THE CHARACTERIZATION OF SILVER SUBCOLLOID USED IN SURFACE ENHANCED RAMAN SPECTROSCOPY

A clear light-yellow silver sol which has the visible spectral absorption at 390 nm, when adsorbed phenylmercaptotetrazole(PMT) or mercaptobenzothiazole(MBT), has a new absorption at 510-550 nm. It was found that the adsorption of halide ions competes with PMT and MBT. However, halide ions have a completely different influence from PMT and MBT on the spectral absorption of the silver sol. The differences may result from the change of the properties of the surface of the silver subcolloidal particles and from the bond forms combining adsorbates with the substrates.

Role of Raman spectroscopy and surface enhanced Raman spectroscopy in colorectal cancer

Colorectal cancer(CRC) is the fourth most commoncancer in the United Kingdom and is the second largest cause of cancer related death in the United Kingdom after lung cancer.Currently in the United Kingdom there is not a diagnostic test that has sufficient differentiation between patients with cancer and those without cancer so the current referral system relies on symptomatic presentation in a primary care setting.Raman spectroscopy and surface enhanced Raman spectroscopy(SERS) are forms of vibrational spectroscopy that offer a nondestructive method to gain molecular information about biological samples.The techniques offer a wide range of applications from in vivo or in vitro diagnostics using endoscopic probes,to the use of micro-spectrometers for analysis of biofluids.The techniques have the potential to detect molecular changes prior to any morphological changes occurring in the tissue and therefore could offer many possibilities to aid the detection of CRC.The purpose of this review is to look at the current state of diagnostic technology in the United Kingdom.The development of Raman spectroscopy and SERS in clinical applications relation for CRC will then be discussed.Finally,future areas of research of Raman/SERS as a clinical tool for the diagnosis of CRC are also discussed.

Application of Monodisperse Thermo-Responsive Composite Microgels with Core-Shell Structure Based on Au@Ag Bimetallic Nanorod as Core in Surface Enhanced Raman Spectroscopy Substrate

The monodisperse Au@Ag bimetallic nanorod is encapsulated by crosslinked poly( N-isopropylacrylamide)( PNIPAM) to produce thermo-responsive composite microgel with well-defined core-shell structure( Au@ Ag NR@ PNIPAM microgel)by seed-precipitation polymerization method using butenoic acid modified Au @ Ag NRs as seeds. When the temperature of the aqueous medium increases from 20℃ to 50℃,the localized surface plasmon resonance( LSPR) band of the entrapped Au @ Ag NR is pronouncedly red-shifted because of the decreased spatial distances between them as a result of shrinkage of the microgels,leading to their plasmonic coupling. The temperature tunable plasmonic coupling is demonstrated by temperature dependence of the surface enhanced Raman spectroscopy( SERS) signal of 1-naphthol in aqueous solution. Different from static plasmonic coupling modes from nanostructured assembly or array system of noble metals,the proposed plasmonic coupling can be dynamically controlled by environmental temperature. Therefore, the thermo responsive hybrid microgels have potential applications in mobile LSPR or SERS microsensors for living tissues or cells.

Facile electrochemical surface-alloying and etching of Au wires to enable high-performance substrates for surface enhanced Raman scattering

Surface-enhanced Raman Spectroscopy(SERS)is a nondestructive technique for rapid detection of analytes even at the single-molecule level.However,highly sensitive and reliable SERS substrates are mostly fabricated with complex nanofabrication techniques,greatly restricting their practical applications.A convenient electrochemical method for transforming the surface of commercial gold wires/foils into silver-alloyed nanostructures is demonstrated in this report.Au substrates are treated with repetitive anodic and cathodic bias in an electrolyte of thiourea,in a one-pot one-step manner.X-rays absorption fine structure(XAFS)spectroscopy confirms that the AuAg alloy is induced at the surface.The unique AuAg alloyed surface nanostructures are particularly advantageous when served as SERS substrates,enabling a remarkably sensitive detection of Rhodamine B(a detection limit of 10^(-14)M,and uniform strong response throughout the substrates at 10^(-12)M).

