Adhesive and Stimulus-Responsive Polydopamine-Coated Graphene

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Adhesive and stimuli-responsive polydopaminecoated graphene oxide system for pesticide loss control Yujia Tong, Leihou Shao, Xianlei Li, Jianqing Lu, Huiling Sun, Sheng Xiang, Zhenhua Zhang, Yan Wu, and Xuemin Wu J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b05500 • Publication Date (Web): 27 Feb 2018 Downloaded from http://pubs.acs.org on February 28, 2018

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Journal of Agricultural and Food Chemistry

Adhesive and stimuli-responsive polydopamine-coated graphene oxide system for pesticide loss control

Yujia Tong 1, Leihou Shao2, Xianlei Li 2, Jianqing Lu 2, Huiling Sun 2, Sheng Xiang 1, Zhenhua Zhang 1, *, Yan Wu 2,* and Xuemin Wu 1, * 1

College of Science, China Agricultural University, 2 Yuanmingyuan West Road, Beijing

100083, China [email protected] [email protected] 2

CAS Key Laboratory for Biomedical Effects of Nanomaterials & Nanosafety, CAS Center

for Excellence in Nanoscience, National Center for Nanoscience and Technology (NCNST), 11 Beiyitiao, Zhongguancun, Beijing 100190, China [email protected]

1

ACS Paragon Plus Environment


1

Abstract:

2

Pesticide carrier system is highly desirable for achieving effective utilization and loss

3

reduction of pesticides. In order to increase utilization and enhance pesticides adhesion on

4

harmful targets, adhesive and stimuli-responsive nanocomposites were prepared using

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graphene oxide (GO) and poly-dopamine (PDA). The results demonstrated that graphene

6

oxide with PDA layer had a high hymexazol loading capacity. Release curve of hymexazol

7

from nanocomposites showed the release was NIR laser dependent and pH dependent.

8

Adhesion performance investigation demonstrated Hy-GO@PDA had more hymexazol

9

persistence than hymexazol technical solution after simulative rainwash experiment and it

10

also had more hymexazol residue than hymexazol solution with surfactant under high

11

concentration. At last, bioactivity of the prepared hymexazol loaded nanocomposites was

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measured against Fusarium oxysporum.sp.cucumebrium Owen and it showed similar

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inhibition activity with hymexazol technical. All these revealed that GO with PDA layer could

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serve as pesticide carrier to solve low utilization and wash-off problems especially for

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water-soluble pesticides.

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Keywords: Hymexazol; Graphene oxide; Poly-dopamine; Loss control; Controlled

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release

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1. Introduction

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Pesticides is widely used to protect crop from diseases, weeds and insects. Constantly

20

increasing dosage of pesticides was applied to satiate the greater demand of food supply.1

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While owing to their leaching, volatilization and runoff, only a small amount of pesticides

22

reaches the harmful targets and the others are great risks to environment and human health.2, 3

23

Advanced multifunctional formulation technology is an effective way to solve these

24

problems. Many materials like organic polymers, inorganic supports and bio-sourced matrices

25

were reported providing pesticides or fertilizers high stability, long-acting and high leaf

26

persistence in previous works.4-10 All these works have their advantages but things cannot be

27

satisfactory to all sides. Most of them providing only a single function to solve the efficiency

28

problem which limit their applications. Thus facile multifunctional approaches to control the

29

loss of pesticides and enhance the utilization efficiency are still highly desired.11

30

Poly-dopamine (PDA), as a mussel-inspired polymer, has photo-thermal effect,

31

film-forming ability and adhesion decoration properties. These features make PDA a good

32

candidate for achieving multifunction in pesticide carrier system, such as controlled release

33

and adhesion improvement.4,

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solid/liquid or liquid/liquid surface in alkalescence aqua solution, which limits its application

35

in water-soluble pesticides.15 Most of the reports about PDA loading pesticides were limited

36

on hydrophobic ones.16, 17 To our knowledge, the reports about multifunctional formulation of

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PDA on water-soluble pesticides were scarce. Compared to hydrophobic pesticides,

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water-soluble pesticides formulations are easier to handle and have less harmful organics.18

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Whereas they are easy to be wash-off which lead to low utilization efficiency and

