Identification of illicit street drugs with swept‐source Raman spectroscopy

Abstract

The identification of the illicit substances in low‐purity seized drugs with Raman spectroscopy is an outstanding problem. The low concentration of the target molecule demands high sensitivity and the presence of impurities produces a strong fluorescence background that makes identification challenging. Although Raman analyzers with 785 and 830 nm excitation wavelengths provide high sensitivity, the longer 1064 nm wavelength produces lower fluorescence. In this work, we demonstrate a Raman spectrometer that simultaneously achieves both high sensitivity and low background fluorescence. We utilize swept‐source Raman spectroscopy in which the spectrometer is replaced by a single high‐collection spectral channel, and the Raman spectrum is swept using a tunable laser. By eliminating the spectrometer and its slit, the optical throughput and sensitivity are improved. Moreover, our swept‐source system requires a single uncooled silicon photodiode that provides higher quantum efficiency at longer wavelengths compared with CCDs. This allowed us to use excitation wavelengths in the 900 nm range to reduce background fluorescence without sacrificing sensitivity. We have demonstrated 6x background fluorescence reduction in colored seized drugs compared with 830 nm excitation. With lower background fluorescence and high sensitivity, we could identify heroin with only 1% purity in a seized sample. Besides forensics and security, the demonstrated swept‐source Raman spectroscopy approach can be a powerful technique in biomedical applications where strong background fluorescence limits detection capabilities.

Performance assessment of portable Raman spectroscopy in determining ecstasy tablets

“…7,9 The presence of fluorescent dye or unknown excipients even at trace levels in ecstasy tablets, can cause fluorescence that then mask the Raman signals. 9,29 Specific dyes such as black and yellow dyes in ecstasy tablets gave absorbance signals in the 1300-2600 nm NIR range and partly obscure the spectral signal from MDMA. 30 Previous studies have reported that samples with black or dark colours caused difficulty for positive detection in Raman spectroscopy.…”

Innovative Vibrational Spectroscopy Research for Forensic Application

“…Kay et al addressed the same issue with a new technique known as Swept Source Raman Spectroscopy (SSRS). 242 In this approach, there is a single collection channel while the excitation laser is tunable.…”

“…When compared to the 785 nm laser, positive identification increased almost 5-fold for both the 1064 nm laser and SSE. Kay et al addressed the same issue with a new technique known as Swept Source Raman Spectroscopy (SSRS) . In this approach, there is a single collection channel while the excitation laser is tunable.…”

Wavelength-swept spontaneous Raman spectroscopy system improves fiber-based collection efficiency for whole brain tissue classification

“…CARS can also be done with a wavelength-swept source to improve the acquisition speed, spectral resolution, and collection efficiency, as we demonstrated in a prior work 17 . More recently, spontaneous Raman spectroscopy has been performed using a low power wavelength-swept source to increase the photon collection and reduce the noise around 2× 18 , 19 . Replacing the fixed laser in Raman spectroscopy with a swept-source can be advantageous, 20 and using a wide-area detector enables enhanced signal collection, supporting remote spectrum acquisition for various applications, such as water quality monitoring and indoor farm plant growth tracking 21 .…”

“… 17 More recently, spontaneous Raman spectroscopy has been performed using a low power wavelength-swept source to increase the photon collection and reduce the noise around 2×. 18 , 19 Replacing the fixed laser in Raman spectroscopy with a swept-source can be advantageous, 20 and using a wide-area detector enables enhanced signal collection, supporting remote spectrum acquisition for various applications, such as water quality monitoring and indoor farm plant growth tracking. 21 In addition, replacing the spectrometers with a detector facilitates the development of handheld and miniaturized Raman spectroscopy setups, and it yields the same spectrum as using a conventional Raman spectrometer.…”