Elsevier

Talanta

Volume 221, 1 January 2021, 121479
Talanta

An electrochemiluminescence sensor for 17β-estradiol detection based on resonance energy transfer in α-FeOOH@CdS/Ag NCs

https://doi.org/10.1016/j.talanta.2020.121479Get rights and content

Highlights

  • As a charming ECL-active material, α-FeOOH@CdS were introduced into ECL sensor.

  • 3D hierarchical structure of α-FeOOH nanospheres were chosen as loading frameworks.

  • More SO4radical dot- could be generated in Fenton-like process for more efficient ECL response.

  • Ag NCs were employed as effective quenching probes for CdS QDs.

  • The ECL sensor showed good stability and sensitivity for E2 detection.

Abstract

An electrochemiluminescence (ECL) resonance energy transfer system is constructed for 17β-estradiol (E2) detection using α-FeOOH@CdS nanospheres as the ECL-active substrates and Ag NCs as an efficient quencher. CdS QDs loaded onto three-dimensional (3D) urchin-like α-FeOOH nanospheres (α-FeOOH@CdS nanospheres) exhibited excellent ECL responses, which is attributed to dual-amplification of α-FeOOH frameworks. The 3D hierarchical structure of the α-FeOOH nanospheres provided abundant sites for loading ECL-active species, thus significantly improving the ECL performance of substrates; While Fe3+ presented on surface of α-FeOOH nanospheres could be reduced to Fe2+ in negative potentials, after which might activate persulfate in a Fenton-like process, resulting in more sulfate free radicals for more effective ECL responses via electron transfer reactions. Additionally, Ag nanoclusters (Ag NCs) stabilized by single stranded oligonucleotide were introduced as quenching probes for CdS QDs owing to the well-matched donor-acceptor spectrum for efficient energy transfer, which makes them appropriate for detection of E2. The proposed strategy displayed a desirable dynamic range from 0.01 to 10 pg mL−1 with a limit of detection of 0.003 pg mL−1. The proposed strategy based on the ECL-RET strategy offered an ideal way for E2 detection, and also revealed an alternative platform for detection of other small molecules.

Introduction

The steroid hormone 17β-estradiol (E2) is mainly secreted by female ovaries or male testes, and plays a vital role in functions of multiple organs, including the brain. E2 works in some life processes, such as neuroprotection, neurogenesis, sexual characteristics, pregnancy, and synaptic plasticity [[1], [2], [3]]. Abnormal metabolism of E2 can disrupt endocrine functions, leading to diseases with potential risk factors such as male infertility, blood-brain barrier damage, and testicular cancers [[4], [5], [6]]. However, E2 is often detected in discharge from sewage treatment plants, biosolids for agricultural purposes and livestock industry pollution [7], and can exist in environment for long time. Methods for E2 detection have been studied, including enzyme-linked immunosorbent assay (ELISA) [8,9], high performance liquid chromatography - mass spectrometry (HPLC-MS) [10,11], gas chromatography-mass spectrometry (GC-MS) [12], chemiluminescence immune-assays [13], and electrochemical methods [14,15]. Although high selectivity or sensitivity can be achieved, there are still certain associated limitations, such as complex sample preprocessing or requirements of expensive equipment. Thus, the development of an effective strategy that is simple to operate and shows high sensitivity and selectivity remains highly desirable.

Electrochemiluminescence (ECL) is generated through electrochemical reactions between electrogenerated species. It is a widely applicable technique that exhibits low background, simple controllability, and a simplified optical setup [16,17], which has been effectively used in numerous analytical fields, such as immunoassays [18], small molecule detection [19], DNA analysis [20], cancer cell [21] and metal ion detection [22]. It is worth noting that two key factors - the design of effective electrogenerated species and the chosen strategy - play a vital role in analytical ability of the ECL sensor. Recently, quantum dots (QDs) have been served as ECL-active materials for various sensors benefited from intrinsic ideal band gaps and excellent sensitivity [23]. In this work, urchin-like α-FeOOH spheres were applied as perfect frameworks for loading CdS QDs to achieve excellent ECL performance. The high specific surface areas of α-FeOOH spheres offer enhanced number of favorable sites for sufficient loading of ECL-active species, thus effectively improving the ECL signal. In addition, as in the Fenton-like process, more powerful sulfate free radicals can be generated through the activation by Fe2+ for persulfate at room temperature [24]. Therefore, in this work, Fe2+ generated by Fe3+ reduction on the surface of α-FeOOH nanospheres acted as an efficient activator for persulfate, enhancing the oxidizing ability of the sulfate radical, and thus enhancing luminous efficiency of the CdS QDs via electron transfer. Recently, ECL resonance energy transfer (ECL-RET) has been considered for designing of advanced ECL sensors owing to appropriate distance between the acceptors and donors [25,26]. In this work, Ag nanoclusters (Ag NCs) stabilized by single stranded oligonucleotide were chosen as an energy acceptor for CdS QDs. The well-matched donor-acceptor spectrum allowed for efficient energy transfer, thereby making the system appropriate for the detection of small molecule E2.

