ZnO/CNT-COOHs based solid-state ECL sensor for tetracycline detection in fishpond water

https://doi.org/10.1016/j.microc.2020.104708Get rights and content

Highlights

  • The ECL application of ZnO anode was expanded with ZnO as the main illuminator and made the related mechanism conjecture.

  • Tetracycline was detected according to the inhibitory effect of tetracycline on ECL of ZnO/ CNTs-COOH.

  • This method proposed a green, fast and low cost sensor for detecting tetracycline.

Abstract

A sensitive electrochemiluminescence (ECL) sensor in solid-state for the detection of tetracycline (TET), based on carboxylated carbon nanotubes modified ZnO (CNT-COOHs/ZnO), was developed in this research. The ZnO, which worked as luminophore here, was an environment-friendly material. Resulted from its tremendously specific surface area, the loading amount of CNT-COOHs increased. The CNT-COOHs played a role of catalyzer to enhance the ECL intensity of CNT-COOHs/ZnO modified glass carbon electrode (GCE) in triethanolamine (TEOA) contained electrolyte. After adding TET in the solution, the ECL intensity significantly quenched. The ΔECL intensity showed a good correlation to the concentration of TET in the range of 1.0 × 10–8–1.0 × 10–4 M and the detection limit achieved to 6.7 × 10–9 M within a response time of 1.0 min. Furthermore, the proposed CNT-COOHs/ZnO based ECL sensor was applied for the detection of TET in fishpond water and exhibited a good accuracy. We believe our system supplied a potential platform for the detection of TET in real world.

Introduction

Tetracycline (TET) is a kind of representative antibiotic that mainly used for the treatment of the infections caused by clinical phthogens, such as mycoplasma pneumonia infection, urogenital tract infection, early cholera, and epidemic typhus [1]. Because of the excellent sterilizing effect, TET is widely used in the aquaculture industry and accredited as an additive for animal feed by the Ministry of Agriculture of China. However, the overuse of TET has led to serious residues in animals, which causes noticeable problems for food safety. Therefore, it is necessary to develop a sensitive and accurate method for the detection of TET in environment, food, and drug.

The common-used methods for detecting TET include microbiological assay [2,3], high-performance liquid chromatography (HPLC) [4,5], liquid chromatography-mass spectrometry (LC-MS) [6,7], thin layer chromatography (TLC) [8], enzyme-linked immunosorbent assay (ELISA) [9,10], capillary electrophoresis (CE) [11,12], electrochemical method [13,14], fluorescence spectrometry [15,16] and so on. Although each method has its advantages and disadvantages, the improvements of sensitivity, specificity, rapidity, miniaturization of instrument, and low cost are the targets that the researchers aim to achieve. Normally, ELISA method has high specificity. Wang et al. [17] developed a direct competition ELISA method and used an enhanced luminol-H2O2 system to initiate light signals to detect tetracycline in milk.. However, the time-cost of this method was high as it had multiple incubations and washing steps. LC-MS, HPLC, and TLC method have excellent separation effect as well as achieving the simultaneous detection of tetracyclines (TET). Du et al. [18] developed a HPLC-FLD based method to simultaneously detect tetracycline, where as it needed large and expensive instruments. Electrochemical method has attracted more attentions, as its simplicity, high sensitivity, low-cost, and easy to miniaturization. Chen et al. [19] developed an aptasensor for electrochemical detection of TET, whose detection limit was achieved to 1.0 ng/mL (2.2 × 10–9 M). The aptasensor showed a high specificity in the presence of interferences. However, the detection time was over-consumed as the interaction between aptamer and TET costs 15 min.

Recently, electrochemiluminescence (ECL) emerged as a potential method for TET detection due to its high sensitivity, wide linear range, and useage of simple instrument. Pang et al. [20] confirmed that TET could inhibit the ECL intensity of Ru(bpy)32+/tripropylamine system with a detection limit of 4.0 ng/mL. However, substantial amount of Ru(bpy)32+ was used in solution phase, this expensive luminophore was excessively wasted and brought enormous burden to environment. Chen et al. [21] improved the Ru(bpy)32+ based ECL sensor for detecting TET. The Ru(bpy)32+ was doped in SiO2/nafion film modified electrode, which saved a certain amount of Ru(bpy)32+. However, the expensive price of Ru(bpy)32+ still limited the large-scale application of this system, and its detection limit was unsatisfied (2.3 × 10–7 M, 1.0 × 102 ng/mL). Therefore, it is urgent to explore advanced materials for fabricating environment-friendly, simple, low-cost, and efficient solid-state ECL sensors.

