A novel acetylcholinesterase biosensor based on ionic liquids-AuNPs-porous carbon composite matrix for detection of organophosphate pesticides

Accepted Manuscript Title: A novel acetylcholinesterase biosensor based on ionic liquids-AuNPs-porous carbon composite matrix for detection of organophosphate pesticides Author: Min Wei Jingjing Wang PII: DOI: Reference:

S0925-4005(15)00139-2 http://dx.doi.org/doi:10.1016/j.snb.2015.01.112 SNB 18039

To appear in:

Sensors and Actuators B

Received date: Revised date: Accepted date:

31-10-2014 27-1-2015 28-1-2015

Please cite this article as: M. Wei, J. Wang, A novel acetylcholinesterase biosensor based on ionic liquids-AuNPs-porous carbon composite matrix for detection of organophosphate pesticides, Sensors and Actuators B: Chemical (2015), http://dx.doi.org/10.1016/j.snb.2015.01.112 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Highlights ► The [BSmim]HSO4-AuNPs-porous carbon was firstly prepared to develop AChE biosensor.

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► The lower Rct of the [BSmim]HSO4-AuNPs-porous carbon/BDD than that of the bare BDD.

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► The AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD biosensor showed higher sensitivity for thiocholine oxidation.

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►The AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD biosensor showed lower detection limit toward dichlorvos detection.

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► The AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD biosensor showed good

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repeatability and favorable stability.

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A novel acetylcholinesterase biosensor based on ionic liquids-AuNPs-porous carbon composite matrix for detection of

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organophosphate pesticides

Min Wei*, Jingjing Wang

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College of Food Science and Technology, Henan University of Technology,

*

Corresponding

author.

Tel.:

+86

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Zhengzhou 450001, PR China

37167758022.

address:

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[email protected]

E-mail

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Abstract

A novel acetylcholinesterase (AChE) biosensor, based on honeycomb-like

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hierarchically ion liquids ([BSmim]HSO4)-AuNPs-porous carbon composite modified

pesticides.

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organophosphate

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boron-doped diamond (BDD) electrode, was developed for the detection of The

surface

morphology

of

the

prepared

[BSmim]HSO4-AuNPs-porous carbon composite was characterized by scanning electron

microscopy

and

transmission

electron

[BSmim]HSO4-AuNPs-porous carbon modified BDD electrode

microscopy.

The

was confirmed by

cyclic voltammogram and electrochemical impedance spectroscopy. For the oxidation of thiocholine, hydrolysis product of acetylthiocholine, the peak current at AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD electrode is more than 4.5 times

that at AChE/BDD electrode. The inhibition of dichlorvos is linearly proportional to its concentration in the range of 10−10 - 10−6 g/L (4.5×10−13 - 4.5×10−9 M), with the

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detection limit of 6.61×10−11 g/L (2.99×10−13 M ) (calculated for 10 % inhibition). The proposed biosensor provided an efficient and promising platform for the immobilization of AChE and exhibited higher sensitivity and acceptable stability for

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the detection of organophosphate pesticides.

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Keywords: [BSmim]HSO4-AuNPs-porous carbon composite, AChE biosensor, BDD

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electrode, dichlorvos 1. Introduction

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Organophosphate pesticides (OPs) play an important role in increasing agricultural productivity due to their high insecticidal activity [1-3]. Unfortunately,

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owing to their high acute toxicity and bioaccumulation effect, the residue in the environment can cause long-term damage to human health [4]. Therefore, the

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detection of OPs has become increasingly necessary. Among the different techniques, biosensors based on acetylcholinesterase (AChE) have attracted much more attention

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in recent years due to their advantages in terms of rapid response, simple operation, decreasing analysis time, low cost and field deployability [5-7]. The detection mechanism for OPs is as follows: AChE can catalyze hydrolysis of acetylthiocholine (ATCl), and the enzymatic reaction product is electro-active thiocholine, which can produce an irreversible oxidation peak. OPs can inhibit the activity of AChE, and then decrease the oxidation of thiocholine. The oxidation peak current of thiocholine is inversely proportional to the concentration of OPs. By monitoring the oxidation peak current of thiocholine before and after inhibition, the OPs concentration can be determined [8]. For the fabrication of AChE biosensor, effective immobilization of

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AChE onto the electrode surface still faces some challenges. For example, the immobilization of AChE needs reinforce adsorption between the enzyme and the substrate material, retain enzyme stability without the loss of bioactivity, and facilitate

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the electron transfer between the biosensor and the electrode surface [9]. In addition,

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conventional analysis methods such as GC, HPLC etc. [5].

