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Fluorescence determination of omethoate based on dual-strategy for improving sensitivity Cuiping Zhang, Bixia Lin, Yujuan Cao, Manli Guo, and Ying Yu J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b00166 • Publication Date (Web): 28 Mar 2017 Downloaded from http://pubs.acs.org on March 30, 2017

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Title: Fluorescence determination of omethoate based on dual-strategy for improving sensitivity

Full Names of the Authors: Cuiping Zhang, Bixia Lin, Yujuan Cao, Manli Guo, Ying Yu*

Affiliations: School of Chemistry and Environment, Guangzhou Key Laboratory of Analytical Chemistry for Biomedicine, South China Normal University, Guangzhou 510006, P. R. China.

Corresponding author：： Prof. Ying Yu Tel: +86-20-39310382 Fax: +86-20-39310187 E-mail: [email protected]

Present/permanent address：： No. 378 Waihuan West Road, University City, Guangzhou, Guangdong, P. R. China, 510006

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Fluorescence determination of omethoate based on dual-strategy for improving sensitivity 1

Cuiping Zhang, Bixia Lin, Yujuan Cao, Manli Guo, Ying Yu*

2 3

School of Chemistry and Environment, Guangzhou Key Laboratory of Analytical Chemistry for Biomedicine, South China Normal University, Guangzhou 510006, P. R. China. 4 5

Abstract

6

Omethoate is a frequently-used organophosphorus pesticide, the establishment of a sensitive,

7

selective and simple method to determine omethoate is very important for food safety. In this

8

paper, dual-strategy was applied to improve the detection sensitivity of omethoate. The first

9

strategy, graphene quantum dots (GQDs) were doped with nitrogen to increase the fluorescence

10

quantum yield to 30%. By coupling N-GQDs with omethoate aptamer, N-GQDs-aptamer probe

11

was synthesized. The fluorescence of N-GQDs-aptamer probe was turned off by graphene oxide

12

(GO), but recovered by omethoate. Based on this principle, the fluorescence method for detecting

13

omethoate was established with detection limit of 0.041 nM. To further improve the detection

14

sensitivity, fluorescence polarization analysis method was applied as another strategy based on the

15

polarization signal of GQDs. The detection limit was decreased to 0.029 pM by using fluorescence

16

polarization method. The detection limits in this paper were lower than those in other reports. The

17

imaging of omethoate on plant leaves shown the probe could be used for visual semi quantitative

18

determination of omethoate.

19

Keywords: dual-strategy; nitrogen-doped graphene quantum dots; omethoate; fluorescence

20

method; fluorescence polarization

21 22 23 2



24

1. Introduction

25

Organophosphorus pesticide is one of the most commonly used pesticides. The over-use of

26

organophosphorus pesticide has threat to human health and harmful effects on the ecology, so it is

27

very important to develop an effective detection method. Omethoate is an organophosphorus

28

pesticide with the simplest chemical structure. Due to the lack of sensitive luminophore or

29

electrochemical active groups, it is difficult to determine omethoate directly by using conventional

30

optical analysis or electrochemical method. Until now it is still a challenge to establish a detection

31

method with good selectivity, high sensitivity and convenience for the determination of low

32

content of omethoate in complex samples.

33

Most of the reported detection methods for omethoate were gas chromatography1, liquid

34

chromatography2, gas chromatography/mass spectrometry3,4, capillary electrophoresis method5.

35

These methods are often combined with complex separation process such as magnetic separation1,

36

solid phase micro extraction6,7 and molecular imprinting8. Other methods such as electrochemical

37

analysis9,10, Raman spectroscopy11-13, optical analysis method14-18 were also reported for

38

determining omethoate. In the literature about optical analysis, Zhang14 used molecularly

39

imprinted polymer separation and Sun15 used flow injection separation combined with

40

chemiluminescence analysis to establish the omethoate determination method. Pang16 utilized the

41

oxidation of R-DmAChE and indoxyl acetate as substratechans to produce blue products. When

42

organic phosphorus pesticides or carbamate pesticides were present, the R-DmAChE enzyme was

43

consumed and the blue product was reduced. Thus the rapid visualization colorimetric detection of

44

organic phosphorus pesticides and carbamate pesticide were realized. Fluorescence method was

45

popular in the optical analysis. Ji17 reported that the molecular beacon was modified on the surface

46

of gold nanoparticle, and their fluorescence was quenched by gold nanoparticle. When ss-DNA

47

was present and bound to the small peptide of the molecular beacon, the fluorescent group in the

48

molecular beacon was far away from the gold nanoparticle, and the fluorescence was recovered.

