pristine graphene ternary composite and fabrication electrochemical sensor to detect dopamine and hydrogen peroxide

Chemical Physics Letters 736 (2019) 136797

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Research paper

Synthesis of Fe3O4/graphene oxide/pristine graphene ternary composite and fabrication electrochemical sensor to detect dopamine and hydrogen peroxide Linlin Caia, Bingjie Houa, Yangyang Shanga, Liao Xua, Bo Zhoua, Xinning Jiangb, Xiaoqing Jianga,

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a

Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, College of Chemistry and Materials Science, Nanjing Normal University, 1 Wenyuan Road, Nanjing 210023, China b Nanjing City Vocational College, 462 Heyan Road, Nanjing 210002, China

H I GH L IG H T S

ternary composite Fe O /GO/PG is successfully prepared by a simple method. • AThenovel O /GO/PG is used to fabricate electrochemical sensor for rapid detection of dopamine and hydrogen peroxide. • The Feelectrochemical sensor based on Fe O /GO/PG exhibits remarkable detection performance. • 3

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A R T I C LE I N FO

A B S T R A C T

Keywords: Pristine graphene Graphene oxide Fe3O4 nanoparticle Dopamine Hydrogen peroxide Sensor

In this work, a new Fe3O4/graphene oxide (GO)/pristine graphene (PG) ternary composite (Fe3O4/GO/PG) was successfully synthesized. The structure of Fe3O4/GO/PG was characterized by transmission electron microscopy (TEM). The TEM result shows that the small PG sheets are attached to the larger GO sheets and the Fe3O4 nanoparticles are anchored on the surface of GO/PG composite. A sensor based on this Fe3O4/GO/PG has been fabricated successfully to detect dopamine (DA) and hydrogen peroxide (H2O2). The linear detection ranges for DA and H2O2 are 0.30–30 μM and 0.50–277 μM, respectively, with detection limits of 0.18 and 0.09 μM.

1. Introduction Dopamine (DA), a type of neurotransmitter secreted by the brain, can activate the cells. It is also related to transmitting pleasure and addiction to drugs. Low level of DA will lead to Parkinson's disease [1,2]. Hydrogen peroxide (H2O2) is the by-product of several oxidative metabolic pathways in the human body [3,4]. Excessive aggregation may lead to many diseases such as cardiovascular disease, Alzheimer's disease, and cancer [5,6]. Thus, it is crucial to detect DA and H2O2 precisely and efficiently. Many methods are developed to detect these biomolecules, including fluorimetry, spectrophotometry, electrochemical sensor, and chemiluminescence [7,8]. Electrochemical sensor draws our attention due to its advantages of high sensitivity, low cost, and saving time [9]. Recently, electrochemical sensors based on graphene play a significant role in detecting analytes. Graphene has been a hotspot in the research field since it was discovered in 2004 [10]. It has attracted

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many scientists’ attention due to its high conductivity, fast charge mobility, large specific area, and strong mechanical strength [11]. Nowadays, composites based on graphene and graphene derivatives play a dominant role in the material field for the new fabrications to show better properties [12]. Graphene oxide (GO), a graphene derivative prepared by chemical oxidation of graphite, exhibits excellent water-solubility owing to oxygen-containing functional groups on the surface. Pristine graphene (PG), prepared by direct exfoliation, has superior conductivity due to better preservation of graphene structures [13–17]. So, the GO/PG composite may exhibit good electrochemical performances with a combination of the high conductivity of PG and the good water solubility of GO [18]. A lot of materials are used to fabricate biosensors, such as noble metal and transition metal oxide. Fe3O4 nanoparticles are one of the most attractive materials owing to their unique peroxidase-like activity [19]. Many methods are used to prepare Fe3O4 nanoparticles including hydrothermal reaction method, ultrasonic chemical method,

Corresponding author. E-mail address: [email protected] (X. Jiang).

https://doi.org/10.1016/j.cplett.2019.136797 Received 22 July 2019; Received in revised form 25 September 2019; Accepted 25 September 2019 Available online 26 September 2019 0009-2614/ © 2019 Elsevier B.V. All rights reserved.

