A method for determining pefloxacin in food

Abstract

The present invention discloses a method for determining pefloxacin in food. The portable sensor consists of a Th-Cu-MOF / MWCNTs / SPCE (thiourea-doped copper-based metal-organic framework / multi-walled carbon nanotubes / screen-printed carbon electrode) electrode, a portable electrochemical workstation, an electrolytic cell and a smart phone. Sodium dodecyl benzene sulfonate (SDBS) is added to the electrolytic cell containing the electrolyte solution, which can significantly improve the enrichment efficiency of pefloxacin on the electrode, thus realizing the efficient determination of pefloxacin. One end of the electrode is inserted into the interface of the portable workstation, and the other end is immersed in the electrolytic cell solution. A portable electrochemical sensor is constructed by connecting to the smart phone via Bluetooth. This method has the characteristics of simple preparation, convenient and rapid detection, easy to carry, high mass transfer efficiency, low detection limit and strong anti-interference ability, and can be applied to on-site rapid detection and realize wireless intelligent analysis of trace residues of pefloxacin in food.

Description

Technical Field

[0001] The present invention relates to the technical field of food safety detection, and in particular to a method for determining pefloxacin in food. Background Art

[0002] Pefloxacin (OFL) is a class of synthetic broad-spectrum antibacterial drugs that inhibit bacterial DNA gyrase and block DNA synthesis. To reduce the risks associated with high-density farming and maximize commercial benefits, many farmers often abuse pefloxacin, leading to drug residues entering the food chain and harming human health. Therefore, it is of great significance to develop a sensitive, simple, and portable method for rapid on-site detection of pefloxacin.

[0003] In recent years, various detection methods for PFL, such as high-performance liquid chromatography, capillary electrophoresis, and liquid chromatography-mass spectrometry, have been developed at home and abroad. These methods have been fully validated and widely accepted, but their operation processes and sample pretreatment are often considered time-consuming and laborious, and there are also problems such as high instrument costs and poor stability. With the rapid development of electrochemical sensors, their simple and rapid detection modes are widely applicable to fields such as environmental monitoring and food safety analysis. However, traditional electrochemical sensors are often limited in their on-site detection applications due to their large size and the need to connect a three-electrode system and a desktop computer through complex wiring.

[0004] Moreover, due to the low enrichment efficiency of pefloxacin on the electrode, the mass transfer efficiency of the sensor is poor, affecting the detection signal and resulting in the sensor being unable to obtain a low detection limit, leading to poor determination of pefloxacin. Summary of the Invention

[0005] (I) Technical Problems to be Solved

[0006] To overcome the technical deficiencies in the above background art, a method for determining pefloxacin in food is proposed. By making the electrolytic cell solution composed of SDBS and an electrolyte solution, the enrichment efficiency of pefloxacin on the electrode can be significantly improved, enabling the sensor to have a high-efficiency determination function for pefloxacin. One end of the Th-Cu-MOF / MWCNTs / SPCE electrode is inserted into the interface of a portable workstation, and the other end is immersed in the electrolytic cell solution. A portable electrochemical sensor is constructed by connecting to a smartphone via Bluetooth, eliminating complex wiring and bulky instruments, and enabling on-site detection applications of pefloxacin.

[0007] (II) Technical Solutions

[0008] The present invention is realized through the following technical solutions: The present invention provides a method for determining pefloxacin in food, comprising the following steps:

[0009] S1. Preparation of Th-Cu-MOF / MWCNTs / SPCE electrode:

[0010] S1.1. Synthesis of Th-Cu-MOF: Using copper nitrate as the metal source, trimesic acid (H3BTC) as the ligand, and thiourea (Th) as the modifier, Th-Cu-MOF was synthesized by the solvothermal method. Specifically, 210.14 mg of H3BTC and 76.12 mg of thiourea were completely dissolved in 15 mL of DMF (N,N-dimethylformamide) solvent to obtain a transparent solution. Meanwhile, another 15 mL of DMF was taken and 362.4 mg of Cu(NO3)2·3H2O was added, and ultrasonic dissolution was carried out to obtain a clear blue solution. The two solutions were mixed into a homogeneous solution by ultrasonic stirring, transferred to a high-pressure reaction kettle, heated to 80 °C and maintained for 24 h. The precipitate was collected by centrifugation and washed 2-3 times with DMF and ethanol respectively. Finally, it was dried overnight in a blast drying oven at 60 °C, and the obtained product was named Th-Cu-MOF;