49

When the analyte and the ss-DNA were coexistent, the analyte combined to ss-DNA, so the

50

fluorescence intensity of the molecular beacon was recovered partly. Based on the above principle,

51

isocarbophos, profenofos, phorate and omethoate were detected. Liu18 reported the fluorescence of

52

hairpin molecular beacon was quenched by organophosphorus pesticide and ss-DNA binding, and

53

recovered by hairpin molecular beacon and ss-DNA combination. Thus the determination of four 3


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pesticides including omethoate was realized. Although there are some reports on optical analysis

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method for omethoate determination, the sensitivity, selectivity, convenience still need to be

56

improved.

57

In recent years, optical sensor has attracted the attention of researchers. Optical sensor

58

consists of two parts, the optical signal component and the recognition component. To construct

59

optical signal components, in addition to the traditional colored materials and fluorescent dyes, the

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nano materials such as Cd system quantum dots19,20, manganese doped ZnS21, MoS222, carbon

61

dots23,24, silicon dots25 and gold nanoparticle26,27 are used widely. To construct recognition

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components, small molecules28,29, single-stranded DNA22,30 and antibodies24 can be used.

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Fluorescent sensors are the most common optical sensors. They have been constructed

64

successfully to detect all kinds of targets, for example, our group24 had designed fluorescence

65

probe for glyphosate by modifying carbon dots with glyphosate antibodies. After the probe

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combined to glyphosate, the excess probe was removed with glyphosate magnetic beads. Thus a

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sensitive detection method for glyphosate was established. Nowadays, fluorescence polarization

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sensors which is based on the mechanism of the depolarisation of linearly polarised light by

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fluorophore molecules with anisotropy is also used for the targets detection31. Layered

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nanomaterial such as graphene oxide is reported to be suitable for constructing fluorescence

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polarization sensors32.

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In order to establish a sensitive, convenient and rapid optical analysis method for omethoate,

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in this paper, luminescent probe (N-GQDs-aptamer) with recognition function was synthesized

74

and the double strategies of doping nitrogen and fluorescence polarization were used for

75

improving the detection sensitivity. In the first strategy, the quantum yield of N-GQDs was

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increased 30% by doping nitrogen in the synthesis of graphene quantum dots. The fluorescence of

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N-GQDs-aptamer probe was turned off by graphene oxide, but recovered by omethoate. Based on

78

this "off-on" sensor, the fluorescence method for omethoate was established with detection limit of

79

0.041 nM. Because the GQDs had fluorescence polarization signal, fluorescence polarization

80

analysis method was also established with low detection limit of 0.029 pM. The detection limit of

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fluorescence method was about 1000 times of fluorescence polarization method. This meant the

82

fluorescence polarization method could be applied as the second strategy to improve the detection

83

sensitivity for omethoate. By applying the dual-strategy for improving sensitivity, the sensitivity 4



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of detection methods established in this paper was superior to the other methods in previous

85

reports. Furthermore, the probe could be directly used for imaging of residual omethoate on leaves

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surface, the method was simple, quick and had the potential for on-site detection. The detection

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mechanism was shown in Scheme.

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Scheme

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2. Materials and methods

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2.1 Materials and Instruments

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Graphene oxide with thickness of 0.8-1.2 nm was purchased from Nanjing xfnano Mstar

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Technology Ltd. Urea was purchased from Tianjin Damao Chemical Reagent Factory.

