Electrochemical luminescence sensor based on double suppression for highly sensitive detection of glyphosate

Journal Pre-proof Electrochemical luminescence sensor based on double suppression for highly sensitive detection of glyphosate Hanbiao Liu, Peipei Chen, Zhen Liu, Jianhui Liu, Jiangle Yi, Fangquan Xia, Changli Zhou

PII:

S0925-4005(19)31563-1

DOI:

https://doi.org/10.1016/j.snb.2019.127364

Reference:

SNB 127364

To appear in:

Sensors and Actuators: B. Chemical

Received Date:

21 August 2019

Revised Date:

24 October 2019

Accepted Date:

29 October 2019

Please cite this article as: Liu H, Chen P, Liu Z, Liu J, Yi J, Xia F, Zhou C, Electrochemical luminescence sensor based on double suppression for highly sensitive detection of glyphosate, Sensors and Actuators: B. Chemical (2019), doi: https://doi.org/10.1016/j.snb.2019.127364

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Electrochemical luminescence sensor based on double suppression for highly sensitive detection of glyphosate Hanbiao Liu, Peipei Chen, Zhen Liu, Jianhui Liu, Jiangle Yi, Fangquan Xia*, Changli Zhou*

Key Laboratory of Interfacial Reaction & Sensing Analysis in Universities of Shandong, School of

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Chemistry and Chemical Engineering, University of Jinan, Jinan 250022, P.R.China

*Corresponding author：Fangquan Xia and Prof.Changli Zhou

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Tel.: +86 531 82765372 Fax: +86 531 82765969

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[email protected] (Changli Zhou)

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E-mail address:

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Highlights

The synthesized luminol-Au-L-cys-Cu(II) composite has dual functions of luminescence and

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peroxidase-like.

The double inhibition strategy increased the sensitivity of glyphosate detection.

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The constructed ECL sensor showed high specificity and good reproducibility.

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

Abstract

An electrochemical luminescence sensor based on a double inhibition strategy for the detection of glyphosate was constructed. In this method, the luminol-gold nanoparticles-L-cysteine-Cu(II) composites (Lu-Au-Lcys-Cu(II)) were used as luminescent reagents, and H2O2 obtained from two-step enzymatic hydrolysis reaction was used as the co-reactive agent of Lu-Au-Lcys-Cu(II). Glyphosate could inhibit the enzymatic reaction, and inhibit catalytic action of the peroxidase-mimicking by competing with L-cysteine to form a

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complex of glyphosate-Cu(II). The electrochemical luminescence intensity decreased with the increase of glyphosate concentration, under the optimal conditions, the linear range of glyphosate concentration was 0.001  1.0 M, and the limit of detection (LOD) could be as low as 0.5 nM.

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Importantly, the Electrochemiluminescence sensor also showed acceptable stability and selectivity.

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Keywords: Electrochemiluminescence sensor, enzyme, double inhibition, Glyphosate,

1. Introduction

Glyphosate is a kind of organophosphorus pesticide. Such compounds have caused neurological disorders by inhibiting the Acetylcholinesterase (AChE)[1]. Due to its toxicity to mammals is lower than other pesticides, glyphosate become one of the most widely used herbicides, which caused environmental pollution. In addition, residues of glyphosate in fruits and vegetables have caused harm to human health. Therefore, the detection of glyphosate in the environment is important [2, 3]. Conventional analytical methods of general pesticides, such as high-performance

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liquid chromatography (HPLC)[4], and Gas Chromatography-Mass Spectrometer (GC-MS)[5], enzyme-linked immune sorbent assays(ELISAs)[6] have been reported. these methods require complex instruments, and can’t detect quickly on site[7]. Therefore, developing detection

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technologies that are simple, rapid and accuracy for pesticide residues in the environment and the diet is highly desired.

