Multicolor malathion detection method based on Fe-Zr bimetallic nano-enzyme

Abstract

The invention discloses a method for multicolor detection of malathion based on Fe-Zr bimetallic nano-enzyme, a Fe-Zr bimetallic active center is formed, the synthesized Fe3O4-coated PDA-coated UiO-66 shows excellent peroxidase-like catalytic activity, the malathion can be combined with a composite material through a Zr-O-P bond, and the composite material can be used for detecting the peroxidase-like catalytic activity of the malathion, so that the malathion-coated UiO-66 can be used for detecting the peroxidase-like catalytic activity of the malathion-coated UiO-66, and the malathion-coated UiO-66 can be used for detecting the peroxidase-like catalytic activity of the malathion. By combining the Au NRs, multicolor detection of malathion is realized. The multicolor colorimetric detection method disclosed by the invention gets rid of the limitation that the traditional colorimetric method depends on different shade changes of a single color, so that the visual resolution is relatively poor, and the colorimetric signal can be combined with the smart phone, so that on-site instant detection is facilitated; meanwhile, a new way is provided for designing and applying the effective nano-enzyme to carry out pesticide field monitoring.

Description

Technical Field

[0001] The present invention relates to the detection of malathion, and specifically to a method for multicolor detection of malathion based on Fe-Zr bimetallic nanozyme. Background Art

[0002] Organophosphorus pesticides (OPs) are widely used in agricultural production due to their highly effective insecticides. However, the health risks posed by their environmental residues have become a global concern. Malathion, a typical example, is widely used to protect a variety of crops, including rice, wheat, and peanuts, due to its broad-spectrum insecticide activity. However, this widespread use has also led to the continued accumulation of malathion in the environment, posing a serious threat to human health. To manage this risk, my country has established a maximum residue limit (MRL) of 0.5 mg / kg for malathion in food. Therefore, the development of efficient and sensitive methods for the detection of malathion is of great practical significance for ensuring food safety and maintaining public health.

[0003] To date, traditional malathion residue detection has primarily relied on laboratory analytical methods such as high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). Although these methods offer high accuracy and reliability, their complex sample preparation, expensive instrumentation, and specialized technical requirements make them difficult to meet the demands of rapid point-of-care testing (POCT), particularly in resource-limited settings.

[0004] In recent years, colorimetric sensing technology based on nanomaterials has become a research hotspot due to its advantages such as simple operation, low cost, and visual detection. Although traditional colorimetry can provide accurate and rapid quantitative analysis, it can also obtain intuitive results without large-scale instruments. However, the signal output of existing colorimetric methods mainly relies on the different shades of a single color, resulting in poor visual resolution, which significantly restricts the accuracy of semi-quantitative analysis by the naked eye. In order to break through this technical bottleneck, it is urgent to build a new functional sensing platform to achieve high-resolution visual detection. The human eye's ability to distinguish multi-color changes is significantly better than that to distinguish the shades of a single color. This feature can greatly improve the accuracy and practicality of on-site detection. Therefore, the development of a high-sensitivity detection strategy based on multi-color colorimetry is of great significance for the quantitative or semi-quantitative analysis of malathion.

[0005] Noble metal nanomaterials, owing to their unique surface plasmon resonance (SPR) effect, have shown great potential in the field of colorimetric biosensing. Among them, gold nanorods (Au NRs) are ideal materials for multicolorimetric analysis due to their exceptional optical response properties. The longitudinal surface plasmon resonance (LSPR) peak of Au NRs is extremely sensitive to changes in the aspect ratio of the nanorods; even slight structural changes can cause significant shifts in the absorption peak and changes in solution color (such as red or blue shifts). This property enables programmable control of solution color by precisely manipulating the morphology of Au NRs, thereby enabling the construction of high-resolution multicolorimetric sensing systems.

