CN114324515A - Electrochemical sensor for detecting glyphosate based on copper porphyrin metal organic framework modified carbon paper electrode - Google Patents

Abstract

The invention discloses an electrochemical sensor for detecting glyphosate based on a copper porphyrin metal-organic framework modified carbon paper electrode, belonging to the technical field of electrochemistry. The invention uses carbon paper as the working electrode for detecting glyphosate for the first time, and prepares an electrochemical sensor based on copper porphyrin metal-organic framework modified carbon paper electrode. The electrochemical sensor has lower detection limit, high stability and good reproducibility. performance and anti-interference ability. Based on the electrochemical sensor, the invention provides a cheap, sensitive and stable detection method for glyphosate, which can realize quantitative detection in the range of 0.2 μM-120 μM, and the detection limit reaches 0.03 μM.

Description

An electrochemical sensor for glyphosate detection based on copper porphyrin metal organic framework modified carbon paper electrode

technical field

The invention relates to an electrochemical sensor for detecting glyphosate based on a copper porphyrin metal-organic framework modified carbon paper electrode, belonging to the technical field of electrochemistry.

Background technique

Glyphosate (GLY), developed by Monsanto in 1971, is a broad-spectrum biocidal, systemic and conductive herbicide. Glyphosate, the most widely used herbicide in the world, has seen a dramatic increase in its consumption in recent years, raising concerns about potential health and environmental hazards. In January 2019, the EPA reassessed the evidence on the carcinogenicity of glyphosate and concluded that "glyphosate is unlikely to cause cancer." In 2019, the French Ministry of Agriculture proposed to phase out the use of glyphosate products by the end of 2020. As the largest producer and major user of glyphosate in my country, its safety is not only related to the sustainable development of the industry, but also to agricultural trade, environmental safety and human health.

At present, many detection methods are based on mature and stable chromatography, including high performance liquid chromatography (HPLC), gas chromatography (GC) and capillary electrophoresis. However, these methods have low efficiency, high equipment requirements and complicated operation. Although GC-MS/MS, HPLC-MS/MS, fluorescence methods, capillary electrophoresis, electrochemical sensors, etc. have all been proved to be "sensitive" in the detection of glyphosate and AMPA. And, even with tap water, the sensitivity is reduced by a factor of 10 due to severe matrix effects. The pretreatment of glyphosate and AMPA samples is difficult. The main reason is that these compounds have strong polarity, are easily soluble in water, hardly volatile, insoluble in organic solvents, and have strong complexes with divalent and trivalent metal ions. There are a large number of complex forms in the actual sample, which affects its derivatization and extraction efficiency. Therefore, there is an urgent need to provide a fast, convenient and efficient detection technology for glyphosate detection to solve the current problems of low electrochemical detection sensitivity, narrow detection range, and complicated operation.

SUMMARY OF THE INVENTION

The present invention proposes for the first time a flower-like porphyrin MOFs material (Cu-TCPP) as a new sensing platform for GLY detection, and uses Cu-TCPP as an electrode modification material for the electrochemical detection of GLY. The 2D layered structure of Cu-TCPP provides a large active site that can selectively cooperate with GLY, enabling indirect determination of GLY. Based on the synergistic electrocatalytic effect of Cu-TCPP and AuNPs and the large specific surface area of carbon paper, the constructed sensor has fast analysis speed, wide linear range and high sensitivity.

The invention establishes an electrochemical sensor for detecting glyphosate based on a copper porphyrin metal-organic framework modified carbon paper electrode. Electrochemical sensors have the advantages of fast detection speed, no complex pretreatment, and low cost. Therefore, it is of great significance to study and prepare electrochemical sensors for pesticide residue detection. First of all, the present invention selects a carbon paper electrode as the working electrode. Compared with the classical glassy carbon electrode, the carbon paper electrode has a larger specific surface area and better electrical conductivity. Uniform gold nanoparticles were electroplated on the carbon paper electrode, which further improved the electrochemically active area of the electrode. Second, sheet Cu-TCPP is selected as the electrode material, which facilitates the diffusion process between the material and the electrode and accelerates the reaction process. And the copper porphyrin metal-organic framework was modified by drop coating, and the synergistic effect of gold nanoparticles and copper porphyrin metal-organic framework improved the sensitivity of electrochemical determination and realized the detection of GLY from non-electroactive to electroactive. .

