New synthesis of self-assembly ionic liquid functionalized reduced graphene oxide–gold nanoparticle composites for electrochemical determination of Sudan I

    New synthesis of self-assembly ionic liquid functionalized reduced graphene oxide-gold nanoparticles composites for electrochemical determination of Sudan I Meiling Wang, Zhengnian Chen, Yaomin Chen, Chunjin Zhan, Jianwei Zhao PII: DOI: Reference:

S1572-6657(15)30066-7 doi: 10.1016/j.jelechem.2015.08.007 JEAC 2231

To appear in:

Journal of Electroanalytical Chemistry

Received date: Revised date: Accepted date:

3 May 2015 18 July 2015 5 August 2015

Please cite this article as: Meiling Wang, Zhengnian Chen, Yaomin Chen, Chunjin Zhan, Jianwei Zhao, New synthesis of self-assembly ionic liquid functionalized reduced graphene oxide-gold nanoparticles composites for electrochemical determination of Sudan I, Journal of Electroanalytical Chemistry (2015), doi: 10.1016/j.jelechem.2015.08.007

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ACCEPTED MANUSCRIPT New synthesis of self-assembly ionic liquid functionalized reduced graphene

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oxide-gold nanoparticles composites for electrochemical determination of Sudan I

Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and

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Meiling Wanga, Zhengnian Chenb, Yaomin Chenb, Chunjin Zhanb, Jianwei Zhaoa

Chemical Engineering, Nanjing University, Nanjing 21008, Jiangsu Province, P. R.

b

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China

College of material engineering, Nanjing Institute of Technology, Nanjing 211167,

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Jiangsu Province, P. R. China

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Corresponding author. Tel. / Fax: +86-25-83596523. E-mail addresses: [email protected] (J. Zhao). 1

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Abstract

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Positively charged gold nanoparticles (AuNPs) were self-assembled onto the

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surfaces of 1-allyl-3-methylimidazolium chloride (AMIM-Cl) functionalized reduced graphene oxide sheets (RGO) here. The AMIM-Cl functionalized RGO (ILRGO)

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loaded with AuNPs (ILRGO@AuNPs) modified glass carbon electrode (GCE) possess larger effective specific surface area which can in favor of more Sudan I dye

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adsorbed to the working electrode. So the ILRGO@AuNPs composites were successfully used for the fabrication of a facile and sensitive sensor for the

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determination of Sudan I. And the prepared sensor exhibits a broad linear range for

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Sudan I spanned 4 orders of magnitude from 1.0×10-10 to 1.0×10-6 M and the detection

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limit as low as 5.0×10-11 M, (S/N=3). It is expected that this green sensor can be

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applied in determination of other similar dyes.

Keywords: Sudan I; Determination; Self-assembled; Gold nanoparticles; Ionic liquid functionalized reduced graphene oxide

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ACCEPTED MANUSCRIPT 1. Introduction

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Synthetic dyes have been widely used as coloring agents in food industry for

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many years. Many synthetic dyes, including lipid-soluble (Sudan dyes) and

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water-soluble (Sunset yellow, Tartrazine, Amaranth, Ponceau 4R, Brilliant blue and Quinoline yellow) colorants [1], contain azo functional groups and aromatic nucleus

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which can be reduced to aromatic amines and may cause frequent headaches for adults, and distraction and hyperaction for children [2, 3]. Sudan I is a kind of

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synthetic chemical coloring agent, which is widely used in many fields, such as

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petroleum, engine oil, coloring hydrocarbon solvents and textile colorants [4-6]. And

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Sudan I have been classified as Group 3 carcinogen by the International Agency for Research on Cancer [7], so it is not allowed to be used as additive in foods according

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to both the Food Standards Agency and the European Union [8-10]. However, Sudan I is still found in foodstuffs as additive due to its low cost, bright colour and stability,

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such as salted duck egg, chili sauce and drugs. Therefore, it is highly desirable to develop a valid strategy for the efficient determination of Sudan I.

