A novel water-soluble flavonol-based fluorescent probe for highly specific and sensitive detection of Al3+ and its application in onion and zebrafish

https://doi.org/10.1016/j.saa.2022.121384Get rights and content

Highlights

  • A novel water-soluble fluorescence probe based on flavonol derivative was developed.

  • The probe displayed high selectivity and sensitivity toward Al3+ detection in aqueous solutions, and the detection limits were significantly lower than WHO limit.

  • The probe has good cell permeability and could be applied for live-cell imaging to detect Al3+ in animal and plant tissues.

Abstract

A novel and simple turn-on fluorescence probe (HD) for Al3+ detection was successfully developed based on flavonol derivatives. This probe exhibited a significantly enhanced fluorescence response toward Al3+ in aqueous solution which could be observed by naked-eye from poor fluorescence to strong light green emission. The probe HD displays highly specific detection for Al3+ over other competitive metal ions, and the detection limit of probe HD for Al3+ was determined to be 2.57 × 10−8 M, which are much lower than the World Health Organization (WHO) guideline value for drinking food/water. The binding stoichiometry of probe HD with Al3+ was determined to be 1:1 according to Job’s plot and ESI-HRMS analysis, and the binding constant was calculated to be 2.01 × 104 M−1. The probe HD exhibited high selectivity, high sensitivity, good anti-interface ability, and wide pH application range as well as the quantitative determination in the detection of Al3+. The coordination mechanism of probe HD with Al3+ was supported by density functional theory (DFT) calculations and HRMS analysis. In addition, the probe HD was found to have good cell permeability and could be applied for live-cell imaging to detect Al3+ in onions and zebrafish.

Graphical abstract

A water-soluble flavonol-based “turn-on” fluorescent probe was developed, and the probe had an excellent selectivity and sensitivity to aluminum ion. It can also be applied for live-cell imaging to detect Al3+ in onions and zebrafish.

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Introduction

With the development of society and technology, the excessive metal ion content causes serious pollution to the ecological environment and brings great harm to human health. In particular, aluminum as the most abundant metallic element in the earth's crust, is readily soluble in nitric acid, hydrochloric acid, sodium hydroxide and so on [1], [2], [3], [4]. It is so easy to form Al3+ that the ecological environment is adversely affected. Studies have shown that plant growth is inhibited with the rise of aluminum ion content in the soil [5]. According to the report of the world health organization (WHO), the acceptable daily intake of Al3+ for human body is about 3–10 mg [6], [7], [8], and also the permissible limit of Al3+ concentration in drinking water is about 7.41 μM [9], and long-term excessive intake can lead to a variety of diseases such as amyotrophic lateral sclerosis, Parkinson’s disease, hemochromatosis, Alzheimer's disease, osteoporosis, etc. [10], [11], [12], [13], [14]. Therefore, the development and research of a fast, effective, convenient and accurate method for the detection of Al3+ is an important significance to the healthy development of the environment and human beings.

There are many methods to detect aluminum ions, such as fluorescence assay, absorption spectrometry, inductively coupled plasma spectrometry, and so on [15], [16], [17]. Compared to other detection techniques, fluorescence analysis has attracted great attention due to its advantages of high sensitivity, high selectivity, high detection efficiency, and simple operation [18], [19], [20], [21]. In recent years, Xu et al developed a series of novel fluorescence probes which displayed high selectivity and sensitivity for detecting aluminum ions and could be successfully applied in biological imaging [22], [23], [24], [25]. Although the content of aluminum ions can be accurately determined by the other methods mentioned above, they have many disadvantages of high cost, long response time and poor selectivity when the number of samples is large [26], [27], [28], [29], [30], [31]. Therefore, it is vitally desirable to develop a novel and simple fluorescent probe which can be easily prepared and can quickly detect Al3+ with low cost, high selectivity and sensitivity.

Flavonol derivatives are significant and known natural botanical functional pigments which widely distribute in fruits, vegetables, and flowers (Fig. 1) [32], [33]. Due to widely available resources in nature, excellent biocompatibility and simple synthesis, flavonol derivatives have been considered as a promising fluorophore in biological applications [34]. Flavonol derivatives as the fluorophores for constructing various fluorescence probes have recently attracted great concern owing to its excellent photophysical properties, such as good photostability, reasonable fluorescent quantum yields, large Stokes shift, and the excited-state intramolecular proton transfer (ESIPT) process [35], [36]. In addition, flavonols have a strong ability to complex with metal ions. A lot of flavonol derivatives have been used in the design of fluorescent chemical sensors for anions [37], cations [38], proteins [39], reactive biological species [40], environmental hazards [41], and other biological imaging applications [42]. In recent years, many flavonol-based fluorescence probes for sensing Al3+ have been developed and reported [43], [44], [45], [46], [47], [48]. However, most of flavonol based fluorescent probes for the detection of Al3+ are soluble only in organic solvents or mixed solvents containing water and have poor solubility in pure water which limits remarkably their application in many fields [49]. Therefore, it is desirable to design and synthesize hydrosoluble flavonol derivatives for constructing the Al3+ fluorescent probe. Herein, we designed and synthesized a new flavonol based fluorescent probe (HD) with the introduction of the polyethylene glycol group to enhance the water-solubility, which can act as a “turn-on” fluorescence chemosensor for the detection toward Al3+ cations. The probe HD was confirmed by using 1H NMR and ESI-HRMS, and could effectively recognize Al3+ in pure aqueous media with advantages of short response time, easy synthesis, low cost, and low detection limit. Furthermore, the probe HD can also be applied in monitoring the changes of intracellular Al3+ in food and biological environments.

Section snippets

Synthesis of probe HD

Ethanol (25 mL), compound 1 (2.2 g, 5 mmol) [50], 2-hydroxyacetophenone (2.52 mL, 5.5 mmol) and sodium hydroxide solid (0.5 g, 12.5 mmol) were in succession added into a 100 mL dried round flask equipped. The mixture was stirred and refluxed for 3 h, and then H2O2 (30 %v, 1.5 mL) was added. The reaction mixture continued to react for another 2 h. The solvent was removed under vacuum, and 50 mL water was put into the residues, extracted three times with methylene chloride (3 × 25 mL), then the

Synthesis and characterization

The synthetic route of probe HD was outlined in Scheme 1. 3,4-bis(2-(2-(2-methoxyethoxy) ethoxy) ethoxy) benzaldehyde (1) was prepared according to previously reported procedures [50]. Compound 2 was obtained by a condensation reaction of 2-hydroxyacetophenone and compound 1 under alkaline conditions, and then compound 2 was directly further oxidized by hydrogen peroxide to produce probe HD in a 70% yield. The synthesized probe HD was confirmed by NMR and ESI-HRMS (See Supporting Information).

Selectivity towards metal ions

Conclusion

In summary, a novel water-soluble flavonol-based fluorescent probe HD was synthesized and characterized. HD exhibits a highly specific turn-on fluorescence response toward Al3+ over other coexisting competitive metal ions. The low detection limit value of HD for Al3+ was calculated to be 2.57 × 10−8 M. HD displays high selectivity and sensitivity for Al3+ based on the inhibition of excited-state intramolecular proton transfer and the chelation-enhanced fluorescence. HD also possesses the

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

Support was provided by Open Research Fund of School of Chemistry and Chemical Engineering, Henan Normal University, China. Dr. Zhonglong Wang gratefully acknowledge the financial support from the National Natural Science Foundation of China (No. 32071707). Authors also thank for Advanced Analysis and Testing Center of Nanjing Forestry University.

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