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Agricultural and Environmental Chemistry
Construction and characterization of a novel sustainedrelease delivery system for hydrophobic pesticides using biodegradable PDA-based microcapsules aihua Zou, Ying Yang, Jiagao Cheng, Vasil M Garamus, and Na Li J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.8b00877 • Publication Date (Web): 30 May 2018 Downloaded from http://pubs.acs.org on May 30, 2018
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Journal of Agricultural and Food Chemistry
Construction and characterization of a novel sustained-release delivery system for hydrophobic pesticides using biodegradable PDA-based microcapsules Aihua Zoua∗#, Ying Yanga#, Jiagao Chengb, Vasil M. Garamusc, Na Lid
a
State Key Laboratory of Bioreactor Engineering and Institute of Applied Chemistry,
Shanghai Key Laboratory of Functional Materials Chemistry, School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai 200237, P.R. China b
School of Pharmacy, East China University of Science and Technology, Shanghai
200237, P.R. China c
Helmholtz-Zentrum Geesthacht, Centre for Materials and Coastal Research,
D-21502 Geesthacht, Germany d
National Center for Protein Science Shanghai and Shanghai Institute of
Biochemistry and Cell Biology, Shanghai 201210, P.R. China
∗
Corresponding author
Aihua Zou School of Chemistry and Molecular Engineering East China University of Science and Technology Meilong Road 130 200237 Shanghai, P.R. China E-mail:
[email protected] Tel: +86 64252231 #
These authors contributed equally to this work. 1
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Abstract
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Microcapsule formulations have been highly desirable and widely developed for
3
pesticide’s effective utilization and environmental pollution reduction. However,
4
commercial and traditional microcapsule formulations of lambda-cyhalothrin (LC)
5
were prepared by complicated synthesis and thereby specific organic solvents were
6
needed. In this work, LC was encapsulated into a versatile, robust and biodegradable
7
polydopamine (PDA) microcapsule by self-polymerization of dopamine. LC-loaded
8
PDA microcapsules were characterized by transmission electron microscopy (TEM),
9
small-angle X-ray scattering (SAXS) and thermogravimetric analysis measurements
10
(TGA). LC-loaded PDA microcapsules have uniform morphology with nanoscale,
11
decent LC loading content (>50.0%, w/w), good physicochemical stability and
12
sustained release properties. The bioassay against sanitary insect pest (Musca
13
domestica) showed that the bioactivity and long-term efficiency of LC-loaded PDA
14
microcapsules was superior to that of the commercial formulation. All of these
15
results demonstrated that LC-loaded PDA microcapsule could be applied as a
16
commercial LC microcapsule formulation with better environmental impact and
17
higher effective delivery.
18
Keywords:
19
self-polymerization; sustained release
lambda-cyhalothrin;
pyrethroids;
microcapsule;
20 21 22 2
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polydopamine;
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1. Introduction
25
Pyrethroids(PRYs), such as lambda-cyhalothrin (LC), are the synthetic analogs
26
of natural insecticide pyrethrum discovered in chrysanthemum flowers,1 and have
27
been widely used as insecticides in hygiene as well as for crop protection.2 Because
28
of PRYs’ high effectiveness at low dosages in agricultural situations, they account
29
for around 30% of insecticides applied globally3 and are still expected to be
30
increased compared with organophosphorus and organochlorine insecticides.
31
However, PRYs have been listed by an EU working group as suspected
32
endocrine-disrupting chemicals,4 and many studies have illustrated excessive
33
exposure to PYRs could cause liver damage.5 Besides, its poor solubility in aqueous
34
media limits the application of pesticide formulations with high efficacy and safety.6
35
Therefore, it is extremely necessary to mitigate the above impacts and reduce the
36
associated risk.