[0011] S1.2. Preparation of Th-Cu-MOF / MWCNTs nanocomposite: 1 mg of Th-Cu-MOF and 0.2 mg of MWCNTs were dispersed in 1 mL of DMF and ultrasonically treated for 15 minutes to obtain Th-Cu-MOF / MWCNTs nanocomposite;

[0012] S1.3. Preparation of Th-Cu-MOF / MWCNTs / SPCE electrode: 5 μL of the dispersion of Th-Cu-MOF / MWCNTs composite was dropped onto a screen-printed carbon electrode (SPCE) and dried under an infrared lamp to obtain Th-Cu-MOF / MWCNTs / SPCE electrode;

[0013] S2. Preparation of the electrolytic cell solution

[0014] S2.1. Prepare a solution that does not participate in chemical reactions and conducts electricity in the electrolytic cell as the electrolyte solution, and introduce an inert gas into the electrolyte solution;

[0015] S2.2. Add SDBS to the electrolyte solution to increase the enrichment efficiency of pefloxacin and thus improve the mass transfer efficiency of the sensor;

[0016] S3. Construction of a portable sensor for the efficient determination of pefloxacin in food:

[0017] S3.1. Construction of a portable electrochemical sensor: One end of the Th-Cu-MOF / MWCNTs / SPCE electrode was embedded in the interface of a portable workstation, and the other end was immersed in the electrolytic cell solution. A portable electrochemical sensor was constructed by connecting to a smartphone via Bluetooth;

[0018] S3.2, Electrode activation: Before detection, the electrode is activated by square wave voltammetry to maintain stable signal output;

[0019] S3.3, Detection procedure: The PSTrace application program is used for detection. The test data can be saved on the mobile phone with one key, and can also be called or transferred to the computer terminal at any time.

[0020] Further, in the step S1.1, the solvent is DMF, acetonitrile or ethanol, and the ligand is any one of H3BTC, H2BDC, H4BTEC and HBSC.

[0021] Further, in the step S1.3, the working electrode is any one of a screen-printed carbon electrode, a screen-printed gold electrode, a screen-printed graphite electrode or a screen-printed platinum electrode.

[0022] Further, the electrolyte solution is a phosphate buffer solution, and the phosphate buffer solution is a mixed solution of 0.1 mol / L disodium hydrogen phosphate, sodium dihydrogen phosphate and 0.9% sodium chloride.

[0023] Further, the inert gas is nitrogen, helium or neon.

[0024] Further, the concentration of SDBS is 0.1 mg / mL.

[0025] Further, the portable sensor for highly efficient determination of pefloxacin in food and its detection method include the following steps:

[0026] S4. Establish a standard working curve for pefloxacin detection:

[0027] S4.1, Dissolve pefloxacin in a solvent that can dissolve it and does not react with pefloxacin to prepare a standard stock solution of pefloxacin;

[0028] S4.2, Place the activated Th-Cu-MOF / MWCNTs / SPCE electrode in the electrolytic cell solution, then add different volumes and a certain concentration of the standard stock solution of pefloxacin to the electrolytic cell solution, stir evenly, and after standing, use square wave voltammetry to detect and analyze the solution to obtain the oxidation peak current of pefloxacin at different concentrations. Then, with the concentration of the standard stock solution of pefloxacin as the abscissa and the oxidation peak current of pefloxacin as the ordinate, establish a standard working curve for pefloxacin detection;

[0029] S5. Rapid quantitative analysis of pefloxacin in actual samples:

[0030] The activated Th-Cu-MOF / MWCNTs / SPCE electrode was placed in the electrolytic cell solution, and the experimental parameter conditions were adjusted. Then, a certain volume of the test solution containing an unknown concentration of pefloxacin was added thereto, stirred evenly, and after standing, the oxidation peak current value of pefloxacin was measured by square wave voltammetry. Finally, according to the pefloxacin detection standard working curve established in step S4, the concentration of pefloxacin in the actual sample was calculated.

