Toward a New Era of SERS and TERS at the Nanometer Scale: From Fundamentals to Innovative Applications.

Surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS) have opened a variety of exciting research fields. However, although a vast number of applications have been proposed since the two techniques were first reported, none has been applied to real practical use. This calls for an update in the recent fundamental and application studies of SERS and TERS. Thus, the goals and scope of this review are to report new directions and perspectives of SERS and TERS, mainly from the viewpoint of combining their mechanism and application studies. Regarding the recent progress in SERS and TERS, this review discusses four main topics: (1) nanometer to subnanometer plasmonic hotspots for SERS; (2) Ångström resolved TERS; (3) chemical mechanisms, i.e., charge-transfer mechanism of SERS and semiconductor-enhanced Raman scattering; and (4) the creation of a strong bridge between the mechanism studies and applications.

ATR-far-ultraviolet spectroscopy: a challenge to new σ chemistry.

This review reports the recent progress on ATR-far ultraviolet (FUV) spectroscopy in the condensed phase. ATR-FUV spectroscopy for liquids and solids enables one to explore various topics in physical chemistry, analytical chemistry, nanoscience and technology, materials science, electrochemistry, and organic chemistry. In this review, we put particular emphasis on the three major topics: (1) studies on electronic transitions and structures of various molecules, which one cannot investigate via ordinary UV spectroscopy. The combined use of ATR-FUV spectroscopy and quantum chemical calculations allows for the investigation of various electronic transitions, including σ, n-Rydberg transitions. ATR-FUV spectroscopy may open a new avenue for σ-chemistry. (2) ATR-FUV spectroscopy enables one to measure the first electronic transition of water at approximately 160 nm without peak saturation. Using this band, one can study the electronic structure of water, aqueous solutions, and adsorbed water. (3) ATR-FUV spectroscopy has its own advantages of the ATR method as a surface analysis method. ATR-FUV spectroscopy is a powerful technique for exploring a variety of top surface phenomena (∼50 nm) in adsorbed water, polymers, graphene, organic materials, ionic liquids, and so on. This review briefly describes the principles, characteristics, and instrumentation of ATR-FUV spectroscopy. Next, a detailed description about quantum chemical calculation methods for FUV and UV regions is given. The recent application of ATR-FUV-UV spectroscopy studies on electronic transitions from σ orbitals in various saturated molecules is introduced first, followed by a discussion on the applications of ATR-FUV spectroscopy to studies on water, aqueous solutions, and adsorbed water. Applications of ATR-FUV spectroscopy in the analysis of other materials such as polymers, ionic liquids, inorganic semiconductors, graphene, and carbon nanocomposites are elucidated. In addition, ATR-FUV-UV-vis spectroscopy focusing on electrochemical interfaces is outlined. Finally, FUV-UV-surface plasmon resonance studies are discussed.

A green approach to nanoplastic detection: SERS with untreated filter paper for polystyrene nanoplastics.

Plastic pollution at the nanoscale continues to pose adverse effects on environmental sustainability and human health. However, the detection of nanoplastics (NPLs) remains challenging due to limitations in methodology and instrumentation. Herein, a "green approach" for surface-enhanced Raman spectroscopy (SERS) was exploited to detect polystyrene nanospheres (PSNSs) in water, employing untreated filter paper and a simple syringe-filtration set-up. This SERS protocol not only enabled the filtration of nano-sized PSNSs, which are smaller than the pore size of the ordinary filter paper, but also offered SERS enhancement by utilizing quasi-spherical-shaped silver nanoparticles (AgNPs) as the SERS-active substrate. The filtering of NPLs was accomplished by adding an aggregating agent to the nanoparticle mixture, which caused the aggregation of NPLs and AgNPs, resulting in a larger cluster and more hot spots for SERS detection. The optimal aggregating agent and its concentration, as well as the volume ratio between the AgNPs and NPLs, were also optimized. This SERS method successfully detected and quantified PSNSs of various sizes (i.e., 100, 300, 460, 600, and 800 nm) down to a limit of detection (LOD) of about 0.31 µg mL-1. The method was also validated against the presence of several interferents (i.e., salts, sugars, amino acids, and surfactants) and was proven practical, as evidenced by the detection of 800nm PSNSs in drinking and tap water (LODs of 1.47 and 1.55 µg mL-1, respectively).

