Using surface-enhanced Raman scattering for simultaneous multiplex detection and quantification of thiols associated to axillary malodour

Axillary malodour is caused by the microbial conversion of human-derived precursors to volatile organic compounds. Thiols strongly contribute to this odour but are hard to detect as they are present at low concentrations. Additionally, thiols are highly volatile and small making sampling and quantification difficult, including by gas chromatography-mass spectrometry. In this study, surface-enhanced Raman scattering (SERS), combined with chemometrics, was utilised to simultaneously quantify four malodourous thiols associated with axillary odour, both in individual and multiplex solutions. Univariate and multivariate methods of partial least squares regression (PLS-R) were used to calculate the limit of detection (LoD) and results compared. Both methods yielded comparable LoD values, with LoDs using PLS-R ranging from 0.0227 ppm to 0.0153 ppm for the thiols studied. These thiols were then examined and quantified simultaneously in 120 mixtures using PLS-R. The resultant models showed high linearity (Q2 values between 0.9712 and 0.9827 for both PLS-1 and PLS-2) and low values of root mean squared error of predictions (0.0359 ppm and 0.0459 ppm for PLS-1 and PLS-2, respectively). To test this approach further, these models were challenged with 15 new blind test samples, collected independently from the initial samples. This test demonstrated that SERS combined with PLS-R could be used to predict the unknown concentrations of these thiols in a mixture. These results display the ability of SERS for the simultaneous multiplex detection and quantification of analytes and its potential for future development for detecting gaseous thiols produced from skin and other body sites.

Trace Detection of Adulterants in Illicit Opioid Samples Using Surface-Enhanced Raman Scattering and Random Forest Classification

The detection of trace adulterants in opioid samples is an important aspect of drug checking, a harm reduction measure that is required as a result of the variability and unpredictability of the illicit drug supply. While many analytical methods are suitable for such analysis, community-based approaches require techniques that are amenable to point-of-care applications with minimal sample preparation and automated analysis. We demonstrate that surface-enhanced Raman spectroscopy (SERS), combined with a random forest classifier, is able to detect the presence of two common sedatives, bromazolam (0.32-36% w/w) and xylazine (0.15-15% w/w), found in street opioid samples collected as a part of a community drug checking service. The Raman predictions, benchmarked against mass spectrometry results, exhibited high specificity (88% for bromazolam, 96% for xylazine) and sensitivity (88% for bromazolam, 92% for xylazine) for the compounds of interest. We additionally provide evidence that this exceeds the performance of a more conventional approach using infrared spectral data acquired on the same samples. This demonstrates the feasibility of SERS for point-of-care analysis of challenging multicomponent samples containing trace adulterants.

Acute psychotropic, autonomic, and endocrine effects of 5,6-methylenedioxy-2-aminoindane (MDAI) compared with 3,4-methylenedioxymethamphetamine (MDMA) in human volunteers: A self-administration study

The acute psychoactive, autonomic, and endocrine effects of the new psychoactive substance (NPS) 5,6-methylenedioxy-2-aminoindane (MDAI; 3.0 mg/kg, range 180-228 mg) were investigated in six healthy volunteers (four males, two females) in a non-blinded fashion without placebo. Subjective, cardiovascular, and endocrine responses were compared with two different doses of 3,4-methylenedioxymethamphetamine (MDMA) (75 mg and 125 mg) described in previously published placebo-controlled studies, which used identical outcome measures including Visual Analogue Scales (VAS), the Adjective Mood Rating Scale (AMRS), and the 5 Dimensions of Altered States of Consciousness (5D-ASC) scale. MDAI was well tolerated and produced subjective effects comparable with those of 125 mg MDMA. MDAI increased blood pressure similar to 125 mg MDMA but did not increase heart rate or body temperature. MDAI increased cortisol and prolactin levels and could be detected in serum about 20 min post ingestion and remained detectable at least for 4 days. In urine, MDAI was detectable over a period of at least 6 days. Further clinical investigations are warranted to assess whether MDAI could serve as drug with medicinal properties.

Recent Advances in the Use of Surface-Enhanced Raman Scattering for Illicit Drug Detection

The rapid increase in illicit drug use and its adverse health effects and socio-economic consequences have reached alarming proportions in recent years. Surface-enhanced Raman scattering (SERS) has emerged as a highly sensitive analytical tool for the detection of low dosages of drugs in liquid and solid samples. In the present article, we review the state-of-the-art use of SERS for chemical analysis of illicit drugs in aqueous and complex biological samples, including saliva, urine, and blood. We also include a review of the types of SERS substrates used for this purpose, pointing out recent advancements in substrate fabrication towards quantitative and qualitative detection of illicit drugs. Finally, we conclude by providing our perspective on the field of SERS-based drug detection, including presently faced challenges. Overall, our review provides evidence of the strong potential of SERS to establish itself as both a laboratory and in situ analytical method for fast and sensitive drug detection and identification.