Chemical Physics Letters 736 (2019) 136797

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2.3. Preparation of Fe3O4/GO/PG composite

microemulsion method, co-precipitation method, iron salt high-temperature pyrolysis method, and so on [20–23]. Among these, co-precipitation is the most conventional method [24]. This method consists of ferric ion and ferrous ion in a 2:1 molar ratio in alkaline solutions:

Briefly, 25 mg GO/PG composite was dispersed in 20 mL ultrapure water and then sonicated for 15 min. Ferric chloride (FeCl3·6H2O (51.4 mg)) and ferrous sulfate (FeSO4·7H2O (26.4 mg)) were dissolved separately in 5 mL ultrapure water with the molar ratio of 2:1. After being mixed and stirred sufficiently, the solution was adjusted to the pH of 11 with ammonia water and kept at 90 °C for 2 h. The whole reaction process was under the protection of nitrogen. Then the Fe3O4/GO/PG composite was magnetically separated from the solution and then washed several times with water until the washing liquid is neutral. The theoretical mass ratio of Fe3O4 to GO/PG in this Fe3O4/GO/PG sample is 0.88. Therefor it is denoted as Fe3O4/GO/PG0.88. Two other Fe3O4/ GO/PG samples with mass ratio of Fe3O4 to GO/PG of 0.70 and 1.04 were also prepared in a similar way, denoted as Fe3O4/GO/PG0.70 and Fe3O4/GO/PG1.04. For comparison, the binary composites Fe3O4/GO and Fe3O4/PG were prepared in a similar way but with GO or PG instead of GO/PG.

Fe2+ + 2Fe3+ + 80H− → Fe3O4 + 4H2O Herein, we utilize the co-precipitation method to in situ synthesize the Fe3O4 nanoparticles on the GO/PG nanosheets to fabricate a new Fe3O4/GO/PG ternary composite. The transmission electron microscopy (TEM) measurement is used to characterize the morphology of the composite. The TEM results show that Fe3O4 nanoparticles were formed on the surface of GO/PG composite successfully. Meanwhile, the electrochemical tests of the sensors fabricated with this Fe3O4/GO/ PG demonstrate that it could efficiently detect DA and H2O2.

2. Experimental 2.1. Materials and instruments

2.4. Fabrication of sensor All reagents used in the experiment are of analytical reagent grade except graphite powder (1200 mesh, 99.95%). Sulfuric acid and H2O2 were purchased from the Sinopharm Chemical Reagent Co. Ltd. Dimethyl sulfoxide (DMSO), potassium persulfate, phosphorus pentoxide, potassium permanganate, dipotassium phosphate, and sodium chloride were purchased from Shanghai Lingfeng Chemical Reagent Co. Ltd. Trisodium citrate (C6H5Na3O7·2H2O) was purchased from Shanghai Chemical Reagent First Factory. DA was bought from Aladdin. Ultrapure water (≥18.2 MΩ cm) was used throughout the work. The concentration of PG was measured by the absorbance of the dispersions at 660 nm in UV–Vis spectra (Cary 50, Varian,’Inc) with an extinction coefficient of 3620 mL mg−1 m−1 [25]. The concentration of GO, GO/PG, and Fe3O4/GO/PG were measured by the gravimetric method. The morphologies of samples were observed using a Hitachi7650 transmission electron microscopy (TEM) operating at an accelerating voltage of 80 kV. The TEM samples of GO/PG, Fe3O4/GO, and Fe3O4/GO/PG were prepared by casting dispersion onto carbon-coated copper grids. X-ray photoelectron spectroscopy (XPS) (Thermo Fisher Scientific ESCALAB Xi+) was used to analyze the elemental compositions of samples. Raman spectra were tested on a confocal 386 laser microRaman spectrometer (Thermo Fischer DXR, USA) at a laser of excitation wavelength of 532 nm. X-ray diffraction (XRD) measurements were carried out using a D/max 2500 VL/PC X-ray diffractometer with graphite-monochromatized Cu Kα radiation. All electrochemical measurements were performed on a CHI660C electrochemical workstation (CH Instruments, Shanghai, China), with a conventional threeelectrode system: a bare or modified GCE (Fe3O4/GO/PG/GCE, Fe3O4/ GO/GCE, Fe3O4/PG/GCE) as the working electrode, platinum wire and Ag/AgCl (saturated KCl) electrodes as the counter and reference electrodes, respectively.