Technical solutions:

The invention provides a preparation method of an electrochemical sensor for detecting glyphosate, comprising the following steps:

(1) The carbon paper is pretreated with an acid solution, and then immersed in a tetrachloroauric acid solution for electrodeposition to obtain a carbon paper electrode modified with gold nanoparticles AuNPs, which is expressed as AuNPs/CP;

(2) Disperse Cu-TCPP in a solvent to obtain a Cu-TCPP dispersion, then drop it on the surface of the AuNPs/CP obtained in step (1), and dry it to obtain an electrochemical sensor probe, denoted as Cu-TCPP /AuNPs/CP;

(3) using the electrochemical sensor probe obtained in step (2) as a working electrode, forming a three-electrode system with a counter electrode and a reference electrode, and combining with an electrochemical workstation to construct an electrochemical sensor.

In an embodiment of the present invention, in the step (1), the acid solution is a nitric acid solution. Specifically, concentrated nitric acid (68 wt%): water, 1:1, v:v.

In an embodiment of the present invention, in the step (1), the pretreatment further includes washing and drying. Specifically, acetone and ethanol are used for washing. Specifically, drying is performed at 60°C.

In an embodiment of the present invention, in the step (1), the chloroauric acid solution is prepared by dispersing 0.1wt% HAuCl ₄ ·3H ₂ O in water.

In an embodiment of the present invention, in the step (1), the electrodeposition process is deposition under the condition of -0.2V for 120s.

In an embodiment of the present invention, in the step (2), the solvent is a mixed solution of water and 0.1% Nafion, and the volume ratio of the two is 20:1.

In an embodiment of the present invention, in the step (2), the concentration of the Cu-TCPP dispersion liquid is 0.7 mgmL ^-1 .

In one embodiment of the present invention, a platinum wire electrode is used as a counter electrode, and a saturated calomel electrode is used as a reference electrode.

The present invention provides an electrochemical sensor for detecting glyphosate based on the above preparation method.

The present invention also provides a method for detecting glyphosate, comprising the following processes:

The above three-electrode system was immersed in a series of glyphosate standard sample solutions of known concentration, and the voltage was controlled for pre-concentration; after the pre-concentration, the corresponding oxidation peak current value was measured by differential pulse voltammetry (DPV) method I, and the oxidation peak current value I ₀ of the blank sample with a glyphosate concentration of 0, calculate the oxidation peak current difference II ₀ (ΔI); then use the obtained oxidation peak current difference and the corresponding glyphosate concentration to perform a linear correlation , to obtain a quantitative detection model.

In one embodiment of the present invention, the enrichment voltage is 0.1V.

In an embodiment of the present invention, the enrichment time is 60s.

In one embodiment of the present invention, the potential range of the differential pulse voltammetry (DPV) method is -0.2-0.6V.

In one embodiment of the present invention, the concentration range of the glyphosate standard sample is 0.2-120 μM.

In one embodiment of the present invention, a series of glyphosate standard samples of known concentration were prepared using 0.1M acetic acid/sodium acetate buffer (pH 6.0) as solvent.

Beneficial effects:

The invention prepares an electrochemical sensor based on a copper porphyrin metal-organic framework modified carbon paper electrode, and adopts the method of electrodepositing gold nanoparticles to improve the conductivity and sensitivity of the electrode, and constructs a fast and simple detection method for glyphosate . The electrochemical sensor exhibits low detection limit, high stability, good reproducibility, and anti-interference ability, indicating that functional electrode-modified material MOFs have unlimited potential in the field of electroanalysis. The present invention uses carbon paper as the working electrode for detecting glyphosate for the first time, and provides a cheap, sensitive and stable electrochemical sensor substrate. That is, the disposable carbon paper electrode can facilitate batch preparation and on-site rapid detection, and is suitable for environmental analysis. and provide effective analytical tools for on-site monitoring of food safety.

