Development of electrochemical gas sensor for early detection of volatile peroxo explosives

The majority of terrorist attacks in the past two decades were carried out using highly explosive organic peroxo compounds, e.g. triacetone triperoxide (TATP), 1,4,7-trimethyl-1,4,7-triethyl-1,4,7-cyclononatriperoxane (TBTP) hexamethylene triperoxide diamine (HMTD), tetramethylene diperoxide dicarbamide (TMDD), etc. These explosives have also been extensively used in improvised explosive devices (IEDs) in recent war zones and still pose a threat since they are very easily made from common household chemicals (with directions easily found on the internet) and as non-nitro explosives, they are very difficult to detect using standard analytical techniques. In the past few years, several detection techniques have been proposed for tackling this threat. They are based on HPLC-MS, GC-MS, IR and Raman spectroscopy, luminescence, chemiresistivity and electrochemical methods (in solutions). These approaches offer excellent sensitivity and selectivity, however, the analyses have to be performed in a specialised laboratory and therefore sampling and analysis take a long time and cannot be performed on-site. In addition, expensive instrumentation and qualified personnel are required. Moreover, organic peroxides have a high affinity to sublimate and are therefore not convenient to be transferred from a site to a laboratory and thus on-site detection is of vital importance. On the other hand, electrochemistry and especially electrochemical gas sensors offer an excellent platform for direct, fast, sensitive and on-site measurements of various electroactive species. Besides, recent electronic and sensor miniaturization offers very small-size device assemblies. The present project will facilitate the development of fast, portable, sensitive and reliable early warning gas sensors for detecting traces (< 50 nM) of peroxo explosives on-site. The project will address several important issues regarding explosive detection: i) development of gel electrolytes providing good solubility of gaseous explosives allowing their accumulation thus improving sensitivity. Direct detection of explosive molecules or if necessary facilitating their hydrolysis leading to the formation of H2O2, which can be easily detected on the electrode surface at ambient conditions; ii) investigation of the suitable electrode materials for sensitive detection of peroxides via electrocatalytic redox processes; iii) assuring portability of sensors by the study of miniaturisation by connectivity with laptops, tablets or smartphones. Based on experience gathered in previous projects focused on detecting gases, we can expect that the proposed investigation will deliver new gas sensors for homemade explosives and important new knowledge in the fields of on-site detection and electrochemical gas sensors in general. Any discovery along this direction will be publishable in the highest-ranking journals in the field and may lead to successful commercialization. In a broader sense, the project results will be of importance for enhancing security. Both project partners (the Department of Materials Chemistry at the National Institute of Chemistry (NIC)) and the Laboratory for Analytical Chemistry and Industrial Analysis at the Faculty of Chemistry and Chemical Engineering, University of Maribor (FKKT UM)) have a long-term experience in the field of the proposed investigation. While the main focus of the NIC group will be developing and testing gas sensors, the FKKT UM group will be focused on elemental analysis of electrocatalytic electrode modifications, including stability and mechanistic studies of electrochemical processes using impedance spectroscopy. The methodologies used by both partners will be to a large extent complementary.