Prior to modification, the glassy carbon electrode (GCE, diameter: 3 mm) was polished orderly with 1.0, 0.3, and 0.05 μm alumina powder. Then the GCE was sonicated in ethanol/water (volume ratio 1:1) and ultrapure water successively for 15 s. Then typically 6 μL of Fe3O4/GO/PG, Fe3O4/GO, or Fe3O4/PG (1.5 mg mL−1) was dropped on the GCE surface and dried at ambient temperature in air. 3. Result and discussion Fig. 1 shows the typical TEM images of GO, PG, GO/PG, Fe3O4/GO, and Fe3O4/GO/PG0.88. In Fig. 1a, the GO sheets with size of several micrometers are almost transparent and folded somewhat, which indicate the sheets are very thin but with defects on them [25]. In contrast, in Fig. 1b, the PG sheets are much flatter but less transparent, demonstrating the sheets are more defect-free but a bit thicker. Besides, the average lateral size of PG is only around 200 nm and much smaller than that of GO. The small lateral size of PG should be due to the sonication-induced cleavage effect and high centrifugation speed in the producing process of PG. As shown in Fig. 1c, the small-sized PG sheets patched on the larger GO sheets, which is in accordance with our previous report [18]. In Fig. 1d of Fe3O4/GO, some nanoparticles were formed on the transparent GO sheet. As shown in Fig. 1e, the TEM image of Fe3O4/GO/PG0.88 shows that many nanoparticles with diameters of less than 10 nm anchored on the surface of GO/PG composite. Fig. 1f shows the black suspension of Fe3O4/GO/PG0.88 and the composite could be rapidly separated from the solution using a magnet within 30 s as shown in Fig. 1g, indicating that the synthesized composite is magnetic. Fig. S1 shows the Raman spectrum of Fe3O4/GO/PG0.88. It exhibits G band (1566 cm−1) and 2D band (2686 cm−1) of PG and D band (1338 cm−1) of GO [14]. The G band is much sharper than those observed in GO, which also evidences the existence of both GO and PG in the composite [14,27]. The peak at 581 cm−1 is a typical peak of iron oxide [27]. Fig. S2 shows the wide scan XPS spectrum of Fe3O4/GO/PG0.88. The binding energy peaks at around 285, 516, and 711 eV should be attributed to C 1s, O 1s, and Fe 2p, indicating the existence of carbon, oxygen, and iron in the sample. The peaks at 712 and 725 eV in the Fe 2p spectrum (the inset in Fig. S2) are the characteristic peaks of Fe 2p1/ 2 and Fe 2p3/2 spin–orbit peaks of Fe3O4, which evidences the formation of the Fe3O4 in the ternary composite [28]. Fig. S3 shows the XRD spectrum of Fe3O4/GO/PG0.88. The diffraction peaks (2θ) at 17.8°, 30.1°, 35.6°, 43.1°, 54°, 57.4° and 62.6° should be ascribed to the (1 1 1), (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1) and (4 4 0) planes of Fe3O4, respectively, which correspond well with

2.2. Preparation of GO/PG composite Graphite oxide was synthesized by the modified Hummers method [26]. GO was prepared by exfoliation of graphite oxide by sonication in water using an ultrasonic cleaner (DTC-15, 40 kHz, 200 W) for 1 h. PG was prepared by direct exfoliation of the graphite powder in DMSO with the assistant of C6H5Na3O7·2H2O as reported in our previous work [13]. The GO/PG composite with the optimized GO to PG mass ratio of 3:2 [25] was prepared by mixing colloidal dispersions of GO/H2O (0.5 mg mL−1) and PG/DMSO (0.5 mg mL−1) and sonicating in the ultrasonic cleaner for 30 min. The resulting homogeneous dispersion was centrifuged using a centrifuge (Hettich Universal 320) at 9000 rpm (relative centrifugal force is 7690g) for 30 min. The obtained precipitate (GO/PG) was re-dispersed in deionized water by sonicating 20 min. 2

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30 Fig. 1. TEM images of (a) GO, (b) PG, (c) GO/PG, (d) Fe3O4/GO, and (e) Fe3O4/ GO/PG0.88. Photographs of (f) Fe3O4/GO/PG0.88 suspension and (g) magnetic separation of Fe3O4/GO/PG0.88 by an external magnet.

