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Bioinspired Development of P(St−MAA)−Avermectin Nanoparticles with High Affinity for Foliage To Enhance Folia Retention Jie Liang,† Manli Yu,† Liya Guo, Bo Cui, Xiang Zhao, Changjiao Sun, Yan Wang, Guoqiang Liu, Haixin Cui,* and Zhanghua Zeng* Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081, People’s Republic of China S Supporting Information *

ABSTRACT: Pesticides are chemical or biological substances to control pests and protect the crop yield. Most pesticides suffering from large amounts of losses in the environment lead to damage of ecological systems and food pollution. To reduce their losses and increase the utilization rate, we have developed bioinspired mussel avermectin nanoparticles [P(St−MAA)−Av− Cat] with strong adhesion to crop foliage by the emulsion−solvent evaporation method and chemical modification. They were near spheres with a diameter of around 120 nm. They displayed remarkable high avermectin content of more than 50% (w/w) and presented excellent storage stability as well as continuous sustained release. The photosensitive avermectins loaded were highly improved against ultraviolet light. Meanwhile, the retention rate of P(St−MAA)−Av−Cat on the crop foliage surfaces was significantly increased. As a result, the indoor toxicity of P(St−MAA)−Av−Cat was highly enhanced. The adhesive property strongly depended upon the functional groups on the nanoparticle surface. The multimodal binding mode of P(St−MAA)−Av− Cat to the crop foliage surface resulted in stronger adhesion and a longer retention time. KEYWORDS: bioinspired, pesticide nanoparticles, foliage adhesion, folia retention, avermectins

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INTRODUCTION Pesticides are chemical substances that are used to destroy, repel, or otherwise lower pest infestations to protect crops from biological disasters and enhance yield.1 According to statistical reports, pesticides have saved over 30% of the total worldwide crop production every year.2,3 However, in an attempt to achieve better or total pest control, pesticides are applied more frequently and at higher dosage rates, which has resulted in increasing selection pressure. The amount of active ingredient used is more than 2.4 million tons annually in the world.4 The large amounts of use and improper disposal of pesticides afford many possible sources of them in water, air, soil, and food, resulting in long-term accumulation in the surrounding environment and toxic risks to animals and humans.5−7 A large amount of pesticide residuals not only influence human health but also destroy the biodiversity and ecological environment.8−12 During the process of spraying, pesticides are first contacting crop foliage and then they transfer to parts of the crop. Previous reports showed that the utilization rate of getting to the crop leaf is generally below 10%, and the rest runs off into the surrounding environment. Around 0.1% of an applied pesticide reaches the target pest.13 Hence, it is highly important to minimize loss by enhancing deposition and adhesion of pesticides to crop foliage. A pesticide formulation with strong adhesion to foliage could be desirable for enhancing retention on the crop surface and improving the effective utilization rate.14 Recently, the development of nanopesticide formulation has proven to improve the performance by formulating nanoparticle-based delivery systems.15−25 The pesticide nanodelivery systems with a small size and large surface area improve the © XXXX American Chemical Society

deposition on foliage and extend the release time. Moreover, in term of the microstructure of the foliage, the nanoparticle surface can be easily modified by affinity groups to improve adhesion and decrease the loss from crop foliage. Avermectin is one of most used biocides worldwide.26 However, it is easily decomposed in ultraviolet (UV) light irradiation, giving rise to a short half-life and decrease of the utilization rate.27,28 Many efforts have been exerted in developing nanoparticles as a carrier to enhance the photostability.29−32 Naturally adhesive polydopamine-containing materials inspired from mussel have been applied in many fields, in which catechol groups play a major role in adhesion to various surfaces.33−35 Polydopamine nanoaparticles encapsulating pesticide exhibited excellently adhesive performance on crop foliage and an enhanced pesticide retention time.36 Given the high cost of dopamine, it is not practical to apply as a pesticide carrier. Here, we developed low-cost nanoparticles [P(St− MAA)−Av−Cat] with the copolymer (styrene and methacrylic acid) as the avermectin carrier and polycatechol as the adhesive group on the surface. The obtained results showed that P(St− MAA)−Av−Cat nanoparticles exhibited excellent adhesive performance on the foliage surface of cucumber and broccoli and better indoor toxicity toward the pest. Special Issue: Nanotechnology Applications and Implications of Agrochemicals toward Sustainable Agriculture and Food Systems Received: Revised: Accepted: Published: A

May 1, 2017 July 17, 2017 July 20, 2017 July 20, 2017 DOI: 10.1021/acs.jafc.7b01998 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

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Journal of Agricultural and Food Chemistry

