Colorimetric recognition of 6-benzylaminopurine in environmental samples by using thioglycolic acid functionalized silver nanoparticles

Accepted Manuscript Colorimetric recognition of 6-benzylaminopurine in environmental samples by using thioglycolic acid functionalized silver nanoparticles

Mingda Zheng, Jiang He, Yingying Wang, Chenge Wang, Shuang Ma, Xiaohan Sun PII: DOI: Reference:

S1386-1425(17)30880-6 doi:10.1016/j.saa.2017.10.073 SAA 15579

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received date: Revised date: Accepted date:

28 August 2017 17 October 2017 27 October 2017

Please cite this article as: Mingda Zheng, Jiang He, Yingying Wang, Chenge Wang, Shuang Ma, Xiaohan Sun , Colorimetric recognition of 6-benzylaminopurine in environmental samples by using thioglycolic acid functionalized silver nanoparticles. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Saa(2017), doi:10.1016/j.saa.2017.10.073

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ACCEPTED MANUSCRIPT Colorimetric recognition of 6-benzylaminopurine in environmental samples by using thioglycolic acid functionalized silver nanoparticles Mingda Zhenga, Jiang Hea,* Yingying Wanga, Chenge Wanga, Shuang Maa, Xiaohan Suna, a. College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China *Corresponding author:

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Jiang He E-mail: [email protected] Tel.: +86 (931) 891 2591, Fax: +86 (931) 891 2582

ACCEPTED MANUSCRIPT ABSTRACT A simple and selective colorimetric sensor thioglycolic acid capped silver nanoparticles (TGA-AgNPs) was developed for the detection of 6-benzylaminopurine (6-BAP). The synthesized TGA-AgNPs were characterized by UV-vis spectroscopy, dynamic light scattering (DLS), and transmission electron microscopic (TEM) techniques. The TGA-AgNPs as a sensor for binding 6-BAP

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through hydrogen-bonding and π-π bonding that causes large conjugate clusters, resulting in a color change from yellow to reddish orange. The surface plasmon resonance (SPR) band of TGA-AgNPs at

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397 nm is red-shifted to 510 nm, which confirms that 6-BAP induces the aggregation of TGA-AgNPs. Under the optimized conditions, a linear relationship between the absorption ratio (A510 nm/A397 nm) and

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6-BAP concentration was found in the range of 4-26 μM. The detection limit of 6-BAP was 0.2 μM, which is lower than the other analytical techniques. Moreover, the proposed sensor was successfully

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applied for the detection of 6-BAP in environmental samples with good recoveries. The proposed assay provids a simple and cost-effective method for the analysis of 6-BAP in vegetable and water samples. silver nanoparticles

6-benzylaminopurine

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Keywords:

thioglycolic acid

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Introduction

colorimetric sensor

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Pesticides can be divided into insecticides, plant growth regulators, acaricides, fungicides, and herbicides, which are widely used for protecting vegetables and crops from insects and diseases [1-3]. Among all pesticides, 6-benzylaminopurine (6-BAP) is the first-generation man made phytohormone.

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It has proven to promote plant cell division and growth, which can be widely used in horticulture and agriculture for plants [4]. Because of its significance in plants, some illegal traders use excessive

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6-BAP to improve organoleptic quality, production and post-harvest of vegetables to achieve more profits. However, excessive intake of 6-BAP from food may cause irritation or damage to eyes, skin, mucous membrane, and some symptoms such as sicchasia and emesia [5-6]. Consequently, the pesticide residues become great problems which are attracting extensive public attention and needing further investigation. In general, several analytical techniques including high-performance liquid chromatography (HPLC) [7], liquid chromatography-mass spectrometry (LC-MS) and pyrolysis

MS [8-9], electrochemical assay (EC) [10-12], enzyme linked immunosorbent assay (ELISA) [13] and gas chromatography/mass spectrometry (GC/MS) [14-16] have been used for the detection of pesticides. The disadvantages of these methods are the requirements for expensive instrumentation,

