Nanoporous Silica-Dye Microspheres for Enhanced Colorimetric Detection of Cyclohexanone

Forensic detection of non-volatile nitro explosives poses a tough analytical challenge. A colorimetric sensor comprising ultrasonically prepared silica-dye microspheres was developed for sensitive gas detection of cyclohexanone, a volatile marker of explosives 1,3,5-trinitro-1,3,5-triazinane (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX). The silica-dye composites were synthesized from the hydrolysis of ultrasonically sprayed organosiloxanes under mildly heating conditions (150 ^oC), which yields microspherical, nanoporous structures with high surface area (~300 m²/g) for gas exposure. The sensor inks were deposited on cellulose paper and gave sensitive colorimetric responses to trace amount of cyclohexanone vapors even at sub-ppm levels, with the detection limit down to ~150 ppb. The sensor showed high chemical specificity towards cyclohexanone against humidity and other classes of common solvents, including ethanol, acetonitrile, ether, ethyl acetate, and ammonia. Paper-based colorimetric sensors with hierarchical nanostructures could represent an alternative sensing materials for practical applications in the detection of explosives.