Detection and identification of medically important alkaloids using the surface-enhanced Raman scattering spectroscopy

Surface-Enhanced Raman Spectroscopy Combined with Multivariate Analysis for Fingerprinting Clinically Similar Fibromyalgia and Long COVID Syndromes

Fibromyalgia (FM) is a chronic central sensitivity syndrome characterized by augmented pain processing at diffuse body sites and presents as a multimorbid clinical condition. Long COVID (LC) is a heterogenous clinical syndrome that affects 10-20% of individuals following COVID-19 infection. FM and LC share similarities with regard to the pain and other clinical symptoms experienced, thereby posing a challenge for accurate diagnosis. This research explores the feasibility of using surface-enhanced Raman spectroscopy (SERS) combined with soft independent modelling of class analogies (SIMCAs) to develop classification models differentiating LC and FM. Venous blood samples were collected using two supports, dried bloodspot cards (DBS, n = 48 FM and n = 46 LC) and volumetric absorptive micro-sampling tips (VAMS, n = 39 FM and n = 39 LC). A semi-permeable membrane (10 kDa) was used to extract low molecular fraction (LMF) from the blood samples, and Raman spectra were acquired using SERS with gold nanoparticles (AuNPs). Soft independent modelling of class analogy (SIMCA) models developed with spectral data of blood samples collected in VAMS tips showed superior performance with a validation performance of 100% accuracy, sensitivity, and specificity, achieving an excellent classification accuracy of 0.86 area under the curve (AUC). Amide groups, aromatic and acidic amino acids were responsible for the discrimination patterns among FM and LC syndromes, emphasizing the findings from our previous studies. Overall, our results demonstrate the ability of AuNP SERS to identify unique metabolites that can be potentially used as spectral biomarkers to differentiate FM and LC.

Unveiling the Crucial Role of Chemical Enhancement in the SERS Analysis of Amphetamine-Metal Interactions on Gold and Silver Surfaces: Importance of Selective Amplification of the Narrow Interval of Vibrational Modes

The use of addictive substances, including drugs, poses significant health risks and contributes to various social problems, such as increased crime rates associated with substance-induced aggressive behavior. To address these challenges, possession of addictive substances is legally prohibited. However, detecting and analyzing these substances remain a complex task for law enforcement, primarily due to the presence of adulterants or limited sample quantities. In response to the evolving illicit market, continuous development and adaptation of analytical techniques are essential. One approach is the utilization of surface-enhanced Raman scattering (SERS) spectroscopy, which involves adsorbing the analyte onto nanostructured plasmonic surfaces. This study explores the potential of SERS in detecting amphetamine-based addictive stimulants with a specific focus on the properties of enhancing surfaces chosen. Comparative investigations were performed using silver and gold surfaces, with gold colloidal systems demonstrating a favorable performance. Moreover, to provide a comprehensive interpretation of the measured spectra, extensive density functional theory (DFT) calculations were conducted, allowing for a deeper understanding of the observed spectral features and molecular interactions with the metal surfaces. This review presents insights into the role of chemical enhancement in SERS analysis of amphetamine-metal interactions, shedding light on the selective amplification of vibrational modes. These findings, supported by DFT calculations, have implications in the fields of spectroscopy, physical chemistry, and drug analysis, providing valuable contributions to forensic applications and a deeper understanding of chemical enhancement phenomena. We present the impact of the secondary resonances of Stokes-scattered photons. This illustrates the significance of recognizing the constraints of the frequently employed "E4" approximation, even in measurements involving multiple molecules rather than single molecules.

Immobilization of green-synthesized silver nanoparticles for micro- and nano-spectroscopic applications: What is the role of used short amino- and thio-linkers and immobilization procedure on the SERS spectra?

Immobilization of nanoparticles (NPs) is a technique suitable for the preparation of large-scale substrates for surface-enhanced vibrational spectroscopy including micro- and nano-spectroscopic applications. The developed immobilization method provides the enhancing properties of the roughened substrate surface to be maintained for techniques like surface-enhanced Raman scattering (SERS) spectroscopy, however, at the same time the morphology is not limiting for related near-field (scanning probe) techniques. The study is focused on the comparison of different immobilization procedures of Ag nanoparticles and finding the relationship between preparation procedures leading to convenient surface morphology and the quality of the observed signal of the model analyte (riboflavin) using SERS. Amino-linker (3-aminopropyl)trimethoxysilane (APTMS) and four thio-linkers (cysteine, 3-mercaptopropanoic acid, 2-mercaptoethanol, and 2,2'-oxydiethanthiol) using five immobilization procedures at three different temperatures (23 °C, 40 °C, and 70 °C) were compared. Surface morphology was monitored by scanning electron microscopy and atomic force microscopy. The SERS spectra of riboflavin were evaluated in terms of the intensity and the resolution of individual bands. The spectral dataset was inspected by multivariate statistical methods - principal component analysis and discriminant analysis. The evaluation of spectra and statistical models show the influence of the used linker and AgNPs immobilization procedure on the spectral output. APTMS linker is less suitable; much more appropriate are thio-linkers deposited on an evaporated Au layer on a glass slide. The best spectral parameters were obtained for 2,2'-oxydiethanthiol and 23 °C.

