单光子调制频谱用于量子点荧光寿命动力学的研究

本文开展了基于单光子调制频谱测量量子点荧光寿命动力学特性的研究.在脉冲激光激发下,对探测到的量子点单光子荧光信号进行频谱分析以获得荧光调制频谱,研究发现特征频谱信号幅值与荧光寿命之间存在确定的非线性对应关系.这种单光子调制频谱方法能有效消除背景噪声和单光子探测器暗计数的影响,用于分析量子点荧光寿命动力学特性时在准确度以及时间分辨率方面都较目前普遍采用的荧光衰减曲线寿命拟合方法呈现出明显优势:当涨落误差为5%时,寿命测量准确度提高了一个数量级;当涨落误差和偏离误差均为5%时,对动力学测量效率以及时间分辨率提高了四倍以上.因此单光子调制频谱可以作为获取量子点在短时间尺度内激发态动力学信息的一种有效技术手段.     

Lifetime measurements with the pinhole method in presence of radiation trapping: I—theoretical model

This paper reports a new theoretical model for the evaluation of the results of the so-called pinhole method for the measurement of the upper level lifetime in doped optical materials exhibiting radiation trapping effects due to resonant reabsorption of the emitted fluorescence. The model correctly predicts that the fluorescence decay has a double exponential behavior with two time constants, with the shorter one near the intrinsic decay time of the upper level, with a correction depending on the effect of the short range reabsorption. As a consequence, a new method is proposed for the data analysis and the interpretation of the results with respect to the previous literature.     

Lifetime measurements with the pinhole method in presence of radiation trapping: II—application to Yb<Superscript>3+</Superscript> doped ceramics and crystals

In this paper, we present an experimental verification of a theoretical model for the evaluation of the results of the so-called pinhole method for the measurement of the upper level lifetime in doped optical materials where the resonant reabsorption of the emitted fluorescence determines significant radiation trapping effects. As an experimental verification of the model, we measured the lifetime of the upper laser level of Yb³⁺ in various crystals and ceramic samples usually employed for the realization of solid state laser sources.     

Determination of the effective upper laser level lifetime from an end-pumped Tm,Ho:YLF laser

We report the measurement of the effective upper laser level lifetime from an end-pumped Q-switched Tm,Ho:YLF laser. When the pump power is 1.58 W, the effective upper laser level lifetime is only 2.5 ms, which is less than the fluorescence lifetime (∼16 ms) of the upper laser level. The dependences of the effective upper laser level lifetime on the pump power and the temperature of laser crystal are firstly obtained experimentally. The experimental results show that the effective upper laser level lifetime decreases with increasing the pump power and the temperature of laser crystal, respectively. Furthermore, the experimental results are compared with the theoretical results.     

激光诱导植物荧光寿命校正技术及其特性分析

激光诱导植物荧光寿命测量法是在植物荧光光谱分析法基础上开发的一种评估植物生长状况及环境监测的新技术。根据植物叶绿素荧光信号的物理特性,利用信息仿真技术开发了一种叶绿素荧光寿命校正方法,可提高植物叶绿素荧光寿命的测量精度。利用激光诱导叶绿素荧光寿命测量系统分别测得叶绿素荧光及其背景信号,先用解卷积法叶绿素荧光信号中分离出荧光衰减函数,可获取荧光寿命估计值。再结合叶绿素荧光寿命校正技术就能反演得到高精度的植物荧光寿命。仿真与实验结果表明：该方法可实现高精度的植物荧光寿命实时监测;并对不同含量的叶绿素提取液进行了测试,构建了植物荧光寿命与叶绿素含量的对应关系模型。未来该技术可用于遥感监测海洋、湖泊、河流中藻类植物的生物含量。     

基于不同泵浦波形的荧光寿命测量

该文从理论上分析了不同泵浦波形下的荧光衰减规律,提出了一种在不同泵浦波形下测量荧光寿命的新方法——双脉冲探测法,即利用探测泵浦脉冲与荧光衰减脉冲的方法测量荧光寿命。通过对样品钕玻璃及Cr:ZnSe晶体的荧光寿命测量表明:利用该方法在不同泵浦波形下能够实现可见及近红外到中红外激光介质的荧光寿命测量。因此,利用该测量方法能够方便、有效的避免通过解卷积求样品荧光寿命的繁琐过程,对测量激光介质在不同泵浦波形下的荧光寿命具有参考价值。     