12-14

However, PDA can only form film onto a variety of

3



40

environmental pollution. Therefore, the development of new formulation to prevent

41

water-soluble pesticides wash-off is desired. Following our works on developing pesticide

42

carrier systems,18-22 we designed to introduce a water insoluble medium to load pesticide

43

before PDA modification, achieving water-soluble pesticides loaded PDA related

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formulation. Graphene oxide (GO) is a kind of carbon allotrope with planar structure. It is

45

water insoluble and can absorb organics owing to its large surface areas, hydrogen bonding

46

and π-electron system.23,

47

modification on its surface.25-27 Consequently, we introduced graphene oxide to absorb

48

water-soluble pesticides then modified it with PDA, aiming at pesticide loading, controlled

49

release and adhesion decoration. Many researches have reported GO and PDA system,

50

achieving multiple applications in green synthesis and molecular imprint.28-31 Compared to

51

PDA system made by emulsion interfacial-polymerization, we valued synergistic

52

photothermal effect with PDA of GO and no harmful organic solvent or surfactants addition

53

in the system.

24

Many studies reported its various application by multifarious

54

Hymexazol was popularly used on various diseases caused by fungi,32 easy-washed-off

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of which by rain is still an unsolved issue. In this report, hymexazol was used as a model

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loaded in GO@PDA system. Morphology was investigated by transmission electron

57

microscopy (TEM). Pesticide loading and adhesion residue was measured by high

58

performance liquid chromatography (HPLC). Dynamic contact angle was measured by

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contact angle meter. After characterization of photothermal effect, release behavior of

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hymexazol from GO and PDA system was investigated. At last, bioactivity of the prepared

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nanocomposite was tested against Fusarium oxysporum.sp.cucumebrium Owen. All the 4


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experiments were perfumed to represent a multifunction composite with controlled release

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and enhanced adhesion, providing a solution for high utilization and low loss of

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water-soluable pesticides.

65 66

2. Method

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2.1. Materials

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Graphene oxide (GO) was obtained from Nanjing XFNANO Materials TECH Co.,Ltd.

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Hymexazol at a purity of 98% (original pesticide) was obtained from Zhejiang Heben

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Technology Co., Ltd. (China). Dopamine hydrochloride at a purity of 98+% was provided by

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Ark Pharm Inc. Methanol at HPLC grade were supplied by Thermo Fisher Scientific Inc.

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(USA). (Tris) buffer was obtained from Beijing Leagene Biotech. Co., Ltd. (Beijing, China).

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2.2. Preparation of hymexazol loaded graphene oxide with poly-dopamine coating

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(Hy-GO@PDA)

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Hymexazol was loaded in GO by absorption then dopamine polymerization happened on

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the surface of GO. Briefly, a portion of hymexazol (2,4,8,10,12,15,20,30,40,50 mg) was

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added in 5mL GO solution (2mg/mL). Centrifuge tubes with the mixed solutions were under

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moderate shaking using an orbital shaker incubator (Yate Co., Jiangsu Province, China) at

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150 rpm for 24h. Then 1M Tris-HCl was added, making the reaction solution as 0.01M

81

Tris-HCl (pH 8.5). Then a portion of dopamine hydrochloride (GO/ dopamine hydrochloride

82

= 3:1) was added. The mixture was agitated at room temperature for 6h. Free pesticide was

83

removed by centrifugation. 5



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2.3. Characterization of Hy-GO@PDA

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Zeta potentials of the Hymexazol, GO, Hy-GO, and Hy-GO@PDA were measured by

87

dynamic light scattering (DLS), on a Zeta Sizer Nano series Nano-ZS (Malvern Instruments

88

Ltd., Malvern, U.K.). Each solution/dispersion was diluted at proper concentration and

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measured in triplicate. The fluorescence spectra of GO and Hy-GO@PDA were measured by

90

LS 55 fluorescence spectrometer (PerkinElmer, Fremont, CA). Morphological examination of

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Hy-GO@PDA was performed by transmission electron microscopy (TEM) (HT7700, Hitachi

92

Ltd.,Tokyo, Japan) and scanning electron microscope (Hitachi, S-4800). The samples were

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dried on copper grids and silicon wafer respectively for observation.

