The effect of 4-hydroxycoumarin and umbelliferone on DPPC bilayers. Ultrasound study

The organisation of two coumarins, 4-hydroxycoumarin and 7-hydroxy- coumarin (umbelliferone) in dipalmitolyphosphatidylcholine (DPPC) was examined in the study. Ultrasound absorption technique was applied to study the effect of the presence in DPPC membranes of one of the coumarines on the parameters of phase transition. 4-hydroxycoumarin was found to change both phase transition temperature of this transition, and cooperativity more than umbelliferone. Different influence of these examined compounds is associated with their different location in the DPPC membrane, what results from different distribution of amphyphilness in molecules of both compounds.     

Analysis of branched oligophenylene by absorption and fluorescence spectra

A branched oligophenylene has been synthesized based on 1,3,5-tri(4′-bromophenyl)benzene. Absorption and fluorescence spectra were studied and fluorescence quantum yields and lifetimes were measured for the compound in solution. It is demonstrated that the absorption spectrum is a superposition of p-quaterphenyl, p-terphenyl, and biphenyl chromophore absorption bands in a 1:2:1 ratio. The oligomer fluorescence spectrum is found to depend on the excitation wavelength. It is shown that the oligomer fluorescence is determined by two fluorochromic groups, namely fragments with branched p-terphenyl and p-quaterphenyl units. The main fluorescence maxima for these fluorochromic groups coincide with each other and lie in the vicinity of λ = 360 nm. A very weak fluorescence band found in the region 380–440 nm is excited by light with a wavelength lying beyond the oligomer self-absorption region. The reasons for a decrease in fluorescence quantum yields of branched models and the studied oligophenylene as compared with those of linear p-polyphenylene chromophores are discussed.     

Spectroscopic investigations on the interaction of an anionic probe with nonionic micelles of Igepal surfactants in aqueous media

The behaviour of the anionic dye 8-anilino-1-napthalenesulfonic acid ammonium salt, or ANS, in aqueous solutions containing the Igepal series of polyoxyethylene nonionic surfactants was investigated using fluorescence spectroscopic technique. The interactions of the dye with the nonionic surfactants were examined in micellar media, to prevent dye aggregate formation and to ensure maximum dye and surfactant interaction. From the relative fluorescence enhancements, binding constants of the dye to the surfactant micelles and aggregation numbers of the micelles were determined. The aggregation numbers were also separately determined by static fluorescence quenching of pyrene by cetylpyridinium chloride in aqueous surfactant mixtures at a fixed concentration of surfactant, and compared with the value obtained from the present investigation of the interaction of the micelles with the ANS probe. The values of binding constants, micropolarity values sensed by pyrene and the Stern–Volmer constants for quenching of pyrene fluorescence by cetylpyridinium chloride were correlated with the number of ethylene oxide groups in the Igepal series.     

Control of Immobilization and Hybridization on DNA Chips by Fluorescence Spectroscopy

A new methodology for the analysis of DNA polymorphisms has been developed using specific oligonucleotide strand arrays bound to a solid silicon support recovered by a thin layer of silica. Arrays of directly synthesized oligonucleotides covalently fixed on Si/SiO₂ wafers have been designed at the macroscopic scale. Using suitable nucleotide-labeled units, the fluorescence emission technique has been used as an experimental control of the molecular network bound to the support and as a method for analyzing the hybridizing abilities of the corresponding oligonucleotide array. Fluorescein has allowed us to control the molecular density of the DNA strand resulting from a complete synthetic growing process. A specific protocol using both complementary and noncomplementary units labeled with two probes, Cy3 and Cy5, was used to distinguish clearly nucleotide units fixed on the array either as hybridized sequences or by the unavoidable adsorption process. The present performance of this fluorescence detection procedure will now be used with a scanning fluorescence device to perform the analysis at the microscopic scale.     

Quenchers Induce Wavelength Dependence on Protein Fluorescence Lifetimes

We have analysed the picosecond resolved fluorescence emission decay of horseradish peroxidase A2 and of HEW lysozyme acquired with a streak camera. Analyses of the fluorescence decay data of both proteins revealed that the dynamics of the decay is dependent on the emission wavelength. Our data strongly indicates that resonance energy transfer occurring between aromatic residues and different protein fluorescence quencher groups, and the nature of the quencher groups, are the causes of the observed wavelength dependent mean lifetime distribution. Using the global analysis data to calculate the fluorescence mean lifetime at each wavelength revealed that for lysozyme, the mean fluorescence lifetime increased with observation wavelength, whereas the opposite was the case for peroxidase. Both proteins contain strong fluorescence quencher groups located in close spatial proximity to the protein’s aromatic residues. Lysozyme contains disulfide bridges as the main fluorescence quencher whereas peroxidase contains a heme group. Both for lysozyme and horseradish peroxidase there is a clear correlation between the observed fluorescence mean lifetime of the protein at a particular emission wavelength and the respective quencher’s extinction coefficient at the respective wavelength. Furthermore, our study also reports a comparison of the analyses of the fluorescence data done with three different methods. Analyses of the fluorescence decay at 10 different fluorescence emission wavelengths revealed significant differences in both fluorescence lifetimes and the pre-exponential factor distributions. Such values differed from the values recovered from the integrated decay curves and from global analyse.     