ACCEPTED MANUSCRIPT complex experimental procedures and inadequate detection limits. Compared with the above methods, colorimetric assay has some advantages due to its simple, quick and low-cost operation [17-21]. Thus, colorimetric sensors which can be achieved for in situ detection of 6-BAP have a great application prospect. In the past decades, semiconductor and metal nanoparticles (NPs) have attracted our attention

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towards the biorecognition process because of excellent electrical and optical properties [22-24]. Gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) are widely used because of their aggregation

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property or anti-aggregation property in solution, which are dependent on the concentration of analyte [25-27], and in turn yield different light absorption capacities according to different-sized NPs. In

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recent years, nanoparticles have been utilized as they promote the determination of pesticide residues due to their rapid simple and sensitive response towards biosensor elements. The nanoparticles have

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some excellent advantages, such as high sensitivity low cost, good responsiveness, easy to synthesis, and can be directly with the naked eye for the detection of organophosphate (OP) pesticides. Wang et al.

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have developed an aptamer-capped gold nanoparticles (AuNPs) [28] as a colorimetric sensor for the detection of omethoate in real samples. Imene et al. have demonstrated an 4-Amino-3-mercaptobenzoic

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acid functionalized AuNPs [29] for colorimetric detection of cyhalothrin in water samples. Our group

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have reported p-aminobenzenethiol functionalized silver nanoparticles (ABT-AgNPs) for the ultrasensitive detection of 6-benzylaminopurine [30]. Li's group has explored AuNPs as colorimetric probe for the detection of mathamidophos [31] in environmental samples. Compared to AuNPs, AgNPs

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has higher extinction coefficients and more cost-effective. However, very few literature reports are available utilizing the optical properties of AgNPs in colorimetric sensing. Therefore, AgNPs can be

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used as a good candidate for optical sensing of organic pesticides. Herein, we designed a highly selective and sensitive colorimetric sensor by using thioglycolic acid functionalized silver nanoparticles (AgNPs) assay for detecting the residues of 6-BAP in environmental samples. Before the addition of 6-BAP, the thioglycolic acid acts as the stabilizer. After adding the analyte into solution, TGA enhances the interaction ability of AgNPs with 6-BAP, the adsorption of 6-BAP can form hydrogen bonding with carboxyl group of thioglycolic acid on the surface of AgNPs, yielding the color changed from light yellow to reddish orange. The colorimetric sensing performance such as the limit of detection (LOD), the linear range, selectivity, precision and applicability for visual detection of 6-BAP was evaluated.

ACCEPTED MANUSCRIPT Experimental Chemicals 6-benzylaminopurine (6-BAP) was received from Bo'ao Biological Technology Co. Ltd (Shanghai, China), silver nitrate (AgNO3) was purchased from Tianjin Kermel Chemical Reagent Co. Ltd (Tianjin, China), Thioglycolic acid (C2H4O2S) was obtained from Shanghai century three factory (Shanghai,

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China), trisodium citrate dehydrate (Na3C6H5O7·2H2O) was purchased from Tianjin Guangfu Chemical Reagent Factory (Tianjin, China), sodium borohydride (NaBH 4) was obtained from Sinopharm

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Chemical Reagent Co. Ltd (Shanghai, China). All reagents were analytical reagent grade without a filtration system. All solutions were prepared with Milli-Q-purified distilled water.

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Apparatus

Transmission electron microscopy (TEM) images of the samples were conducted using a Tecnai G2F30

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instrument (FEI, USA). The absorbance spectra were recorded on a Lambda 35 UV-visible spectrometer (Perkin Elmer, USA). Dynamic light scattering (DLS) data were obtained by Zetasizer

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Nano BI-200SM instrumentation (Brookhaven, USA).

