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.

Nano-FTIR spectroscopy of surface confluent polydopamine films - What is the role of deposition time and substrate material?

Polydopamine (PDA) is a widely used anchoring layer for multiple purposes. While simple to prepare, PDA is characterized by high chemical and topological diversity, which can limit its versatility. Unraveling the formation mechanism and physicochemical properties of continuous confluent layer and adherent nanoparticles on the nanoscale is crucial to further extend the prospective applications of PDA. Utilizing nano-FTIR spectroscopy, we investigate layers of PDA on three different substrates (silicon/silicon dioxide, nitrogen-doped titanium oxide, and gold substrates) at varying times of deposition (ToD). We observed a good correlation between the nano-FTIR and macroscopic FTIR spectra that reflected the changes in the relative abundance of PDA and polymerization intermediates as ToD increased. To gain analytical power, we utilized the principal component analysis (PCA) and extracted additional information from the resulting loadings spectral curves and data distribution in the score plots. We revealed a higher variability of the spectra of ultrathin surface confluent layers compared to the adherent nanoparticles. While the spectra of nanoparticles showed no apparent dependency on either ToD or the substrate material, the spectra of layers were highly affected by the increasing ToD and exhibited a rise in the absorption of PDA. Concomitantly, the spectra of layers grouped according to the substrate material at the lowest ToD point to the fact that the substrate material affects the PDA's initial physicochemical structure. The observed separation gradually diminished with the increasing ToD as the PDA physicochemical structure became less influenced by the substrate material.

Laser-Induced Reactions of 4-Aminobenzenthiol Species Adsorbed on Ag, Au, and Cu Plasmonic Structures Followed by SERS Spectroscopy. The Role of Substrate and Excitation Energy - Surface-Complex Photochemistry and Plasmonic Catalysis.

This study focuses on investigating the laser-induced reactions of various surface complexes of 4-aminobenzenethiol on Ag, Au, and Cu surfaces. By utilizing different excitation wavelengths, the distinct behavior of the molecule species on the plasmonic substrates was observed. Density functional theory (DFT) calculations were employed to establish the significant role of chemical enhancement mechanisms in determining the observed behavior. The interaction between 4-aminobenzenethiol (4-ABT) molecules and plasmonic surfaces led to the formation of surface complexes with absorption bands red-shifted into the visible and near-infrared regions. Photochemical transformations were induced by excitation wavelengths from these regions, with the nature of the transformations varying based on the excitation wavelength and the plasmonic metal. Resonance with the electronic absorption transitions of these complexes amplifies surface-enhanced Raman scattering (SERS), enabling the detailed examination of ongoing processes. A kinetic study on the Ag surface revealed processes governed by both first- and second-order kinetics, attributed to the dimerization process and transformation processes of individual molecules interacting with photons or plasmons. The behavior of the molecules was found to be primarily determined by the position and variability of the band between 1170 and 1190 cm-1, with the former corresponding to molecules in the monomer state and the latter to dimerized molecules. Notably, laser-induced dimerization occurred most rapidly on the Cu surface, followed by Ag, and least on Au. These findings highlight the influence of plasmonic surfaces on molecular behavior and provide insights into the potential applications of laser-induced reactions for surface analysis and manipulation.

Chiral, Magnetic, and Photosensitive Liquid Crystalline Nanocomposites Based on Multifunctional Nanoparticles and Achiral Liquid Crystals.

Nanoparticles serving as a multifunctional and multiaddressable dopant to modify the properties of liquid crystalline matrices are developed by combining cobalt ferrite nanocrystals with organic ligands featuring a robust photosensitive unit and a source of chirality from the natural pool. These nanoparticles provide a stable nanocomposite when dispersed in achiral liquid crystals, giving rise to chiral supramolecular structures that can respond to UV-light illumination, and, at the same time, the formed nanocomposite possesses strong magnetic response. We report on a nanocomposite that shows three additional functionalities (chirality and responsiveness to UV light and magnetic field) upon the introduction of a single dopant into achiral liquid crystals.

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.

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.