[0006] Among the related patents for detecting malathion that have been published, CN119086665A discloses an electrochemiluminescence aptamer sensor based on NH2-Luminol / Ag@SiO2NSs and its preparation method and application. This application discloses an electrochemiluminescence (ECL) aptamer biosensor based on functionalized nanomaterials. First, gold nanoparticles (AuNPs) were deposited on the surface of multi-walled carbon nanotubes (MWCNTs) at constant potential to provide a good fixing site for complementary single-stranded DNA (cDNA). Secondly, amino-modified luminol / nanosilver@spherical nanosilica (NH2-Luminol / Ag@SiO2 NSs) composite nanomaterials were synthesized by a one-pot method. Finally, NH2-Luminol / Ag@SiO2NSs are combined with malathion aptamers to create signaling probes (SPs) for sensor construction. This invention provides an effective method for building fast, highly sensitive, and low-cost aptamer sensors. However, this method is costly, requires complex synthesis, and requires specialized equipment.

[0007] CN115980032A discloses a method and kit for detecting malathion using nanogold aptamer colorimetric sensing. This method involves adding a malathion aptamer solution to a nanogold solution, then adding a test sample solution, and finally adding a sodium chloride solution. Malathion is detected by observing the color change of the solution. Based on this method, a kit was also developed that includes a black background plate, a specially designed continuous cuvette with three transparent sides and one white side, and a red to blue gradient standard colorimetric card. This method allows for semi-quantitative detection of malathion by analyzing the solution color change. This method is simple, rapid, and intuitive. However, this method is costly, and the minimum detection limit of the established visual detection method is 45.5 ng / mL.

[0008] CN118191045A A method for electrochemiluminescence detection of malathion. The method first connects an S1 / Apt hybrid duplex with TPE-UiO-66-CH=CH2 nanoparticles modified on an electrode surface through a click reaction, and utilizes H2O2 to quench the initial ECL signal of TPE-UiO-66-CH=CH2. When malathion is present in the system, the malathion aptamer (Apt) binds to malathion, causing the primer chain (S1) to be exposed, thereby utilizing hairpin probes H1 and H2 to trigger an HCR reaction to form a G-quadruplex. The G-quadruplex then binds to hemin (Hemin) to form a Hemin / G-quadruplex complex that can consume H2O2, thereby restoring the ECL signal of TPE-UiO-66-CH=CH2. Simultaneously, manganese porphyrin (MnTMPyP) is used to enhance the ECL signal. This method can achieve highly sensitive ECL detection of malathion. However, this detection method requires the use of professional ECL instruments and is expensive. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this paper proposes a multicolor detection method for malathion based on an Fe-Zr bimetallic nanozyme. The Fe₃O₄@PDA@UiO-66 prepared in this paper exhibits excellent peroxidase-like catalytic activity. The specific binding of malathion and Fe₃O₄@PDA@UiO-66 inhibits the material's enzyme-like activity. Furthermore, the combination of Fe₃O₄@PDA@UiO-66 and gold nanorods (Au NRs) enables multicolor detection of malathion.

[0010] The technical solution for achieving the purpose of the present invention is: A method for multicolor detection of malathion based on Fe-Zr bimetallic nanozymes was proposed. The Fe3O4@PDA@UiO-66 material was first synthesized. Due to the formation of Fe-Zr bimetallic active centers, the synthesized Fe3O4@PDA@UiO-66 exhibited excellent peroxidase-like catalytic activity. Malathion can be bound to the composite material through Zr-OP bonds, inhibiting the enzyme-like activity of the material. Combined with Au NRs, multicolor detection of malathion was achieved.