[0031] Further, the method for preparing the pefloxacin standard stock solution is to dissolve pefloxacin in a 0.02% glacial acetic acid solution to prepare a pefloxacin standard stock solution with a concentration of 0.001 mol / L.

[0032] (III) Beneficial effects

[0033] The present invention has the following beneficial effects compared with the prior art:

[0034] 1. In the present invention, by modifying the Th-Cu-MOF / MWCNTs composite material on a screen-printed carbon electrode (SPCE), embedding it in a portable electrochemical workstation and connecting it to a smartphone via Bluetooth, wireless intelligent analysis of the residue of pefloxacin in food is realized, eliminating complex wiring and bulky instruments, and providing a new method for rapid on-site detection of pefloxacin in food.

[0035] 2. In the present invention, by using SDBS, the enrichment efficiency of pefloxacin on the electrode can be greatly improved, thereby improving the mass transfer efficiency of the sensor, enabling the portable sensor to have the function of highly efficient determination of pefloxacin.

[0036] 3. In the present invention, the portable sensor establishes a standard working curve based on the relationship between the oxidation peak current of pefloxacin and the concentration of pefloxacin, and measures the pefloxacin with an unknown concentration through the pefloxacin detection standard working curve. The method is simple, portable, easy to operate, has a rapid response, high efficiency in determination, good repeatability and reproducibility, and strong anti-interference ability, and can be used for rapid quantitative detection of pefloxacin in actual samples such as pork, shrimp meat and water samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] By reading the following detailed description of the non-limiting embodiments with reference to the accompanying drawings, other features, objects and advantages of the present invention will become more apparent:

[0038] Figure 1 It is a sensor construction diagram of the present invention;

[0039] Figure 2Cyclic voltammograms of the Th-Cu-MOF / MWCNTs modified electrode, Cu-MOF / MWCNTs modified electrode, MWCNTs modified electrode, Th-Cu-MOF modified electrode, Cu-MOF modified electrode and unmodified blank electrode in a buffer solution containing 2 µM pefloxacin and 0.1 mg / mL SDBS in the present invention;

[0040] Figure 3 Square wave voltammetric response curves of the Th-Cu-MOF / MWCNTs modified electrode and the unmodified blank electrode in the present invention for 2 µM pefloxacin in buffer solutions with and without 0.1 mg / mL SDBS respectively;

[0041] Figure 4 Square wave voltammograms of the Th-Cu-MOF / MWCNTs modified electrode in a buffer solution containing 0.1 mg / mL SDBS with different concentrations of pefloxacin in the present invention;

[0042] Figure 5 Standard working curves of the Th-Cu-MOF / MWCNTs modified electrode in a buffer solution containing 0.1 mg / mL SDBS with different concentrations of pefloxacin in the present invention;

[0043] Figure 6 Interference resistance diagram of the Th-Cu-MOF / MWCNTs modified electrode in the present invention;

[0044] Figure 7 Reproducibility diagram of the Th-Cu-MOF / MWCNTs modified electrode in the present invention;

[0045] Figure 8 Repeatability diagram of the Th-Cu-MOF / MWCNTs modified electrode in the present invention;

[0046] Figure 9 Long-term stability diagram of the Th-Cu-MOF / MWCNTs modified electrode in the present invention; Detailed implementation manners

[0047] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0048] The present invention provides a method for determining pefloxacin in food, and the abbreviations involved in the embodiments of the present invention include:

[0049] 1. Pefloxacin (PFL)

[0050] 2, Trimesic acid (H3BTC)

[0051] 3, N,N-Dimethylformamide (DMF)

[0052] 4, Copper-based metal-organic framework (Cu-MOF)

[0053] 5, Multi-walled carbon nanotubes (MWCNTs)

[0054] 6, Screen-printed carbon electrode (SPCE)

[0055] 7, Sodium dodecylbenzenesulfonate (SDBS)

[0056] 8, Terephthalic acid (H3BDC)

[0057] 9, Pyromellitic acid (H4BTEC)

[0058] 10, Benzoic acid (HBSC)

[0059] 11, Phosphate buffer solution (PBS) Example 1

[0060] A portable sensor for the efficient determination of pefloxacin in food and its preparation method, comprising the following steps:

[0061] S1. Preparation of Th-Cu-MOF / MWCNTs / SPCE electrode:

[0062] S1.1 Synthesis of Th-Cu-MOF: Using copper nitrate as the metal source, trimesic acid (H3BTC) as the ligand, and thiourea (Th) as the modifier, Th-Cu-MOF was synthesized by solvothermal method. Specifically, 210.14 mg of H3BTC and 76.12 mg of thiourea were completely dissolved in 15 mL of DMF (N,N-dimethylformamide) solvent to obtain a transparent solution. At the same time, another 15 mL of DMF was taken and 362.4 mg of Cu(NO3)2·3H2O was added, and ultrasonic dissolution was carried out to obtain a clear blue solution. The two solutions were mixed into a uniform solution by ultrasonic stirring, transferred to a high-pressure reaction kettle, heated to 80 °C and maintained for 24 h, the precipitate was collected by centrifugation, washed 2-3 times with DMF and ethanol respectively, and finally dried overnight in a blast drying oven at 60 °C. The obtained product was named Th-Cu-MOF;

[0063] S1.2 Preparation of Th-Cu-MOF / MWCNTs nanocomposite: 1 mg of Th-Cu-MOF and 0.2 mg of MWCNTs were dispersed in 1 mL of DMF and ultrasonicated for 15 minutes to obtain Th-Cu-MOF / MWCNTs nanocomposite;

[0064] S1.3. Preparation of Th-Cu-MOF / MWCNTs / SPCE electrode: Take 5 μL of the dispersion of Th-Cu-MOF / MWCNTs composite material and drop it onto the screen-printed carbon electrode (SPCE), and dry it under an infrared lamp to obtain the Th-Cu-MOF / MWCNTs / SPCE electrode;

[0065] S2. Preparation of the electrolytic cell solution

[0066] S2.1. Prepare a solution that does not participate in chemical reactions and is conductive in the electrolytic cell as the electrolyte solution, and introduce an inert gas into the electrolyte solution;

[0067] S2.2. Add SDBS to the electrolyte solution to increase the enrichment efficiency of pefloxacin and thus improve the mass transfer efficiency of the sensor;

[0068] S3. Construction of a portable sensor for the efficient determination of pefloxacin in food (as Figure 1 )

[0069] S3.1. Construction of a portable electrochemical sensor: Insert one end of the Th-Cu-MOF / MWCNTs / SPCE electrode into the interface of the portable workstation, and immerse the other end into the electrolytic cell solution, and construct a portable electrochemical sensor by connecting to a smartphone via Bluetooth;

[0070] S3.2. Electrode activation: Before detection, the electrode is activated by square wave voltammetry to maintain a stable signal output;

[0071] S3.3. Detection procedure: Use the PSTrace application program for detection, and the test data can be saved on the mobile phone with one key, and can also be called or transferred to the computer at any time. Example 2

[0072] Use the portable sensor prepared in Example 1 to detect pefloxacin, and the specific steps of its analysis method are as follows:

[0073] Establish a standard working curve for pefloxacin detection:

[0074] ① Dissolve 1.67 mg of pefloxacin in 5 mL of 0.02% glacial acetic acid solution to prepare a standard stock solution of pefloxacin with a concentration of 0.001 mol / L;

[0075] ② Place the activated Th-Cu-MOF / MWCNTs / SPCE electrode into the prepared electrolytic cell solution. Then, add different volumes of the prepared standard pefloxacin mother solution with a certain concentration into the electrolytic cell solution, stir evenly, and after standing, use square wave voltammetry (SWV) to detect and analyze the standard working solution of pefloxacin in the concentration range of 9 nmol / L to 2.5 μmol / L. The oxidation peak current of pefloxacin at different concentrations can be obtained. Taking the concentration as the abscissa and the oxidation peak current as the ordinate, establish the standard working curve for pefloxacin detection. This portable electrochemical sensor has a good linear relationship with pefloxacin (R2 = 0.9927, as Figure 5 shown), and for the square wave voltammogram of the standard solution of pefloxacin with different concentrations ( Figure 4 ), the detection limit can be calculated to be as low as 2.6 nmol / L, meeting the international limit standard.

