Construction of Fe 3 O 4 /PDA/Ag Nanoparticles and Coupling with SERS for Detection of Pesticide Residue

doi:10.21203/rs.3.rs-4340791/v1

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Construction of Fe 3 O 4 /PDA/Ag Nanoparticles and Coupling with SERS for Detection of Pesticide Residue

https://doi.org/10.21203/rs.3.rs-4340791/v1

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Carbendazim and thiophanate-methyl are highly toxic persistent organic pollutant. Prolonged exposure to them may bring a wide variety of disease. For this, a facile and high sensitive approach (surface-enhanced Raman scattering: SERS) with nanocomposite (Fe₃O₄/PDA/Ag) as substrates was developed for detection of carbendazim and thiophanate-methyl. The core of Fe₃O₄ nanoparticles (NPs) were synthesized by coprecipitation method, and it was coated with polydopamine (PDA). Ag NPs was obtained by chemical reduction-oxidation. The three-layer structure of magnetic composite nanomaterial with noble metal, namely Fe₃O₄/PDA/Ag was fabricated via the interaction between Ag and the amino groups of PDA. The prepared Fe₃O₄/PDA/Ag composites was characterized by XRD, UV-VIS, IR and VSM. The Fe₃O₄/PDA/Ag as SERS substrates was employed to detect carbendazim and thiophanate-methyl by Raman technology. It was demonstrated that the number of Raman peaks were obvious increased, and intensity for carbendazim and thiophanate-methyl were significantly enhanced due to the substrate of Fe₃O₄/GO/Ag. A new substrate for SERS was designed with the detection signal significant amplification. New approach for high sensitive, rapid and facile detection of pesticide residues was developed in the study.

Fe3O4@PDA@Ag

SERS

Carbendazim

Thiophanate-methyl

Pesticide

Recent years, with the continuous development of economics, pesticide residue as contaminant damage the ecological environment, seriously endanger human’s health and life[1-4]. Pesticide residue is widely found in agricultural products, cash crops, Chinese medicinal materials, fruits and vegetables, grain and oil and other products. Carbendazim and thiophanate-methyl are common pesticide widely used to control the growth of insects in various plants. The use of carbendazim and thiophanate-methylis may cause hazardous health effects such as skin disease, muscle twitching, damage kidney, nervous systems.

Detection of pesticide residue is one of the method for strictly controlling food safety, improving product quality and protecting ecological environment. The development of high sensitivity, high efficiency and simple detection technology is the key to control product quality. There are several analytical techniques such as gas chromatography, high performance liquidchromatography and UV were reported for determination of carbendazim and thiophanate-methylis. In recent years, SERS technique has been widely used in biochemistry, food safety, biomedicine and environmental detection[5-8].The excellent SERS technique with signal amplification can detect the trace pesticide residues in environment, toxins, pigments and additives in food, and even single molecule[9-13]. Compared with the traditional detection technology, SERS has the characteristics of high sensitivity, strong applicability, fast and non-destructiveness. These advantages are closely related to the substrates[14-16]. With suitable substrates and measurement equipment, SERS can even detect single molecule. Raman signal enhancement in SERS arises from the electromagnetic enhancement at areas that are known as “hot spots” on the substrate. Nanomaterials are often used as substrates for Raman detection because of their simplicity, rapidity and pollution-free synthesis[17-18]. Scientific research has found that some metal nanomaterials, such as Au and Ag, and nano-oxides, ZnO, TiO₂, Ni₂O and CeO₂ can make the signal of surface enhancing Raman amplify[19-23]. When the nanomaterials with rough surface were used as substrate, hot spot formed, and the strong signal can be obtained. In particular, Ag NPs have surface plasmon resonance effect and other excellent physical and chemical properties, and is often used as substrates for Raman detection[24-30]. With the advancement of SERS, simple Ag NPs may not completely meet the analysis. Therefore, in the study, magnetic particles loaded Ag NPs as Raman substrates to detect pesticide residues.

1.1 Reagent and solution preparations

All the chemical substances used were analytical grade reagents. Silver nitrate, Tris (hydroxymethyl) aminomethane, trisodium citrate and ammonium hydroxide were purchased from Xi 'an Chemical Reagent Factory. Ferrous sulfate, ferric chloride were obtained from Tianjin Kemeiou Chemical Reagent Co., LTD. Dopamine hydrochloride were purchased from Sigma Aldrich.The ultrapure water was prepared by a Milli-Q system.

1.2 Preparation of Fe₃O₄/PDA/Ag NPs

1.2.1 Preparation of Fe₃O₄ nanoparticles

The Fe₃O₄ NPs were prepared by coprecipitation method with Fe(II) and Fe(III) (Fe_II/Fe_IIIratio of 0.5) in an alkaline solution. Brieﬂy, 0.2780 g of ferrous sulfate and 0.5401 g ferric chloride accurately weighed and dissolved in 50 mL of deionized water in the presence of nitrogen with mechanical stirring vigorously. Subsequently, ammonium hydroxide was added into the mixture and adjusted the pH of the solution to be maintained at 10~11. Light yellow solution changed to brown and ﬁnally became dark black, the water bath kept at 60 °C for half an hour. After 30 min, the temperature was set at 80°C and aged for 1 h. Then, separation was carried out with magnet and washed with deionized water.