[0011] Furthermore, the synthesis of the Fe3O4@PDA@UiO-66 material includes the following steps: (1) Synthesis of Fe3O4@PDA material: (1.1) Dissolve 1,3-propane sultone (1,3-PS) and 1-(2-aminoethyl)piperazine (AEP) in acetonitrile, respectively. Mix the acetonitrile solution containing 1,3-PS and the acetonitrile solution containing AEP, stir, and collect the resulting white product, aminoethylpiperazine propane sulfonate (AEPPS). (1.2) Ultrasonic dispersion of Fe3O4 in ethanol-water solution, then adding dopamine hydrochloride (DH·HCl) ethanol-water solution and stirring for a certain period of time; (1.3) The AEPPS synthesized in step (1.1) was dissolved in an ethanol-water solution, and then added to the mixed solution of step (1.2) to react for a period of time, and finally washed with ethanol and vacuum dried to obtain Fe3O4@PDA material; (2) Synthesis of Fe3O4@PDA@UiO-66 material (2.1) Fe3O4@PDA was ultrasonically treated for a period of time and then dispersed in N,N-dimethylformamide (DMF); (2.2) Zirconium chloride (ZrCl4) and terephthalic acid (PTA) are dispersed in DMF to prepare a MOF precursor solution. The solution from step (2.1) is then added to the MOF precursor solution and reacted at a certain temperature for a period of time to obtain Fe3O4@PDA@UiO-66 material.

[0012] Furthermore, the synthesis of the gold nanorods Au NRs comprises the following steps: (a) Gold seeds are prepared by sequentially adding tetrachloroauric acid (HAuCl4) and sodium borohydride (NaBH4) to cetyltrimethylammonium bromide (CTAB), stirring the mixture at room temperature, and aging it for several hours. (b) CTAB, HAuCl4, silver nitrate (AgNO3), hydrochloric acid (HCl) solution, and ascorbic acid (AA) are mixed to obtain a growth solution. The gold seeds synthesized in step (a) are then added to the growth solution. After standing overnight, the solution is centrifuged and collected to obtain AuNRs.

[0013] Furthermore, the multicolor detection of malathion comprises the following steps: (A) A series of malathion standard solutions with different concentrations were added to a centrifuge tube containing Fe3O4@PDA@UiO-66 and shaken for reaction. (B) TMB and H2O2 were added to the solution after the shake reaction in step (A). The supernatant was transferred to a 96-well plate and the OD value at 652 nm was measured. At 37°C, the OD value of the solution decreased with increasing malathion concentration. The sample was imaged using a smartphone camera and the image was analyzed using RGB color analysis software. The linear relationship between OD value and malathion content was used to achieve colorimetric detection of malathion. If the actual sample of malathion is to be measured, replace the malathion standard solution in step (A) with the actual sample of malathion to be measured; (C) adding hydrochloric acid to the final solution obtained in step (B) to terminate the catalytic reaction, and observing the color of the solution; (D) The terminated solution was removed and Au NRs were added, and the reaction was shaken at 37°C. After the shaking reaction, the solution was taken out and the absorption spectrum in the range of 200-1000 nm was measured. The standard curve was constructed by plotting the Δλ change of different concentrations of malathion.

[0014] Furthermore, in the synthesis of the Fe3O4@PDA material, in step (1.1), the mass ratio of 1,3-PS to acetonitrile is 1-10:1; The mass ratio of AEP to acetonitrile is 1:1~20; The dosage ratio of 1,3-PS and AEP is 1:1~10; The stirring reaction time is 3~6 h; In step (1.2), the ratio of Fe3O4 to ethanol aqueous solution is 1:100~500; The volume ratio of ethanol to water in ethanol-water solution is 2:1~10; The ultrasonic dispersion time of Fe3O4 is 10~80 min; The molar ratio of Fe3O4 to DH·HCl is 1:100~500; Stirring time is 1~3 h; In step (1.3), the volume ratio of ethanol to water in the ethanol-water solution is 2:1-10; The reaction time is 1~10 h.

[0015] Furthermore, in the synthesis of the Fe3O4@PDA@UiO-66 material, in step (2.1), the amount of Fe3O4@PDA used is 0.01~0.1 g; The amount of DMF used is 10-100 mL; Ultrasound time is 10–30 min; In step (2.2), the mass ratio of ZrCl4 to PTA is 1-10:1; The amount of DMF added is 5~20 mL; The reaction temperature is 80~100℃ and the reaction time is 24~48 h.

