SERS of nitro group compounds for sensing of explosives.

Detecting small concentrations of nitro-compounds surface-enhanced Raman spectroscopy (SERS) is reported. In particular, explosive analogues, such as 4-nitrophenol, 1-nitronaphthalene, and 5-nitroisoquinoline, and an explosive material (picric acid) are investigated and prepared by measurements using two different methods. One method involved mixing the analyte with plasmonic silver nanoparticles (Ag NPs) in a solution, followed by subsequent drop-casting of the mixture onto a silicon substrate. In the second method, the analyte solution was drop-casted onto SERS substrates formed by annealing of thin Ag films deposited over self-assembled layers of SiO spheres. Both approaches allowed for the SERS detection of analyte concentrations down to 10-10 M. Furthermore, the possible reasons for the different enhancements of the above analytes as well as their differences in the liquid (drop) and dried states are discussed.