Electrochemical methods have significant advantages over other traditional methods [2, 5] including high selectivity and sensitivity, ease of operation, fast response and time-saving [11, 12]. However, electrochemical detection of Sudan I at bare electrodes is seriously suffers from high over potential, interference issues and less sensitivity [13]. Hence, it is important to design electrodes that are specific, selective and sensitive towards this analyte which means that it is necessary to explore 3

ACCEPTED MANUSCRIPT new materials. RGO, one kind of chemically derived graphene, has shown similar

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characteristics to graphene in many aspects [14-16] which has stimulated research

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interest because of its unusual electronic properties and ability to improve catalytic properties [17, 18]. In recent years, RGO-nanoparticle composites have been a good option as electrode materials because the composite process can be an effective

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strategy to enhance their electronic, chemical, and electrochemical properties [19].

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However, the RGO are easy aggregation in aqueous solution [20, 21], so it is very hard to obtain completely dispersed single RGO-nanoparticle composites. Recently,

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Liu reported ionic liquid (IL) of IL-NH2 functionalized graphene sheet (GS) loaded

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with gold nanoparticle (AuNPs) [22] to resolve such problems. However, the

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IL-GS-Au composite fabricated with this strategy involves complicated processes and harsh alkaline condition.

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Here, ionic liquid (IL) of 1-allyl-3-methylimidazolium chloride (AMIM-Cl) functionalized reduced graphene oxide sheets (ILRGO) loaded gold nanoparticles composites (ILRGO@AuNPs) were successfully constructed by assembling AuNPs onto ILRGO with a very new route. The ILRGO and AuNPs offer a synergistic electrocatalytic effect towards Sudan I including large specific surface area of graphene and electrically conductivity property of AuNPs. The fabricated Sudan I sensor reveals a wide linear range from 1.0×10-10-1.0×10-6 M, low detection limit of 5.0×10-11 M (S/N=3), high selectivity, and long-term stability. It is expected that this new method will have broad applications in determination of biological substance and 4

ACCEPTED MANUSCRIPT food colorants.

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2. Experiment

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2.1. Chemicals

Chopped red chili, tomato sauce, apple juice and grape juice samples were

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purchased from local market. Sudan I, Sudan II, Sudan III, Sudan VI were also purchased from Aladdin. 1-allyl-3-methylimidazolium chloride (AMIM-Cl), gold acid

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chloride trihydrate (HAuCl4·xH2O), sodium borohydride (NaBH4) were also from

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Aladdin. Britton-Robinson (BR) buffer solutions with different pH values were

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prepared by adjusting mixed acid solutions containing phosphoric acid, glacial acetic acid and borax with 1.0 M NaOH. Deionized water was used for the preparation of all

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solutions. All other chemicals were purchased from Aldrich or Aladdin and used without further purification. The AuNPs were prepared according to a literature [23].

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And graphite oxide was prepared from graphite powder with modified Hummers method [24].

2.2. Apparatus

The morphologies of IL of 1-allyl-3-methylimidazolium chloride (AMIM-Cl) functionalized reduced graphene oxide sheets (ILRGO) loaded gold nanoparticles composites (ILRGO@AuNPs) were observed by s high-resolution transmission electron microscopy, HRTEM (JEOL JEM-200CX). Electrochemical measurements performed on a CHI 660d electrochemical workstation (Co., CHI, U.S.A.) using 5

ACCEPTED MANUSCRIPT saturated calomel electrode (SCE) and a platinum wire as reference and counter electrode, respectively. The ILRGO@AuNPs modified glassy carbon electrode (GCE;

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2.3. Preparation of ILRGO@AuNPs composite

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diameter = 3 mm) was used as the working electrode.

Typically, there are two strategies including in situ synthesized method and

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electrostatic adsorption has been utilized to fabricate graphene-metallic nanoparticle

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composite. In our work, the electrostatic adsorption method was used. Fig. 1 shows the schematic route of new synthesis of the ILRGO@AuNPs composites. The ILRGO

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was synthesized according to the literature with modifications [25]. Firstly, sonication

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was carried out with a bath sonicator for 1 hour to yield the exfoliation of GO “water”

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(2.5 mg/mL). With that, GO water (20 mL) and AMIM-Cl (12.5 g) was mixed together at 180 °C under stirring. This step was keeping for 2 hour at 180 °C. The

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mixture underwent a change in color from brown to black, indicative of the reduction of GO (Step 1). Then the formed ILRGO interacted with AuNPs and then self-assembled at room temperature for 15 min (Step 2). The resultant was centrifuged at 10000 rpm for 10 min and then thoroughly washed with water (Step 3). In order to control the weight contents of gold nanoparticles in the composites, HAuCl4 (0.01%) with various volumes of 10-90 mL were used in the synthetic process. Obviously, the volume of sodium citrate solutions (1%) also varied correspondingly.