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Rct

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the standard data of Fe3O4 (JCPDS no. 19-0629). The XRD peak at around 10.6°, which is commonly observed for graphene oxide, is not observed in Fig. S3, indicating that the sheets of graphene oxide did not re-stacked during the preparation of ternary composite. The diffraction peak at around 26.4° should be ascribed to PG, suggesting the partially re-stacking of PG sheets during the preparation of ternary composite [14]. Fig. 2a displays cyclic voltammograms (CVs) of bare GCE, Fe3O4/ GO/GCE (hereafter denoted as Fe3O4/GO), and Fe3O4/GO/PG/ GCE0.88 (hereafter denoted as Fe3O4/GO/PG0.88) in 0.1 M KCl containing 5 mM [Fe(CN)6 ]4−/3− at a scan rate of 50 mV s−1. All the curves show a pair of redox peaks. The Fe3O4/GO/PG0.88 shows the highest peak current, higher than that of GCE; whereas, the Fe3O4/GO has the lowest peak current, much lower than that of GCE. These may be attributed to the good conductivity of PG/GO and the poor conductivity of GO. In order to evidence it, the electrochemical impedance spectroscopy (EIS) of the three electrodes were further carried out. Fig. 2b shows the EIS of the three electrodes at a frequency from 0.01 to 100 kHz in 0.1 M KCl containing 5 mM [Fe(CN)6 ]4−/3−. Usually, the diameter of the semicircle at high frequency in EIS displays the electron transfer resistance (Rct) on the surface of the electrode [29]. In Fig. 2b, an obvious semicircle can be clearly observed for Fe3O4/GO, but not for Fe3O4/GO/PG0.88 or GCE. The Rct of Fe3O4/GO is estimated to be around 240 Ω. The high-frequency zone of the EIS of GCE and Fe3O4/ GO/PG0.88 is magnified in Fig. 2c for more clear observation. The Rct of GCE in Fig. 2c is about 23 Ω, comparable to the Rct value reported for GCE [30]. However, Fe3O4/GO/PG0.88 almost has no charge transfer resistance, indicating a very fast charge transfer in the surface of this electrode. According to the results of CV and EIS, we can conclude that

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Z'/ohm Fig. 2. (a) CVs of GCE, Fe3O4/GO, and Fe3O4/GO/PG0.88 in 0.1 M KCl containing 5 mM [Fe(CN)6 ]4−/3− at a scan rate of 50 mV/s. (b) EIS of GCE, Fe3O4/ GO, and Fe3O4/GO/PG0.88 at frequency from 0.01 to 100,000 Hz. (c) Magnified high frequency zone of the EIS of GCE and Fe3O4/GO/PG0.88.

the Fe3O4/GO/PG0.88 composite possesses good conductive performance. Fig. 3a shows CVs of GCE, Fe3O4/GO, and Fe3O4/GO/PG0.88 in phosphate buffer saline (PBS) (pH = 7.0) in the absence or presence of 1 mM DA at the scan rate of 50 mV s−1. It can be observed that a pair of nearly quasi-reversible redox peaks appeared on each of the three electrodes in the presence of 1 mM DA. The peak current of Fe3O4/GO/ PG0.88 is much higher than those of Fe3O4/GO and GCE. Fig. S4a shows CVs of GCE modified with Fe3O4/GO/PG0.70, Fe3O4/GO/ PG0.88, Fe3O4/GO/PG1.04, and Fe3O4/PG in PBS with 1 mM DA at the scan rate of 50 mV s−1. The Fe3O4/GO/PG0.88 shows the largest response current. The influence of loading amount of Fe3O4/GO/PG0.88 on the GCE is also investigated and the results are shown in Fig. S5a, which indicates the best loading amount of Fe3O4/GO/PG0.88 is 9 μg (6 μL of 1.5 mg mL−1). The catalytic rate constant of DA (kcat-DA) on Fe3O4/GO/PG0.88 was also measured by chronoamperometry [31] and the results are shown in Fig. S6a, in which kcat-DA is estimated to be 2.08 × 104 M−1 s−1. 3

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Table 1 The linear ranges and detection limits of different modified electrodes for the detection of DA. Materials

Liner range (μM)

Detection limit (μM)

Refs.

