-6 times, and then transfer it to a vacuum drying oven and dry at 60 ℃ overnight. After vacuum drying is completed, grind the PS@Co1-Fe1-ZIF into a powder.

[0042] Place the PS@Co1-Fe1-ZIF in a porcelain boat, and heat it at a rate of 5 ℃ per minute until the temperature reaches 950 ℃ under an N2 inert atmosphere, and maintain the temperature for 2 hours, and then grind to obtain PS@Co1-Fe1-NC.

[0043] (3) Preparation of a self-powered sensor Grind the obtained PS@Co1-Fe1-NC catalyst at room temperature, weigh 1.0 mg of PS@Co1-Fe1-NC with an electronic balance, add 0.5 mL of ethanol for dispersion, and then add 10 μL of a 0.25 wt% solution of perfluorosulfonic acid resin, and place it in an ultrasonic machine for ultrasonic treatment for more than 30 min to obtain PS@Co1-Fe1-NC ink.

[0044] Add 15 μL of PS@Co1-Fe1-NC ink to the surface of a glassy carbon electrode to obtain PS@Co1-Fe1-NC / GCE, and then add 5 μL of a LOx solution with a concentration of 300 U·mL -1 to the surface of the PS@Co1-Fe1-NC / GCE to obtain LOx / PS@Co1-Fe1-NC / GCE, and then use the LOx / PS@Co1-Fe1-NC / GCE as a cathode and a Zn sheet as an anode to assemble a self-powered sensor. Example

[0045] A self-powered sensor preparation method and application for lactic acid detection, comprising the following steps: (1) Preparation of solution A Dissolve 0.15 g PS spheres and 0.2 g PVP in 30 mL methanol, labeled as solution A. Then stir the A solution for 30 min, ultrasonic for 30 min, three times alternately.

[0046] (2) Preparation of PS@Co1-Fe1-NC Dissolve 2.4 g Zn(NO3)2·6H2O in 80 mL methanol, labeled as ①; dissolve 2.8 g 2-methylimidazole (2-Meln) in 80 mL methanol, labeled as ②, successively add ① to A and stir for 30 min, then add ② to A and stir for 8 h. Dissolve 0.2348 g Co(NO3)2·6H2O and 0.2360 g Fe(NO3)3·9H2O in 10 mL methanol, labeled as ③; dissolve 0.14 g 2-Meln in 10 mL methanol, labeled as ④, successively add ③ to A and stir for 30 min, then add ④ to A and stir for 8 h. Finally, centrifuge the A solution, wash the product with methanol for 4-6 times, and then transfer it into a vacuum drying box and dry at 60 ℃ overnight. After vacuum drying is completed, grind the PS@Co1-Fe1-ZIF into powder.

[0047] Place the PS@Co1-Fe1-ZIF in a porcelain boat, and heat at a rate of 5 ℃ per minute until the temperature reaches 950 ℃ in an N2 inert atmosphere, and maintain at this temperature for 3 hours, and obtain PS@Co1-Fe1-NC by grinding.

[0048] (3) Preparation of self-powered sensor Grind the obtained PS@Co1-Fe1-NC catalyst at room temperature, weigh 2.0 mg PS@Co1-Fe1-NC with an electronic balance, add 0.8 mL ethanol for dispersion, and then add 10 μL 0.25wt% perfluorosulfonic acid resin solution, and ultrasonic for more than 30 minutes in an ultrasonic machine to prepare PS@Co1-Fe1-NC ink.

[0049] Drop 15 μL of PS@Co1-Fe1-NC ink on the surface of a glassy carbon electrode to obtain PS@Co1-Fe1-NC / GCE, drop 8 μL of LOx solution with a concentration of 300 U·mL -1 on the surface of PS@Co1-Fe1-NC / GCE to obtain LOx / PS@Co1-Fe1-NC / GCE, and assemble a self-powered sensor with LOx / PS@Co1-Fe1-NC / GCE as the cathode and a Zn sheet as the anode.

[0050] Results analysis Figure 1In the self-powered sensor mode, the cathode of the sensor is composed of the cathode LOx / PS@Co1-Fe1-NC / GCE and the anode Zn sheet. In the absence of lactic acid, O2 in the electrolyte solution is reduced under the catalysis of the cathode PS@Co1-Fe1-NC, and the anode zinc sheet is oxidized at the same time, which forms an electron channel and generates a potential difference. In the presence of lactic acid, part of O2 in the electrolyte solution will participate in the LOx catalytic reaction of lactic acid, thereby generating H2O2. This establishes an O2 consumption competition model in the ZAB, resulting in a decrease in the open circuit potential (E0) E OCP ) and thus realizing the detection of lactic acid.

[0051] Figure 2 The scanning electron microscope images of PS@Co1-Fe1-ZIF and PS@Co1-Fe1-NC prepared in Example 1 of the present application are shown in FIG. 1. Figure 2 It can be seen that both before and after graphitization, they exhibit typical polyhedral structures, and PS@Co1-Fe1-NC is smaller in size than PS@Co1-Fe1-ZIF, and is more regular and uniform.