2.4. Preparation of ILRGO@AuNPs modified GCE

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ACCEPTED MANUSCRIPT The glassy carbon electrode (GCE, 3.0 mm in diameter) was polished with 0.3 and 0.05 mm alumina slurry, and then successively washed with 1:1 HNO3 solution,

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deionized water and acetone in an ultrasonic bath. The ILRGO@AuNPs composite

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modified GCE was made by directly transferring 5.0 μL ILRGO@AuNPs composite onto the surface of bare GCE and dried in air. For comparison, the same procedures

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were used for the preparation of ILRGO/GCE and AuNPs/GCE.

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2.5. Analytical procedure

0.1 M BR buffer (pH 7.0) was used as the supporting electrolyte for the detection

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of Sudan I. Cyclic voltammetry (CV) and square wave stripping voltammetry (SWSV)

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methods were recorded from 0.3 to 1.0 V after 5-min accumulation at open circuit,

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and the oxidation peak current at 0.595 V was measured as the analytical signal.

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2.6. Sample pretreatment

About 5.0 g of chopped red chili and tomato sauce were weighed exactly, and then 15.0 mL ethanol was added. After 30 min ultrasonication, the mixture was filtrated and the liquid phase was collected in a 100.0 mL volumetric flask. In addition, the apple juice and grape juice were used directly without pretreatment.

3. Experimental

3.1. Characterizations

The morphology of the produced ILRGO@AuNPs composite was observed by 7

ACCEPTED MANUSCRIPT HRTEM. Fig. 2A and B shows the composite at different magnification. It is clear that the self-assembled ILRGO@AuNPs composite is uniform and the ILRGO decorated

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with dispersed AuNPs. The size of AuNPs is about 15 nm.

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3.2. Electrochemical behavior of Sudan I at the GCE, AuNPs/GCE, ILRGO/GCE, ILRGO@AuNPs/GCE

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The CV (Fig. 3A, A’) and square wave voltammetry (SWV) curves (Fig. 3B, B’)

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of Sudan I (0.5 μM) at different electrodes in 0.1 M BR solution (pH 7.0) were studied. It can be seen Fig. 3A that a broad oxidation peak at 0.691 V is observed on

ILRGO@AuNPs/GCE,

respectively,

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and

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the bare GCE, while this peak shifted to 0.608 V and 0.595 V on the ILRGO/GCE and

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peak

currents

on

the

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ILRGO@AuNPs/GCE increased a lot than on other electrodes. In addition, it can be seen that the oxidation of Sudan I at the bare GCE and AuNPs/GCE is irreversible

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while a couples of well-defined redox peaks on the ILRGO/GCE and ILRGO@AuNPs/GCE occurred. And the reversibility of the redox of Sudan I improved a lot on the ILRGO@AuNPs/GCE than at the ILRGO/GCE. In addition, the SWV curves of Sudan I at different electrodes (B and B’) were similar to their CV curves and the SWV peak current of Sudan I was also remarkably increased at the ILRGO@AuNPs/GCE. These results indicate that the ILRGO@AuNPs/GCE can be used for the determination of Sudan I. This may be due to the catalytic activity of the AuNPs, the superior conductivity of ILRGO and large effective surface area of ILRGO@AuNPs composites. 8

ACCEPTED MANUSCRIPT 3.3. Optimization of the condition for the electrode fabrication

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Firstly, the weight contents of gold nanoparticles in the composites for the

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fabrication of ILRGO@AuNPs/GCE were one important parameter affecting the

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performance of the electrode. It was evaluated by changing volumes of HAuCl4 added in the synthetic process. As shown in Fig.4 A, with an increasing volume of HAuCl4

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from 10 to 50 mL, the oxidation peak currents of Sudan I increased. However, the peak current of Sudan I decreased when the volume of HAuCl4 was increased higher

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than 50 mL. Thus, 50 mL of HAuCl4 was used to synthesis the composites. This is

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possibly due to that the increase of the volume of HAuCL4 actually increased the

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weight contents of AuNPs in the composites, which would result in coagulation of the

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ILRGO@AuNPs composites.