94 95

2.4. Determination of hymexazol loading capacity of GO@PDA

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Supernatant of Hy-GO@PDA was filtered and measured by high-performance liquid

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chromatography (HPLC, Shimadzu) with an ultraviolet detector. The determination of

98

hymexazol was performed on a Spuril-C18 column (4.6 mm×250 mm, 5 mm, Dikma

99

Technologies Inc., China) with methanol–water (70/30, v/v) as the mobile phase. The sample

100

(10 µL) was injected into the HPLC system with a constant flow rate of 1.0 mL min-1 under

101

212 nm wavelength. Adsorbing capacity was calculated as follows: adsorption capacity

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(mg/mg) = (initial quantity of hymexazol – quantity of hymexazol in supernatant) / quantity

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of GO; adsorption percentage (%) = 100% (initial quantity of hymexazol – quantity of

104

hymexazol in supernatant) / initial quantity of hymexazol.

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2.5. Photothermal Heating Effect of Hy-GO and Hy-GO@PDA.

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To determinate the photothermal heating effects of Hy-GO@PDA, different

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concentration of Hy-GO@PDA dispersion was irradiated by an 808 nm laser (1.5 W/cm2,

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Beijing Laserwave Optoelectronics Technology Co., Ltd.). The changes in temperature were

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measured. Hymexazol solution and Hy-GO dispersion was applied as control groups. The

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temperatures of solutions were monitored by an infrared thermal imaging camera (Ti27,

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Fluke) for 10 minutes.

113 114

2.6. In Vitro Release Experiment

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To evaluate the release behavior of hymexazol from Hy-GO@PDA, a dialysis method

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was used.33 Briefly, a portion of 2 mL Hy-GO@PDA dispersion was added into a dialysis bag

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which molecular weight cutoff was 3500 Da (Mym Biological Technology Company

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Limited). Then the dialysis bag was immersed in 20 mL of different solutions (pH 5.0, 7.0,

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9.0) in centrifuge tubes. Furthermore, some dialysis bags were dialyzed against 20 mL

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solution with or without exposure to 808 nm laser irradiation (1.5 W/cm2) for 5 min. All the

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centrifuge tubes were vibrated at 150 rpm. A 1mL portion of supernatant was sampled at

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different intervals and 1 mL of fresh medium was added. The sample solution was filtered

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through a cellulose membrane filter (diameter, 13 mm; pore size, 0.22 µm; Dikma

124

Technologies Inc.) and then injected into the HPLC system to measure the concentration.

125 126

2.7. Pesticide persistence measurement

7



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Pesticide persistence measurement was investigated according to a reported method but

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with some modifications.34 The 0.5 mL Hy-GO@PDA dispersion (at hymexazol

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concentration of 1000, 500, 250, 125 mg/L) was dropped on cucumber leaf evenly in a Petri

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dish and naturally dried for uniform time. Then, the dish was put at an angle of 30 degrees

131

from the table and 3.0 mL of deionized water was dropped on the resulting leaf to simulate

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rainwater washing. The washing solution was filtered through a cellulose membrane filter and

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then analyzed by HPLC system. In consideration of surfactant which may be used in

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hymexazol formulation, hymexazol solution with 1% Tween 20 was evaluated as a contract.

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Hy-GO dispersion and hymexazol solution were control groups. Similar experimental process

136

was repeated for control and contract groups. All the experiment was measured in triplicate.

137 138

2.8. Dynamic contact angle test

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In order to study surface property of Hy-GO@PDA dispersion, dynamic contact angle of

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the prepared nanocomposites was measured using Contact Angle Meter (Kruss, DSA-100). A

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portion of 3 µL hymexazol solution, Hy-GO dispersion, Hy-GO@PDA dispersion and 1%

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Tween 20 hymexazol solution were dropped on the platform. Then the droplet profile was

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observed and contact angle was measured for 10 min.

144 145

2.9. In vitro bacteriostatic test

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In this experiment, the fungicidal activity of Hy-GO@PDA against Fusarium

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oxysporum.sp.cucumebrium Owen was determined by the growth rate method.35 Mycelial

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discs (6 mm in diameter) of P. asparagi grown on potato dextrose agar plates were cut from 8


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the margins of the colony and placed on culture medium plates containing different

150

concentrations of hymexazol technical and Hy-GO@PDA (400, 100, 25, 6.25 mg/L). All the

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plates were incubated at 30oC for 7 days and the diameter of mycelial discs was measured.

