| The detection of nitro-explosives is a current priority due to global security concerns. This Ph.D. project aims at developing novel electronic and optical (fluorescent) sensors for fast, sensitive, selective, reliable and cost-effective detection of nitro-explosives, with major effort focusing on the direct sensing routes.;Electronic resistor-type sensing materials were first investigated for detecting NO2, which could be applied as indirect methods in downstream analysis of fragmentation products from nitro-explosives. Started with core-sheath TiO2-PEDOT nanocables, their well-defined 3D nanostructure and enhanced sensing performance was discussed. In order to explore molecular interaction for the rational design of sensing devices, single walled carbon nanotubes (SWNTs) were noncovalently functionalized with corrole molecules through π-π interactions. The formed donor-acceptor (D-A) heterojunction provided an excellent sensing platform for gaseous NO2.;On the other hand, fluorescent sensing materials respond to nitro-explosives directly and hold much promise as effective sensing platforms for explosives detection in field. Early research focused on the vapor phase nitro-explosives detection based on a highly emissive nanofibrous membrane, which was fabricated via electrospinning pyrene with polystyrene and an organic salt. The potential π-π stacking of pyrene and phenyl units may form a "sandwich-like" binding with electron-deficient nitro-explosives, resulting in an amplified response (e.g. 90% quenching by DNT within 6 min). Its applications for ultrasensitive detecting nitro-explosives vapors, solid residues on handprint and buried explosives are demonstrated using naked eye and a handheld UV light. Further enhancement in sensitivity and dynamic detection range were achieved by novel pyrene/amine hybrid polymers. The formation of Meisenheimer complex between amine and nitroaromatic explosives could result in a highly efficient FRET based quenching, thus achieving superior sensitivity. These results reveal that the effective nitro-explosive sensing platforms could be built by rational designs to bring in well-defined 3D structures and tunable electronic/photonic properties. The methodologies discussed in this dissertation can be extended to the design and synthesis of other sensing materials for a broad range of applications beyond nitro-explosives. |