[0016] Furthermore, in the synthesis of the gold nanorods Au NRs, in step (a), The concentration of HAuCl4 is 0.01~0.05 mol / L, and the volume is 0.1~0.5 mL; The concentration of NaBH4 is 0.01~1 mol / L, and the volume is 0.1~0.5 mL; The concentration of CTAB is 0.1–10 mol / L, and the volume is 8–20 mL; The stirring time is 5 to 30 minutes, and the aging time is 0.5 to 3 hours; In step (b), the concentration of CTAB is 0.1-10 mol / L and the volume is 100-200 mL; The concentration of HAuCl4 is 0.01~0.05 mol / L, and the volume is 5~10 mL; The concentration of AgNO3 is 0.1~1 mol / L, and the volume is 0.1~2 mL; The concentration of HCl is 1 to 10 mol / L solution, and the volume is 1 to 5 mL; The concentration of AA is 0.1–1 mol / L, and the volume is 1–10 mL; The volume of gold seeds ranged from 0.1 to 5 mL.

[0017] Furthermore, in the multicolor detection of malathion, in step (A), the concentration of Fe3O4@PDA@UiO-66 is 50-200 μg / mL, the volume is 10-100 μL, and the shaking time is 10-60 min; In step (B), the volumes of TMB and H2O2 are both 10-100 μL, and the reaction time is 10-60 min; In step (C), the concentration of hydrochloric acid is 0.1-10 mol / L, the volume is 10-200 µL, and the color of the solution changes from blue to bright yellow; In step (D), the volume of the terminated solution is 50-500 μL, the volume of Au NRs is 10-200 μL, and the shaking reaction time is 10-50 min.

[0018] The present invention combines obvious gradient color development with hue changes to achieve quantitative and semi-quantitative visual analysis with high sensitivity. At the same time, the synthesis process of the Fe3O4@PDA@UiO-66 composite material of the present invention is simple and low-cost. The constructed multicolor colorimetric detection method breaks away from the limitation of traditional colorimetry that relies on different shades of a single color, resulting in poor visual resolution. The colorimetric signal can be combined with a smartphone to facilitate on-site instant detection, and at the same time provides a new approach for the design and application of effective nanozymes for on-site monitoring of pesticides. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the process of synthesizing Fe3O4@PDA@UiO-66 material in the embodiment; Figure 2 Schematic diagram of the multicolor detection process of malathion in Example; Figure 3Fourier transform infrared spectra of Fe3O4, Fe3O4@PDA, UiO-66, and Fe3O4@PDA@UiO-66 in the examples; Figure 4 The P 2p high-resolution XPS spectra before and after adding malathion in the examples are shown; Figure 5 is a linear relationship graph of ΔOD 652 nm value and malathion concentration in the examples; Figure 6 is a linear relationship diagram between the (R + G) / B value and the malathion concentration obtained by analyzing the digital photographs in the examples; Figure 7 Graph showing the linear relationship between Δλ and malathion concentration in the examples. DETAILED DESCRIPTION

[0020] The present invention will be further described below with reference to the embodiments and drawings, but the present invention is not limited thereto. Example

[0021] A multicolor detection method for malathion based on Fe-Zr bimetallic nanozymes was first synthesized Fe3O4@PDA@UiO-66 material, and then Figure 1 , including the following steps: (1) Synthesis of Fe3O4@PDA material: (1.1) Dissolve 5.9 g of 1,3-PS in 5 g of acetonitrile solution and 6.4 g of AEP in 65 g of acetonitrile solution. The acetonitrile solution containing 1,3-PS was slowly added to the acetonitrile solution containing AEP, mixed and stirred for 5 h to obtain AEPPS; (1.2) Ultrasonicate a solution of 0.094 g Fe₃O₄ in 10 g ethanol-water (ethanol:H₂O = 2:5) for 20 min, then add 10 g DH·HCl ethanol-water solution and stir for 1 h. (1.3) Slowly add 15 mL of AEPPS ethanol aqueous solution (ethanol:H2O = 2:5) to the mixed solution of step (1.2) and react for 6 h. Finally, wash with ethanol and vacuum dry to obtain Fe3O4@PDA material; (2) Synthesis of Fe3O4@PDA@UiO-66 material: (2.1) Disperse 0.025 g of Fe3O4@PDA in 10 mL of DMF and sonicate for 20 min. (2.2) 0.025 g ZrCl4 and 0.018 g PTA were dispersed in 8 mL DMF to prepare a MOF precursor solution. The solution from step (2.1) was then added to the MOF precursor solution, and the resulting mixture was reacted at 80 °C for 36 h to obtain Fe3O4@PDA@UiO-66 material.