37
LC, as the model pesticide of PRYs, its conventional formulations mainly involve
38
emulsifiable concentrate (EC), wettable powders (WP), microemulsion (ME), and
39
emulsion in water (EW). These formulations have some problems including dust
40
drift, rain fastness, and poor dispersion, which will further cause low pest control
41
efficacy and severe environmental pollution.7,8 More importantly, conventional
42
formulations usually experience a rapid decrease in effect after the early burst
43
release of active ingredient which has induced serious concerns on ecological 3
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environment.9 Currently, microcapsule has been developed and commercialized as
45
controlled delivery system. The loading of pesticide into microcapsule could
46
improve pesticide utilization by the continuous and stable release of pesticide for a
47
specified period of time, which also would result in the long-term pesticide validity,
48
the decrease of pesticide application frequency and environmental pollution. 10-13
49
Moreover, the encapsulation of LC in microcapsule can kept LC unaffected by the
50
external environment, which consequently enhance the physicochemical stability of
51
the active ingredients.14,
52
For the microencapsulation of active ingredient, the paramount problem is
53
selecting environmentally friendly and biodegradable wall materials, and the
54
polymer carriers have aroused evolving interests. Polymers, including octyl-grafted
55
amphiphilic alginate-amide derivative (OAAD),15 polyacrylamide,16 chitosan,17 and
56
polylactide (PLA),18 have been widely applied in pesticide delivery systems.
57
Polydopamine (PDA), inspired by the composition of adhesive proteins in mussels,
58
is a fascinating and natural material with outstanding properties.19,20 Many different
59
methods have been utilized for the assembly of DA (dopamine) on various templates
60
by the spontaneous oxidative polymerization. Hard templates, such as silica (SiO2)
61
particles,21 polystyrene (PS) microspheres,22 calcium carbonate (CaCO3) particles,23
62
and magnetic nanoparticles particles24,25 have been used as sacrificial templets. On
63
the contrary, emulsion droplets, such as dimethyldiethoxysilane (DMDES) emulsion
64
system, can be used as soft templates as well.26,27 However, as DA can 4
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self-polymerize in a weekly alkaline solution (pH = 8.5), soft templates have
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restricted its application for the pesticides that tend to hydrolyze in alkaline
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medium.27 More importantly, conventionally emulsions are generated by surfactants
68
which may cause foam problems in further applications.
69
Herein, LC-loaded PDA microcapsules are prepared by the spontaneous oxidative
70
polymerization of a dopamine solution on silica particles, followed by removal of
71
the template to form microcapsules. Compared with traditional commercial LC
72
microcapsule formulations, the LC-loaded PDA microcapsule is free of organic
73
solvents and surfactants and is based on biodegradable material. The structure, LC
74
loading content, sustained release, and insecticidal biological assays of LC-loaded
75
PDA microcapsule are investigated (Figure 1) in this study, to our best knowledge
76
the first time. Results show that the versatile and robust microcapsules display
77
decent loading content, excellent stability and controlled-release behavior as well as
78
good biological activeness on sanitary insect pest. Therefore, it is assumed that this
79
LC-loaded PDA microcapsule is more environmental friendly for further exploration
80
as a commercial LC microcapsule formulation.
81
2. Materials and Methods
82
2.1 Materials
83
Lambda-Cyhalothrin (LC, >95%) were kindly provided by Yangnong Chemical
84
Co., Ltd. (Yangzhou, China). Dopamine hydrochloride (DA, ≥99%) was from
85
Sigma-Aldrich Company. Tris- (hydroxymethyl) aminomethane (TRIS), tetraethyl5
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orthosilicate (TEOS), N, N-Dimethylformamide (DMF), hydrofluoric acid (HF),
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ammonium fluoride (NH4F), and ammonium hydroxide (NH3H2O) were from
88
Shanghai Titan Scientific Co., Ltd. All other chemicals were of analytical grade
89
without further purification.
90
2.2 Preparation of the LC-loaded PDA microcapsule
91
Blank PDA microcapsules were formed using layer-by-layer (LBL) assembly
92
method that was firstly described by Frank Caruso et al.21 50 mg silica particles
93
were dispersed in 20 mL 10 mM Tris-HCl buffer solution (pH= 8.5); subsequently,
94
40 mg dopamine(DA) was added under constant agitation for 24 hours at room
95
temperature. The preparation of silica particles was also investigated (Supporting
96
Information). PDA film was deposited on silica particles by the oxidative
97
self-polymerization of dopamine.19,21,22 PDA capsules were then obtained by etching
98
the SiO2 from the PDA-coated silica particles with 2 M HF/8 M NH4F solution (pH
99
= 5). The precipitate was centrifuged (6000 rpm) and washed at least thrice with
100
deionized water, and then dried under vacuum at 40 °C for 12 h.
