High Resolution Tip Enhanced Raman Mapping on Polymer Thin Films

Advanced tip enhanced Raman mapping (TERM) was applied to high resolution chemical identification on nanoscale. Thin poly(methyl methacrylate)/poly(styrene acrylonitrile) (SAN28/PMMA) blend films were measured at different stages of phase separation. New insights into the phase evolution behavior of the thin films were obtained, when the TERM images were compared. An unexpected morphology transition was observed after a few minutes annealing at 250 °C. No surface enrichment of PMMA was observed, differing from the previous reports on a similar well-studied system of SAN33/PMMA. The glass transition temperature, the surface and interfacial tension were found to be the main factors responsible for the phase evolution behavior of SAN28/PMMA films.     

Towards rapid nanoscale chemical analysis using tip-enhanced Raman spectroscopy with Ag-coated dielectric tips

The influence of dielectric substrates on the Raman scattering activities of Ag overlayers has been investigated. Materials with low refractive indices, such as SiO₂, SiO_x and AlF₃, were found to provide suitable supporting platforms for Ag films to give strong surface-enhanced Raman scattering for dye molecules when illuminated at 488 nm. This finding was then extended to tip-enhanced Raman scattering (TERS). Huge enhancements of 70–80×, corresponding to net enhancements of >10⁴, were observed for brilliant cresyl blue test analyte when Ag-coated tips made from or precoated with low refractive index materials were applied. The yield of fabricated tips that significantly enhance the Raman signals was found to be close to 100%. These findings provide crucial steps towards the use of TERS as a robust technique for rapid chemical imaging with nanometer spatial resolution. Figure Silver-coated dielectric tips for tip-enhanced Raman scattering (TERS) are capable of more than 10,000-fold enhancement     

Fast Fabrication and Judgement of Tip-Enhanced Raman Spectroscopy-Active Tips

The quality of the scanning tip is crucial for tip-enhanced Raman spectroscopy (TERS) experiments towards large signal enhancement and high spatial resolution. In this work, we report a controllable fabrication method to prepare TERS-active tips by modifying the tip apex at the atomic scale, and propose two important criteria to in-situ judge the tip's TERS activity for tip-enhanced Raman measurements. One criterion is based on the downshift of the first image potential state to monitor the coupling between the far-field incident laser and near-field plasmon; the other is based on the appearance of the low-wavenumber Raman peaks associated with an atomistic protrusion at the tip apex to judge the coupling efficiency of emissions from the near field to the far field. This work provides an effective method to quickly fabricate and judge TERS-active tips before real TERS experiments on target molecules and other materials, which is believed to be instrumental for the development of TERS and other tip-enhanced spectroscopic techniques.     

适用于针尖增强拉曼技术的Au针尖的研制

采用针尖增强拉曼光谱技术(TERS)研究了刻蚀电位对Au针尖刻蚀效果的影响, 初步探讨了刻蚀过程的机理. 通过监控刻蚀过程中的振荡电流-时间曲线并与扫描电镜得到的结果比较, 发现可以直接利用电流-时间曲线简单地判断刻蚀后针尖的可能形状, 而无需再借助扫描电镜进行表征. 这不但提高了实验效率, 而且还可以避免针尖在转移和电镜表征过程中可能引入的污染. 研究结果表明, 在体积比为1:1的发烟盐酸和无水乙醇的刻蚀液中, 于2.2 V的电压下, 结合电化学方法控制终点可以得到形状对称尖锐的针尖. 这种针尖不但适合于TERS研究, 而且可用作STM针尖和微纳电极并用于其它针尖增强光学技术.     

The Association of Tetraalkylammonium Ions with Poly(vinyl methyl ether) in Water and its Effect on Phase‐Separation Behavior as Studied by Micro‐Raman Spectroscopy

Summary: The thermosensitive phase‐separation of poly(vinyl methyl ether) in water has been investigated by micro‐Raman spectroscopy in the presence of tetraalkylammonium bromides. The equilibrium distribution of both polymer and salts to the polymer‐rich and solvent‐rich phases was determined as a function of temperature. Tetraalkylammonium ions with longer alkyl chains associate more strongly with PVME and raise the phase‐transition temperature due to an increase in hydrophilicity.