[0076] Electrochemical response of pefloxacin:

[0077] In the electrolytic cell solution containing 2.0 μmol / L PFL, the Th-Cu-MOF / MWCNTs modified electrode has an oxidation peak for pefloxacin at 0.98 V. And compared with the blank electrode, the Cu-MOF modified electrode, the Th-Cu-MOF modified electrode, the MWCNTs modified electrode, and the Cu-MOF / MWCNTs modified electrode, the Th-Cu-MOF / MWCNTs modified electrode of the present invention has the most obvious electrochemical response to pefloxacin, indicating that the sensor constructed by this modified electrode has good electrocatalytic oxidation activity for pefloxacin. The results are as Figure 2 shown.

[0078] Effect of SDBS:

[0079] The SWV responses of 2.0 μmol / L PFL were studied using the blank electrode and the Th-Cu-MOF / MWCNTs modified electrode in 0.1 mol / L PBS (pH 5.0) buffer solutions with and without 0.1 mg / mL SDBS, respectively. The results show that compared with the absence of SDBS, when SDBS is present, the oxidation peaks of pefloxacin for both the blank electrode and the Th-Cu-MOF / MWCNTs modified electrode are significantly enhanced, confirming that SDBS can significantly improve the enrichment efficiency of pefloxacin on the electrode, as Figure 3 shown.

[0080] Anti-interference evaluation of pefloxacin detection by the portable sensor:

[0081] The portable electrochemical sensor constructed by the present invention has strong anti-interference ability. After adding KCl, Na2SO4, CaCl2, glucose, ascorbic acid, vitamin B6, lysine, phenylalanine, glycine, cysteine, enrofloxacin, norfloxacin and ofloxacin, there is no obvious change in the electrochemical signal, that is, there is no obvious interference in the detection, indicating that the portable sensor has good anti-interference ability, as Figure 6 shown.

[0082] Reproducibility evaluation of the portable sensor for detecting pefloxacin:

[0083] Seven Th-Cu-MOF / MWCNTs modified electrodes were used to measure a 2 µM pefloxacin solution in parallel under the optimal conditions (buffer pH = 5.0, stirring time = 4 min). The relative standard deviation (RSD) of the measured peak current was 2.3%, indicating that the constructed portable sensor has good reproducibility, as Figure 7 shown.

[0084] Repeatability evaluation of the portable sensor for detecting pefloxacin:

[0085] Using the same Th-Cu-MOF / MWCNTs modified electrode, a 2 µM pefloxacin solution was measured in parallel 7 times under the optimal conditions. The relative standard deviation (RSD) of the measured peak current was 3.5%, indicating that the constructed portable sensor has good repeatability, as Figure 8 shown.

[0086] Long-term stability evaluation of the portable sensor for detecting pefloxacin:

[0087] After the Th-Cu-MOF / MWCNTs modified electrode was placed at 4°C for 1, 4, 7, 10, 13, 16, 19, 22, 25 days respectively, 2 µM pefloxacin was detected under the optimal conditions. After 25 days, the current still exceeded 90% of the initial current, indicating that the sensor has good long-term stability, as Figure 9 shown.

[0088] Detection performance evaluation of the portable sensor:

[0089] The constructed sensor was compared with other reported pefloxacin analysis methods. The results confirmed that the portable sensor has a lower detection limit and a wider linear range for PFL, indicating that the constructed portable pefloxacin sensor has satisfactory detection performance under the action of SDBS. At the same time, compared with other methods, this sensor is easy to carry. As shown in Table 1:

[0090] Table 1

[0091] Analysis method Modified electrode Linear range (μM) LOD (μM) Time-resolved fluorescence analysis method - 0.075 – 0.75 0.041 Fluorescence spectroscopy - 1.0 – 11.0 0.24 High performance liquid chromatography - 0.15 – 30 0.15 Fluorescence spectrophotometry - 0.03 – 0.18 <![CDATA[4.6×10 -3 > Surface-enhanced Raman - 150 – 1500 8.7 Electrochemical analysis - differential pulse anodic stripping voltammetry CTAB-Cu-GR / carbon paste electrode 0.04 – 20 <![CDATA[2.5×10 -3 > Electrochemical analysis - differential pulse voltammetry <![CDATA[P-L CuO:Tb 3+ NS / Glassy Carbon Electrode]]> 0.01 – 800 <![CDATA[2.3×10 -3 > Electrochemical analysis - square wave voltammetry Boron-doped diamond electrode 2 – 200 0.154 Electrochemical analysis - differential pulse voltammetry dsDNA / carbon paste electrode 0.1 – 10 0.05 Electrochemical analysis - square wave voltammetry (the present invention) Th-Cu-MOF / MWCNTs / SPCE 0.009 – 2.5 0.0026