152 153

2.10. Statistical Analysis.

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Data were expressed as mean standard deviation (S.D.). Statistical analysis was

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determined using Student’s t test and *p < 0.05, **p < 0.01, and ***p < 0.001 were used to

156

show statistical significance.

157 158

3. Results and discussion

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3.1. Preparation and Characterization of Hy-GO@PDA

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The synthesis process of Hy-GO@PDA nanocomposites was illustrated in Figure 1. In

161

this report, we introduced graphene oxide (GO) to PDA system. GO is a kind of popular

162

carbon material and it can be used for organics adsorption and photo-thermal therapy.25, 36

163

Here in this research, GO was used for hymexazol loading, providing a solid liquid interface

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for dopamine polymerization and photo-thermal synergistic effect with PDA. Hymexazol was

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absorbed in GO and self-polymerization of dopamine happened on Hy-GO. The morphologies

166

of Hy-GO and Hy-GO@PDA was illustrated by transmission electron microscope (TEM) and

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scanning electron microscope (SEM) in Figure 1. In TEM images, GO sheets were

168

transparent with some folds, showing a small thickness. After PDA treatment, it was less

169

transparent and smooth, indicating thin PDA layer was successfully adhered on GO sheets.37

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Similarly in SEM images, GO sheet showed smooth appearance and Hy-GO@PDA was 9



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plicated and has more wrinkles. To investigate the changes in surface charge and conform the

172

preparation of the composites, Zeta (ζ) potential analysis and fluorescence spectra was

173

performed in this report (Figure 2). As shown in Figure 2 A, GO displays characteristic

174

absorption peaks at 230nm and 300nm. After hymexazol loading and PDA coating, the

175

characteristic peaks were blue-shifted indicating the PDA coating.38,39

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In figure 2 B, hymexazol (- 4.87 mv) and GO (-39.33 mv) showed negative charge.

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Hymexazol loading decreased the Hy-GO charge to – 42.4 mv slightly. After PDA coating,

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the zeta potential increased to – 30.5 mv. Though zeta potential was increased but stability of

179

nanocomposite was not affected significantly.

180

Pesticide loading was measured through centrifugation. Graphene has large delocalized

181

π-electron system and high surface area which make it suitable for adsorption of heavy metals

182

and organics.40 In previous work, drug could be loaded in GO by π−π stacking and/or

183

hydrophobic interaction.41 In this work, different concentration of hymexazol was incubated

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with GO dispersion. Supernatant with free hymexazol was injected in HPLC to measure the

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concentration. Absorption capacity data was showed in Figure 3. The result (Figure 3 A and

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B) showed that with the increasing concentration of hymexazol, pesticide loading capacity

187

was increasing as well. Hymexazol loading capacity was 1.6 mg/mg GO under the experiment

188

maximum concentration. The adsorption process was found to be spontaneous and

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energetically favorable.36,42 The effect of pH values on hymexazol absorption by GO was

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tested and the results depended on the conditions (Figure 3 C). Under experimental

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conditions, pH effect on hymexazol loading was not significant (p>0.05) when hymexazol

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was at relatively low concentrations. While at relatively high concentrations, hymexazol 10


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loading increased when the pH value of dispersion increased from 4.0 to 8.0. In addition,

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when the ratio of DA/GO were 1/3, 1/2 and 1/1, the hymexazol loading were 0.20, 0.42 and

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1.07 mg/mg GO respectively (hymexazol/GO=3/1).