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the detection limit of AChE biosensor cannot reach the detection level of those

Recently, with the rapid development of nanotechnology, various novel

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nanomaterials have been applied in different strategies including adsorption, entrapment and covalent coupling for the effective fabrication of AChE biosensor

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[10-16] and other biosensors [17, 18]. Moreover, the utilization of different immobilization approaches has shown synergic effect to improve the biosensor

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performance [9, 19, 20]. Herein, our research purpose is to develop a highly sensitive and stable AChE biosensor by synergic effect to improve AChE adsorption, retain

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enzyme activity, and enhance the sensitivity of response for the detection of OPs. In recent years, macro-/meso-/porous carbon materials have attracted enormous

attention due to their remarkable properties including open pore structure, high specific surface area, large pore volume, efficient mass transportation, high conductivity and good chemical stability [21]. These advantages lead to their wide variety of applications as catalyst supports [22], electrode materials for batteries [23], fuel cells [24] and supercapacitors [25], and substrate materials for sensors [26]. On the other hand, due to their unique physicochemical properties such as good biocompatibility, active surface, catalytic properties and excellent conductivity, gold

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nanoparticles (AuNPs) can enhance the electron transfer between redox centers and electrode surfaces, and act as catalysts for electrochemical reactions. So, AuNPs are suitable for designing improved electrochemical sensors and biosensors [27-32].

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In addition, because of their desirable properties in terms of high chemical and

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thermal stability, high ionic conductivity, and wide electrochemical window, ionic

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liquids (ILs) have been extensively reported for detection of various substances to facilitate electron transfer and enhance the sensitivity of response [33-36].

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In this work, in an effort to develop a highly sensitive AChE biosensor platform for the detection of OPs, honeycomb-like hierarchically porous carbon, AuNPs, and

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ILs are combined firstly as an immobilization matrix to produce the synergic effect, which boost the biosensor performance including improving AChE adsorption,

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retaining enzyme activity, and enhancing the sensitivity of response. The immobilized AChE exhibits greater affinity to its substrate and excellent catalytic effect on

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hydrolysis of ATCl. The proposed AChE biosensor is applied to detect dichlorvos, as a model compound for OPs, and shows higher sensitivity, lower detection limit, good reproducibility and acceptable stability. 2. Materials and methods 2.1. Reagents

Acetylthiocholine chloride (ATCl) and acetylcholinesterase (AChE, Type C3389, 500 U/mg from electric eel) were obtianed from Sigma-Aldrich. Dichlorvos (≥99%) was obtained from Augsburg (Germany). 0.1 M phosphate buffer solution (PBS) was prepared by mixing stock solutions of NaH2PO4 and Na2HPO4 and adjusting the pH

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with 0.1 M HCl or 0.1 M NaOH. All other chemicals were of analytical-reagent grade. Double distilled water (DW) was used throughout the experiments. 2.2. Apparatus

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All the electrochemical experiments were performed on a CHI 660D

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Electrochemical Workstation (Shanghai Chenhua Instrument Corporation, China). A

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three-electrode system was comprised of boron-doped diamond (BDD) as working electrode [37], platinum wire as auxiliary electrode, and Ag/AgCl as reference

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electrode. Surface morphology and microstructure of samples were characterized by field-emission scanning electron microscopy (FESEM, JSM-7001F, JEOL Ltd., Japan)

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and Transmission electron microscopy (TEM, JEM-2100UHR (JEOL Ltd., Japan). 2.3. Preparation of [BSmim]HSO4-AuNPs-porous carbon composite

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The honeycomb-like hierarchically porous carbon material was simply synthesized according to the literature report [24]. The AuNPs grown on porous

