Elsevier

Talanta

Volume 144, 1 November 2015, Pages 1036-1043
Talanta

The use of tungsten disulfide dots as highly selective, fluorescent probes for analysis of nitrofurazone

https://doi.org/10.1016/j.talanta.2015.07.055Get rights and content

Highlights

  • WS2 dots was successfully synthesized with the use of a simple hydrothermal method.

  • The original WS2 dots emitted blue fluorescence and had a high quantum yield.

  • Analysis of the nitrofurazone (NFZ) by WS2 dots based on the FRET mechanism.

  • The proposed method is environmentally friendly and harmless in organisms.

Abstract

Tungsten disulfide (WS2) is a two-dimensional transition metal dichalcogenide, which is of particular interest because it has highly anisotropic bonding, which leads to strongly anisotropic electrical and mechanical properties. Thus, in this work, a simple hydrothermal process was developed to produce photoluminescence from WS2 dots. This was achieved in the presence of sodium tungstate and reduced L-glutathione; the emitted fluorescence produced a quantum yield as high as 0.066. The WS2 dots and the associated fluorescence were investigated with the use of transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared and UV–vis spectroscopies. The WS2 dots were used as a fluorescent probe to analyze nitrofurazone (NFZ). The associated fluorescence resonance energy transfer (FRET) mechanism was also investigated and the emitted fluorescence was found to be linear in the range of 0.17–166 μmol L−1 with a detection limit of 0.055 μmol L−1. The proposed method was successfully applied for analysis of NFZ in nasal drops and water samples.

Introduction

Graphene is a two-dimensional (2D) crystalline substance, which has unique electronic, thermal, optical, mechanical and chemical properties, and it has been widely used since its discovery in 2004 [1], [2], [3]. These unique properties depend on the atomic-layer thickness of graphene and its 2D morphology. Such properties have stimulated research for other kinds of 2D nanomaterial. These materials are generally inorganic substances similar to graphite; particularly, they are substances, which are layered materials of ultrathin nanosheets of transition metal dichalcogenides (TMDCs) with strong in-plane bonding and weak out-of-plane interactions. Such structures facilitate exfoliation into two-dimensional layers of single unit cell thickness, which has been widely used in a many applications including solid lubricants, catalysts, batteries, various nanoelectronic and energy storage devices [4], [5], [6], [7]. To date, a number of methods have been developed to prepare TMDC nano-sheets, -tubes and -particles. These methods include liquid exfoliation [8], [9], hydrothermal synthesis [10], [11], pyrolysis [12], chemical vapor deposition [13] and electrochemical Li-intercalation [14]. TMDCs have a wide variety of mechanical and electronic applications with semiconductors of MoS2 [15], [16], MoSe2 [17], [18], WS2 [19], [20] and WSe2 [21], [22]. In particular, the WS2 material consists of 2D covalently bonded S–W–S layers separated by a van der Waals gap. Also, weak van der Waals forces hold the adjacent sulfur sheets together with an S–W–S layer sequence [5], [23].

Recently, WS2 has attracted particular attention because of its highly anisotropic bonding influences the strongly anisotropic electrical and mechanical properties, which are useful in catalytic reactions [19], as solid state lubricants [24], solar cells [25] and field-effective transistors [26]. Also it has been noted that the mono-layered WS2 sheets, which are characterized by strong luminescence, change from indirect to direct band gap semi-conductors; this occurs when WS2 is converted from multi- to mono-layer sheets [9], [26]. Such unique physical and chemical properties of the mono-layered sheets are observed because the WS2 can be significantly affected by the edge structure and atomic defects associated with small nanostructures [27], [28]. Elsewhere [26], bulk WS2 was exfoliated to form monolayers of WS2 quantum dots (QDs) with side lengths in the range of 8–15 nm; such WS2 QDs fluoresce strongly and this suggests the presence of direct band gaps. However, while the above information is readily available, comparatively little is known about the optical properties of WS2 materials, especially those concerned with photoluminescence (PL).

Nitrofurazone (NFZ, 5-nitro-2-furaldehyde semicarbazone) is a nitrofuran, which is the first therapeutic 5-nitrofuran drug [29]. NFZ is an effective fungicide, amoebicide and skin sensitizer, which resists various allergies and infections related to animals and humans [30]. It can also be used for the treatment of enteritis, and boils caused by coli or salmonella bacteria. Therefore, NFZ is still used as a broad-spectrum, antimicrobial drug [31], [32]. However, NFZ is often found in animal food and thus, it can find its way into muscles, liver and milk of animals as residual. It has serious effects on human health [33]. In addition, this drug is potentially carcinogenic and mutagenic, and can promote mammary tumor growth in mammals [31]. Consequently, rapid and sensitive analytical methods for NFZ are required, particularly in the fields of bioassay and chemistry. In this context many methods have been developed: spectrophotometry [34], chromatography [35], high performance liquid chromatography (HPLC) with fluorescence detection (HPLC-FLD) [36], voltammetry [30], FI-CL method [37] and fluorescence [38].

In this work, a completely new approach was proposed. Thus, the initial aim was to synthesize novel photo-luminescent WS2 dots, which could emit strong fluorescence with a high quantum yield. This was to be achieved with the use of a hydrothermal process involving sodium tungstate and reduced L-glutathione. Given that the latter step was successful, a novel photoluminescence sensor containing the WS2 dots was to be constructed and used as a fluorescent probe for the quantitative analysis of NFZ in water and in other samples.

Section snippets

Chemicals and materials

Sodium tungstate (Na2WO4·2H2O, Hongqi Chemical Co., Jiangsu, China), reduced L-glutathione (GSH, Aladdin Chemistry Co., Shanghai, China), and nitrofurazone (NFZ, Sigma-Aldrich Co., Shanghai, China) were purchased from local chemical shop and their aqueous solutions with suitable concentration were prepared as needed. A series of Britton-Robinson (B-R) buffers with different pHs, was prepared by mixing 0.04 mol L1 mixed acid made of 85% H3PO4, CH3COOH and H3BO3 and 0.2 mol L−1 NaOH in different

Characterization of the prepared WS2 dots

The WS2 dots, which were synthesized by the hydrothermal method, were characterized by several techniques, including XRD, TEM, XPS and FT-IR. The XRD spectra of WS2 dots (Fig. 1A) clearly showed three major diffraction peaks, i.e. the reflections at 14.1°, 33°, and 39.8°, which corresponded to the (002), (100), and (103) planes. The relatively weak intensity of these peaks indicated that the as-prepared WS2 dots contained only a few crystals and displayed a hexagonal phase structure [39]. The

Conclusions

A simple hydrothermal process was used to develop a method of analysis for the important compound, Nitrofurazone, (NFZ), which is used as a treatment against fungicides, amoebicides and other skin ailments. NFZ is also, effective against various allergies and infections related to animals, humans and livestock. The method involves the emission of blue fluorescence from WS2 dots with the use of sodium tungstate and reduced L-glutathione; the associated fluorescence quantum yield was found to be

Acknowledgments

The authors gratefully acknowledge the financial support of this study by the National Natural Science Foundation of China, China (NSFC–21365014 and NSFC–21305061), the Natural Science Foundation of Jiangxi Province, China (20132BAB213011 and 20132BAB203011), the Education Department Science Foundation of Jiangxi Province, China (GJJ13026), and the State Key Laboratory of Food Science and Technology of Nanchang University (SKLF–ZZA201302).

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