Accurate standard‐based quantification of X‐ray fluorescence data using metal‐contaminated plant tissue

Quantitative X‐ray fluorescence (XRF) measurements have been conducted on naturally lead‐contaminated samples. The calibration procedure using the ratio of fluorescence to Compton scattered radiation was investigated using Monte Carlo simulation. Experimental results with low‐energy photons (14 keV) and simulations show a very good linearity of the fluorescence to Compton ratio as a function of metal concentration. Lead (Pb), iron (Fe) and zinc (Zn) are measured in samples of Phaseolus vulgaris (bean seeds) that have been grown using a nutritive solution with different Pb dopings. Naturally contaminated samples are thus obtained. The calibration must be done for fixed conditions of X‐ray energy and scattering angle, while X‐ray beam intensity and detector to sample distance can change from one sample to another. Simulation allows to evaluate the matrix effect on the calibration curve, and shows that linearity is preserved even in the presence of other heavy elements in the fluorescence spectrum. However, calibration must be done using samples with similar matrix as it affects the slope of the curve. Copyright © 2010 John Wiley & Sons, Ltd.     

Application of Fluorescence with Polarized Light to Evaluate the Orientation of Dyes Adsorbed in Layered Materials

A new method of fluorescence polarization is applied to evaluate the angle of the preferential orientation of Rhodamine 6G (R6G) dye adsorbed in supported thin films of Laponite (Lap) clay. The method is based in the determination of the fluorescence dichroic ratio, obtained from the recorded fluorescence spectra with the detection polarizer horizontally and vertically oriented, as a function of the twisted angle of the film around its vertical axis, keeping the excitation polarizer in a fixed direction. The validity of the method is checked by comparing the experimental results obtained with both vertically and horizontally polarized excitations to that previously provided by absorption spectroscopy with linearly polarized light. A preferential orientation angle with respect to the normal to the clay layer of 62° is derived for R6G monomers adsorbed in Lap films.     

Photoluminescence study of tetra-dendron dendrimers derived from ethylenediamine cores and di-dendron dendrimers derived from mono-Boc-protected ethylenediamine cores

Strong UV absorbance spectra and fluorescence spectra from tetra-dendron dendrimers derived from ethylenediamine cores with different terminal groups (-NH₂, -COOCH₃) or di-dendron dendrimers derived from mono-Boc-protected ethylenediamine cores were studied under different conditions by varying experimental parameters such as pH value and concentration. The result shows a rapid increase of fluorescence intensity at low pH. It was reasonable that the formation of a fluorescence-emitting moiety had a close relationship to protonated tertiary amine groups in tetra-dendron dendrimers derived from ethylenediamine cores or di-dendron dendrimers derived from mono-Boc-protected ethylenediamine cores. Furthermore, it was confirmed that the concentration of two dendrimers plays an important role in fluorescence intensity. The increase in fluorescence intensity was linear with respect to concentration at low concentration regions but the intensity increases slowly at high concentration regions.     

355 nm纳秒激光作用下荧蒽的时间分辨荧光光谱特征

多环芳烃由于具有三致(致癌、致畸、致突变)特性,其在环境中的检测受到人们广泛关注。利用时间分辨光谱技术,研究了荧蒽乙醇溶液的荧光光谱随延时时间和门宽改变的特性。研究了不同浓度荧蒽的时间分辨荧光光谱特性,以原始浓度的荧蒽为初始溶液,通过逐级稀释的方式,最终将原始溶液稀释16倍,拟合了不同稀释倍数下的荧蒽荧光强度衰减随延时时间变化的动力学曲线,得到了不同浓度荧蒽的拟合荧光寿命。研究结果表明,荧蒽的荧光光谱特性与光谱仪探测器延时时间和门宽宽度密切相关。固定延时时间,随着光谱仪门宽宽度的变化,荧蒽的荧光强度随着门宽的增大而逐渐增强。固定门宽,改变延时时间的过程中,荧蒽的荧光强度随延时时间呈现先增大,后减小的趋势。荧蒽的荧光强度随延时时间的衰减过程符合指数衰减过程,将荧蒽乙醇溶液进行逐级稀释,荧蒽荧光强度与延时时间的衰减进行指数拟合后,得到不同稀释倍数的荧蒽乙醇溶液的衰减动力学参数,随着稀释倍数的增大,拟合得到的荧蒽荧光寿命增大。多环芳烃时间分辨光谱特征的研究,可以为环境中多环芳烃的检测提供技术基础,由于不同荧光物质具有特征的荧光寿命,因此,可以利用多环芳烃与环境中其他荧光物质的不同荧光寿命特性,准确识别环境中的多环芳烃污染物。     