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carbon was prepared according to the previous report [31]. The synthesis of 1-(4-Sulfonic acid) butyl-3-methylimidazolium hydrogensulfate ([BSmim]HSO4), a

kind of ionic liquids (ILs), was carried out according to the literatue [38]. 0.1 M 1-methylimidazol and 0.1 M 1,4-butane sultone were charged into a 100 mL round-bottom flask. Then, the mixtures were stirred at 80
for 12 h. The white solid zwitterion was washed repeatedly with ether to remove any unreacted materials and dried in vacuum. Then, a stoichiometric amount of concentrated sulfuric acid was added and the mixture was stirred for 6 h at 60
during which time the solid zwitterion dissolved/liquefied, resulted in the formation of [BSmim]HSO4. The

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obtained [BSmim]HSO4 was then washed repeatedly with dichloromethane and ether to remove non-ionic residues, and dried in vacuum. 1H NMR (300 MHz, D2O-d2, 25 °C, TMS); δ (ppm) 1.605 (m, 2H), 1.888 (m, 2H), 2.809 (t, 2H), 3.754 (s, 3H), 4.110

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(t, 2H), 7.305 (s, 1H), 7.364 (s, 1H), 8.60 (s, 1H).

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The [BSmim]HSO4-AuNPs-porous carbon composite were obtained by adding 25

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μL [BSmim]HSO4 into 4 mL AuNPs-porous carbon solution under stirring to allow complete dispersion.

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2.4. Preparation of AChE biosensor

BDD was sequentially ultrasonicated in acetone, double distilled water, and dried

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at room temperature. The BDD electrode was spread with 8 μL the above-mentioned [BSmim]HSO4-AuNPs-porous carbon composite solution, and dried at room

albumin

to

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temperature. Then 10.0 μL, 25U/mL AChE solution (containing 1 % bovine serum maintain

the

stability

of

AChE)

was

dropped

on

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[BSmim]HSO4-AuNPs-porous carbon/BDD electrode and incubated at 25 °C. After

evaporation of water, the modified electrode was washed with PBS (pH7.5) to remove the

unbound AChE, and the obtained AChE/[BSmim]HSO4-AuNPs-porous

carbon/BDD electrode was stored at 4 °C when not in use. 3. Results and discussion 3.1.

Characterization

of

porous

carbon,

AuNPs-porous

carbon

and

[BSmim]HSO4-AuNPs-porous carbon Here Fig.1 The SEM image and TEM images are employed to investigate the structure of

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the prepared materials. The SEM image of the prepared porous carbon (Fig. 1A) shows the macroporous honeycomb-like monolith. The surface of the monolith is made up of shell-connected hollow hemispheres. The insert of Fig. 1A displays the

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magnified image of the macroporous monolith. It can be seen that the average

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diameter of the porous carbon is about 600 nm. The TEM image of the prepared

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porous carbon (Fig. 1B) clearly shows the macroporous inner structure and the interconnected framework of the carbon product. The TEM image of

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AuNPs-porous carbon (Fig. 1C) shows the little agglomeration of particles on the porous carbon supports, indicating that AuNPs were successfully adhered to the

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thin walls and the interior of porous carbon. The change from transparency of Fig.1C to opacity of Fig. 1D indicates that [BSmim]HSO4 was uniformly added on

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the surface of AuNPs-porous carbon. The TEM images indicate that the porous morphology was basically retained after the incorporation of AuNPs (Fig. 1C),

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whereas became blurry after the incorporation of [BSmim]HSO4 (Fig. 1D).