101
The blank and dry PDA microcapsules were then dispersed in DMF with LC
102
dissolved in and stirred for 24 hours to obtain LC-loaded PDA microcapsules. The
103
precipitate was centrifuged and washed with deionized water thrice to remove
104
unentrapped and resuspended pesticide, and then dried under vacuum at 40 °C for 12
105
h to get LC-loaded PDA microcapsules.
106
2.3 Characterization of PDA microcapsule 6
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The morphology and structure of PDA microcapsule were determined by
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Transmission electron microscopy (TEM) using JEM-1400 electron microscope
109
(JEOL, Japan).
110
Small angle X-ray scattering (SAXS) provides statistically relevant information
111
on internal structure of mesoporous materials in solution during the different steps
112
from formation of carrier to the loading with active compound.28-31
113
The mean or global features of blank PDA microcapsule and LC-loaded PDA
114
microcapsule were evaluated SAXS data collected at beamline BL19U2 of the
115
National Center for Protein Science Shanghai at Shanghai Synchrotron Radiation
116
Facility. Both samples were dispersed in water at low concentration. The detecting
117
range of momentum transfer q (q = 4π sin θ/λ, where θ is half of the scattering angle)
118
was 0.002-0.5 Å−1 by setting the sample-to-detector distance. Scattered X-ray
119
intensities were detected by a Pilatus 1M detector (DECTRIS Ltd).
120
The thermal stability of LC-loaded PDA microcapsule was measured by
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thermogravimetric analysis (PerkinElmer Pyris Diamond TG/DTA). It was
122
performed by heating the specimens from 40 to 800 ℃ at 10 ℃/min in air flow (100
123
mL/min).
124
2.4 Lambda-Cyhalothrin loading content
125
To determine the amount of LC loaded in the microcapsules, the content of the LC
126
loading was tested as follows: a certain amount of LC-loaded PDA microcapsules
127
was suspended in ethanol solution and sonicated for 30 min to destroy the 7
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microcapsules structure, making all the loaded LC dissolved in ethanol solution. The
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concentration of LC was determined by UV-vis spectroscopy. The calibration curve
130
of absorbance versus LC concentration was plotted in Supporting information. LC
131
loading content was calculated as the following equation:
132
LC loading content =
133
2.5 In vitro release of lambda-cyhalothrin from LC-loaded PDA microcapsule
× 100%
(1)
134
The in vitro release behavior of LC from LC-loaded PDA microcapsule in
135
different release medium was investigated. A certain amount of LC-loaded PDA
136
microcapsules was added separately to ethanol solution, 50% ethanol/water (50:50,
137
v/v) mixture, and 45% ethanol/water (45:55, v/v) mixture under magnetic agitation
138
at ambient temperature. 4.0 mL samples were removed at predetermined intervals,
139
and the same volume fresh medium was added. The collected samples were
140
centrifugated (6000 rpm) to obtain the supernatant of the mixture, and the amount of
141
released LC was quantified by UV-vis spectrophotometer analysis. The calibration
142
curve of absorbance versus LC concentration was plotted in Supporting information.
143
All experiments were conducted at room temperature (25 ℃).