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

Currently, trace detection of drugs, medicinal products, psychoactive substances, poisons and other natural or synthetic compounds in the human body has become one of the most important areas of interest in medicine, toxicology and forensic research. Due to the rapid development of nanotechnology, applications in forensic and biological sciences, food industry and art preservation there is an increasing interest in surface-enhanced Raman scattering (SERS) spectroscopy as a technique capable of low detection limits in the analysis of small amounts of studied analytes. In this study, different excitation wavelengths (785 nm and 1064 nm) were used to find the appropriate experimental conditions for the detection and identification of medically significant alkaloids - atropine and pergolide - by means of surface-enhanced Raman scattering spectroscopy. SERS spectra of selected alkaloids were measured in the concentration range 10-3-10-9 mol∙L-1 using large-scaled platinum substrates coated with electrochemically prepared gold or silver SERS-active layers. Identification was based on the assignment of surface-enhanced characteristic vibrational bands using theoretical (DFT) calculations and comparing them with normal (non-enhanced) Raman spectra of pure compounds. All sets of spectral data were subjected to multivariate statistical approach (partial least squares regression) aiming at prediction of alkaloids concentration in developed models and its comparison with experimental results.

Preparation of surfaces of composite samples for tip based micro-analyses using ion beam milling.

Ion beam milling, as a method of surface design for tip analytical techniques, was explored. A sample of clay, embedded in a resin, was treated by the ion beam and allowed AFM (a typical tip technique) to be successfully applied. The method is suitable for advanced tip analyses based on AFM, like TERS or SNOM, and for samples that are not possible to prepare by standard mechanical methods. The approach can be useful for characterisation of the surfaces of many different types of materials in versatile applications such as catalysis, corrosion science or advanced material characterisation.

The use of infrared spectroscopic techniques to characterize nanomaterials and nanostructures: A review.

Recent advances in nanotechnology have opened a lot of new possibilities for nanomaterials application in wide variety of industrial, pharmaceutical, medicinal and environmental applications. This review aims to description of various Fourier Transform Infrared (FTIR)-based spectroscopic techniques suitable to characterize (i) different types of nanomaterials and (ii) various macroscopic samples at their nanoscale. In the introductory section, nanomaterials are classified according to their crucial properties, i.e. chemical composition, size and surface morphology. Application of traditional FTIR techniques, such as Attenuated Total Reflection (ATR), Diffuse Reflection (DRIFT) and infrared micro (spectro)scopy, for characterization of nanomaterials and nanostructures is compared with novel optical nanoscopic techniques derived from scanning probe microscopy which enable to overcome the diffraction limit and to characterize nanomaterials at molecular scale.

Synthesis and Properties of Nanosized Stoichiometric Cobalt Ferrite Spinel.

Nanoparticles with controllable sizes of ferrite spinel CoFe2O4 were formed by thermal treatment of cobalt-iron glycerolate. Thermal behavior during the heating was studied by differential thermal analysis combined with thermogravimetry. The precursor, as well as the prepared nanoparticles, were analyzed by a broad spectrum of analytic techniques (X-Ray photoelectron spectroscopy (XPS), X-Ray diffraction (XRD), Energy dispersive spectroscopy (EDS), Atomic absorption spectroscopy (AAS), Scanning electron microscopy (SEM), and Raman spectroscopy). The particle size of nanoparticles was obtained from Transmission electron microscopy and also calculated using Scherrer formula. A vibrating sample magnetometer (VSM) in a Physical Property Measurement System was used to analyze the magnetic properties of nanoparticles.

SERS study of riboflavin on green-synthesized silver nanoparticles prepared by reduction using different flavonoids: What is the role of flavonoid used?

Spectroscopy of surface-enhanced Raman scattering (SERS) is nowadays widely used in the field of bio-science and medicine. These applications require new enhancing substrates with special properties. They should be non-toxic, environmentally friendly and (bio-) compatible with examined samples. Flavonoids are natural antioxidants with many positive effects on human health. Simultaneously, they can be used as reducing agent in preparation procedure of plasmonic enhancing substrate for SERS spectroscopy. The best amplifiers of Raman vibrational spectroscopic signal are generally silver nanoparticles (AgNPs). In this study, several flavonoids (forming a logical set) were used as reducing agent in AgNPs preparation procedures. Reactivity of 10 structurally arranged flavonoids (namely flavone, chrysin, apigenin, luteolin, tricetin, 3-hydroxyflavone, galangin, kaempferol, quercetin and myricetin) was compared and SERS-activity of prepared AgNPs was tested using model analyte riboflavin. Riboflavin was detected down to concentration 10-9mol/l.