The interests on developing semiconductor materials based solid-state ECL sensors increased rapidly [22], [23], [24], [25]. ZnO is a kind of metal oxide semiconductor with wide band gap and used in many fields. Especially, ZnO possesses a rich variety of structures and has a great potential application for the design of ECL sensor [26]. Liu et al. reported that Ru (bpy) 32+ was used as the main luminescent object. Compound ZnO enhanced the luminescence of Ru (bpy) 32+ by increasing the contact area to improve the sensitivity of the sensor. The sensor was applied to detect E. coli O157:H7 [27]. Zhang et al. prepared ZnO nanorods as main illuminant, and applied it for the detection of cytochrome C, obtaining a very low detection limit [28]. Recently, several studies have confirmed that the ECL efficiency of ZnO could be improved when it was modified with carbonaceous materials [29]. Carbon nanotubes (CNTs) were considered as promising support materials for semiconductor with ECL efficiency due to their excellent electronic properties, meanwhile, their mesoporous character could promote the diffusion of substances. Furthermore, CNTs could be easily modified with various functional groups [30,31]. The functional groups modified CNTs have better dispersibility and are easier to interact with some other materials. Therefore, it is promising to develop a CNTs/ZnO based solid-state ultrasensitive ECL sensor for TET.

In this work, we developed a solid-state ECL sensor for detecting TET based on the composite of flower-liked ZnO and carboxylated CNTs (CNT-COOHs/ZnO). Flower-liked ZnO had considerable specific surface area, which could increase the contact area with CNT-COOHs. With the assistance of CNT-COOHs, the electron transfer of flower-liked ZnO was improved to enhance the ECL capacity. As a result, a novel sensor has been constructed, which showed excellent performances for TET sensing with high sensitivity, wide detection range, and good anti-interference ability. Moreover, the application of CNT-COOHs/ZnO based solid-state sensor for the detection of TET in fishpond water was discussed here. The proposed ECL sensor extended the application of flower-liked ZnO and CNT-COOHs and could be a promising method for the TET monitoring in environment.

Section snippets

Reagents and apparatus

All chemicals were reagent grade. Ultrapure water (>18 MΩ cm) was used in all experiments. The tetracycline (TET) was purchased from Aladdin Industrial Inc. (China). Zn(NO3)2•6H2O, NH3•H2O and triethanolamine (TEOA) were purchased from Sinopharm Chemical Reagent Co. (China). Carbon nanotubes were purchased from Nanjing XFnano materials Technology Co. Ltd., China.

ECL measurement was performed on MPI-B multifunctional ECL system (Xi'an Remex Analyse Instrument Co., Ltd., China). Electrochemical

Characterizations of different electrodes

The structures and morphologies of flower-liked ZnO, CNT-COOHs and CNT-COOHs/ZnO modified GCE electrode were characterized by SEM, XRD, and FT-IR. As shown in Fig. 1A, it could be found that the ZnO formed a flower structure in a micro-size, which contains numerous ZnO petals. The flower structure increased the specific surface area of ZnO material, which is helpful for its application in the following detection of TET. In the SEM image of CNT-COOHs (Fig. 1B), morphologies of tube-liked fibers

Conclusion

In summary, a solid-state and green ECL sensor for TET detection in fishpond water was developed. Due to the considerable specific surface area of flower-liked ZnO and its effective combination with carbonaceous material, CNT-COOHs, the ECL intensity was significantly enhanced. Meanwhile, the CNT-COOHs/ZnO composite modified GCE based ECL sensor showed a good sensitivity, anti-interference ability for the TET detection, and it was also successfully applied to the detection of TET in fishpond

CRediT authorship contribution statement

Xueling Shan: Methodology, Data curation, Writing - original draft. Yuting Pan: Data curation, Investigation. Fanzhuo Dai: Data curation, Investigation. Xiaohui Chen: Data curation, Investigation. Wenchang Wang: Data curation, Investigation. Zhidong Chen: Writing - review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The authors are grateful to the financial support by the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (18KJB150001), the National Natural Science Foundation of China (51574047) and the Foundation of Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology (BM2012110).

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