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Up to now, many methods for rapidly detecting of glyphosate have been reported, such as

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differential pulse voltammetry (DPV)[8, 9], colorimetry[10], fluorescence[11], photoelectrochemical (PEC)[12, 13], and electrochemiluminescence (ECL)[14-17], etc. Among

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them, due to ECL sensors have the advantages of fast detection speed, simple equipment, high sensitivity, and low detection cost, it is the most widely studied in glyphosate detection[15, 16]. In

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the ECL sensor research, many researchers have designed a variety of analytical strategies, such as

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steric hindrance[18], energy transfer[19], enzyme inhibition reactions[20], etc. Among them, ECL sensors based on enzyme inhibition have low cost and low background signals and were widely used for detecting pesticides. For example, Wang[21] used β-cyclodextrin (CD) to functionalize graphitized carbonitride (gC3N4) as a luminescent reagent, and the detection of organophosphorus pesticides by the use of Et3N as a co-reactant of HAc produced by AChE enzymatic reaction. Miao [22] enhanced the luminescence intensity of the luminol-H2O2 system by H2O2 produced from

AChE enzymatic reaction to detected organophosphorus pesticides. However, the luminescent signal is easily affected by the enzyme inhibition strategy, and its sensitivity and selectivity are poor[23]. Therefore, increasing the sensitivity and selectivity of enzyme inhibition sensors is of greatest concern. On the other hand, the luminescence efficiency of the luminescent reagent also seriously affects the ECL sensitivity. Due to its high quantum yield, easy synthesis and good water solubility, luminol is commonly used as a chemiluminescent reagent.[24]. In order to improve the

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luminescence ability of luminol, many nanomaterials were applied to the luminol luminescence system, such as AgNPs[25], hemin-silver nanoparticles[26], hydrotalcite[27], gold nanoparticles[28] and so on. In this paper, the luminol-gold nanoparticles-L-cysteine-Cu(II) composites

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(Lu-Au-Lcys-Cu(II)) was used as a luminescent reagent, and a novel ECL sensor based on double suppression for detection of glyphosate was constructed.

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Herein, the graphene-gold nanoparticle composite (rGO-Au) was used as the capture substrate

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for AChE and choline oxidase (ChOx). The Lu-Au-Lcys-Cu(II) composite was synthesized and used as a luminescent reagent. Meanwhile, Cu(II) in the composite could act as a

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peroxidase-mimicking enhancing the ECL signal. In PBS (pH 7.4) with 0.1 M acetylcholine chloride (AChCl), hydrogen peroxide (H2O2) obtained by a two-step enzymatic hydrolysis reaction

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was used as a co-reactant to increase the ECL signal. The disadvantage of the hydrogen peroxide

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solution system easily causes other disturbances were avoided. When glyphosate was dropped on the above electrode, glyphosate inhibited the AChE activity. And formed a complex with Cu(II), which separates Cu(II) from the surface of the electrode and loses its catalytic effect. The sensor-based on Lu-Au-Lcys-Cu(II) and dual suppression strategy showed high sensitivity detection of glyphosate. The sensor constructed in this paper effectively improves the selectivity of the enzyme inhibition sensor and is of important influence in the detection of pesticide residues.

2. Experimental 2.1 Reagents and Materials Acetylcholinesterase (AChE), Choline Oxidase (ChOx), Acetylcholine chloride (AChCl), gold chloride trihydrate (HAuCl4·3H2O) were supplied by Sigma. Lumino, ammonia, L-cysteine were obtained in shanghai Macklin. The composite of rGO-Au was homemade by our laboratory[29]. Glyphosate, deltamethrin, acetamiprid, chlorpyrifos, and carbendazim were purchased from

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Shanghai pesticide research institute Co., Ltd. Ultrapure water (specific resistance of 18 M·cm) obtained from a Millipore water purification system.

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2.2 Apparatus

The ECL emission was monitored with a model MPI-A electroluminescence analyzer (Xi’an

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Remax, China). Transmission electron microscope (TEM) images were obtained using JEM-2100

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TEM (Japan Electronics Co. Ltd.). All the electrochemical measurements were performed on the CHI 760E (Shanghai Chenhua InstrumentCo.). The conventional three-electrode system consists of

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the Ag/AgCl (sat. KCl) reference electrode, a platinum wire as a counter electrode with the glassy

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carbon electrode (GCE) as a working electrode.