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Synthesis of Cit-AgNPs and TGA-AgNPs

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The AgNPs colloid solution was synthesized by the well-known NaBH4 reduction of AgNO3 according to previous literature [32] with little modification. 5 mL 1.0×10-2 M Na3C6H5O7·2H2O was mixed with 20 mL 1.0×10-3 M AgNO3 in 250 mL round-bottom flask. Then 50 mL H2O was mixed with

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solution. Finally, 10 mL 2.7×10-3 M freshly prepared NaBH4 was added dropwise to the solution, and then stirred for 48 hours at room tempreture. The AgNPs were functionalized with TGA by the

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following procedure: 100 μL 0.1mM TGA was added into 25 mL round-bottom flask that contained 5 mL freshly prepared Cit-AgNPs solution. The above solutions were stirred for 2 hours at room temperature. The sample was named as TGA-AgNPs. The prepared TGA-AgNPs were stored in dark bottles at 4.0±2.0°C. The resultant TGA-AgNPs which could keep uniform even for several months

The sensitivity of assay To evaluate the applicability of TGA-AgNPs, 500 μL TGA -AgNPs solutions were mixed with 500 μL buffer solution (pH=6.0), a certain amount of 6-BAP was added to solution, finally, 1mL H2O was added to this solution at room temperature. The color changes were observed with naked eyes and

ACCEPTED MANUSCRIPT UV-vis spectra were also recorded by UV-vis spectrometer at room tempreture.

Analysis of 6-BAP in environmental samples Water samples were obtained from the Yellow River (Lanzhou, China). It was filtrated by syringe filter (0.45 μm) and then spiked with various concentrations of 6-BAP. As 0.5 mL TGA-AgNPs were separately added into the solution after 1 minute, UV-vis spectra measurements and photographs were

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immediately recorded.

The vegetable samples (soybean sprout) were collected from the local supermarket (Lanzhou,

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China). For vegetable samples, extraction procedure was performed according to previous method [33]

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with a little modification. Firstly, 5g of vegetable samples were homogenized, secondly, extracted with 25 mL ethyl alcohol and they were sonicated for 15 minutes, then the supernatants were filtered

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through a 0.45 μm membrane, finally spiked with different concentrations of 6-BAP. All sample

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extracts were stored at 4±2°C prior to use.

Results and discussion

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Characterization of the Cit-AgNPs and TGA-Ag NPs

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The TEM imaging and DLS technology were also studied to confirm Cit-AgNPs and TGA-AgNPs were successfully synthesized (Fig. 1). TEM image (Fig. 1d) shows that the formed Cit-AgNPs were spherical and well dispersed, which was in good agreement with the DLS technique, Fig. 1a reveals

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that the average diameter of Cit-AgNPs is 7 nm. Fig. 1b and 1e reveals that the prepared TGA-AgNPs were well dispersed with an average size of 12 nm, which further confirmed the TGA-AgNPs were

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successfully synthesized. Fig. 1f shows the TEM image of aggregated TGA-AgNPs in the presence of 6-BAP, the average particle size of TGA-AgNPs was increased to 67 nm (Fig. 1c). These results reveal that the size and morphology of TGA-AgNPs were drastically changed by the addition of 6-BAP, which confirmed that the aggregation of TGA-AgNPs was occurred in the presence of 6-BAP.

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Fig.1. DLS data of (a) Cit-AgNPs, (b) TGA-AgNPs, (c) the aggregation of TGA-AgNPs induced by

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6-BAP. TEM images of (d) Cit-AgNPs, (e) TGA Ag NPs, (f) the aggregation of TGA-AgNPs induced

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by 6-BAP.

Cit-AgNPs exhibit a typical absorption peak at 394 nm, indicating the nanoparticles are well

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synthesized. However, compared to Cit-AgNPs, TGA-AgNPs exhibit an absorption peak at 397 nm with a little red-shifted, which illustrated the TGA molecules were successfully absorbed on the surface of AgNPs (Fig.2a). The UV-vis spectra of dispersed and aggregated TGA-AgNPs were also recorded

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by UV-vis spectrometer. Fig. 2b showed the UV-vis spectra of well-dispersed TGA-AgNPs. After the

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addition of 6-BAP, the absorption intensity of TGA-AgNPs decrease at 397 nm and a new typical absorption peak at 510 nm appeared, resulting in the aggregation of TGA-AgNPs and the color

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changed from faint yellow to reddish orange (the inset of Fig. 2b).

