Raman Spots Hidden Danger

To airport security personnel, an opaque plastic bottle is a potential danger: Does it carry shampoo or explosives? Researchers in the Netherlands have now demonstrated that a Raman spectroscopy technique can detect and identify explosives hidden inside opaque plastic containers (Anal. Chem., DOI: 10.1021/ac2018102). Security personnel and emergency response teams often carry Raman-based handheld devices to quickly spot harmful materials in the field. But these devices struggle to collect spectra of chemicals concealed behind opaque plastic. Freek Ariese of Free University of Amsterdam and colleagues thought time-resolved Raman spectroscopy could peer past the plastic by closing the gate in front of the spectrometer’s detector for an instant after exciting a sample with a laser. With the gate closed, the researchers avoid signals from the plastic container. When the gate opens, the spectrometer collects photons from deep within the sample. Ariese’s team tested the method on a cuvette filled with dinitrotoluene, a by-product of TNT, located behind a variety of common white plastics up to 5 mm thick. Both the type of plastic and its thickness affected the optimum gating delay—between 300 and 500 picoseconds—but the researchers successfully detected the dinitrotoluene in each case.