Synthesis of magnetic polyphosphazene-Ag composite particles as surface enhanced Raman spectroscopy substrates for the detection of melamine

Magnetic polyphosphazene(MPZS) particles coated by Ag nanoparticles(MPZS-Ag) have been developed as surface enhanced Raman spectroscopy(SERS) substrates for sensitive detection of melamine in aqueous solutions and milk samples.5,5’-Dithiobis-(2-nitrobenzoic acid)(DTNB) was used as model analyte to test the SERS activity of the MPZS-Ag particles.The prepared MPZS-Ag particles possess both magnetic responsiveness and excellent SERS properties.SERS detection of different concentrations of melamine aqueous solutions and spiked milk samples were performed by the MPZS-Ag particles.The limit of detection(LOD) of the melamine in aqueous solutions was 10^-7 mol/L(0.0126 mg/L) and 0.6 mg/L in real milk samples using the MPZS-Ag particles as SERS substrates.The LOD of the melamine are much lower than the safety values of Food and Drug Administration and Codex Alimentarius Commission.These results indicate that the MPZS-Ag particles have promising application prospect for SERS analysis in food safety fields.

Detection of chlorpyrifos in apples using gold nanoparticles based on surface enhanced Raman spectroscopy

In this study,gold nanoparticles(AuNPs)were synthesized for rapid and sensitive characterization and quantification of chlorpyrifos in apples.Min-max signal adaptive zooming and second derivative transformation method were adopted to pre-process Raman spectral signal.The min-max signal adaptive zooming method showed a higher correlation coefficient than derivative transformation when developing linear calibration curve between chlorpyrifos pesticide and Raman spectral peak intensity.The present method had a high reproducibility with the relative standard deviation less than 15%.Regression models showed a good linear relationship(R=0.962)between intensity of characteristic spectral peaks(at 677 cm-1)and chlorpyrifos concentration on whole apples ranging from 0.13 mg/kg to 7.59 mg/kg.The application of surface enhancement Raman spectroscopy(SERS)detected chlorpyrifos pesticide to the detection limit of 0.13 mg/kg,which can be applied further for lower concentration in the future.The method presented in this study can provide a way-out for detection of pesticide residue in whole apple to trace amount.

Sensitive and Label-Free Detection of Protein Secondary Structure by Amide Ⅲ Spectral Signals using Surface-Enhanced Raman Spectroscopy

Proteins and peptides perform a vital role in living systems, however it remains a challenge for accurate description of proteins at the molecular level. Despite that surface-enhanced Raman spectroscopy (SERS) can provide the intrinsic fingerprint information of samples with ultrahigh sensitivity, it suffers from the poor reproducibility and reliability. Herein, we demonstrate that the silver nanorod array fabricated by an oblique angle deposition method is a powerful substrate for SERS to probe the protein secondary structures without exogenous labels. With this method, the SERS signals of two typical proteins (lysozyme and cytochrome c) are successfully obtained. Additionally, by analyzing the spectral signals of the amide Ⅲ of protein backbone, the influence of concentration on the folding status of proteins has been elucidated. With the concentration increasing, the components of α-helix and β-sheet structures of lysozyme increase while the secondary structures of cytochrome c almost keep constant. The SERS method in this work offers an effective optical marker to characterize the structures of proteins.

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.

Rapid Identification of Legionella Pathogenicity by Surface-Enhanced Raman Spectroscopy

Objective To establish Surface-enhanced Raman Spectroscopy（SERS） can be used as a rapid and reliable method to distinguish virulent strain and mild strain of L. pneumophila. Methods We isolated and characterized of bacterial strains from ATCC and water samples strains, while we analyzed data from SERS technology using gold nanoparticles as a base and cell infections were employed to rapidly detect L. pneumophila strains. Origin 8.0 was used to collect Raman spectra, smooth and homogenize data, and to contrast spectra. Principal component analysis（PCA） was conducted to discriminate differences between groups using the multivariate analysis package Py Chem 3.0.5. Results Our results indicated that the peaks of high virulence strains reached ≥4000. This criterion was verified by subsequent cell experiments. In addition, we also conducted SERS rapid identification on the virulence of several collected clinical strains and obtained accurate results. Conclusion The present study indicates that the established SERS protocol can be used as a rapid and reliable method to distinguish virulent and mildly virulent strains of L. pneumophila, which can be further used in clinical samples.