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tion was purified by centrifugation at 15000 rpm for 15 min, and the pellet was collected. Determination of the Content of Nanoparticles. The avermectin content (AC, w/w) of P(St−MAA)−Av and P(St− MAA)−Av−Cat nanoparticles was determined by high-performance liquid chromatography (HPLC). The procedure were listed as follows: A proper amount of nanoparticles (M0) was dispersed in 5 mL of mixture solvent of tetrahydrofuran and DMSO (4:1, v/v) and was sonicated for 5 min at room temperature. After it was completely dissolved, it was carefully diluted to an appropriate volume (V) with a mixture solvent of CH3CN, CH3OH, and H2O (80:15:5, v/v/v). After the insoluble residue was filtered off, the filtrate was subjected to analysis by HPLC. After the avermectin concentration (C, mol/L) was determined by HPLC, and the AC could be calculated according to the calibration curve by the following equation:

MATERIALS AND METHODS

Styrene (99%) and methacrylic acid (MAA, 99%) purchased from J&K Chemical, China, were distilled under reduced pressure before use. Sodium n-dodecyl sulfate (SDS, 99%) was purchased from J&K Chemical, China. Avermectins (95.6%) were obtained from Qilu Pharmaceutical Company, Ltd., China. Poly(vinyl alcohol) (PVA) was purchased from Sigma-Aldrich. Chloroform (CHCl3, 98.5%), dichloromethane (CH2Cl2, 99.8%), 3,4-dihydroxybenzaldehyde (DBA), and ptoluenesulfonic acidmonohydrate (TsOH) were purchased from J&K Chemical Company, Ltd., China. 2,2′-Azobis(4-methoxy-2,4-dimethylvaleronitrile) (V70) was from Wako Chemical, Japan. Emulsifiable concentrate (EC) and water-dispersible granule (WDG) formulations of avermectins were commercially available from Noposion Agrochemicals Co., Ltd., China. All chemicals mentioned above were directly used without further purification. Deionized water (18 MΩ cm) was applied throughout this work. Fresh cucumber and broccoli foliage were carefully selected for use to ensure reproducibility. The morphology of nanoparticles was investigated by transmission electron microscopy (TEM, HT7700, Hitachi, Ltd., Japan). The hydrodynamic size distribution, ζ potential, and polydispersity index (PDI) of the nanoparticles were carried out on a particle size analyzer (Nano-ES90, Malvern Instruments, U.K.). For data reliability, each sample was tested in triplicate and the average value was taken. Synthesis of P(VA-co-HBA). The synthesis of P(VA-co-HBA) was followed by a previous report.37 In brief, PVA (5 g) was suspended and vigorously stirred in 60 mL of dimethyl sulfoxide (DMSO). It was slowly heated to 85 °C until completely dissolved. After it naturally cooled to 20 °C, 1.3 g of DBA and 0.4 g of TsOH were added. The mixed solution was heated to 85 °C and vigorously stirred for 16 h under an argon atmosphere. After it naturally cooled to 20 °C, the reaction mixture was poured into 1.0 L of acetone and the precipitate was collected by filtration. The white solid was extracted by a Soxhlet apparatus with dichloromethane as the solvent for 30 h under an argon atmosphere to give 5.8 g of P(VA-co-HBA) (yield of 95.2%). Proton nuclear magnetic resonance (1H NMR, 400 MHz, DMSOd6) δ: 1.24−1.78 (m), 1.96 (m), 3.81−3.90 (m), 4.24−4.70 (m), 5.77 (s), 6.41 (m), 6.54 (s), 6.60 (d), 8.58 (s), 8.72 (s). Synthesis of P(St-co-MAA). Styrene (1 g) and MAA (1 g) were dissolved in 10 mL of chloroform, and V70 (50 mg) chosen as the initiator was added. The mixture was stirred at room temperature for 1 h and slowly heated to 45 °C. The polymerization reaction was carried out at this temperature for 24 h. After polymerization, the mixed reaction solution was naturally cooled to room temperature. The insoluble solid was filtered off, and the filtrate was concentrated. The copolymer [P(St-co-MAA)] was obtained after precipitation from ethyl ether twice (yield of 75%). 1 H NMR (400 MHz, CDCl3) δ: 0.83−0.89 (m), 1.38−1.94 (m), 6.62−7.19 (m). Preparation of Nanoparticles. A total of 500 mg of the obtained copolymer P(St-co-MAA) and different amounts of avermectins were dissolved in 20 mL of the mixture solvent of chloroform and tetrahydrofuran (4:1, v/v). The mixed solution was stirred vigorously (600 rpm) for 1 h at room temperature until the solid was completely dissolved. A total of 20 mL of aqueous solution consisting of 100 mg of SDS was added. The mixture solution was emulsified by ultrasonication for 240 s in intervals of 20 s with a 10 s pause using a sonifier (JY90-IIN, Ningbo Scientz Biotechnology Company, Ltd.) under an ice−water bath, avoiding chloroform evaporation. The emulsion solution was then stirred for 24 h at room temperature to naturally evaporate the organic solvent. After solvent evaporation, P(St−MAA) avermectin [P(St−MAA)−Av] nanoparticles were formed. The nanodispersion was centrifuged at 1000 rpm for 10 min to remove precipitate. Finally, P(St−MAA)−Av nanoparticles were further purified by dialysis bags [molecular weight cut-off (MWCO) of 100 000 Da]. P(St−MAA)−Av−Cat was obtained via the esterification reaction of P(St−MAA)−Av and P(VA-co-HBA) in the presence of 1-ethyl-3(3-(dimethylamino)propyl)carbodiimide (EDC). The reaction solu-