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2.3 Preparation of the Lu-Au-Lcys-Cu(II) composite

The Lu-Au NPs composite has obtained by 1.0 mL of luminol (15 mM) was added to 5.0 mL

of HAuCl4 (0.25 mM) solution and stirring vigorously for 12 h at room temperature. One hundred microliters of L-Cys (6.0 mM) aqueous solution was mixed with 1.0 mL of Lu-Au NPs solution at room temperature, the mixture was then incubated at 4℃ for 5 h. Then, 100.0 μL of Cu(II) solution (6 mM) was mixed with the mixture and shaken for 5 min at room temperature to obtain a

composite material of Lu-Au-Lcys-Cu(II).

2.4 Fabrication of the ECL sensor and measurement procedure

The sensor was prepared by the layer-by-layer assembly. The modified electrode (rGO-Au/GCE) was prepared by dropped 8 μL of rGO-Au complex onto the treated GCE surface and air-drying. Then, 10 μL of ChOx and 2.0 μL of AChE were applied dropwise to the

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rGO-Au/GCE surface overnight to obtain a modified electrode AChE-ChOx/rGO-Au/GCE. The Lu-Au-Lcys-Cu(II)/AChE-ChOx/rGO-Au/GCE was prepared by adding 8.0 μL of

Lu-Au-Lcys-Cu(II) composite on the AChE-ChOx/rGO-Au/GCE while cross-linking with

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glutaraldehyde and incubate at 4°C for 2 h. Finally, the sensor was washed by PBS (pH 7.4). The fabrication process and mechanism of this ECL sensor were shown in Scheme 1.

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For the analysis of glyphosate, 10 μL of different concentrations of glyphosate was dropped to

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the above-constructed sensor, incubated at 37°C for 1 h and then rinsed with PBS solution (pH 7.4). Finally, the ECL emission was recorded in PBS (pH 7.4) with 0.1 M AChCl. The voltage of the

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Scheme 1

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photomultiplier tube set at 800 V and the cyclic potential scan from −1.6 to 0.0 V.

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3. Results and discussion

3.1 Characterization of rGO-Au and Lu-Au-Lcys-Cu(II) composite

The morphology and size of rGO, rGO-Au and Lu-Au-Lcys-Cu(II) were characterized by TEM (Fig 1). rGO exhibits a sheet-like structure and has a large number of pleats, providing many active sites for the assembly of other materials (Fig. 1A). AuNPs were about 6~7 nm in diameter

and were evenly distributed on the rGO surface (Fig. 1B). The Lu-Au-Lcys-Cu(II) composite was a spherical structure and the average size was about 70 nm (Fig. 1C).

Fig 1 3.2 The ECL mechanism of the Lu-Au-Lcys-Cu(II) system

In the ECL system of Luminol-H2O2, Luminol can be oxidized to luminol anion free radicals

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(LH-)(eq.3), further generated luminol anion radicals (L•-) by continuous chemical reaction (eq.4). The L•- can react with superoxide anion (O2•-) (eq.5) generated by H2O2 to form luminol excitation (AP*) (eq.8, 9). Finally, AP* returns the ground state (AP) from the excited state and transmits hν

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(eq.10)[30, 31]. However, in our system of Lu-Au-Lcys-Cu(II), the co-reactant H2O2 was derived

RSH+HAc

ChOx

RSSR+2H2 O2

(1)

(2)

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RSH+H2 O+2O2 →

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AChE

AChCl+H2 O →

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from a two-step enzymatic reaction in the presence of the substrate AChCl (eq.1, 2).

