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1.
    
We utilize a novel, high-power, tunable, continuous wave (CW) deep UV laser to measure resonance Raman spectra of phenolate solutions with high signal-to-noise ratios (SNR). In UV resonance Raman (UVRR), increased coupling of the excitation light with a chromophore can transfer molecules into excited states that cause increased heating and photochemistry. Deep UV lasers have traditionally utilized high peak powers to enable efficient single-pass nonlinear conversion from visible into near infrared light. Nonlinear phenomena such as the formation of transient radical species, Raman saturation, thermal heating, and dielectric breakdown can introduce extraneous light sources that can complicate the interpretation of the Raman spectrum. Dielectric breakdown can increase the baseline, increase noise, and sometimes saturate the detector, preventing Raman detection. Spontaneous Raman scattering intensities should scale linearly with the excitation light intensity. However, this linear behavior does not always occur with pulsed laser excitation. This occurs because stimulated Raman scattering can cause a superlinear intensity response, or transient absorption can cause sublinear intensity responses. CW laser excitation excites samples with electric fields that are much lower than typical pulsed laser excitation. This eliminates the nonlinear responses. The geometry of our new CW laser enables high gain in the harmonic generation cavities that achieve high harmonic generation efficiencies. Average power in the deep UV is >30 mW for wavelengths as short as 206 nm. In the work here, we demonstrate that CW excitation is ideal for resonance Raman measurements in general to reduce spectral complexity.  相似文献   

2.
    
Raman spectra of the monocytes were recorded with laser excitation at 532, 785, 830, and 244 nm. The measurements of the Raman spectra of monocytes excited with visible, near‐infrared (NIR), and ultraviolet (UV) lasers lad to the following conclusions. (1) The Raman peak pattern of the monocytes can be easily distinguished from those of HeLa and yeast cells; (2) Positions of the Raman peaks of the dried cell are in coincidence with those of the monocytes in a culture cell media. However, the relative intensities of the peaks are changed: the peak centered around 1045 cm−1 is strongly intensified. (3) Raman spectra of the dead monocytes are similar to those of living cells with only one exception: the Raman peak centered around 1004 cm−1 associated with breathing mode of phenylalanine is strongly intensified. The Raman spectra of monocytes excited with 244‐nm UV laser were measured on cells in a cell culture medium. A peak centered at 1485 cm−1 dominates the UV Raman spectra of monocytes. The ratio I1574/I1613 for monocytes is found to be around 0.71. This number reflects the ratio between proteins and DNA content inside a cell and it is found to be twice as high as that of E. coli and 5 times as high as that of gram‐positive bacteria. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

3.
    
Raman spectra obtained by UV laser excitation above 260 nm are contaminated by spectrally overlapping UV-excited fluorescence. Here, we demonstrate a picosecond UV Kerr-gated Raman spectroscopy setup to suppress the fluorescence in Raman spectra excited by 280 nm laser pulses. Specifically, we use a model sample that consists of acetonitrile contaminated by a small amount of toluene for generating UV-excited fluorescence. We were able to acquire a Raman spectrum of acetonitrile by suppressing the UV-excited fluorescence of toluene by the action of a 1-mm thick fused silica-based UV Kerr gate operated by 1030 nm, ~1 ps gating pulses. These results also indicate the challenges that must be overcome in the future for realizing UV-fluorescence-free UV resonance Raman (UVRR) spectroscopy studies of molecules exhibiting electronic resonances around 280 nm using laser excitation wavelengths right at or close to this resonance.  相似文献   

4.
    