Structure of water at ionic liquid/Ag interface probed by surface enhanced Raman spectroscopy

The potential-dependent adsorption behavior of water and ionic liquid was probed by surface-enhanced Raman spectroscopy （SERS） at the Ag electrode surface in the ionic liquids containing water with different concentrations. The configuration of water at the ionic liquid/electrode interface and the relationship between the potential of zero charge （pzc） and the molar frac- tion of water were deduced through the changes in the vibrational frequency of OH stretching mode. A small Stark effect value was determined in the system with lower molar fraction of water. With the increase of the water concentration, the OH stretching vibrational frequency gradually shifted to the high wavenumber region, the pzc was also moved positively, and the Stark effect value of OH stretching vibrational mode increased. It reached about 76 cm-1 V-I in the 1 tool L-1 [BMIM]Br aqueous solution. These differences were mainly contributed by hydrogen bonding and the configuration of water in the ionic liquid solution. In the solution with lower water content, water molecules existed at the interface layer through hydrogen bond- ing with cations, while in the higher content solution, the intermolecular hydrogen bonding between water molecules was strengthened and the possibility of the direct interaction between the water molecule and electrode surface increased.

Monitoring the penetration and accumulation of gold nanoparticles in rat skin ex vivo using surface-enhanced Raman scattering spectroscopy

Contamination by accidental cutaneous contact with the commercial products and the air pol-hutants raised a considerable health and safety issue.This study aimed to trace the dynamics of the 20 nm gold nanopartide(GNP)penetration and accumulation in rat skin tissues using a surface-enhanced Raman scattering(SERS)techmique.After the topical application of GNPs on rat skin surface,the SERS spectra were recorded for every 15 pum to an overall depth of 75 pum from skin surface for 150 min.The processes of GNP penetration in rat skin were accompanied by aggregation of GNPs,which affected SERS spectra.The results revealed that 20 nm GNPs can penetrate through stratum corneum layer,viable epidermis layer,and then into dermis layer.This study demonstrated for the first time the potential of SERS spectroscopy to monitor the penetration and accumulation of GNPs in rat skin.

Probing the role of surface speciation of tin oxide and tin catalysts on CO_(2) electroreduction combining in situ Raman spectroscopy and reactivity investigations

Electrochemical CO_(2)reduction to formate is a promising approach to store renewable electricity and utilize CO_(2).Tin oxide catalysts are efficient catalysts for this process,while the mechanisms underneath,especially the existence and role of oxidized tin species under CO2 electroreduction conditions remain unclear.In this work,we provide strong evidence on the presence of oxidized tin species on both SnO_(2)and Sn during CO_(2)reduction via in situ surface‐enhanced Raman spectroscopy,while in different nature.Reactivity measurements show similar activity and selectivity to formate production on SnO_(2)and Sn catalysts.Combined analysis of Raman spectra and reactivity results suggests that Sn(IV)and Sn(II)oxide species are unlikely the catalytic species in CO_(2)electroreduction to formate.

Raman光谱对离子液体及其可支撑离子液体膜的表征

利用Raman及其表面增强Raman光谱对不同阴离子的3种丁基咪唑离子液体及其负载膜的结构进行测定分析表征.结果表明:3种离子液体其[C4mim]+阳离子结构非常相近,受不同阴离子的影响较小.在室温常压下阳离子[C4mim]+同时存在偏移和扭转两种同分异构体.相比于亲水性支撑离子液体膜,疏水性PVDF可支撑离子液体膜的普通Raman难以测定,采用以银溶胶作为表面增强活性基底的表面增强Raman与亲水性可支撑离子液体膜的普通Raman,以及纯离子液体的普通Raman高度一致,充分显示出表面增强Raman光谱对支撑离子液体膜结构表征的适用性及优越性,为今后在离子液体膜方面的Raman研究开启了新的方向.

