Probing chemical reactions: evidence for exploration of an excited potential energy surface at thermal energies

The reaction K + NaBr --> KBr + Na is probed during the reactive collision by a continuous wave laser tuned to frequencies not resonant with excitation in either reagents or products. Transient [K..Br..Na] absorbs a laser photon giving [K..Br..Na](*), which can decompose to Na(*) + KBr. Emission from excited Na(*) at the sodium D lines provides direct evidence of laser absorption during the reaction. Different excitation spectra were observed, depending on which sodium D line was monitored. This difference is explicable if, in the absence of the laser, the reaction flux partially bifurcates to a second potential energy surface during the reaction.     

Alterations of single molecule fluorescence lifetimes in near-field optical microscopy

Fluorescence lifetimes of single Rhodamine 6G molecules on silica surfaces were measured with pulsed laser excitation, time-correlated single photon counting, and near-field scanning optical microscopy (NSOM). The fluorescence lifetime varies with the position of a molecule relative to a near-field probe. Qualitative features of lifetime decreases are consistent with molecular excited state quenching effects near metal surfaces. The technique of NSOM provides a means of altering the environment of a single fluorescent molecule and its decay kinetics in a repeatable fashion.     

An efficient two-photon-generated photoacid applied to positive-tone 3D microfabrication

A two-photon-activatable photoacid generator, based on a bis[(diarylamino) styryl]benzene core with covalently attached sulfonium moieties, has been synthesized. The photoacid generator has both a large two-photon absorption cross section (delta = 690 x 10(-50) centimeter(4) second per photon) and a high quantum yield for the photochemical generation of acid (phiH+ = 0.5). Under near-infrared laser irradiation, the molecule produces acid after two-photon excitation and initiates the polymerization of epoxides at an incident intensity that is one to two orders of magnitude lower than that needed for conventional ultraviolet-sensitive initiators. This photoacid generator was used in conjunction with a positive-tone chemically amplified resist for the fabrication of a three-dimensional (3D) microchannel structure.     

异硫氰酸荧光素标记壳聚糖的研究

[目的]探究FITC和壳聚糖不同物料比对反应产物标记率和特性粘数的影响,并研究2种不同pH值下FITC-Chitosan吸收光谱和荧光光谱的变化。[方法]采用异硫氰酸荧光素对壳聚糖进行荧光标记,考查不同物料比时荧光素与壳聚糖的结合情况、产物的特性粘数以及标记物在pH值1.0、6.0的吸收光谱和荧光光谱。[结果]结果表明,物料比在小于0.5%时,标记物的特性粘数变化较小,适合用于标记壳聚糖;FITC-Chitosan在pH值1.0时可见吸收波长为438 nm,荧光激发波长440 nm,发射波长520 nm;在pH值6.0时可见吸收波长为488 nm,荧光激发波长493 nm,发射波长515 nm。[结论]该研究为FITC-Chitosan获得更深入的关注和更广泛的应用提供了试验依据。     

基于荧光高光谱图像的柑桔糖度无损检测

采用632nm的连续波激光作为激发光,应用激光诱导荧光高光谱成像技术对柑桔的糖度值进行无损测量。先将该激光照射到南丰蜜桔和脐橙样品上,后用高光谱图像采集系统收集诱导出的荧光散射图像;接下来对荧光散射图像进行分析,选取100×50像素的荧光区域作为感兴趣区域(ROIs);再提取感兴趣区域在波长700～1000nm的光谱值作为荧光高光谱图像数据;最后用线性回归方法建立荧光高光谱图像数据预测果实糖度值的预测模型。结果表明,该模型预测柑桔糖度值的相关系数分别为南丰蜜桔的R=0.970,脐橙的R=0.960。因此可以看出,应用激光诱导荧光高光谱成像对柑桔糖度值进行无损检测是一种很有效的方法。     

Apparent Concentration Quenching of Morphine Fluorescence

Fundamental fluorescence equations were examined. Deviations from the theoretical were observed by varying the light path length to determine effects on "apparent" fluorescence. It was found that the decrease in emission of morphine solutions with the increase in concentration was caused by absorption effects that prevented excitation of the whole system.     

激光共聚焦显微镜的样品前处理技术研究

激光共聚焦显微镜是近代生物医学图像应用中最重要的仪器之一,在定量共聚焦图像分析、定量荧光测量、三维重组分析生物结构等方面具有重要的作用.该研究主要介绍了实验室中最常用的激光共聚焦显微镜的几种样品前处理技术,即FM4-64染色法、BFA处理、双分子荧光互补技术（BiFC）等,同时介绍这些方法的原理、使用范围以及在相关领域中的应用情况等,以期更好地将激光共聚焦显微镜技术应用于科研实践中.     