Spectroscopic methods based on Raman scattering have for many years employed synthetic oligonucleotides in a broad range of applications, either as probes or as model analytes for biophysical investigations. Benzamide is commonly used as a protecting group in the phosphoramidite synthesis of oligonucleotides and, while standard desalting used after synthesis yields sufficiently pure reagents for most assay reactions or other routine uses of the oligomer, it does not completely remove benzamide. We show that the 1609 cm−1 band of residual benzamide contamination can interfere with certain nucleic acid bands, particularly when using excitation wavelengths near 244 nm where the benzamide band is strongly enhanced. For example, the 1609 cm−1 band of benzamide could obscure (or be mistaken as) a weak vibration attributed to an  NH2 scissoring. The extent of benzamide contamination in desalted preparations varies considerably among different commercial sources, and hence caution is advised when making direct comparisons of ultraviolet Raman data of oligonucleotides from different sources. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

5.
    
Time‐resolved Raman spectroscopy, spatially offset Raman spectroscopy and time‐resolved spatially offset Raman spectroscopy (TR‐SORS) have proven their capability for the non‐invasive profiling of deep layers of a sample. Recent studies have indicated that TR‐SORS exhibits an enhanced selectivity toward the deep layers of a sample. However, the enhanced depth profiling efficiency of TR‐SORS, in comparison with time‐resolved Raman spectroscopy and spatially offset Raman spectroscopy, is yet to be assessed and explained in accordance to the synergistic effects of spatial and temporal resolutions. This study provides a critical investigation of the depth profiling efficiency of the three deep Raman techniques. The study compares the efficiency of the various deep Raman spectroscopy techniques for the stand‐off detection of explosive precursors hidden in highly fluorescing packaging. The study explains for the first time the synergistic effects of spatial and temporal resolutions in the deep Raman techniques and their impact on the acquired spectral data. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

6.
本文给出了紫外激发下的PNBA水溶液的拉曼光谱图,并对图中峰位做了相应的归属认证。本文还报道了PNBA在银胶中的表面非增强拉曼散射现象,并分析了导致该现象可能的原因  相似文献   

7.
    
The partitioning of a hydrophobic hexapeptide, N‐acetyl‐tryptophan‐pentaleucine (AcWL5), into self‐associated β‐sheets within a vesicle membrane was studied as a model for integral membrane protein folding and insertion via vibrational and electronic spectroscopy. Ultraviolet resonance Raman spectroscopy allows selective examination of the structures of amino acid side chains and the peptide backbone and provides information about local environment and molecular conformation. The secondary structure of AcWL5 within a vesicle membrane was investigated using 207.5‐nm excitation and found to consist of β‐sheets, in agreement with previous studies. The β‐sheet peptide shows enhanced Raman scattering cross‐sections for all amide modes as well as extensive hydrogen‐bonding networks. Tryptophan vibrational structure was probed using 230‐nm excitation. Increases in Raman cross‐sections of tryptophan modes W1, W3, W7, W10, W16, W17, and W18 of membrane‐incorporated AcWL5 are primarily attributed to greater resonance enhancement with the Bb electronic transition. The W17 mode, however, undergoes a much greater enhancement than is expected for a simple resonance effect, and this observation is discussed in terms of hydrogen bonding of the indole ring in a hydrophobic environment. The observed tryptophan mode frequencies and intensities overall support a hydrophobic environment for the indole ring within a vesicle, and these results have implications for the location of tryptophan in membrane protein systems. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

8.
    
Deep-learning-based spectral identification received intensive interests benefiting from the availability of large scale spectral databases. However, for the identification of spectroscopic data such as Raman, the massive experimental data remained challenging, impeding the application of deep neural networks. Here, we describe a new approach with a transfer-learning model pretrained on a standard Raman spectral database for the identification of Raman spectra data of organic compounds that are not included in the database and with limited data. Our results show that, with transfer learning, classification accuracy improvement of our convolutional neural network reaches 4.1% and that of our fully connected deep neural network reaches 5.0%. By investigating the influence of the source datasets, we find that our transfer learning method is able to incorporate both relevant and seemingly irrelevant source datasets for pretraining, and the relevant source dataset brings better classification accuracy than that of the seemingly irrelevant source dataset. This study demonstrates that the transfer learning technique has great potential in the effective identification of Raman spectra when the number of Raman data is limited.  相似文献   

9.
    