In order to study the catalytic performance of Cu(II) to ECL, the modified electrode was

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prepared by dropped Lu-Au-Lcys and Lu-Au-Lcys-Cu(II) onto the treated GCE surface and

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air-drying, respectively. Fig 2 showed the ECL and CV responses of the Lu-Au-Lcys/GCE and Lu-Au-Lcys-Cu(II)/GCE in 0.1 M PBS (pH 7.4) containing 0.1 mM H2O2 solutions, respectively. The ECL intensity of the Lu-Au-Lcys-Cu(II)/GCE (Fig.2A, curve b) was about 3 times higher compared to that of the Lu-Au-Lcys/GCE (Fig.2A, curve a). Meanwhile, relative higher polarization current was also recorded at 0.6 V (Fig.2B, curve b), indicated that Cu(II) could efficiently catalyze the electrochemical oxidation of H2O2. Therefore, the ECL enhancement of

Lu-Au-Lcys-Cu(II) in the H2O2 system could be owing to obvious electrocatalytic oxidation of H2O2 by Cu(II), which given rise to more abundant O2•− (eq.6, 7). Here Cu(II) had peroxidase-mimicking activity[32]. The ECL mechanism of Lu-Au-Lcys-Cu(II) in our system could be elucidated as follows: (3)

LH−﹣e−  LH•  L•− + H+

(4)

H2O2  HO2− + H+  HO2• + e−  O2•− + H+

(5)

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luminol  LH− + e− + 2H+

Cu(II) + e−  Cu(I)

(6)

Cu(I) + H2O2  Cu(II) + O2•−

(7)

L•− + O2•−  LO22−

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(8)

LO22−  AP* + N2

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AP*  AP + hv

(9) (10)

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Furthermore, the inhibitory effect of glyphosate on the peroxidase-mimicking function of Cu(II) was investigated by CV in PBS solution. As shown in Fig 2B inset, no redox peak was

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detected in Lu-Au-Lcys/GCE (Fig.2B inset, curve a). However, a pair of redox peaks (0.09 and -0.20 V) could be observed (Fig.2B inset, curve b) on Lu-Au-Lcys-Cu(II) /GCE, which belonged to

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the redox of Cu(II). After glyphosate was dropped on the Lu-Au-Lcys-Cu(II) /GCE, the oxidation

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peak decreased significantly, and the reduction peak disappeared (Fig.2B inset, curve c). This was due to the strong complexation of glyphosate with Cu(II)[33], glyphosate-Cu(II) complexes were formed and separated from the surface of the modified electrode. Furthermore, the polarization current at 0.6 V was significantly reduced (Fig.2B, curve c) and the corresponding lower ECL emission of the Lu-Au-Lcys-Cu(II) modified electrode has also recorded (Fig.2A, curve c), indicating that the efficiently inhibitory effect of glyphosate on the peroxidase-mimicking function

of Cu(II) due to the formation of glyphosate-Cu(II) complexes.

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3.3 EIS characterization of the stepwise fabrication of the ECL sensor

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EIS can characterize the interface properties of different modified electrodes. Fig.3 was the EIS about the stepwise modification processes in 0.1 M KCl containing 5.0 mM [Fe(CN)6]3−/4− solution. The Nyquist plots were fitted by the Randles equivalent circuit (Fig.3, inset), where Rs is

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the solution resistance, Rct is charge-transfer resistance and equal to the semicircle diameter of the Nyquist diagram, Q is constant phase element, an equivalent model of double-layer capacitance,

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and Zw is Warburg element. As shown in Fig.3, the bare GCE showed a larger semicircle domain

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with the Rct of 280 Ω (curve a). After the rGO-Au film was modified on the GCE, the value of Rct decreased to 76 Ω (curve b), which was the result of the good conductivity of rGO-Au. Subsequent

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rGO-Au/GCE was stepwise modified with AChE-ChOx and Lu-Au-Lcys-Cu(II), the semi-circular gradually increased (Fig.3, curve c, d). The Rct values of the AChE-ChOx/rGO-Au/GCE and

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Lu-Au-Lcys-Cu(II)/AChE-ChOx/rGO-Au/GCE were estimated as 533 and 740 Ω, respectively.