Based on the electrochemical sensor, the present invention can realize quantitative detection of GLY in the range of 0.2 μM-120 μM. Among them, at 0.2μM-10μM, its linear equation is ΔI _p =1.0932C _GLY +8.4697(R ² =0.994); at 10-120μM, the linear equation is ΔI _p =0.0687C _GLY +18.562(R ² =0.996); The detection limit of GLY was 0.03 μM (S/N=3).

Description of drawings

Figure 1 shows the SEM micrographs of (A) CP, (B) AuNPs/CP and (C) Cu-TCPP/AuNPs/CP; (D) FT-IR spectra of TCPP monomer and synthesized Cu-TCPP.

Figure 2 is a micrograph of the Cu-TCPP material (a, b are different magnifications, respectively).

Figure 3 shows different electrodes (glassy carbon electrode, conductive glass, pencil lead electrode, carbon paper electrode) in 1mmol/L [Fe(CN) ₆ ] ^3- /[Fe(CN) ₆ ] ⁴ containing 0.2mol/L KCl ^- Cyclic voltammetry in solution.

Figure 4 shows (A) bare CP and (C) Cu-TCPP/AuNPs/CP in 1.0 mmol/L [Fe(CN) ₆ ] ^3- /[Fe(CN) ₆ ] ^4- redox probe (containing 0.2mol/L KCl) cyclic voltammetry superposition curves at scan rates of 10-200mV/s; (B) bare CP and (D) Cu-TCPP/AuNPs/CP redox peak currents and scan rates between ^1/2 linear relationship.

Fig. 5 shows (A) cyclic voltammetry and (B) AC of different modified electrodes in 1 mmol/L [Fe(CN) ₆ ] ^3- /[Fe(CN) ₆ ] ^4- solution containing 0.2 mol/L KCl impedance curve.

Figure 6 is a cyclic voltammogram of different electrodes in acetate buffer aqueous solution (ABS) at pH 6 and a scan rate of 50 mV s ⁻¹ .

FIG. 7 is a differential pulse voltammogram of the determination of glyphosate by different Cu-MOF modified materials.

FIG. 8 is a graph showing the effect of pH on the change of oxidation peak current.

FIG. 9 is a graph showing the effect of different mass concentrations of Cu-TCPP on the change of the oxidation peak current.

Figure 10. Change diagram of the effect of different enrichment voltages on the change of oxidation peak current.

Fig. 11 Change diagram of the effect of different enrichment time on the change of oxidation peak current.

Figure 12 is (A) differential pulse voltammograms of the sensor for different concentrations of glyphosate solutions; (B) the relationship between oxidation peak current and GLY concentration.

Figure 13 shows (A) the relative responses of six modified carbon paper electrodes to solutions containing 10 μmol L ^-1 GLY; (B) the relative responses of Cu-TCPP/AuNPs/CP electrodes at different storage times.

Figure 14 shows the peak current values measured with Cu-TCPP/AuNPs/CP electrode containing 2 μM GLY(A) in the presence and absence of different anions and cations (200 μM) and 2 μM organophosphorus pesticides.

Figure 15 is a schematic diagram of the preparation process of Cu-TCPP/AuNPs/CP modified carbon paper.

Detailed ways

Materials and reagents: glyphosate, aminomethylphosphonic acid, Aladdin Reagent (Shanghai) Co., Ltd.; carbon paper (thickness 0.19mm), Shanghai Hesen; tetrachloroauric acid, Sanshui, Shanghai Titan Technology Co., Ltd. ; Meso-tetrakis (4-carboxyphenyl) porphine (97%), Beijing Inuokai Technology Co., Ltd.; Nafion (5% w/w), Bailingwei (Shanghai) Technology Co., Ltd.; Organophosphorus pesticides, Shanghai McLean Biochemical Technology Co., Ltd.; trifluoroacetic acid, copper nitrate, trihydrate (Cu(NO ₃ ) ₂ ·3H ₂ O, 99%), polyvinylpyrrolidone, trifluoroacetic acid, potassium chloride, anhydrous sodium sulfate, anhydrous sulfuric acid Magnesium, ferric sulfate heptahydrate, calcium chloride·dihydrate, cadmium chloride·2.5 water, lead acetate·trihydrate, anhydrous sodium acetate, glacial acetic acid, anhydrous ethanol, Sinopharm Reagent (Shanghai) Co., Ltd.;