The coating amount of ILRGO@AuNPs was also optimized for the

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electrochemical detection of Sudan I. The optimal volume of ILRGO@AuNPs suspension dropped on the GCE surface was studied by SWSV method. As displayed in Fig. 4B, the oxidation peak currents of Sudan I (0.7 μM) increased with the amount of ILRGO@AuNPs composite varying from 0 μL to 10.0 μL, and the peak current reached the maximum value at 5.0 μL, suggesting that the film thickness influenced the interface electron transfer process. So, 5.0 μL of the ILRGO@AuNPs composite was chosen for the subsequent experiments.

3.4. Optimization of parameters

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ACCEPTED MANUSCRIPT 3.4.1. Effects of accumulation condition

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In Fig. 5A, the influence of accumulation time on the oxidation peak current of

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0.7 μM Sudan I in 0.1 M BR was studied. As the accumulation time changed from 0

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to 450 s, the oxidation peak currents increased gradually and reached maximum value at 300 s. Therefore, 5 min was used as accumulation time for determination of Sudan

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I.

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3.4.2. Effects of pH

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Effects of pH values on the peak potentials and the peak currents of Sudan I were

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also investigated by CV method (Fig. 5B). The oxidation peak current of Sudan I reached the maximum value at pH 7.0 (Fig. 5B) and then decreased upon further

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increase of pH to 11.0. The peak potential shifted almost linearly towards negative potential along with the pH value increased (Fig. 5B and C), indicating that the

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protons are involved in the electrochemical redox process. The Epa of Sudan I was proportional to the pH value and the regression equation can be expressed as: Epa= -0.0289 pH + 0.827 (R = 0.998) and Epc = -0.0258 pH + 0.750 (R = 0.999), respectively. Therefore, considering the sensitivity of determination for Sudan I, BR (pH 7.0) was selected as the optimal supporting electrolyte for the subsequent studies.

3.4.3. Effects of scan rates

The influence of scan rates on the electrochemical behavior of 0.5 μM Sudan I in 0.1 M BR (pH 7.0) on the ILRGO@AuNPs/GCE was also studied by CV method (Fig. 10

ACCEPTED MANUSCRIPT 6A). Obviously, the redox peak current was dependent on the scan rate. And the oxidation peak potential shifted positively and the reduction peak potential shifted

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with the increase of scan rate. As shown in the Fig. 6B, a perfect linear relationship

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between the peak current and the scan rate from 20 to 600 mV s-1 was obtained by plotting the peak current against the scan rate. The linear regression equations are Ipa = 0.0128 υ (mV) + 0.126 (R2 = 0.996) and Ipc = -0.0123 υ (mV) + 0.521 (R2 = 0.995),

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respectively. These results indicated that the electrode reaction of Sudan I on the

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ILRGO@AuNPs/GCE was a typical diffusion-controlled process.

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3.5. Calibration curves for determination of Sudan I

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The electrochemical response of ILRGO@AuNPs/GCE was investigated as a

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function of the Sudan I concentrations (0.0001-1.0 μM) using the SWSV technique in BR buffer solutions (0.1 M, pH 7.0). Fig. 7A shows the SWV curves of different

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concentrations of Sudan I on ILRGO@AuNPs modified GCE. An extended linear range of 0.0001-1.0 μM is shown in Fig. 7B. The linear relation has a regression equation of Ipa (μA) = 0.21+10.99 C (μM) with a correlation coefficient of 0.998 and with detection limit of 5.0×10-11 M. The results obtained in our work are also compared with different modified electrodes for determination of Sudan I [3, 13, 26-32]. The linear range and detection limit are listed in Table 1. It shows that the linear range of Sudan I at the ILRGO@AuNPs/GCE is wider, and the detection limit is lower than previously published works.

3.5. Reproducibility, stability and selectivity of ILRGO@AuNPs/GCE 11

ACCEPTED MANUSCRIPT The reuse stability of the ILRGO@AuNPs modified GCE is shown in Fig. 8A, indicating that the repeated usage of the working electrode is possible, at least 6 times.

