表面增强拉曼光谱技术检测新型冠状病毒刺突蛋白

开发具有高灵敏度、高准确性的新型冠状病毒（SARS-CoV-2）快速检测技术对疫情防控具有重要作用。本文利用表面增强拉曼光谱（SERS）技术对人体唾液中的痕量SARS-CoV-2病毒刺突蛋白（S蛋白）进行了检测。结果表明,含S蛋白的唾液样本与原始唾液样本的拉曼光谱具有显著区别,含S蛋白的唾液样本谱图中可清晰观察到属于S蛋白的拉曼谱线。该结果为后续SERS技术在SARS-CoV-2病毒快速检测方面的应用奠定了坚实基础。

     

Fabrication and surface enhanced Raman spectroscopy of single Au@SiO2 dimers linked by benzenedithiol

Metal nanoparticle dimers with controllable gap distance have attracted considerable attention because of their promising application in plasmonics. Generally, gaps with nanometer or subnanometer dimensions generate localized surface plasmon resonance (LSPR) coupling effect, thus contributing to a strong electromagnetic field for improving surface enhanced Raman scattering (SERS) effect. Here, we developed a facile approach to fabricate Au@SiO₂ dimers through the steric hindrance effect, in which the SiO₂ shell functioned as a block and a rigid dithiol molecule was employed as linker. The thickness of the SiO₂ shell played a critical role in improving the yield of dimers. The dimerization efficiency increased significantly as the shell thickness decreased to ~1 nm. When 1,4‐benzenedithiol was used as linker molecule, the yield of dimers was ~30%. Few dimers were obtained when mecaptobenzonic acid was used as linker. A thicker shell is associated with a low yield of dimer, whereas a thinner shell resulted in the formation of multimers and linear structures. The low number of linker molecules on the exposed area of monodisperse single nanoparticles and the lack of LSPR coupling effect (‘hot spots’) resulted in the disappearance of SERS signals of the linkers. The estimated SERS enhancement factor was about eight fold because of the strong coupling effect in the gap of the dimer with the distance of the dithiol molecular length. From the above results, SERS combined with SEM could be developed into powerful tools for monitoring the formation of dimers and positioning of single dimers. It may aid the control of assembly of Au nanoparticles and in probing key issues about SERS enhancements. Copyright © 2015 John Wiley & Sons, Ltd.     

Different classification algorithms and serum surface enhanced Raman spectroscopy for noninvasive discrimination of gastric diseases

In this study, surface enhanced Raman spectroscopy (SERS) was used to investigate the spectral characteristics of blood serum for the purpose of diagnosing stomach diseases. SERS spectral data was collected from patients with atrophic gastritis, both pre‐operation and post‐operation gastric cancer, and from healthy individuals. Visual differences in the SERS spectra were observed between the four groups which indicate corresponding biomolecule concentration changes in blood. To further investigate the diagnostic ability of human serum, the spectral data was analyzed with three chemometric processes. These three methods extracted features and classified from the spectral data. Principal component analysis (PCA) was first performed to reduce the dimensionality of the original spectral data. Then, the classification methods support vector machine (SVM), linear discriminant analysis (LDA) and classification and regression tree (CART) were used for the evaluation of diagnostic ability. Accuracies of 96.5%, 88.8% and 87.1% were obtained for PCA‐SVM, PCA‐LDA and PCA‐CART, respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

Experimental and statistical analysis methods for peptide detection using surface‐enhanced Raman spectroscopy

Surface‐enhanced Raman spectroscopy (SERS) has the potential to make a significant impact in biology research due to its ability to provide information orthogonal to that obtained by traditional techniques such as mass spectrometry (MS). While SERS has been well studied for its use in chemical applications, detailed investigations with biological molecules are less common. In addition, a clear understanding of how methodology and molecular characteristics impact the intensity, the number of peaks, and the signal‐to‐noise of SERS spectra is largely missing. By varying the concentration and order of addition of the SERS‐enhancer salt (LiCl) with colloidal silver, we were able to evaluate the impact of these variables on peptide spectra using a quantitative measure of spectra quality based on the number of peaks and peak intensity. The LiCl concentration and order of addition that produced the best SERS spectra were applied to a panel of synthetic peptides with a range of charges and isoelectric points (pIs) where the pI was directly correlated with higher spectral quality. Those peptides with moderate to high pIs and spectra quality scores were differentiated from each other using the improved method and a hierarchical clustering algorithm. In addition, the same method and algorithm was applied to a set of highly similar phosphorylated peptides, and it was possible to successfully classify the majority of peptides on the basis of species‐specific peak differences. Copyright © 2008 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman spectroscopy for trace‐level detection of explosives