Instruments and equipment: CHI660C electrochemical workstation, saturated calomel electrode, platinum electrode, Shanghai Chenhua Instrument Company; KQ-100DB CNC ultrasonic cleaner, Kunshan Ultrasonic Instrument Co., Ltd.; SHA-B constant temperature oscillator, Changzhou Guohua Company ; SU8100 scanning electron microscope, Hitachi, Ltd. Fourier Transform Infrared (FT-IR) Spectrometer Model IS10, Nicolet, USA. T9 double beam UV-Vis spectrophotometer, Beijing Puxi General Instrument Co., Ltd.

Example 1 Preparation of electrochemical sensor

(1) Preparation of Cu-TCPP:

The Cu-TCPP modified material was synthesized by solvothermal method: 3.6 mg Cu(NO ₃ ) ₂ ·3H ₂ O, 10 μL trifluoroacetic acid (1M), 10 mg polyvinylpyrrolidone PVP were dissolved in 12 mL DMF and ethanol (V:V=3 : 1) in the mixed solvent to obtain mixed solution A; Weigh 4mg TCPP and dissolve it in the mixed solvent of 4mL DMF and ethanol (V:V=3:1) to obtain mixed solution B; Mixed solution B is added dropwise to Mixture A (under stirring conditions), sonicated for 10 min, poured into a polytetrafluoroethylene reaction tube and sealed in a stainless steel reaction kettle, heated to 80 ° C, and reacted for 20 h; after the reaction was completed, cooled to room temperature, washed with absolute ethanol The Cu-TCPP was washed 3 times at 8000 rpm for 10 min to remove the monomers that did not participate in the reaction; the precipitate was collected by centrifugation, vacuum dried at 50°C overnight, and finally Cu-TCPP was obtained.

(2) AuNPs deposition modified carbon paper electrode (preparation of AuNPs/CP):

Before modifying the electrodes, the carbon paper was pretreated: ultrasonically cleaned in nitric acid (68wt% concentrated nitric acid:water, 1:1, v:v), acetone, and ethanol in sequence for 30 min, and dried at 60°C. The pretreated carbon paper electrode was immersed in HAuCl ₄ ·3H ₂ O (0.1%) solution and deposited at -0.2 V for 120 s to obtain the carbon paper electrode modified by AuNPs deposition, denoted as AuNPs/CP.

(3) Preparation of Cu-TCPP/AuNPs/CP:

The Cu-TCPP nanomaterials were dispersed in a mixture of water and 0.1% Nafion (20:1, v:v) to obtain a Cu-TCPP dispersion, and the concentration of the Cu-TCPP dispersion was controlled to be 0.7 mg mL ^-1 . 30 μL Cu-TCPP dispersion droplets were applied to the surface of the AuNPs/CP electrode, and dried at 60 °C to obtain an electrochemical sensor probe, denoted as Cu-TCPP/AuNPs/CP.

(4) Construction of electrochemical sensor:

The obtained electrochemical sensor probe was used as the positive electrode, the platinum wire electrode was used as the counter electrode, and the saturated calomel electrode was used as the reference electrode to establish a three-electrode system; it was combined with an electrochemical workstation to construct an electrochemical sensor.