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The reproducibility of the ILRGO-Au/GCE was examined at the BR solution

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containing of 0.5 μM Sudan I with SWSV method which can be seen in Fig. 8B, the relative standard deviations (RSDs) of the currents at six independently ILRGO@AuNPs/GCE were calculated 4.12%, indicating acceptable fabrication

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reproducibility. The long-term stability of the ILRGO@AuNPs/GCE was explored

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over three weeks. The fabricated sensor was stored at 4 °C in peacetime and used every 3 days. It can be seen that the response retains more than 91.3% of its initial

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value in response to 0.5 μM Sudan I after 21 days, indicating an acceptable stability

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of the ILRGO@AuNPs/GCE.

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The influences of some potential interfering species, including metal ions, phenolic compounds, and organic molecules such as Sudan II, Sudan III and Sudan IV

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on the determination of 0.5 μM Sudan I were studied by SWSV method. It was found that 500-fold Cl−, Na+, K+, Ca2+, Zn2+, Fe3+, NO3−, SO42−, and 100-fold glucose, saccharose, saccharin, lycoypene, capsaicine and potassium sorbate did not interfere with determination of Sudan I, and the variation in current caused by the interference species was less than 5%. The Sudan II, Sudan III and Sudan IV are analogues of Sudan I. They might be added into food products with Sudan I simultaneously. Also, they may be added as additive separately. It was found that they were also can be detected with our working electrode and their SWV responses were shown in Fig. 9. It can be seen that all these Sudan dyes possess similar electrochemical behavior. 12

ACCEPTED MANUSCRIPT Therefore, the four dyes also can be detected quantitatively as they exist alone with the ILRGO@AuNPs/GCE. Obviously, the total amount of all Sudan dyes in the

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practice samples also can be determined quantitatively by the area of overlapped

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peaks [31].

3.6. Sample analysis

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The utilization of the ILRGO@AuNPs/GCE sensors in real samples was also

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studied. The chopped red chili, tomato sauce, apple juice and grape juice samples were detected separately with the ILRGO@AuNPs/GCE. It was found that may be

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there was no Sudan I in the food samples. So proper amounts of Sudan I was added to

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the sample matrices to determine recovery. It was found that the recovery of the

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spiked samples ranged from 95.0% to 98.6%, and the RSD (n=3) was less than 5.0% (Table 2). This indicates that the fabricated electrochemical sensors may have

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practical applications in food samples.

4. Conclusion

In summary, we have demonstrated a new route synthesizing of the ILRGO@AuNPs composite and investigated the potential application of this composite as an electrode material used to detection of Sudan I. The ILRGO@AuNPs composite were formed through a self-assembly process. Electrochemical data indicate that the ILRGO@AuNPs composite exhibits good electrocatalytic activity toward Sudan I and the prepared ILRGO@AuNPs/GCE shows a wider linear range, 13

ACCEPTED MANUSCRIPT lower detection limit, higher selectivity and long-term stability toward the determination of Sudan I. We expect this green composite can be applied to other

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colorants or biological analysis.

Acknowledgements

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This research was financially supported by the National Natural Science

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Foundation of China (Grant Nos. 21121091 and 21273113).

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Figure captions

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Fig. 1. Schematic presentation of green synthesis of the ILRGO@AuNPs composites.

Fig. 2. (A, B) TEM images of ILRGO@AuNPs composite with different

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magnification.

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Fig. 3. (A) CV curves of 0.7 μM Sudan I on the surfaces of (a) GCE, (b) AuNPs/GCE, (c) ILRGO/GCE and (d) ILRGO@AuNPs/GCE in 0.1 M BR solutions (pH 7.0): scan

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rate, 0.1 V s-1. (B) SWV curves of (a) GCE, (b) AuNPs/GCE, (c) ILRGO/GCE and (d)

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ILRGO@AuNPs/GCE in 0.1 M BR solution (pH 7.0) containing 0.5 μM Sudan I. (A’

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and B’) Amplified calibration curves of Sudan I obtained with GCE and AuNPs/GCE.

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Fig. 4. (A) Effect of volumes of HAuCl4, and (B) influence of content of ILRGO@AuNPs on the peak current of Sudan I.

Fig. 5 Effects of accumulation time (A) and pH value of accumulation media (B and C) on the oxidation peak current of the Sudan I. When one parameter changed other parameters were at their optimal values.