144
2.6 Insecticidal biological assays
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2.6.1Insecticidal activity against sanitary insect pest (Musca domestica)
146
A bioassay of LC-loaded PDA microcapsules against sanitary insect pest, musca
147
domestica, was evaluated according to the method described in the previous report32
148
using a commercial formulation as control. The LC- loaded PDA microcapsules 8
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were dispersed in water with Tween 80 as wetting agent and the concentration of
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800 mg/L was considered for the present study. Two glass plates (200 mm × 200 mm)
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with nonabsorbent surface were treated with 0.5 mL insecticide formulations
152
separately and dried by airing. For each glass forced-exposure device, 20 individuals
153
were introduced after a mild anesthesia with ethyl ether; the devices were then put
154
on the glass plates when the individuals resumed normal activities. The number of
155
dead individuals was recorded every minute until the completion of 20 minutes. For
156
evaluation, three replicates were carried out. Evaluation were made on a dead/alive
157
basis, toxicity regression equations, half knock-down time (KT50), and confidence
158
limits were calculated by Origin software. 18 The toxicity regression equation was
159
given as below:
160 161
Y = bX + a
(2)
Where Y is the mortality rate of treated group. X is the logarithm of time. KT50
162
means the time when the mortality rate of the treated group was 50%.
163
2.6.2 Skin irritation test
164
In order to investigate the opportunities for safe application,33 the skin irritation
165
experiment of LC-loaded PDA microcapsules was conducted. Considering people
166
usually wash up after the pesticide application procedure, so the time of applying
167
pesticide is less than 4 hours, and the skin irritation within 4 hours is pivotal. 0.03 g
168
LC-loaded PDA microcapsules and the commercial formulation were diluted by 40
169
times and then were applied to the back of the hand (2 cm ×3 cm) to observe the 9
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skin irritation within 4 hours, respectively.
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3. Results and discussion
172
3.1 Optimization of LC-loaded PDA microcapsule
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As described by Feng Zhou et al., DMF is a good dispersing solvent for PDA MC.
174
And DMF has an appropriate dielectric constant, which resulting in the occurrence
175
of a chemical potential gradient for LC loading into PDA MC.22 Therefore, DMF
176
was chosen as the solvent for the preparation of LC loading into PDA MC, as
177
illustrated in Figure 1.
178
In order to optimize the formulation of LC-loaded PDA microcapsule, the effect
179
of LC concentration, the volume of LC solution, and the amount of added blank
180
PDA microcapsules on the LC loading were studied. The details were evaluated in
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Table 1. As shown in Table 1, the LC concentration was changed from 10.0 to 50.0
182
mg/mL with a distinct increase in LC loading content from 26% to 48%. Under the
183
same LC concentration (50 mg/mL) and blank PDA microcapsule amount (30 mg), a
184
decrease in LC loading content from 48% to 30% was observed with the volume
185
change of LC solution from 45.0 to 10.0 mL. With the increase of the amount of
186
blank PDA microcapsules from 20 to 50 mg, the loading content of LC existed a
187
reduction from 53% to 43%. From Table 1, it can be concluded that the desired LC
188
loading content (>50%) can be achieved with relative high LC concentration (30-50
189
mg/mL), moderate LC solution volume (35-45 mL) and blank PDA microcapsules
190
amount (20-40 mg). And the LC loading content of these LC-loaded PDA MC 10
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almost kept the same after 30 days, which revealed a good stability over time.
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Therefore, No.9 formulation was chosen for further study.
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3.2 Morphology and structure characterization of PDA microcapsule
194
TEM images of PDA microcapsule were determined by using JEM-1400 electron
195
microscope. As shown in Figure 2a and 2b, the dark part (core) was the silica
196
particle and the light part (shell) was deposited PDA with a thickness of 20-30 nm.
197
After removing the silica core by HF/ NH4F solution, the blank PDA capsules were
198
obtained (Figure 2c, 2d). As shown in Figure 2c and 2d, the PDA microcapsules
199
with a diameter of 300-400 nm were uniform with intact shells, confirming the
200
successful preparation of blank PDA microcapsules. Then LC were loaded in the
201
blank microcapsules, and the morphology and structure of LC-loaded PDA MC were
202
same as the blank MC.