Using gold colloid nanoparticles to modulate the surface enhanced fluorescence of Rhodamine B

Enhanced fluorescence from Rhodamine B (RB) mixed with gold colloids has been observed under ultraviolet irradiation. Spectroscopic studies show that with the increasing gold colloids content, the fluorescence of RB at about 590 nm increases firstly and then decreases with slight red shift. These features observed in the experiment can be explained by the local electric field enhancement via surface plasmon resonance (SPR) of gold nanoparticles. Fluorescence enhancement is obtained when the emission frequency of RB lies within the bandwidth of local field enhancement from gold nanoparticles. Theoretical calculation results show that the local field band red shifts obviously with increase the thickness of dye shell which capped on gold particle, whereas the fluorescence band of RB is fixed around 590 nm. Therefore, the red shift and non-monotonic change of fluorescence intensity from RB is attributed to the dye shell dependent red shift of local field band of gold particles.     

Er^3+,Cr^3+共掺杂BaAl2Si2O8荧光粉的发光性质及能量传递

利用高温固相法合成BaAl2Si2O8:Cr^3+,Er^3+系列荧光粉,研究了Cr^3+和Er^3+掺杂对BaAl2Si2O8材料发光特性的影响.BaAl2Si2O8:Er^3+荧光样品在393 nm激发波长下只呈现出峰值为550 nm的绿色荧光,来源于2H11/2→4I15/2和4S3/2→4I15/2跃迁的叠加.BaAl2Si2O8:Cr^3+荧光样品在550 nm激发波长下呈现峰值为694 nm的红色荧光,来源于2E→4A2的跃迁.在共掺杂样品BaAl2Si2O8:Cr^3+,Er^3+中,用Cr^3+激发峰的凹槽处380 nm作为激发光,得到的发射峰不仅有Er^3+的发射峰位,还有Cr^3+的发射峰位,说明两个离子之间可能存在辐射能量传递;对共掺杂BaAl2Si2O8:1%Cr^3+,x%Er^3+样品的荧光光谱进行测试,随着x的增加,Cr^3+的激发和发射光谱强度均有所增加,并且当x=0.5时,光谱强度是原来的4倍.另外,当固定Cr^3+的浓度时,随着Er^3+的浓度增加,Cr^3+的荧光寿命逐渐增加;当固定Er^3+的浓度时,随着Cr^3+的浓度增加,Er^3+的荧光寿命逐渐减小.这些现象表明了Er^3+和Cr^3+之间存在共振能量传递,通过理论计算得到Er^3+和Cr^3+之间的能量临界距离为4.5 nm,属于电偶极-电偶极相互作用.     

Enhancement of fluorescence of porous silicon upon saturation by liquid crystal

The fluorescence of samples of porous silicon of various morphologies that are filled with a liquid crystal (LC), n-pentyl-n′-cyanobiphenyl (5CB), is studied. The fluorescence spectra of the sample, along with the long-wavelength band of porous silicon with a maximum in the range 627–667 nm, exhibit a short-wavelength band of 5CB with a maximum in the range 385–410 nm. The radiative relaxation times of porous silicon and 5CB lie in the micro- and nanosecond ranges, respectively. It is found that the filling of pores with 5CB enhances the fluorescence of porous silicon by two to three times. This enhancement is caused by non-radiative energy transfer from 5CB to the porous matrix as a result of efficient interactions between LC molecules and pore walls. Using IR spectroscopy, it is shown that the formation of hydrogen bonds between cyano groups of 5CB molecules and silanol groups of pore surface is the predominant type of these interactions. A transfer mechanism is suggested according to which excited associates of 5CB molecules transfer their energy via surface channels to excitons of porous silicon, enhancing its fluorescence.     