     

Optical fibre SERS sensors

Surface-enhanced Raman scattering (SERS) has established itself as an important analytical technique. However, efforts to transfer the technology from the laboratory to the production line, clinic or field have been frustrated by the lack of robust affordable substrates and the complexity of interfacing between sample and spectrometer. Prompted by the success of optical fibre systems for implementing normal Raman scattering spectroscopy in remote locations and biomedical applications, attention has now shifted to the development of SERS-active optical fibres. Other workers have attempted to develop SERS probes with extended interaction lengths and both far-field and near-field SERS imaging techniques for high-resolution chemical mapping of surfaces. This review discusses the development of these technologies and presents the current state of the art. Although recent developments show great promise, some outstanding challenges and opportunities remain to be addressed.     

乙二醛诱导细胞凋亡的近红外表面增强拉曼光谱

将60 nm金纳米粒子导入到活的人骨肉瘤细胞中, 用近红外表面增强拉曼散射(SERS)技术获取细胞内化学成分的高分辨SERS信息. 对正常活性细胞和乙二醛诱导的凋亡细胞的比较研究表明, 对于正常活性的细胞, 金纳米探针主要分布在细胞质内(围绕细胞核), 而凋亡细胞内的金纳米探针的分布较为均匀, 在遍布凋亡细胞内的各个位置包括细胞表面均容易找到DNA片段的信息.     

热致相分离制备聚乳酸纳米纤维支架

本研究以二氧六环/叔丁醇为溶剂体系,采用热致相分离方法制备出具有多级孔径的三维连通的聚乳酸纳米纤维支架. 探讨了陈化、陈化温度、聚合物浓度、二氧六环/叔丁醇 (溶剂/非溶剂)比例对纳米纤维支架的结构和纤维直径大小的影响. 结果表明,陈化对较低聚合物浓度下(≤7%)纳米纤维结构的形成影响明显,而在较高聚合物浓度时(＞10%),只要控制在一定温度下相分离即可形成纳米纤维结构的支架;较低的陈化温度(≤5℃)有利于纳米纤维状网络结构(直径约20-300nm)的形成,且随着陈化温度的下降,纤维网络结构分布更加均匀;聚乳酸浓度增加, 纤维细化,网络结构分布更均匀,所形成的孔结构也更致密;叔丁醇含量≤12%时,纤维直径变化不大;当叔丁醇含量＞12%时,纤维直径明显增加(约500 nm).     

高效液相色谱法同时测定水体中氧氟沙星及其手性异构体

建立了一种简单快捷的手性配位交换高效液相色谱测定地表水中氧氟沙星及其手性异构体的方法,并研究了常见金属阳离子（Ca²⁺、Mg²⁺、Fe³⁺、Zn²⁺）和腐殖酸（HA）对二者分离的影响。采用C₁₈色谱柱（25 cm×0.46 cm,5 μm）,流动相为pH值4.5的20%（v/v）甲醇水溶液（含4 mmol/L异亮氨酸（配体）和3 mmol/L CuSO₄）,流速为1.0 mL/min,柱温为40℃,检测波长为293 nm。氧氟沙星及其手性异构体左氧氟沙星可在18 min内分离,分离度（R）为2.70。结果表明,不同金属阳离子和腐殖酸对手性分离未见明显影响,但会降低氧氟沙星及其手性异构体的峰面积,其中Fe³⁺和高浓度腐殖酸的影响最大。该法能够快速高效测定地表水中氧氟沙星及其手性异构体,但在测试中需考虑Fe³⁺和高浓度腐殖酸的影响。     

Towards chemical analysis of nanostructures in biofilms II: tip-enhanced Raman spectroscopy of alginates

