Template-assisted preparation of Au nanowires and their application in nitrite ions sensing

https://doi.org/10.1016/j.jelechem.2016.03.021Get rights and content

Highlights

  • a novel method for synthesizing Au nanowires was developed using Te nanowires as sacrificial templates.

  • Au nanowire-modified electrodes are selected as electrode materials for detecting nitrite ion. The result demonstrate that the fabricated nitrite ion sensor exhibits excellent performance, including high sensitivity, a good linear relationship limit, a low detection limit, good reproducibility and long-term stability.

  • The proposed sensor was successfully utilized to detect nitrite ion in tap water and pickled food. Satisfactory results were obtained.

Abstract

Au nanowires synthesized via a template-assisted method using Te nanowires as templates are selected as electrode materials for detecting nitrite ions. The result is verified through a series of electrochemical measurements to demonstrate that Au nanowire-modified electrodes exhibit high catalytic activity for nitrite ions. Au nanowire-modified electrodes with a loading of 0.006 μg/mm2 achieve a relatively high catalytic current oxidation with a potential of + 0.83 V. The proposed sensor exhibits a rapid response to nitrite ions (less than 5 s), and the oxidation current shows a linear relationship (R = 0.9982) with the nitrite ions concentration ranging from 1 μM to 0.97 mM, at a detection limit of 0.2 μM (S/N = 3). The proposed sensor also demonstrates high sensitivity and excellent selectivity. This study emphasizes on the practicality of the proposed sensor in the measurement of nitrite ions in tap water and pickled food.

Introduction

Pickled foods become a popular food product because of their unique flavor and high content of vitamins, calcium, phosphorus, and other inorganic substances. They are typically preserved using nitrite ions. However, nitrite ions are known to be potentially toxic. Nitrite reacts with secondary amines in food or in the stomach to form nitrosamines, which are known to cause stomach, and bowel cancers, leukemia, and brain tumors in children [1], [2], [3], [4]. A series of rules that restrict the level of nitrites in food products are currently being implemented. For example, the World Health Organization regulates the maximum admissible level of nitrite ion to 0.2 mg/kg in pickled food and 3 mg·L 1 in drinking water. Moreover, sodium nitrite and nitrite in meat products should not exceed 0.3 and 30 mg/kg, respectively. Therefore, the accurate quantification of nitrite ions is important to reduce health risks.

As a result of technological development, various analytical methods for detecting nitrite in food have been reported. Examples of such analytical methods include chemiluminescence [5], chromatography [6], fluorometry [7], gas chromatography–mass spectrometry [8], polarography [9], spectrophotometry [10], and electrochemistry [11], [12], [13]. Electrochemical sensors are also widely used to measure nitrite ions because of their easy operation, fast response and relatively low cost [14], [15], [16]. Developing new types of modified materials for sensors is crucial in discovering electrochemically active areas, reducing oxidation potentials and improving detection sensitivity. A large number of researchers have focused on the study of noble metal nanomaterials and their application as materials for electrode modification.

Au nanomaterials are usually employed as electrochemical interfaces to effectively accelerate electron transfer between electrodes and nitrite ions because of their desirable properties, including high effective surface area, excellent electronic transport properties, and good biocompatibility. Muthukumar et al. [17] reported the electrochemical determination of ions using nitrite–citrate–gold nanoparticles decorated on a Co(II)MTpAP self-assembly bare glass electrode. The as-produced sensor not only shifted the nitrite ion oxidation potential toward a lower positive potential but also greatly enhanced the current with respect to that of bare and Co(II)MTpAP-modified electrodes. Jiao et al. [18] developed a novel nitrite ion sensor based on Au-RGO/poly (diallyldimethylammonium chloride) nanocomposites and used poly (diallyldimethylammonium chloride) as a reducing and stabilizing agent. The as-prepared sensor features low detection limit, good selectivity, low cost, and wide linear range as well as high stability for long-term application. However, compared with Au nanoparticles, Au nanowires have not been frequently reported as enhanced elements for the detection of nitrite ions. However, one-dimensional nanowires can provide large electrochemically active areas to accelerate the electron transfer of substrate on electrode surfaces. Such capability is highly desirable and presents an excellent opportunity to explore new strategies to synthesize nanowires as electrode materials.