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These results could be explained by the assembled enzyme layers at the electrode surface forming a barrier for electron transfer and hindered the electron transfer of [Fe(CN)6]3-/4- on the interface of the modified electrode. The Lu-Au-Lcys-Cu(II) composite further hindered the transmission of electrons. However, the interface impedance decreased as glyphosate was dropped on the Lu-Au-Lcys-Cu(II)/AChE-ChOx/rGO-Au/GCE (curve e, 665 Ω), this was attributed to the formation of glyphosate-Cu(II) complexes and separated from the surface of the modified electrode.

The above results could illustrate the successful preparation of the sensor.

Fig. 3 3.4 Experimental condition optimization

So as to improve the sensitivity of the ECL sensor, we have to select the optimal experimental

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conditions, including the volume ratio of ChOx to AChE, the choice of metal ions, Cu(II) concentration and the influence of pH. First, the influence of the volume ratio of ChOx and AChE on the ECL intensity was studied, which is the key factor affecting the sensitivity of the sensor. Fig

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4A showed that the ECL intensity increased with the increasing of the volume ratio when the ratio was less than 5:1 and then reached a constant at 5:1. Next, the influence of different metal ions on

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the ECL behaviors was investigated (Fig. 4B). Cu(II) could form a complex with cysteine to

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catalyze the luminescence system, and the influence of other metal ions on the luminescence system was negligible. The ECL intensity reached a maximum at 0.6 mM of Cu(II) concentration

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(Fig. 4C). Concomitantly, the Alkaline environment is conducive to luminescence properties of the

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Fig. 4

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luminol-H2O2 system, and the ECL responses were best at pH 7.4 (Fig.4D).

3.5 Performance of the ECL sensor

Under the optimum experimental conditions, The ECL responses of different glyphosate concentrations were determined. The intensity of ECL decreased with the increasing of glyphosate

concentration. (Fig.5). The ECL intensity was negatively correlated with the logarithm of the concentration of glyphosate in the range from 0.001 to 1.0 M. The linear regression equations was I =﹣454 lgc (M) + 465 (r = 0.992) (inset). The detection limit was 0.5 nM (S/N=3). Comparison of other biosensors (Table 1), the analytical performance of the constructed double suppression ECL sensor for glyphosate was more excellent.

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Fig. 5

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Table 1

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3.6 Stability, selectivity and reproducibility of the proposed ECL sensor

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Based on the same experimental conditions, the inter-reproducibility was evaluated with 5 electrodes fabricated independently. The relative standard deviation (RSD) was 2.02 %, indicated

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that the proposed ECL sensor maintained good inter-reproducibility. Furthermore, after the sensor was kept at 4°C for 10 days, More than 92.2 % of the original current response was retained

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(RSD 2.25 %), indicated that the sensor had desirable stability (Fig.6A). In order to investigate

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the selectivity of the ECL sensor, these pesticide residues such as deltamethrin, acetamiprid, chlorpyrifos, carbendazim were used as interfering pesticides. As shown in Fig.6B, the ECL signals were no obvious change compared with the result of without target, when the ECL sensor was incubated with 1.0 M interfering pesticides, respectively. However, the ECL intensity obtained from the mixture of 0.1 M glyphosate with other pesticides (1.0 M each) was approximated to that of the 0.1 M glyphosate alone. Therefore, the proposed ECL sensor had

great specificity for glyphosate.

Fig.6

3.7 Real sample analysis To evaluate the practical application performance of this ECL sensor, the designed ECL sensor

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was applied to detect the glyphosate in water samples, including local river water and lake water. The results were in comparison with the reference value of the Ion Chromatography (IC) (Table 2). The relative standard deviation (RSD) was between 3.59 % and 6.52 %, indicated that our ECL

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sensor was consistent with the IC method. The recoveries for glyphosate were in the range of 98.9 to 105 %. The results suggested that our ECL sensor could provide a promising alternative to detect

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glyphosates in water samples.

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4. Conclusions

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Table 2

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In this paper, an ECL sensor was constructed based on the principle of double suppression for highly sensitive detection of glyphosate. First, a graphene-gold nanoparticle composite was synthesized to improve the specific surface area of the electrode as an enzyme capture substrate. Secondly, the Lu-Au-Lcys-Cu(II) was synthesized as a luminescent reagent and a peroxidase-mimicking to enhance the ECL signal. When glyphosate was dropped on the sensor, glyphosate can inhibit the enzymatic reaction and catalytic effection of the peroxidase-mimicking.