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Carbodiimide hydrochloride (EDC·HCl, 98.5%), N-hydroxysuccinimide (NHS, 98%), omethoate

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(99%), NaOH, Na2HPO4·12H2O and NaH2PO4·2H2O were purchased from Aladdin Chemical

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Company. Aptamer (5′-NH2-AAGCT TTTTT GACTG ACTGC AGCGA TTCTT GATCG

96

CCACG GTCTG GAAAA AGAG-3′) was purchased from Shanghai Sangon Biological

97

Engineering Co. Ltd. All chemicals used were of analytic grade or of the highest purity available.

98

Double-distilled water was used throughout the experiments.

99

Fluorescence spectra were obtained using an F-4600 fluorometer with polarizer (Hitachi,

100

Japan) under voltage of 400 V, slit width of 5 nm and scanning speed of 300 nm/min. UV-vis

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absorption spectra were measured with a 2700 UV-vis spectrophotometer (Shimadzu, Japan).

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Transmission electron micrographs were carried out on 2100 HR microscope (Hitachi).

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Fluorescence images were performed with an OLYMPUS IX73 biological fluorescence

104

microscope (Olympus Co. Ltd).

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2.2 Synthesis of N-GQDs

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N-GQDs were prepared using a modified method33. Briefly, 0.0251 g graphene oxide, 40 ml

107

distilled water were added into 100 ml beaker and ultrasonic for 60 min at 180 w, 59 kHz. After

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the mixture was disperse evenly, 400 µL of 0.625 mg/ml urea solution was added. The pH was

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adjusted to 7 with 0.1 M NaOH solution, the mixture was transferred to Teflon autoclave and

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reacted at 200 °C for 12 h. After the reaction was completed, the reaction mixture was cooled to

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room temperature and filtered through a 0.22 µM microfiltration membrane to remove black

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insoluble matter. The concentration of brown-yellow filtrate calculated by graphene oxide was

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0.625 mg/ml. The filtrate was dialyzed with 1000 Da dialysis bags, 500 ml secondary distilled 5


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water and the water was changed every 30 min until the conductivity of the dialyzate near that of

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distilled water. Finally the dialyzate was collected and stored at 4 °C.

116

2.3 Synthesis of N-GQDs-aptamer probe

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N-GQDs-aptamer was prepared using a modified method33. Briefly, 5.0 ml N-GQDs, 5 ml

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PBS at pH 7.0 and 1.2 ml of 8 mM/2 mM EDC/NHS mixed solution were sequentially added to

119

the flask and stirred for 30 min. Then 19 µL of 100 µM omethoate aptamer solution was slowly

120

added and stirred for 18 h. A clear yellow solution of N-GQDs-aptamer was obtained, and the

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concentration of N-GQDs-aptamer calculated by graphene oxide was 0.279 mg/ml.

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2.4 Determination of omethoate in actual samples

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The working curve for determination of omethoate: 0.5 ml omethoate standard solution at

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different concentrations, 1.0 ml GO...N-GQDs-aptamer solution, 3.5 ml PBS solution at pH 6.5

125

were added to 5 ml colorimetric tubes and diluted to a constant volume of 5.0 ml. After incubating

126

at room temperature for 45 min, the fluorescence intensity of mixture was measured at λex/λem of

127

310/413 nm. The working curve was plotted between the fluorescence intensities and omethoate

128

concentrations. The parallel polarization intensity (i// and I//) and vertical polarization intensity (i⊥

129

and I⊥) of above solutions were also measured at λex/λem of 310/413 nm. The polarization intensity

130

(P) was calculated according to the formula P =

131

for fluorescence polarization method was also plotted between the polarization intensities and

132

omethoate concentrations.

I// − G × I ⊥ and G = i ⊥ , and the working curve I// + G × I ⊥ i//

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Preparation of actual samples: The water samples were originated from the Pearl River,

134

filtered to remove insolubles and stored at 4 °C. 2.0 g cabbage sample was crushed with a mortar

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and transferred to a beaker. 50 ml of the double-distilled water was added, and the mixture was

136

extracted with ultrasonic for 20 min. The extractant was filtered, transferred to the flask and

137

diluted to constant volume of 100 ml and stored at 4 °C.