Fig. 2. (a) UV-vis absorption spectra of Cit-AgNPs and TGA -AgNPs (b) UV-vis absorption spectra of TGA -AgNPs before and after addition of 6-BAP.

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Colorimetric detection of 6-BAP using TGA-AgNPs as a sensor TGA has a strong electrostatic interaction with AgNPs, which replaces citric acid and causes aggregation of AgNPs [34]. So it is important to choose an appropriate concentration of TGA to modify AgNPs. To evaluate the effect of TGA concentration on AgNPs, Fig.3 showed the UV-vis spectra of different concentrations of TGA modified on AgNPs in the range of 0.01 mM to 0.2 mM, with the

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amounts of TGA increased, the absorption peak at 397 nm gradually decreased. Based on the result,

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0.01 mM was chosen as the optimal concentration for the following experiments.

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Fig. 3. UV-visible spectra of Cit-AgNPs solution with different concentrations of TGA range from

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0.01 mM to 0.2 mM.

The pH value of buffer was found to play an important role in the aggregation of AgNPs. Thus the effect of pH was investigated by UV-vis spectra on the assay. ΔA was the ratio of A510 nm/A397 nm in presence of 6-BAP withdraw the background in absence of 6-BAP, which was applied into showing the aggregation degree of TGA-AgNPs. It revealed that a higher ΔA presented higher aggregation degree of TGA-AgNPs. As described in Fig. 4, the results revealed that the ΔA rapidly increased from 2.0 to 5.0, as pH values varied from 5.0 to 6.0, the aggregation degree tended to balance. However, ΔA gradually decreased drastly when the pH value from 6.0 to 10.0, under alkaline conditions, the electrostatic force was reduced by deprotonation of TGA, thus induced aggregation of TGA-AgNPs.

ACCEPTED MANUSCRIPT Therefore, the buffer solution pH=6.0 was chosen as an optimized value for the subsequent

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experiments.

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Fig. 4. The influences of buffer solution pH.

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Since TGA has a mercapto group and two carboxyl groups, it can be easily absorbed onto the

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surface of AgNPs to replace the carboxyl group of citric through the Ag-S bond [34]. Simultaneously, two carboxyl groups protect AgNPs from aggregation. The synthesized TGA-AgNPs were highly dispersed and extremely stable due to the electrostatic repulsion of TGA on the AgNPs surface at

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optimum buffer solution (pH=6.0), both TGA-AgNPs (PKa of 3.73) and 6-BAP (PKa1 of 3.86) exhibit negative charges, they are neutralized and suitable to form the hydrogen bonding between TGA and

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6-BAP. The addition of 6-BAP to the TGA-AgNPs solution resulted in the aggregation of TGA-AgNPs with color change from yellow to reddish orange, because 6-BAP could result in aggregation of TGA-AgNPs via strong π-π bonding and hydrogen bonding (Scheme 1). The mechanism illustrated that 6-BAP induce the aggregation of TGA-AgNPs.

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Scheme 1. Schematic representation for the colorimetric detection of 6-BAP using TGA-AgNPs as a

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colormetric probe.

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To confirm the mechanism, we also use density functional theory (DFT) method (Fig. 5). All possible ways of binding [TGA+6-BAP] (Fig. 5a) and [6-BAP+6-BAP] (Fig. 5b) are listed, the major

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possible intermolecular and intramolecular hydrogen bondings are represented dashed lines. The

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distance and energy values (ΔE) for TGA and 6-BAP were listed. The simulated results confirm that the mechanism of TGA-AgNPs aggregation induced by 6-BAP due to the binding affinity of hydrogen

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bonding between TGA and 6-BA and π-π bonding between 6-BAP and 6-BAP.