This study examines the feasibility of using tip-enhanced Raman spectroscopy (TERS) for label-free chemical characterization of nanostructures in biological systems. For this purpose, a well-defined model system consisting of calcium alginate fibers is studied. In a companion paper, calcium alginate fibers and their network structures were shown to be a good model for the extracellular polysaccharides of biofilms at the nanoscale. TERS analysis of biological macromolecules, such as alginates, is complicated by heterogeneity in their sequence, molecular weight, and conformations, their small Raman cross-section, and the large number of functional groups, which can chemically interact with the silver surface of the tip and cause significant band shifts. Due to these effects, Raman frequencies in TERS spectra of biopolymers do not necessarily resemble band positions in the normal Raman spectrum of the bulk material, as is the case for less complex samples (e.g., dye molecules) studied so far. Additionally, analyte decomposition due to laser heating can have a significant influence, and carbon contamination signals can sometimes even overwhelm the weak analyte signals. Based on the investigation of alginates, strategies for spectra correction, choice of appropriate reference samples, and data interpretation are presented. With this approach, characteristic frequency ranges and specific marker bands can be found for biological macromolecules that can be employed for their identification in complex environments. Figure TERS spectrum of a calcium alginate fiber bundle     

纤维素衍生物手性固定相高效液相色谱法分离盐酸川丁特罗对映体

以纤维素三-(3,5-二甲基苯基氨基甲酸酯)为手性固定相(Lux Cellulose-1),建立了在正相色谱条件下直接分离盐酸川丁特罗对映体的高效液相色谱法。考察了乙醇、异丙醇等有机改性剂,三氟乙酸、二乙胺等流动相添加剂和柱温对对映体分离的影响。结果显示,酸性和碱性添加剂对对映体分离的影响最为显著: 添加二乙胺时两对映体无分离趋势;添加三氟乙酸时对映体保留强,且分离趋势明显;而同时添加三氟乙酸和二乙胺则两对映体分离显著改善,分离度可达4.0。优化后的色谱条件: 色谱柱为Lux Cellulose-1手性柱(250 mm×4.6 mm, 5 μm),流动相为正庚烷-乙醇-三氟乙酸-二乙胺(88:12:0.3:0.05, v/v/v/v),流速为1.0 mL/min,紫外检测波长为246 nm,柱温为25 ℃。该方法简便,快速,可用于左旋盐酸川丁特罗原料中右旋异构体杂质的检查。     

Semi-quantitative trace analysis of nuclear fast red by surface enhanced resonance Raman scattering

The dye nuclear fast red has been detected and determined semi-quantitatively by means of surface enhanced resonance Raman scattering (SERRS) and surface enhanced Raman scattering (SERS), using laser exciting wavelengths of 514.5 and 632.8 nm, respectively, by employing a citrate-reduced silver colloid. A good linear correlation is observed for the dependence of the intensities of the SERRS bands at 989 cm⁻¹ (R=0.9897) and 1278 cm⁻¹ (R=0.9872) on dye concentration over the range 10⁻⁹ to 10⁻⁷ M, when using an exciting wavelength of 514.5 nm. At dye concentrations above 10⁻⁷ M, the concentration dependence of the SERRS signals is non-linear. This is almost certainly due to the coverage of the colloidal silver particles being in excess of a full monolayer of the dye. A linear correlation is also observed for the dependence of the intensities of the SERS bands at 989 cm⁻¹ (R=0.9739) and 1278 cm⁻¹ (R=0.9838) on the dye concentration over the range 10⁻⁸ to 10⁻⁶ M when using an exciting wavelength of 632.8 nm. Strong fluorescence prevented collection of resonance Raman scattering (RRS) spectra from powdered samples or aqueous solutions of the dye using an exciting wavelength of 514.5 nm, but weak bands were observed in the spectra obtained from both powdered and aqueous samples of the dye using an exciting wavelength of 632.8 nm. A study of the pH dependence of SERRS/SERS and UV–VIS absorption spectra revealed the presence of different ionisation states of the dye. The limits of detection for nuclear fast red by SERRS (514.5 nm), SERS (632.8 nm) and visible spectroscopy (535 nm) are 9, 89 and 1000 ng ml⁻¹, respectively.     