Validation of the cell culture monitoring using a Raman spectroscopy calibration model developed with artificially mixed samples and investigation of model learning methods using initial batch data.

The development of calibration models using Raman spectra data has long been challenged owing to the substantial time and cost required for robust data acquisition. To reduce the number of experiments involving actual incubation, a calibration model development method was investigated by measuring artificially mixed samples. In this method, calibration datasets were prepared using spectra from artificially mixed samples with adjusted concentrations based on design of experiments. The precision of these calibration models was validated using the actual cell culture sample. The results showed that when the culture conditions were unchanged, the root mean square error of prediction (RMSEP) of glucose, lactate, and antibody concentrations was 0.34, 0.33, and 0.25 g/L, respectively. Even when variables such as cell line or culture media were changed, the RMSEPs of glucose, lactate, and antibody concentrations remained within acceptable limits, demonstrating the robustness of the calibration models with artificially mixed samples. To further improve accuracy, a model training method for small datasets was also investigated. The spectral pretreatment conditions were optimized using error heat maps based on the first batch of each cell culture condition and applied these settings to the second and third batches. The RMSEPs improved for glucose, lactate, and antibody concentration, with values of 0.44, 0.19, and 0.18 g/L under constant culture conditions, 0.37, 0.12, and 0.12 g/L for different cell lines, and 0.26, 0.40, and 0.12 g/L when the culture media was changed. These results indicated the efficacy of calibration modeling with artificially mixed samples for actual incubations under various conditions.

Detection and analysis of microplastics in tissues and blood of human cervical cancer patients.

Microplastics (MPs) can enter the reproductive system and can be potentially harmful to human reproductive health. In this study, 13 types of microplastics (MPs) were identified in patient blood, cancer samples, and paracarcinoma samples using Raman spectroscopy, with polyethylene, polypropylene and polyethylene-co-polypropylene being the most abundant polymer types. Futher, cotton was also found in our study. The diversity and abundance of MPs were higher in blood samples than in cancerous tissues, and there was a significant positive correlation between diversity (p < 0.05). Furthermore, the diversity and abundance of MPs in cancerous tissues were higher than in paracancerous tissues. The dimensional sizes of MPs in these samples were also very similar, with the majority of detected MPs being smaller in size. Correlation analysis showed that patient's age correlated with the abundance of MPs in blood samples, body mass index (BMI) correlated with the abundance of MPs in cancerous tissues. Notably, the frequency with which patients consume bottled water and beverages may also increase the abundance of MPs. This study identifies for the first time the presence of MPs and cotton in cancerous and paracancerous tissues of human cervical cancer patients. This provides new ideas and basic data to study the risk relationship between MP exposure and human health.

SERS Tracking Oxidative Stress on a Metalloporphyrin Framework by Vitamin C.

Accurate control of charge transfer is crucial to investigate the catalytic reaction mechanism of the biological oxidation process that biomedicine participates in. Herein, we have established an assembly model of metalloporphyrin framework (MPF) nanosheets as the active centers of biological enzymes. The introduction of Vitamin C (VC) into the MPF system can precisely modulate its content of charges. The surface-enhanced Raman scattering activity and peroxidase-like catalytic performance are enhanced simultaneously for the first time by manipulating the optimal molar ratio of an MPF to VC and the reaction sequence with target model molecules. We have confirmed that the formation of the intermediate of Fe(2+)-OOH species is specifically enhanced after VC modulation, which indicates that VC can regulate the oxidative stress of the active center of biological enzymes. This discovery not only accurately resolves the mechanism of VC-selective anticancer therapy but also has important significance for the precise treatment of VC synergistic targeting medicines.

A new approach to recognizing the correct pattern of cross-peaks from a noisy 2D asynchronous spectrum by detecting intrinsic symmetry via the Kolmogorov-Smirnov test.