[0022] The Fourier transform infrared spectrum of the prepared Fe3O4@PDA@UiO-66 material is as follows: Figure 3 As shown: In the spectrum of Fe3O4, 575 cm -1 The peak is attributed to the Fe-O-Fe stretching vibration. Compared with Fe3O4, a new peak (1615 cm -1 and 1040 cm -1 ), which are attributed to the NH bending vibration and O=S=O stretching vibration of the secondary amino group, respectively. In addition, the 1628 cm -1 The C=O stretching vibration, 1397 cm -1 The OCO stretching vibration in the “BDC” ligand, 1506 cm -1 The C=C stretching vibration in the benzene ring, 745 cm -1 Originated from C–H bending vibration, 1158 cm -1 and 661cm -1 The results indicate that Fe3O4@PDA@UiO-66 was successfully synthesized.

[0023] A method for multicolor detection of malathion based on Fe-Zr bimetallic nanozymes, and then synthesizing gold nanorods AuNRs, comprising the following steps: (a) Gold seeds were prepared by adding 0.25 mL of HAuCl4 (0.02 mol / L) and 0.1 mL of NaBH4 (0.01 mol / L) to 9.75 mL of CTAB (0.5 mol / L), stirring at room temperature for 30 min, and aging for 2 h. (b) 5.15 mL of HAuCl4 (0.02 mol / L), 0.1 mL of AgNO3 (0.1 mol / L), 2 mL of HCl (1 mol / L) solution, 0.8 mL of AA (0.1 mol / L), and 100 mL of CTAB (0.5 mol / L) were mixed to obtain a growth solution. Subsequently, 0.5 mL of the gold seeds synthesized in step (a) was added to the growth solution. After standing overnight, the solution was centrifuged to obtain Au NRs. Reference Figure 4The high-resolution XPS spectra of P 2p before and after the addition of malathion showed that the characteristic peak of P 2p appeared after the addition of malathion, which proved that malathion could be adsorbed on Fe3O4@PDA@UiO-66 by forming a stable Zr-OP bond, thereby inhibiting the enzyme-like activity of Fe3O4@PDA@UiO-66.

[0024] refer to Figure 2 , a multicolor assay for malathion, comprising the following steps: (A) Dilute the malathion stock solution into standard solutions of different concentrations and store them for future use; 20 μL of malathion standard solution and 50 μL of Fe3O4@PDA@UiO-66 (100 μg / mL) were added to a centrifuge tube and shaken at 37°C for 30 min; (B) To the shaken solution from step (A), 20 μL of TMB and 20 μL of H₂O₂ were added and the reaction was continued for 30 min. The supernatant was transferred to a 96-well plate and the OD value was measured at 652 nm. The OD value of the solution decreased with increasing malathion concentration at 37°C. The sample was imaged using a smartphone camera and subjected to RGB analysis using smartphone color analysis software. The linear relationship between OD value and malathion content was used to enable colorimetric detection of malathion. (C) Add 90 μL of 2 mol / L hydrochloric acid to the final solution obtained in step (B) to terminate the catalytic reaction. The color of the solution changes from blue to bright yellow. (D) 100 μL of the terminated solution was removed and added to 80 μL of Au NRs, and the mixture was shaken at 37°C for 20 min. After the reaction, 150 μL of the solution was taken out to measure the absorption spectrum in the range of 200−1000 nm. The concentration of malathion was quantified by Δλ, where Δλ represents the wavelength change corresponding to the longitudinal peak between the experimental group and the control group.

[0025] Figure 5 is a linear fitting curve of the concentration change of malathion and ΔOD value in the embodiment; Figure 5 The results showed that when the concentration of malathion was in the range of 1-140 ng / mL, ΔOD showed a good linear relationship with the malathion concentration.