AC = (CVM w )/M 0 × 100%

(1)

where Mw is the avermectin molecular weight. Sustained Release Behavior of Nanoparticles. P(St−MAA)− Av and P(St−MAA)−Av−Cat nanoparticles (25 mg) were separately suspended in a 100 mL mixture of methanol and phosphate-buffered saline (PBS, pH 7.4, 3:2, v/v), respectively. The suspended solution was carefully added to various dialysis bags (MWCO of 20 000 Da). After sealed tightly, the dialysis bags were put into a 95 mL mixture of methanol and PBS (pH 7.4, 3:2, v/v) as releasing media. Each 5 mL aliquot in outside media of the dialysis bags was collected at a specific time, and 5 mL of mixed solvent of methanol and PBS was added to keep the same volume of releasing media. According to the calibration curve, the concentration of slowly released avermectins at each aliquot was determined by HPLC at 245 nm. The plot curve of accumulated release percentages of avermectins versus different times was obtained from the sustained release amounts. Meanwhile, the active avermectins were chosen as a comparison. Photodegradation Behavior of Nanoparticles. P(St−MAA)− Av and P(St−MAA)−Av−Cat nanoparticles (60 mg) were irradiated at room temperature by an UV light incubator (XT5409-XPC80, 400 W, Xutemp Technic Apparatus Co., Ltd., China). The samples revolved around the light source at a distance of 10 cm. Samples (10 mg) were collected at each time interval (12, 24, 48, 72, and 96 h). After collection, each sample was analyzed at 245 nm by HPLC. The plot curve of avermectin photodegradation behavior versus different irradiation times was obtained from the remnant amount of avermectins. Meanwhile, the active avermectins were chosen as a comparison. Contact Angle (CA) Measurement of Nanoparticles. Fresh cucumber and broccoli foliage obtained from indoor cultivation were carefully selected and gently washed using deionized water several times to completely remove dust on their surface. This foliage cleaning process was carried out very carefully, ensuring that cucumber and broccoli foliage surfaces were not damaged. After naturally dried in air, the foliages were cut into small pieces and put smoothly on glass slides. The aqueous solutions containing P(St−MAA)−Av and P(St− MAA)−Av−Cat nanoparticles (6.0 μL, 2.0 mg/L) were slowly added to the crop foliage. The images of each droplet were taken, and the corresponding CA value was calculated. Given the difference of the crop foliage surface and experiment reliability, each CA value was repeated at least 6 times and the average values are given. Meanwhile, the deionized water was chosen as a comparison. Avermectin Residue Analysis on Crop Foliage Using HPLC. P(St−MAA)−Av, P(St−MAA)−Av−Cat, WDG, and EC containing the same amount of avermectins were sprayed onto the fresh and clean crop (cucumber and broccoli) foliages. After naturally dried in air, the halves of leaf were washed with 100 mL of deionized water. Each leaf was cut into small and thin pieces, and they were subjected to extraction by a Soxhlet apparatus with tetrahydrofuran as the extracting solvent for 20 h. After filtering off the insoluble solid, the filtrate was slowly concentrated on vacuum at 40 °C to give a colored and sticky solid. A 5 mL mixture solvent of CH3CN, CH3OH, and H2O (80:15:5, v/v/v) was added to dissolve this solid. The mixture solution was stirred at room temperature for 1 h and then B

DOI: 10.1021/acs.jafc.7b01998 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

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Scheme 1. Schematic Illustration of the Synthesized Route to P(St-co-MAA), P(St−MAA)−Av, and P(St−MAA)−Av−Cat

Table 1. Mean Size, PDI, ζ Potential, and m-AC of Nanoparticles sample

mean size (nm)

PDI

ζ potential (mV)

m-AC (%)

P(St−MAA)−Av P(St−MAA)−Av−Cat

101.5 ± 6.0 122.4 ± 12.5

0.06 ± 0.03 0.08 ± 0.04

−20.5 ± 0.7 −12.6 ± 0.4

58.2 56.9

ultrasonicated for 15 min. The insoluble solid was filtered off, and the filtrate was collected and analyzed using HPLC. For data reliability, each experiment was repeated 3 times and the average values are given. Indoor Toxicity Test. Here, the foliage dipping method was adapted to assess the indoor toxicity of avermectins toward aphids. Avermectin contents of 1.875, 3.75, 7.5, 15, 30, 60, and 120 mg/L were finely formulated in all kinds of avermectin test samples, including P(St−MAA)−Av, P(St−MAA)−Av−Cat, WDG, and EC. The Cleaning and fresh leaves were cut into rounded pieces with a diameter of 5 cm and were fully immersed in each avermectincontaining solution for 15 s. After naturally dried in air, each treated foliage piece was placed into a cell culture dish and 25 aphids with similar activity were transferred to the culture dish. The dishes were incubated at a temperature of 25 °C, humidity of 75%, and 16:8 light/ dark. The median lethal concentration (LC50) were determined according to the number of dead aphids after 48 h. For experiment data reliability, each experiment was paralleled 5 times and average values are given. Deionized water was chosen for the control experiment.