Fig. 8. (a) the optimal structure of [TGA+6-BAP] and (b) [6-BAP+6-BAP].

The UV-vis spectra and colorimetric assay were both used to estimate the sensitivity of 6-BAP detection system. Under the optimized conditions, absorption spectra of TGA-AgNPs in the presence

ACCEPTED MANUSCRIPT of 6-BAP with different concentrations were examined for quantitative detection of 6-BAP at ambient temperature, the change of different 6-BAP concentrations could be observed by naked eyes. As presented in Fig. 6, upon addition of increasing concentrations of 6-BAP, the probe has an obvious color change from yellow to reddish orange gradually, resulting in the SPR peak the intensity of TGA-AgNPs at 397 nm was decreased; meanwhile, a new SPR at 510 nm was gradually increased.

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Under the optimal conditions, the ratio (A510 nm/A397 nm) of the absorption intensity could express the molar ratio between dispersed and aggregated AgNPs. To quantitatively detect 6-BAP, the absorbance

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ratio at A510 nm/A397nm was linear with a correlation coefficient of 0.985 within the range of 4-26 μM of 6-BAP concentration, The limit of detection (LOD) (S/N ratio =3) was found as low as 0.2 μM. Table 1

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presented the comparative data of limit of detection (LOD) and the linear range with various analytical techniques regarding the detection of 6-BAP. Clearly, the fabricated TGA-AgNPs as a sensor for the

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detection of 6-BAP had a lower LOD and wider linear range, which reveals the high sensitivity of the

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TGA-AgNPs probe.

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Fig. 6. (a) the corresponding photograph of TGA-AgNPs with different concentrations of 6-BAP, (b) UV-vis spectral changes of TGA-AgNPs solutions upon addition of different concentrations of 6-BAP

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(1 μM to 26 μM) at buffer pH=6.0 and (c) calibration curve of TGA-AgNPs (A510 nm/A397 nm) against log10 of different concentrations of 6-BAP (4 μM to 26 μM).

Table 1 Comparison of this work with other previous methods for the detection of 6-BAP. Name of the analytical

Linear

Technique

Range(μM)

fluorescence

LOD(μM)

reference

0.2-66.6

0.076

[35]

LC-TMS

0.09-0.17

0.0129

[36]

Voltammetry

0.7-60

0.235

[37]

20-200

7.0

[38]

0.71-12.0

0.0394

[39]

a

b

MECC c

FDS

ACCEPTED MANUSCRIPT UV-vis Spectrometry This work a

0.1

[30]

4-26

0.2

Present method

liquid chromatography-tandem mass spectrometry

b c

1-20

Micellar electrokinetic capillary chromatography

Frequency double scattering

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Evaluating the stability of TGA-AgNPs is also an essential parameter to ensure the reproductivity of analytical performance. To investigate the stability of TGA-AgNPs, as shown in Fig. 7, the material

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was measured by UV-vis spectra under optimal conditions for one month, the result shows that

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high stability and can be storaged for a long time at 4±2°C.

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TGA-AgNPs probe could remain stable without obvious change. The result indicated that the probe has

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Fig. 7. The normalized absorbance change of TGA-AgNPs in one month.

The selectivity of the assay In order to investigate the selectivity of TGA-AgNPs towards 6-BAP, the absorption spectra of TGA-AgNPs on addition of other common cations , anions and pesticides in the case of 6-BAP were also investigated. An assay was put forward by measuring the A510 nm/A397 nm of the TGA-AgNPs probe for detecting 10 μM 6-BAP with a series of co-existing ions and molecules, including cations (Fe 2+, Al3+, Ba2+, Ca2+, Cd2+, Co2+, Cu2+, K+, Mn2+, Pb2+, NH4+, 1.0 mM), anions (NO3-, CH3COO-, Br-, SO42-, 1.0 mM), pesticides (chlorothalonil, glyphosate, parathion, carbendazim, triazolone, phoxim, 10 μM),