白洋淀沉积物中溶解有机质荧光特性及其与铜的相互作用

在实验条件下通过三维荧光光谱、荧光猝灭滴定和质子核磁共振(1HNMR),分析了白洋淀污染水体沉积物中溶解有机质(DOM)与Cu(Ⅱ)的相互作用。结果表明:DOM的结构以碳水化合物及多糖为主且具有明显的类蛋白(峰B)和类富里酸(峰A和峰C)荧光峰,类蛋白的荧光强度较强于可见类富里酸;3类荧光基团荧光强度由于Cu(Ⅱ)猝灭,呈明显不同程度的降低;并且DOM与Cu(Ⅱ)络合常数及1HNMR分析表明DOM中荧光基因与Cu(Ⅱ)络合或螯合能力较大,配位的配位基较多。     

脉冲激光轰击法连续制备纳米钨及其性质表征

采用脉冲激光轰击法连续制备纳米钨及脂肪醇聚氧乙烯醚(平平加O)原位修饰的油溶性纳米钨,用紫外可见吸收光谱(UV-Vis)、荧光光谱、傅里叶红外光谱(FT-IR)、X射线衍射(XRD)和透射电子显微镜(TEM)等对其结构和性质进行表征.UV-Vis结果表明,纳米钨乙醇溶胶在230.00和275.00nm附近有强吸收;荧光...     

A Rotationally Resolved Fluorescence Excitation Spectrum of all-trans-1,4-Diphenyl-1,3-butadiene

Band 1 in the jet-cooled one-photon S(1) <-- S(0) fluorescence excitation spectrum of all-trans-1,4-diphenyl-1,3-butadiene has been rotationally resolved with a molecular beam laser spectrometer. Both the orientation of the optical transition moment and the rotational constants of the two vibronic levels have been measured. The molecule shows no evidence of being significantly distorted from a C(24) geometry when it is low in the vibrational manifolds of either of the two electronic states.     

Selective Laser Photocatalysis of Bromine Reactions: Laser light excites gaseous bromine molecules to single bound quantum states near the dissociation continuum

The results have shown that selective excitation obtained with a tunable monochromatic laser is a useful technique for studying photochemical and energy transfer processes. A new phenomenon in the photochemistry of bromine was observed, in which bound excited molecules, and not atoms, were formed in the primary process. The mechanism of the subsequent reaction consists of collisional dissociation of the excited molecules into atoms, which then initiated free-radical chains. A quantitative estimate of the collisional electronic relaxation rate for excited bromine molecules was obtained, and a new upper limit to the continuous absorption strength at 14,400 cm(-1) was determined.     

An unusual phycoerythrin from a marine cyanobacterium

Phycoerythrin conjugates are reagents for cell sorting and analyses in which the argon-ion laser line at 488 nanometers is used for excitation. Many marine Synechococcus strains contain phycoerythrins with absorption maxima at approximately 490 and 550 nanometers; these maxima indicate the presence of phycourobilin and phycoerythrobilin prosthetic groups in the protein. Phycoerythrins of red algae contain both groups, but those of freshwater and soil cyanobacteria contain only phycoerythrobilin. Phycoerythrin purified from Synechococcus WH8103 has molecular properties typical of red algal phycoerythrins, but its phycourobilin content is higher than that of other phycoerythrins. The protein has absorption maxima at 492 and 543 nanometers and corresponding molar extinction coefficients of 2.78 and 1.14 x 10(6); it fluoresces maximally at 565 nanometers with a quantum yield of 0.5. Conjugates of Synechococcus WH8103 phycoerythrin could increase the sensitivity of cell analysis techniques to almost twice that possible with other phycoerythrin conjugates.     

UV Spectrum and Proposed Role of Diethylberyllium in a 7Li-7Be Solar Neutrino Experiment

Although measurement of the solar neutrino flux via the (7)Li(v(e),e(-))(7)Be reaction was proposed many years ago, no experiment has been implemented since it has been difficult to identify a sensitive (7)Be detection technique. Here it is proposed that the (7)Be atom be incorporated into a volatile molecule, placed in a buffer-gas-filled cell, and then extracted by photodissociation; after excitation by a tunable laser, bursts of photons would be detected. The absorption spectrum of the molecular candidate diethylberyllium has been measured between 186 and 270 nanometers in a spectrophotometer to determine the required photodissociation laser wavelength and intensity.     