1.2.2 Preparation of Fe₃O₄/PDA

Tris-HCl buffer solution was prepared by taking 0.1200 g of Tris (hydroxymethyl) aminomethane solid and dissolving it in 100.0 mL deionized water. The pH of the solution was adjusted to 8.50 with hydrochloric acid. 0. 2000 g of dopamine hydrochloride and 0.2000 g of Fe₃O₄ NPs were added to 90.0 mL of the new prepared Tris-HCl buffer solution. The mixed solution was subjected to sonication for 40 min and then mechanical stirred for 12 h at room temperature to obtain Fe₃O₄/PDA.

1.2.3 Synthesis of Ag NPs

0.0183 g sodium citrate and 0.0106 g silver nitrate were weighed and dissolved in 250.0 mL deionized water, stored for use. 0.1mol/L of ascorbic acid solution was prepared. 100.0 mL of the prepared silver nitrate mixed with 3.0 mL of ascorbic acid solution, with sonication for 30 min, Ag NPs was obtained.

1.2.4 Fabrication of Fe₃O₄/PDA/Ag composite nanomaterials

0.1007 g of the prepared Fe₃O₄/PDA dispersed in 20.0 mL deionized. 20.0 mL of the obtained Ag NPs were added, with sonication for 15 min, stand for 15 min, then separation by magnet. Follow the operation for eight times to get Fe₃O₄/PDA loading Ag NPs.

1.3 Characterization

The crystal structure and phase purity of the NPs were examined with XRD. It was recorded with a 2θ range of 10^◦-80^◦ by Cu Kα in steps of 0.05^◦ min⁻¹. The accelerating voltage and applied current were 36 kV and 20 mA, respectively. The magnetic properties of Fe₃O₄/PDA/Ag NPs were measured with a Quantum Design Magnetic Properties Measurement System (MPMS) XL-7. The absorption spectra of composite NPs were recorded by UV–VIS and FT-IR spectrophotometer.

1.4The application of composite nanomaterials

1.4.1 SERS Performance of the nanomaterials

The glass slide was washed clearly and blown dry. 200 µL of the obtained composite nanomaterial was dropped onto the slide and air-dried. 200 µL of 10^-5 M rhodamine 6G (R6G) was dropped onto the slide, and Raman spectrometer was employed to annlysis R6G at a wavelength of 514 nm.

1.4. 2 Detection of pesticides

The prepared composites were mixed with 10^-5 mol/L of carbendazim and thiophanate-methyl, respectively, mechanically stirred for 6 h, dropped onto a glass slide, and air-dried. Raman spectra were collected, as well as the pure carbendazim and methyl thiothiazim. The power of the Raman spectrometer was 0.05W, the excitation wavelength was 785 nm, the scanning range was 400-1800 cm^-1, and the acquisition time was 10 s with 2 accumulations.

2.1 Characterization

2.1.1 XRD

The X-ray diffraction patterns of the NPs was shown in Fig. 2. The XRD patterns of the products recorded peaks were well matched with the Fe₃O₄ (JCPDS No: 99-0629), Ag (JCPDS No: 01-089-3697crystal planes[31-33]. Reflections from (220), (311), (400), (422), (511) and (440) planes of the Fe₃O₄ were observed. For Fe₃O₄, the main XRD peaks: 30.1, 35.5, 43.1, 53.4, 57.0, 62.6° were in Fig. 2 with red color. For Fe₃O₄/PDA/Ag, the added peaks: 37.9, 44.5º, 64.8º, 77.5º, indicated corresponding indices (111), (200), (220), and (311) in Fig. 2 with black color. These X-ray diffraction data were basically coincided with reported values. Compared with the high content of Fe₃O₄, the peak of Ag was weak in some degree.

2.1.2 UV-VIS

The UV spectra of Fe₃O₄, Ag and Fe₃O₄/PDA/Ag were shown in Fig. 3. There is no peak of Fe₃O₄ in the visible region. There is a strong absorption peak at the wavelength of 400 nm, which is consistent with the Ag UV absorption peak. Compared with Ag, the peak of Fe₃O₄/PDA/Ag is slightly shifted. This result maybe attribute to the Surface Plasmon Resonance(SPR) of Ag.

2.1.3 IR

The infrared spectra of the sample shown in Fig. 4. It can be clearly seen from the figure that the sample has strong absorption peaks at 596 cm-1, 1276 cm-1, 1524 cm-1, 1643 cm-1 and 3230 cm-1, where the peak of Fe-O bond is at 596 cm-1 and the peak of C-O bond is at 1276 cm-1. The peak of C=C bond and C=N bond is at 1524 cm-1, and the peak of C-C bond is at 1643 cm-1. There is a wide peak at 3230 cm-1 for Fe3O4/PDA and Fe3O4@PDA@Ag, which is the peak of N-H bond.