Fig. 6. Effect of scan rates on the redox behaviors of 5.0×10-7 M Sudan I. The scan rate is 20, 40, 60, 80,100, 200, 300, 400, 500, 600 mV s-1. 19

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Fig. 7. (A) SWV curves of ILRGO@AuNPs/GCE in 0.1 M BR (pH 7.0) containing

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0.0001, 0.0005, 0.001, 0.005, 0.03, 0.05, 0.08, 0.1, 0.2, 0.4, 0.5, 0.7, and 1.0 μM

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Sudan I (from lowest to highest peak currents). (B): linear calibration curve.

Fig. 8. (A) Six independently ILRGO@AuNPs/GCEs were used to detection 5.0×10-7

MA

NU

M Sudan I. (B) Square wave voltammograms for 5.0×10-7 M Sudan I for 6 assays.

Fig. 9. Square wave stripping voltammetric responses of 5.0×10-7 M Sudan I, Sudan

TE

AC

CE P

(pH 7.0), respectively.

D

II, Sudan III, and Sudan IV at the ILRGO@AuNPs/GCE in 0.1 M BR buffer solution

20

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 1

21

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

SC R

Fig. 2

22

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

Fig. 3

23

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 4

24

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

Fig. 5

25

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 6

26

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 7

27

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

NU

Fig. 8

28

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

D

MA

Fig. 9

29

ACCEPTED MANUSCRIPT Tables

2.4×10 -1.8 ×10

-9

-9

7.1×10

MWNTs-IL-Gel/GCE

4.0×10

Fe3O4/GCE

1.0×10

Pt/CNTs/ILCPE

3.0×10

ZnO/CNTs/IL/CPE

8.0×10

MWNT/GCE

2.0×10

OMC/GCE

2.4×10

poly(p-ABSA)/GCE

1.2×10

AgNPs@GO/GCE

-9

-8

-8

-6

-6

-5

2.5×10 -2.0×10

-5

-3

(Chailapakul etal 2008)

1.0×10 -2.0×10

-8

-5

(Yin etal. 2011)

-9

-4

(Elyasi etal. 2013)

-7

-4

(Najafi etal. 2014)

-8

-6

(Yang etal. 2010)

8.0×10 -6.0×10

2.0×10 -8.0× 10

MA

-8

TE

(Wu, 2010)

4.0×10 -4.0×10

(Meiju etal. 2007)

-9

4.0×10 -6.6×10

-7

-5

(Yang etal. 2009)

-9

4.0×10 -2.0×10

-9

-6

(Li etal. 2015)

-7

3.9×10 -3.2×10

-6

-5

(Prabakaran etal. 2015)

-10

2.0×10 -1.0×10

-9

-4

(Mao etal. 2014)

-11

1.0×10 -1.0×10

-10

-6

This work

11.4×10

CE P

IP

-7

AGCE

Ref.

SC R

5.0×10 -2.0×10

1.0×10

ILRGO@AuNPs/GCE

Linear range (M)

-8

Iron(III)-porphyrin-SWNT/GCE

CTAB-GNS/GCE

a

Detection limit (M)

NU

a

D

Electrodes

T

Table 1 A list of literatures on electrochemical sensors of Sudan I.

7.0×10 5.0×10

SWNT, single-walled carbon tube; AGCE, activated glassy carbon electrode; MWNT, multi-walled

AC

carbon nanotube; OMC, ordered mesoporous carbon; IL, ionic liquid; GN, grapheme；AgNPs@GO, Ag nanoparticles decorated graphene oxide; poly(p-ABSA), poly(p-amino benzene sulphonic acid); CTAB-GNS, CTAB-functionalized graphene nanosheets.

30

ACCEPTED MANUSCRIPT Table 2

Found (μM )

Chopped red chili

0.5

0.475

Tomato sauce

0.5

0.490

Apple juice

0.5

Grape juice

0.5

SC R 31

Recovery (%) 95.0 98.0

0.486

97.2

0.493

98.6

NU

CE P

TE

D

MA

Values reported are mean of three replicates.

IP

Added (μM)

AC

a

a

Samples

T

Determine Sudan I in 4 kinds of practical samples.

ACCEPTED MANUSCRIPT

SC R

IP

T

Highlights

1. The ionic liquid functionalized RGO-AuNPs composites (ILRGO@AuNPs)

NU

has been builded by a new route.

MA

2. The ILRGO@AuNPs composites were employed in the sensitive

D

determination of Sudan I in foods.

TE

3. This new sensor exhibits lower detection limit for Sudan I (5.0×10-11

AC

CE P

M) which is much lower than previously published works.

32