TiO2/Gra Au/Gr ZnS/rGOb SnO2/PANI/N-GQDc Cu NWs-GOd Fe3O4/CNT-Ne Fe3O4/rGO Fe3O4/GO/PG0.88

5–200 6.8–410 1.0–500 0.5–200 1–100 2.5–65 0.5–100 0.20–3.00 3.00–30.00

2 1.4 0.5 0.22 0.41 0.05 0.12 0.18

[33] [34] [35] [36] [37] [38] [39] This work

a b c d e

Graphene (Gr). Reduced graphene oxide (rGO). Polyaniline (PANI), N-doped graphene quantum dots (N-GQD). Nanowires (NWs), graphene oxide (GO). N-doped carbon nanotubes (CNT-N).

such as TiO2/graphene (Gr) [33], Au/Gr [34], ZnS/reduced graphene oxide (rGO) [35], SnO2/PANI/N-GQD [36], and Cu NWs [37]. Besides, this Fe3O4/GO/PG sensor has a wider linear range in the low concentration region compared with Fe3O4/doped carbon nanotubes (CNTN) [38] and Fe3O4/rGO [39]. This new Fe3O4/GO/PG0.88 sensor has been also explored to detect H2O2. Fig. 4a shows CVs of it in PBS (pH = 7.0) containing different concentrations of H2O2 at the scan rate of 50 mV s−1. A significant oxidation peak appears near 0.75 V with the addition of 1 mM H2O2. With the increase in the concentration of H2O2, the current intensity increases. Similar to the effect on sensing DA, Fe3O4/GO/PG0.88 also shows the best performance to H2O2 as shown in Fig. S4b. For H2O2, the best loading volume is 6–8 μL as shown in Fig. S5b, and 6 μL is used in this work. The catalytic rate constant of H2O2 (kcat-H2O2) on Fe3O4/GO/ PG0.88 was also measured and the results are shown in Fig. S6b, in which kcat- H2O2 is estimated to be 4.64 × 102 M−1 s−1. Fig. 4b displays amperometric response of Fe3O4/GO/PG0.88 to the successive additions of H2O2 in 0.1 M PBS (pH = 7.0) at the selected working potential of 0.75 V. The current response in the range of low concentration of H2O2 is shown in Fig. 4c. Fe3O4/GO/PG0.88 has a distinct current response in the range of low concentration and a stable current response in the range of high concentration. It is worth noting that this Fe3O4/GO/PG0.88 sensor is very sensitive to the change of concentration of H2O2. When a small amount of H2O2 is added, the current signal has a significant step and could reach a stable level within 5 s, illustrating the sensor based on Fe3O4/GO/PG0.88 can detect H2O2 sensitively. The relationship between the current response and the concentration of H2O2 is exhibited in Fig. 5a. This Fe3O4/GO/PG0.88 sensor also shows two linear ranges for H2O2. One is from 17.00 to 277.00 μM with a sensitivity of 0.31 μA μM−1 and R2 of 0.998 and another one is from 0.50 to 17.00 μM with a sensitivity of 0.18 μA μM−1 and R2 of 0.996. The calibration plot in the range of lower concentration is magnified and shown in Fig. 5b. The detection limit is 0.09 μM at S/N of 3. Table 2 shows the comparison of different electrodes for the detection of H2O2. The sensor based on Fe3O4/GO/PG0.88 has the lowest detection limit compared with sensors based on Fe3O4 or other material based on metal oxides. This is not only due to the good water solubility and high conductivity of GO/PG composite, but also due to that Fe3O4 nanoparticles have peroxidase-like activity [40]. Therefore, the Fe3O4/GO/ PG0.88 is an ideal electrode material for detecting H2O2. The anti-interference ability of the sensor is also investigated. The results are show in Fig. S7. Although it is well known that some potentially coexisting compounds such as Cl−, Na+, Fe3+, or K+ in the biological system will affect the sensor response, they do not significantly disturb the determination of DA, neither influence the determination of H2O2. The 5-fold addition of H2O2 does not influence the

Fig. 3. (a) CVs of GCE, Fe3O4/GO, and Fe3O4/GO/PG0.88 in PBS in the absence or presence of 1 mM DA with the scan rate of 50 mV/s. (b) DPVs of Fe3O4/GO/ PG0.88 in 0.1 M PBS with different concentration of DA from 0 to 30 μM. (c) The calibration curve based on the DPV peak current versus the DA concentration on Fe3O4/GO/PG0.88.