Numerous approaches to the fabrication of Au nanowires have been reported [19], [20]. However, no study has explored the template-assisted production of Au nanowires using Te nanowires as sacrificial templates. In the current work, we developed a novel method to synthesize Au nanowires using Te nanowires as sacrificial templates. Following the use of a Benchtop Incubator Shaker at a rotation rate of 260 rpm, a replacement reaction occurred automatically between the Te nanowires and chloroauric acid without the presence of other agents. This method for synthesis Au naowire is not only well-morphology (super length, uniform diameter), but also a sustainable and environment-friendly technique. The method for synthesis for Te nanowires is researched for a long time. The technology has been relatively mature [21], [22], [23]. Te nanowires, via hydro-thermal synthesis that sodium tellurate is reduced by hydrazine hydrate in alkaline solution, not only exist well-morphology, but also have high yield [24], [25]. Furthermore, Te nanowires are prone to being reduced in steady metal salt solution [16], [24], [25]. This characteristic of Te nanowires was utilized for synthesized Au nanowires. The XRD figures show that Au nanowire is synthesized successfully. The SEM figures show Au nanowires exist well-morphology and high yield. In addition, Au nanowires modified on the surface electrodes prepared nitrite ions sensor showing excellent performance. The as-prepared Au nanowires were fixed on the surface of electrode to measure the nitrite ions. The experiment data revealed that Au nanowire-modified electrodes exhibit excellent catalytic activity for oxidation of nitrite ions and feature a wide linear range, good selectivity, and long-term stability. In this study, the as-prepared Au nanowire-modified electrode was successfully employed to quantify nitrite ions in actual samples, including tap water and pickled food, with satisfactory results.

Section snippets

Materials

NaNO2, ammonium hydroxide, Na2TeO3, acetone, hydrazine (50%), poly-(N-vinyl-2-pyrrolidone), and Na2SO4, were purchased from Guangzhou Chemical Factory (Guangzhou, China). HAuCl4·3H2O was obtained from Sigma-Aldrich. All the chemicals were of analytical grade. Distilled water was used in the experiments.

Apparatus

The electrochemical experiments were performed using an Autolab PGSTAT 128 N electrochemical workstation at 25 °C. A standard three-electrode system (Au nanowire-modified electrode as work

Characterization

Fig. 1 shows the SEM images of the Au nanowires that originated from the Te nanowires. The Au nanowires automatically set off a galvanic displacement reaction upon the addition of HAuCl4·3H2O in water. A proposed mechanism for the formation of Au nanostructures is shown in Scheme 1.

At an early stage, some of the Au nanoparticles began to appear on the outer surface of the Te nanowires. As the reaction proceeded, the Au nanoparticles gradually increased and formed nanoshells around the

Conclusions

Au nanowires were successfully obtained using Te nanowires as the sacrificial template. The proposed synthesis system is a promising route for the synthesis of other nanomaterials. The fabricated nitrite ion sensor exhibits excellent performance, including high sensitivity, a good linear relationship limit and a low detection limit. In addition, the sensor exhibits good reproducibility and long-term stability. Therefore, the sensor has potential practical application. The proposed sensor was

Acknowledgments

This work was supported by the National Natural Science Foundation of China (no. 21375016), the Natural Science Foundation of Guangdong Province (no. S2013010014324), Science and Technological Program for Dongguan's Higher Education, Science and Research, and Health Care Institution (no.2011108101016) and Youth Found of College of Science and Technology of Dongguan of City College, Dongguan(no.2015QJY001z).

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