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alized groups were formulated using the emulsion−solvent evaporation method. On the basis of P(St−MAA)−Av, P(St− MAA)−Av−Cat was prepared via a one-step esterification reaction of P(VA-co-HBA) and P(St−MAA)−Av nanoparticles. The mean size, PDI, maximum AC (m-AC), and ζ potential of P(St−MAA)−Av and P(St−MAA)−Av−Cat nanoparticles are characterized by dynamic light scattering (DLS). These data were provided in Table 1. The mean size of P(St−MAA)−Av was almost equal to 100 nm, and that of P(St−MAA)−Av−Cat increased to around 120 nm after chemical modification of the surface (Figure 1a). The PDI of P(St−MAA)−Av and P(St− MAA)−Av−Cat was less than 0.1, indicating that these nanoparticles were highly monodispersed. The ζ potentials of P(St−MAA)−Av and P(St−MAA)−Av−Cat are −20.5 ± 0.7 and −12.6 ± 0.4, respectively. The SDS concentration used in the process of preparation showed some effects on the ζ potentials (Figure S1 of the Supporting Information). The higher concentration of SDS afforded more negative ζ potentials of nanoparticles, indicating that SDS increased stability of nanoparticles. Given the high cost performance, a 1:5 ratio of SDS and P(St-co-MAA) (w/w) was taken. The mAC of P(St−MAA)−Av and P(St−MAA)−Av−Cat nanoparticles was above 50% (w/w), and the various AC below m-AC can be easily obtained. TEM images offer a higher resolution and precise size of the nanoparticle. The TEM images of P(St−MAA)−Av and P(St−MAA)−Av−Cat confirmed that P(St−MAA)−Av and P(St−MAA)−Av−Cat nano-

RESULTS AND DISCUSSION

Preparation and Characterization of P(St−MAA)−Av and P(St−MAA)−Av−Cat. The detailed synthetic procedure of polymer P(VA-co-HBA) was afforded in Scheme S1 of the Supporting Information. P(St-co-MAA) via one-step polymerization was obtained, and the preparation of P(St−MAA)−Av as well as P(St−MAA)−Av−Cat nanoparticles was summarized in Scheme 1 and Scheme S2 of the Supporting Information. P(St−MAA)−Av nanoparticles with carboxylic acid functionC

DOI: 10.1021/acs.jafc.7b01998 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

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Figure 2. Responsive photodegradation curves of active Av, P(St− MAA)−Av, and P(St−MAA)−Av−Cat versus irradiated time (UV light).

loaded in P(St−MAA)−Av and P(St−MAA)−Av−Cat were about 20% (Figure 2), indicating their higher photostability, probably as a result of nanoencapsulation protection as a drug carrier. Sustained Release Behavior of P(St−MAA)−Av and P(St−MAA)−Av−Cat. The continuously sustained release of pesticide formulations is very important to enhance the utilization efficacy. The sustained release curve profiles of active avermectins, P(St−MAA)−Av, and P(St−MAA)−Av− Cat versus time were plotted. As shown in Figure 3, the release

Figure 1. (a) DLS size data and TEM images of (b) P(St−MAA)−Av and (c) P(St−MAA)−Av−Cat. The scale is 1.0 μm.

particles had near spherical sharpness, with both diameters of around 100 nm (panels b and c of Figure 1). These results agree well with DLS data. Stability of P(St−MAA)−Av and P(St−MAA)−Av−Cat under Different Temperature and pH Conditions. The stability of P(St−MAA)−Av and P(St−MAA)−Av−Cat at different temperatures and pH values is highly important. The stability of P(St−MAA)−Av and P(St−MAA)−Av−Cat nanoparticles at various temperatures (4, 25, and 54 °C) and pH values (5.0, 7.0, and 9.0) was conducted. The variation of the mean size and PDI data was used to evaluate their stability in 14 days of storage and various pH values. As shown in Figure S2 of the Supporting Information, the change on the mean size and PDI of P(St−MAA)−Av was very small at various temperatures and pH values, suggesting high storage stability toward temperature and pH change. In the case of P(St− MAA)−Av−Cat, there was very small variation of the mean size and PDI against various temperatures and very little change under acidic and neutral pH conditions. At high pH, the mean size and PDI exhibited a moderate increase, presumably because catechol groups are easily oxidized at alkaline pH, leading to aggregation. The contents of avermectins analyzed by HPLC in P(St−MAA)−Av and P(St−MAA)−Av−Cat at different storage temperatures were kept almost unchanged. These results suggest that P(St−MAA)−Av−Cat was very stable against the temperature and should be used at acidic and neutral pH conditions. Photodegradation Behavior of P(St−MAA)−Av and P(St−MAA)−Av−Cat. As a biocide, avermectins are very prone to degradation upon exposure to UV light. To improve the photostability of them, encapsulation formulation is seemly practical. The response curves of the photodegradation rate of active avermectins, P(St−MAA)−Av, and P(St−MAA)−Av− Cat versus irradiation time were shown in Figure 2. These results clearly implied that the photodegradation rate of active avermectins was very fast, with more than 50% degradation after 96 h of exposure to continuous UV light irradiation. At the same time, the photodegradation rates of the avermectins