The characteristic cluster pattern of cross-peaks in a 2D asynchronous spectrum provides an effective way to reveal the specific physicochemical nature of subtle spectral changes caused by intermolecular interactions. However, the inevitable presence of noise in the 1D spectra used to construct a 2D asynchronous spectrum is significantly amplified, which poses a serious challenge in identifying the correct cluster pattern of the cross-peaks. While mirror symmetry occurs in some types of cross-peaks, it does not occur in other types. The Kolmogorov-Smirnov test provides a statistical means to check whether the mirror symmetry exists or not between a pair of cross-peaks covered by heavy noise. Thus, different types of cross-peak clusters can be distinguished by excavating intrinsic spectral features from the noisy 2D asynchronous spectrum. The effectiveness of this approach in investigating the nature of intermolecular interactions was showcased in both a simulated model system and a real artemisinin/N-methyl pyrrolidone system.

Novel Method for Extracting the Spectrum of a Supramolecular Complex via a Comprehensive Approach Involving Two-Dimensional Correlation Spectroscopy, Genetic Algorithm, and Grid Searching.

A supramolecular complex may be formed by two solutes via a weak intermolecular interaction in a solution. The spectrum of the complex is often inundated by the spectra of the solutes that are not involved in the intermolecular interaction. Herein, a novel spectral analysis approach is proposed to retrieve the spectrum of the supramolecular complex. First, a two-dimensional (2D) asynchronous spectrum is constructed. Then, a genetic algorithm is used to obtain a heuristic spectrum of the supramolecular complex. The heuristic spectrum is a linear combination of the spectrum of the complex and the spectrum of a solute. The coefficients of the linear combination are then obtained, according to which the equilibrium constants are invariant among the sample solutions used to construct the 2D asynchronous spectrum. We have applied the approach to a supramolecular system formed by benzene and I2. In the analysis, several binding models are evaluated, and a benzene molecule interacting with two iodine molecules via halogen bonding turns out to be the only possible model. Hence, the characteristic band of the benzene/I2 supramolecular complex around 1819 cm-1 in the Fourier transform infrared (FTIR) spectrum and the corresponding equilibrium constant are obtained. The above results indicate that the novel approach provides a chance to get new insight into various intermolecular interactions studied by spectroscopy.

Robust Approach to Estimating the Stoichiometric Ratio of Supramolecular Complexes Using the Volume of Cross-Peaks in 2D Asynchronous Spectra and the Jonckheere-Terpstra Test.

Estimation of the stoichiometric ratio of a supramolecular aggregate formed by different compounds is very important in elucidating the structure and function of the aggregate. Many spectroscopic methods used to estimate the stoichiometric ratios of coordination complexes become invalid when characteristic peaks of the aggregate overlap with peaks of compounds that form the aggregate. Previously, we combined the asynchronous orthogonal sample design with Job's method to address the abovementioned problem. However, the interference of noise may lead to incorrect results. Herein, a new method has been developed. In the generation of corresponding Job's curve, the intensity of a cross peak at a single apex is replaced by the volume of the cross peak. Since most noise is canceled in the calculation of the volume of the cross peak, resultant Job's curve is robust to noise. Moreover, the Jonckheere-Terpstra statistical test, a famous nonparametric method to detect whether the data has an upward or downward trend, could further reduce the risk of yielding incorrect results caused by noise. We have applied this approach to two real-world examples (resveratrol/ß-Cyclodextrin (ß-CD) and N, N-diethyl-N'-benzoylthiourea (DEBT)/Cu2+) with satisfactory results. The method described in this paper provides a robust way to measure the stoichiometric ratio in supramolecular systems.

Retrieving Spectra of Pure Components from the DOSY-NMR Experiment via a Comprehensive Approach Involving the 2D Asynchronous Spectrum, 2D Quotient Spectrum, and Genetic Algorithm Refinement.