[0092] Recovery and Rapid Quantitative Detection of Pefloxacin in Actual Samples

[0093] Calculation of the recovery rate of pefloxacin in actual samples by this method

[0094] Add a known concentration of pefloxacin to an actual sample without pefloxacin (the actual sample has been detected by high-performance liquid chromatography according to the determination standard and no pefloxacin has been found. For water samples, refer to the determination standard DB32 / T 3771-2020 for quinolone antibiotics in fishery aquaculture water in Jiangsu Province, and for pork and shrimp, refer to the determination standard GB / T 20366-2006 for the determination of quinolone residues in animal products in China). Then add it to the electrolytic cell solution and adjust experimental parameters such as pH to the conditions when the standard curve was established. Then place the activated Th-Cu-MOF / MWCNTs / SPCE electrode prepared in Example 1 into it, stir for 4 min, and after standing, measure it 3 times in parallel by square wave voltammetry to obtain the average oxidation peak current value. Finally, according to the pefloxacin detection standard working curve established in step (1), obtain the measured value of the pefloxacin concentration in the actual sample, calculate the recovery rate and relative standard deviation, and finally compare this method with the traditional electrochemistry sensing method and high-performance liquid chromatography method (Table 2) to evaluate the precision and accuracy of this method.

[0095] ②Rapid quantitative detection of pefloxacin in actual samples by this method

[0096] Add a certain volume of the pretreated test solution containing an unknown concentration of pefloxacin, such as chicken, fish, and water samples, to the electrolytic cell solution and adjust the pH to 5.0. Stir evenly, place the activated Th-Cu-MOF / MWCNTs / SPCE electrode prepared in Example 1 into the electrolytic cell solution, and after stirring for 4 min, measure and calculate the concentration of pefloxacin in the test solution with an unknown concentration by square wave voltammetry.

[0097] The conditions of square wave voltammetry are: voltage scanning range 0.6 - 1.3 V, potential increment 0.01 V, amplitude 0.025 V, and pulse frequency 15 Hz.

[0098] Table 2

[0099]

[0100] As can be seen from Table 2, the recoveries of the portable sensor for chicken, fish and water samples after multiple repeated tests were between 87.92% and 104.35%, and the RSDs were between 1.0% and 4.0%. The recoveries of the traditional electrochemical sensor were between 88.95% and 105.98%, and the RSDs were between 1.2% and 4.9%. The recoveries of the high performance liquid chromatography method were between 84.95% and 103.74%, and the RSDs were between 0.5% and 4.2%. The results showed that there were no significant differences in the recoveries of the three methods, and they were all within the acceptable range of 80% - 110%, indicating that the portable sensor had reliable analysis results and high precision, and was expected to become a new method for rapid on-site detection of PFL residues in the field of intelligent sensing.

[0101] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification are only preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A method for determining pefloxacin in food, characterized in that, It includes the following steps: S1. Preparation of Th-Cu-MOF / MWCNTs / SPCE electrode: S1.

1. Synthesis of Th-Cu-MOF: Using copper nitrate as the metal source, trimesic acid (H3BTC) as the ligand, and thiourea (Th) as the modifier, Th-Cu-MOF is synthesized by solvothermal method. Specifically, 210.14 mg of H3BTC and 76.12 mg of thiourea are completely dissolved in 15 mL of DMF (N,N-dimethylformamide) solvent to obtain a transparent solution. Meanwhile, another 15 mL of DMF is taken and 362.4 mg of Cu(NO3)2·3H2O is added, and it is ultrasonically dissolved to obtain a clear blue solution. The two solutions are mixed into a homogeneous solution after ultrasonic stirring, transferred to a high-pressure reaction kettle, heated to 80 °C and maintained for 24 h. The precipitate is collected after centrifugation, washed 2 - 3 times with DMF and ethanol respectively, and finally dried overnight in a blast drying oven at 60 °C. The obtained product is named Th-Cu-MOF; S1.

