Elsevier

Forensic Science International

Volume 259, February 2016, Pages 101-105
Forensic Science International

Application of CdSe quantum dots for the direct detection of TNT

https://doi.org/10.1016/j.forsciint.2015.12.028Get rights and content

Highlights

  • Oleic acid and oleyl amine wrapped CdSe quantum dots were synthesized.

  • A novel method for determination TNT has been investigated.

  • The fluorescence of CdSe quantum dots can be regularly quenched with addition of TNT.

  • Proposed method for sensing TNT was sensitive and selective.

  • Established method has been successfully performed determination of TNT in real samples.

Abstract

CdSe quantum dots were synthesized through a simple, green organic-phase method. Paraffin was used as the reaction solvent and a reducing agent, oleic acid was the reaction ligand, and oleyl amine was the stabilizer. Based on the phenomenon of TNT quenched oil-soluble CdSe quantum dot fluorescence, a simple, fast, and direct method of TNT detection was established. Under optimum conditions, the degree of fluorescence quenching of oil-soluble CdSe quantum dots had a good linear correlation with TNT concentration in the 1.0 × 10−7–5.0 × 10−5 mol/L range, and the correlation coefficient was 0.9990. TNT detection limit was 2.1 × 10−8 mol/L. The method was successfully used to determine TNT-explosion dust samples, results were satisfactory. The fluorescence quenching mechanism of oil-soluble CdSe quantum dots by TNT was also discussed.

Introduction

As a dangerous explosive, 2,4,6-trinitrotoluene (TNT) is frequently involved in issues of public safety and contributed to environmental pollution because of its high toxicity. TNT can exist in the air, water, soil and oil [1], [2]. TNT is known for its toxicity, mutagenicity, and carcinogenicity, which make it harmful to human beings, aquatic life, and terrestrial creatures. Therefore, the development of a highly sensitive, highly selective, and real-time analytical method for monitoring TNT is essential for social stability, human health, and environmental safety.

A variety of different detection methods have been widely used to assay TNT in the past ten years, including gas chromatography [3], [4], high-performance liquid chromatography [5], [6], mass spectrometry [7], [8], cyclic voltammetry [9], [10], ion mobility spectrometry [11], [12], and surface-enhanced Raman spectroscopy [13], [14]. These methods are all effective but require complicated instruments and tedious operation procedures. The methods were also difficult to apply during on-site analysis in case of emergency. Therefore, the establishment of a simple and efficient method for the determination of TNT is desired in modern analytical testing research.

Over the past decade, the preparation of nanomaterials, especially the research on semiconductor nanomaterials, has achieved rapid development. The synthetic method has been perfected. In combination with high-sensitivity fluorescence analysis, nanomaterials have led to new opportunities to address the difficulties in TNT detection.

Quantum dots (QDs) have been developing very rapidly in recent years; these QDs are composed of II–IV group elements and are a three-dimensional limited inorganic semiconductor nanocrystals [15], [16]. Compared with conventional organic fluorescent dyes, QDs have several unique fluorescent properties, such as the wide and continuous fluorescence excitation spectra, narrow and symmetric fluorescence emission spectra, high fluorescence quantum yield, strong resistance to photobleaching, and strong fluorescence stability; their fluorescence emission wavelength also varies with size and is adjustable [17], [18], [19]. These superior properties of fluorescent QDs account for their widespread use in fluorescence sensors [20], [21], [22], [23], [24]. QDs have been reported as fluorescent probes for TNT determination [25], [26], [27], [28], [29], [30]. Yang et al. [27] reported polyacrylamide (PAM)-capped CdTe(S) QDs as fluorescent quenching probes for sensitive and selective TNT detection. Their group illustrated that the quenching may be attributed to the resonance energy transfer via the formation of a PAM–TNT complex between amide groups and TNT. Ban and coworkers [28] have used amine-functionalized silicon QDs (SiQDs) as recognition probes for the detection of TNT. The quenching processes were attributed to the strong interactions within the TNT–amine SiQDs complexes. Such a fluorescence quenching response could be explained by fluorescence resonance energy transfer. To reveal the mechanism of TNT determination by amine-capped QDs, the structures and optical properties of the products of TNT after reacting with cysteine were studied by Lou et al. [29] via density functional theory calculations. Their theory showed that the key to the success of TNT detection is to control the particle size of QDs and adjust the emission wavelength of QDs to overlap with absorption bands of amine–TNT complexes. To reinforce the sensitivity of a QD-based sensor, a nanocomposite of luminescent europium organic framework (EuOF) and CdSe QDs has been developed for the determination of TNT [30]. The fluorescence signal of the EuOF/QDs quenching process is based the influence of core electron–hole recombination when TNT was intercalated into hydrophobic layers around the CdSe cores. Compared with the traditional instrument analysis, the proposed method based QD detection is low cost, time saving, easy to operate, and without complicated sample pretreatment and mathematical treatment.