Figure 3. Continuously sustained release profiles of avermectins and P(St−MAA)−Av and P(St−MAA)−Av−Cat nanoparticles. The accumulated release percentages were obtained by the plotting curve of the sustained release amounts versus time.

rate of active avermectins was very fast, and more than 95% of the drug was released within 24 h. In contrast, P(St−MAA)− Av and P(St−MAA)−Av−Cat presented similarly slow and mild release (Figure 3). The release behavior was still continuous after more than 10 days. These sustained release data indicated that P(St-co-MAA) as a drug carrier is beneficial to prolong the leaching time of the drug, which is supposed to be very important to enhance utilization efficacy. The accumulated release percentages obey first-order kinetics, with R2 values over 0.99. Deposition and Retention of P(St−MAA)−Av and P(St−MAA)−Av−Cat on the Surface of Crop Foliages. The efficient deposition of pesticide formulations on the crop foliage surface is highly important to minimize losses and increase utilization efficacy. The wetting behavior of P(St− MAA)−Av and P(St−MAA)−Av−Cat on the cucumber and D

DOI: 10.1021/acs.jafc.7b01998 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

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Journal of Agricultural and Food Chemistry broccoli foliage surfaces was investigated by measuring CA. The CA of deionized water was applied as a control. The CA images were shown in Figure S3 of the Supporting Information, and the data were summarized in Table S1 of the Supporting Information. The calculated CA values of droplets on cucumber foliage were 79.8 ± 5.2°, 63.5 ± 6.4°, 66.2 ± 7.3°, and 52.6 ± 6.1° for water, SDS solution with the same content as that in nanoparticles, P(St−MAA)−Av, and P(St−MAA)−Av−Cat, respectively. The calculated CA values of droplets on broccoli foliage were 130.8 ± 8.2°, 119.1 ± 3.8°, 125.1 ± 4.9°, and 106.7 ± 6.2° for water, SDS solution with the same content as that in nanoparticles, P(St−MAA)−Av, and P(St−MAA)−Av−Cat, respectively. SDS exhibited little effect on folia wettability, and P(VA-co-HBA) on the surface of P(St−MAA)−Av−Cat might play a vital role in enhancing folia wettability. These results suggested that P(St−MAA)−Av−Cat had slightly improved wettability on crop foliage compared to P(St−MAA)−Av. To demonstrate that P(St−MAA)−Av−Cat have better adhesive properties. The avermectin retention rate by washing was applied to roughly evaluate the adhesive force of the nanoparticles to crop foliage. Conventionally, HPLC is a general method to analyze the avermectin concentration and determine the retention rates. The retention rates on weakly hydrophilic cucumber foliage were 38.1, 72.3, 38.4, and 42.6% for P(St−MAA)−Av, P(St−MAA)−Av−Cat, WDG, and EC, respectively. Meanwhile, the retention rates on highly hydrophobic broccoli foliage were 12.1, 36.5, 17.1, and 14.8% for P(St−MAA)−Av, P(St−MAA)−Av−Cat, WDG, and EC, respectively (Figure 4). The effect of the SDS concentration

Table 2. Indoor Toxicity of P(St−MAA)−Av and P(St− MAA)−Av−Cat and Commercially Available Formulations (WDG and EC) cucumber

a b

broccoli

sample

LC50 (ppm)

relative toxicity (ppm)a

LC50 (ppm)

relative toxicity (ppm)b

P(St−MAA)−Av P(St−MAA)−Av−Cat WDG EC

13.5 4.3 12.4 10.1

0.75 2.35 0.81 1

179.6 55.4 150.3 124.6

0.69 2.24 0.83 1

The relative toxicity of EC was normalized as 1 on cucumber foliage. The relative toxicity of EC was normalized as 1 on broccoli foliage.