Elemental mapping of frozen‐hydrated cells with cryo‐scanning X‐ray fluorescence microscopy

Visualizing the elemental distributions of cells and tissues is of growing importance in biology and medical science because such data deepen our understanding of the behavior of metal‐binding proteins and ions. Elemental mapping by X‐ray fluorescence analysis with a hard X‐ray nanobeam is very well suited for this purpose owing to its high sensitivity and high resolution. Using this technique, samples must be prepared without artifacts that are caused by treatments such as chemical fixation and staining procedures. In many studies of elemental mapping, sample preparation is not explicitly considered. To overcome this deficiency, we developed a cryo‐scanning X‐ray fluorescence microscope and installed it in the second experimental hutch of BL29XUL of SPring‐8. We used it to observe frozen‐hydrated cells that had been fixed by a quick‐freezing technique to preserve elemental data of the living state at an X‐ray energy of 11.5 keV. The distributions of K, Ca, Fe, Cu and Zn were successfully visualized. The distributions of these elements (especially those of K, Ca and Fe) differed from those in cells fixed with paraformaldehyde. Copyright © 2010 John Wiley & Sons, Ltd.     

C_(60)在室温有机溶剂中荧光的研究

本文在室温下对C60分别在吡啶、甲苯和乙腈中的荧光了研究,实验表明:C60在吡啶中的荧光由以440nm、570nm和700nm为中心的三个荧光带组成;C60在甲苯中的荧光由以430nm和700nm为中心的两个荧光带组成;C60在乙腈中的荧光由以570nm和700nm为中心的两个荧光带组成。经比较分析发现C60-有机溶剂体系700nm区域的荧光带的发射与溶剂的种类无关,而440nm和570nm区域的荧光带及其精细结构可以反映C60与溶剂分子的特殊相互作用。进一步提出C60-吡啶体系以570nm为中心的荧光带是由吡啶分子通过含孤对电子的N与C60形成的电荷转移络合物发出的。     

光纤面板窗多碱光电阴极荧光谱特性研究

论述了光致荧光的特点以及微光像增强器多碱光电阴极光致荧光的测量原理, 测量了光纤面板输入窗多碱光电阴极的荧光谱. 测试结果表明, 光纤面板窗的多碱阴极的荧光谱不是一条光滑的高斯型曲线, 而是在一条高斯型曲线上叠加了一些小的干涉峰的曲线. 原因是光纤面板窗所传输的荧光中, 有两束特殊的光线. 一束光为准直光, 另一束光为入射角刚好等于全反射临界角的反射光. 这两束光具有固定的相位差或光程. 当这两束光的相位差相差λ的整数倍时, 它们将干涉并产生干涉加强峰;当这两束光的相位差相差1/2λ的奇数倍时, 它们将干涉并产生干涉减弱峰. 如果在荧光谱的峰值波长处刚好产生干涉加强峰, 那么所测量的峰值荧光强度较其固有的峰值荧光强度要高; 反之, 如果在荧光谱的峰值波长处刚好出现干涉减弱峰, 那么所测量的荧光强度就小于其固有的荧光强度. 另外由于受到干涉的影响, 荧光曲线半峰宽也不能精确确定,所以在分析光纤面板窗光电阴极的荧光谱时, 要考虑到干涉因素的影响.     

谱聚类结合LIF在矿井突水水源类型识别中的应用

突水事故威胁井下人员的生命安全和造成财产损失,因此准确检测出突水水源类型具有重大意义。使用水化学分析法检测水源类型耗时长、过程复杂。激光诱导荧光（LIF）技术具有快速、灵敏、干扰小等优点,将LIF技术结合智能算法建立突水水源识别模型可以准确检测出突水水源的类型。目前这类模型一般需要对荧光光谱进行去噪、降维、波段选取等处理,过程繁琐,并且模型都是在均匀分组的突水水源荧光光谱上建立的,并没有讨论不均匀分组对模型的影响,也没有针对不均匀分组建立模型。在实际工程应用中,采集的样本数量是有很大概率呈现不均匀的,因此本文提出一种飞蛾扑火（MFO）算法结合谱聚类（SC）的方法实现对不均匀分组的突水水源荧光光谱的识别。实验中,首先从淮南煤矿获取5种实验水样,使用激光诱导荧光实验设备采集所有水样的荧光光谱,五种水样的组数分别为75,80,80,30和135。其次,建立MFO-SC水样识别模型,通过对比后标签映射方式选择K-Means、相似矩阵的计算方式选择高斯核函数和划分准则选择ncut,用MFO对高斯核函数的参数寻优得到σ的值为1.745并且固定模型的初始聚类中心。随后,分别建立K-Means,SVM和MFO-SVM3种水样识别模型。对比MFO-SC模型与K-Means模型,得到MFO-SC模型的最优准确率为100%且平均准确率也为100%,K-Means模型的最优准确率为99.75%,而平均准确率为79.57%;再分别计算SVM模型和MFO-SVM模型的训练集准确率和测试集准确率,SVM模型训练集准确率为80%,测试集准确率为80%;MFO-SVM模型训练集准确率为100%,测试集准确率为95.625%。最后,使用4种模型对其他三个不均匀分组的突水水源荧光光谱进行识别,研究结果表明将MFO-SC算法用于突水水源类型的识别上是有效的,可以准确地检测出突水水源的类型,对煤矿生产安全有重要意义。     