As the silicon industry continues to push the limits of device dimensions, tools such as Raman spectroscopy are ideal to analyze and characterize the doped silicon channels. The effect of inter‐valence band transitions on the zone center optical phonon in heavily p‐type doped silicon is studied by Raman spectroscopy for a wide range of excitation wavelengths extending from the red (632.8 nm) into the ultra‐violet (325 nm). The asymmetry in the one‐phonon Raman lineshape is attributed to a Fano interference involving the overlap of a continuum of electronic excitations with a discrete phonon state. We identify a transition above and below the one‐dimensional critical point (E = 3.4 eV) in the electronic excitation spectrum of silicon. The relationship between the anisotropic silicon band structure and the penetration depth is discussed in the context of possible device applications. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

10.
    
The molten globule (MG) state can aid in the folding of a protein to a functional structure and is loosely defined as an increase in structural disorder with conservation of the ensemble secondary structure content. Simultaneous observation of persistent secondary structure content with increased disorder has remained experimentally problematic. As a consequence, modeling how the MG state remains stable and how it facilitates proper folding remains difficult due to a lack of amenable spectroscopic techniques to characterize this class of partially unfolded proteins. Previously, deep‐UV resonance Raman (dUVRR) spectroscopy has proven useful in the resolution of global and local structural fluctuations in the secondary structure of proteins. In this work, dUVRR was employed to study the MG to ordered transition of a model four‐helix bundle protein, HP7. Both the average ensemble secondary structure and types of local disorder were monitored, without perturbation of the solvent, pH, or temperature. The MG to ordered transition is induced by stepwise coordination of two heme molecules. Persistent dUVRR spectral features in the amide III region at 1295–1301 and 1335–1338 cm−1 confirm previous observations that HP7 remains predominantly helical in the MG versus the fully ordered state. Additionally, these spectra represent the first demonstration of conserved helical content in a MG protein. With successive heme binding, significant losses are observed in the spectral intensity of the amide III3 and S regions (1230–1260 and 1390 cm−1, respectively), which are known to be sensitive to local disorder. These observations indicate that there is a decrease in the structural populations able to explore various extended conformations with successive heme binding events. DUVRR spectra indicate that the first heme coordination between two helical segments diminishes exploration of more elongated backbone structural conformations in the inter‐helical regions. A second heme coordination by the remaining two helices further restricts protein motion. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

11.
    
The damage induced by heavy-ion irradiation has been studied in yttrium iron garnet (Y3Fe5O12 or YIG) films, doped with Ca, Tb and Tm, grown by liquid-phase epitaxy on gadolinium gallium garnet (Gd3Ga5O12 or GGG) substrates. Irradiations of doped-YIG epitaxial films and GGG substrates with 36-MeV 183W and 12-MeV 197Au ions were applied for fluences between 1 × 1013 and 3 × 1015 cm–2 near room temperature. The radiation damage was monitored by micro-Raman spectroscopy and UV–visible optical absorption spectroscopy. Raman spectra revealed that amorphisation was achieved in YIG for both ions, whereas a high lattice disorder was induced in GGG without reaching amorphisation for the Au ion irradiation. Raman spectra also showed that a major damage of the tetrahedral sites was induced in GGG, as previously found for YIG. It is concluded that with such ions reaching the stopping power threshold of track formation in YIG and GGG the observed rate of amorphisation may result from a combination of electronic and nuclear energy losses as calculated using the unified thermal spike model.  相似文献   