When diffusion coefficients of different components in a mixture are similar, NMR spectra of pure individual components are difficult to be obtained via a diffusion-ordered spectroscopy (DOSY) experiment. Two-dimensional correlation spectroscopy (2D-COS) is used to analyze the data from the DOSY experiment. Through the properties of the systematic absence of cross-peak (SACP) in the 2D asynchronous spectra, spectra of pure components can be obtained even if their diffusion coefficients are similar. However, fluctuations in peak-position and peak-width are often unavoidable in NMR spectra, which makes SACPs unrecognizable. To address the problem, a 2D quotient spectrum is used to identify the masked SACPs. However, undesirable interference peaks due to the fluctuations in peak-position and peak-width are still present when we extract a spectrum of a component by slicing the 2D asynchronous spectrum across the SACP. A genetic algorithm (GA) is used to select a suitable subset of spectra where the diversities of peak-position and peak-width are significantly reduced. Then, we used the selected spectra to construct a refined 2D asynchronous spectrum so that the spectra of pure components with significant attenuated interference can be obtained. The above approach has been proven to be effective on a model system and a real-world example, demonstrating that 2D-COS possesses a bright perspective in the analysis of the bilinear data from DOSY experiments.

Determination of the Influence of Various Factors on the Character of Surface Functionalization of Copper(I) and Copper(II) Oxide Nanosensors with Phenylboronic Acid Derivatives.

In this work, we attempt to determine the influence of the oxidation state of copper [Cu(I) vs Cu(II)], the nature of the interface (solid/aqueous vs solid/air), the incubation time, and the structure of N-substituted phenylboronic acids (PBAs) functionalizing the surface of copper oxide nanostructures (NSs) on the mode of adsorption. For this purpose, 4-[(N-anilino)(phosphono)-S-methyl]phenylboronic acid (1-PBA) and its two analogues (2-PBA and bis{1-PBA}) and the copper oxide NSs were synthesized in a surfactant-/ion-free solution via a synthetic route that allows controlling the size and morphology of NSs. The NSs were characterized by scanning electron microscopy, ultraviolet-visible spectroscopy, Raman spectroscopy, and X-ray diffraction, which confirmed the formation of spherical Cu2O nanoparticles (Cu2ONPs) with a size of 1.5 µm to 600 nm crystallized in a cubic cuprite structure and leaf-like CuO nanostructures (CuONSs) with dimensions of 80-180 nm in width and 400-700 nm in length and crystallized in a monoclinic structure. PBA analogues were deposited on the surface of the copper oxide NSs, and adsorption was investigated using surface-enhanced Raman spectroscopy (SERS). The changes in the orientation of the molecule relative to the substrate surface caused by the abovementioned factors were described, and the signal enhancement on the copper oxide NSs was determined. This is the first study using vibrational spectroscopy for these compounds.

In situ SERS monitoring of intracellular H2O2 in single living cells based on label-free bifunctional Fe3O4@Ag nanoparticles.

Visualization of signaling molecules in single living cells is crucial for understanding cellular metabolism and physiology, which can provide valuable insights into early diagnoses and treatments of diseases. Highly sensitive in situ monitoring of intracellular analytes released from single living cells by virtue of label-free nanosensors is urgently needed, which can avoid interferences from molecular labeling. Here, we proposed an ultrasensitive strategy for in situ imaging of intracellular H2O2 in single living cancer cells by surface-enhanced Raman scattering (SERS) spectroscopy with the utilization of label-free Fe3O4@Ag core-satellite nanoparticles (NPs). The Fe3O4@Ag NPs can efficiently and selectively catalyze the oxidation of the peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. Additionally, they exhibit excellent SERS activity that allows for in situ monitoring of intracellular H2O2 in living cells through establishing the correlation between the H2O2 level and the SERS intensity of the catalytic oxidation product of TMB. The H2O2 concentration is revealed through the SERS intensity of oxidized TMB with a good linear response in a wide range from 1 fM to 1 mM. Moreover, the intracellular H2O2 level in live cancer cells and imaging of the distribution of H2O2 inside single cells can be achieved by using such a label-free nanosensor based strategy. Our work demonstrates that the label-free Fe3O4@Ag NP-based SERS imaging and quantification strategy is a promising and powerful approach to assess intracellular H2O2 in living cells and allows us to monitor single-cell signaling molecules with nanoscale resolution.

