Highly reproducible and sensitive silver nanorod array for the rapid detection of Allura Red in candy

Accepted Manuscript Highly reproducible and sensitive silver nanorod array for the rapid detection of Allura Red in candy

Yue Yao, Wen Wang, Kangzhen Tian, Whitney Marvella Ingram, Jie Cheng, Lulu Qu, Haitao Li, Caiqin Han PII: DOI: Reference:

S1386-1425(18)30098-2 https://doi.org/10.1016/j.saa.2018.01.072 SAA 15791

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received date: Revised date: Accepted date:

31 October 2017 9 January 2018 25 January 2018

Please cite this article as: Yue Yao, Wen Wang, Kangzhen Tian, Whitney Marvella Ingram, Jie Cheng, Lulu Qu, Haitao Li, Caiqin Han , Highly reproducible and sensitive silver nanorod array for the rapid detection of Allura Red in candy. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Saa(2017), https://doi.org/10.1016/j.saa.2018.01.072

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ACCEPTED MANUSCRIPT Highly Reproducible and Sensitive Silver Nanorod Array for the Rapid Detection of Allura Red in Candy Yue Yaoa,c, Wen Wanga,c, Kangzhen Tiana,c, Whitney Marvella Ingramd, Jie Chenge, Lulu Qub* , Haitao Lib, Caiqin Hana,c* Jiangsu Key Laboratory of Advanced Laser Materials and Devices, School of Physics and Electronic

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Engineering, Jiangsu Normal University, Xuzhou, Jiangsu 221116, China School of Chemistry and Materials Science, Jiangsu Normal University, Xuzhou, Jiangsu 221116,

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China

Jiangsu Collaborative Innovation Center of Advanced Laser Technology and Emerging Industry,

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Jiangsu Normal University, Xuzhou, Jiangsu 221116, China Department of Physics and Astronomy, and Nanoscale Science and Engineering Center,

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University of Georgia, Athens, Georgia 30602, United States Institute of Quality Standards and Testing Technologies for Agro -products, Chinese Academy of

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Agricultural Sciences, Beijing 100081, China

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* Corresponding author: [email protected]; [email protected]

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ACCEPTED MANUSCRIPT Abstract Allura Red (AR) is a highly stable synthetic red azo dye, which is widely used in the food industry to dye food and increase its attraction to consumers. However, the excessive consumption of AR can result in adverse health effects to humans. Therefore, a highly

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reproducible silver nanorod (AgNR) array was developed for surface enhanced Raman

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scattering (SERS) detection of AR in candy. The relative standard deviation (RSD) of AgNR

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substrate obtained from the same batch and different batches were 5.7% and 11.0%, respectively, demonstrating the high reproducibility. Using these highly reproducible AgNR

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arrays as the SERS substrates, AR was detected successfully, and its characteristic peaks

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were assigned by the density function theory (DFT) calculation. The limit of detection (LOD) of AR was determined to be 0.05 mg/L with a wide linear range of 0.8 ~ 100 mg/L.

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Furthermore, the AgNR SERS arrays can detect AR directly in different candy samples

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within 3 min without any complicated pretreatment. These results suggest the AgNR array can be used for rapid and qualitative SERS detection of AR, holding a great promise for

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expanding SERS application in food safety control field.

Keywords: SERS; Allura red; Silver nanorods; DFT

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ACCEPTED MANUSCRIPT 1 Introduction Synthetic dyes have been wildly used in food processing to make food more attractive and boost sales. Among them, red azo dye Allura Red (AR, E129) is the one of most commonly used food colorant in food such as candy, ice cream and beverage [1, 2]. The

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Acceptable Daily Intake (ADI) of AR should not exceed 7 mg/kg [3, 4] recorded by the Joint

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FAO/WHO Expert Committee ON Food Additives (JECFA) [5] and the EU Scientific

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Committee for Food (SCF). The stipulation of using AR in food was on account of the adverse effects on human health by the reaction of aromatic azo compounds when people

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intake it for a long-term, especially in increasing hyperactivity in children [6]. Hence, it’s

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important to analyze and monitor AR in food production industry. Over the past few decades, different detection methods have been reported such as high

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performance liquid chromatography (HPLC) [7-10] and spectrophotometry [11, 12]. For