12.
紫外拉曼光谱具有拉曼散射强度高、易于荧光光谱分离、受环境干扰影响小以及人眼安全性高等特性,所用的紫外拉曼光谱仪采用波长266 nm激光器,拉曼和荧光光谱会有部分重叠,增加了准确获取拉曼光谱特征信息的难度,进一步影响样品的辨识。因此,需要在分析拉曼光谱之前进行基线校正来消除荧光干扰。根据紫外拉曼+荧光混合光谱中,荧光光谱具有逐渐增加且接近分段线性递增的特点,利用分段线性函数拟合荧光光谱基线是一种较简捷的方法,于是针对传统分段线性拟合基线校正方法基线点定义过度依赖操作人员、自动化水平较低等问题,研究了一种改进的紫外拉曼光谱分段线性拟合基线校正方法：(1)首先求原始信号经不同次平滑迭代后的光谱数据。由于波峰相对于基线是高频信号,在多次平滑过程中,波峰附近的光谱强度逐渐下降且变化较大,基线部分逐渐上升且相对变化很小,经不同次迭代平滑的光谱波峰和基线点处的光谱强度标准差SD差异较大。(2)然后通过对光谱强度偏差的比较确定准有效基线点位置。通过适当设定的阈值SD0提取出准有效基线点位置;(3)再利用线性迭代拟合法提取并修正过校正基线点。准有效基线点将整个拉曼光谱分割成N个特征峰区间,分别连接特征峰区间两端点得到一条直线,若特征峰全部在直线以上表明不存在过校正,否则区间端点向其峰方向移动并再次直线连接,重复以上过程,直到特征峰全部在直线以上,得到有效基线点;(4)最后逐段直线连接所有相邻有效基线点得到整个光谱的基线。原始光谱减去基线就是基线校正后的拉曼光谱。通过对模拟和实际测量的紫外混合光谱的基线校正处理实验表明：该方法能自动确定基线点位置,且较传统方法能获得更好的基线校正效果,为下一步的光谱分析提供更准确的光谱信息。  相似文献   

13.
β-胡萝卜素广泛存在于植物体中,是典型的线性多稀分子,具有重要的生物功能。由于β-胡萝卜素是碳碳单、双键(C-C,C=C)交替的短链共轭多稀分子,含有大量离域的π电子,具有重要的光电特性。根据Andreas等对拉曼散射强度的研究,当激发光波长落在分子的电子吸收带时,会产生共振拉曼效应,能使拉曼光谱强度提高106倍。利用共振拉曼光谱技术,测量了β胡萝卜素分子及胡萝卜、青萝卜、白萝卜肉质直根不同部位其拉曼光谱,发现含β-胡萝卜素较高的胡萝卜的拉曼光谱与β-胡萝卜素的吻合很好。Gellerman等研究表明,样品浓度与拉曼峰强成正比关系,从拉曼光谱中容易发现三种萝卜的光谱强度纵向根头到主根及横向表皮到根芯逐渐降低,且青萝卜和白萝卜拉曼光谱强度都很低,并在碳碳单键的振动峰处发生峰劈裂。分别计算了碳碳单键和碳碳双键与碳氢键拉曼强度比,三种萝卜的ICC/IC-H随着测量部位(横向和纵向)的不同变化幅度接近：胡萝卜的表皮和根芯纵向的变化率分别为A1=0.213 3和A2=0.215 9,青萝卜表皮外和里的变化率分别为B1=0.219 1和B2=0.211 4,白萝卜表皮外和里分别为D1=0.223 9和D2=0.224 1;而对于IC-C/IC-H随着测量部位不同其变化率相差很大：胡萝卜的变化率a1=0.212 1和a2=0.232 4,青萝卜的变化率b1=0.263 5和b2=0.268 7,白萝卜的变化率d1=0.369 0和d2=0.304 9。对比发现三种萝卜的碳碳单键与碳氢键振动强度比随着测量部位的不同变化幅度相差很大,而从碳碳双键与碳氢键振动强度比发现三种萝卜中不同部位的β胡萝卜含量有相似的分布。这是由于青萝卜和白萝卜中β-胡萝卜素的含量少, 随着测量部位的不同C-C伸缩振动峰发生峰劈裂, 即在1 130和1 156 cm-1处出现两个振动峰, 经过计算和分析这两个峰都属于碳碳单键的伸缩振动峰, 且随着β-胡萝卜素含量的减少C-C整体的强度降低, 劈裂的新峰峰强度却有增加的趋势, 这使得原峰位的峰强度大幅度降低, 这与计算IC-C/IC-H的结果一致,不同品种的萝卜中β-胡萝卜素含量随测量部位的不同变化幅度截然不同。因此, 当样品中β-胡萝卜含量较少时,利用C=C振动峰峰强度同时分析样品不同部位的β-胡萝卜素含量分布变化会更准确。同时,研究和了解萝卜中不同部位β-胡萝卜素的含量为日常消费和膳食营养提供了很好的理论依据。  相似文献   