The detection of explosives and their associated compounds for security screening is an active area of research and a wide variety of detection methods are involved in this very challenging area. Surface‐enhanced Raman scattering (SERS) spectroscopy is one of the most sensitive tools for the detection of molecules adsorbed on nano‐scale roughened metal surface. Moreover, SERS combines high sensitivity with the observation of vibrational spectra of species, giving complete information on the molecular structure of material under study. In this paper, SERS was applied to the detection of very small quantities of explosives adsorbed on industrially made substrates. The spectra were acquired with a compact Raman spectrometer. Usually, a high signal‐to‐noise (S/N) spectrum, suitable for identification of explosive molecules down to few hundreds of picograms, was achieved within 30 s. Our measurements suggest that it is possible to exploit SERS using a practical detection instrument for routine analysis. Copyright © 2010 John Wiley & Sons, Ltd.     

Concentric toroids as a wideband and efficient substrate for surface-enhanced Raman spectroscopy applications

Designing a structure having high local field enhancement, wideband resonance, and large hot spot area is the key element to obtain a large enhancement factor for surface-enhanced Raman spectroscopy applications. Here, the concentric toroid structures in dimer configuration is proposed, which shows a large local field intensity in a wide spectral range and the region that leads to a high-surface-enhanced Raman scattering signal intensity. Calculations show that the average surface-enhanced Raman scattering enhancement is up to 60 times more compared to the conventional dimer toroid structures with similar size.     

Characterization of polycyclic aromatic hydrocarbons using Raman and surface‐enhanced Raman spectroscopy

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous atmospheric pollutants and food contaminants, which exhibit potent carcinogenicity, mutagenicity, and teratogenicity. Vibrational spectroscopy techniques, especially Raman spectroscopy and surface‐enhanced Raman spectroscopy (SERS), can be potentially used as an alternative technique to liquid and gas chromatography in PAH analysis. However, there is limited information on the intrinsic Raman and SERS fingerprints of PAHs. In this study, we have acquired the Raman and SERS spectra of seven PAH compounds and compared their experimental spectra with theoretical Raman spectra calculated by density function theory (DFT). The vibrational modes corresponding to the Raman peaks have also been assigned using DFT. Characteristic Raman and SERS peaks have been identified for five PAH compounds, and the limits of detection were estimated. Such information could be useful for developing SERS assays for simple and rapid PAH identification. Copyright © 2014 John Wiley & Sons, Ltd.     

Detection of melamine in liquid milk using surface‐enhanced Raman scattering spectroscopy

Melamine, a nitrogen‐rich chemical, has recently caused enormous economic losses to the food industry due to the cases of milk products adulterated by melamine. This has led to an urgent need of rapid and reliable methods for detection of melamine in food. In this study, surface‐enhanced Raman scattering (SERS) spectroscopy was used to detect melamine in liquid milk. The sample preparation with liquid milk is very easy; it has to be only diluted with double‐distilled water followed by centrifugation. By using a silver colloid, at least a 10⁵‐fold enhancement of the Raman signal was achieved for the measurement of melamine. The limit of detection by this method was 0.01 µg ml⁻¹ for melamine standard samples. Based on the intensity of the Raman vibrational bands normalised to that of the band at 928 cm⁻¹ (CH₂), an external standard method was employed for quantitative analysis. The linear regression square (R²) of the curve was 0.9998; the limit of quantitation using this approach was 0.5 µg ml⁻¹ of melamine in liquid milk; the relative standard deviation was ≤10%; and recoveries were from 93 to 109%. The test results for SERS were very precise and as good as those obtained by liquid chromatography/tandem mass spectrometry. The method was simple, fast(only needs about 3 min), cost effective, and sensitive for the detection of melamine in liquid milk samples. Therefore, it is more suitable for the field detection of melamine in liquid milk. Copyright © 2010 John Wiley & Sons, Ltd.     

