Trace detection of explosives and their precursors by surface enhanced Raman spectroscopy

Surface Enhanced Raman Spectroscopy measurements on some common military explosives were performed with a table-top micro-Raman system integrated with a Serstech R785 minispectrometer. Serstech R785 is a miniaturised spectrometer suitable for Raman and NIR measurements. Integration of R785 in our table-top system aims to the realization of a portable SERS detector, able to perform in-situ measurements. SERS Spectra were obtained exciting the substance of interest with a 785 nm diode-laser, while these substances were deposited starting from commercial solutions on commercial SERS substrates, to improve the detection sensitivity. The amount of the sampled substance was determined through the analysis of images of the substrate covered with the residue of explosive. In fact, once the solvent is completely evaporated, the residue of explosive was observed to be uniformly distributed on the substrate surface. Images acquired with a Scanning Electron Microscope provided further details of the deposition process showing that a fraction of the active SERS sites are completely covered with the analyte while other sites appear to be empty; from the analysis of the images the sampled quantity was estimated to be about 200 pg. The main Raman features of each substance were clearly identified, the spectral resolution was sufficiently high to clearly distinguish spectra belonging to different substances.