[0026] The relevant equation is ΔOD=0.00239+0.00478C 马拉硫磷 (R 2 =0.9915), the calculated LOD value was 0.68 ng / mL. According to the formula, accurate detection of malathion can be achieved.

[0027] Figure 6 is a linear fitting curve diagram of the concentration of malathion and the (R+G) / B value in the embodiment; Figure 6 The results showed that when the concentration of malathion was in the range of 1~140 ng / mL, the change of (R+G) / B value was linearly related to the concentration of malathion.

[0028] The relevant equation is ΔOD=196.92+1.45C 马拉硫磷 (R 2 =0.9914), the calculated LOD value was 0.97 ng / mL. According to the formula, accurate detection of malathion can be achieved.

[0029] Figure 7 is a linear fitting curve diagram of the concentration of malathion and the Δλ value in the embodiment; Figure 7 The results showed that when the concentration of malathion was in the range of 10-120 ng / mL, the change of Δλ value was linearly related to the concentration of malathion.

[0030] The regression equation is Δλ=21.12+1.0382C 马拉硫磷 (R 2 = 0.9918), the calculated LOD value was 5.93 ng / mL. According to the formula, accurate detection of malathion can be achieved.

Claims

1. A method for multicolor detection of malathion based on Fe-Zr bimetallic nanozymes, characterized by: The Fe3O4@PDA@UiO-66 material was first synthesized. Due to the formation of Fe-Zr bimetallic active centers, the synthesized Fe3O4@PDA@UiO-66 exhibited excellent peroxidase-like catalytic activity. Malathion could bind to the composite material through Zr-OP bonds, inhibiting the material's enzyme-like activity. Combined with gold nanorods (AuNRs), enzyme-free multicolor detection of malathion was achieved. The synthesis of the Fe3O4@PDA@UiO-66 material includes the following steps: (1) Synthesis of Fe3O4@PDA material: (1.1) Dissolve 1,3-PS and AEP in acetonitrile solution separately. Mix the acetonitrile solution containing 1,3-PS with the acetonitrile solution containing AEP, stir, and collect the resulting white product AEPPS. (1.2) Ultrasonic dispersion of Fe3O4 in ethanol-water solution, then adding DH·HCl ethanol-water solution and stirring for a certain period of time; (1.3) The white product AEPPS synthesized in step (1.1) was dissolved in an ethanol-water solution, then added to the mixed solution of step (1.2) and reacted for a period of time. Finally, it was washed with ethanol and vacuum-dried to obtain Fe3O4@PDA material; (2) Synthesis of Fe3O4@PDA@UiO-66 material: (2.1) Fe3O4@PDA was ultrasonicated for a period of time and then dispersed in DMF; (2.2) Dispersing ZrCl4 and PTA in DMF to prepare a MOF precursor solution, then adding the solution from step (2.1) to the MOF precursor solution and reacting at a certain temperature for a period of time to obtain Fe3O4@PDA@UiO-66 material; The synthesis of the gold nanorods Au NRs comprises the following steps: (a) HAuCl4 and NaBH4 were added to CTAB in sequence, stirred at room temperature, and aged for several hours to prepare gold seeds; (b) CTAB, HAuCl4, AgNO3, HCl solution, and AA were mixed to obtain a growth solution. The gold seeds synthesized in step (a) were then added to the growth solution. After standing overnight, the solution was centrifuged to obtain Au NRs. The multicolor detection of malathion comprises the following steps: (A) A series of malathion standard solutions with different concentrations were added to a centrifuge tube containing Fe3O4@PDA@UiO-66 and shaken for reaction. (B) TMB and H2O2 were added to the solution after the shake reaction in step (A). The supernatant was transferred to a 96-well plate and the OD value at 652 nm was measured. At 37°C, the OD value of the solution decreased with increasing malathion concentration. The sample was imaged using a smartphone camera and the image was analyzed using RGB color analysis software. The linear relationship between OD value and malathion content was used to achieve colorimetric detection of malathion. If the actual sample of malathion is to be measured, replace the malathion standard solution in step (A) with the actual sample of malathion to be measured; (C) adding hydrochloric acid to the final solution obtained in step (B) to terminate the catalytic reaction, and observing the color of the solution; (D) The terminated solution was removed and Au NRs were added, and the reaction was shaken at 37°C. After the shaking reaction, the solution was taken out and the absorption spectrum in the range of 200-1000 nm was measured. The standard curve was constructed by plotting the Δλ change of different concentrations of malathion.