14.
    
Here we demonstrate the simultaneous recovery of multiplexed physical information of surface-enhanced Raman scattering (SERS) nanoparticles (pH and depth) using deep Raman spectroscopy. As has been shown previously and in accordance with theory, inelastically scattered photons arising from spectral peaks that are suitably separated can exhibit different optical properties in the media through which they travel. These differences can impact the relative intensities of the Raman peaks as a function of the transmission path length; thereby, the depth of signal generation is inherently encoded in the spectra; assuming the target is clustered at a single depth or location, its depth can be readily determined. Moreover, Raman spectroscopy is very sensitive to chemistry of a sample, and changes in pH are observed not only as changes in peak intensity through relevant protonation and deprotonation but also as shifts in spectral features. Here, we show it is possible to precisely predict the depth (root-mean-square error [RMSE] 5 %) of SERS nanoparticles in scattering media (0.5% intralipid) while also being able to noninvasively monitor simultaneously the pH levels (RMSE ~0.2 pH units) of the media surrounding the nanoparticles. This is important as it demonstrates that nanoparticles can be used to report on multiple physical properties including their depth. This opens avenues for a range of new applications including the noninvasive diagnosis and localisation of cancer lesions in clinical environment in vivo.  相似文献   

15.
转基因技术对实现作物增产增质,降低农药使用量,降低生产成本等具有重要作用,但对生态环境也存在一定的潜在威胁。为了防止转基因大豆在食品化中的滥用,对转基因产品快速鉴别技术的研究尤为迫切。紫外拉曼光谱检测技术具备外场远距离无损遥测检测,简单高效,快速准确等优点,可有效用于物质遥测鉴别领域。基于紫外拉曼光谱的转基因/非转基因大豆油以及与其他类别食用油鉴别方法,采集了五种不同食用油(两种品牌转基因/非转基因大豆油各500组样本和一种稻米油100组样本,共2 100组样本)在3 500~400 cm-1(268~293 nm)范围内的日盲紫外拉曼光谱信息,为提高光谱数据的信噪比并保证分类识别的准确性,对上述光谱数据采用Savitzky-Golay滤波降噪、基于自适应迭代加权惩罚最小二乘法(airPLS)的基线校正以及多元散射校正(MSC)的光谱数据修正等预处理。根据大豆油的紫外拉曼指纹图谱,分析出主要化学成分包含脂肪类、蛋白质类、酰胺类。将每种大豆油样本按1∶1划分为训练集和测试集,输入训练集数据至支持向量机(SVM)进行训练,采用10折交叉验证建立最佳模型,识别准确率达99.81%,对转基因大豆油的判别效果显著;采用主成分分析法(PCA)进行数据降维处理,提取出8个主成分,累计贡献率为74.84%,可代表大部分原始数据特征。在此基础上,将预处理后的光谱数据按4∶1划分为训练集和测试集,采用偏最小二乘回归判别分析方法(PLS-DA),结合10折交叉验证法建立全谱的最佳PLS-DA模型(判别阈值设置为0.5),判别准确率达到70.95%。研究表明,紫外拉曼光谱分析方法可较为准确地鉴别非转基因/转基因大豆油,同时可鉴别大豆油与稻米油,实现对转基因大豆食品的快速无损鉴别,可望成为转基因大豆油及其食品的现场检测新的技术途径,对推动转基因产品遥测鉴别技术的发展具有进步意义。  相似文献   