179.6, 55.4, 150.3, and 124.6 for P(St−MAA)−Av, P(St− MAA)−Av−Cat, WDG, and EC, respectively. In comparison to these commercially available formulations, the indoor toxicities of P(St−MAA)−Av on both crop foliages were preserved. However, in the case of high leaf adhesive P(St−MAA)−Av− Cat, the indoor toxicity was significantly enhanced, probably as a result of more pesticide retention on the foliages during the process of leaf dipping. To prove it, the retention amount of drug based on the leaf dipping method was investigated by HPLC. As expected, the retention amount of P(St−MAA)− Av−Cat had 55% more than that of P(St−MAA)−Av on the cucumber foliage. On broccoli foliage, this retention amount of P(St−MAA)−Av−Cat had 63% more than that of P(St− MAA)−Av. Apparently, these results showed that P(St− MAA)−Av−Cat with strong leaf adhesion improved effective utilization efficacy. Interaction between Nanoparticles and the Crop Foliage Surface. In general, the crop leaf surface has a waxy layer, which consists of various kinds of higher fatty alcohols, higher fatty acids, and higher fatty aldehydes. Additionally, there are several kinds of glycoside groups consisting of many hydroxyl groups on cucumber foliage.38,39 These groups on the cucumber and broccoli foliage surfaces play a vital role in the interaction of the nanoparticle surface. There are many carboxylic groups on the P(St−MAA)−Av surface, which could bind to cucumber and broccoli foliage surfaces via a hydrogen bond by the carboxylic groups on P(St−MAA)−Av and hydroxyl groups on the foliage surface. For P(St−MAA)− Av−Cat, the surface is covered with many catechol groups, which could form a stronger hydrogen bond between phenols on nanoparticles and carboxylic or hydroxyl groups on the foliage surface. The folia retention rate of nanoparticles on cucumber and broccoli foliages decreased by washing solvent containing urea, a hydrogen-bond-disrupting agent, instead of deionized water, and it gradually decreased along with an increased concentration of urea (Figure S5 of the Supporting Information). The folia retention rate of P(St−MAA)−Av was more sensitive to the concentration of urea compared to that of P(St−MAA)−Av−Cat. Apparently, these results confirmed that the interaction force between nanoparticles and the surface of cucumber and broccoli foliages mainly came from a hydrogen bond and P(St−MAA)−Av−Cat showed stronger binding to the crop foliage surface. In addition, there are also possible coordination bonds between P(St−MAA)−Av−Cat and crop foliage, because catechol can easily coordinate many metal ions. These multimodal bindings between P(St−MAA)−Av−Cat and the crop foliage surface gave rise to strong adhesive attraction of them.

Figure 4. Retention rates on the cucumber and broccoli foliage surfaces of P(St−MAA)−Av, P(St−MAA)−Av−Cat, and commercially available formulations (WDG and EC) determined by HPLC.

on the retention rate of nanoparticles on folia surfaces was negligible (Figure S4), indicating that the catechol groups played the main role in adhesive binding to the folia surface. These results clearly confirmed that P(St−MAA)−Av−Cat had excellent adhesion to crop foliage compared to other formulations, presumably as a result of the great quantity of catechol groups enhancing the adhesive binding to the crop foliage surfaces. These conclusions agree well with those previous reports of polydopamine. Indoor Toxicity Evaluation. Here, a simple leaf dipping method was applied to evaluate the indoor toxicity of P(St− MAA)−Av, P(St−MAA)−Av−Cat, WDG, and EC. The results are provided in Table 2. LC50 values on cucumber were determined to be 13.5, 4.3, 12.4, and 10.1 for P(St−MAA)−Av and P(St−MAA)−Av−Cat nanoparticles, WDG, and EC, respectively. LC50 values on broccoli were determined to be E

DOI: 10.1021/acs.jafc.7b01998 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