Compared with CV, differential pulse voltammetry (DPV) is more sensitive [32]. Fig. 3b shows the DPVs of Fe3O4/GO/PG0.88 in 0.1 M PBS (pH = 7.0) with concentration of DA from 0 to 30 μM. It can be seen the peak current near 0.2 V increases with the increasing of the concentration of DA. Fig. 3c shows the corresponding linear relationship between the DPV peak current and the concentration of DA on a Fe3O4/GO/PG0.88 sensor. This sensor has two linear ranges: one from 0.20 to 3.00 μM with a sensitivity of 5.96 μA μM−1 and a correlation coefficient (R2) of 0.998, and another one from 3.00 to 30.00 μM with a sensitivity of 2.40 and R2 of 0.996. The detection limit is 0.19 μM at a signal-to-noise ratio (S/N) of 3. Table 1 shows the comparison of different electrodes for the detection of DA. The sensor based on Fe3O4/ GO/PG0.88 has a lower detection limit compared with other sensors 4

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3 Fig. 5. (a) The calibration curve between current signal and H2O2 concentration for Fe3O4/GO/PG0.88. (b) The calibration plot for lower concentrations of H2O2.

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Table 2 The linear ranges and detection limits of different modified electrodes for the detection of H2O2.

0

Materials

200

300

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Fe3O4/rGO AuFe3O4/Pt/rGO Fe3O4/SiO2/HRPa NiO/Gr Fe3O4/Gr-chitosan α-MoO3/GO/GCE GO Fe3O4/GO/PG0.88

Time/sec Fig. 4. (a) CVs of Fe3O4/GO/PG0.88 in PBS containing different concentration of H2O2 at a scan rate of 50 mV/s. (b) Amperometric current–time curves of Fe3O4/GO/PG0.88 with additions of H2O2 in 0.1 M PBS at the potential of 0.75 V. (c) The amperometric response in the range of lower concentration of H2O2.

a

determination of DA either, however, DA disturbs the determination of H2O2 seriously. The relative standard deviation (RSD) for 5 detection results from parallel electrodes was 6.9% for DA (20 μM) and 5.7% for H2O2 (20 μM). The electrode still maintained 82.3% of its response for DA (1 mM) and 82.8% for H2O2 (1 mM) after 20 measurements.

Liner range (μM) 3

100–6 × 10 0.5–11.5 2–24 250–4.75 × 103 24.9–1.67 × 103 0.92–2.46 × 103 500–2.5 × 104 0.50–17 17–277

Detection limit (μM)

Refs.

3.2 0.1 0.43 0.7664 3.05 0.31 97.5 0.09

[40] [41] [42] [43] [44] [45] [46] This work

Horseradish peroxidase.

for DA and H2O2 are 0.30–30 and 0.50–277 μM, with detection limits of 0.18 and 0.09 μM, respectively. Declaration of Competing Interest

4. Conclusion

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.

In this work, a new Fe3O4/GO/PG ternary composite was prepared successfully by in-situ formation of Fe3O4 nanoparticles on GO/PG and further used to construct an electrochemical sensor to detect DA and H2O2 efficiently. Compared to the bare GCE and Fe3O4/GO, Fe3O4/GO/ PG0.88 exhibits outstanding properties, which is related to the good water solubility and high electrical conductivity of GO/PG and the catalytic performance of Fe3O4. The sensor based on Fe3O4/GO/PG0.88 exhibits good sensitivity for DA and H2O2. The linear detection ranges

Acknowledgements This work is supported by Huaian Bio-Medical Functional Materials and Analysis Technology Service Platform (HAP201612) and the Priority Academic Program Development of Jiangsu Higher Education 5

Chemical Physics Letters 736 (2019) 136797

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Institutions.

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