纳米银粒子表面增强拉曼光谱在宠物饲料中三聚氰胺的速测研究

研究将制备的纳米银粒子作为表面增强拉曼光谱的增强试剂,实现对宠物饲料中三聚氰胺的快速定性定量分析。以709与1542cm-1处拉曼位移作为定性依据,以1149cm-1峰强度作为归一化标准,在1.0～10.0mg·kg-1浓度范围实现定量计算,检测限0.5mg·kg-1。研究发现,纳米银粒子对三聚氰胺具有较强的拉曼增强效应,特征峰信号强度与纳米银粒子加入时间,溶液涡旋强度有很大的关系,同时也受提取溶剂的种类、提取方式及样品加入量的影响。本方法中每个样品5min内完成分析,与现有方法相比,快速简便,对宠物饲料中三聚氰胺实现现场、快速检测。     

Surface-enhanced resonance Raman scattering spectroscopy of single R6G molecules

Surface-enhanced resonance Raman scattering (SERRS) of Rhodamine 6G (R6G) adsorbed on colloidal silver clusters has been studied. Based on the great enhancement of the Raman signal and the quench of the fluorescence, the SERRS spectra of R6G were recorded for the samples of dye colloidal solution with different concentrations. Spectral inhomogeneity behaviours from single molecules in the dried sample films were observed with complementary evidences, such as spectral polarization, spectral diffusion, intensity fluctuation of vibrational lines and even ``breathing' of the molecules. Sequential spectra observed from a liquid sample with an average of 0.3 dye molecules in the probed volume exhibited the expected Poisson distribution for actually measuring 0, 1 or 2 molecules. Difference between the SERRS spectra of R6G excited by linearly and circularly polarized light were experimentally measured.     

Quantitative detection of captopril in tablet and blood plasma samples by the combination of surface‐enhanced Raman spectroscopy with multiplicative effects model

With p‐thiocresol as internal standard, quantitative analysis of captopril, a synthetic angiotensin converting enzyme inhibitor, was achieved by the combination of the multiplicative effects model with surface‐enhanced Raman spectroscopy (SERS). The multiplicative effects model was adopted to correct the detrimental effects caused by the heterogeneity in the physical properties of enhancing substrate (i.e. Ag nano‐particles). Experimental results showed that the calibration model built on the SERS spectra of the calibration captopril samples prepared with ultrapure water could attain quite satisfactory concentration predictions for captopril in both real‐world tablet samples and plasma samples. The recovery rates were in the range of 94.3% to 109.8%, which were in substantial agreement with the corresponding results of LC‐MS/MS. The limit of detection and limit of quantification were estimated to be 0.149 and 0.451 μM, respectively. The proposed approach has advantages of relatively low cost, simplicity, high sensitivity and good accuracy and therefore can be further developed and extended to a routine method for the quantification of captopril in complex systems. Copyright © 2015 John Wiley & Sons, Ltd.     

Quick detection of contaminants leaching from polypropylene centrifuge tubes with surface‐enhanced Raman spectroscopy and ultraviolet absorption spectroscopy

Anomalous surface‐enhanced Raman scattering (SERS) peaks were identified for liquid sample stored in polypropylene (PP) centrifuge tubes for months. We observed unexpected Raman peaks during experiments with thiamine hydrochloride aqueous solutions stored in PP tubes for 2 months. In order to identify the contaminants, we have performed SERS experiments on deionized (DI) water stored in PP centrifuge tubes for 2 months and compared them with those from fresh DI water sample. We have also carried out ultraviolet (UV) absorption spectra for both fresh and contaminated water. We believe that the water is contaminated because of chemicals leaching from the PP tube. From the gas chromatography‐mass spectrometry data, the main contaminants were found to be phthalic acid (PA) and its derivatives. Further SERS and UV absorption experiment for PA correlated well with the anomalous peaks identified earlier. We qualitatively confirmed the identification and quantitatively estimated the concentration of the suspect contaminants as between 1 and 10 µM with both SERS and UV absorption spectroscopy. With UV absorption spectroscopy, we precisely estimated the concentration as 2.1 µM . We have shown that the sample in PP tube can be contaminated by the leaching chemicals upon long‐term storage, and suggest SERS and UV absorption spectroscopy as two quick and simple techniques to detect the contamination. Copyright © 2011 John Wiley & Sons, Ltd.     