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example, the identification of AR in a beverage was achieved by ultra-HPLC combining mass spectrometry method [13]. A simple, rapid and sensitive detection of trace levels of AR in water sample was reported by spectrophotometry [14]. Other method such as capillary

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electrophoresis (CE) [15-17] was also applied to the detection of AR. However, these methods are time-consuming and expensive. Therefore, the development of high effective detection method for AR is highly important. Recently, surface-enhanced Raman spectroscopy (SERS) has been recognized as a rapid, sensitive and inexpensive detection method [18-20]. The most critical aspect to perform a SERS experiment is the choice and/or fabrication of the noble-metal substrates such as silver or gold nanoparticles [21, 22], silver or gold coated structures [23-25], metal nanorods [26, 3

ACCEPTED MANUSCRIPT 27] and other composite nanostructures [28, 29]. Thus, to further widen the applications of SERS technique, it is crucial to fabricate SERS-active metallic nanostructures with both high enhancement performance and excellent reproducibility. For this purpose, many different methods such as e-beam lithography [30, 31], colloidal lithography [32, 33] and vapor

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deposition [34, 35] have been explored extensively to create or fabricate functional noble

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metal SERS substrates. In recent years, oblique angle deposition (OAD) has been recognized

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as a stable and effective method for the fabrication of SERS-active nanostructure. Our previous work demonstrated that the silver nanorod (AgNR) array substrate exhibited an

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excellent SERS enhancement factor (EF) (over 10 8 ) in detection of the Raman probe [36]

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with minimal relative standard deviation (RSD) for each substrate. They have already been applied to many applications such as food and environmental safety. For example, Du et al.

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[37] reported the qualitative and quantitative determination of melamine by AgNR substrates

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with a limit of detection (LOD) of 0.1 mg/L. Han et al. [38] used SERS-based method in monitoring metronidazole and ronidazole from different environmental water samples, which achieved the highly sensitive detection requirements. Moreover, this AgNR array was applied

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in detecting some biochemical and bacteria. Meshik et al. [39] achieved the SERS spectrum of the peptide thymosin-β4 by AgNR substrates, and the significant Raman peaks were analyzed. Chen et al. [40] deposited AgNR on the smooth surface of Anodisc and GA-8 filters which were used for pre-concentration of Escherichia coli and subsequent on-chip SERS detection. However, there is no report concerning the SERS detection of AR using AgNR arrays as substrates.

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ACCEPTED MANUSCRIPT In this work, the highly sensitive AgNR substrates were fabricated by OAD and were applied to detect AR. A density functional theory (DFT) calculation was performed to confirm the characteristic peaks and corresponding vibrational modes of AR. The SERS intensity versus AR concentration was systematically determined and the LOD is obtained.

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Moreover, the SERS system was used in quantitative detection of AR from many candy

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samples. It will provide a new potential method for rapid identification of AR in food safety

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control.

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Fig. 1 (A) Schematic diagram of oblique angle deposition system. (B) Flow diagram of candy sample pretreatments.

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ACCEPTED MANUSCRIPT 2 Materials and Methods 2.1 Materials Silver (99.999%) and titanium (99.995%) pellets were purchased from Kurt J. Lesker Co., Ltd. (USA). Allura Red (≥ 99.9%) and trans-1, 2-bis (4-pyridyl) ethylene (BPE, ≥ 99%)

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were acquired from J&K China Chemical Ltd. (China). Methanol (≥ 99.7%) was acquired

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from Sinopharm Chemical Reagent Co., Ltd. (China). Candy samples were purchased from

2.2 Fabrication of AgNR array SERS substrates

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the local supermarkets. Ultrapure water (≥ 18.2 MΩ) was used in all experiments.

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AgNR array substrates were fabricated by the OAD technique using a custom-built

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e-beam deposition system (DE500, DE Technology Inc., Beijing, China). Briefly, multiple 1 cm × 1 cm glass chips were cleaned in ethanol for 5 min by an ultrasonic cleaning machine

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for at least 3 times. After drying with N2 , the glass chips were loaded onto the substrate

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holder by Teflon tape. The pressure in the deposition chamber was under 5 × 10-7 Torr. Firstly, a 20 nm of Ti and a 100 nm of Ag were deposited successively at a normal incidence angle under the rates of 0.2 nm/s and 0.3 nm/s, respectively. The substrate surface normal

