Fluorescence quenching of CdSe quantum dots by nitroaromatic explosives and their relative compounds

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Abstract

CdSe quantum dots (QDs) were synthesized in oleic acid and octadecene medium under high-temperature and dispersed in chloroform. Nitroaromatic explosives and their relative compounds, 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), nitrobenzene (NB), 2,4-dinitrochlorobenzene (DNBCl) and p-nitrotoluene (NT) can obviously cause the fluorescence quenching of the synthesized QDs. Under the optimum conditions, a nonlinear response was observed over the concentration range of 10−8 to 10−5 M for them all. The modified Stern–Volmer quenching equations of ln I0/I versus C show a good linear relation in 10−5 M order of magnitude, and the detection limits approach 10−6 to 10−7 M.

Introduction

With the surge of terrorism and the increased use of modern bombs in terrorist attacks, the detection of hidden explosives as well as unrecovered land mines has become an important but difficult international problem. The development of new devices capable of rapidly and cost-efficiently detecting explosives has become an urgent worldwide necessity [1]. Various physical methods such as gas chromatography coupled with a mass spectrometer, nuclear quadrupole resonance, energy-dispersive X-ray diffraction as well as electron capture detection have been used for this purpose [2], [3], [4], [5]. These techniques are highly selective, but some of them are expensive and others are difficult to be fielded in a small, low-power package. Over the past several years, chemical sensors based on absorption, fluorescence and conductivity transduction mechanisms have attracted much attention in the rapid detection of explosives because they can be easily incorporated into inexpensive and portable microelectronic devices. In this respect, the fluorescence-based sensor schemes are very promising [6], [7], [8], [9], [10].

Quantum dots (QDs), a brand new class of fluorescent nanoprobes, are advantageous over fluorescent dyes because of their tunable emission color, high quantum yield and long-term photostability. Moreover, the emission of QDs is narrow, symmetric, and independent of the excitation wavelength [11], [12]. Due to their unique properties, QDs have found increased uses in a variety of practical biological applications [13], [14], [15], [16]. As novel luminescent probes, QDs have also attracted considerable attention for the development of sensitive and selective fluorescence sensors in recent years [17], [18]. The studies revealed that the interactions between some substances and the surface of QDs would change their physical properties. Thus, expanding applications of QDs to develop sensitive and simple sensors for the detection of different analytes is a topic of current interest [19], [20], [21], [22], [23], [24]. Also the potential applications of QDs in the detection of nitroaromatic explosives based on directive fluorescence quenching of QDs [25], [26] or fluorescence resonance energy transfer [27] have been paid to attention.

Herein, we report that fluorescence of oleic acid covered CdSe QDs could be efficiently quenched by nitroaromatic analytes, which might provide a new pathway to detection of the nitroaromatic explosives and their relative compounds.

Section snippets

Reagents

Cadmium oxide (CdO, 99.99%), selenium (Se, power, 100 mesh, 99.99%), trioctylphosphine (TOP, 90%), oleic acid (OLE, 90%) and octadecene (ODE, 90%) were all purchased from Aldrich (Milwaukee, WI, USA). Chloroform was purchased from Beijing Reagent Factory. The p-nitrotoluene (NT), 2,4-dinitrochloro benzene (DNBCl), nitrobenzene(NB) was purchased from Shanghai Reagent Factory. DNT was purchased from The British Drug Houses Ltd. and used as received. TNT was obtained from the PSB of Shanxi and

TEM images of CdSe QDs

Fig. 1A and B shows TEM image of the synthesized CdSe QDs with the excitonic absorption peak at 587 nm. As seen in Fig. 1A, the size distribution of QDs was nearly monodisperse with the average size of 4 nm. Absorption and photoluminescence measurements in chloroform solutions of QDs confirmed their quantum-confined nature and considerable quantum yield (Fig. 1B). Taken together, these data confirm the successful preparation of high-quality QDs.

Selection of the QDs concentration

The fluorescence intensity of CdSe QDs solution,

Conclusions

In conclusion, the nitroaromatic explosives or their relative compounds caused the fluorescence quenching of CdSe QDs. Recently the detect limit reported were general 10−6 to 10−7 mol l−1 [35], [36], [37], [38]. The most sensitive method may detect 10−12 mol l−1 TNT [39], [40]. Here we demonstrated the potential application of luminescent QDs to develop new fluorescence sensors for the detection of explosives. The synthesized CdSe QDs show large fluorescence quenching effects with exposives, making

Acknowledgements

We gratefully acknowledge the financial support from NSFC (Nos. 20475035 and 20239486), The Liuxue Guiguo Foundation of Shanxi Province and the Ministry of Education CFKSTIP (705010).

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