{"id":2794,"date":"2011-07-19T15:06:26","date_gmt":"2011-07-19T15:06:26","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/?p=2794"},"modified":"2011-07-19T15:06:26","modified_gmt":"2011-07-19T15:06:26","slug":"nano-line-fracture-sensor-for-explosive-detection","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/nano-line-fracture-sensor-for-explosive-detection\/","title":{"rendered":"Nano Line Fracture Sensor for Explosive Detection"},"content":{"rendered":"

Selective detection of explosive compounds is critical for national defense and homeland security. Nitroaromatic compounds pose a particular threat; 2,4,6-trinitrotoluene (TNT), for example, is an inexpensive and readily available component of fifteen of the most widely used blends [1<\/a>] <\/sup>. Existing methods to detect explosives include biosensors [2<\/a>] <\/sup>, electrochemical sensors\u00a0 [3<\/a>] <\/sup> and fiber optic [4<\/a>] <\/sup> sensors. Devices utilizing chromatography [5<\/a>] <\/sup> and Raman spectroscopy [6<\/a>] <\/sup> are used for the same purpose. However, sensors using the aforementioned techniques require complicated sensing and readout components; moreover, they are comparatively large in size and consume significant amounts of power during operation. In this work we describe the fabrication and demonstration of a chemical sensor capable of detecting nitroaromatic explosives in air. The aim of this work is the development of a simple sensor that has the unique features of micro-scale dimensions, simple and inexpensive fabrication, and low power consumption. It consists of a nano-patterned conductive metal line placed on top of a patterned responsive polymer, poly(4-vinylpyridine) (P4VP), as shown in Figure 1. Due to polymer-solvent interactions, P4VP swells when it encounters the target analyte, producing a large stress. Detection takes place by monitoring the change in device resistance as the metal nano line deforms or fractures when P4VP swells and transfers mechanical stress.<\/p>\n

Fabricated devices were tested for their response to nitroaromatic exposure using a previously described system((W. E Tenhaeff, L. D. McIntosh, and K. K. Gleason, \u201cSynthesis of poly(4-vinylpyridine) thin films by initiated chemical vapor deposition (iCVD) for selective nanotrench-based sensing of nitroaromatics,\u201d Adv<\/em>anced Functional Materials<\/em>, vol. 20, no. 7, pp. 1144-1151, 2010.)) [7<\/a>] <\/sup>. Test devices were located on a cooled stage within a flow cell; swelling responses of P4VP films were measured via in situ interferometry. Figure 2 illustrates the change in device resistance for a 200-nm-thick, 5-\u03bcm-wide P4VP line intersected by a 100-nm-thick, 300-nm-wide Au line sensor upon exposure to 500 ppm of nitrobenzene. The concentration was increased to 650 ppm at t=15mins. The change in resistance corresponds well to the calculated change in exposure concentration. A permanent increase (8.5%) in resistance is clearly observed as the result of permanent deformation and micro-cracks; this change is large enough to be easily detected.<\/p>\n\n\t\t