[0052] The CV and ORR performance tests were carried out with PS@Co1-Fe1-NC, Co1-Fe1-NC, PS@NC and 20 wt% Pt / C catalysts as the working electrode, a silver-silver chloride electrode as the reference electrode, a carbon rod as the counter electrode, and 0.1M PBS as the electrolyte, as shown in FIG. 2. Figure 3 Compared with Co1-Fe1-NC, PS@NC and 20 wt% Pt / C, PS@Co1-Fe1-NC exhibits significantly enhanced oxygen reduction reaction (ORR) activity in 0.1M PBS solution. The PS@Co1-Fe1-NC catalyst exhibits the most effective ORR catalytic activity, with a half-wave potential (E1 / 2) E 1 / 2 ) value of 0.79 V, which is higher than that of Co1-Fe1-NC ( E 1 / 2 = 0.72 V), PS@NC ( E 1 / 2 = 0.61 V) and 20 wt% Pt / C ( E 1 / 2 = 0.76 V).

[0053] The LSV curves of the PS@Co1-Fe1-NC catalyst prepared in Example 1 at different scan rates were obtained. As shown in FIG. 3, Figure 4(a) As shown, it can be observed that the current density increases proportionally with the increase of scan rate, which can be explained by the shortening of oxygen diffusion distance. The PS@Co1-Fe1-NC, Co1-Fe1-NC, PS@NC and 20 wt% Pt / C catalysts prepared in Example 1 and 20 wt% Pt / C were used as working electrodes, a silver-silver chloride electrode as a reference electrode, a carbon rod as a counter electrode, and 0.1 M PBS as an electrolyte to test the performance of hydrogen peroxide (H2O2) production and electron transfer number, as shown in Figure 4 (b) As shown, compared with Co1-Fe1-NC and PS@NC, the hydrogen peroxide (H2O2) production and electron transfer number of PS@Co1-Fe1-NC are closer to 20 wt% Pt / C as a benchmark.

[0054] The PS@Co1-Fe1-NC catalyst and 20 wt% Pt / C+RuO2 were respectively used as cathodes with nickel mesh and carbon cloth, and zinc sheet as anode to assemble zinc-air batteries, and the specific capacity, polarization curve, power density and durability of the batteries were tested in a mixed solution of 4 M NH4Cl and 0.2 M ZnCl2, as shown in Figure 5 As shown, the zinc-air battery assembled using PS@Co1-Fe1-NC has a higher specific capacity of 709.1 mA·h·g -1 , a charge-discharge voltage gap close to commercial Pt / C+RuO2, a higher peak power of 70.3 mW·cm -2 , and better stability.

[0055] The bare electrode, PS@Co1-Fe1-NC, PS@Co1-Fe1-NC+LOx and PS@Co1-Fe1-NC+LOx+Lactic electrodes prepared in Example 1 were respectively used as cathodes, and zinc sheet as anode to construct zinc-air battery self-powered systems. The open circuit voltage of the four electrodes was measured in 0.1 M PBS solution. As shown in Figure 6 It can be seen that the open circuit voltage of the zinc-air battery constructed with PS@Co1-Fe1-NC as cathode and zinc sheet is the highest, and the open circuit voltage decreases slightly when LOx is loaded on the surface of PS@Co1-Fe1-NC, and continues to decrease when lactic acid is further loaded, and the open circuit voltage of GCE is the lowest.

[0056] LOx / PS@Co1-Fe1-NC / GCE was used as cathode, and Zn sheet as anode to construct a self-powered sensor for lactic acid detection. The zinc-air battery self-powered system was placed in 0.1 M PBS buffer solution with pH of 7.4 to test the open circuit voltage. The open circuit voltage of different lactic acid concentrations is shown in Figure 7 As shown, the linear relationship between the open circuit voltage and the logarithmic value of lactic acid concentration isFigure 8 As shown, the corresponding linear regression equation is obtained as follows: E OCP (V) = -0.03124 lg c (μM)+1.38, the correlation coefficient R 2 =0.993; the detection range of the linear regression equation is 0.1 μM~100mM, and the lowest detection limit is 0.35 μM.

[0057] The most common coexisting substances, such as glucose, ethanol, ascorbic acid, urea and L-tyrosine (the concentration of L-tyrosine is 100 μM, and the concentrations of other substances are 1000 μM), are selected as potential interference substances. Figure 9 As shown, compared with the change of open circuit potential after the addition of lactic acid, the change of open circuit potential in the presence of interference substances is relatively small. The results show that the constructed SPES exhibits excellent anti-interference ability in lactic acid detection.

