NoteCdZnSeS quantum dots condensed with ordered mesoporous carbon for high-sensitive electrochemiluminescence detection of hydrogen peroxide in live cells
Graphical abstract
Introduction
Reactive oxygen species (ROS) are oxygen-derived species, including singlet oxygen, superoxide anions, hydroxyl radicals, and hydrogen peroxide (H2O2), which play imperative roles in various physiological processes [1], [2], [3], [4]. As a prominent member of the ROS family, H2O2 is closely associated with cellular growth and proliferation. Besides, as secondary messengers, H2O2 is playing significant roles in essential cellular processes [5,6]. The excessive levels of H2O2 are closely related to several diseases such as cardiovascular disease, cancer, and neurodegenerative disorders [7], [8], [9]. The accurate and rapid determination of H2O2 levels is of great significance because of the far-ranging impacts of H2O2 homeostasis on human health. Existing analytical techniques to determine H2O2 include colorimetric, chemiluminescence, fluorescence, electrochemical method, and electrochemiluminescence (ECL) [10], [11], [12], [13]. Among these, ECL method has attracted increasing attention because of smaller sample size, easier of monitoring, and higher sensitivity.
ECL is a modern analytical technique that combines chemiluminescence and electrochemistry [14], [15], [16]. Since the first studies on ECL were reported in the 1960s, many efforts have been exerted to investigate the mechanisms of ECL and the development of ECL detection platform [17,18]. The co-reactant mechanism is one of the major ECL reaction mechanisms. It has been well documented that the bimolecular electrochemical reaction between the ECL luminophore and suitable co-reactants plays a key role in co-reactant mechanism [19,20]. In other words, both co-reactant and luminophore are reduced or oxidized at the electronic surface forming intermediate states and radicals. Then, the co-reactant radical reduces or oxidizes the luminophore producing its excited state. Coincidentally, H2O2, as a desirable and efficient co-reactant, has attracted much attention recently [21]. Yuan's group reported a luminol ECL immunosensor that H2O2 was used to be co-reactant for the luminophore luminol [22]. Xu and co-workers explored the stainless-steel electrode and applied to construct a platform for ECL detection of H2O2 [23]. Wang et al. reported a procedure for the preparation of quantum dots-hierarchical nanotube arrays, and demonstrated their enhanced ECL in H2O2 solution [24]. To date, extensive efforts have been developed detection methods for H2O2, however, there are several limitations such as expensive cost and tedious pretreatment. Therefore, the development of low cost, simple, and reliable strategies for H2O2 assay is still highly desired.
Quantum dots (QDs), known as colloidal semiconductor nanocrystals, possess many useful properties such as high molar extinction coefficient, wide adjustable band gap, and high quantum yield [25], [26], [27]. QDs play roles in both academic research and commercial fields for being adjusted by altering not only the composition of the QDs but also the particle size [28], [29], [30], [31]. In addition, the QDs-based ECL sensors have been actively studied in recent years due to their low background noise, simplified setup, fast sample analysis, and wide dynamic range [32], [33], [34], [35]. To achieve efficient ECL responses of QDs for bioanalysis, QDs-based composites, especially integrating QDs with carbon nanomaterials, have received particular interest. Ordered mesoporous carbon (OMC) with good stability, exceptional electrical conductivity, large specific surface area, and low fabrication cost has been established and continuously developed [36], [37], [38]. Recent studies have shown, the acid-functionalized OMC containing -COOH sites can be binding with other nano-entities [39,40]. Moreover, as highly conductive substrates, OMC materials can reduce over-potential of ECL systems and amplify the ECL intensity by combining with QDs for efficient electron transfer.
Herein, we developed an ECL biosensor based on QDs immobilized on OMC. OMC serves as highly conductive substrates to combine QDs for efficient electron transfer, which not only enhances the electrochemical performance but also significantly amplifies the ECL signal of QDs in the presence of H2O2 as a co-reactant. Moreover, the ECL biosensor platform was developed for reliable and sensitive H2O2 detection in different cells, revealing its promising applications in diagnosis and physiological research.
Section snippets
Materials
Glucose (Gl), N-hydroxysuccinimide (NHS), ascorbic acid (AA), 1-ethyl-3-(3-dimethylaminepropyl) carbodiimide hydrochloride (EDC), and glutathione (GSH) were obtained from Macklin Biochemical Co. Ltd. (Shanghai, China). NaOH, KCl, and sucrose were provided by Energy Chemical Industry Co. Ltd. HNO3 and ethanol absolute were obtained from Tianjin Bohua Chemical Co. Ltd. Mili-Q ultrapure water (>18 MΩ) was used throughout the study. All reagents were of analytical reagent grade.
Instrumentation
The morphology and
Characterization of the as-prepared CdZnSeS QDs and CdZnSeS QDs/OMC
Transmission electron microscopy (TEM) image (Fig. 1A) and corresponding size distribution of CdZnSeS QDs (Fig. 1B) were analyzed, suggesting the CdZnSeS QDs are uniform with an average diameter of 4.5 nm. A wide absorption band in UV–vis absorption (Fig. 1C, black curve) and a strong fluorescent emission peak at 615 nm of QDs (Fig. 1C, red curve) showed their prominent absorption and emission features. The CdZnSeS QDs/OMC materials were also characterized by confocal microscopy in the Fig. 1D,
Conclusions
In summary, we developed a reliable and high-sensitivity ECL biosensor for H2O2 detection in live cells based on QDs and OMC. In particular, OMC materials could serve as highly conductive substrates to combine QDs for efficient electron transfer, which can significantly amplify the ECL signal of QDs. More importantly, researches on the stability and selectivity of the prepared ECL biosensor showed satisfactory results. The construction of ECL biosensor may be further extended to diagnostic
Author statement
Lei Wang: Methodology, Investigation, Data curation, Writing-original draft preparation. Xue-Hui Shi: Validation. Yu-Fan Zhang: Conceptualization, Investigation. An-An Liu: Validation, Methodology. Shu-Lin Liu: Methodology, Writing-review & editing. Dai-Wen Pang: Supervision, Project administration. Zhi-Gang Wang: Project administration, 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.
Acknowledgments
This work was supported by National Key Research and Development Program of China (2019YFA0210500), the National Natural Science Foundation of China (Nos. 21535005, 21877102, 21977054 and 91953107) and Tianjin Research Innovation Project for Postgraduate Students (No. 2019YJSB083).
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