高效液相色谱手性流动相添加法拆分奥昔布宁对映体

采用C18固定相,以羟丙基-β-环糊精为手性流动相添加剂,建立了奥昔布宁对映体的高效液相色谱拆分方法。考察了手性添加剂、有机极性调节剂、缓冲盐的种类和浓度以及流动相的pH值和流速及柱温等因素对对映体分离的影响。在最佳分离条件下,奥昔布宁对映体的分离度为1.54,检测限为1.0 ng。该方法简便,重复性好,比手性固定相法更加经济。     

Nanoscale Chemical Imaging Using Tip‐Enhanced Raman Spectroscopy: A Critical Review

Methods for chemical analysis at the nanometer scale are crucial for understanding and characterizing nanostructures of modern materials and biological systems. Tip‐enhanced Raman spectroscopy (TERS) combines the chemical information provided by Raman spectroscopy with the signal enhancement known from surface‐enhanced Raman scattering (SERS) and the high spatial resolution of atomic force microscopy (AFM) or scanning tunneling microscopy (STM). A metallic or metallized tip is illuminated by a focused laser beam and the resulting strongly enhanced electromagnetic field at the tip apex acts as a highly confined light source for Raman spectroscopic measurements. This Review focuses on the prerequisites for the efficient coupling of light to the tip as well as the shortcomings and pitfalls that have to be considered for TERS imaging, a fascinating but still challenging way to look at the nanoworld. Finally, examples from recent publications have been selected to demonstrate the potential of this technique for chemical imaging with a spatial resolution of approximately 10 nm and sensitivity down to the single‐molecule level for applications ranging from materials sciences to life sciences.     

Raman spectral study of solid and dissolved poly(vinyl alcohol) and ethylene-vinyl alcohol copolymer

We have measured the Raman spectra of ethylene-vinyl alcohol copolymer (EVOH) and poly(vinyl alcohol) (PVOH). Spectra of 88% hydrolyzed PVOH were examined from the partially crystalline solid, from PVOH dissolved in both H₂O and D₂O, and from films precipitated from these solutions. The spectrum in H₂O differs from that of the starting material by disappearance of sharp bands having Raman shift values of 1146 and 1093 cm^?1, strengthening of a band near 915 cm^?1, decrease in frequency of bands at 480, 1356, and 1441 cm^?1, and increase in frequency of bands at 369, 413, 1023, 1371, and 2910 cm^?1. The spectrum of the film shows partial reversal of these trends. With D₂O as the solvent, the band shifts are slightly different from those listed above and new bands appear. These changes are indicative of loss of crystallinity, change in stereochemistry, and partial deuteration of hydroxyl during dissolution of this PVOH sample at room temperature. © 1994 John Wiley & Sons, Inc.     

Variable-temperature UV and Raman study of complicated thermochromic phase transition of order—disorder type in poly(di-n-decylsilane) [(n-C10H21)2Si] n

A complicated thermochromic phase transition (PT) of order—disorder type in poly(di-n-decylsilane) has been studied in detail by variable-temperature UV and Raman spectroscopy. Not less than five polymer modifications were shown to participate in this PT. Above the equilibrium PT temperature T _c (60 °C), the polymer exists as a hexagonal columnar mesophase (HCM) with a disordered silicon backbone and disordered side chains. PT proceeds not abruptly but over a temperature range 60—5 °C and does not reach completion, being stopped by glassification. At room temperature, a coexistence in the polymer of HCM and a few crystalline phases with ordered backbone is observed. The latter are separated in space, what was evidenced by Raman micromapping of a polymer film. The temperature intervals of existence of different ordered phases also do not coincide, this enables one to identify in the UV and Raman spectra the components, corresponding to the modifications possessing trans (anti) and, supposedly, AD ₊ AD _– main chain conformations. As the relaxation processes in this comb-like polymer occur slowly, the quantitative ratio of different phases is not a single-valued function of temperature but depends on the thermal prehistory of the sample. Ordering of long side chains on cooling was demonstrated by the Raman method.     