2.1.4 VSM

As shown in Fig.5, the the saturation magnetization of Fe₃O₄, Fe₃O₄/PDA, Fe₃O₄/PDA/Ag were 63.98, 56.52 and 43.17 emu/g, respectively, indicating the strong magnetism. Compared with the Fe₃O₄, the value of Fe₃O₄/PDA and Fe₃O₄/PDA/Ag reduced, may because of the PDA and Ag without magnetism.

2.2 Application

2.2.1 SERS performance of materials

The Raman spectra of R 6G and R6G loading Fe₃O₄/PDA/Ag as substrate were shown in Fig. 6. Compared with pure R6G Raman peaks, the number and intensity of R6G peaks increased when using Fe₃O₄/PDA/Ag as substrate. It is demonstrate that the prepared Fe₃O₄/PDA/Ag has better Raman enhancement effect. It is promising to be powerful SERS substrate for detection organic molecule and biological molecular .

2.2.2 Detection of carbendazim and thiophanate-methyl

Raman spectra of carbendazim was shown in Fig. 7, at the presence of Fe₃O₄/PDA/Ag in black line, without Fe₃O₄/PDA/Ag in red line. There are few peaks for carbendazim and the signal intensity is relatively weak in Fig. 7(b). When Fe₃O₄/PDA/Ag was employed as substrate, the number of Raman peaks increased obviously, and the signal intensity also significantly strong. In Fig. 7, there were strong Raman signals at 590 cm^-1, 853 cm^-1, 985 cm^-1, 1048 cm^-1, 1191 cm^-1, 1369 cm^-1, 1457 cm^-1 and 1520 cm^-1, which were the characteristic peaks of carbendazim. 590 cm^-1 is the bending vibration of C-C-C. 853 cm^-1 and 985 cm^-1 were the bending vibration of C-H in the benzene ring. 1048 cm^-1 and 1191 cm^-1 are the deformation vibration of the benzene ring and the bending vibration of N-H, respectively. 1369 cm^-1 is the coupling vibration of C-N and C-H bond. 1457 cm^-1is the deformation vibration of -CH₃, and 1520 cm^-1 is the stretching vibration of C-C.

As for thiophanate-methyl in Fig. 8, it is similar to carbendazim, the number of peaks and the intensity sharp increase at the presence of Fe₃O₄/PDA/Ag. There were strong Raman signal at 603 cm^-1, 719 cm^-1, 814 cm^-1, 964 cm^-1, 1050 cm^-1, 1187 cm^-1, 1225 cm^-1, 1274 cm^-1, 1416 cm^-1, 1457 cm^-1, 1506 cm^-1, 1596 cm^-1, which were the characteristic peak of thiophanate-methyl. The 603 cm^-1 is the deformation vibration of N-H. 719 cm^-1 and 1050 cm^-1 were the deformation vibration of C-H on the benzene ring. 964 cm^-1 and 1187 cm^-1 were the deformation vibration of C-H and -CH₃ on the benzene ring, respectively. 1225 cm^-1 and 1274 cm^-1 were the deformation vibrations of N-H and C-H, respectively.

In the current study, Fe₃O₄ loading Ag NPs with magnetism was designed via PDA as bridge. The materials were characterized by XRD, UV-VIS, IR and VSM. Take the R6G as probe, the performance Fe₃O₄/PDA/Ag was absolutely superb. With the aim of evaluating the enhancement, R6G act as probe for SERS. When employed Fe₃O₄/PDA/Ag as Raman substrate to detect carbendazim and methyl thiometrin, the numbers and intensity of their Raman spectra increased significantly. The results showed that Fe₃O₄/PDA/Ag can significantly enhance and amplify their Raman signal. The SERS effect has been attributed to the carbendazim and thiophanate-methyl that are located on or within very close proximity to the surface of Fe₃O₄/PDA/Ag, especially Ag. The results in significant Raman signal enhancement chemically adsorbed carbendazim and thiophanate-methyl on Fe₃O₄/PDA/Ag nanostructures for the strong interaction between Ag and sulfhydryl, amino groups of the two kinds of pesticides. It bring them closer together, so forming more hot spot on Ag NPs. In addition, the magnetic composite nanoparticle can provide strong enhancement of the electromagnetic field. Therefore, the use of Fe₃O₄/PDA/Ag as powerful Raman substrate is expected to detect various analytes. It will broad application in environmental protection, food safety and biomedicine.

Funding

This work was supported by the Natural science foundation of Shaanxi Province (2024GX-YBXM-318), Shaanxi University of educational research project (JYYJ2023-16), National Natural Science Foundation of China (22177066).

Author contributions

Rui Wu: Conceptualization, Data curation, Funding acquisition, Project administration, Validation. Xi Song: Investigation, Writing original, Resources, draft Methodology, Review, editing, Supervision. Guanghui Tian: Formal analysis.

Ethics approval

This study does not involve animal experiments or human participants, and there is no ethical problem.

Declarations

Consent to participate All the authors consent to participate in this article.

Consent to publication All the authors consent to publish this article.

Competing interests The authors declare no competing interests.

Availability of data and materials

All data included in this study are available upon request by contact with the corresponding author.

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Construction of Fe 3 O 4 /PDA/Ag Nanoparticles and Coupling with SERS for Detection of Pesticide Residue

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