ACCEPTED MANUSCRIPT mixed cations (NH4+, Cu2+, Mn2+, Ca2+, Pb2+, 1.0 mM), mixed anions (NO3-, M-, SO32-, Br-, SO42-, 1.0 mM) and mixed pesticides (chlorothalonil, glyphosate, parathion, 10 μM), respectively. It reveas that these interfering ions (metal cations, anions, and pesticides) did not trigger the aggregation of TGA-AgNPs, after added 6-BAP into solutions, the color changed and the new SPR band was observed at 510 nm. As shown in Fig. 8, this result indicats that this method showed an excellent

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anti-interference ability for the detection of 6-BAP in presence of so many co-existing ions and common organic pesticides. Hence this method has a high specificity to detect 6-BAP and can be

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applied into environmental samples in the future.

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Fig. 8. Absorbance ratio (A510 nm/A397 nm) of the TGA-AgNPs solutions before and after addition of 6-BAP in presence of different ions and pesticides. 6-BAP: 1.0×10-5 M, cations, anions, mixed ions:

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1.0×10-3 M, pesticides and mixed pesticides: 1.0×10-5 M.

Determination of 6-BAP in samples

To further evaluate the applicability and accuracy of the probe in environmental samples, environmental water (Yellow River and tap water) and vegetable (Bean sprout) sample were analyzed by proposed method. According to the obtained calibration curve of UV-vis spectra and regression equation, the ultimate concentration of 6-BAP can be calculated. These results are listed in Table 2. The recoveries were obtained from real samples ranged from 83.9% to 114.9% and relative standard deviation (RSD) was within 5.0%, it revealed that there were no obvious interferences in real samples.

ACCEPTED MANUSCRIPT Consequently, it was believed that the TGA-AgNPs probe as a colorimetric sensor can be successfully applied into detection of 6-BAP and exhibited excellent reproducibility and accuracy in environmental samples.

Table 2 Determination of 6-BAP in environmental water and vegetable samples using TGA-AgNPs as

Founded (μM)

Recovery(％)

RSD (％, n=3)

8

8.6

107.5

3.97

20

20.05

100.25

3.44

26

24.61

94.65

4.49

104.87

2.48

93.75

1.60

92.23

4.25

Yellow River

8

8.39

20

18.75

26

23.98

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Bean sprouts

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Added (μM)

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Samples

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a colorimetric probe.

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Conclusion

In summary, we have demonstrated a rapid and reliable colorimetric assay for the detection of 6-BAP using TGA-AgNPs as a sensor. The SPR peak of TGA-AgNPs showed significant red shift from

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397 nm to 510 nm in the presence of 6-BAP, resulting in color changed from yellow to reddish orange,

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which can be easily observed with naked eyes or measured by UV-vis spectrophotometer. Furthermore, there was no significant red shift in the SPR peak of TGA-AgNPs in presence of other interferences.

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This novel probe shows high selectivity and economy for the detection of 6-BAP in presence of other interferences, This method was successfully applied into detecting 6-BAP in environmental water and

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vegetable samples without any sophisticated instrument, indicating this visual sensor appears to have huge potential for the detection of 6-BAP in environmental samples.

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Nanoparticles for the Naked Eye Detection of Aromatic Isomers, ACS nano. 4 (2010) 6387-6394. [27] J. M. Zheng, H. J. Zhang, J. C. Qu, Q. Zhu, X. G. Chen, Visual detection of glyphosate in

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environmental water samples using cysteamine-stabilized gold nanoparticles as colorimetric probe, Anal. Methods. 5 (2013) 917-924.

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[28] B. Imene, Zhi M. Cui, 4-Amino-3-mercaptobenzoic acid functionalized gold nanoparticles: Synthesis, selective recognition and colorimetric detection of cyhalothrin, Sensors and Actuators

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B 199 (2014) 161-167.