138

Measurement of actual samples: 0.5 ml of the prepared sample solution, 1 ml of 162 nM

139

GO...N-GQDs-aptamer probe, 3.5 ml PBS at pH 6.5 were transferred into 5 ml colorimetric tube.

140

After diluting to 5 ml, the sample solutions were measured at λex/λem of 310/413 nm, the amount

141

of omethoate in the samples was calculated according to the working curves. The standard

142

addition method was used to determine the recovery rate. Briefly, in a series of 5 ml colorimetric 6



143

tubes, 0.5 ml of prepared sample solution, different concentrations of omethoate were added, the

144

final spiked concentrations of omethoate were 0.10 pM, 0.050 nM and 4.0 nM. The spiked

145

samples were measured at λex /λem of 310/413 nm, and the recovery rates for each method were

146

calculated.

147

2.5 Imaging of omethoate in plants

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Cabbage leaves were dripped with omethoate pesticide at different concentrations of 20, 5,

149

0.1 µg/L, followed by adding with 162 nM of GO...N-GQDs-aptamer. After laying at room

150

temperature for 45 min, the cabbage leaves were observed under IX73 fluorescent biological

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microscope with 40X objective lens. The blank and leaf with only omethoate or

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GO...N-GQDs-aptamer were set as control groups.

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3. Results and discussion

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3.1 Synthesis and Characterization

155

The probe designed was composed of two parts, the optical signal component and the

156

recognition component. N-GQDs with good biocompatibility were chosen as optical signal

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component. Omethoate aptamer was chosen as the recognition component and assembled on the

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surface of N-GQDs by coupling agents EDC and NHS.

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GQDs emitted blue fluorescence at 410 nm with excitation at 320 nm. In order to increase the

160

fluorescence intensity, GQDs was doped with nitrogen. The effects of doping amount, pH value,

161

reaction time and reaction temperature on the fluorescence intensity of N-GQDs were investigated.

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The results in Figure 1A shown when the doping amount of urea was 1.0%, the reaction pH was

163

7.0, the reaction time was 12 h and the reaction temperature was 200 °C, the strongest

164

fluorescence intensity was achieved. After obtaining the N-GQDs with good fluorescence

165

properties, N-GQDs were modified with omethoate aptamer to obtain the N-GQDs-aptamer

166

probes. The effects of different conditions for the synthesis of N-GQDs-aptamer probe were also

167

tested. Because the suitable temperature for aptamer was no more than 25 °C, the coupling

168

reaction was carried out under 25 °C. The effects of other conditions were shown in Fig. 1B. The

169

results shown the optimal conditions were the mass ratio of aptamer was 1.0%, the pH was 7 and

170

the coupling reaction time was 18 h.

171

Figure 1

172 7


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Fig. 2A shown the fluorescence spectra of GQDs, N-GQDs and N-GQDs-aptamer. Both the

174

emission peaks of GQDs and N-GQDs were 423 nm, a new excitation peak at 260 nm could be

175

observed in the excitation spectra of N-GQDs. This excitation peak could be ascribed to the

176

formation of more complex energy level causing by nitrogen doped31. Furthermore, the

177

fluorescence intensity of N-GQDs was increased about one time, and the quantum yield reached

178

about 30% when using quinoline sulfate as reference substance. These meant the doped nitrogen

179

greatly improved the fluorescence property of GQDs. N-GQDs shown strongest fluorescence

180

signa at λex / λem = 320 nm / 423 nm, while the excitation and emission peaks of N-GQDs-aptamer

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were blue shifted to λex / λem =310 nm / 413 nm. And the fluorescence intensity of

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N-GQDs-aptamer probe was approximately doubled compared with that of N-GQDs. The blue

183

shift of excitation and emission wavelength, the enhancement of fluorescence intensity proved that

184

aptamer was successfully coupled to GQDs. The coupling was also further confirmed by the

185

fluorescence polarization experiment. Fig. 2B showed that the polarization spectrum of N-GQDs

186

had a significant peak at 360 nm, indicating N-GQDs were not dots but roundles. However, when

187

N-GQDs were coupled with aptamer, the polarization peak at 360 nm disappeared. This was

188

because the aptamer on N-GQDs decreased the directionality of N-GQDs-aptamer.