Silica‐overcoated substrates for detection of proteins by surface‐enhanced Raman spectroscopy

Ag film over nanosphere (AgFON) substrates for surface‐enhanced Raman spectroscopy (SERS) are shown to be ineffective for the detection of proteins in phosphate buffer solution (PBS) because of the decomposition of the substrate resulting in a total loss of SERS activity. However, modification of these substrates with SiO₂ overlayers overcomes this problem. The SiO₂ overlayers are produced by filtered arc deposition (FAD) and are characterised by atomic force microscopy (AFM). Their porosity is examined using Raman spectroscopy and the detection of cytochrome c and bovine serum albumin in PBS is successfully demonstrated. These findings show promise for the detection of proteins in biologically relevant conditions using Ag‐based SERS substrates. Copyright © 2008 John Wiley & Sons, Ltd.     

Understanding tip‐enhanced Raman spectra of biological molecules: a combined Raman,SERS and TERS study

Although conventional Raman, surface‐enhanced Raman (SERS) and tip‐enhanced Raman spectroscopy (TERS) have been known for a long time, a direct, thorough comparison of these three methods has never been carried out. In this paper, spectra that were obtained by conventional Raman, SERS (on gold and silver substrates) and TERS (in ‘gap mode’ with silver tips and gold substrates) are compared to learn from their differences and similarities. Because the investigation of biological samples by TERS has recently become a hot topic, this work focuses on biologically relevant substances. Starting from the TER spectra of bovine serum albumin as an example for a protein, the dipeptides Phe–Phe and Tyr–Tyr and the tripeptide Tyr–Tyr–Tyr were investigated. The major findings were as follows. (1) We show that the widely used assumption that spectral bands do not shift when comparing SER, TER and conventional Raman spectra (except due to binding to the metal surface in SERS or TERS) is valid. However, band intensity ratios can differ significantly between these three methods. (2) Marker bands can be assigned, which should allow one to identify and localize proteins in complex biological environments in future investigations. From our results, general guidelines for the interpretation of TER spectra are proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

A novel approach to determine leucomalachite green and malachite green in fish fillets with surface‐enhanced Raman spectroscopy (SERS) and multivariate analyses

The use of illegal fish drugs, such as malachite green (MG) in aquaculture has raised growing concerns over the safety of aquatic food products, and sensitive and rapid methods for detection of these drugs in fish muscle are much needed. Simplified extraction methods coupled with surface‐enhanced Raman spectroscopy were used for analysis of MG and its metabolite leucomalachite green (LMG) in tilapia fillets containing 0–50 ng g⁻¹ LMG or MG. Principal component analysis and partial least squares (PLS) regression were used for spectral data analyses. High sensitivity (MG or LMG could be detected at 1–2 ng g⁻¹ levels) and PLS models with good predictability [root mean square error of validation (RMSEV) = 1.97–2.21 ng g⁻¹, R² = 0.984–0.988] were possible with suitable sample extraction methods. The simplest extraction method developed provided an RMSEV of 9.32 ng g⁻¹ and R² of 0.788, and although this was not ideal, detection of MG and LMG at 5 ng g⁻¹ level with this method could reduce sample throughput time and provide for faster detection of LMG and MG. Copyright © 2012 John Wiley & Sons, Ltd.     

Silver nanoparticles synthesized by direct photoreduction of metal salts. Application in surface‐enhanced Raman spectroscopy

A simple synthesis method of silver nanoparticles and its application as an active surface‐enhanced Raman spectroscopy (SERS) colloid are presented in this work. The photoreduction of AgNO₃ in presence of sodium citrate (NaCit) was carried out by irradiation with different light sources (UV, white, blue, cyan, green, and orange) at room temperature. The evaluation of silver nanoparticles obtained as a function of irradiation time (1–24 h) and light source was followed by UV‐visible absorption spectroscopy. This light‐modification process results in a colloid with distinctive optical properties that can be related to the size and shape of the particles. The Ag colloids, as prepared, were employed as active colloids in SERS. Pyridine and caffeine were used as test molecules. Copyright © 2008 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman evidence for Rhodamine 6 G and its derivative with different adsorption geometry to colloidal silver nanoparticle

