Abstract
Surface-enhanced Raman spectroscopy (SERS) measurements of some common military explosives were performed with a table-top micro-Raman system integrated with a Serstech R785 miniaturized device, comprising a spectrometer and detector for near-infrared (NIR) laser excitation (785 nm). R785 was tested as the main component of a miniaturized SERS detector, designed for in situ and stand-alone sensing of molecules released at low concentrations, as could happen in the case of traces of explosives found in an illegal bomb factory, where solid microparticles of explosives could be released in the air and then collected on the sensor’s surface, if placed near the factory, as a consequence of bomb preparation. SERS spectra were obtained, exciting samples in picogram quantities on specific substrates, starting from standard commercial solutions. The main vibrational features of each substance were clearly identified also in low quantities. The amount of the sampled substance was determined through the analysis of scanning electron microscope images, while the spectral resolution and the detector sensitivity were sufficiently high to clearly distinguish spectra belonging to different samples with an exposure time of 10 s. A principal component analysis procedure was applied to the experimental data to understand which are the main factors affecting spectra variation across different samples. The score plots for the first three principal components show that the examined explosive materials can be clearly classified on the basis of their SERS spectra.
Highlights
The struggle against international terrorism has become a crucial task for the safety of citizens.An important aspect of this task is the development of sensitive, low-cost and compact technologies able to reveal ultra-low quantities of explosives, which nowadays is still a difficult challenge
Among the available detection technologies, Raman spectroscopy [1] has recently gained increasing interest in forensic science [2] and it has been already applied for the analysis of illicit drugs or medications [3,4,5] as well as for the characterization of different types of excipients [6,7] and for the detection of explosives [8,9,10]
Because the Raman band frequencies relate to the chemical bonding in the compound to be identified, the technique offers the distinct advantage of chemical specificity and benefits from the ability to generate valid reference Raman spectra under laboratory conditions, comparable with spectra obtained in the field
Summary
An important aspect of this task is the development of sensitive, low-cost and compact technologies able to reveal ultra-low quantities of explosives (pictograms or less), which nowadays is still a difficult challenge. Challenges 2016, 7, 14 drawback of Raman spectroscopy is the low cross-section [1] of the spontaneous Raman scattering, which affects the detection of substances at the trace level. In 1974 it was discovered that the magnitude of the Raman signal can be greatly enhanced when the scatterer is placed on a roughened noble-metal substrate [11], a process that is nowadays known as surface-enhanced Raman spectroscopy (SERS) [12,13]
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