Characterization of Cu-TCPP: Fourier transform infrared spectroscopy was used to characterize the chemical bonds of Cu-TCPP (as shown in Figure 1D). The FTIR spectra of TCPP and Cu-TCPP showed characteristic absorption peaks of macrocyclic frameworks at 716,1000 cm ^-1 . The peak at about 1400 cm ⁻¹ corresponds to the stretching vibration of the C=N bond of the pyrrole ring. In addition, the absorption peaks at 1108 and 1607 cm ^-1 are the skeleton vibration of the outer benzene ring, the peak at 1660 cm ^-1 is the vibration peak of C=O on the carboxyl group, and the peak at 772 cm ^-1 is the characteristic peak of benzene ring substitution. In addition, the absorption peaks at 1108 and 1607 cm ^-1 are the skeleton vibrations of the outer benzene ring. Compared with TCPP, the peak intensity at 1270 cm in Cu ^- TCPP nanomaterials is significantly weakened because the hydrogen on -OH is replaced by metal ions to form Cu-O bonds, which indicates that Cu ²⁺ is successfully coordinated with the carboxyl groups in TCPP . The characteristic peak at 1000 cm ^-1 is attributed to the N-Cu bond stretching vibration absorption, indicating that the metal ion Cu ²⁺ in the synthesized metalloporphyrin derivatives has formed a coordination compound with the porphyrin ring.

Characterization of Cu-TCPP/AuNPs/CP modified electrodes: The surface morphologies of Cu-TCPP MOFs and Cu-TCPP/AuNPs were characterized by scanning electron microscopy. The Cu-TCPP MOFs displayed a three-dimensional flower-like structure composed of ultrathin nanoflakes (Fig. 2). It provides a larger specific surface area and an efficient π-electron system on the electrode surface. Figure 1A is an image of a bare CP, which consists of carbon fibers with a porous structure. After electrodeposition, the gold nanoparticles were uniformly distributed on the surface of the carbon paper. (Fig. 1C) SEM image of the synthesized Cu-TCPP/AuNPs nanocomposite. Many gold nanoparticles are uniformly deposited on the surface.

Characterization of the electrochemical properties of Cu-TCPP/AuNPs/CP: First, the electrochemically active area of the modified electrode was investigated in the redox probe by CV method at different scan rates, and the voltage was set at -0.2-0.6V. (Fig. 4) It can be seen that in the range of 10-200 mV/s, the redox peak current of the modified electrode increases linearly with the increase of the scan rate. The linear equations of the redox peak current and v ^1/2 of the CP electrode are: I _pa (μA)=41.735ν ^1/2 +39.806 (R ² =0.998), I _pc (μA)=42.469ν ^1/2 + 39.328 (R ² =0.991). The linear equations of the redox peak current and v ^1/2 of the Cu-TCPP/AuNPs/CP modified electrode are: I _pa (μA)=783.607ν ^1/2 -22.107 (R ² =0.998), I _pc (μA) =754.426ν ^1/2 +21.456 (R ² =0.999). According to the Randles-sevick equation ^[42] , the electroactive area of Cu-TCPP/AuNPs/CP was calculated: I _p =268600n ^3/2 AD ^1/2 Cν ^1/2 ,

In the formula, Ip, n, A, C and v represent the anodic peak current, the electron transfer number electroactive area of redox reaction, the concentration of [Fe(CN) ₆ ] ^3- /[Fe(CN) ₆ ] ^4- and scan rate. The diffusion coefficient of D is 7.60×10 ^-6 cm ² s ^-1 . We found that the electroactive area of the electrode modified with Cu-TCPP and AuNPs was significantly increased, which was 18.8 times larger than that of the bare CP electrode.

Cyclic voltammetry (CV) in 1 mmol L ^-1 [Fe(CN) ₆ ] ^3- /[Fe(CN) ₆ ] ^4- redox probe (containing 0.2 mol L ^-1 KCl) at 100 mV s ^- A scan rate of ¹ was used to study the electrochemical properties of different electrodes (Fig. 5A). The redox peak currents on Cu-TCPP/AuNPs/CP and AuNPs/CP electrodes were significantly higher than those on bare CP electrodes, indicating that AuNPs had good electrical conductivity. The Cu-TCPP/AuNPs/CP modified carbon paper electrode exhibits a pair of reversible redox peaks, wherein the redox peak potential difference is 77mV, and the peak currents are -223.5μA and 206.5μA, respectively. Compared with the AuNPs/CP electrode, the conductivity It has been improved to a certain extent. This response is not only a simple superposition of AuNPs and Cu-TCPP, but mainly due to the good synergistic effect between AuNPs with uniform particles and excellent performance and Cu-TCPP, which improves the electrode surface performance. , which accelerates the electron transfer rate, thereby improving the sensitivity of the sensor.

