Dual-Signaling Amplification Electrochemical Aptasensor Based on

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Biological and Medical Applications of Materials and Interfaces

Dual-Signaling Amplification Electrochemical Aptasensor Based on Hollow Polymeric Nanospheres for Acetamiprid Detection Peipei Chen, Xueying Qiao, Jianhui Liu, Fangquan Xia, Dong Tian, and Changli Zhou ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b00308 • Publication Date (Web): 02 Apr 2019 Downloaded from http://pubs.acs.org on April 2, 2019

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ACS Applied Materials & Interfaces

Dual-Signaling Aptasensor

Amplification

Based

on

Electrochemical

Hollow

Polymeric

Nanospheres for Acetamiprid Detection Peipei Chen, Xueying Qiao, Jianhui Liu, Fangquan Xia, Dong Tian, Changli Zhou* Key Laboratory of Interfacial Reaction & Sensing Analysis in Universities of Shandong, School of Chemistry and Chemical Engineering, University of Jinan, Jinan 250022, P. R. China KEYWORDS:

hollow

polymeric

nanospheres;

dual-signaling

amplification;

polyethylenimine; acetamiprid ABSTRACT: In this work, we first reported a dual-signaling electrochemical aptasensor based on layer-by-layer template technology and catalytic amplification for acetamiprid detection. Herein, the signal probe of the ferrocene (Fc)-based hollow polymeric nanospheres (Fc-HPNs) were prepared with repeated electrostatic adsorption between anionic poly (acrylic acid) and hyperbranched cationic polyethylenimine. In addition, ascorbic acid (AA) as enhancer can catalyze the reduction of Fc-HPNs, which results in significant enhancing the oxidation peak current of Fc-HPNs. Remarkably, the Fc-HPNs played dual roles: as nanocarriers, to significantly increase the load amount of Fc, and as nanoreducers, to effectively catalytic reduction by AA for further signal amplification. Therefore, due to their special nanostructures of Fc-HPNs and effectively catalytic effect of AA, dual-signaling electrochemical aptasensor was proposed. Surprisingly, this proposed assay for trace amounts of target detection exhibites excellent sensitivity with a linear range from 10 nM~1 fM and

1

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limit of detection down to 0.33 fM (S/N = 3), which opened a novel avenue and versatile strategy for monitoring the acetamiprid.

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1. INTRODUCTION With increased globalization of neonicotinoid insecticides, acetamiprid has been utilized widely in agriculture products1-5. Acetamiprid could be absorbed mainly by the roots once applied, and then transferred to various tissues of organisms, including flowers, leaves, and fruits6. Under the perspective of pest control, acetamiprid seems to offer better efficacy of absorption over other insecticides and advantages of the ease of application7-8. Nevertheless, from the concern of human exposures and ecological friendly, acetamiprid will undoubtedly affect non-target organisms that may contact with the plant production9-10. Acetamiprid has been banned in many countries due to the pesticide-resistance, threaten to mammal, severe environmental pollution11. So, in our country, the effective analysis of acetamiprid is an urgent demand to protect people from possible hazards and safeguard the ecosystem. There were abundant reports on detection of acetamiprid content, such as fluorescence spectrophotometry12 and UV–vis absorption13-14. Herein, compared with the existing method, electrochemical does have some potential supreriorities, such as on-site rapid detection and the miniaturization of instruments. Meanwhile, aptasensor has been widely applied to identify the promising biomolecule15-16. Significantly, electrochemical aptasensor has been applied gradually for the detection of trace-level substances. Recently, signal amplifications have generated a series of excitement for a wide variety of promising electrochemical applications due to their remarkable high sensitivity property. In order to achieve highly sensitive detection, a lot of efficient signal amplification approaches have been constructed, such as rolling

circle

amplification17-18,

hybridization

chain

reaction

amplification19-20,

nanomaterial-based amplification21-22, enzyme-assisted target recycling amplification23-25, dendrimer-loaded signal amplification26-27, and layer-by-layer template technique signal amplification28-31. Comparing the methods mentioned above, dendrimer-loaded has aroused widespread attention in chemical and biological fields by the means of their tremendous 3



