Electrochemical Detection of Dinitrobenzene on Silicon Electrodes: Toward Explosives Sensors

Essam M Dief,Nadim Darwish,Natasha Hoffmann

doi:10.3390/surfaces5010015

Abstract

Detection of explosives is vital for protection and criminal investigations, and developing novel explosives’ sensors stands at the forefront of the analytical and forensic chemistry endeavors. Due to the presence of terminal nitro groups that can be electrochemically reduced, nitroaromatic compounds (NACs) have been an analytical target for explosives’ electrochemical sensors. Various electrode materials have been used to detect NACs in solution, including glassy carbon electrodes (GCE), platinum (Pt), and gold (Au) electrodes, by tracking the reversible oxidation/reduction properties of the NACs on these electrodes. Here, we show that the reduction of dinitrobenzene (DNB) on oxide-free silicon (Si–H) electrodes is irreversible with two reduction peaks that disappear within the successive voltammetric scanning. AFM imaging showed the formation of a polymeric film whose thickness scales up with the DNB concentration. This suggest that Si–H surfaces can serve as DNB sensors and possibly other explosive substances. Cyclic voltammetry (CV) measurements showed that the limit of detection (LoD) on Si–H is one order of magnitude lower than that obtained on GCE. In addition, EIS measurements showed that the LoD of DNB on Si–H is two orders of magnitude lower than the CV method. The fact that a Si–H surface can be used to track the presence of DNB makes it a suitable surface to be implemented as a sensing platform. To translate this concept into a sensor, however, it would require engineering and fabrication prospect to be compatible with the current semiconductor technologies.

Highlights

Detection of explosive substances and their resources using simple and versatile methods stands at the forefront for protection and criminal investigations
The reduction of the two nitro groups leads to the formation of dinitro radical anions (RA), dinitro diradical anions (DA) that reversibly convert back to DNB in aprotic solvent (Figure 1b), and the current increases linearly with the concentration of the analyte [38]
Irreversible redox chemical characteristics of DNB were previously observed when DNB derivatives are exposed to diphenyl urea, and this was attributed to a proton transfer process from the urea to the DA species of the DNB [40]

Summary

Introduction

Detection of explosive substances and their resources using simple and versatile methods stands at the forefront for protection and criminal investigations Analytical techniques, such as mass spectroscopy (MS), high performance liquid chromatography (HPLC), gas chromatography (GC), and UV-Vis absorption spectroscopy, have been used to detect nitroaromatic compounds (NACs) that are extensively used to detect NACs with ppm limits of detection [1–4]. MS and electrochemical methods are dominating the quantitative methods for detecting NACs. Recently, thermally unstable NACs including ethylene glycol dinitrate, nitroglycerin, and pentaerythritol tetranitrate were detected using MS with limits of detection (LoD) down to 0.1 μg mL−1 [11]. The sensor system was flexible and portable, the LoD was found to be ∼1.4, ∼8.4, and ∼249.5 μg mL−1 for TNT, DNB, and NB, respectively [13]

Methods

Results

Conclusion