Development of an amino acid sequence-dependent analytical method for peptides using near-infrared spectroscopy.

We aimed to develop an amino acid sequence-dependent analytical method using near-infrared (NIR) spectroscopy. The detailed analysis of the NIR spectra of eight different amino acid aqueous solutions (glycine, alanine, serine, glutamine, lysine, phenylalanine, tyrosine, and proline) revealed different spectral patterns characteristic of different amino acid residues in the 6200-5700 and 5000-4200 cm-1 regions, and the amino acids were identified based on the patterns. The spectra in the region of 5000-4500 cm-1 for tripeptide organic solutions that were composed of the aforementioned eight amino acids clearly showed the spectral differences depending on the amino acid species and amino acid sequences. Namely, tripeptide species were clearly differentiated from each other based on the spectral pattern of NIR bands due to the combinations of N-H stretching and amide II/III modes and those derived from the first overtones of amide II and amide I. The quantitative evaluation of changes in the concentrations of dipeptides and tripeptides composed of two different amino acids, glycine and proline was performed using partial least squares regression (PLSR) analysis and a combination of bands for amide modes. The calibration and validation results with high determination coefficients (R2 ≥ 0.99) were successfully obtained based on the amino acid sequences. The results not only revealed the usefulness of NIR spectroscopy as a process analytical technology (PAT) tool for synthesizing peptides in a micro flow reactor but also proposed a general method for quantitatively analyzing NIR spectra obtained in the course of chemical synthesis.

Deprotonation from an OH on myo-Inositol Promoted by µ2-Bridges with Possible Regioselectivity/Chiral Selectivity.

Single-crystal structures of myo-inositol complexes with erbium ([Er2(C6H11O6)2(H2O)5Cl2]Cl2(H2O)4, denoted ErI hereafter) and strontium (Sr(C6H12O6)2(H2O)2Cl2, denoted SrI hereafter) are described. In ErI, deprotonation occurs on an OH of myo-inositol, although the complex is synthesized in an acidic solution, and the pKa values of all of the OHs in myo-inositol are larger than 12. The deprotonated OH is involved in a µ2-bridge. The polarization from two Er3+ ions activates the chemically relatively inert OH and promotes deprotonation. In the stable conformation of myo-inositol, there are five equatorial OHs and one axial OH. The deprotonation occurs on the only axial OH, suggesting that the deprotonation possesses characteristics of regioselectivity/chiral selectivity. Two Er3+ ions in the µ2-bridge are stabilized by five-membered rings formed by chelating Er3+ with an O-C-C-O moiety. As revealed by the X-ray crystallography study, the absolute values of the O-C-C-O torsion angles decrease from ∼60 to ∼45° upon chelating. Since the O-C-C-O moiety is within a six-membered ring, the variation of the torsion angle may exert distortion of the chair conformation. Quantum chemistry calculation results indicate that an axial OH flanked by two equatorial OHs (double ax-eq motif) is favorable for the formation of a µ2-bridge, accounting for the selectivity. The double ax-eq motif may be used in a rational design of high-performance catalysts where deprotonation with high regioselectivity/chiral selectivity is carried out.

Experimental verification of increased electronic excitation energy of water in hydrate-melt water by attenuated total reflection-far-ultraviolet spectroscopy.

