Surface‐enhanced Raman spectroscopy, Raman, and density functional theoretical analyses of fentanyl and six analogs

Abstract

We examined fentanyl and its six analogs using wB97XD/cc‐pVTZ density functional theoretical (DFT) calculations as well as Raman and Surface‐enhanced Raman spectroscopy (SERS). The in silico DFT calculations provided the vibrational frequencies, Raman activities, and normal mode assignment for each analog. Raman spectroscopy can detect crystalline fentanyl analogs but cannot obtain bands for samples in solution. Therefore, we utilized gold/silver nanospheres and gold/silver nanostars to examine them. The gold/silver nanostars provided stronger signals for the fentanyl analogs, and their SERS spectra can easily distinguish these fentanyl analogs from nonfentanyl opioids and other common drugs of abuse using principle component analysis and other statistical tests. Overall, our results demonstrate that SERS shows great potential to distinguish fentanyl analogs and detect trace quantities of these compounds in mixtures of seized drugs.

A Semi‐quantitative method for the detection of fentanyl using surface‐enhanced Raman scattering (SERS) with a handheld Raman instrument

“…The highest intensity peak was a doublet centered at approximately 1000 cm −1 , along with the smaller peak at approximately 1026 cm −1 (Figure 1). These correspond to C-C-C trigonal bends and aromatic C-C stretches in the aromatic ring respectively and correlate well with previous experiments (Table 3) [ 26,27]. The second peak at 1026 cm −1 was used for diagnostic and data integration purposes because the peak at 1000 cm −1 contained contributions from both normal Raman and the "SERS enhancement"…”

“…Fentanyl samples were measured using the SERS process, across a range of concentrations (Table 2). The observed spectra were similar across all the concentrations with respect to peak positions and relative intensities [27]. The highest intensity peak was a doublet centered at approximately 1000 cm −1 , along with the smaller peak at approximately 1026 cm −1 (Figure 1).…”

“…Samples above this concentration have already been shown to be easily detectable [30]. The relative standard deviations (RSD) for the peak area values across the three replicates was 5 to 30%, which is within an acceptable range for samples of this type [26,27,31], although it is probably less accurate than laboratory‐based instruments. In addition, solution‐based SERS is known to suffer from poor reproducibility, especially in comparison to more commonly used quantitative methods (e.g., GC‐MS) [7–10,13,14].…”

“…Significant work using SERS has been performed across a range of applications, including biological imaging and labeling, water impurity testing, explosive residue identification, and detection of chemical warfare agents (e.g., sarin, VX, and decomposition products) [23][24][25]. More recently, analysis and identification of fentanyl, carfentanyl, and six other analogues have been achieved [17,26,27].…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XIV

“…Their study demonstrates that SRS imaging can be used as a novel fast molecular mapping technique for pharmaceutical tablet characterization. Wang et al [ 177 ] combined SERS, Raman, and DFT analyses to identify fentanyl and six of its analogs. Their results demonstrate that SERS shows great potential to distinguish fentanyl analogs and detect trace quantities of these compounds in mixtures of seized drugs.…”