Article

Journal of Agricultural and Food Chemistry

(5) United States Department of Agriculture (USDA). Agricultural Statistics; United States Government Printing Office: Washington, D.C., 1992. (6) Bradberry, S. M.; Proudfoot, A. T.; Vale, J. A. Poisoning Due to Chlorophenoxy Herbicides. Toxicol. Rev. 2004, 23, 65−73. (7) Eyer, P. The Role of Oximes in the Management of Organophosphorus Pesticide Poisoning. Toxicol. Rev. 2003, 22, 165− 190. (8) Eddleston, M.; Eyer, P.; Worek, F.; Mohamed, F.; Senarathna, L.; vonMeyer, L.; Juszczak, E.; Hittarage, A.; Azhar, S.; Dissanayake, W.; Sheriff, M. H. R.; Szinicz, L.; Dawson, A. H.; Buckley, N. A. Differences between Organophosphorus Insecticides in Human Selfpoisoning: A Prospective Cohort study. Lancet 2005, 366, 1452−1459. (9) Eddleston, M.; Worek, F.; Eyer, P.; Thiermann, H.; vonMeyer, L.; Jeganathan, K.; Sheriff, M. H. R.; Dawson, A. H.; Buckley, N. A.Q. Poisoning with the S-Alkyl Organophosphorus Insecticides Profenofos and Prothiofos. QJM 2009, 102, 785−792. (10) Fenner, K.; Canonica, S.; Wackett, L. P.; Elsner, M. Evaluating Pesticide Degradation in the Environment: Blind Spots and Emerging Opportunities. Science 2013, 341, 752−758. (11) Malaj, E.; von der Ohe, P. C.; Grote, M.; Kühne, R.; Mondy, C. P.; Usseglio-Polatera, P.; Brack, W.; Schäfer, R. F. Organic Chemicals Jeopardize the Health of Freshwater Ecosystem on the Continental Scale. Proc. Natl. Acad. Sci. U. S. A. 2014, 111, 9549−9554. (12) Köhler, H. R.; Triebskorn, R. Wildlife Ecotoxicology of Pesticides: Can We Track Effects to the Population Level and Beyond Science. Science 2013, 341, 759−765. (13) Nuruzzaman, M.; Rahman, M. M.; Liu, Y.; Naidu, R. Nanoencapsulation, Nano-guard for Pesticides: A New Window for Safe Application. J. Agric. Food Chem. 2016, 64, 1447−1483. (14) Wang, B.; Song, J. L.; Zeng, A. J.; Liu, Y. J.; Zhang, J.; He, X. K. Effects of Formulations and Surfactants on the Behavior of Pesticide Liquid Spreading in the Plant Leaves. Chin. J. Pestic. Sci. 2012, 14, 334−340. (15) Ghormade, V.; Deshpande, M. V.; Paknikar, K. M. Perspectives for nano-biotechnology enabled protection and nutrition of plants. Biotechnol. Adv. 2011, 29, 792−803. (16) Morris, J.; Willis, J.; De Martinis, D.; Hansen, B.; Laursen, H.; Sintes, J. R.; Kearns, P.; Gonzalez, M. Science Policy Considerations for Responsible Nanotechnology Decisions. Nat. Nanotechnol. 2011, 6, 73−77. (17) Nair, R.; Varghese, S. H.; Nair, B. G.; Maekawa, T.; Yoshida, Y.; Kumar, D. S. Nanoparticulate Material Delivery to Plants. Plant Sci. 2010, 179, 154−163. (18) Nuruzzaman, M.; Rahman, M. M.; Liu, Y.; Naidu, R. Nanoencapsulation, Nano-guard for Pesticides: A New Window for Safe Application. J. Agric. Food Chem. 2016, 64, 1447−1483. (19) Gogos, A.; Knauer, K.; Bucheli, T. D. Nanomaterials in Plant Protection and Fertilization: Current state, Foreseen Applications, and Research Priorities. J. Agric. Food Chem. 2012, 60, 9781−9792. (20) Ghormade, V.; Deshpande, M. V.; Paknikar, K. M. Perspectives for Nano-biotechnology Enabled Protection and Nutrition of Plants. Biotechnol. Adv. 2011, 29, 792−803. (21) Khot, L. R.; Sankaran, S.; Maja, J. M.; Ehsani, R.; Schuster, E. W. Applications of Nanomaterials in Agricultural Production and Crop Protection: A Review. Crop Prot. 2012, 35, 64−70. (22) Kah, M.; Hofmann, T. Nanopesticides Research: Current Trends and Future Priorities. Environ. Int. 2014, 63, 224−235. (23) Boehm, A. L.; Martinon, I.; Zerrouk, R.; Rump, E.; Fessi, H. Nanoprecipitation Technique for the Encapsulation of Agrochemical Active Ingredients. J. Microencapsulation 2003, 20, 433−441. (24) Bordes, P.; Pollet, E.; Avérous, L. Nano-biocomposites: Biodegradable Polyester/nanoclay Systems. Prog. Polym. Sci. 2009, 34, 125−155. (25) Li, Z. Z.; Xu, S. A.; Wen, L. X.; Liu, F.; Liu, A. Q.; Wang, Q.; Sun, H. Y.; Yu, W.; Chen, J. F. Controlled Release of Avermectin from Porous Hollow Silica Nanoparticles: Influence of Shell Thickness on Loading Efficiency, UV-shielding Property and Release. J. Controlled Release 2006, 111, 81−88.

In this study, P(St−MAA)−Av−Cat with high adhesive force to crop foliage were developed by the emulsion−solvent evaporation method and chemical modification. They had near spherical sharpness, with a diameter of around 120 nm. These nanoparticles showed remarkable m-AC (>50%, w/w). They presented excellent storage stability and continuous sustained release behavior. The photosensitive avermectins loaded in P(St−MAA)−Av−Cat were protected against UV light irradiation. The indoor toxicity of avermectins loaded in P(St−MAA)−Av−Cat was highly enhanced as a result of the improvement of the retention rate on the crop foliage surfaces. The adhesive property strongly depended upon the functional groups on the nanoparticle surface. The multimodal bindings of P(St−MAA)−Av−Cat to cucumber and broccoli foliage surfaces resulted in higher adhesion and a longer retention time. We envision that the leaf-adhesive P(St− MAA)−Av−Cat nanoaprticles could be considered as a resource-saving and environmentally friendly pesticide formulation, which decreases the spraying dosage and pollution in food and the ecological environment.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jafc.7b01998. Detailed information on the synthetic routes to P(VA-coHBA) and supporting schemes, figures, and table (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*Telephone: 0086-10-82105997. E-mail: [email protected]. *Telephone: 0086-10-82106004. E-mail: zengzhanghua@caas. cn. ORCID

Haixin Cui: 0000-0002-1274-1987 Zhanghua Zeng: 0000-0002-8102-4770 Author Contributions †

Jie Liang and Manli Yu contributed equally to this work.