In addition, EIS can characterize the surface characteristics of the electrode, and then investigate the electron transfer efficiency of the electrode in solution to study the electrical conductivity of the electrode modification material. Measurements were performed with an amplitude of ⁵ mV in the frequency range 0.1-105 Hz. Each EIS map has two regions: a semicircular region and a linear region. The semicircle is related to the electron transfer resistance (Ret), which is linked to the dielectric and insulating properties of the electrode/electrolyte junction. In the EIS diagram, the smaller the semicircle diameter, the smaller the impedance, that is, the faster the electron transfer rate. As shown in Fig. 5B, the Cu-TCPP/CP exhibits the highest impedance, which is due to the weak conductivity of the 2D MOF material and its high stacking tendency, resulting in the reduction of exposed active sites and the limitation of electron transfer. However, the impedance of the Cu-TCPP/AuNPs/CP modified electrode was significantly reduced because the introduction of AuNPs increased the electroactive area of the CP and greatly improved the conductivity of the electrode.

Example 2 Detection of glyphosate based on electrochemical sensor

Electrochemical detection process:

The electrochemical sensor prepared in Example 1 was used as the positive electrode, the platinum wire electrode was used as the counter electrode, and the saturated calomel electrode was used as the reference electrode to establish a three-electrode system.

A series of known concentrations (0μM, 1μM, 3μM, 5μM, 7μM, 10μM, 20μM, 10μM, 20μM, 40 μM, 60 μM, 80 μM, 100 μM, 120 μM) of glyphosate standard samples.

The three-electrode system was immersed in the glyphosate standard sample solution of a series of concentrations prepared above, enriched for 60 s at a voltage of 0.1V, and then applied differential pulse voltammetry (DPV) in the potential range of -0.2-0.6V. The corresponding oxidation peak current value I and the oxidation peak current value I ₀ of the blank sample with glyphosate concentration of 0 were measured by the method, and the oxidation peak current difference II ₀ was calculated; using the obtained oxidation peak current difference and the corresponding glyphosate Concentrations were linearly correlated to obtain a quantitative detection model.

The results are shown in Figure 12, where (A) the differential pulse voltammogram of the sensor for glyphosate, and (B) the oxidation peak current versus GLY concentration. In the concentration range of 0.2-120μM, the oxidation peak current decreases with the increase of GLY concentration, which is linear in two sections: in the range of 0.2-10μM, the linear equation is △I _p =1.0932C _GLY +8.4697(R ² =0.994) . The linear equation from 1.0-120 μM was ΔI _p = 0.0687C _GLY + 18.562 (R ² =0.996), and the detection limit of GLY was all 0.03 μM (S/N=3).

Example 3 Optimization of the working electrode of the electrochemical sensor

(1) Influence of different modified electrodes

The glassy carbon electrode, conductive glass, pencil lead electrode and carbon paper electrode were selected for comparison, and their peak currents were 14.2 μA, 75.8 μA, 43.7 μA and 182.2 μA, respectively. Compared with conventional electrodes, the electrodes have larger specific surface areas, as shown in Figure 3. Compared with the bare CP electrode, the electrochemical active area of the Cu-TCPP/AuNPs/CP modified electrode was significantly increased by 18.8 times, as shown in Figure 4. The electrochemical effects of different modified electrodes were compared by cyclic voltammetry and AC impedance method, and it was found that there was a good synergistic effect between AuNPs and Cu-TCPP, which improved the electrode surface properties and accelerated the electron transfer rate, such as Figure 5. The synthesized copper porphyrin metal-organic framework material produces an oxidation peak of copper ions at 0.192V. After adding GLY, the oxidation peak is suppressed, and the reduced current value is linear with the glyphosate concentration, indicating that the present invention can be applied to GLY. detection, as shown in Figure 6.