196 197

3.2. Photothermal Heating Effect

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Photothermal heating effect was widely used in release control.43 When composites

199

exposed to NIR laser, temperature of them increased and had a ripple effect on drug carrier

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system. Here in this pesticide carrier system, phototheral heating effect was used to achieve

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the purpose of light controlled release. In order to investigate the photothermal effect of

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Hy-GO@PDA, changes of temperature were detected after 808nm NIR laser irritation

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(1.5W/cm2). As shown in Figure 4 A and D, Hy-GO@PDA has a higher temperature growth

204

than Hy-GO and hymexazol itself. Dispersion temperatures of Hy-GO@PDA and Hy-GO

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increased rapidly within 10 minutes and reached 40.5 and 50.9 oC respectively. While

206

hymexazol solution only increased to 28.8 oC under the same condition. GO had photothermal

207

heating effect and PDA layer also had obvious NIR absorption and photothermal conversion

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efficiency.44, 45 Both these properties contributed to this result. Furthermore, the influence of

209

concentration (with GO concentration from 0.08 to 2 mg/mL) was studied by monitoring

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temperature changes under the same laser condition (808 nm, 1.5W/cm2). Figure 4 B and C

211

indicated that Hy-GO@PDA showed concentration-dependent and PDA layer-dependent

212

manner.

213

Next, hymexazol release experiment in vitro in pH 5, pH 7 and pH 9 with and without

214

NIR was performed. As shown in Figure 4 E, the release behavior of hemexazol from

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Hy-GO@PDA was pH dependent and NIR laser dependent. About 38%, 48% and 65% 11



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hymexazol released from the nanocomposite in 120 hours. Furthermore, groups treated with

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NIR irradiation exhibited more hymexazol release than groups without irradiation. NIR laser

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irradiation dependent release was due to the bonding change between pesticide and GO.46 In

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addition, pH dependent was due to the different electrostatic interactions between PDA and

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the hymexazol molecules on GO sheet. At low pH, PDA could be protonated and at high pH,

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amino groups of PDA were deprotonated which made PDA negatively charged.16 On the

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other side, hymexazol was negative charged. Thereby, change of pH resulted in electrostatic

223

attraction and repulsion between PDA and hymexazol. Thus, the release of hymexazol could

224

be controlled by pH and NIR laser. As shown in Figure 4 F, the release behavior of

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hemexazol from Hy-GO@PDA was also PDA layer dependent.16 With the increasement of

226

PDA, hymexazol release profiles were reduced. Moreover, the release data were analyzed by

227

fitting Korsmeyer−Peppas model “Mt/M∞ = ktn” (Table 1). All the correlation coefficients

228

(R2) were higher than 0.9. The n values were key parameters from which release mechanism

229

could be inferred. All of the n values were below 0.45 which indicated that diffusion was the

230

main mechanism of Hy-GO@PDA release during the experiment time.47

231 232

3.3. Adhesion Performance Investigation

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The adhesion performance on cucumber leaf of Hy-GO@PDA was investigated under

234

different concentrations of hymexazol. In consideration of surfactants which may be used in

235

practical application of pesticides, hymexazol solution with and without 1% Tween 20 was

236

introduced in the test. Tween 20 was a kind of hydrophilic surfactant and commonly used in

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pesticide formulation. The surfactant could improve wetting and infiltrating of pesticides.

238

Hence, hymexazol solution with Tween-20 and Hy-GO dispersion were used as contract to 12


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evaluate the pesticide residue performance of Hy-GO@PDA. As shown in Figure 5 A and B,

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with the concentration increasing, hymexazol loss of all the groups increased. While the

241

percentage of hymexazol loss decreased. The data showed that hymexazol loss of Hy-GO was

242

less than hymexazol solution. Owing to its irregularly layered lamellar surface and carbon

243

matrix, GO showed a certain extent effects on adhesion on leaf.42 Hy-GO@PDA showed less

244

pesticide loss than the two formers not only because of the irregularly layered lamellar surface

245

of GO, but also the catechol side chain of PDA which made it strongly adhere to surfaces both

246

organic and inorganic.48 As shown in Fig 5 C and D, after Hy-GO@PDA treatment, the leaf

247

was covered by the composites sheets with folds and ripples. Hy-GO@PDA also exhibited

248

less hymexazol loss than hymexazol with 1% Tween 20 under certain high concentration but

249

under low concentration, difference was not significant. This result indicated that GO@PDA

250

nanocomposites increased the adhesion of hymexazol on leaves. Comprised with surfactant, it

251

exhibited less pesticide loss than Tween 20 at certain high concentration. We hold the

252

hypothesis as follows: Tween 20 was a kind of surfactant which could promote madefaction,

253

permeation and deposition of pesticide solution.49-51 Thus a certain extent effect of pesticide

254

loss control was observed. While at high concentration, it might need a certain longer time to

255

permeate and deposit than it at low concentration which made it less efficient under these

256

conditions. Furthermore, pesticide residue on leaves is a comprehensive result and it depends

257

on many factors, such as carrier properties, surface properties and application conditions.