[0058] In summary, the present application realizes the sensitive detection of lactic acid by constructing a novel self-powered electrochemical sensor (SPES) based on oxygen consumption competition mode by combining lactic acid oxidase (LOx) on the PS@Co1-Fe1-NC catalyst, the detection limit is lower than 0.35 μM, which can be used for the actual sample detection of lactic acid in human sweat and yogurt samples. The synthesized PS@Co1-Fe1-NC not only provides a new type of catalyst for high-performance ZAB, but also provides a new idea for the construction of SPES.

[0059] It should be noted that when the numerical range is involved in the present application, both endpoints of each numerical range and any number between the two endpoints can be selected. Since the same steps and examples are used, the preferred embodiments are described in the present application to prevent redundancy. Although the preferred embodiments of the present application have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended protection scope is intended to include the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0060] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the present application and its equivalent technologies, the present application also intends to include these modifications and variations.

Claims

1. A method for the preparation of a self-powered sensor for lactic acid detection and its application, characterized by, Comprising the following steps: (1) Preparation of solution A: the polystyrene nanospheres (PS balls) and polyvinylpyrrolidone (PVP) are dissolved in methanol to obtain solution A; (2) Preparation of PS@Co1-Fe1-NC: a soluble zinc salt is dissolved in methanol, denoted as ①; 2-methyl imidazole (2-Meln) is dissolved in methanol, denoted as ②, ① is added into A in turn, and then ② is added into A for stirring. A soluble cobalt salt and a soluble iron salt are dissolved in methanol, denoted as ③; 2-methyl imidazole is dissolved in methanol, denoted as ④, ③ is added into A for stirring in turn, and then ④ is added into A for stirring, and PS@Co1-Fe1-ZIF is obtained after treatment. The PS@Co1-Fe1-ZIF is calcined and carbonized under a protective atmosphere to obtain a PS@Co1-Fe1-NC catalyst; (3) Construction of a self-powered sensor: the PS@Co1-Fe1-NC catalyst is dispersed in ethanol containing a perfluorosulfonic acid resin solution to obtain PS@Co1-Fe1-NC ink; The PS@Co1-Fe1-NC ink is dropped on the surface of a glassy carbon electrode to obtain a PS@Co1-Fe1-NC / GCE, a lactate oxidase solution is dropped on the surface of the PS@Co1-Fe1-NC / GCE to obtain a LOx / PS@Co1-Fe1-NC / GCE, and the LOx / PS@Co1-Fe1-NC / GCE is used as a cathode and a zinc sheet is used as an anode to construct a self-powered sensor for lactic acid detection; (4) Lactic acid detection: PBS solutions containing different concentrations of lactic acid are prepared, and the concentrations are tested in turn from low to high; due to the presence of lactic acid, the lactic acid oxidase at the cathode interface catalyzes the decomposition of lactic acid to consume oxygen, and competes with the ORR reaction at the cathode to form oxygen consumption, which causes the open-circuit voltage of the zinc-air battery to decrease, and the greater the decrease in the open-circuit voltage signal, the greater the concentration of lactic acid, thereby achieving the purpose of detecting lactic acid.

2. The method of claim 1, wherein, The use amount ratio of PS balls to methanol is 0.05g-0.15g:15mL-30mL.

3. The method of claim 1, wherein the self-powered sensor is prepared by, The use amount ratio of the soluble zinc salt to methanol is 0.6g-2.4g:20mL-80mL, the use amount ratio of 2-methyl imidazole to methanol is 0.7-2.8g:20-80mL, and the mass ratio of the soluble cobalt salt to the soluble iron salt is 0.0587g-0.2348g:0.0815g-0.2360g.

4. The method of claim 1, wherein, The calcination and carbonization temperature is 900°C-950°C, and the calcination and carbonization time is 2 hours-3 hours.

5. The method of claim 1, wherein, The use amount ratio of the PS@Co1-Fe1-NC catalyst to ethanol is 1mg-3mg:0.5mL-1mL, the use amount ratio of the PS@Co1-Fe1-NC to the perfluorosulfonic acid resin solution is 1mg-3mg:5μL-10μL, and the mass concentration of the perfluorosulfonic acid resin solution is 0.25%.

6. The method of claim 1, wherein, The concentration of the lactate oxidase solution is 100U / mL-300U / mL.

7. The method of claim 1, wherein the self-powered sensor is prepared by, The polystyrene nanospheres are prepared by mixing deionized water and polyvinylpyrrolidone, carrying out oil bath reaction, adding styrene and K2S2O8 aqueous solution as an initiator after reaction, and carrying out post-treatment on the reaction product to obtain the polystyrene nanospheres.

8. The method of claim 7, wherein the self-powered sensor is prepared by, The ratio of the amount of deionized water to polyvinylpyrrolidone is 100 mL: 0.25-1 g, the ratio of the amount of styrene to K2S2O8 aqueous solution is 6.5 mL-13 mL: 10 mL-20 mL, the oil bath reaction temperature is 60-80°C, and the oil bath reaction time is 20-24 hours.

9. A self-powered sensor prepared by the preparation method of any one of claims 1-8.

10. Application of the self-powered sensor of claim 9 in lactic acid detection.

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