Explore and compare the cyclic voltammetry curves of different modified electrodes, as shown in Figure 5. It was found that there is no reversible redox peak at the bare CP electrode, and it should be that the target GLY rarely exhibits the desired electrochemical activity at an accessible potential. The Cu-TCPP/AuNPs/CP composite modified electrode was used to measure the target, and it was found that an obvious anodic peak was generated at 0.192V, indicating that Cu ⁺ oxidized Cu ²⁺ , and copper was completely reduced at -0.6V. When 20 μM of GLY was added, the anodic peak current of copper ions decreased. GLY can be indicated by a change in the current signal.

(2) Effects of different Cu-MOF modified materials

The selection of Cu-TCPP as the electrode modification material not only provides the complexation of metal ions with GLY, and realizes the indirect determination of the target. Compared with other Cu-MOF materials, such as Cu-BTC, its combination with gold nanoparticles produces two different stable peaks, while Cu-TCPP due to its excellent catalytic properties, synergizes with gold nanoparticles for better catalytic performance and better sensitivity, as shown in Figure 7.

(3) Effects of different concentrations of Cu-TCPP materials

The content of metal-organic framework material Cu-TCPP on the electrode surface plays an important role in the electrocatalytic behavior of the sensor. The effect of Cu-TCPP content on the electrode surface on electrochemical sensing was investigated by DPV method. It can be seen from Fig. 9 that when the content of Cu-TCPP is 0.7 mg mL ^-1 , Cu ²⁺ has the maximum oxidation peak current, and with the increase of material concentration, the current response decreases, which may be due to the influence of material stacking and agglomeration. Electron transfer process between electrode surfaces. So we choose 0.7 mg mL ^-1 as the optimal concentration of Cu-TCPP to modify the electrode surface.

Embodiment 4 Detection condition optimization

(1) The effect of pH

The pH of the acetic acid/sodium acetate (ABS) buffer solution has a significant effect on the acid-base dissociation of GLY, resulting in changes in its oxidation potential and oxidation current. Therefore, the effect of pH on the electrochemical oxidation of GLY was first investigated using DPV (Fig. 8). The results showed that the response peak current of Cu ²⁺ gradually increased with the increase of pH, indicating that protons were involved in the reaction process between Cu-TCPP/AuNPs/CP and GLY. The peak currents for both targets then plateaued at higher pH. Considering the influence of pH value on the electrochemical oxidation current of the target, the ABS buffer at pH 6 was finally selected as the best system for detecting GLY.

(2) Influence of enrichment voltage

To obtain the best sensitivity, we optimized the enrichment potential of GLY on the Cu-TCPP/AuNPs/CP surface (Fig. 10) for the best sensitivity. Under acidic conditions, GLY is negatively charged, and the application of positive voltage can drive GLY to enrich on the electrode surface, so the peak current value increases in the stage of -0.1V~0.1V. , since the oxidation potential of Cu ⁺ /Cu ²⁺ is around 0.192V, when copper is completely oxidized, copper ions on the electrode surface are saturated and partially dissolved, resulting in a current drop. So we choose 0.1V as the best enrichment potential.

(3) Influence of enrichment time

In the system of 0.1mol L ^-1 ABS buffer (pH=6), the effect of deposition time on the oxidation of copper ions was studied. As shown in FIG. 11 . Due to the enrichment of glyphosate on the electrode surface, this may be due to the saturation of glyphosate loading on the active sites on the electrode surface. _ΔIP increases with deposition time. After 60 seconds, the current tends to drop, and in this study, 60 seconds was chosen as the optimal deposition time.

Example 5: Reproducibility and Interference Verification of Electrochemical Detection of Sensors

Investigate electrode reproducibility, interference, and stability under optimal conditions. In order to investigate the reproducibility of the sensor, six carbon paper electrodes were prepared by the same modification method, and the glyphosate solution with the same concentration was detected. As shown in Figure 13, the relative standard deviation of the resulting response currents was 2.5%, indicating good reproducibility of the sensor. After the prepared sensor was stored at 4°C for 1 month, the peak current signal maintained 82.2% of the original value. The results show that the prepared sensor has good stability and reproducibility, and can be used for the detection of GLY.