2. The method for multicolor detection of malathion according to claim 1, wherein: In the synthesis of the Fe3O4@PDA material, in step (1.1), the mass ratio of 1,3-PS to acetonitrile is 1-10:1; The mass ratio of AEP to acetonitrile is 1:1~20; The dosage ratio of 1,3-PS and AEP is 1:1~10; The stirring reaction time is 3~6 h.

3. The method for multicolor detection of malathion according to claim 1, wherein: In the synthesis of the Fe3O4@PDA material, in step (1.2), the ratio of Fe3O4 to ethanol aqueous solution is 1:100-500; The volume ratio of ethanol to water in ethanol-water solution is 2:1~10; The ultrasonic dispersion time of Fe3O4 is 10~80 min; The ratio of Fe3O4 to DH·HCl is 1:100~500; The stirring time is 1~3 h.

4. The method for multicolor detection of malathion according to claim 1, wherein: In the synthesis of the Fe3O4@PDA material, in step (1.3), the volume ratio of ethanol to water in the ethanol-water solution is 2:1-10; The reaction time is 1~10 h.

5. The method for multicolor detection of malathion according to claim 1, wherein: In the synthesis of the Fe3O4@PDA@UiO-66 material, in step (2.1), the amount of Fe3O4@PDA used is 0.01~0.1g; The amount of DMF used is 10-100 mL; The ultrasound time is 10~30 min.

6. The method for multicolor detection of malathion according to claim 1, wherein: In the synthesis of the Fe3O4@PDA@UiO-66 material, in step (2.2), the mass ratio of ZrCl4 to PTA is 1-10:1; The amount of DMF added is 5~20 mL; The reaction temperature is 80~100℃ and the reaction time is 24~48 h.

7. The method for multicolor detection of malathion according to claim 1, wherein: In the synthesis of the gold nanorods Au NRs, in step (a), the concentration of HAuCl4 is 0.01-0.05 mol / L and the volume is 0.1-0.5 mL; The concentration of NaBH4 is 0.01~1 mol / L, and the volume is 0.1~0.5 mL; The concentration of CTAB is 0.1–10 mol / L, and the volume is 8–20 mL; The stirring time is 5~30 min, and the aging time is 0.5 h~3 h.

8. The method for multicolor detection of malathion according to claim 1, wherein: In the synthesis of the gold nanorods Au NRs, in step (b), the concentration of CTAB is 0.1-10 mol / L and the volume is 100-200 mL; The concentration of HAuCl4 is 0.01~0.05 mol / L, and the volume is 5~10 mL; The concentration of AgNO3 is 0.1~1 mol / L, and the volume is 0.1~2 mL; The concentration of HCl is 1 to 10 mol / L solution, and the volume is 1 to 5 mL; The concentration of AA is 0.1–1 mol / L, and the volume is 0.5–10 mL; The volume of gold seeds ranged from 0.1 to 5 mL.

9. The method for multicolor detection of malathion according to claim 1, wherein: The multicolor detection of malathion, In step (A), the concentration of Fe3O4@PDA@UiO-66 was 50–200 μg / mL, the volume was 10–100 μL, and the shaking time was 10–60 min; In step (B), the volumes of TMB and H2O2 are both 10-100 μL, and the reaction time is 10-60 min; In step (C), the concentration of hydrochloric acid is 0.1-10 mol / L, the volume is 10-200 µL, and the color of the solution changes from blue to bright yellow; In step (D), the volume of the terminated solution is 50-500 μL, the volume of Au NRs is 10-200 μL, and the shaking reaction time is 10-50 min.

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