[29] S. Wu, D. D. Li, Gold nanoparticles dissolution based colorimetric method for highly detection of

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organophosphate pesticides Sensors and Actuators B 237 (2017) 427-433. [30] S. Ma, J. He, M. Z. Guo, X. H. Sun, M. D. Zheng, Facile colorimetric detection of

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6 (2016) 106608-106614.

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6-benzylaminopurine based on p-aminobenzenethiol functionalized silver nanoparticles, RSC Adv.

[31] H. K. Li J. J. Guo Visual detection of organophosphorus pesticides represented by mathamidophos using Au nanoparticles as colorimetric probe. Talanta 87 (2011) 93-99.

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[32] D. Sun, H. Zhang, Voltammetric determination of 6-benzylaminopurine (6-BAP) using an acetylene black-dihexadecyl hydrogen phosphate composite film coated glassy carbon electrode.

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Anal. Chim. Acta. 557 (2006) 64-69. [33] G. Zhao, K. Z. Liu, S. Lin, J. Liang, X. Y. Guo, Z. J. Zhang, Application of a carbon nanotube modified electrode in anodic stripping voltammetry for determination of trace amounts of 6-benzylaminopurine. Microchim. Acta. 143 (2003) 255-260. [34] F. Q. Zhang, L.Y. Zeng, Y.X. Zhang, H.Y. Wang, A. G. Wu, A colorimetric assay method for Co 2+ based on thioglycolic acid functionalized hexadecyl trimethyl ammonium bromide modified Au nanoparticles (NPs). Nanoscale 3 (2011) 2150-2154. [35] X. Y. Li, Z. Shang, H. Wei, J. D. Yang, Effects of the interaction between Na2Wo4-6-benzylaminopurine anionic chelate and rhodamine 6G on the resonance Rayleigh

ACCEPTED MANUSCRIPT scattering and fluorescence spectra and their analytical application. Luminescence 28 (2013) 294-301. [36] L. Y. Ge, J. W. H. Yong, S. N. Tan, X. H. Yang, E. S. Ong, Analysis of some cytokinins in coconut (Cocos nucifera L.) water by micellar electrokinetic capillary chromatography after solid-phase extraction. J. Chromatogr. A. 1048 (2004) 119-126.

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[37] S. S. Lu, Y. P. Wen, L. Bai, G. B. Liu, Y. X. Chen, H. Du, X. Q. Wang, pH-controlled voltammetric behaviors and detection of phytohormone 6-benzylaminopurine using MWCNT/GCE. J.

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Electroanal. Chem. 750 (2015) 89-99.

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spectrometry. Food Chem. 208 (2016) 239-244.

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growth regulator and pesticides in bean sprouts by liquid chromatography-tandem mass

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[39] M. Qiao, S. P. Liu, Z. F. Liu, J. D. Yang, J. H. Zhu, X. L. Hu, Overlapping of second order scattering and frequency double scattering spectra method and resonance rayleigh scattering

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method for the determination of 6-benzyladenine in bean sprout. Food. Anal. Methods. 7 (2014)

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1737-1744.

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Graphical abstract

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Schematic presentation of 6-benzylaminopurine (6-BAP) induces silver nanoparticles capped with thioglycolic acid (TGA-AgNPs) aggregation and triggers a visible color change. The TGA-AgNPs bind

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up with 6-BAP through hydrogen bonding and π-π bonding, resulting in the color change from yellow

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to reddish orange.

ACCEPTED MANUSCRIPT Research Highlights

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Color change is induced by TGA-AgNPs aggregation in the presence of 6-benzylaminopurine (6-BAP).

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The sensor exhibits excellent selectivity for 6-BAP over other metal cations, anions and pesticides.

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The present assay method can detect 6-BAP range from 4 μM to 26 μM, with a detection limit of

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This method appears to have huge potential for the detection of 6-BAP in environmental samples.

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4.

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0.2 μM.