203
The rearrangement of PDA microcapsules after LC loading was determined by
204
SAXS. Figure. 3 showed the relative scattering intensity (I) of blank PDA
205
microcapsule and LC-loaded PDA microcapsule as a function of the scattering
206
vector q (Supporting information) The internal of scattering vectors corresponds to
207
studied objects of length scale from 4-310 nm (2π/qmax- 2π/qmin).34 There are no
208
Bragg diffraction peaks at scattering patterns that points on absence the long-range
209
order in the system. Instead of Bragg peaks the maximum in the low q range has
210
been observed, indicating that there is repulsive interaction between the
211
microcapsules in both of the blank and LC-loaded PDA microcapsule system. The 11
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peak position is connected with distance between the microcapsules in first
213
approximation as 2π/q (q is position of maximum),35,36 and they were 150 nm (blank
214
MC) with qmax = 0.00414 nm-1 and 130 nm (LC MC) with qmax= 0.00468 nm-1
215
separately. Loading with LC resulted in decreasing distance between PDA MC due
216
to decreasing repulsion between microcapsules. It could be explained that part of LC
217
was located at the surface of PDA MC.
218
The linearity of the log I-log q scattering profile revealed the fractals property of
219
the PDA MC. As shown in Figure 3, the α (the absolute value of slope) of scattering
220
intensities for both samples for q > 0.03 were 4.95±0.35 (blank MC) and 4.67±
221
0.38 (LC MC). Because both of the α values for two samples were larger than 4
222
(diffuse interface), there was penetration of solvent (i.e. water, the dispersion
223
medium) into the surface of microcapsules (i.e. the shell).37 And after loaded with
224
LC, the α value was decreased, meaning that the extent of penetration was
225
decreased;37 it further confirmed once more that part of LC was loaded on the
226
surface of the microcapsules.
227
3.3 Thermal stability of LC-loaded PDA microcapsule
228
The thermal stability of blank PDA microcapsule and LC-loaded PDA
229
microcapsule were systematically evaluated by thermogravimetric analysis (TGA) in
230
air flow. Figure 4a showed that the thermal degradation temperature at 5% weight
231
loss (T5%) of LC-loaded PDA microcapsule was around 200 ℃, which is slightly
232
higher than that of blank PDA microcapsule (170 ℃). The higher T5% of LC-loaded 12
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PDA microcapsule could be ascribed to the effect of LC (decomposition temperature
234
275 ℃, ) which slowing down the degradation of PDA microcapsule to some extent.38
235
To get the differential thermogravimetry analysis (DTG) peak temperature (the
236
temperature at maximum weight loss rate), the DTG curves39 were demonstrated in
237
Figure 4b and 4c. For LC-loaded PDA microcapsule (Figure 4c), there presented a
238
sharp peak (around 250 ℃) of main degradation ahead of a low shoulder peak,
239
while this phenomenon was in opposite to the result of blank PDA microcapsule
240
(Figure 4b). Combined with Figure 4a, the sharp peak (around 250 ℃) of LC-loaded
241
microcapsule was considered as the result of a combination of both PDA and LC
242
degradation.38 The DTG curves were in consistence with the TG curves, which
243
demonstrated together the successful preparation of LC-loaded PDA MC with good
244
thermal stability.
245
3.4 In vitro release behavior of lambda-cyhalothrin from LC-loaded PDA
246
microcapsule
247
The release behaviors of LC from the LC-loaded PDA microcapsules were
248
studied in different solvents (Figure 5), such as ethanol, 50% ethanol aqueous
249
solution, and 45% ethanol aqueous solution. The profiles indicated that the lower the
250
ethanol concentration was, the slower the release rate of microcapsules was. LC
251
release was fastest in ethanol, and reached release equilibrium after 30 min.
252
However, in 50% and 45% ethanol aqueous solution, the equilibriums were achieved
253
after 12 hours and 24 hours, respectively. 13
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The loading and release behavior are both primarily determined by the properties
255
of the microcapsules, the gradient of chemical potential across the capsules, the
256
nature of the active ingredient, solvent, and temperature, among other things.22,40-43
257
DMF is chosen as the solvent in the preparation of LC-loaded PDA MC, and the
258
loading efficiency is above 50%, which could be because DMF is a good dispersing
259
medium for PDA MC and also has an appropriate dielectric constant, resulting in the
260
presence of a chemical potential gradient, which finally propelled LC loading.22,44,45
261
In addition, there exists hydrogen bonds between LC and the catechol groups of
262
PDA. In ethanol, the LC inside the LC-loaded PDA microcapsules leads to a
263
concentration gradient across the wall, and as a consequence, high osmotic pressure
264
derives within the system; what’s more, compared with DMF, there is strong
265
hydrogen bonding between LC and ethanol. Therefore, the release of LC from
266
microcapsules is supposed to be easy in ethanol solution. Also considering the
267
solubility difference of LC in ethanol, 50% ethanol aqueous solution, and 45%
268
ethanol aqueous solution, the release rate was decreased with the decreased LC
269
solubility in these solvents46 The release profiles of LC in above solvents
270
demonstrated the sustained-release properties of LC-loaded PDA microcapsules;
271
more importantly, it provided theoretical basis for further study of LC-loaded PDA
272
microcapsule suspension.