258 259

3.4. Dynamic contact Angle measurement

260

To investigate the adhesion of Hy-GO@PDA, interfacial property was measured by

261

dynamic contact angle measurement. Similarly, Hy-GO dispersion, hymexazol solution with 13



262

and without Tween 20 was measured as contract groups. As shown in Figure 6, contact angle

263

of all groups decreased with time. Contact angle of Hy-GO@PDA dispersion and hymexazol

264

solution was 41o and 62o respectively after 10 minutes. While hymexazol solution with 1%

265

Tween 20 spread quickly and contact angle reached 30o in 10 minutes. The result indicated

266

that GO@PDA carrier could reduce surface tension of hymexazol solution but was not as

267

efficient as Tween 20. Surfactants is widely used in pesticide formulations to lower the

268

surface tension of pesticide diluent. Low surface tension usually signified high spreading

269

ability and high contact area between pesticide solution and leaf.52 While the amount pesticide

270

residue depends on not only the contact angle between solution/dispersion and target. It was

271

not the only and most important factor which influence the pesticide persistence on target.

272

Here for PDA system, more pesticide residue is a result of adhesion and it comes from

273

catechol side chain of PDA which can strongly adheres to both organic and inorganic

274

surfaces.

275 276

3.5. In vitro bacteriostatic test

277

To investigate bioactivity of prepared nanocomposites, the growth method against

278

Fusarium oxysporum.sp.cucumebrium Owen was performed. Hymexazol solution was tested

279

as comparison. The inhibition data and images of Hy-GO@PDA and hymexazol technical

280

after 7 days were summarized in Figure 7. As shown in Figure 7, adhesive nanocomposites

281

Hy-GO@PDA demonstrated almost the same activity (p >0.05) with Hymexazol technical

282

(with GO as control). This result indicated that GO@PDA carrier did not weaken bioactivity

283

of hymexazol. 14


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In summary, Hy-GO@PDA nanocomposites was prepared as a multifunctional system

286

for pesticide controlled release and loss control. The prepared composites showed a high

287

hymexazol loading efficiency. The result of TEM and zeta-potential revealed the morphology

288

of Hy-GO@PDA. NIR laser and pH dependent release of hymexazol from GO@PDA was

289

observed in release study. In further study, adhesion investigation with simulated rainwash

290

was perfumed and hymexazol persistence was much higher when it was loaded in GO@PDA.

291

When compared with surfactant, hymexazol persistence of Hy-GO@PDA was higher than

292

hymexazol solution with 1% Tween 20 under relatively high pesticide concentration. On the

293

other side, contact angle of Hy-GO@PDA was tested and it was smaller than hymexazol

294

solution but not as small as hymexazol with Tween 20 solution. Finally, the bioassay about

295

inhibition activity against Fusarium oxysporum.sp.cucumebrium Owen also showed that the

296

bioactivity of Hy-GO@PDA nanocomposites had no significant difference with hymexazol

297

technical. All of these experiments showed that hymexazol loaded in GO@PDA carrier have

298

controlled release and improved adhesion performance. This new formulation achieved

299

efficient utilization and loss control of pesticide. The study provided a potential solution to

300

reduce pesticides loss and improve application efficiency, especially for hydrophilic

301

pesticides.

302 303 304 305

Acknowledgements This work was supported by The National Key Research and Development Program of China (2017YFD 0200301). The authors declare no competing financial interest. 15



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24


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459

Figure 1. TEM images of Hy-GO (A) and Hy-GO@PDA (B); SEM images of Hy-GO (C)

460

and Hy-GO@PDA (D)

461

Figure 2. (A) Fluorescence spectra of GO and Hy-GO@PDA; (B) Zeta potentials of

462

hymexazol, GO, Hy-GO and Hy-GO@PDA.

