Structures Of Sensing Element For Explosive Detector Based On Fluorescent Polymers

With the surge of international terrorism and the increased use of explosives in terrorist attacks, law enforcement agencies throughout the world are faced with the problem of detecting hidden bombs in luggage, mail, vehicles, and aircraft, as well as on suspects. This has become a major analytical problem, which requires highly sensitive, specific, and fast methods for its solution.Timothy M. Swager, Prof. of MIT, with his colleague demonstrated that pentiptycene-derived phenyleneethynylene fluorescent polymers are very sensitive to 2,4,6-trinitrotoluene (TNT). Further experiments show attenuated lasing in optically pumped the fluorescent polymers thin films displays a sensitivity to vapour of TNT more than 30 times higher than is observed from spontaneous emission. To achieve lasing action in the fluorescent polymers, a few of sensing element structures were fabricated.1. nanowire array and single nanowire structures. The nanowire array and single nanowire structures of sensing element for TNT detector were fabricated using TNT sensitive polymers such as PPE, TPA-PBPV and TPA-PPV with porous anodic aluminum (PAA) template. Nanowires range from 80 to 100 nm in diameter, and from 150 to 200 nm in length for the nanowire array. But for the single nanowire structure, the polymer nanowire is as long as a few micrometers.2. Spectrum characteristics of the nanowire array and single nanowire structures. Compared with that of spin-coated polymer films, the emission maxima of PPE,TPA-PBPV and TPA-PPV in nanowire array were blueshifted from 460 nm to 432 nm, from 485 to 455 nm and from 495 to 475 nm respectively. In addition, the emission maxima of TPA-PBPV and TPA-PPV in the single wire structure were blueshifted from 485 to 452 nm and from 495 to 467 nm respectively. The blueshifted emission suggests the polymer nanowire structure can prevent low energy emission trap. Therefore, it is a promising technique for further enhancing the TNT sensory performance.3. SU-8 multi-pipeline array structure. The SU-8 multi-pipeline array structures were fabricated employing MEMS technology preliminarily. The inner diameter of the pipeline is about 15μm and the space between pipelines is 30μm. This work offers a foundation for multi-pipeline array structure.