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was then rotated to an oblique angle of 86⁰ with respect to the vapor incident direction, and 2000 nm of Ag was continued to be deposited under a rate of 0.3 nm/s, as shown in Fig. 1A. The deposition thickness and rate were monitored by a quartz crystal microbalance (QCM). The surface morphology of the prepared AgNR array substrates were characterized by a field-emission scanning electron microscopy (SEM, SU8010, Hitachi, Tokyo, Japan). As the AgNR array were fabricated, they were stored in a vacuum chamber under the pressure of 10-3 Torr. Before SERS detection, the AgNR array was cleaned by plasma to remove the 6

ACCEPTED MANUSCRIPT impurities and the oxidation layer, which did not change the surface morphology of AgNR array (Fig. S1). 2.3 Preparation of AR samples Different concentrations of AR solution (CAR = 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1, 2, 4, 6, 8,

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10, 20, 40, 60, 80, 100 mg/L) were prepared using ultrapure water and methanol (V Water :

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VMethanol = 9 : 1) to determine the SERS intensity versus CAR calibration curve. A simple

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pretreatment of candy samples was developed for the SERS-based detection. AR aqueous solution (10 mg/L) was used to determine the SERS enhancement factor (EF) of AgNR array.

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The candy samples (1.0 ~ 4.4 g) were soaked in ultrapure water (2 mL) and shake for 15 s by

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a vortex mixer. Then, the dissolved candy sample (1 mL liquid sample) was centrifuged for 60 s under 15000 rpm (Fig. 1B). The supernatant (2 µL) was used for SERS detection.

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2.4 SERS measurements

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2 µL of BPE solution was tested and the peak at Δυ = 1200 cm-1 was selected to determine the reproducibility of AgNR array from spot-to-spot and batch-to-batch. Before SERS detection of the AR samples, the background signals of AgNR substrates were

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obtained to determine the noise of the SERS system. 2 µL of AR standard solutions were added onto the AgNR substrate surface, and dried before SERS measurements. The Raman spectrum of AR was recorded from the powder on a Si wafer. The SERS EF was calculated using the Raman spectra of 1000 mg/L AR solution, and SERS spectra were obtained from AgNR array with 100 mW laser power and 10 s integration time. A Raman analyzer (ProRaman-L-785A2, Enwave Optronics, Irvine, CA) equipped with a 785 nm diode laser was used to record the SERS spectra of each sample. The integration time and the laser 7

ACCEPTED MANUSCRIPT power were 5 s and 30 mW for the AR aqueous solution and the candy sample. At least nine random spots were scanned from each sample dried on the substrate surface. 2.5 Density function theory (DFT) calculation In order to identify the characteristic peaks of AR and the corresponding vibrational

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modes, the Gaussian 09 W DFT package was used to calculate the Raman spectra of AR. The

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DFT calculations were based on Becke’s three-parameter exchange function (B3) [41] with

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the dynamic correlation function of Lee, Yang, and Parr (LYP) [42]. The molecular structure of AR was optimized using the B3LYP function in conjunction with a modest 6-311g (d)

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basis set.

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2.6 Data analysis

All of the SERS spectra were plotted with Origin 8.5 software (Origin Lab, Northampton, MA). The raw spectra obtained from the Raman analyzer were used without

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further processing unless otherwise specified. GRAMS/AI spectroscopy software suite (Thermo Fisher Scientific, Waltham, MA) was applied to subtracting the baseline and fitting

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the characteristic peaks. Image J (National Institute of Mental Health, Bethesda, MD) software was applied to analysis the SEM image of the AgNR array, which can obtain the

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average value of the length and diameter of single AgNR, the gap between AgNR and the angle between AgNR and the under-layer thin films (Ag).

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ACCEPTED MANUSCRIPT 3 Results and Discussion 3.1 Characterization of AgNR array substrates Fig. 2A shows SEM images of an AgNR array substrate. It can be observed that the prepared AgNR array was highly reproducible. Over 30 nanorods were measured to

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determine the average parameters of the prepared AgNR array. The result shows that t he

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nanorod length was L ≈ 900 ± 90 nm with a tilting angle of approximately 73º relative to the

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substrate normal. The magnified SEM image shows that the diameter of the nanorod and the gap between rods were 100 nm and 150 nm, respectively. 10 -5 mol/L BPE standard solution

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was dropped on the AgNR array substrates and used to estimate the reproducibility of AgNR

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array substrates. No obvious changes in intensity was observed from SERS spectra of BPE recorded from the 20 random spots of an AgNR array substrate, as shown in Fig. 2B.