terminal groups that can be functionalization32. Layer-by-layer template technology as the further extention of dendrimer-loaded signal amplification has attracted much interest. It’s an excellent versatile approach that can be utilized to construct the nanostructured materials with specific properties. This process involves the sequential assembly with all sorts of species (eg, polymers, dye molecules, lipids, nanoparticles, and proteins) onto various templates that will laterly be removed to establish a free-standing structure. In various templates, SiO2 nanoparticles has attracted lots of interest due to its advantages of biocompatibility, good water dispersity, highly-uniform, controllable size and easy surface functionalization33. Based on SiO2 nanoparticles, layer-by-layer template technology can be readily adjusted by simply changing the type of adsorbed species and controlling the assembly process34. For the electrostatic adsorption, the water-dissolvable sodium sulfate nanowires were fabricated from anionic poly(acrylic acid) (PAA) and cationic polyethylenimine(PEI)35. In addition, anionic poly(styrenesulfonate) and cationic poly(allylamine hydrochloride) were combined to prepare polyelectrolyte functioned electrospun fibers36. It’s well known that ferrocene (Fc) is the outstanding redox probe with excellent catalytic activity and electrochemical activity. Inspired by the above-mentioned unique properties of the layer-by-layer template technology and outstanding properties of Fc, anion PAA and cationic PEI-Fc were selected as perspective precursors to synthesize Fc based hollow polymeric nanomaterials. The proposed Fc based hollow polymeric nanomaterials can be expected to significantly improve the electrochemical signal and the sensitivity of detection. Taking into account the above findings, we first reported a dual-signaling electrochemical DNA aptasensor based on layer-by-layer template technology and catalytic amplification for acetamiprid detection. Herein, ferrocene (Fc)-based hollow polymeric nanospheres (Fc-HPNs) were formed with precursor of cationic PEI-Fc and served as signal probe. First, PEI-Fc was obtained by covalently cross-linking PEI with Fc-COOH via amino 4


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linkage. Subsequently, the positively charged PEI-Fc and the negatively charged PAA are continuously coated into SiO2 nanoparticles by electrostatic adsorption (Scheme 1). After the layers were cross-linked to reinforce the framework, the SiO2 nanoparticles were etched away by HF to produce the desired Fc-HPNs. After that, complementary DNA (cDNA) was attached to the prepared hollow polymeric nanospheres of Fc-HPNs. In addition, the working buffer solution of PBS containing 1 mM ascorbic acid (AA). Herein, ascorbic acid as enhancer can catalyze the reduction of Fc-HPNs, which results in significant enhancing the oxidation peak current of Fc-HPNs. It must be pointed out that hollow polymeric nanospheres of the Fc-HPNs played dual roles: as nanocarriers, to significantly increase the load amount of Fc, and as the nanoreducers, to effectively catalytic reduction by AA for further signal amplification. The fabricated aptasensor utilized layer-by-layer template technology to prepare the Fc-based hollow polymeric nanospheres and catalytic amplification by AA, which opened a novel avenue and versatile strategy for monitoring the acetamiprid. 2. EXPERIMENTAL SECTION 2.1. Reagents and apparatus. Polyethylenimine (PEI), poly(acrylic acid)(PAA), ferrocene monocarboxylic acid (Fc-COOH), chloride

trihydrate

tetraethyl orthosilicate,

(HAuCl4·3H2O),

N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide

ascorbic acid (AA), gold

6-Mercaptohexanol hydrochloride

(EDC),

(MCH), and

N-hydroxysuccinimide (NHS) were supplied by Sigma Chemicals Co. (St. Louis, MO). Phosphate-buffered solution (PBS) containing 0.1 M KCl, 0.1 M KH2PO4, 0.1 M Na2HPO4, and 1 mM AA, which was used as working buffer solution. Ultrapure water (>18 MΩ cm) obtained from an Easy Ultra-pure water system was used throughout this study. The DNA oligonucleotides were booked from Shanghai Sangon Biological Engineering Technology & Services Co., Ltd (Shanghai, China) and the sequences of DNA oligonucleotides are listed below: 5