3.2. Characterization of bare BDD electrode, AuNPs-porous carbon/BDD electrode and [BSmim]HSO4-AuNPs-porous carbon/BDD electrode Here Fig.2

Cyclic voltammogram (CV) and electrochemical impedance spectroscopy (EIS)

are used as a tool to confirm the electrode surface modification. The CV results of different electrodes are obtained in 0.1 M KCl solution containing 2×10−3 M [Fe(CN)6]3− (Fig. 2A). The oxidation peak current of [BSmim]HSO4-AuNPs-porous carbon/BDD electrode (c) was 89.15μA, which was more than 1.3 times that of

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AuNPs-porous carbon/BDD electrode (66.45 μA) (b), and more than 2.2 times that of bare BDD electrode (39.91 μA) (a). The peak-to-peak separation (∆Ep) at bare BDD electrode, AuNPs-porous carbon/BDD electrode and [BSmim]HSO4-AuNPs-porous

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carbon/BDD electrodes was 594 mV, 401 mV and 348 mV, respectively. The

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decrease of ∆Ep and the increase of peak current at [BSmim]HSO4-AuNPs-porous

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carbon/BDD electrode are ascribed to that [BSmim]HSO4-AuNPs-porous carbon composite can increase the surface area, provide better electric linkage between

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electrode active sites, promote the electrocatalytic ability, and accelerate the electron transfer. Fig.2B shows the Nyquist plots of EIS at different electrodes using 1×10−2 M

BDD

electrode

(a),

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[Fe(CN)6]3−/4− as the electrochemical probe. The electron transfer resistance of bare AuNPs-porous

carbon/BDD

electrode

(b)

and

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[BSmim]HSO4-AuNPs-porous carbon/BDD electrode (c) was about 483 Ω, 320 Ω, and 250 Ω respectively, suggesting that the presence of porous carbon, AuNPs and

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[BSmim]HSO4 on the electrode surface can improve the reactive site, reduce the interfacial resistance, and make the electron transfer easier. 3.3. Electrochemical behaviors of acetylthiocholine at different electrodes Here Fig.3

Fig.3 shows the results of differential pulse voltammetry (DPV) response of 0.5

mM acetylthiocholine in pH 7.5 PBS at different electrodes. It can be seen that the obvious oxidation peaks were produced at different electrodes, which comes from the oxidation of thiocholine, hydrolysis product of acetylthiocholine, catalyzed by the immobilized AChE. The general reactions on the electrode surface can be as follows

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[39]: AChE

2Thiocholine (red) The

oxidation

Thiocholine + Acetic acid

anodic oxidation

peak

Disulfide (ox) + 2H+ + 2e-

current

of

thiocholine

was

(1) (2)

2.23μA

at

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Acetylthiocholine

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AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD electrode (Fig. 3c), which was

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more than 1.5 times that at AChE/AuNPs-porous carbon/BDD electrode (1.44 μA) (Fig. 3b), and more than 4.5 times that at AChE/BDD electrode (0.49 μA) (Fig. 3a).

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This improvement is ascribed to the synergic effect of porous carbon, AuNPs, and [BSmim]HSO4. Herein, porous carbon can improve AChE adsorption and retain the

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enzyme activity due to its three-dimensional marcoporous structure and good biocompatibility. The existence of AuNPs and [BSmim]HSO4 can accelerate the

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electron transfer and enhance the sensitivity of response due to their good active

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surface, catalytic properties and excellent conductivity. Here Fig.4

The effect of solution pH and AChE loading on the peak current was studied, and

the results were shown in Fig. 4. As shown in Fig. 4A, the peak current increased with increasing pH and the maximum peak current appeared at pH 7.5. So, pH 7.5 was chosen as the optimal parameter. Fig. 4B displayed the effect of AChE loading on biosensor response. The peak current increased with increasing the amount of AChE and reached the maximum at 0.25 U, then decreased when the amount of AChE was increased further. This is ascribed that the excess amount of AChE could slow the electron transfer between substrate and electrode. So, 0.25 U was chosen as the

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optimal amount of AChE. 3.4. Detection of dichlorvos at AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD Here Fig.5 5A shows DPV responses

of AChE/[BSmim]HSO4-AuNPs-porous

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Fig.