273
3.5 Insecticidal biological assays
274
With the purpose of demonstrating the applicability of the LC-loaded PDA 14
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microcapsule as a favorable formulation in public hygiene and agriculture, an
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insecticidal biological assay of this formulation against Musca domestica was
277
studied with a commercial LC microcapsule formulation as control. Haixin Cui et
278
al.18 have organized the bioassay tests of LC-loaded polylactic microcapsules against
279
plutella xylostella; the microcapsule (0.68 µm) had the lowest half lethal
280
concentration value (LC50, around 25 µg/mL) among the other two microcapsules,
281
suggesting that efficacy of pesticide gradually increased with the decrease of the
282
microcapsule size.
283
Compared with the above formulations, as indicated in Figure 6 and Table 2, both
284
of the commercial LC microcapsule formulation and the LC-loaded PDA
285
microcapsule had a high 24 h mortality around 100%, but the LC-loaded PDA
286
microcapsule had a lower KT50 (half knock-down time)value, suggesting an
287
advantage of high efficiency. Both samples were treated against Musca domestica
288
after 30 days storage. The results showed that the KT50 value of commercial
289
microcapsule experienced a large increase while the one of the LC-loaded PDA
290
microcapsule presented a slight rise, implying that the LC-loaded PDA microcapsule
291
had an improvement in long-term validity when compared with the commercial one.
292
The high efficacy and long-term validity of LC-loaded PDA MC could be explained
293
by the nanoscale formulation and the adhesion of PDA microcapsules on the surface
294
of pests, which can improve the permeability and absorptivity of pesticide.47,48
295
Polydopamine is inspired by the composition of adhesive proteins in mussels. Phillip 15
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296
B.
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surface-adherent polydopamine films onto a wide range of inorganic and organic
298
materials.19 More importantly, there were rapid release (absorbed on the PDA MC
299
surface) and sustained release (loaded into the PDA MC) of LC in practical
300
application, and this combined release profile also gave the LC-loaded PDA MC
301
formulation fine efficacy and long-time validity.
Messersmith
has
used
dopamine
self-polymerization
to
form
thin,
302
According to the skin irritation test, both of the samples were diluted by 40 times,
303
and had no irritate to hands after 1 hour’s contact, LC-loaded PDA microcapsule
304
formulation had slight irritate to hands after 3 hours contact, while the control group
305
still had no irritation. Compared with the nanoscale of LC-loaded PDA MC, the
306
controlled commercial formulation was micro-sized, resulting in the difficulty of
307
absorption through the skin. Considering that most sold commercial LC
308
microcapsule formulations presented irritation after 1 hour’s contact, the LC-loaded
309
PDA microcapsule was thought to have been improved in irritation, which could be
310
attributed to its biocompatible material and free of hazardous organic solvents.
311
There was a connection between the irritation and pesticide efficacy, and it was
312
supposed that higher pesticide efficacy leaded to higher irritation.49 Therefore, the
313
results of skin irritation test had confirmed that the LC-loaded PDA microcapsule
314
had stroked a good balance between pesticide efficacy and irritation compared with
315
the commercial LC microcapsule formulations.