Study on gastric cancer blood plasma based on surface-enhanced Raman spectroscopy combined with multivariate analysis

A surface-enhanced Raman spectroscopy (SERS) method combined with multivariate analysis was developed for non-invasive gastric cancer detection. SERS measurements were performed on two groups of blood plasma samples: one group from 32 gastric patients and the other group from 33 healthy volunteers. Tentative assignments of the Raman bands in the measured SERS spectra suggest interesting cancer-specific biomolecular changes, including an increase in the relative amounts of nucleic acid, collagen, phospholipids and phenylalanine and a decrease in the percentage of amino acids and saccharide in the blood plasma of gastric cancer patients as compared with those of healthy subjects. Principal components analysis (PCA) and linear discriminant analysis (LDA) were employed to develop effective diagnostic algorithms for classification of SERS spectra between normal and cancer plasma with high sensitivity (79.5%) and specificity (91%). A receiver operating characteristic (ROC) curve was employed to assess the accuracy of diagnostic algorithms based on PCA-LDA. The results from this exploratory study demonstrate that SERS plasma analysis combined with PCA-LDA has tremendous potential for the non-invasive detection of gastric cancers.

One-pot synthesis of silver colloid with body-heat for surface-enhanced Raman spectroscopy detections

In this study,a convenient method of preparing the substrate is proposed with one-pot synthesis of silver colloid under body heat,and the SERS detection uses the fresh substrate to avoid the drawback of substrates’short life of use.The synthesis of silver colloid is carried out in a 10 mL vial by using ascorbic acid as a reductant and trisodium citrate as a stabilizer.The vial is grasped with the palm of the experimenter for several minutes without shaking.The proposed method is simple,rapid,green energy and cost-effective.By adjusting the concentration of trisodium citrate,not only the particle size can be controlled from about 110 nm to 50 nm but also the homogeneity of nanoparticles can be improved.As a SERS substrate,the silver colloid has high batch reproducibility and showed good SERS activity.The relative standard deviation between different manufacturers is 5.51%when the substrate of silver colloid is used for the detection of rhodamine 6 G.Using the substrate,the lowest detection concentrations of rhodamine 6 G,crystal violet,enrofloxacin,melamine and leucomalachite green are 1.0×10-8,6.1×10-8,1.4×10-6,7.1×10-5 and 5.1×10-8 mol/L,respectively.Results demonstrate that the developed method has the advantage of convenience and high efficiency in the field preparation of reliable SERS substrate.

Rapid Detection of Sildenafil Drugs in Liquid Nutraceuticals Based on Surface-Enhanced Raman Spectroscopy Technology

In this study, surface-enhanced Raman Spectroscopy （SERS） technology was used to rapidly detect illegally added sildenafil drugs. A detailed attribution analysis by density functional theory （DFT） was used to guide specific experiments. The Raman signals were obtained from a silver colloid （Ag col） substrate, and they increased in the presence of the mineral salt, potassium iodide （KI）. These methods detected sildenafil in aqueous solutions as low as 1 μg/mL with high signal uniformity （RSD=3.77%）. Prior to this study, traditional Raman techniques detected substances in solid samples only. Here, Raman technology detected low contents of sildenaful drugs in liquid nutraceuticals. Therefore, SERS technology has great potential for on-site and real-time detection of illegal drugs in water and in liquid nutraceuticals.

Detection of pesticides on navel orange skin by surface-enhanced Raman spectroscopy coupled with Ag nanostructures

Residual pesticides such as phosmet and chlorpyrifos in fruit have become a public concern problem in recent years.In this study,surface-enhanced Raman spectroscopy(SERS)was used to detect and characterize pesticides extracted from navel orange surfaces.Silver colloid was prepared for getting the SERS of phosmet and chlorpyrifos.Enhanced Raman signals of phosmet over a concentration range of 5 mg/L to 30 mg/L and chlorpyrifos over a concentration range of 5 mg/L to 20 mg/L were acquired.Partial least squares(PLS)regression combined with different data preprocessing methods was used to develop quantitative models.With the second derivative data preprocessing,the best prediction model of phosmet pesticide was achieved with a correlation coefficient(r)of 0.852 and the root mean square error of prediction(RMSEP)of 5.177 mg/L.The best prediction model of chlorpyrifos pesticide was achieved with r of 0.843 and the RMSEP of 2.992 mg/L using the multiplicative scatter correction(MSC)and first derivative data preprocessing.This study indicated that SERS coupled with Ag nanostructures is a potential tool for analysis of phosmet and chlorpyrifos pesticide residues.