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carbon/BDD electrode before (a) and after (b) inhibition with dichlorvos. In comparison with that for 0 min (a), when AChE/[BSmim]HSO4-AuNPs-porous

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carbon/BDD was immersed in 10-5g/L dichlorvos solution for 12 min., the oxidation

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peak current of thiocholine decreased from 2.23μA to 0.51μA, and the inhibition was 77.13%, which is calculated as follows: inhibition(%)=[(I0-I)/I0] ×100%. where I0 is

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the peak current of thiocholine, and I is that with dichlorvos inhibition. This is because that dichlorvos, as one of the OPs, can combine with AChE to form

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intermediate complex. This combination irreversibly inhibits AChE activity, and reduces the yield of thiocholine [7]. According to the obvious change of

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electrochemical response at AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD

electrode, the simple method for detection of dichlorvos can be established. Fig.5B shows the effect of inhibition time on AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD

biosensor

response.

The

AChE/[BSmim]HSO4-AuNPs-porous

carbon/BDD biosensor was incubated in 10-8g/L dichlorvos solution for different time. As shown in Fig. 5B, the inhibition increased with inhibition time and obtained basically stable response at 12 min. So, the optimum inhibition time was chosen as 12 min. Here Fig.6

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Fig.6

shows

the

relationship

AChE/[BSmim]HSO4-AuNPs-porous

carbon/BDD

between

inhibition

biosensor

and

of

different

concentrations of dichlorvos with inhibition time of 12 min.. Obviously, the inhibition

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increased sharply at low concentration then changed slowly at high concentration with

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increasing dichlorvos concentrations ranging from 10−11 to 10−4 g/L, which indicated

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that the bonding interaction between dichlorvos and AChE tended to saturation. Good linear relationship between inhibition and –Log [dichlorvos] was obtained in the

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range of 10−10−10−6 g/L (4.5×10−13−4.5×10−9 M) with the regression equation of Inhibition (%) = −14.0847x +153.5203(%) (R2=0.9993), and the detection limit was

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6.61×10−11 g/L (2.99×10−13 M) (calculated for 10% inhibition). The performance of the fabricated biosensor was compared with those of other reported AChE biosensors.

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As shown in Table 1, the performance of AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD was superior to other reports [40-45]. This result may be attributed to the

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synergic effect of [BSmim]HSO4-AuNPs-porous carbon composite including high accessible surface area to improve AChE adsorption, good biocompatibility to retain the AChE activity, and satisfying conductivity to enhance the sensitivity of response.

3.5.

Regeneration,

Here Table 1 Reproducibility,

and

stability

of

AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD biosensor AChE reactivation is necessary for practical application. According to the literature [46], the inhibited AChE can be reactivated by pralidoxime iodide. In the present work, the AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD biosensor

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inhibited by dichlorvos could be regenerated 91.7 % of its original activity after immersing in 5.0 mM pralidoxime iodide for 15 min. The intra-assay reproducibility of AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD biosensor was evaluated for ten

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replicate measurements in 0.5 mM ATCl after incubating in 10−8 g/L dichlorvos for

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12 min each time. Similarly, the inter-assay precision was estimated at five different

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electrodes. The coefficient of variation of intra-assay and inter-assay was 4.83 % and 6.47 %, respectively, which indicated that AChE/[BSmim]HSO4-AuNPs-porous

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carbon/BDD biosensor was reproducible and precise. The prepared

AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD biosensor was stored at 4°C when

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not in use. After a 30-day storage period, the biosensor retained 95.42 % of its initial current response, proving the acceptable stability.

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3.6. Analysis of dichlorvos in lettuce leaves sample The AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD biosensor was employed

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to detect the content of dichlorvos in lettuce leaves sample. A standard addition method was adopted to assess the reliability of the prepared biosensor. As shown in Table 2, the recoveries were found to be between 80.8 % and 93.1 %. The results indicated that the proposed biosensor could be used for the analysis of real samples. Here Table 2

4. Conclusions In this work, [BSmim]HSO4-AuNPs-porous carbon composite has been prepared to immobilize AChE for the detection of OPs. The constructed biosensor showed favorable performance toward OPs detection due to the synergic effect of

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[BSmim]HSO4-AuNPs-porous carbon composite including high accessible surface area to improve AChE adsorption and boost the reactive site, good biocompatibility to retain the AChE activity, and excellent conductivity to make the electron transfer

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easier and enhance the sensitivity of response. This work provides a efficient

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[BSmim]HSO4-AuNPs-porous carbon matrix for immobilizing biological molecules

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and developing novel biosensors. Acknowledgments

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This research was supported by National Natural Science Foundation of China (Grant No. 21105022), Plan for Scientific Innovation Talent of Henan University of

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Technology (2012CXRC01), program for Science and Technology Development of Zhengzhou (20130876), Foundation for University Youth Key Teachers from Henan

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(2013GGJS-073),

and

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Province

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the quality supervision public industry research special funds (201310059) .