acetamiprid aptamer： 5'-NH2-(CH2)6-TGTAATTTGTCTGCAGCGGTTCTTGATCGCTGACACCATATTATGA AGA-3'; complementary DNA(cDNA): 5'-NH2-(CH2)6-CATAATATGGTGTCAGCG-3'. Differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) were monitored with electrochemical workstation (CHI 760E, Shanghai Chenhua Instrument Co.). The transmission electron micrographs (TEM) could be taken by using the JEM-2100 TEM (Japan Electronics Co., Ltd.). A typical three-electrode system was utilized throughout the experiment, in which the Ag/AgCl reference electrode was containing saturated KCl, the counter electrode was a platinum electrode, and the working electrode was the functionalized glassy carbon electrode (GCE). 2.2. Synthesis of SiO2 nanoparticles. The uniform spherical SiO2 nanoparticles were prepared by hydrolyzing tetraethyl orthosilicate in ethanol medium in sodium hydroxide medium37. A quantity of 1.5 mL TEOS was taken into 45 mL of ethanol with sonicating 10 min. Successively, the certain volume 28% ammonia was dropped into the reaction solution to promoting the condensation reaction. Sonication couldn’t be stopped until the mixed solution became into milky. Then, the ultimate mixed solution was centrifuged, washed, and dried for further utilize. 2.3. Preparation of the Fc-HPNs-cDNA bioconjugate. The hyperbranched PEI-Fc was covalently cross-linking PEI with Fc-COOH via amino linkage in existing of EDC and NHS. 0.115 g of Fc-COOH was dropped into 8 mL ultrapure water with continuous stirring. After 10 min, 1 mL of EDC (4.0 mM) and NHS (1.0 mM) coupling reagent was put into above solution with pH 6.18, which can be worked to activate the carboxyl group of Fc-COOH. The

6


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ultimate products were prepared successfully when PEI was blended with the activated Fc-COOH solution after 2 h. Accurately weigh 2 mg dried SiO2 nanoparticles and dispersed in 20 mL ethanol. After that, the dispersed SiO2 solution could be mixed with PEI-Fc with the aid of stirring for 30 min. PEI-Fc coated SiO2 nanoparticles (SiO2@PEI-Fc) were obtained by centrifugation at 8000 rpm for 5 min, washed to separate the residual PEI-Fc. Then PAA was added to the SiO2@PEI-Fc solution with speedy stirring for 30 min. After repeated washings with ethanol, the functionalized materials as described above were encapsulated with PEI-Fc, PAA, and PEI-Fc sequentially to obtain SiO2@PEI-Fc-PAA core-shell polymeric nanomaterials. After the SiO2@PEI-Fc-PAA core-shell polymeric nanomaterials were redispersed in ultrapure water (pH 7.0). EDC (4.0 mM) and NHS (1.0 mM) coupling reagent were added to the solution of SiO2@PEI-Fc-PAA core-shell polymeric nanomaterials and stirred at 4 °C for 2 h. The coupling reagent can be utilized to cross-link the PAA and PEI-Fc layers and reinforce the framework of the polymeric capsule. The sythesis route of SiO2@PEI-Fc-PAA core-shell polymeric nanomaterials can be observed from Scheme 1A. The resultant SiO2@PEI-Fc-PAA core-shell polymeric nanomaterials were centrifugation (8000 rpm, 5 min), dispersed, and preserved at 4 °C for further use. The Fc-HPNs were prepared by making use of HF to etch away of SiO2. In brief, 0.1 M HF was dropped to the SiO2@PEI-Fc-PAA core-shell polymeric mixture solution and the reaction time was 15 min. The expected Fc-HPNs were collected by washing with deionized water and ethanol, and preserved in 2 mL of PBS (0.1 M, pH 7.4). 2 mL 2.5% glutaraldehyde solution and Fc-HPNs were viberated gently at room temperature for 1.5 h to form Fc-HPNs labled cDNA bioconjugate (Fc-HPNs-cDNA).

After collection by centrifugation and wash

with PBS (0.1 M, pH 7.4) for 3 times, the final product was dissolved in 2 mL of PBS (0.1 M, pH 7.4) and preserved at 4 °C. 7