16.
UV–visible, infrared and Raman spectra, together with thermal properties, were measured for glasses from the system Bi2O3–B2O3–V2O5 before and after successive gamma irradiations. The UV–visible spectrum of the undoped glass before irradiation reveals five UV bands at 210, 275, 310, 350 nm, an intense band at 380 nm and a visible band at 420 nm due to the possible combined presence of trace iron impurities and Bi3+ ions. The V-doped glasses reveal six UV bands and two visible bands, probably arising from vanadium ions in three possible valencies, V3+, V4+ and V5+, beside that due to trace iron impurity beside Bi3+ ions. The spectra reveal an obvious resistance of the glasses to successive gamma irradiation. The Raman and infrared spectra show characteristic absorption bands, which indicate the sharing of Bi3+ ions as glass-forming (BiO6) octahedral units together with the presence of various groups of the borate network.  相似文献   

17.
    
Nineteen green-coloured gems adorning a cross-shaped pendant from the end of 19th century, belonging to Einsiedeln Abbey (Switzerland), were examined using non-destructive methods. Estimated weights of the gems are ranging from about 0.19 to 2.34 carats. Natural multiphase inclusions with jagged outlines were observed in all samples under optical microscope. Raman bands characteristic of beryl were observed in all samples with a 532-nm laser excitation. Raman spectra of the samples with a 785-nm laser at higher wavenumber found to be similar to emeralds containing low concentration of alkali elements. Their ultraviolet–visible–near-infrared (UV–Vis–NIR) spectra display absorption bands related to chromium and vanadium; no absorption bands related to iron were observed. Using a combination of spectroscopic and microscopic methods, the samples were adequately identified as natural emeralds, with Colombia as their most probable source.  相似文献   

18.
    
Ultraviolet‐resonance Raman (UV‐RR) micro‐spectroscopy is an appropriate and sensitive tool to assess the chromophore structures in bleached cellulosic pulps used for papermaking. The particular selectivity in detection and identification of chromophores in pulps is achieved by acquiring the UV‐RR spectra in the solid state with laser excitation at 325 nm. This wavelength corresponds to absorption of poly‐unsaturated chromophore structures in partially bleached/fully bleached pulps, and linearly correlated with the signal at ca 1600 cm−1 in the UV‐RR spectra. The characteristic vibrations from particular pulp chromophore structures have been assigned from experiments with model compounds, thus allowing the establishment of a UV‐RR database. Among the components of bleached pulp, the xylan–lignin complex was suggested to be an important source of chromophores. The monitoring of pulp bleaching by UV‐RR allowed us to suggest that it is the formation of new polysaccharide‐derived chromophores upon bleaching that hinders development of further brightness and is co‐responsible for the brightness reversion of fully bleached pulps. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

19.
本文采用常规的等体积浸渍法制备了不同担载量的V2 O5 γ -Al2 O3担载氧化物催化剂 ,在水气存在的条件下分别使用不同的激发波长得到了相应的可见拉曼光谱和紫外拉曼光谱。结果表明在表面钒物种微弱水合的情况下 ,3 2 5nm波长紫外激光激发的紫外拉曼光谱由于部分的共振拉曼效应 ,仍然可以灵敏的检测到表面钒物种配位结构随担载量增加而发生的变化。低担载时表面钒物种主要以孤立状态存在 ,随担载量增加逐渐向聚合态结构过渡 ,当担载量超过钒在载体表面的单层分散容量时形成体相V2 O5晶体覆盖表面钒物种造成拉曼信号的减弱 ,由此可以从另一个角度判断表面单层分散容量。  相似文献   

20.
    
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.  相似文献   

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