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The morphology and size of N-GQDs and N-GQDs-aptamer were characterized by

190

transmission electron microscopy. The experimental results are shown in Fig. 2C. It could be seen

191

that N-GQDs had good dispersibility, and the particle diameter was 5 nm. Because the layer

192

thickness of graphene oxide was about 0.8 to 1.2 nm, it could be concluded that N-GQDs were

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roundles with diameter of about 5 nm and thickness of about 0.8~1.2 nm. No significant change in

194

particle size and dispersibility was observed after the modification of omethoate aptamer. The

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hydrodynamic diameter and zeta potential of N-GQDs and N-GQDs-aptamer in Fig. S1 and S2

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also proved the successful conjugation of aptamer on N-GQDs.

197

Figure 2

198 199

3.2 Construction of off-on sensor

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The prepared N-GQDs-aptamer probe had obvious fluorescence at λex / λem = 310/413 nm.

201

After different carbon nanomaterials were added, the fluorescence was quenched diversely.

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However, some of the fluorescence could be recovered by omethoate added. As shown in Fig. 3A, 8



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the fluorescence of the probe was quenched by the same amount of carbon dots, carbon nanotube

204

and graphene oxide to about 40%, 55% and 100%, respectively. When omethoate was added, only

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the fluorescence quenched by graphene oxide was almost fully recovered. Therefore, GO could be

206

used as the quencher.

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The effects of the GO amount and the quenching time on the fluorescence intensity of

208

N-GQDs-aptamer probe were further studied. The results in Fig. 3B1 and Fig. 3B2 shown the

209

fluorescence intensity of the N-GQDs-aptamer probe decreased with increasing the amount of GO

210

and quenching time. When the concentration of GO was 0.16 mg/ml and the quenching time was

211

45 min, the fluorescence of the probe was almost completely quenched. The effect of GO on the

212

fluorescenec intensity of N-GQDs was served as control group in Fig. 3B3. The results showed

213

that both the fluorescence of N-GQDs-aptamer and N-GQDs could be quenched by GO. But the

214

quenching effect on N-GQDs-aptamer was greater than that on N-GQDs. Figure 4A shown only

215

the existence of GO could cause the obvious fluorescence quenching, and the absorption spectrum

216

of GO was overlapped partly with the fluorescence spectrum of N-GQDs-aptamer. Thus, it was

217

reasonable to consider that the fluorescence quenching of N-GQDs was due to the collision of the

218

increased particles in the solution when GO was added. When N-GQDs were conjugated with

219

omethoate aptamer, which got close to GO due to the strong π-π stacking interactions between

220

aptamer over N-GQDs surface and GO, therefore, the probability of fluorescence resonance

221

energy transfer between N-GQDs and GO increased, leading to the greater quenching effect. This

222

was also confirmed by the TEM in Figure 4B. After adding GO to N-GQDs-aptamer,

223

N-GQDs-aptamer could been found adhering onto the surface of GO sheet.

224

Figure 3

225

Figure 4

226 227

3.3 Sensitivity and selectivity of the probe

228

Based on the fluorescence recovery of N-GQDs-aptamer by omethoate, a sensor for the

229

determination of omethoate was constructed. The effects of buffer system and dosage, reaction

230

time on fluorescence recovery were tested. The results in Figure S3 shown the optimal buffer was

231

3.5 mL PBS with pH 6.5, the optimal time was 50 min. As illustrated in Figure S4, under the

232

optimal conditions, the fluorescence intensity of probe was proportional to the concentration of 9


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omethoate in the range of 0.1 to 17 nM with the equation of △F = 56.42 + 73.32c (nM), the

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correlation coefficient R2 was 0.999, and the detection limit was 0.041 nM. Since

235

N-GQDs-aptamer had polarization signal, polarization fluorescence could be utilized to measure

236

omethoate. The working curve equation was △mP = 413.8 + 102.7lgc (pM) with detection limit of

237

0.029 pM and correlation coefficient of 0.999.