2.4. Fabrication of the aptasensor and electrochemical detection.

Scheme 1. Preparation of the Fc-HPNs-cDNA bioconjugate (A). Schematic representation of the acetamiprid aptasensor based on the dual-signaling amplification (B). Before immobilization on the GCE, Au nanoparticles (Au NPs) were first synthesized38. 7 μL of Au NPs mentioned above was drop-casted to the pretreated GCE and dried in the nitrogen atmosphere to form Au NPs modified GCE (denoted as Au NPs/GCE). Subsequently, aptamer was chemically bonded to Au NPs/GCE through incubating overnight at 4 °C. And then 2 mM MCH was utilized to inhibit the nonspecific DNA adsorption. Lastly, Fc-HPNs-cDNA was dripped on the formed, followed by washing after 60 min. For the analysis of acetamiprid, 8 μL of different concentrations of targets were dripped on the formed Fc-HPNs-cDNA/MCH/aptamer/Au NPs/GCE. After incubation about 1 h, the aptasensor was rinsed with PBS (0.1 M, pH 7.4) to get rid of reagents. Then, DPV measurements were performed from -0.2 ~ 0.6 V at the working buffer solution of PBS containing 1 mM AA and detection signal of the aptasensor was related to the acetamiprid concentration. The fabrication process and dual-signaling amplification mechanism of the modified immunosensor were shown in Scheme 1. 8


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3. RESULTS AND DISCUSSION 3.1. Characterization of the materials. TEM was used to attest the successfully preparation of SiO2, layer-by-layer polymeric capsuled SiO2 and Fc-HPNs. As shown in Figure 1A, TEM image of the resulting SiO2 nanoparticles show even solid sphere with a diameter about 200 nm. After the layer-by-layer template assembly technology of PEI-Fc and PAA, the SiO2 nanoparticles were encapsulated with polymers are clearly visible (Figure 1B), indicating PEI-Fc and PAA were modified on the surface of SiO2 nanoparticles as expected. Figure 1C showed the diameter of 280 nm with cotton-like nanostructure, which manifested the successful synthesis of the Fc-HPNs. The distribution and particle size of the various nanomaterials were measured by DLS from Figure 1 (D, E, F), respectively. The mean particle size observed by the laser light scattering method for SiO2 nanoparticles, SiO2@PEI-Fc-PAA core-shell polymeric nanomaterials and the synthesized Fc-HPNs are approximately 230, 300, 290 nm, respectively. The DLS results could be the hydrodynamic diameter and showed the larger hydrodynamic volume owing to solvent effect39. Meanwhile, compared with SiO2@PEI-Fc-PAA core-shell polymeric nanomaterials, the DLS results of Fc-HPNs are reduced. After the etched away of SiO2, the reduction of particle size due to the lost of support. And the changing trend for particle size is consistent with the results of TEM.

9



Figure 1. TEM images and DLS investigations of SiO2 nanoparticles (A, D), SiO2@PEI-Fc-PAA core-shell polymeric nanomaterials (B, E), the synthesized Fc-HPNs (C, F). The FT-IR spectra of the SiO2 nanoparticles, SiO2@PEI-Fc-PAA core-shell polymeric nanomaterials and the synthesized Fc-HPNs in the range from 500 to 4000 cm-1 were displayed in Figure 2A. For SiO2 nanoparticles (curve a), the peaks at 1088, and 3390 cm-1 were assigned to the asymmetric stretching vibrating of typical Si-O-Si bands and stretching vibration peak of -OH that belongs to Si-OH. And meanwhile, 3150 and 3430 cm-1 represented the asymmetric stretching vibrating of -NH2 and 1400 cm-1 confirmed the asymmetry peak of -COOH. Importantly, the peak emerged at 1631 cm-1 in curve b marked the formation of -CONH- between PEI-Fc and PAA. Besides, Si-O-Si absorption peak (curve c) declined sharply compared with curve b, suggesting the SiO2 nanoparticles were etched away by HF to produce the desired Fc-HPNs. DSC measurements of SiO2 nanoparticles, SiO2@PEI-Fc-PAA core-shell polymeric nanomaterials and the synthesized Fc-HPNs give more details in the range from 30 to 600 °C. SiO2 nanoparticles have no endothermic peak due to its own property from curve a (Figure 2B). Compared with Figure 2B curve b, the endothermic peak of Fc-HPNs (curve c) is narrower. It’s reasonable to suppose that above result was probably due to the restriction of SiO2. All these observations above vividly confirmed the formation of the nanomaterials step by step.