自由基型光引发剂的瞬态及稳态荧光特性研究

利用荧光光谱技术研究了不同自由基型光引发剂的瞬态及稳态荧光光谱特性,从分子结构出发分析了共轭结构对光引发剂荧光光谱的影响.实验结果表明随共轭效应的增强,荧光激发与发射峰波长逐渐增大;瞬态荧光谱的衰减受电子基团的影响较为明显,含有吸电子基团的光引发剂荧光衰减快,而含有给电子基团的光引发剂荧光衰减慢.通过对溶剂极性及粘度研...     

A Study of the Intrinsic Autofluorescence of Poly (ethylene glycol)-co-(<Subscript><Emphasis Type="Italic">L</Emphasis></Subscript>-Lactic acid) Diacrylate

Poly (ethylene glycol)-co-( _L -Lactic acid) diacrylate (PEG-PLLA-DA) copolymers have been extensively investigated for a number of applications in medicine. PEG-PLLA-DA is biodegradable and the human body can process its degradation products. In this study, we describe the autofluorescence of PEG-PLLA-DA copolymers and compared it to the fluorescence of poly(ethylene glycol) diacrylate (PEG-DA) and the precursor molecules used for their synthesis. In addition, we examined the influence of pH on the fluorescence spectra. We found that PEG-PLLA-DA exhibits higher fluorescence than PEG-DA and all reagents involved in the synthesis of PEG-PLLA-DA. The fluorescence of PEG-PLLA-DA was affected by pH with fluorescence decreasing at high pH values. At high pH, PEG-PLLA-DA could not polymerize into hydrogels and exhibited a dramatic decrease in autofluorescence, suggesting that hydrolysis of the ester bond affected its autofluorescence. At low pH, PEG-PLLA-DA exhibited higher fluorescence and it was able to form crosslinked hydrogels. The autofluorescence of PEG-PLLA-DA could be exploited to monitor polymer degradation and material structure without the need to introduce exogenous fluorescent probes. The origin of fluorescence is not clear at this point in time but it appears to result from a synergetic effect of both lactate units and diacrylate groups in the PEG-PLLA-DA backbone. The observed autofluorescence of PEG-PLLA-DA persists after reaction of the acrylate groups in the polymerization reaction. This autofluorescence is advantageous because it could assist in the study of polymers used for drug delivery and tissue engineering applications.     

Phase-Modulation Fluorometer Using an Ultraviolet Light-Emitting Diode

We have constructed a phase-modulation fluorometer using a commercially-available ultraviolet light-emitting diode (UV LED) as an excitation light source. The center wavelength of the UV LED is 370 nm and its spectral bandwidth is 10 nm. A 10 mApp modulation-current was superimposed on a bias current of 5 mA with a fixed frequency in the range of 1-20 MHz. The average UV power on the sample was 250 μW. The fluorescence signal was detected by a photomultiplier tube and was fed into a versatile digital oscilloscope. The phase difference between the fluorescence signal and the reference signal obtained from a diffusion plate was directly read out using the operational functions of the digital oscilloscope. To demonstrate the system performance, fluorescence lifetimes of 25 ppm rhodamine 6G in ethanol and of 10 ppm quinine sulfate in 0.1 N H₂SO₄ were measured. The calculated lifetimes of 5.8 ns and 19.1 ns, respectively, agreed with those reported in the literature. The combination of the UV LED and the digital oscilloscope made the fluorometer simple and easy to construct with low cost.     

基于激光诱导荧光的常见机油快速识别方法

基于激光诱导荧光光谱原理,提出一种常见机油的快速识别方法。利用激光器发射波长为355 nm的紫外激光,诱导九种常见机油样品发射荧光,共采集450组荧光光谱数据,其中360组数据用于分类训练,90组数据用于识别。分析发现不同机油的荧光光谱特征有明显差异,利用主成分分析结合聚类分析法实现了对90组待识别光谱数据的快速识别,识别率可达97.8%。实验证明,激光诱导荧光光谱结合多元分析可以实现不同机油的快速识别与检测。