The constructed ECL sensor based on Lu-Au-Lcys-Cu(II) and dual inhibition strategy showed excellent detection performance for glyphosate with high sensitivity, desirable reproducibility, stability, and accuracy. This method is of great significance for the development of an ultrasensitive biosensing platform for pesticide residue in agricultural production.

Declaration of interests

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☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

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Acknowledgements

This work was financially supported by the Foundation of Shandong Provincial Natural Science

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Foundation, China (ZR2017MB063), National Natural Science Foundation of China (NSFC) (No.

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31370090), and Project of Key R&D of Shandong Province in China (No. 2015GSF121006).

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metal-organic frameworks, Anal. Chim. Acta, 1050(2019) 51-9. [30] F. Luo, Y. Lin, L. Zheng, X. Lin, Y. Chi, Encapsulation of Hemin in Metal-Organic Frameworks for Catalyzing the Chemiluminescence Reaction of the H2O2-Luminol System and Detecting Glucose in the Neutral Condition, ACS Appl. Mater. Inter., 7(2015) 11322-9. [31] W. Xiuhua, L. Chao, T. Yifeng, Microemulsion-enhanced electrochemiluminescence of luminol-H2O2 for sensitive flow injection analysis of antioxidant compounds, Talanta, 94(2012)

289-94. [32] M. Vazquez-Gonzalez, W.C. Liao, R. Cazelles, S. Wang, X. Yu, V. Gutkin, et al., Mimicking Horseradish Peroxidase Functions Using Cu(2+)-Modified Carbon Nitride Nanoparticles or Cu(2+)-Modified Carbon Dots as Heterogeneous Catalysts, ACS Nano, 11(2017) 3247-53. [33] J. Sheals, P. Persson, B. Hedman, IR and EXAFS spectroscopic studies of glyphosate protonation and copper(II) complexes of glyphosate in aqueous solution,

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4302-4309 [34] M.L. Xu, Y. Gao, Y. Li, X. Li, H. Zhang, X.X. Han, et al., Indirect glyphosate detection based on ninhydrin reaction and surface-enhanced Raman scattering spectroscopy, Spectrochim Acta

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A-Mol. Biomol. Spectrosc., 197(2018) 78-82.

[35] C. Vaghela, M. Kulkarni, S. Haram, R. Aiyer, M. Karve, A novel inhibition based biosensor

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using urease nanoconjugate entrapped biocomposite membrane for potentiometric glyphosate

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detection, Int. J. Biol. Macromol., 108(2018) 32-40.

[36] H.U. Lee, D.U. Jung, J.H. Lee, Y.S. Song, C. Park, S.W. Kim, Detection of glyphosate by

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quantitative analysis of fluorescence and single DNA using DNA-labeled fluorescent magnetic core–shell nanoparticles, Sensor. Actuat. B-chem., 177(2013) 879-86.

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[37] J. Zheng, H. Zhang, J. Qu, Q. Zhu, X. Chen, Visual detection of glyphosate in environmental

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water samples using cysteamine-stabilized gold nanoparticles as colorimetric probe, Anal. Methods, 5(2013) 917-24.

Hanbiao Liu is a current master student, studies in School of Chemistry and Chemical Engineering, University of Jinan. He is working on constructing biological sensor. Peipei Chen is a current master student, studies in School of Chemistry and Chemical Engineering, University of Jinan. She is working on constructing biological sensor. Zhen Liu received his Ph.D. degree from Shandong University in 2016. He is the postdoctor in the

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University of Jinan. His research interests focus on the design and synthesis of plasmonic nanomaterials and their applications in the photoelectrocatalysis, SERS and sensor field.

Jianhui Liu is a current master student, studies in School of Chemistry and Chemical Engineering,

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University of Jinan. He is working on constructing biological sensor.