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Moreover, 10 AgNR array substrates from the same batch and the different batches were also tested. The results displayed in Fig. 2C & 2D show the spot-to-spot and batch-to-batch

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intensity variation of the characteristic Δυ = 1200 cm-1 peak of BPE. The variation in peak intensity was quantified and the relative standard deviations (RSDs) were 5.7% and 11.0%,

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respectively. This illustrates that the AgNR array exhibits high reproducibility.

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Fig. 2 (A) SEM image of an AgNR array substrate. (B) SERS spectra of 10 -5 M BPE taken

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from 20 random spots on the AgNR substrate. (C) SERS intensity of 10 -5 M BPE recorded

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from 10 pieces of AgNR substrates from the same batch. (D) The SERS intensity of 10-5 M BPE on AgNR substrates recorded from the 10 different batches.

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3.2 Detection of AR using AgNR array substrates As the AgNR array substrates with high reproducibility and uniformity have been prepared, next, SERS detection of AR was performed. In order to determine the characteristic peaks of AR and their corresponding vibrational modes, a comparison of Raman spectrum of AR calculated by DFT, the SERS spectrum of 10 mg/L AR, and Raman spectrum of AR powder were shown in Fig. 3B. All spectra were normalized in order to compare the corresponding peaks position. Experimentally, both the SERS spectrum and the Raman 10

ACCEPTED MANUSCRIPT spectrum exhibit similar characteristic peaks. However, the DFT calculation result didn’t match the experimental spectra perfectly because of the base group setting [43] and the experimental conditions. The most dominant peaks are found at Δυ = 488, 751, 1187, 1221, 1272, 1410, 1496, and 1578 cm-1 . According to the DFT calculation result, the corresponding

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vibrational mode was shown in Table 1. The peaks at Δυ = 1221 cm-1 and Δυ = 1410 cm-1

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were attributed to the -CH3 rocking. The C-H wagging mode was originated from the peaks

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such as Δυ = 973, 1384 and 1496 cm-1 . Moreover, the ring stretching plays a lead role in the peaks at Δυ = 588, 1126, 1579 and 1607 cm-1 . The other main peaks were obtained because of

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the O-S wagging such as Δυ = 488 cm-1 , 1187 cm-1 and 1272 cm-1 .

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ACCEPTED MANUSCRIPT Fig. 3 (A) The optimized structure of AR molecular. (B) The Raman spectrum ca lculated by DFT (black) and the corresponding bulk Raman (red) and SERS (blue) spectra of AR. All the spectra were normalized by the highest peak in each spectrum. Table 1 Band assignments for the DFT-Raman, experimental Raman, and SERS spectra of

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AR. Raman

SERS

Vibrational modes

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488

488

O20 -S17 wagging

582

595

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Ring 2 & Ring 3 asymmetric stretching

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755

751

Ring 1 wagging

972

975

973

1112

1126

1126

1177

1187

1187

1211

1221

1221

1271

1268

1272

O32 -C26 stretching

1381

1384

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C2 -H9 wagging

1404

1407

1410

H39 -C37 -H38 rocking

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1492

1591

1575

1610

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DFT

C13 -H16 & C11 -H15 wagging

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Ring 2 & Ring 3 asymmetric stretching

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O19 -S17 -O 20 & O44 -S41 -O43 asymmetric H36 -Cstretching 33 -H35 rocking

C-H wagging

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Ring 1 asymmetric stretching

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1496 1607

Ring 2 & Ring 3 asymmetric stretching

In order to determine the SERS EF of AgNR array for AR, the SERS spectrum and the

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Raman spectrum were obtained (Fig. 4). The SERS EF was calculated according to the following equations [46],

(1)

(2)

(3) 12

ACCEPTED MANUSCRIPT where ISERS ( = 3.7 × 104 ) is the SERS intensity of AR solution (CSERS = 10 mg/L) recorded from AgNR array substrate and IRaman ( = 76) is the bulk Raman intensity of AR solution (CRaman = 1000 mg/L) at Δυ = 1221 cm-1 . NSERS and NRaman are the estimated amount of AR molecules contributed to SERS and Raman spectrum. The volume of AR solution

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added to the AgNR array substrate surface was V=2 µL. In fact, the 2 µL solution was spread

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circularity in the diameter of 2 mm, so SSERS = 3.14 × 10-6 m2 . SLaser = πr2 = 7.6 × 10-12 m2 (r =

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3.1 × 10-6 m) is the calculated laser beam area at the substrate surface [47, 48]. The volume of AR solution produced Raman scattering was calculated to be VLaser = 2.5 × 10-12 m3 [47, 48].