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Table and Figure captions: Table 1. Comparison with other reported AChE biosensors for dichlorvos detection

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Table 2. Recovery of dichlorvos in lettuce leaves sample (n=3)

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Fig. 1. SEM image of porous carbon (A) and TEM images of porous carbon (B),

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AuNPs-porous carbon (C) and [BSmim]HSO4-AuNPs-porous carbon (D)

Fig. 2. (A) CVs of (a) bare BDD, (b) AuNPs-porous carbon/BDD and (c)

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[BSmim]HSO4-AuNPs-porous carbon/BDD in the presence of 2×10−3 M [Fe(CN)6]3− (B) Nyquist plots of (a) bare BDD,

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in 0.1 M KCl solution. Scan rate was 50 mV s-1.

(b) AuNPs-porous carbon/BDD and (c) [BSmim]HSO4-AuNPs-porous carbon/BDD

te

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in 0.1 M KCl solution containing 1×10−2 M [Fe(CN)6]3−/4−.

(a) AChE/BDD, (b) AChE/AuNPs-porous carbon/BDD

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Fig. 3. DPV responses of

and (c) AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD in PBS (pH 7.5)

containing 0.5 mM acetylthiocholine.

Fig. 4. Effect of pH (A) and AChE loading (B) on the response of AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD biosensor in PBS containing 0.5

mM acetylthiocholine. . Fig. 5. (A) DPV responsess of AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD in PBS (pH 7.5) containing 0.5 mM acetylthiocholine withthout inhibition (a) and with

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inhibition in 10-5 g/L dichlorvos solution for 12 min (b). (B) The effect of inhibition time on the response of AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD biosensor inhibition in 10-8 g/L dichlorvos solution.

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with

cr

Fig. 6. The inhibition of the AChE/[BSmim]HSO4-AuNPs-porous carbon/BDD

biosensor versus the logarithm of dichlorvos concentration ranging from 10−11 to 10−4

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g/L (A), and 10−10−10−6 g/L (B). The inhibition time is 12 min.

Table 1 Comparison with other reported AChE biosensors for dichlorvos detection Linearity range/M

Nanoporous carbon matrix TEOS sol-gel film Glass/sol-gel indicator /polyvinylidenefluoride membrane Polyethyleneimine (PEI) Al2O3 sol–gel matrix Chitosan and prussian blue membrane [BSmim]HSO4-AuNPs -porous carbon

10-12-10-6 1×10-3-3×10-3

Detection limit/M 10-12 10-7

Incubation time /min 10 10

Referen ces [40] [41]

2.3×10-8

10

[42]

10-10 10-8

24h 15

[43] [44]

10

[45]

12

This work

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Modified material

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2.3×10-8-1.3×10-7

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NR* 10-7-8×10-6

4.5×10-11-4.5×10-8 1.1×10-11 4.5×10−13−4.5×10 −9

2.99×10−13

NR*: Not reported Table 2

Recovery of dichlorvos in lettuce leaves sample (n=3)

Pesticide

Added(μg/L)

Found(μg/L)

Recovery(%)

RSD(%)

Dichlorvos

0.01 0.05 0.1

0.00931 0.0404 0.0846

93.1 80.8 84.6

7.2 5.7 4.7

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Figures:

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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

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Biographies Min Wei received M.S. degree from Taiyuan University of Technology in 2006, and got a Ph.D in

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State Key Laboratory of Bioelectronics, Southeast University in 2009. Now, she is an associate Professor at Henan University of Technology and her research focuses on electrochemical biosensors and fabrication of nanomaterials.

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Jinging Wang is an undergraduate student at Henan University of Technology. Her research focuses on electrochemical biosensors.

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