Electro‐optical properties of electropolymerized poly(3‐hexylthiophene)/carbon nanotube composite thin films

3‐hexylthiophene was electropolymerized on a carbon nanotube (CNT)‐laden fluorine‐doped tin oxide substrate. Scanning electron microscopy and Raman spectroscopy revealed that the polymer was infused throughout the thickness of the 150‐nm thick CNT mat, resulting in a conducting composite film with a dense CNT network. The electropolymerized poly(3‐hexylthiophene) (e‐P3HT)/CNT composites exhibited photoluminescence intensity quenching by as much as 92% compared to the neat e‐P3HT, which provided evidence of charge transfer from the polymer phase to the CNT phase. Through‐film impedance and J‐V measurements of the composites gave a conductivity (σ) of 1.2 × 10^?10 S cm^?1 and zero‐field mobility (μ₀) of 8.5 × 10^?4 cm² V^?1 s^?1, both of which were higher than those of neat e‐P3HT films (σ = 9.9 × 10^?12 S cm^?1, μ₀ = 3 × 10^?5 cm² V^?1 s^?1). In electropolymerized samples, the thiophene rings were oriented in the (010) direction (thiophene rings parallel to substrate), which resulted in a broader optical absorbance than for spin coated samples, however, the lack of long‐range conjugation caused a blueshift in the absorbance maximum from 523 nm for unannealed regioregular P3HT (rr‐P3HT) to 470 nm for e‐P3HT. Raman spectroscopy revealed that π‐π stacking in e‐P3HT was comparable to that in rr‐P3HT and significantly higher than in regiorandom P3HT (ran‐P3HT) as shown by the principal Raman peak shift from 1444 to 1446 cm^?1 for e‐P3HT and rr‐P3HT to 1473 cm^?1 for ran‐P3HT. This work demonstrates that these polymer/CNT composites may have interesting properties for electro‐optical applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1269–1275, 2011     

Analysis of carbamate pesticides by micellar electrokinetic chromatography

Capillary elcctrophoresis (CE) was used for the qualitative and quantitative analysis of eleven compounds of the carbamate, thio-carhamate, and dithiocarbamate classes of pesticides. Micellar elec-trokinetic chromatography (MEKC) was employed for the separation of these substances. The analysis was performed using an uncoated fused silica column, in borate buffer containing SDS and 10% methanol at basic pH, and UV detection at 230 nm. The addition of methanol to the buffer increased the separation and affected intrinsic migration of analytes. The working standard solutions were prepared in acetonitrile/water 50:50. Although these compounds are structurally different, with a large spectrum of chemical properties, such as polarity and solubility, good separation and sensitivity were obtained. Moreover, good recovery of car-bamates was obtained from tap-water using a styrene-divinylben-zene polymer column with the solid phase extraction (SPE) technique.     

手性高效液相色谱法测定板蓝根中表告依春和告依春含量

采用Chiralpak IC手性柱(250 mm×4.6 mm, 5 μm),建立了正相高效液相色谱测定板蓝根中表告依春(R-告依春)和告依春(S-告依春)含量的方法。考察了流动相组成、流速和柱温对分离度的影响。经优化后的实验条件: 以正己烷-异丙醇(体积比为90:10)为流动相,流速为0.8 mL/min;检测波长为245 nm,柱温为20 ℃。在此优化条件下,表告依春和告依春分离度为3.4,检出限为2.0 mg/L,在0.02～2.0 g/L范围内有良好的线性关系,平均回收率为101%,相对标准偏差(RSD)小于3.0%(n=6)。本方法可将具有抗病毒活性的表告依春与其对映体告依春基线分离并测定,专属性强,能有效控制板蓝根的质量。     

高效液相色谱手性固定相法拆分阿折地平对映体

建立了阿折地平对映体的高效液相色谱拆分方法。采用Chiralpak AD-H (250 mm×4.6 mm, 5.0 μm, Daicel公司)手性色谱柱在正相条件下直接拆分阿折地平对映体,考察了固定相种类、流动相组成及柱温等对阿折地平对映体分离的影响。确定了最佳的拆分条件: 流动相为正己烷-异丙醇(90:10, v/v),流速为0.8 mL/min,检测波长为254 nm;柱温为20 ℃;在此条件下阿折地平对映体的分离度为3.3。该法简单快速,重现性好。