463

Figure 3. Hymexazol loading curve of Hy-GO@PDA (A, B) and pH effect on hymexazol

464

absorption by GO (C).

465

Figure 4. (A) Temperature variation curves of the aqueous dispersions of hymexazol, Hy-GO

466

and Hy-GO@PDA exposed to the 808 nm laser at a power density of 1.5 W/cm2 for 10 min.

467

(B) Temperature variation curves of the Hy-GO@PDA disperesion with different

468

concentrations. (C) Temperature variation curves of Hy-GO@PDA with different PDA layer.

469

(D) IR thermal image of hyexazol, Hy-GO and Hy-GO@PDA solution under continuous NIR

470

laser irradiation (1.5 W/cm2) for 10 min. (E) Release curves of Hy-GO@PDA under different

471

conditions. (F) PDA layer effect on hymexazol release.

472

Figure 5. (A) Hymexazol loss quantity and (B) percentage of hymexazol solution, Hy-GO,

473

Hy-GO@PDA and hymexazol solution with 1% Tween 20. (C) Image of cucumber leaf after

474

Hy-GO@PDA treatment (D) Image of blank cucumber leaf.

475

Figure 6. Contact angle images of hymexazol solution, Hy-GO dispersion, Hy-GO@PDA

476

dispersion and hymexazol solution with 1% Tween 20.

477

Figure

478

oxysporum.sp.cucumebrium Owen.

7.

Growth

inhibition

test

of

nanocomposites

25


against

Fusarium


479

Table 1. Constants of fitting Korsmeyer−Peppas model to the release of hymexazol from

480

Hy-GO@PDA under different conditions

conditions

n

lg k

R2

pH 5

0.0998

1.4111

0.9144

pH 7

0.0946

1.5118

0.9014

pH 9

0.1270

1.5657

0.9550

pH 5 + NIR

0.0836

1.5016

0.9161

pH 7 + NIR

0.1235

1.4977

0.9293

pH 9 + NIR

0.1084

1.6463

0.9053

481 482

26


Page 26 of 35

Page 27 of 35

483


TOC Graph:

484

27



Figure 1. TEM images of Hy-GO (A) and Hy-GO@PDA (B); SEM images of Hy-GO (C) and Hy-GO@PDA (D) 84x75mm (300 x 300 DPI)


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Figure 2. Fluorescence spectra of GO and Hy-GO@PDA; Zeta potentials of hymexazol, GO, Hy-GO and HyGO@PDA. 32x12mm (300 x 300 DPI)



Figure 3. Hymexazol loading curve of Hy-GO@PDA (A, B) and pH effect on hymexazol absorption by GO (C). 141x37mm (300 x 300 DPI)


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Figure 4. (A) Temperature variation curves of the aqueous dispersions of hymexazol, Hy-GO and HyGO@PDA exposed to the 808 nm laser at a power density of 1.5 W/cm2 for 10 min. (B) Temperature variation curves of the Hy-GO@PDA disperesion with different concentrations. (C) Temperature variation curves of Hy-GO@PDA with different PDA layer. (D) IR thermal image of hyexazol, Hy-GO and Hy-GO@PDA solution under continuous NIR laser irradiation (1.5 W/cm2) for 10 min. (E) Release curves of Hy-GO@PDA under different conditions. (F) PDA layer effect on hymexazol release. 141x72mm (300 x 300 DPI)



Figure 5. (A) Hymexazol loss quantity and (B) percentage of hymexazol solution, Hy-GO, Hy-GO@PDA and hymexazol solution with 1% Tween 20. (C) Image of cucumber leaf after Hy-GO@PDA treatment (D) Image of blank cucumber leaf. 105x77mm (300 x 300 DPI)


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Figure 6. Contact angle images of hymexazol solution, Hy-GO dispersion, Hy-GO@PDA dispersion and hymexazol solution with 1% Tween 20. 84x70mm (300 x 300 DPI)



Figure 7. Growth inhibition test of nanocomposites against Fusarium oxysporum.sp.cucumebrium Owen. 84x59mm (300 x 300 DPI)


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TOC Graph 47x26mm (300 x 300 DPI)


Adhesive and Stimulus-Responsive Polydopamine-Coated Graphene

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