Furthermore, the selectivity of the developed sensor was evaluated by introducing cations and anions that were 100-fold higher than the analyte concentration and organics in the same amount as the analyte. Two interfering substances were analyzed in this study: one group was GLY metabolites and organophosphorus pesticides. The other category is the common anions (Na ⁺ , K ⁺ , Pb ²⁺ , Cd ²⁺ , Ca ²⁺ , Fe ²⁺ , Cl ^- , SO ₄ ^2- ) that can be coordinated by GLY and interfere with the measurement. The experimental results showed that these interfering substances had almost no interfering effect (Fig. 14).

Embodiment 6 Actual sample detection

Food samples (soybeans, wheat, carrots, drinking water) were purchased from local supermarkets and processed according to standard methods (National Standard of the People's Republic of China GB/T 23750-2009). GLY standard solutions of different concentrations (1, 5 μM) were added to food samples for pretreatment and analyzed by this method. The results are shown in Table 1.

Table 1 Content of GLY in actual samples

The practical application of Cu-TCPP/AuNPs/CP was verified by detecting the concentration of glycine in real samples such as soybean, carrot, wheat and water in Table 1. Glycine was detected in soybean with a content of 6.35μM, which met the national standard limit requirements. The recovery test was carried out by the standard addition method, and the accuracy of the fabricated sensor was evaluated. When the four food samples were added, the recoveries of GLY were 97.5%-110.7% (RSD<10.0%).

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Anyone who is familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, The protection scope of the present invention should be defined by the claims.

Claims (10)

1. A preparation method of an electrochemical sensor for detecting glyphosate is characterized by comprising the following steps:

(1) pretreating carbon paper by using an acid solution, and then soaking the carbon paper into a tetrachloroauric acid solution for electrodeposition to obtain a gold nanoparticle AuNPs modified carbon paper electrode, which is expressed as AuNPs/CP;

(2) dispersing Cu-TCPP in a solvent to obtain Cu-TCPP dispersion liquid, then dripping the Cu-TCPP dispersion liquid on the surface of AuNPs/CP obtained in the step (1), and drying to obtain an electrochemical sensor probe which is recorded as Cu-TCPP/AuNPs/CP;

(3) and (3) forming a three-electrode system by using the electrochemical sensor probe obtained in the step (2) as a working electrode, a counter electrode and a reference electrode, and combining the three-electrode system with an electrochemical workstation to construct an electrochemical sensor.

2. The method according to claim 1, wherein in the step (2), the concentration of the Cu-TCPP dispersion is 0.7mg mL^-1。

3. The method of claim 1, wherein the electrodeposition process is carried out at-0.2V for 120 s.

4. The method according to claim 1, wherein the solvent in step (2) is a mixture of water and 0.1% Nafion at a volume ratio of 20: 1.

5. An electrochemical sensor for detecting glyphosate obtained by the preparation method of any one of claims 1-4.

6. A method for detecting glyphosate is characterized by comprising the following steps:

immersing the three-electrode system obtained in claim 1 in a series of standard glyphosate sample solutions of known concentration, and controlling the voltage to perform pre-enrichment; after pre-enrichment is over, the difference is passedMeasuring corresponding oxidation peak current value I and oxidation peak current value I of a blank sample with the glyphosate concentration of 0 by pulse voltammetry₀Calculating to obtain the oxidation peak current difference I-I₀(ii) a And performing linear correlation by using the obtained oxidation peak current difference value and the corresponding glyphosate concentration to obtain a quantitative detection model.

7. The method of claim 6, wherein the enriched voltage is 0.1V.

8. The method of claim 6, wherein the time for enrichment is 60 s.

9. The method of claim 6, wherein the concentration of the glyphosate standard sample is in the range of 0.2-120 μ M.

10. A method according to any of claims 6-9, characterized in that the potential of the differential pulse voltammetry is in the range-0.2-0.6V.

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