Stable and unique graphitic Raman internal standard nanocapsules for surface-enhanced Raman spectroscopy quantitative analysis

Graphitic nanomaterials have unique, strong, and stable Raman vibrations that have been widely applied in chemistry and biomedicine. However, utilizing them as internal standards （ISs） to improve the accuracy of surface-enhanced Raman spectroscopy （SERS） analysis has not been attempted. Herein, we report the design of a unique IS nanostructure consisting of a large number of gold nanoparticles （AuNPs） decorated on multilayered graphitic magnetic nanocapsules （AGNs） to quantify the analyte and eliminate the problems associated with traditional ISs. The AGNs demonstrated a unique Raman band from the graphitic component, which was localized in the Raman silent region of the biomolecules, making them an ideal IS for quantitative Raman analysis without any background interference. The IS signal from the AGNs also indicated superior stability, even under harsh conditions. With the enhancement of the decorated AuNPs, the AGN nanostructures greatly improved the quantitative accuracy of SERS, in particular the exclusion of quantitative errors resulting from collection loss and non-uniform distribution of the analytes. The AGNs were further utilized for cell staining and Raman imaging, and they showed great promise for applications in biomedicine.

Preparation of Large-area Controllable Patterned Silver Nanocrystals for High Sensitive and Stable Surface-enhanced Raman Spectroscopy

A novel and facile method for fabricating large-area pattemed silver nanocrystals was introduced and the investigation on the high sensitive and stable surface-enhanced Raman spectroscopy（SERS） of the nanocrystals was carried out. Nanostructured silicon substrate was processed by laser interference and used as a template for growing silver nanocrystals via galvanic battery reaction method. The substrate with large area for violent chemical reaction was tailored into a nanocell array. The limited reaction area hindered the growth of silver nanocrystals and made their size uniform and controllable. The size and gaps of the nanocrystals could be controlled by template period and ratio, which were easily reproduced by laser interference. Taking 10^-8 to 10^-11 mol/L RhoG for example, the optimized silver arrays exhibited great potential for ultrasensitive molecular sensing in terms of its high SERS enhancement ability, favorable stability, and excellent reproducibility.

Diagnosis of breast cancer by analysis of sialic acid concentrations in human saliva by surface-enhanced Raman spectroscopy of silver nanoparticles

Breast cancer is the most common type of malignant tumor among women and their second leading cause of cancer-related deaths.The most common method for screening and diagnosis is mammography.Nonetheless,two main problems have been identified.First,the dose of radiation received during the test prevents the method from the use on women who are 〈 40 years old.Second,there can be mammogram failure owing to the lack of tumor contrast with the fibrous tissue.Therefore,there is a need for screening methods that will help to identify high-risk cases.We developed a biological marker test that can help to identify them.Increased levels of sialic acid （SA） in saliva are known to correlated with breast cancer.In this study,we evaluated the feasibility of Raman spectroscopy as a method for quantification of SA in saliva,using citrate-reduced silver nanoparticles （cit-Ag-NPs） as a surface-enhanced Raman spectroscopy （SERS） substrate.Quantification of SA was accomplished by measuring its intensity in saliva and comparing it with a calibration curve of SA standards.The mean SA concentration in saliva was found to be significantly higher among 100 breast cancer patients （18.3 ＆#177; 9.4 mg＆#183;dL-1;mean ＆#177; SD） than among 106 healthy controls （3.5 ＆#177; 1.0 mg＆#183;dL-1）.The SERS test showed sensitivity of 94% and specificity 98% for detection of patients with breast cancer,assuming that SA concentration 〉 7 mg＆#183;dL-1 is a cutoff for positive test results.Our findings prove the usefulness of this SERS technique as a simple,convenient,and highly sensitive method of quantitative analysis of SA in saliva.The simplicity of this nanotechnological test may help to substantially reduce the mortality among patients with breast cancer by providing women with a simple,noninvasive screening test that can be applied regardless of age or density of breast tissue.