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NA is the Avogadro constant (NA = 6.02 × 1023 mol-1 ), and M is the molar mass of AR (M =

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496.43 g/mol). The SERS EF of AgNR array substrate for AR was calculated to be 2.5 × 104 , which proved that the AgNR array has the excellent enhancement for AR. The AR molecule

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has the azo group (C-N=N-C), which has strong affinity with the AgNR, thus resulting in a

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excellent SERS response on AgNR [44]. Moreover, the high sensitivity of AgNR for AR was due to that the high local E-field distributions are mainly located at the top of the nanorods and the corners between the nanorods and the Ag thin film [45]. When the AR molecules fall

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into the “hot spot” region, they would generate enhanced Raman signals.

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Fig. 4 SERS spectrum of AR aqueous solution (10 mg/L) recorded from the AgNR array

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substrate (bule), Raman spectrum of AR (1000 mg/L) aqueous solution (red), and the

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background SERS signal of AgNR array substrate (black). Fig. 5A shows the representative SERS spectra of AR samples with different

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concentrations. No significant SERS peaks were observed from the background AgNR substrate spectrum, which shows the lower noise and is benefit to the SERS detection. The

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characteristic peaks of AR at Δυ = 488, 589, 751, 1221, 1270, 1326, 1495, and 1578 cm-1 were observed under different concentrations of AR solution (1 mg/L ≤ CAR ≤ 100 mg/L).

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The peaks at Δυ = 1221 cm-1 and Δυ = 1272 cm-1 can be identified even at CAR = 0.05 mg/L. Moreover, the characteristic peak at Δυ = 1221 cm-1 was used to determine the LOD of AR. Fig. 5B plots the SERS peak intensities at Δυ = 1221 cm-1 versus the CAR. The intensity increased with the increasing of CAR in the range of 0.05 ~ 100 mg/L, which was due to the more AR molecules adsorbed on AgNR. Moreover, the reliably linear range of AR was determined to be 0.8 ~ 100 mg/L (I1221 = 192.5CAR + 2147.8) with the R2 = 0.986. The exponential fitting was determined to be I1221 = 1747.1 - 1879.9exp(-8.1CAR) when CAR were 14

ACCEPTED MANUSCRIPT in the range of 0.05 ~ 0.8 mg/L, and R2 = 0.991. The limit of detection (LOD) was determined to be 0.05 mg/L with the 3σ method (σ is the mean square root of the noise signal, which was determined by standard deviation of the spectral intensity at a spectral region: 1700 ~ 1800 cm-1 ). This above results suggested the AgNR array substrates combined with

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the portable Raman spectrometer can provide the potential for quantitative detection of AR.

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Fig. 5 (A) SERS spectra of AR with different concentrations (C1 ~ C8: 100 mg/L, 80 mg/L, 60 mg/L, 40 mg/L, 20 mg/L, 10 mg/L, 1 mg/L, 0.05 mg/L). (B) & (C) The characteristic peaks intensities of AR are offset for clarification. The black line indicates the threshold 3σ values used to determine positive or negative responses.

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ACCEPTED MANUSCRIPT 3.3 Discrimination of AR from different coated candy The characteristic peaks of AR at Δυ = 488, 752, 1221, 1271, 1411, 1496, and 1578 cm-1 can be used to identify the existence of AR in candy samples. 10 different candy samples were suspected to contain AR due to their red appearance. A simple pretreatment procedure

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was carried out to achieve the simple separation of AR from candy. The candy samples were

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first dissolved in DI water, aiming at obtaining the coated pigment. The dissolved samples

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were centrifuged to remove the solid precipitation. After the dissolving and centrifuging progress, the supernatants were tested by AgNR. Fig. 6 shows the comparison of the SERS

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spectra obtained from 10 candy samples and AR standard solution. According to the

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identification of the AR peaks (Δυ = 753, 1221, 1272, 1495, and 1578 cm-1 ), 8 candy samples (except S4 & S7) were confirmed to contain AR. However, these SERS spectra show some

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differences in Raman peaks, which was due to the different ingredients in the candy. The

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result also suggested that SERS detection of AR by AgNR array did not be interfered with

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other components, such as other dyes in candy samples (Fig. S2).