Herein, E2 was detected based on ECL quenching effect resulting from ECL-RET based on CdS QDs and Ag NCs. The complete fabrication of the proposed ECL strategy is shown in Scheme 1A. First, urchin-like α-FeOOH nanospheres were synthesized through a hydrothermal method, and then CdS QDs were loaded onto the α-FeOOH by EDC/NHS crosslinking. The obtained α-FeOOH@CdS nanocomposites exhibited excellent ECL responses, which could be attributed to the high capacity of the 3D hierarchical structure and increased generation of sulfate free radicals through activation by Fe2+ for persulfate in a Fenton-like process. The obtained α-FeOOH@CdS nanocomposites were applied to glassy carbon electrodes (GCE) as the ECL-active materials. Subsequently, the surface of the above electrodes was modified with aptamer through EDC/NHS crosslinking, and then MEA was introduced to block the vacant active sites. Next, various concentrations of E2 were introduced and incubated with the above electrodes. AgNCs-DNA were finally applied as quenching probes and the reduced ECL signal achieved quantitative detection of E2. The established ECL platform offers a simple and sensitive approach for E2 detection, while also opening up a new way in the area of small molecule analysis.

Section snippets

Materials and reagents

Iron(Ⅱ) sulfate heptahydrate (FeSO4·7H2O, 99%), glycerol (C3H8O3, ≥99.0%), silver nitrate (AgNO3, ≥99.8%) and sodium borohydride (NaBH4, 98%) were all purchased from Sinopharm Chemical Reagent Shanghai Co., Ltd. 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC, 98.5%), 3-Aminopro-pyltriethoxysilane (APTES, 98%), and cadmium chloride (CdCl2, 99.99%) were obtained from Aladdin Reagent Database Inc. (Shanghai, China). N-hydroxysuccinimide (NHS) and β-Estradiol (E2, ≥98%) were

Characterization of nanomaterials

The adopted nanomaterials in ECL sensor were characterized by SEM and TEM. As can be seen in Fig. 1A, urchin-like α-FeOOH nanospheres were successfully obtained via a hydrothermal method. The average diameter of α-FeOOH nanospheres was about 800–1000 nm. Furthermore, the magnified SEM image of the α-FeOOH nanospheres clearly showed the 3D hierarchical structure (Fig. 1B), which enhanced the number of favorable sites for loading CdS QDs. The SEM images with different magnification (Fig. 1C and D

Conclusions

In summary, an ECL sensor was successfully constructed in this work based on an ECL-RET strategy, providing a promising new platform for E2 detection. 3D urchin-like α-FeOOH nanospheres, which were synthesized using a hydrothermal reaction, acted as ideal frameworks for loading CdS QDs. The high specific surface area of the hierarchical structure offered abundant sites for ECL-active materials. In addition, more sulfate free radicals were generated through activating of persulfate by Fe2+ in a

Credit author statement

Yixin Liu, Conceptualization, Methodology, Software, Writing - original draft. Binxiao Li, Methodology, Proofread the manuscript. Yuanyuan Yao, Characterization of the samples. Beibei Yang, Characterization of the samples. Tongtong Tian, Characterization of the samples. Yan Miao, Supervision, Guidance, Reviewing the manuscript, Funding acquisition. Baohong Liu, Supervision, Guidance, Reviewing the manuscript, Funding acquisition.

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.

Acknowledgements

This study was supported by the National Natural Science Foundation of China (21775028), and Science and Technology Commission of Shanghai Municipality (16391903900).

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