Abstract
Our work deals with detection of the two most widely used taggants in explosives (2-nitrotoluene and 2,3-dimethyl-2,3-dinitrobutane) on metal/silver phthalocyanine chemiresistors, when the analyte vapors are activated by ultraviolet radiation (λ=266nm). As the first step, morphological and electrical properties of gold, palladium and silver non-continuous layers deposited on silver phthalocyanine (AgPc) have been studied. Experiments monitored by SEM confirmed formation of metal clusters on organic surface if subthreshold amount of metal is deposited onto the AgPc layer (i.e. layer of equivalent thickness of 4nm for Pd, 5nm for Au and 8nm for Ag) and thermal stabilization follows.We demonstrated that metallic non-continuous layers on AgPc can be used for effective adjustment of chemiresistor's electrical resistance. Resistance of all modified sensors in reference atmosphere (synthetic air) − R0 − was effectively shifted by one to four orders of magnitude to lower values, so that cheaper devices and set-ups can be used for resistance measurements. Moreover, measurements of responses of Me/AgPc chemiresistors to 1ppm of NO2 revealed that the presence of metal reduces the sensor response time (τ90). On basis of optimal R0 and τ90 values, Pd(1nm)/AgPc chemiresistor was selected to be the most prospective for detection of taggants.Finally, the taggants were detected on Pd (1nm)/AgPc chemiresistor in two modes: without- or with- photoactivation. While the dc-response (Sdc) to 190ppm of non-activated 2-nitrotoluene vapors was negligible, on photoactivation we reached the value of Sdc=5.8. This significant improvement, which is attributed to the formation of nitrogen dioxide during photoactivation of 2-nitrotoluene, and also negligible interaction of sensor with water vapor as the most common interferent make our method applicable for early detection of tagged explosives in real “field” conditions. The Pd(1nm)/AgPc sensors exhibited excellent recovery after detection of photoactivated 2-NT. The recovery was achieved by thermal regeneration steps (sensor temperature switches from 40 °C to 120°C and vice-versa)
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