With the increased use of explosives such as nitroaromatics in terrorist attacks the development of efficient, portable and low-cost explosion detection devices has become an urgent worldwide necessity. For 10 years, many studies have been performed on the detection of nitroaromatics compounds using chemical gas sensors as highly sensitive and selective detectors of various explosives [1,2].

A new promising material based on nanostructured high-porosity silica coating has been developed and tested regarding chemical sensing of nitroaromatics. The silica nanoparticles contained in the sensing coating are prepared in solution (so-called sol) using the ammonia-catalysed hydrolysis of tetraethylorthosilicate (TEOS) [3].

High- porosity values of the deposited films were evaluated using BET specific surface area measurement (450m2/g). The hydroxyl surface coverage of nano-sized silica particles can be adjusted depending on solvent selected for dispersion (water or ethanol) or by further exposition to catalytic vapour-curing (ammonia hardening or hydrophobic curing). The type of particle surface species coverage was highlighted to direct impact onto structural properties of the films and therefore onto detection performances.

Evaluation of the detection performances of silica-based coatings when used as sensitive coating for quartz crystal microbalance (QCM) sensors or as fluorescent sensor when grafted with a fluorescent molecule show remarkable results. Among the different silica coatings, we have selected a fluorescent film showing high sensibility (@0.1ppm and @1ppm), excellent reversibility (80% of fluorescent intensity), robustness, good selectivity regarding V.O.C interfering compounds (Volatil Organic Compounds).

Moreover, an hydrophilic silica thin film used as a detecting material shows a good sensibility whatever the operating humidity conditions (from 0 to 80%RH).

[1] M.la Grone, proceeding of SPIE conference, 3710,1999,409

[2] F. Thery-Merland, Proceeding of Eurosensors XVII,2003,550

[3] W.Stöber,A.Fink,and E.Bohn, J.colloid Interface Sci. 26 (1968)

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