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Figure 2. The FT-IR spectra (A) and DSC curves (B) of SiO2 nanoparticles (a), SiO2@PEI-Fc-PAA core-shell polymeric nanomaterials (b), the synthesized Fc-HPNs (c). 3.2. EIS characterization of the stepwise fabrication of the aptasensor. Figure 3A exhibited the EIS for different modification stage electrodes that the measured were carried out in 5.0 mM [Fe(CN)6]3-/4- solution containing 0.1 M KCl. The inset of Figure 3A was the fitted Randles equivalent circuit of the Nyuist plots. Resistance (Rct) presents interfacial resistance, which equivalent to the diameter of the semicircle in the Nyquist plot. Compared with bare Au NPs/GCE (curve b), the GCE (curve a) showes weaker semicircle domain, which indicate an inferior charge-transfer Rct value. The real Rct values of the bare GCE and Au NPs/GCE are 134 and 309 Ω, respectively. After the incubation with aptamer, the Ret increases greatly to 535 Ω (curve c). After modified with MCH, the further increase of EIS was found clearly (curve d, 819 Ω), which was owing to the defects of the modified GCE was sealed off. Lastly, the Ret increases to 986 Ω after further loaded of Fc-HPNs-cDNA which make it convinced that the aptasensor was fabricated successfully. Furthermore, the electrochemical behaviors of MCH/aptamer/Au NPs/GCE and Fc-HPNs-cDNA/MCH/ aptamer/Au NPs/GCE were studied using DPV and cyclic voltammetry (CV). As shown in the Figure 3B, no redox peaks could be observed at the MCH/aptamer/Au NPs/GCE (curve a´).

However,

a

pair

of

well-defined

redox

peaks

could

be

observed

at

Fc-HPNs-cDNA/MCH/aptamer/Au NPs/GCE (curve b´). The oxidation peak (Epa= 0.18 V) and the reduction peak (Epc= 0.32 V) belonged to redox reaction of Fc. The peak-to-peak potential separation (ΔEp) between the anodic peak and the cathodic peak was 140 mV, which indicated that the redox process of Fc was a quasi-reversible process. This result indicated that the modification electrode of Fc-HPNs-cDNA/MCH/aptamer/Au NPs/GCE was fabricated successfully, which consistent with the characterization results of EIS. Compared with CV result, the remarkable enlargement of DPV current response was noticed 11



(Figure 3B, curve b). Based on the above results, DPV was selected for the determination of acetamiprid.

Figure 3. (A) EIS curves of (a) GCE, (b) Au NPs/GCE, (c) aptamer/Au NPs/GCE, (d) MCH/aptamer/Au NPs/GCE, (e) Fc-HPNs-cDNA/MCH/aptamer/Au NPs/GCE. Frequency range of 1 mHz to 100 kHz. (B) DPV and CV responses of MCH/aptamer/Au NPs/GCE (a, a´) and Fc-HPNs-cDNA/MCH/aptamer/Au NPs/GCE (b, b´). 3.3. Performance comparison of diverse DPV probes and working solution. To verify the superior performance of the synthesized Fc-HPNs and effective catalytic oxidation of ascorbic acid for further signal amplification, the contrast experiments were conducted to compare the DPV responses. Three species of labeled cDNA bioconjugates were prepared: PEI-Fc labeled cDNA (Figure 4A, inset), SiO2@PEI-Fc-PAA core-shell polymeric nanomaterials labeled cDNA (Figure 4B, inset), Fc-HPNs labeled cDNA (Figure 4C, inset). For Figure 4A, 4B and 4C, the working buffer solution was PBS (pH 7.4). As shown in Figure 4D, the aptasensor was proposed by Fc-HPNs labeled cDNA and the working buffer solution was PBS (pH 7.4) containing 1 mM AA. As we can obtain from curve a (Figure 4A, 4B, and 4C), a weak DPV signal (1.52 μΑ, RSD=5.52%) was measured when Fc-COOH was labeled with cDNA as the signal probe. After the preparation of PEI-Fc and labeled with cDNA, about 1.62 μΑ(RSD=4.37%) increased DPV response was received(Figure 4A, curve 12