238

In order to investigate the selectivity of the sensor, the interference of coexisting ions and

239

biomolecules was studied. in Fig. 5A. When the concentration of Na+, K+, Ca2+, Mg2+, Ba2+, Fe3+

240

reached 1000 times of omethoate concentration, the concentration of Cu2+ and Ni2+ was 100 times,

241

the concentration of L-proline, L-phenylalanine, RNA, DNA, vitamin B, lysozyme, albumin and

242

lysine was 10 times, no obvious change in fluorescence intensity was observed. The effects of

243

structurally similar pesticides were also investigated in Fig. 5B. The results shown that only

244

omethoate could recover the fluorescence of the sensor. The other five pesticides had no

245

significant effects on the fluorescence intensity, suggesting that the constructed sensor had good

246

selectivity for omethoate pesticide.

247

Figure 5

248 249

3.4 The determination of actual samples

250

In order to evaluate the application of the sensor in actual samples, the Pearl River water and

251

Chinese cabbage were selected as actual samples. Omethoate was not detected in water sample

252

and cabbage sample, the standard addition method was used to determine the recovery rate. As

253

illustrated in Table 1, when the added concentration of omethoate was 4.0 nM, the detected

254

concentration by fluorescence analysis, fluorescence polarization method was consistent with

255

HPLC, which suggested the excellent reliability of the fluorescence analysis and fluorescence

256

polarization method. When the added concentration was 0.050 nM, omethoate could be detected

257

only by fluorescence analysis and fluorescence polarization method, which suggested the

258

sensitivity of these methods was superior to HPLC. When the added concentration was 0.10 pM,

259

omethoate could be detected only by fluorescence polarization method, which suggested the

260

sensitivity of fluorescence polarization method was further improved.

261 262

Table 1 To visually detect the residual omethoate on the plants in situ, the GO...N-GQDs-aptamer 10



263

probe was utilized for imaging of omethoate in Chinese cabbage leaves under fluorescence

264

microscope. The control leaf, leaf with only omethoate, leaf with only GO...N-GQDs-aptamer

265

probe shown the spontaneous yellow-green fluorescence of cabbage leaves in Figure 6A-C. When

266

the leaves were treated with both omethoate and GO...N-GQDs-aptamer in Figure 6D-F, blue

267

fluorescence was observed, and the intensity reduced with the decreasing concentration of

268

omethoate. This meant the imaging could be used as visual semi-quantitative analysis of

269

omethoate. When the concentration of omethoate soulution was as low as 0.1 µg/L which was

270

much lower than 20 µg/kg from the food safety standard on omethoate in vegetables in China (GB

271

2763-2012) , blue fluorescence could still be observed (Fig. 6F).

272

Figure 6

273 274

Compared with other omethoate detection methods reported in the last five years in Table 2,

275

the detection limits of fluorescence analysis and fluorescence polarization analysis method in this

276

paper were lowest. The method had high sensitivity, good selectivity, wide detection range.

277

Furthermore, it could be used for visual semi quantitative determination of omethoate.

278

Table 2

279 280

Acknowledgments: This work was supported by the National Natural Science Foundation of

281

China (Nos. 21575043, 21275056, 21605052, 51478196); and the Platform Construction Project

282

of Guangzhou Science Technology and Innovation Commission (No. 15180001).

283 284 285

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Jiang, H.; Ouyang, J. Distinguish cancer cells based on targeting turn-on fluorescence imaging by

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385

Figure captions

386

Scheme. The detection mechanism based on the N-GQDs-aptamer probe.

387

Figure 1. The synthesis conditions optimization of N-GQDs (A) and N-GQDs-aptamer probe (B).

388

A1: the doping amount (mA and mB respectively for urea and graphene oxide); A2: pH; A3:

389

reaction time; A4: reaction temperature; B1: the coupled aptamer amount (mA and mN are the

390

amount of aptamer and N-GQDs); B2: pH and reaction time.