316
In summary, PDA microcapsules were used as a carrier for LC via the assembly 16
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of DA on the template. The PDA microcapsule with proper size and surface property
318
was versatile, robust and biodegradable, also it eliminated the requirement of
319
considerable hazardous organic solvent and surfactants used by common
320
commercial formulations. The results of TEM and SAXS showed the uniform
321
morphology and hollow structure. Furthermore, the microcapsules exhibited
322
superior bioactivity and long-term validity than the commercial formulation, which
323
should be explained by the sustained-release properties and the adhesion of PDA
324
microcapsule on the surface of pests. It is envisioned that such an environmentally
325
friendly microcapsule formulation using biodegradable material for LC shows great
326
potential for wide applications in public health & agriculture. Further research has
327
been conducted to make the LC-loaded PDA microcapsule a well-dispersed
328
microcapsule suspension with decent suspending rate and pourability.
329 330
Abbreviations Used
331
PDA, polydopamine; LC, lambda-cyhalothrin; LC-PDA MC, LC-loaded PDA
332
microcapsule; TEM, transmission electron microscopy; SAXS, small-angle X-ray
333
scattering; PRYs, pyrethroids; EC, emulsifiable concentrate; WP, wettable powders;
334
ME, microemulsion; EW, emulsion in water; OAAD, octyl-grafted amphiphilic
335
alginate-amide derivative; PLA, polylactide; DA, dopamine; PS, polystyrene;
336
DMDES,
337
N-dimethylformamide; KT50 , half knock-down time; TGA, thermogravimetric
dimethyldiethoxysilane;
LBL,
layer-by-layer;
17
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DMF,
N,
Journal of Agricultural and Food Chemistry
338
analysis; T5%, the thermal degradation temperature at 5% weight loss; DTG, the
339
differential thermogravimetry analysis; LC50, half lethal concentration value.
340
Acknowledgement
341
Funding
342
The present study was supported by grants from the National Key Research and
343
Development Plan (No. 2017YFD0200306), the National Natural Science
344
Foundation of China (No. 31200617), and Knowledge Innovation Program of CAS
345
(Grant No. 2013KIP103).
346
Supporting Information Description
347
Additional information on preparation of silica particles, SAXS results and
348
standard curves of LC in different solvents.
349
References
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Table1 Optimization of LC-loaded PDA microcapsule formulation No.
LC conc.
vol. of LC solution
MC amt.
LC loading content
(mg/mL)
(mL)
(mg)
(%)
1
10.0
45.0
30.0
26
2
20.0
45.0
30.0
28
3
30.0
45.0
30.0
47
4
40.0
45.0
30.0
48
5
50.0
45.0
30.0
48
6
50.0
35.0
30.0
45
7
50.0
15.0
30.0
37
8
50.0
10.0
30.0
30
9
50.0
45.0
20.0
53
10
50.0
45.0
40.0
49
11
50.0
45.0
50.0
43
Table 2 Toxicity regression equations of the formulations and the 95% confidence interval of the KT50 values formulation
regression equation
95% confidence interval
cml/1d
Y = 1.915X - 1.117
6.18 - 7.90
cml/30d
Y = 2.791X - 2.166
8.73 - 9.30
LC-PDA MC/1d
Y = 1.645X - 0.817
4.84 - 8.26
LC-PDA MC/30d
Y = 2.976X - 1.994
6.12 - 7.74
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Figure 1. Schematic representation of the preparation of LC-loaded PDA microcapsule and their application in sanitary insect pest.
Figure 2 TEM images of PDA coated silica particles (a,b) and blank PDA microcapsules (c,d) ( b, d:
zoom of up to 2× was performed to visualized the
details for the PDA coated silica particle and blank PDA MC, respectively . )
a
c
b
d
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Figure 3 SAXS curves of blank PDA microcapsule and LC-loaded PDA microcapsule
Figure 4 (a) TG curves of blank PDA microcapsule and LC-loaded PDA microcapsule in air flow; (b) DTG curves of blank PDA microcapsule (c) DTG curves of LC-loaded PDA microcapsule in air flow
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Figure 5 Release profiles of LC from LC-loaded PDA microcapsules in different solvents. Data are presented as the mean ± standard deviation (n = 3)
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Figure 6 The KT50 values and 24h mortality of LC-loaded PDA microcapsule formulation and the commercial LC microcapsule formulation
TOC Graphic
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