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b), which could be contributed to the hyperbranched of PEI40. When SiO2@PEI-Fc-PAA core-shell polymeric nanomaterials were labled as signal probe, Figure 4B, curve b exhibited an increase of 5.39 μΑ(RSD=7.16%). However, when Fc-HPNs were preferred to act as signal probe(Figure 4C, curve b), the remarkably increased DPV response about 8.15 μΑ(RSD=6.56%) was noticed, manifesting that hollow polymeric nanospheres possessed superior DPV properties41. When the aptasensor was incubated with Fc-HPNs labeled cDNA, and the working buffer solution of PBS (pH 7.4) containing 1 mM AA, the DPV response was increased about 6.53 μA (Figure 4D, curve b, RSD=3.12%) compared with Figure 4C, curve b. Herein, AA as enhancer can catalyze the reduction of Fc-HPNs, which results in significant enhancing the oxidation peak current of Fc-HPNs26. The reason can be benefited from the amount of load Fc, and catalysis of AA to the Fc-HPNs reduction, leading to further amplification of the signal. The possible mechanism of significant enhance was shown in Scheme 1. 3.4. Experimental condition optimization. In order to achieve the best performance for acetamiprid detection, it is of great significance to choose optimal experimental conditions including the AA concentrations, pH value of solution and incubation time of acetamiprid. Firstly, the influence of AA concentrations on the DPV responses was investigated, which was a key parameter to the sensitivity of the sensor. Figure S1A(Supporting Information) revealed that with the enlargement of AA concentration, the oxidation peak current increases significantly, and then reached to a constant while the AA concentration was 1.0 mM. As a result, 1.0 mM of AA could be selected as the optimal concentration for the aptasensor in this experiment. The pH value of PBS was evaluated and it was shown in Figure S1B(Supporting Information). The Ip of the modified electrode increased from pH 4.0 to 7.0, achieveing the maximum value at pH 7.4. Therefore, the optimized pH value of PBS was 37 °C for the further investigation. The incubation time of acetamiprid was another essential factor for the 13



aptasensor. The aptasensor was incubated with acetamiprid range from 10 to 70 min. A decrease in the Ip was observed when the incubated time was lower than 60 min and then reached a constant in 60 min (Figure S1C, Supporting Information). In the subsequent experiments, 60 min of incubated time was chosen as the reaction time.

Figure 4. The DPV curves of the aptasensors with diverse signal probes labeled cDNA of : (A): (a) Fc-COOH, (b) PEI-Fc; (B): (a) Fc-COOH, (b) SiO2@PEI-Fc-PAA core-shell polymeric nanomaterials; (C): (a) Fc-COOH, (b) the synthesized Fc-HPNs with PBS (pH 7.4) for the absence of 1.0 mM AA. (D): (a) Fc-HPNs with PBS (pH 7.4) for the absence of 1.0 mM AA; (b) Fc-HPNs with PBS (pH 7.4) containing 1.0 mM AA. 3.5. Performance of aptasensor. Under the above optimization experimental conditions, the construction of aptasensor was employed to evaluate acetamiprid with diverse concentrations. The decline of the DPV signal with fixed concentration was recorded, and exhibited a good linear relationship with the logarithm of acetamiprid from 10 nM to 1 fM(Figure 5). The regression equation wasΔIp = 0.842lgc + 5.72 (ΔIp=Ipc-Ip0, where Ip0 and Ipc are peak current 14


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of the modified electrodes before and after incubation with acetamiprid and c is concentration of acetamiprid) with limit of detection down to 0.33 fM (S/N = 3) and the correlation coefficient of 0.998. Futhermore, the comparison of the analytical performance between our aptasensor strategy and other paper reported previously was performed (Table S1, Supporting Information). This result can be attributed to hollow polymeric nanomaterials with the amount of load Fc and effective catalysis reduction by AA.

Figure 5. (A) DPV responses of the resulting acetamiprid aptasensor with concentrations range from 10 nM to 1 fM; (B) the corresponding calibration curve for acetamiprid measurement.

3.6. Selectivity, stability and reproducibility of the acetamiprid aptasensor. Selectivity is a major criterion for accessing the performance of acetamiprid sensor. The selectivity of acetamiprid apatasensor was measured by using interfering pesticides: methyl parathion, carbendazim, cypermethrin, chlorpyrifos. As you can see in Figure S2A(Supporting Information), the changes of the DPV signal could be ignored when the methyl parathion, carbendazim, cypermethrin, and chlorpyrifos were utilized to replace the target acetamiprid. Additionally, a very slight variation (RSD = 5.22%) was observed in the mixtures containing all interfering pesticides and target acetamiprid, suggesting the selectivity of the proposed 15