聚球藻、盐藻荧光特性研究

[目的]研究聚球藻和盐藻的荧光特性,确定其在特征激发、发射波长下藻浓度和荧光强度的关系,寻找一种确定藻类浓度的简便方法。[方法]以岛津RF5301型荧光分光光度计分析检测聚球藻和盐藻的激发和发射光谱,并获得它们的荧光强度与以血球计数板计数的藻浓度之间的关系。[结果]聚球藻和盐藻的激发、发射光谱有着明显的不同。在它们特征的激发、发射波长下,其浓度与荧光强度呈良好的线性关系。[结论]通过测定藻类的荧光强度就可推算出特定藻类的浓度,且该方法比血球计数板计算藻类的浓度更为便捷。     

奶牛血清激发荧光强度的试验研究

根据荧光分析技术,对奶牛血清的荧光特性进行了研究,研究了正常和异常奶牛血清经不同的光激发后所产生的荧光及其变化情况。初步结果表明,异常奶牛血清的荧光强度比正常奶牛血清的荧光强度要弱。提出通过对奶牛血清的荧光强度进行分析,将其应用于奶牛疾病诊断这一国内外较少涉足的研究课题。     

Quantum-dot spin-state preparation with near-unity fidelity

We have demonstrated laser cooling of a single electron spin trapped in a semiconductor quantum dot. Optical coupling of electronic spin states was achieved using resonant excitation of the charged quantum dot (trion) transitions along with the heavy-light hole mixing, which leads to weak yet finite rates for spin-flip Raman scattering. With this mechanism, the electron spin can be cooled from 4.2 to 0.020 kelvin, as confirmed by the strength of the induced Pauli blockade of the trion absorption. Within the framework of quantum information processing, this corresponds to a spin-state preparation with a fidelity exceeding 99.8%.     

降雨事件对不同流域背景河流DOM组成及入海通量的影响

通过调查2014年7月"麦德姆"台风影响期间福建九龙江北溪(流域以林地为主)和西溪(农业流域和城市背景)下游定点站DOM的时间序列,测定样品的DOC含量及其吸收光谱和三维荧光光谱,以评估不同流域背景对河流DOM动力学降雨响应的差异性,并为流域-河口系统的一体化管理提供重要参考。降雨期间,两条河流DOC浓度、吸收系数aCDOM(350)以及总荧光强度均随径流量升高而增大,并在水位下降期持续增加,且西溪增加量明显高于北溪,说明受人类活动扰动大的流域河流有机质对暴雨事件的响应更为灵敏;北溪和西溪的SUVA254分别显示出增大和减小的相反变化趋势,表明林地背景的流域主要冲刷芳香度高的DOM到河流,农业和城市背景则相反;降雨期西溪对九龙江DOM入海通量的贡献率高于北溪,与基流期北溪贡献率占主导恰巧相反,这种碳通量的逆转表明暴雨事件会放大人类活动对下游河口生态环境的影响。     

激光扫描共聚焦显微镜在植物研究中的应用

荧光成像技术、光学显微镜和计算机成像分析系统的完美结合催生了激光扫描共聚焦显微镜(LSCM)的出现,其优越的结构特点实现了将较厚样品能够逐点逐层扫描成清晰图像,有利于各种荧光信号的采集,直观进行三维重建和样品多重荧光信号采集进行的定量分析。这些优势功能极大地提高了从细胞、分子水平来探求生物时空表达基本功能的能力。本文详细阐述了近年来随着该项技术发展的日益多样化,激光扫描共聚焦显微镜技术在植物组织化学、植物细胞器和细胞骨架、植物发育方面的应用。     

Evaluation of plant seedling water stress using dynamic fluorescence index with blue LED-based fluorescence imaging

A dynamic fluorescence image index system capable of non-destructive assessment of water stress in cabbage seedlings was developed. The quenching curves of chlorophyll fluorescence characteristic to the plant's water stress status under reduced excitation energy were acquired via a multispectral imaging system. The dynamic fluorescence index (DFI), a fluorescence index derived from quantitative modeling of the quenching curves in this study, was found superior to conventional indices such as the fluorescence decrease ratio (Rfd) in evaluating water stress status in cabbage seedlings, with respect to due mainly to its significantly reduced measuring time and enhanced precision of the chlorophyll fluorescence responses. The best results of the quantitative model to predict water stress status of seedlings using the dynamic fluorescence index were r = 0.944 and SEE = 0.286 MPa using the 720 nm channel. The blue (460 nm) LED-excited fluorescence multispectral imaging system (FMSIS) coupled with DFI provides a powerful research tool for plant physiology studies as well as for improving greenhouse and agriculture management practices where quantitative assessment of water potential in leafy plants is critical.     

Interband electronic excitation-assisted atomic-scale restructuring of metal surfaces by nanosecond pulsed laser light

Interaction of high-power laser light with materials often causes irreversible damage of the near-surface region. It is shown that copper single-crystal surfaces can be patterned by laser light. Irradiation with green light produced adatoms and vacancies, which self-organized into nanoscale pyramids. This restructuring can be removed by annealing. In contrast to green light, infrared laser irradiation at equivalent absorbed energy density did not produce any structural change. This, for metallic systems, unforeseen spectral difference in laser light action points to a concerted process as the source for structural modification, which involves long-lived primary excitation of localized d-electrons through interband transition together with phonon excitation.