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Raman spectroscopy is a potent and widespread optical analytical technique thanks to its non-invasive and high-specification for the detection of targeted molecules. However, for the case of trace detection, it is common that a weak Raman signal is easily swamped by noise and thus unable to be resolved. Here, we demonstrated a facile fabrication of a three-dimensional surface enhanced Raman spectroscopy (SERS) substrate, based on low-vacuum sputtering of gold nanofilm on hierarchically rough fumed silica monolayers deposited by layer-by-layer self-assembly technique. Due to the much lower surface energy of the silica-air heterostructure compared to metallic materials, deposited gold layers dewetted the surface spontaneously, forming nano-sized spherical gold particles without the requirement of an extra annealing process. Plasmonic effects were studied through optical absorption measurements, while the surface morphology and topography were examined using SEM and AFM for various sputtering durations. Furthermore, the enhancement of Raman spectrum was investigated for 10−4 M of methylene blue (MB), using 532 nm and 0.57 mW excitation laser. An initial Raman enhancement factor of 17 was observed at 1645 cm−1 peak, even with yet to be optimized fabrication procedures.

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Near real-time detection and identification of explosives from safe distances remains a challenging defense technology that requires both scientific and engineering perspectives in the design and development. Here, we demonstrated a cost-effective standoff Raman system for detecting explosive materials from distances up to 30 m. The optical system consists of an 8-inch Schmidt–Cassegrain telescope for Raman scattering light collection, while a compact grism was used to generate Raman spectrogram. An image intensifier from night vision technology was incorporated for amplifying the extremely weak Raman spectrum to a level detectable by a thermoelectric-cooled CMOS camera. A nanosecond pulsed laser at 440 nm with peak power of 0.41 MW was used as an excitation source, and the standoff Raman measurement was performed for test samples, including Ba(NO3)2, BaSO4 and NaNO3 powders. The spectral resolution and signal-to-noise ratio performance of the system were evaluated for the samples placed at distances of 10, 20 and 30 m. It was found that the standoff Raman system can resolve such Raman spectra, showing clear characteristic peaks of Ba(NO3)2, BaSO4 and NaNO3 at 1,045.9, 986.4 and 1,066.5 cm−1, respectively. These spectrum results agree well with the Raman spectra obtained from a standard close-range Raman system.