Electrochemical Voltammogram Recording for Identifying Varieties of Ornamental Plants

An electrochemical voltammogram recording method for plant variety identification is proposed. Electrochemical voltammograms of Vistula, Andromeda, Danuta, Armandii 'Apple Blossom,' Proteus, Hagley Hybrid, Violet Elizabeth, Kiri Te Kanawa, Regina, and Veronica's Choice were recorded using leaf extracts with two solvents under buffer solutions. The voltametric data recorded under different conditions were derived as scatter plots, 2D density patterns, and hot maps for variety identification. In addition, the voltametric data were further used for genetic relationship studies. The dendrogram deduced from the voltammograms was used as evidence for relationship study. The dendrogram deduced from voltametric data suggested the Andromeda, Danuta, Proteus, Regina, and Hagley Hybrid were closely related, while Violet Elizabeth and Veronica's Choice were closely related. In addition, Vistula and Armandii 'Apple Blossom' could be considered outliers among the varieties.

Fabrication of large scale uniform copper-island thin film for ultrasensitive surface enhanced Raman scattering

Nanostructured metals with designable and controllable structures have received increasing attention in surface enhanced Raman scattering (SERS) due to the single molecular detection limit. Great challenges still remain in creating large scale substrates with high-density 'hotspots' to provide a uniform and stable enhancement of Raman signals. Here, we fabricated a copper island thin film over an 80 cm² scale substrate with tunable particle sizes by combining sputtering with dealloying processes. The island size can be tailored from 150 nm to 370 nm by controlling parameters and etching conditions and possesses an optimized surface morphology structure. The detection limit of crystal violet (CV) molecules reached 0.1 pM. Meanwhile, the copper island thin film presents good homogeneity and stability. Our method is promising to repeatedly fabricate novel metal SERS substrates on a large scale with standard properties for sensing applications.

Vibrational spectroscopic study of selected alkaloids with therapeutic effects

Nowadays, scientists from various fields of chemistry, biochemistry or biology are interested in trace detection of different natural or synthetic substances such as alkaloids which can either positively or negatively affect human physical and mental health. Linked with that, growing interest in broad applications of advanced vibrational spectroscopic techniques encourage higher demands in this rapidly developing field. This study is focused on a detailed description of infrared and Raman spectra of two natural alkaloids (namely galantamine and buprenorphine) and study of their optical response in the vicinity of gold and silver nanostructured surface. The interpretation of individual bands was supported by DFT calculations. Both alkaloids were also studied using surface-enhanced Raman scattering technique aiming at a comparison with non-enhanced vibrational data construction of concentration-dependent series and determination of their limit of detection. From SERS spectral series the regression models were developed to predict alkaloids concentration in the range of 10^-3-10^-7 mol/l, in the case of buprenorphine adsorbed on Ag substrate we were able to broaden this range down to 10^-9 mol/l.

Direct detection of melamine in infant formula milk powder solution based on SERS effect of silver film over nanospheres

A direct and sensitive method to detect melamine in infant formula milk powder solution based on the SERS effect of silver film over nanospheres (AgFON) was developed. AgFON was prepared by vacuum magnetron sputtering and dip-coating methods. The surface morphology and roughness were characterized by using scanning electron microscope and atomic force microscope. AgFON was used as a substrate to detect the SERS spectra of melamine in infant formula milk powder solution directly without any pretreatments. Semi-quantitative analyses of melamine with various concentrations in milk powder solution were carried out. A good linearity with correlation coefficient of 0.9926 between peak intensity and concentration was obtained from 2 to 25 mg/L. Furthermore, the as-prepared AgFON substrate had good uniformity with relative standard deviation value of 5.56% collected from ten randomly selected positions. The electric field distribution of AgFON was simulated by finite difference time domain solution, which revealed that the huge enhancement of Raman signals was ascribed to the high-density hot spots of the substrate.