391

Figure 2. Characterization of N-GQDs and N-GQDs-aptamer. A: excitation and emission spectra,

392

curves 1-3 represented GQDs, N-GQDs and N-GQDs-aptamer, respectively. B: the fluorescence

393

polarization spectra. C: TEM images of N-GQDs (C1) and N-GQDs-aptamer (C2). The

394

concentration of N-GQDs or N-GQDs-aptamer was 0.279 mg/ml.

395

Figure 3. Quenching of N-GQDs-aptamer by different materials (A1: carbon dots, A2: carbon

396

nanotube, A3: GO) and recovery by omethoate (A). Curve 1, 2, 3 represented respectively

397

N-GQDs-aptamer，N-GQDs-aptamer + quencher，N-GQDs-aptamer + quencher + omethoate，the

398

concentrations of quencher and omethoate were 0.625 mg/ml and 10 nM respectively. The effects

399

of different conditions on the quenching of N-GQDs-aptamer (B). (B1: GO amount, B2:

400

quenching time, B3: The quenching effect of GO on N-GQDs and N-GQDs-aptamer), the

401

concentration of N-GQDs or N-GQDs-aptamer was 0.279 mg/ml.

402

Figire 4. Fluorescence spectra of 1: omethoate; 2:N-GQDs-aptamer; 3:GO; 4: 1+2; 5:1+3; 6:2+3;

403

7:1+2+3 and UV-visual spectra of GO (A). TEM of GO (B), B1: GO; B2: GO+N-GQDs-aptamer;

404

B3: GO+N-GQDs.

405

Figure 5. Interference of coexisting ions, biomolecules (A) and structurally similar pesticides (B).

406

Figure 6. Imaging of Chinese cabbage leaves. A: blank; B: leaf with omethoate; C: leaf with

407

GO...N-GQDs-aptamer; D-F: leaf with both GO...N-GQDs-aptamer and omethoate at

408

concentration of 20, 5, 0.1 µg/L.

409 410 411 412

16



413

Table 1 Determination of omethoate in river water and cabbage

Fluorescence analysis Samples

Pearl river water

Page 18 of 25

Fluorescence polarization

Added Detected

Recovery

RSD

Detected

(nM)

(%)

(%)

(nM)

0

ND

—

—

0.10 pM

ND

—

0.050

0.0475

4.0

Recovery

HPLC Recovery

RSD

Detected

（%）

(%)

(nM)

（%）

(%)

ND

—

—

ND

—

—

—

0.0912 pM

91.2

6.0

ND

—

—

95.0

7.1

0.0489

97.8

4.8

ND

—

—

3.76

94.0

4.1

3.83

95.7

3.6

3.58

89.5

6.3

0

ND

—

—

ND

—

—

ND

—

—

0.10 pM

ND

—

—

0.0958 pM

95.8

5.0

ND

—

—

0.050

0.0496

99.2

8.0

0.0492

98.4

4.0

ND

—

—

4.0

3.94

98.5

3.6

3.78

94.5

4.3

4.01

100.2

5.4

(nM)

RSD

cabbage

414

ND: not found

415 416

Table 2 Comparison of omethoate detection methods Detection methods

Detection range (nM)

Detection limit (nM)

-1

literature

-2

this paper *

cabbage, Pearl

1.0×10 -1.7×10

4.1×10

this paper **

River water

1.0×10-4-1.0×103

2.9×10-5

2.7×10-2 -2.7×104

2.3×103

[9]

carbohydrate

—

2.3×10

[10]

apple juice

—

2.4×105

[16]

fruits

3.0×102 -1.0×104

2.3×102

[5]

water

—

2.3×10-1

[13]

4.7×102 -4.2×104

1.2×102

[12]

fluorescence fluorescence polarization surface enhancement capillary electrophoresis light induction chemiluminescence

417

Samples

orange peel, running water

pears, carrots, eggplant

* fluorescence analysis method

** fluorescence polarization method

17


Page 19 of 25


Scheme 219x151mm (96 x 96 DPI)



Figure 1 171x194mm (96 x 96 DPI)


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Fluorescence determination of omethoate based on dual-strategy for

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