Journal of Raman Spectroscopy最新文献

Vibrational spectroscopy combined with machine learning has a great potential for forensic applications. For example, handheld Raman spectroscopic instruments are already used by law enforcement agencies for precise, confirmatory identification of drugs. Beyond drug identification, several emerging technologies based on vibrational spectroscopy are currently under development for forensic investigative purposes, including the analysis of questioned documents, gunshot residue, fabrics, soil, hair, nails, and nail polish. This article provides a comprehensive overview of the application of vibrational spectroscopy in various areas of forensic analysis, particularly focusing on forensic serology and the analysis of trace evidences. In the case of forensic serology, the methodology allows for determining complex aspects of serological casework, including the time since deposition of a stain, as well as the phenotypic profile of the stain donor—namely, sex, race, and age. Furthermore, gunshot residues can be accurately identified by grain, caliber, and manufacturer when Raman spectroscopy is paired with machine learning. This integration of advanced spectroscopic techniques with machine learning holds great promise for furthering both the accuracy and efficiency of investigations, helping to reduce the total backlog of evidence investigation currently plaguing modern forensic laboratories.

This study aimed to characterize ammonium nitrate lattice vibrations in an ammonium nitrate and fuel oil mixture (ANFO) following authentic explosive events using confocal Raman microscopy and single-crystal X-ray diffraction (XRD). Two simulated IEDs were constructed and detonated, consisting of several different substrate materials, using ANFO as the main charge. Crystalline material was observed to be growing on several of the postblast substrates. Microscopical examination revealed the crystalline material to have isotropic and anisotropic characteristics. Following recrystallization from water, the material was identified as ammonium nitrate. Single-crystal X-ray diffraction enabled the identification of the unit cells and molecular structures of the crystals formed after the blast. The values corresponded to the known Phase IV structure of recrystallized ammonium nitrate; however, there were minor yet statistically significant variations in the distances in the unit cell dimensions and O–N–O angles. Ex situ analysis of isotropic crystalline fragment using confocal Raman microscopy determined that lattice vibrations within the material were different than the ANFO intact reference, with the blue shifting of several bands, the emergence of new bands, and the loss of other characteristic bands. It was determined that the isotropic crystalline material observed in the postblast residue consisted of stressed state Phase IV AN. This suggests that a thermal change of AN can be observed in the microscopical characteristics and Raman spectrum of the crystals, demonstrating the importance of low frequency Raman spectroscopy (10–250 cm⁻¹), which allows the identification of distinct spectral features of crystalline salts.

Surface enhanced Raman scattering (SERS) is a widely used vibrational spectroscopic technique employing metallic nanostructures to enhance an inherent Raman signal. This study aimed to develop a method for the characterization of SERS substrates in a single analysis by inductively coupled plasma mass spectrometry (ICP-MS) equipped with the single particle module (spICP-MS). For this development, the well-known Lee-Meisel protocol was selected as starting point to synthesize gold nanoparticles (AuNps) and silver nanoparticles (AgNps). A spICP-MS method was successfully developed and gave the mean size, size distribution, and concentration of nanoparticles in only one single analysis. Reference techniques were used to confirm these results namely dynamic light scattering, transmission electron microscopy, and UV–Visible spectroscopy. Thanks to the ICP-MS characterization, it was observed that AgNps synthesized by chemical reduction presented more variability than the AuNps. The dissolved elements concentration in the suspension was investigated. It appeared that reaction yields were close to 100% for the six syntheses. This analysis may be repeated over time to evaluate the suspension stability and monitor any potential degradation of Nps. To conclude, ICP-MS is a powerful technique to characterize SERS substrates and could be an interesting alternative to other characterization techniques.

Understanding the effects of particle size is necessary for quantifying minerals in mixtures using Raman spectroscopy. Raman signal intensity is evaluated using six common silicate minerals (two olivines, two pyroxenes, and two feldspars) at 10 particle size ranges. For olivines and feldspars, the highest peak intensities are observed in samples with 38–63 and 63–106 μm particle sizes. There is no such consistent trend for the pyroxene samples, although the overall low signal strength complicates those measurements. Raman spectra of samples with varying particle sizes appear to be influenced by two competing effects: scattering from particle boundaries and effective sampling volume.

Understanding the variation of proton concentration near the surface of the electrochemical interface is of great significance for understanding the mechanism of electrochemical reactions. In this work, 4-Mpy molecules that are protonated and deprotonated depending on the surrounding pH value adsorb on the Au nanoparticle film electrode with high SERS activity, and by virtue of the highly interfacial-sensitive EC-SERS technique, we systematically studied the effects of electrolyte pH value and external voltage on the protonation and deprotonation of 4-Mpy at the interface between Au-NP film electrode and phosphate buffer, to analyze the changes of near-surface proton concentration at the electrochemical interface. It is found that the pH value of the electrolyte plays a decisive role in the protonation process of 4-Mpy at the electrode interface at low reduction voltage (< −0.1 V). In acidic and neutral solution, 4-Mpy exists mainly in protonated form on the electrode surface. However, in alkaline solutions, 4-Mpy exists mainly on the electrode surface in the form of deprotonation. At high reduction voltage (≥ −0.1 V), the protonation and deprotonation of 4-Mpy on the electrode surface are mainly determined by the adsorption structure of 4-Mpy on the electrode surface. At the same time, we conducted a comparative study of 2-Mpy and 4-Mpy molecules and found that the adsorption modes were different depending on the position of the N atom. 2-Mpy is inclined adsorbed on the surface of the Au-NP film electrode, and 4-Mpy is vertically adsorbed on the surface of the Au-NP film electrode.

Raman spectra of KAl(SO₄)₂·12H₂O and KAl(SO₄)₂·12D₂O crystals in the range of 10–4000 cm⁻¹ were experimentally obtained and studied. An increase in the number of sulfate ions, oriented by oxygen atoms towards the K⁺ ion, was detected upon deuteration of the sample. Low-intensity Stokes components ν = 2485 cm⁻¹ (ν = 1820 cm⁻¹ for the deuterated crystal) were recorded, which indicates the formation of hydrogen bonds O–H•••SO₄²⁻ (O–D•••SO₄²⁻), where the donors are water molecules of the [Al(H₂O)₆]³⁺ complex and the oxygen atoms of the sulfate ion act as acceptors. The decrease in the wavenumbers of internal vibrations of the sulfate ion during deuteration was explained by an increase in the strength of hydrogen bonds. The results obtained indicate the direct influence of deuteration on the degree of initial disordering of sulfate ions and on the stability of the crystal structure of potassium alum.