Instant detection and identification of concealed explosive-related compounds: Induced Stokes Raman versus infrared

Novel molecular laser-induced photoluminscence signature with hyperspectral imaging for instant and remote detection of trace explosive materials

Instant detection of explosive material is highly appreciated for counterterrorism activity and homeland security. Nitro group (high energy rich bond) is responsible for explosive characteristics. Nitro group includes intense competition between two highly electronegative atoms. Nitro group is frequently encountered in all explosive materials. This function group includes delocalized π bond; that could secure intense photoluminescence (fluorescence and phosphorescence) signature. In this study, the main classes of explosive materials including nitro-compounds (i.e. TNT), nitramines (i.e. RDX), and nitric esters (i.e. PETN) were stimulated with green laser source of 532 nm and 5 mW power. The photoluminescence signature of each tested material was captured via hyperspectral camera. The tested explosives demonstrated characteristic fluorescence signature at 571, 587, and 613 nm for RDX, PETN, and TNT respectively. Furthermore, TNT demonstrated characteristic phosphorescence signature at 975 nm. The customized laser induced photoluminescence technique offered facile detection of trace explosive material via clustering approach based on K-m clustering (k = 8); this technique was able to detect RDX, PETN and TNT traces on the finger nail via processed hyperspectral images at 581 nm, 797 nm and 953 nm, respectively. This study shaded the light on novel customized photoluminescence technique for facile detection and identification of trace explosive materials.

Non-invasive caries detection and delineation via novel laser-induced fluorescence with hyperspectral imaging

Carious is a global chronic disease; 2 billion people and 520 million children suffer from permanent and primary teeth caries respectively. Early caries detection via precise, non-invasive, non-ionizing radiation is highly appreciated. Carious deteriorate the chemical structure of sound tooth tissues, with variation in its optical properties. In this study, customized laser-induced fluorescence system consists of non-ionizing laser light source and hyperspectral camera was developed for early caries detection. Tested tooth sample was illuminated with laser source of 385 nm and 5 mW power. The emitted spectrum signature for main tooth elements including enamel, dentin, stain, and caries were captured. Logarithmic scale of spectrum signature was applied in an attempt to enhance system sensitivity to fluorescent signal. Fluorescence signature at 500 nm secured the maximum fluorescence intensity difference for different tooth elements. Consequently 2D hyperspectral image at 500 nm was constructed. Enhanced 2D image was accomplished via nonlinear filter to enhance contrast. Segmentation via K mean clustering was adopted for precise caries delineation. This narrative, facile, non-invasive, non-ionizing technique experienced precise and accurate delineation of different caries stages (normal, moderate, and severe).

Interpol review of detection and characterization of explosives and explosives residues 2016-2019

This review paper covers the forensic-relevant literature for the analysis and detection of explosives and explosives residues from 2016-2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/Resources/Documents#Publications.

Identification of inorganic oxidizing salts in homemade explosives using Fourier transform infrared spectroscopy

Recently, inorganic low explosives, such as pyrotechnic composition, black powder, and ammonium nitrate, are commonly used in improvised explosive devices (IEDs) by the rioter or terrorists since these energetic materials can be obtained easily and legally from civilian markets. Identification of inorganic oxidizing salts in these homemade explosives, including nitrates, chlorates, and perchlorates, is a necessary procedure for forensic investigators to provide criminal evidences. In this article, Fourier transform infrared (FTIR) spectroscopy was used to discriminate NO₃^-, CO₃^2-, ClO₃^-, ClO₄^-, SO₄^2-, and NH₄⁺, whose characteristic absorption bands were explained by vibration modes of the covalent bonds. Then the spectral absorption features of nitrate salts with monovalent or divalent cations were discussed. Furthermore, it was studied whether nitrates or perchlorates can be unequivocally distinguished with the presence of carbonate and sulfate impurities through FTIR technique. Finally, the feasibility of this method was verified through an analytical case of homemade explosives.

Real time recognition of explosophorous group and explosive material using laser induced photoacoustic spectroscopy associated with novel algorithm for time and frequency domain analysis

Energy-rich bonds such as nitrates (NO₃^-) and percholorates (ClO₄^-) have an explosive nature; they are frequently encountered in high energy materials. These bonds encompass two highly electronegative atoms competing for electrons. Common explosive materials including urea nitrate, ammonium nitrate, and ammonium percholorates were subjected to photoacoustic spectroscopy. The captured signal was processed using novel digital algorithm designed for time and frequency domain analysis. Frequency domain analysis offered not only characteristic frequencies for NO₃^- and ClO₄^- groups; but also characteristic fingerprint spectra (based on thermal, acoustical, and optical properties) for different materials. The main outcome of this study is that phase-shift domain analysis offered an outstanding signature for each explosive material, with novel discrimination between explosive and similar non-explosive material. Photoacoustic spectroscopy offered different characteristic signatures that can be employed for real time detection with stand-off capabilities. There is no two materials could have the same optical, thermal, and acoustical properties.

Design and implementation of novel hyperspectral imaging for dental carious early detection using laser induced fluorescence

Early detection of carious is vital for demineralization reversal, offering less pain, as well as precise carious removal. In this study, the difference in optical properties of normal tissue and human carious lesion has been used for early diagnosis, using laser induced fluorescence spectroscopy. The optical system consists of light source in visible band and hyperspectral camera, associated with designed digital image processing algorithm. The human tooth sample was illuminated with visible band sources at 488, and 514 nm with energy of 5 m watt. The reflected and emitted light from the tested sample was captured using hyperspectral camera in an attempt to generate multispectral images (cubic image). The variation of reflected and emitted energy as function of wavelength was employed to generate characteristic spectrum of each tooth tissue. Human teeth carious tissue lesion releases its excess energy by emitting fluorescence light producing chemical footprint signature; this signature is dependent on the elemental composition of tooth elements and carious state. This non-invasive, non-contact and non-ionizing imaging system with associated novel pattern recognition algorithm was employed to diagnose and classify different carious types and stages. It was reported that the perceived fluorescence emission is function of the illuminating wavelength. While enamel and dentin carious were distinguished and characterized at 514 nm illuminating wavelength; white spot lesion were contoured and recognized at 488 nm. Therefore, full recognition could be achieved through generated cubic image after sample irradiation at 488 nm and 514 nm. In conclusion, this study reports on a customized optical image system that can offer high sensitivity, high resolution, and early carious detection with optimum performance at 514 nm and 488 nm.