Explosive colorimetric discrimination using a smartphone, paper device and chemometrical approach

In this report we introduce a novel approach for an inexpensive and disposable colorimetric paper sensor array for the detection and discrimination of five explosives - triacetone triperoxide (TATP), hexamethylene triperoxide diamine (HMTD), 4-amino-2-nitrophenol (4A2NP), nitrobenzene (NB), and picric acid (PA). The colorimetric sensor comprised a disposable paper array fabricated using a wax printer and three reagents (KI, creatinine, and aniline) that produced a unique color pattern for each explosive based on chemical interactions between the explosive species and the chemical reagents. The analytes were discriminated from one another as per the color change profiles, which were readily distinguishable after 15 min, using hierarchical clustering analysis (HCA) and principal component analysis (PCA); there were no misclassifications in any of the trials conducted. The colorimetric pattern values were extracted using a smartphone, custom-made software and a closed chamber to circumvent the illumination problems commonly found in other paper approach devices. A semi-quantitative analysis was performed and it was possible to use as low as 0.2 mu g of explosives.