2. Preparation of Th-Cu-MOF / MWCNTs nanocomposite: 1 mg of Th-Cu-MOF and 0.2 mg of MWCNTs are dispersed in 1 mL of DMF and ultrasonically treated for 15 minutes to obtain Th-Cu-MOF / MWCNTs nanocomposite; S1.

3. Preparation of Th-Cu-MOF / MWCNTs / SPCE electrode: 5 μL of the dispersion of Th-Cu-MOF / MWCNTs composite is dropped onto a screen-printed carbon electrode (SPCE), and dried under infrared light to obtain Th-Cu-MOF / MWCNTs / SPCE electrode; S2. Preparation of the electrolytic cell solution S2.

1. A solution that does not participate in chemical reactions and is conductive is prepared in the electrolytic cell as the electrolyte solution, and an inert gas is introduced into the electrolyte solution; S2.

2. Sodium dodecylbenzenesulfonate (SDBS) is added to the electrolyte solution to increase the enrichment efficiency of pefloxacin and thus improve the mass transfer efficiency of the sensor; S3. Construction of a portable sensor for determining pefloxacin in food: S3.

1. Construction of a portable electrochemical sensor: One end of the Th-Cu-MOF / MWCNTs / SPCE electrode is embedded in the interface of a portable workstation, and the other end is immersed in the electrolytic cell solution. A portable electrochemical sensor is constructed by connecting to a smartphone via Bluetooth; S3.

2. Electrode activation: Before detection, the electrode is activated by square wave voltammetry to maintain a stable signal output; S3.

3. Detection procedure: The PSTrace application program is used for detection, and the test data can be saved on the mobile phone with one key, and can also be called or transmitted to the computer terminal at any time.

2. The method according to claim 1, wherein: In step S1.1, the solvent is DMF, acetonitrile or ethanol, and the ligand is any one of H3BTC, H2BDC, H4BTEC and HBSC.

3. The method according to claim 1, wherein: In step S1.3, the working electrode is any one of a screen-printed carbon electrode, a screen-printed gold electrode, a screen-printed graphite electrode or a screen-printed platinum electrode.

4. The method according to claim 1, wherein: The electrolyte solution is a phosphate buffer solution, and the phosphate buffer solution is a mixed solution of 0.1 mol / L disodium hydrogen phosphate, sodium dihydrogen phosphate and 0.9% sodium chloride.

5. The method according to claim 1, characterized in that: The inert gas is nitrogen, helium or neon.

6. The method according to claim 1, wherein: The concentration of SDBS is 0.1 mg / mL.

7. The method according to any one of claims 1-6, characterized in that, It also includes the following steps: S4. Establish a standard working curve for pefloxacin detection: S4.

1. Dissolve pefloxacin in a solvent that can dissolve it and does not react with pefloxacin to prepare a standard stock solution of pefloxacin. S4.

2. Place the activated Th-Cu-MOF / MWCNTs / SPCE electrode in the electrolytic cell solution, then add different volumes of the standard stock solution of pefloxacin with a certain concentration to the electrolytic cell solution, stir evenly, and after standing, use square wave voltammetry to detect and analyze the solution to obtain the oxidation peak currents of pefloxacin at different concentrations. Then, with the concentration of the standard stock solution of pefloxacin as the abscissa and the oxidation peak current of pefloxacin as the ordinate, establish a standard working curve for pefloxacin detection. S5. Rapid quantitative analysis of pefloxacin in actual samples: Place the activated Th-Cu-MOF / MWCNTs / SPCE electrode in the electrolytic cell solution, adjust the experimental parameter conditions, then add a certain volume of the test solution containing an unknown concentration of pefloxacin to it, stir evenly, and after standing, use square wave voltammetry to measure the oxidation peak current value of pefloxacin. Finally, according to the standard working curve for pefloxacin detection established in step S4, calculate the concentration of pefloxacin in the actual sample.

8. The method according to claim 7, characterized in that: The preparation method of the standard stock solution of pefloxacin is to dissolve pefloxacin in a 0.02% glacial acetic acid solution to prepare a standard stock solution of pefloxacin with a concentration of 0.001 mol / L.

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