Optimization of Parameters for the Quantitative Surface-Enhanced Raman Scattering Detection of Mephedrone Using a Fractional Factorial Design and a Portable Raman Spectrometer

Abstract

A new optimization strategy for the SERS detection of mephedrone using a portable Raman system has been developed. A fractional factorial design was employed, and the number of statistically significant experiments (288) was greatly reduced from the actual total number of experiments (1722), which minimized the workload while maintaining the statistical integrity of the results. A number of conditions were explored in relation to mephedrone SERS signal optimization including the type of nanoparticle, pH, and aggregating agents (salts). Through exercising this design, it was possible to derive the significance of each of the individual variables, and we discovered four optimized SERS protocols for which the reproducibility of the SERS signal and the limit of detection (LOD) of mephedrone were established. Using traditional nanoparticles with a combination of salts and pHs, it was shown that the relative standard deviations of mephedrone-specific Raman peaks were as low as 0.51%, and the LOD was estimated to be around 1.6 μg/mL (9.06 × 10(-6) M), a detection limit well beyond the scope of conventional Raman and extremely low for an analytical method optimized for quick and uncomplicated in-field use.

Identification of new psychoactive substances (NPS) using handheld Raman spectroscopy employing both 785 and 1064 nm laser sources

“…[33] More recently, a number of studies have evaluated the use of Raman for NPS products. [32,[34][35][36][37][38] Maheux and Copland (2011) used a range of analytical techniques including Raman spectroscopy for the identification of cathinones in seized samples. [34] Studies also reported on the use of Raman spectroscopy to discriminate between cathinone regioisomers [35] and derivatives [32] using benchtop Raman instruments employing a laser excitation wavelength (λ ex ) of 785 nm.…”

“…[31,39,40] Goodacre and coworkers investigated the use of surface enhanced Raman spectroscopy (SERS) to enhance the Raman signal while also reducing interference due to fluorescence. [36,37] Although SERS is a viable approach for fluorescence reduction, careful and invasive sample preparation is often needed. An alternative approach which requires no sample preparation is the use of a longer λ ex (e.g., 1064 nm) which has been shown to improve identification of traditional drugs of abuse such as cocaine and amphetamine.…”

Quantitative detection of codeine in human plasma using surface-enhanced Raman scattering via adaptation of the isotopic labelling principle

“…The colloid was assessed using UV-visible spectroscopy and scanning electron microscopy (SEM) and was very similar to that used in previously pub-lished studies. 25,26,34,35 Instrumentation Initial experiments were carried out to generate conventional Raman spectra of powdered codeine and codeine-d6, which were placed on a calcium fluoride (CaF2) disc and Raman spectra were recorded using 633 nm excitation (see ESI † for more details of the conventional Raman measurements). SERS spectra were recorded using a DeltaNu Advantage portable Raman spectrometer (DeltaNu, Laramie, WY, USA), equipped with a 633 nm HeNe laser emitting ∼3 mW on to the sample.…”

“…20 -24 Several studies have reported the application of SERS for the successful detection, identification and quantification of illicit drugs. 25,26 Alharbi and colleagues also used this approach for the quantitative detection of the opioid tramadol in artificial urine. 27 Dong et al employed (dynamic) D-SERS and support vector machines for the quanti-tative detection of methamphetamine in human urine.…”

An overview of recent developments in the analytical detection of new psychoactive substances (NPSs)

“…48,49 Smith et al 50,51 provided an alternative to chromatography and proposed a novel sensing protocol based upon the electrochemical methods. 52,53 In this novel approach, the usually required thin metallic surface (typically gold or silver) was provided by galvanising a British two pence coin with silver. 50 Analysed in pH 4.3 acetate buffer, limits of detection were found to correspond to 11.80 μg mL −1 for 4-MMC and 11.60 μg mL −1 for 4-MEC.…”