Rapid SERS Quantification of Trace Fentanyl Laced in Recreational Drugs with a Portable Raman Module

Rapid identification and quantification of opioid drugs are of significant importance and an urgent need in drug regulation and control, considering the serious social and economic impact of the opioid epidemic in the United States. Unfortunately, techniques for accurate detection of these opioids, particularly for fentanyl, an extremely potent synthetic drug of abuse and a main perpetrator in the opioid crisis, are often not readily accessible. Therefore, a fast, highly sensitive, and preferably quantitative technique, with excellent portability, is highly desirable. Such a technique can potentially offer timely and crucial information for drug control officials, as well as health professionals, about drug distribution and overdose prevention. We therefore propose a portable surface-enhanced Raman scattering (SERS) approach by pairing an easy to perform yet reliable SERS protocol with a compact Raman module suitable for rapid, on-site identification and quantification of trace fentanyl. Fentanyl spiked in urine control was successfully detected at concentrations as low as 5 ng/mL. Portable SERS also enabled detection of trace fentanyl laced in recreational drugs at mass concentrations as low as 0.05% (5 ng in 10 μg total) and 0.1% (10 ng in 10 μg total) in heroin and tetrahydrocannabinol (THC), respectively. Drug interaction with the nanoparticle surface was simulated through molecular dynamics to investigate the molecular adsorption mechanism and account for SERS signal differences observed for opioid drugs. Furthermore, resolution of fentanyl in binary and ternary opioid mixtures was readily achieved with multivariate data analysis. In sum, we developed a rapid, highly sensitive, and reliably quantitative method for trace fentanyl analysis by synergizing a streamlined SERS procedure and a portable Raman module at low cost.

Discrimination of phenethylamine regioisomers and structural analogues by Raman spectroscopy

In this study, the Raman spectra of 21 phenethylamines were obtained using far-red excitation (785 nm). The distinguishing ability of Raman for phenethylamines, especially for phenethylamine regioisomers and structural analogues, was investigated. Here, the evaluation of a cross section of Raman spectra demonstrated that all types of phenethylamines were distinguishable, even for certain structural analogues with high spectrum similarity. Raman exhibited high distinguishing ability for phenethylamine regioisomers that differ in the substitution position of halogen, methoxy, alkyl, or other substituted groups; as well as for structural analogues containing different groups, such as furanyl, 2,3-dihydrofuranyl, halogen, and alkyl substituted at the same position. The Raman spectra for homologues with differences in only a methyl group were found to be highly similar; however, their spectra demonstrated small but detectable differences. Four analogue mixtures and 59 seized samples were also analyzed to study the practical use of the Raman method in forensic field. 95% of the seized samples were correctly identified, which significantly validated the ability of Raman method in identifying the correct isomers. Accordingly, this study provides a non-destructive, high-throughput and minimal sample preparation technique for the discrimination of phenethylamines.

Preparation of the plasmonic Ag/AgBr/ZnO film substrate for reusable SERS detection: Implication to the Z-scheme photocatalytic mechanism

In this work, a novel Ag/AgBr/ZnO SERS substrate was prepared by calcinating spin-coated zinc acetate on glass slides in the presence of ethanolamine (EA), followed by the process of impregnating-precipitation-photoreduction treatment. The SERS performances of Ag/AgBr/ZnO substrates were evaluated using aqueous crystal violet (CV) and Rhodamine 6G (R6G) as target analytes. The effects of initial immersion precursor concentration and irradiation time on the SERS performance were systematically studied. The as-prepared SERS substrate exhibited good chemical detection sensitivity, reproducibility and reusability. The optimal Ag/AgBr/ZnO (10 mM-30 min) substrates were capable of detecting 10^-12 M CV and 10^-11 M R6G aqueous solutions. The quantitative detection by the SERS substrate was investigated by constructing a linear corresponding calibration plot. The Ag/AgBr/ZnO SERS substrate was regenerated by a simple visible light driven photocatalytic process. A plausible Z-scheme visible light photocatalytic mechanism seems to account for the Ag-ZnO-AgBr system. This SERS substrate can be separated from the reaction easily, and the results indicated that the film was reusable for eight times without significantly losing the SERS efficiency, each time accompanied by a simple photo-driven regeneration. This study reveals that the Ag/AgBr/ZnO film on glass is practically applicable as an ultra-highly sensitive SERS substrate that can be readily regenerated.

Rapid detection of synthetic cannabinoids in herbal highs using surface-enhanced Raman scattering produced by gold nanoparticle co-aggregation in a wet system

Synthetic cannabinoids (SCs) are a major category of new psychoactive substances that are frequently distributed after addition to plants. To date, various SCs with small differences in their chemical structures have prevailed in the illegal drug market. Thus, the development of a method for rapid detection with high discrimination capability is critically important for the forensic field. Vibrational spectroscopy is a possible analytical technique for this purpose because it can sensitively reflect differences among chemical structures. In this study, we applied surface-enhanced Raman scattering (SERS) with gold nanoparticle co-aggregation in a wet system to plant samples containing SCs. The experimental protocol used was simple and involved only mixing of the sample with several other solutions. It was possible to detect SERS spectra from various stock solutions of SCs by this method. The method was then applied to street samples containing SCs. Some of the plant samples containing SCs did not produce significant SERS signals even though stock solutions of the same SCs did produce SERS spectra. We investigated the reason for this discrepancy and speculated that the solubility in aqueous solutions was a factor determining whether a significant SERS signal could be detected or not. According to this hypothesis, minimal sample pre-treatment methods were applied. This allowed for the detection of SERS spectra from the examined plant samples. The developed approach is a powerful method for screening analysis of SCs in plant fragments.