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Fig. 6 SERS spectra of 10 different candy samples recorded from the Ag NR array substrates.

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The intensity of the peak at Δυ = 1221 cm-1 was closely related to the concentration of

equations:

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AR in candy. Thus, the mass of AR in candy was estimated according to the following

(4)

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where m AR is the mass of AR in candy; CAR is the concentration of AR that estimated by the curve: I1221 = 192.5CAR + 2147.8 (0.8 mg/L < CAR ≤ 100 mg/L), and I1221 = 1747.1 + 1879.9exp(-8.1CAR) (0.05 mg/L ≤ CAR ≤ 0.8 mg/L); Vcandy (2 mL) is the ultrapure water dissolving the candy samples. The SERS intensity of S1, S2 and S5 were below the minimal value requirement of the linear relationship (when CAR = 0.8 mg/L, IAR = 2914.9 ± 217.3), which met the exponential relationship. However, the calculated result shows that S3 was under the minimal detectable intensity of the exponential relationship (when CAR = 0.05 mg/L, 18

ACCEPTED MANUSCRIPT IAR = 466.1 ± 167.5) where the concentration cannot be determined. What’s more, the S6, S8, S9 and S10 samples contained more AR and their SERS intensity were in the range of 0.8 ~ 100 mg/L, which can be estimated by the established linear curve, as shown in Table 2. The above results demonstrated the high sensitivity and good quantitative analysis capabilities of

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Table 2 Quantitative AR detection results of 10 candy samples.

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the AgNR array substrates for rapid sensing AR in real candy samples.

Mass (m)

I1221

Qualitative analysis

Quantitative analysis

S1

1.6 g

1470.6

√

0.071 mg/kg

S2

4.4 g

1712.4

S3

3.2 g

348.6

S4

2.7 g

×

S5

1.2 g

695.4

S6

1.7 g

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Samples

0.056 mg/kg

√

× ×

√

0.0299 mg/kg

2401.1

√

0.392 mg/kg

1.2 g

×

×

×

S8

1.3 g

10638.0

√

16.963 mg/kg

S9

1.9 g

3656.9

√

2.063 mg/kg

S10

1.0 g

2918.3

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2.001 mg/kg

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×

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√

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ACCEPTED MANUSCRIPT 4 Conclusion A highly reproducible silver nanorod array substrate was fabricated for SERS detection of AR in candy. The RSD of different AgNR array substrates from the same batch and the different batches were less than 6% and 11%, respectively, confirming that these AgNR array

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substrates fabricated by OAD have a high reproducibility. In addition, the AgNR array

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substrates provided excellent enhancement ability for AR detection with minimal background

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interferences. An AR LOD of 0.05 mg/L can be achieved. More importantly, AR was detected rapidly and successfully in different coated candy by identifying the characteristic

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peaks and reached the quantitative detection within 3 min. This SERS based method can

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provide a potential strategy for detection of AR in other food.

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publication of this paper.

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Conflict of Interest: The authors declare that there is no conflict of interests regarding the

Funding Sources: This research was funded by the National Natural Science Foundation of

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China (Grant No. 61575087, 21505057), the Natural Science Foundation of Jiangsu Province (Grant No. BK20151164, BK20150227), Foundation of Xuzhou City (KC15MS030), and the Innovation Project of Jiangsu Province (KYLX16_1322).

Acknowledge ments: The authors would like to thank a Project Funded the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

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Graphical abstract

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ACCEPTED MANUSCRIPT Highlights 1. A highly reproducible silver nanorod (AgNR) array was first developed for surface

enhanced Raman scattering (SERS) detection of AR (Allura red) in candy. 2. The relative standard deviation (RSD) of AgNR substrate obtained from the same batch

and different batches were 5.7% and 11.0%, respectively.

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3. The limit of detection (LOD) of AR was determined to be 0.05 mg/L with a wide linear

range: 0.8-100 mg/L.

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4. AR was detected rapidly and successfully in different candy samples by identifying the

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characteristic peaks and reached the quantitative detection within 3 min.

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