Some high‐affinity functional groups or resonant molecules were often used as probe molecules adsorbed on silver nanoparticles for Surface‐enhanced Raman scattering (SERS). However, it is still unclear how the attached molecules interact with the silver nanoparticles' surface, and how the anchoring groups affect the optical and electronic properties of molecules. Here, we report that surface‐enhanced Raman studies of two organic compounds; rhodamine 6G (R6G) and its aminated derivative (R‐NH₂) have very different functional groups for surface binding but nearly identical SERS spectroscopic properties at pH = 7 and UV–vis at pH = 3, respectively. A surprise was found that under the same experimental conditions, the SERS signal intensity for R6G is nearly 50‐fold higher than that of R‐NH₂. Furthermore, the pH‐dependent study reveals that the structure of R6G is irreversibly stabilized or ‘locked’ in its form and no longer responsive to pH changes. In contrast, R‐NH₂ is still sensitive to pH, and can be switched between its open‐ring and closed‐ring structures. Copyright © 2013 John Wiley & Sons, Ltd.     

Electrochemical in situ surface enhanced Raman spectroscopic characterization of a trinuclear ruthenium complex,Ru‐red

To study the fate of a molecular di‐μ‐oxo‐bridged trinuclear ruthenium complex, [(NH₃)₅Ru–O–Ru(NH₃)₄–O–Ru(NH₃)₅]⁶⁺, also known as Ru‐red, during the electro‐driven water oxidation reaction, electrochemical in situ surface enhanced Raman spectroscopy (SERS) investigations have been conducted on an electrochemically roughened gold surface in acidic condition. It was previously described that on a basal plane pyrolitic graphite electrode in 0.1 M H₂SO₄ aqueous solution, Ru‐red undergoes one electron oxidative conversion into a stable higher oxidation state ruthenium complex, Ru‐brown, at <1.0 V (vs normal hydrogen electrode (NHE)), and this leads to water oxidation and dioxygen release, but the fate of Ru‐red during electrochemistry was not studied in much detail. In this investigation, Ru‐red dispersed in acid electrolyte and immobilized on a roughened gold electrode without Ru‐red in solution has been subjected to anodic controlled potential experiments, and in situ SERS was carried out at various potentials in succession. The electrochemical SERS data obtained for Ru‐red are also compared with in situ SERS results of an electrodeposited ruthenium oxide thin film on the Au disk. Our study suggests that on a gold electrode in sulfuric acid solution containing Ru‐red, one electron oxidative conversion of Ru‐red to a higher oxidation state ruthenium compound, Ru‐brown, occurs at ca. 0.74 V (vs NHE), as supported by the electrochemical in situ SERS experiments. Moreover, at higher potentials and on Au disk, the Ru‐red / Ru‐brown are not stable and slowly decompose or electro‐oxidize leading to deactivation of the tri‐ruthenium catalytic system in acidic medium. Copyright © 2013 John Wiley & Sons, Ltd.     

Raman and surface‐enhanced Raman spectra of flavone and several hydroxy derivatives

The Raman and surface‐enhanced Raman spectra (SERS) of flavone and three of its hydroxy derivatives, 3‐hydroxyflavone (3‐HF) and 5‐hydroxyflavone (5‐HF) and quercetin (3,5,7,3′,4′ pentahydroxyflavone) have been obtained. The normal Raman (NR) spectra were taken in the powder form. The SERS spectra were obtained both on Ag colloids and Ag electrode substrates. Assignments of the spectrally observed normal modes were aided by density functional theory (DFT) calculations using the B3LYP functional and the 6‐31 + G* basis, a split valence polarized basis set with diffuse functions. Excellent fits were obtained for the observed spectra with little or no scaling. The most intense lines of the NR spectra are those in the CO stretching region (near 1600 cm⁻¹). These lines are often weakened by proximity to the surface, while other lines at lower wavenumbers, due to in‐plane ring stretches, tend to be strongly enhanced. The SERS spectrum of flavone is weak both on the colloid and on the electrode, indicating weak attachment to the surface. In contrast, the SERS spectra of the hydroxy derivatives of flavone are intense, indicating the assistance of OH groups in attachment to the surface. The spectra of the various species are compared, and a case study of application to detection of a textile dye (Persian berries), which contains quercetin, is presented. Copyright © 2007 John Wiley & Sons, Ltd.