Assignment help

加拿大代写 The List Of Abbreviations

加拿大代写 The List Of Abbreviations 总之,我们提出了一种新的双通道比色法和碘离子荧光识别(我)在水房样品具有很高的灵敏度和选择性。碘淬PVP的ZnS纳米颗粒的荧光响应以浓度依赖的方式指出我的定量测量与5.4 nm检测下限的方法的可行性。此外,纳米粒子的溶液的颜色从无色到淡黄色,由于复合物的形成,其次是由碘离子的氧化。这种“关闭”的光学传感器被发现是高度敏感的,并没有干扰,从所有测试的阴离子。到目前为止,我们所知道的,这是由znsnps描述负离子具有高度特异性识别的第一个报告。这里报道的实验结果开辟了一个创新的方法,快速和可靠的识别碘。由于其巨大的实际潜力的双通道检测的碘在实际样品中,这种成本效益的传感系统可以开发在一个基于带的套件系统的现场分析。

We have developed a simple, rapid, and cost-effective fluorescent turn off nanosensor, by polyvinylpyrrolidone capped ZnS nanoparticles for the selective and sensitive detection of iodide ions in high briny solution, edible salt and other real samples. PVP capped ZnS nanoparticles has been prepared by simple green chemical synthesis using Zn-acetate di-hydrate, sodium sulphide and polyvinylpyrrolidone (PVP) at room temperature in aqueous solution. PVP modified ZnS nanoparticles were approximately 29 nm in diameter with intense, narrow fluorescence properties and long term stability than uncapped ZnSNps. The PVP-ZnSNps provide a highly sensitive method for the determination of iodide via significant FL intensity quenching. The optimum pH range for iodide determination is 5 to 10. Under optimal conditions, the relative FL intensity decreases linearly with increasing iodide concentration in the range 2Ã- 10-9 to 1Ã-10-7 M with a detection limit of 3.4 Ã- 10-9 M. No other ions excluding iodide can induce a considerable FL quenching. The quenching mechanism can be demonstrated by the “heavy atom” effect for the quenching of PVP-ZnSNps FL intensity; this mechanism induced the oxidation of quencher ion (iodide ion). This method is simple and relatively free from interference of closely associated ions and is successfully applied to the determination of iodide in real samples.

1. INTRODUCTION

The design and construction of efficient anion sensors is an emerging research area because they play a major role in biological systems and play a crucial role in industrial and environmental processes [1]. Some micro and macro molecules have been described as selective anion-responsive receptors for sensing of sulphides [2], fluoride [3-4] nitrates [5], and cyanide [6]. However, most of these molecules involve complex synthetic procedures; have poor water solubility or weak photo-stability which makes the process of anion sensing rather complicated [7-8].

Most of these complexities can be surpassed by using metal nanoparticles as sensing agents. Their synthetic procedures are simple as well as straightforward and they have fascinating semiconducting, piezoelectric, and pyroelectric properties making them smart and sensitive sensors [9-10]. Among these semiconductor metal nanoparticles have gained considerable attention due to their size dependent physical and optical properties. Additionally, these nanoparticles have high surface area and show fast electron communication features [11-12]. The detection and determination of anions by these nanosensors is usually done by spectroscopic or electrochemical techniques [13-15]. In the various spectroscopic methods for detection, fluorescence seems to be the most promising due to its high sensitivity, quick response and facile quantification of signal.

Of the various semiconductor nanoparticles, zinc sulphide (ZnS) nanoparticles are the least toxic and are characterized with a wide band gap at room temperature, high index of refraction and high transmittance in the visible range [16]. Due to these properties ZnS nanoparticles have been widely used as an important phosphor for photoluminescence, electroluminescence and cathodoluminescence [17-19]. They can be easily synthesized in an aqueous medium and are less expensive than any other semiconductor nanoparticles with good photocatalytic properties. Hence they have been extensively used as nanosensors for a range of ions and biomolecules [20-21]. Furthermore, the key properties such as optical stability and aqueous solubility of these nanoparticles can be tuned by the surface modification with organic ligands [22-24]. The presence of such ligands on the surface generates new traps, facilitating an enhancement in the selectivity and efficiency of optical reactions occurring on the surface of nanoparticles. For example, sodium thioglycolate capped ZnS nanoparticles have been used as a sensor for human serum albumin (protine) [22], L-carnitine modified ZnS nanoparticles functions as a selective optical probe of mercury ion [23] and thiolactic acid capped ZnS nanoparticles have been used as sensors for silver ions [24].

One of the most frequently used organic capping agents for metal nanoparticles is poly (N-vinyl-2-pyrrolidone) (PVP). This water-soluble polymer covers nanoparticle surface via physical and chemical bonding; hence restricts particle-particle contact and prevents agglomeration of nanoparticles. It has been extensively used as a protecting agent against agglomeration of metal colloids in the well-known polyol process [25-26]. Recently PVP has been reported as a capping agent with ZnS nanoparticles for detection of cholesterol [27].

Iodine, as we know, is a crucial trace element on earth and mainly exists in seawater; elemental iodine is used as a chemical reagent in some organic chemical synthesis, in medicine etc; it also plays essential roles in neurological activity and thyroid gland function [28-29]. In fact, the world health organization (WHO) has stated that the biggest cause for mental retardation on a global scale is due to iodine deficiency. Altered levels of iodide stimulate various diseases, such as cretinism, congenital abnormalities and goiter [30]. The daily intake of iodine for human nutrition should be controlled above certain limits; hence the need to determine iodine in the body, foodstuffs and drinks is very important. In previous literature, several methods has been reported for the detection and determination of iodide in trace levels; such as gas chromatography in combination with mass spectrometry, ion chromatography, chemiluminescence, potentiometry, colourimetry ,optical and redox method etc [1,31-35]. Many of these methods are frequently used although these approaches are time consuming, laborious, expensive and less sensitive. Thus, it is crucial to develop simple, sensitive and rapid analytical sensor for the estimation of iodide in different samples in trace level.

In the present work we sought to combine the interesting optical properties of ZnS nanoparticles with the complexing ability of PVP for the detection of iodide ions. Here, we have synthesized PVP capped ZnS nanoparticles and used them for the detection of iodide ions. PVP was specifically chosen as the capping agent because of its well known complexing ability with electron acceptors such as iodide [36]. It was expected that the complexed iodide on the surface will interact more efficiently with the ZnS nanoparticles. The improved interaction may cause sufficient changes in the optical properties of the nanoparticles facilititating detection.

发表评论

电子邮件地址不会被公开。 必填项已用*标注