Funding

This work was funded by National Key Project of Research and Development Plan Program of China (2017YFD0200900), Thousand Talents Plan Program, and National Key Basic Research Program of China (973 Program) from Ministry of Science and Technology of China (2014CB932200). Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Mogul, M. G.; Akin, H.; Hasirci, N.; Trantolo, D. J.; Gresser, J. D.; Wise, D. L. Controlled Release of Biologically Active Agents for Purposes of Agricultural Crop Management. Resour. Conserv. Recycl 1996, 16, 289−320. (2) Food and Agriculture Organization of the United Nations (FAO). International Code of Conduct on the Distribution and Use of Pesticides; FAO: Rome, Italy, 2007. (3) Lamberth, C.; Jeanmart, S.; Luksch, T.; Plant, A. Current Challenges and Trends in the Discovery of Agrochemicals. Science 2013, 341, 742−746. (4) Grube, A.; Donaldson, D.; Kiely, T.; Wu, L. Pesticides Industry Sales and Usage; United States Environmental Protection Agency (U.S. EPA): Washington, D.C., 2011. F

DOI: 10.1021/acs.jafc.7b01998 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

Article

Journal of Agricultural and Food Chemistry (26) Lankas, G. R.; Gordon, L. R. Ivermectin and Abamectin; SpringerVerlag: New York, 1989. (27) Crouch, L. S.; Feely, W. F.; Arison, B. H.; VandenHeuvel, W. J.A.; Colwell, L. F.; Stearns, R. A.; Kline, W. F.; Wislocki, P. G. Photodegradation of Avermectin B1a Thin Films on Glass. J. Agric. Food Chem. 1991, 39, 1310−1319. (28) Mrozik, H.; Eskola, P.; Reynolds, G. F.; Arison, B. H.; Smith, G. M.; Fisher, M. H. Photoisomers of Avermectins. J. Org. Chem. 1988, 53, 1820−1823. (29) Guan, H. N.; Chi, D. F.; Yu, J.; Zhang, S. Y. Novel Photodegradable Insecticide W/TiO2/Avermectin Nanocomposites Obtained by Polyelectrolytes Assembly. Colloids Surf., B 2011, 83, 148−154. (30) Meng, F.; Zhong, Z.; Feijen, J. Stimuli-Responsive Polymersomes for Programmed Drug Delivery. Biomacromolecules 2009, 10, 197−209. (31) Liu, R.; Guo, Y.; Odusote, G.; Qu, F.; Priestley, R. D. Core-Shell Fe3O4 Polydopamine Nanoparticles Serve Multipurpose as Drug Carrier, Catalyst Support and Carbon Adsorbent. ACS Appl. Mater. Interfaces 2013, 5, 9167−9171. (32) Zhao, D.; Zhang, Y.; Lv, L.; Li, J. Preparation and Release of Avermectin-loaded Cellulose Acetate Ultrafine fibers. Polym. Eng. Sci. 2013, 53, 609−614. (33) Ochs, C. J.; Hong, T.; Such, G. K.; Cui, J.; Postma, A.; Caruso, F. Dopamine-Mediated Continuous Assembly of Biodegradable Capsules. Chem. Mater. 2011, 23, 3141−3143. (34) Lee, H.; Dellatore, S. M.; Miller, W. M.; Messersmith, P. B. Mussel-Inspired Surface Chemistry for Multifunctional Coatings. Science 2007, 318, 426−430. (35) Postma, A.; Yan, Y.; Wang, Y.; Zelikin, A. N.; Tjipto, E.; Caruso, F. Self-Polymerization of Dopamine as a Versatile and Robust Technique to Prepare Polymer Capsules. Chem. Mater. 2009, 21, 3042−3044. (36) Jia, X.; Sheng, W.; Li, W.; Tong, Y.; Liu, Z.; Zhou, F. Adhesive Polydopamine Coated Avermectin Microcapsules for Prolonging Foliar Pesticide Retention. ACS Appl. Mater. Interfaces 2014, 6, 19552−19558. (37) Mu, Y.; Wan, X. Simple but Strong: A Mussel-Inspired Hot Curing Adhesive Based on Polyvinyl Alcohol Backbone. Macromol. Rapid Commun. 2016, 37, 545−550. (38) Cosmetic Ingredient Review Expert Panel. Cucumis sativus (Cucumber)-Derived Ingredients as Used in Cosmetics, Tentative Safety Assessment; Cosmetic Ingredient Review: Washington, D.C., March 16, 2012; www.cir-safety.org/sites/default/files/cucum032012tent.pdf. (39) Holloway, P. J. Surface factors affecting the wetting of leaves. Pestic. Sci. 1970, 1, 156−163.

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DOI: 10.1021/acs.jafc.7b01998 J. Agric. Food Chem. XXXX, XXX, XXX−XXX