Rapid Detection and Quantification of Novel Psychoactive Substances (NPS) Using Raman Spectroscopy and Surface-Enhanced Raman Scattering

With more than a million seizures of illegal drugs reported annually across Europe, the variety of psychoactive compounds available is vast and ever-growing. The multitude of risks associated with these compounds are well-known and can be life threatening. Hence the need for the development of new analytical techniques and approaches that allow for the rapid, sensitive, and specific quantitative detection and discrimination of such illicit materials, ultimately with portability for field testing, is of paramount importance. The aim of this study was to demonstrate the application of Raman spectroscopy and surface-enhanced Raman scattering (SERS) combined with chemometrics approaches, as rapid and portable techniques for the quantitative detection and discrimination of a wide range of novel psychoactive substances (methcathinone and aminoindane derivatives), both in powder form and in solution. The Raman spectra of the psychoactive compounds provided clear separation and classification of the compounds based on their core chemical structures; viz. methcathinones, aminoindanes, diphenidines, and synthetic cannabinoids. The SERS results also displayed similar clustering patterns, with improved limits of detections down to ~2 mM (0.41 g L⁻¹). As mephedrone is currently very popular for recreational use we performed multiplexed quantitative detection of mephedrone (4-methylmethcathinone), and its two major metabolites (nor-mephedrone and 4-methylephedrine), as tertiary mixtures in water and healthy human urine. These findings readily illustrate the potential application of SERS for simultaneous detection of multiple NPS as mixtures without the need for lengthy prior chromatographic separation or enrichment methods.

Rapid detection of hypnotics using surface-enhanced Raman scattering based on gold nanoparticle co-aggregation in a wet system

Sensitive detection of drugs using a method with high qualification capability is important for forensic drug analysis. Vibrational spectroscopy is a powerful screening technique because it can provide detailed structural information of the compounds included in samples with simple experimental protocols. Among various spectroscopic techniques, surface enhanced Raman scattering (SERS) spectroscopy has attracted enormous attention owing to its ultra-high sensitivity. In this study, we developed a method for rapid detection of hypnotics using SERS with gold nanoparticle co-aggregation in a wet system. The developed method required a simple analytical protocol. This enabled rapid analysis with high stability and repeatability. We analyzed various hypnotics (19 types including benzodiazepines and nonbenzodiazepines) to investigate the structure-spectrum relationship. As a proof of concept for application to real crime samples, simulated spiked beverages containing one hypnotic (etizolam, flunitrazepam, zolpidem, or zopiclone) were analyzed. Diluting the beverage samples decreased the matrix effect and allowed for detection of these hypnotics. Except for flunitrazepam, strong signals were observed for all hypnotics, and the estimated lower limit of detection was 50 ppm in apple drink. The developed approach is a rapid method for screening analysis of hypnotics with low sample requirements.

Review of SERS Substrates for Chemical Sensing

The SERS effect was initially discovered in the 1970s. Early research focused on understanding the phenomenon and increasing enhancement to achieve single molecule detection. From the mid-1980s to early 1990s, research started to move away from obtaining a fundamental understanding of the phenomenon to the exploration of analytical applications. At the same time, significant developments occurred in the field of photonics that led to the advent of inexpensive, robust, compact, field-deployable Raman systems. The 1990s also saw rapid development in nanoscience. This convergence of technologies (photonics and nanoscience) has led to accelerated development of SERS substrates to detect a wide range of chemical and biological analytes. It would be a monumental task to discuss all the different kinds of SERS substrates that have been explored. Likewise, it would be impossible to discuss the use of SERS for both chemical and biological detection. Instead, a review of the most common metallic (Ag, Cu, and Au) SERS substrates for chemical detection only is discussed, as well as SERS substrates that are commercially available. Other issues with SERS for chemical detection have been selectivity, reversibility, and reusability of the substrates. How these issues have been addressed is also discussed in this review.

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

In this study surface-enhanced Raman scattering (SERS) combined with the isotopic labelling (IL) principle has been used for the quantification of codeine spiked into both water and human plasma.

Au nanoparticle-based sensor for apomorphine detection in plasma

Artificially roughened gold surfaces with controlled nanostructure produced by pulsed laser deposition have been investigated as sensors for apomorphine detection aiming at clinical application. The use of such gold surfaces has been optimized using aqueous solutions of apomorphine in the concentration range between 3.3 × 10(-4) M and 3.3 × 10(-7) M. The experimental parameters have been investigated and the dynamic concentration range of the sensor has been assessed by the selection of two apomorphine surface enhanced Raman scattering (SERS) peaks. The sensor behavior used to detect apomorphine in unfiltered human blood plasma is presented and discussed.