The demand for Li secondary batteries is increasing, with the need for batteries with a higher level of performance and improved safety features. The use of a highly concentrated aqueous electrolyte solution is an effective way to increase the safety of batteries because it is possible to use "water-in-salt" (WIS) and "hydrate-melt" (HM) electrolytes for practical applications. These electrolytes exhibit a potential window of >3.0 V, which is attributed to the difference between the HOMO and the LUMO energies of the n orbital of the pure water molecules and that of the water molecules in the hydration shells of a metal ion, according to theoretical predictions. Thus, in the present study, the attenuated total reflectance (ATR)-far-ultraviolet (FUV) spectra of water and super-concentrated aqueous solutions, such as WIS and HM using a Li salt, were experimentally investigated. The effects of anions, cations, and deuteriums on the ATR-FUV spectra were examined. The ATR-FUV method is an excellent means of studying highly concentrated aqueous salt solutions. The results suggest that the transition energy of water molecules in an ultrahighly concentrated aqueous electrolyte containing HM and WIS increased by nearly 0.4 eV (corresponding to an energy shift of over 10 nm) compared to an aqueous electrolyte with a typical water concentration. It was also revealed that the transition energy of water changes depending on the environment of the non-bonding electron, which is directly connected with or affected by hydrogen bonding with other water molecules or directly connected with Li+.

Advances, challenges and perspectives of quantum chemical approaches in molecular spectroscopy of the condensed phase.

The purpose of this review is to demonstrate advances, challenges and perspectives of quantum chemical approaches in molecular spectroscopy of the condensed phase. Molecular spectroscopy, particularly vibrational spectroscopy and electronic spectroscopy, has been used extensively for a wide range of areas of chemical sciences and materials science as well as nano- and biosciences because it provides valuable information about structure, functions, and reactions of molecules. In the meantime, quantum chemical approaches play crucial roles in the spectral analysis. They also yield important knowledge about molecular and electronic structures as well as electronic transitions. The combination of spectroscopic approaches and quantum chemical calculations is a powerful tool for science, in general. Thus, our article, which treats various spectroscopy and quantum chemical approaches, should have strong implications in the wider scientific community. This review covers a wide area of molecular spectroscopy from far-ultraviolet (FUV, 120-200 nm) to far-infrared (FIR, 400-10 cm-1)/terahertz and Raman spectroscopy. As quantum chemical approaches, we introduce several anharmonic approaches such as vibrational self-consistent field (VSCF) and the combination of periodic harmonic calculations with anharmonic corrections based on finite models, grid-based techniques like the Numerov approach, the Cartesian coordinate tensor transfer (CCT) method, Symmetry-Adapted Cluster Configuration-Interaction (SAC-CI), and the ZINDO (Semi-empirical calculations at Zerner's Intermediate Neglect of Differential Overlap). One can use anharmonic approaches and grid-based approaches for both infrared (IR) and near-infrared (NIR) spectroscopy, while CCT methods are employed for Raman, Raman optical activity (ROA), FIR/terahertz and low-frequency Raman spectroscopy. Therefore, this review overviews cross relations between molecular spectroscopy and quantum chemical approaches, and provides various kinds of close-reality advanced spectral simulation for condensed phases.

Method of Monitoring the Number of Amide Bonds in Peptides Using Near-Infrared Spectroscopy.

Using near-infrared (NIR) spectroscopy, we aimed to develop a method of monitoring the increasing number of amide bonds with the elongation of the chain length of peptides. Because peptide synthesis can be monitored by evaluating the increasing number of amide bonds with dehydration occurring between amino acids, polyglycine, which has the simplest structure among polyamino acids, was studied, and the key bands whose absorption intensities increased with the elongation of the chain length, such as the bands attributed to glycine, diglycine, triglycine, and tetraglycine, were searched. The bands due to the combinations of the amide A and amide II/III modes in the region of 5000-4500 cm-1 were revealed to be good candidates for key bands, their second derivative intensities increased as the number of amide bonds increased, regardless of pH, solvent species, and the presence of protecting groups. The number of amide bonds was evaluated by a partial least square regression using the abovementioned combination bands, and a calibration model with a high determination coefficient (≥0.99) was constructed. These results not only have demonstrated the usefulness of NIR spectroscopy as a process analytical technology tool for the process of synthesizing the peptide in a microflow reactor but also have provided basic knowledge for analyzing amide bonds in the NIR spectra of proteins, polyamino acids, polypeptides, and polyamides.

MCR-ALS with sample insertion constraint to enhance the sensitivity of surface-enhanced Raman scattering detection.