The above mentioned methods for the QD detection of TNT have good selectivity and sensitivity. However, some of the synthesis procedures are time-consuming. Compared with the traditional methods, the method developed in the present work has the following advantages: Oleic acid, oleyl amine, and paraffin were used as solvents, which are all low-cost, environment friendly, and stable; these materials also did not require the absence of oxygen in the synthesis system. Compared with the aqueous phase process for QD synthesis, the QDs prepared in the green organic phase in the present study have a high fluorescence intensity, stability, and quantum yield, thereby guaranteeing TNT detection with higher sensitivity and stability. The proposed method also avoids the tedious process of modification. Moreover, the synthesized QDs have a high boiling point and flexible long alkane chains, which can improve the QD stability and effectively prevent the release of heavy metal ions from the QD core center. Appropriate surface modifications can also enhance the capture of TNT and improve the detection sensitivity. Consequently, the oil-soluble CdSe QDs were directly used for analysis and detection of TNT in a process that was more stable, effective, sensitive, selective, versatile, and simplified than the existing analytical procedures. This work is based on particular optical properties of CdSe QDs combined with the high sensitivity of these QDs to the quenching effect of TNT. Thus, a simple, fast, sensitive, and selective method is established for TNT detection based oil-soluble CdSe QDs, and the quantitative analysis of the real samples is realized. The relevant mechanism involved in the testing process was studied to expand the universality of the approach.

Section snippets

Apparatus

Fluorescence spectra were obtained with a LS-55 luminescence spectrometer (Perkin-Elmer, USA). The absorption spectra were recorded with an UV-2550 spectrometer (Shimadzu China Corporation). Two different cuvettes of 1 cm path length were used to measure the fluorescence spectra and absorption spectra, respectively. All optical measurements were performed at room temperature under ambient conditions. Transmission electron microscopy (TEM) with a Philips EM420 microscope was used to characterize

Characterization of CdSe QDs

The UV–vis absorption spectra and fluorescence spectra of the synthesized oil soluble CdSe QDs are shown in Fig. 1. The absorption spectra of oil soluble CdSe QDs followed a continuous distribution in the wavelength range of 450–700 nm, with a very obvious exciton absorption peak at 578 nm, thereby indicating that the particle size distribution of CdSe QDs was very uniform [32]. According to the position of the QD exciton absorption peak [33], the calculated average particle size of the CdSe QDs

Conclusions

This research proposed a novel method for TNT detection based on the TNT-quenched fluorescence intensity of CdSe QDs. The proposed method is simple, fast, and accurate. Under the optimized experimental conditions, the degree of quenched fluorescence of CdSe QDs presented a good linear relationship with the TNT concentration in the range of 1.0 × 10−7–5.0 × 10−5 mol/L. The correlation coefficient was 0.9990 and the detection limit was 2.1 × 10−8 mol/L. In the study, a 2.0 × 10−6 mol/L TNT standard solution

Acknowledgments

In this study, the author gratefully acknowledge the financial supports of the Faculty Research Grant from National Natural Science Foundation of China (No. 20875011), Ministry of public security of key technology research project (No. 2014JSYJA025), Ministry of public security of application innovation projects (No.2012YYCXXJXY130), and Innovation Subject of National Police University of China Undergraduates (No. 201210175033).

References (33)

  • R. Kaur et al.

    Nanocomposite of europium organic framework and quantum dots for highly sensitive chemosensing of trinitrotoluene

    Forensic Sci. Int.

    (2014)
  • Q. Xiao et al.

    Systematically investigation of interactions between BSA and different charge-capped CdSe/ZnS quantum dots

    J. Photochem. Photobiol. A

    (2012)
  • L.C. Shriver-Lake et al.

    On-site detection of TNT with a portable fiber optic biosensor

    Environ. Sci. Technol.

    (1997)
  • T.H. Kim et al.

    Selective and sensitive TNT sensors using biomimetic polydiacetylene-coated CNT-FETs

    ACS Nano

    (2011)
  • K. Farhadi et al.

    Gas chromatographic detection of some nitro explosive compounds in soil samples after solid-phase microextraction with carbon ceramic copper nanoparticle fibers

    J. Sep. Sci.

    (2014)
  • G.W. Cook et al.

    Using gas chromatography with ion mobility spectrometry to resolve explosive compounds in the presence of interferents

    J. Forensic Sci.

    (2010)
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