strategy. To evaluate the stability of the acetamiprid sensor, long-term storage over 30 days (at 4 °C) was investigated. The initial DPV response remained 91.0 % after half a month and 84.7 % after a month, which indicated acceptable stability of the aptasensor. Additionally, the reproducibility of the aptasensor was measured with seven electrodes for 10 pM acetamiprid and RSD of 4.67 % were obtained in Figure S2B (Supporting Information). This above result proved that the reproducibility of the aptasensor for acetamiprid detection was acceptable. 3.7. Practical sample analysis of acetamiprid. The ingredient of practical samples, such as environment and agricultural samples, are usually extremely complicated. In order to verify the applicability of acetamiprid aptasensor in practical samples, acetamiprid in cucumbers and apples was quantitative detection by our aptasensor and LC-MS in parallel. All practical samples were purchased from the local market. A quantitative amount of 100 g of every fresh sample was prepared to homogenization with high speed homogenizer. The obtained homogenate of every fresh sample was immediately frozen and subsequent freeze-dried. The freeze-dried powder from the samples could be dispersed in ultrapure water to obtained 1 g mL-1 mixed solution, respectively. The mixed solutions were subsequent centrifuged for 15 min at 5000 rpm. The filter membrane was used to filter the centrifuged supernatant. Then, the filtrate was diluted to proper concentration with ultrapure water for the detection range. Meanwhile, the recovery experiments were carried out by standard addition method. The standard addition method has transferred a quantitative acetamiprid to the sample and the other of the treatment was the same as above mentioned process. Both of the measured and calculated results were demonstrated with Table 1. For the comparison between our aptasensor and LC-MS, the determination results by our aptasensor could be in accordance with LC-MS. According to GB/T 23584-2009, the content of acetamiprid from our practical samples could be safe enough. One thing deserves to be mentioned is that our sample pretreatment is more convenient and rapid. The recovery for the acetamiprid was from 92.3% 16


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to 104% and the RSD of the results was less than 5.21%. The recovery results further demonstrated that the accuracy of our aptasensor could be available. The practical sample analysis of acetamiprid can be good enough, which makes it possible for monitoring the acetamiprid. Table 1. Analysis of practical samples and recoveries with various concentrations of acetamiprid (n=3). LC-MS

Samples

Cucumber

Apple

(g g-1 )

This aptasensor (n=3) Detected

Added

Total

Recovery

RSD

(g g-1 )

(g g-1 )

(g g-1 )

(%)

(%)

1#

0.03

0.0280

0.100

0.129

101

5.21

2#

0.008

0.00820

0.050

0.0564

96.4

3.91

3#

-

-

0.300

0. 277

92.3

2.65

1#

0.15

0.0157

0.100

0.111

95.3

3.42

2#

-

-

0.300

0.312

104

3.16

3#

0.06

0.0620

0.100

0.157

95.0

4.25

4. CONCLUSION Highly efficient signal probe of the novel hollow polymeric nanospheres (Fc-HPNs), which combined AA as the catalytic amplification regent during the DPV detection process of acetamiprid, was observed for the first time. Remarkably, the Fc-HPNs played dual roles: as nanocarriers, to significantly increase the load amount of Fc, and as the nanoreducers, to effectively catalytic reduction by AA for further signal amplification. Specifically, our aptasensor still does not eliminate the drawbacks of traditional aptasensors such as long-incubation time and difficulty in regeneration. In view of above advantages, this work opened a novel avenue and versatile strategy for monitoring the acetamiprid, which demonstated great potential for practical sample analysis.

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ASSOCIATED CONTENT Supporting Information Optimization of experimental parameters: AA concentrations, pH value of PBS and incubation time of acetamiprid; Selectivity of the prepared acetamiprid aptasensor against other interference from 1 to 6: methyl parathion, carbendazim, cypermethrin, chlorpyrifos, acetamiprid and mixture (each at 10 pM); Reproducibility of the prepared aptasensor with seven electrodes for the detection of 10 pM acetamiprid; Performance comparison of this aptasensor and referenced aptasensors for acetamiprid detection.

AUTHOR INFORMATION *Corresponding author： Prof.Changli Zhou Tel.: +86 531 82765372 E-mail address: [email protected]

Notes The authors declare no competing financial interest.

AKNOWLEDGEMENTS This work was financially supported by the Foundation of Shandong Provincial Natural Science Foundation, China (ZR2017MB063) and the Science and Technology Development Plan Project of Shandong Province (2012G0022116).

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Based on layer-by-layer template technology and catalytic amplification by ascorbic acid, a dual-signaling electrochemical aptasensor was reported for acetamiprid detection.

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Dual-Signaling Amplification Electrochemical Aptasensor Based on

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