The multivariate curve resolution-alternative least squares (MCR-ALS) algorithm was modified with sample insertion constraint to deconvolute the overlapping peaks in SERS spectra. The developed method was evaluated by the spectral data simulated using a Gaussian distribution function to generate two independent peaks corresponding to a capping agent and an analyte. The spectra were generated with different overlapping levels and various intensity ratios of the analyte to the capping agent. By using MCR-ALS with the sample insertion constraint, the peak of the capping agent was completely excluded to obtain a calibration model of the analyte with R2 > 0.95 under all conditions. Furthermore, our developed method was later applied to a real SERS measurement to quantify carbofuran (analyte) using the azo-coupling reaction with p-ATP (capping agent) on silver nanoparticles as a SERS substrate. A calibration model of derivative carbofuran phenol was generated with R2 = 0.99 and LOD = 28.19 ppm. To assess the performance of the calibration model, the model was used to estimate the concentration of carbofuran in an external validation set. It was found that the RMSE of prediction was only 2.109 with a promising R2 = 0.97.

Half-raspberry-like bimetallic nanoassembly: Interstitial dependent correlated surface plasmon resonances and surface-enhanced Raman spectroscopy.

Correlated localized surface plasmon resonance (SPR), surface-enhanced Raman scattering (SERS) and localized electromagnetic (EM) field distributions of pure and modified gold (Au) nanoassemblies have been demonstrated. The Au nanoassemblies were decorated as half-raspberry-like nanostructures by silver (Ag) mists, and the characteristics of their SPR and SERS were observed at the same spatial position with and without decoration. The decoration of Au nanoassemblies was analyzed in-depth and confirmed by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). Multifunctional and lab-built microscopy was used to capture correlated SPR and SERS imaging and spectral measurements. Without decoration, strong SPR peaks and enhanced SERS signals were observed, whereas intense plasmon excitation deteriorated with a broadening and diminishing peak and the SERS enhancement dropped at least by 10 fold upon the modification. Preferential enhancement near the edge was observed in the correlated SPR and SERS measurements. The variations in localized SPR, subsequent SERS enhancement, and preferential confinement were speculated concerning localized EM near-field deformation. A typical tetramer with five interstitials was modeled and simulated by finite difference time domain (FDTD) analysis at different incident polarizations. The EM near-field distributions were extracted with and without decoration of constituent interstitials by Ag mists. Without the modification of participating interstitials, the EM near-field distributions were found confined, whereas additional EM near-field confinements were observed in the presence of Ag mists. Such EM near-field deformations due to the modification of constituent interstitials were supposed to broaden and deteriorate SPR characteristics of Au nanoassemblies as observed under this investigation.

Solvent effect on the competition between weak and strong interactions in phenol solutions studied by near-infrared spectroscopy and DFT calculations.

Near-infrared (NIR) spectra of phenol in a series of non-aromatic and aromatic solvents were recorded to study the competition between various types of solute-solute and solute-solvent interactions. Depending on the phenol concentration, the free OH and OH involved in the OH⋯OH interactions in the dimers and higher associates are present in cyclohexane solutions. On the other hand, free OH does not appear in Cl-containing solvents since at a low phenol content the OH groups participate in the OH⋯Cl interactions. In CCl4 and tetrachloroethylene this interaction is weak, while in chlorobenzene the strength of this interaction is higher. In the aromatic solvents the solute-solute OH⋯OH interactions compete with the solute-solvent OH⋯π and aromatic CH⋯OH ones. Consequently, the degree of self-association of phenol in aromatic solvents is smaller than that in non-aromatic ones. The strength of the OH⋯π interactions increases with growing electron-donating ability of the substituents in the benzene derivatives. This observation obtained from the NIR spectra is in line with the results of the theoretical calculations (DFT). A clear correlation appears between the number of methyl groups in aromatic solvents and the population of the free OH groups. The methyl groups are steric hindrances and impede the formation of the OH⋯OH and OH⋯π interactions. Our results suggest the presence of aromatic CH⋯OH solute-solvent interactions, not observed in previous studies. NIR spectroscopy appears to be a powerful tool for exploration of free and weakly-bonded OH groups.