Jiangle Yi is a current master student, studies in School of Chemistry and Chemical Engineering,

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University of Jinan. She is working on constructing biological sensor.

mainly focus on electrochemistry.

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Fangquan Xia received his Ph.D. degree from Shandong University in 2006. His research works

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Changli Zhou is a professor of analytical chemistry in University of Jinan. He received his Ph.D. degree in analytical chemistry from Lanzhou Institute of Chemical Physics, Chinese Academy of

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biosensors.

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Sciences, PR China in 1999. His research interests are focused on electroanalytical chemistry and

Figure captions Scheme 1

Fig. 1

The fabrication process and mechanism of the ECL sensor

TEM images of (A) rGO, (B) rGO-Au, (C) Lu-Au-Lcys-Cu(II).

Fig. 2 ECL (A) and CVs (B) of Lu-Au-Lcys/GCE (a), Lu-Au-Lcys-Cu(II)/GCE (b), and glyphosate/Lu-Au-Lcys-Cu(II)/GCE (c) in 0.1 M PBS (pH 7.4) containing 0.1 mM H2O2

solutions.

Fig. 3

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solutions. Inset: CVs of the above different modified electrodes in 0.1 M PBS (pH 7.4)

EIS curves of GCE (a), rGO-Au/GCE (b), AChE-ChOx/rGO-Au/GCE (c),

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Lu-Au-Lcys-Cu(II)/AChE-ChOx/rGO-Au/GCE (d), and

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Glyphosate/Lu-Au-Lcys-Cu(II)/AChE-ChOx/rGO-Au/GCE (e). Inset: Randles equivalent circuit of the Nyquist plots. Electrolyt solution: 0.1 M KCl solution containing 5.0 mM [Fe

The effects of the volume ratio of ChOx and AChE (A), the different metal ion (B), the

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Fig. 4

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(CN) 6]3-/4- . Frequency range: from 1 mHz to 100 kHz.

Fig. 5

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concentration of Cu(II) (C), and pH of PBS (D) on ECL intensity.

ECL intensity of the sensor to different concentrations of glyphosate: (a) 0.001, (b) 0.005,

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(c) 0.01, (d) 0.05, (e) 0.1, (f) 0.5, (g) 1.0 M. Inset: The corresponding linear calibration curve.

Fig. 6

Stability (A) and selectivity (B) of the proposed ECL sensor

Table 1

Comparison of different analytical methods of glyphosate

Table 2

Analysis results of glyphosate in water samples (n=3)

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Scheme 1

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Fig. 1

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Fig. 2

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Fig. 3

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Fig.4

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Fig.5

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Fig.6

Table 1 Strategy

Linear range

LOD

Ref.

Raman scattering spectroscopy

based on ninhydrin reaction

0.1~100 μM

14.3 nM

[34]

ECL

ECL sensor based on electrodes modified with self-assembled monolayers

1~100 μM

6.42 μM

[17]

ECL

ECL sensor based on Ru(bpy)32+

0.03~2.81 mg L-1

0.01 mg L-1

[16]

Potentiometric biosensor

potentiometric biosensor based on inhibition of urease activity by glyphosate

0.5~50 ppm

0.5 ppm

[35]

Fluorescence

DNA-labeled fluorescent magnetic core–shell nanoparticles

1~10,000 nM

0.27 nM

[36]

0.01~100 μM

3 nM

[14]

0.500~7.00 μM

58.8 nM

[37]

0.5 nM

This work

Colorimetric

ECL sensor based on enzyme-assisted cysteamine-stabilized gold nanoparticles as colorimetric probe ECL sensor based on double inhibition

0.001~1 μM

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ECL

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Detection method

Table 2 Added(g L-1)

Water sample

Lake

1.0 5.0

3# 1# 2# 3#

10.0 1.0 5.0 10.0

RSD (%)

Recovery (%) 105 99.6 98.9 103 99.8 101.3

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4.98

4.5 6.5

9.90 10.0 8

9.89 1.03 4.99 10.13

4.7 3.59 4.35 6.52

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River

1# 2#

Found (g L-1) IC ECL sensor 1.05