A General Method for Constrained Analysis of Fluorescence Anisotropy Decay: Application of the Steady-State Anisotropy

Time-resolved fluorescence anisotropy is an invaluable method for investigating the internal and rotational dynamics of biomolecules. The range of rotational motions detectable by anisotropy decay is limited by the fluorescence lifetime; typically, a depolarizing motion may be resolved if the associated correlation time is between 0.1 and 10 times the intensity decay lifetime. To extend that range and to improve the recovery of anisotropy decay parameters, a general analytical method has been developed. This procedure utilizes a modification of Lagrange multiplier methods to constrain the values of the iterated kinetic parameters during nonlinear least-squares analysis of anisotropy decay data. The form of the constraint equation is derived from the classic relationship between the decay parameters and the steady-state anisotropy, which can be simply and accurately measured. Application of the constraint to analyses of synthetic data sets increased the accuracy of recovery by decreasing the uncertainty in the iterated parameters. The constraint also enabled the accurate recovery of correlation times that were a factor of 30 greater than the fluorescence lifetime, although it did not improve recovery of correlation times that were much shorter than the lifetime. Using this technique, it should now be possible to characterize the dynamics of larger macromolecules and assemblies than those that can currently be studied by fluorescence anisotropy decay.     

Effects of Refractive Index and Viscosity on Fluorescence and Anisotropy Decays of Enhanced Cyan and Yellow Fluorescent Proteins

The fluorescence lifetime strongly depends on the immediate environment of the fluorophore. Time-resolved fluorescence measurements of the enhanced forms of ECFP and EYFP in water–glycerol mixtures were performed to quantify the effects of the refractive index and viscosity on the fluorescence lifetimes of these proteins. The experimental data show for ECFP and EYFP two fluorescence lifetime components: one short lifetime of about 1 ns and a longer lifetime of about 3.7 ns of ECFP and for EYFP 3.4. The fluorescence of ECFP is very heterogeneous, which can be explained by the presence of two populations: a conformation (67% present) where the fluorophore is less quenched than in the other conformation (33% present). The fluorescence decay of EYFP is much more homogeneous and the amplitude of the short fluorescence lifetime is about 5%. The fluorescence anisotropy decays show that the rotational correlation time of both proteins scales with increasing viscosity of the solvent similarly as shown earlier for GFP. The rotational correlation times are identical for ECFP and EYFP, which can be expected since both proteins have the same shape and size. The only difference observed is the slightly lower initial anisotropy for ECFP as compared to the one of EYFP.     

农药荧光寿命测试系统的原理与设计

介绍荧光的产生、荧光寿命的产生机理以及荧光寿命测量的基本原理。设计了一种利用直接记录法(光子计数法)测量农药荧光寿命的测试系统。该系统针对待测样品的特性，选用了相应的脉冲光源、光学元件和半导体探测器等器件，优化了各器件的工作参数，进行了简易而又科学的模块化设计，并对西维因农药的荧光寿命在无激励光干扰情况下进行了实际测试，测得了西维因溶液在500μg／L浓度时的荧光衰减曲线和荧光寿命(0.30～0.40ns)。结果表明，该系统具有结构简易、操作方便的优点，能测量100ps级的荧光寿命，适合于对能发荧光的农药进行荧光寿命的定量测量。     

血啉甲醚的时间分辨荧光光谱研究

实验研究了用于肿瘤光动力学诊断的第二代新型光敏剂血啉甲醚(HMME)分别在不同血型人血清和生理盐水环境中的时间分辨光谱,同时还研究了在不同荧光发射峰处的荧光寿命以及光敏剂浓度对荧光寿命的影响。结果表明:HMME在625和690nm处的荧光寿命基本相同,无显著差异。HMME在生理盐水和人血清环境中的荧光寿命具有显著差异,分别为14.6和16.6ns,同时实验结果还表明光敏剂浓度对荧光寿命没有影响。结论对于开展肿瘤的时间分辨药物荧光光谱诊断与成像技术具有重要的指导意义。     

Fluorescence decay time measurements in tetracene crystals excited with synchrotron radiation

Fluorescence decay times from tetracene single crystals excited at room temperature with synchrotron radiation have been recorded as a function of the excitation wavelength (in the 400–500 nm range). A non-exponential decay with two decay rates is observed. The analysis of our data shows that the first singlet exciton level of tetracene (single crystal) decays radiatively mainly through, as we call it, channel 1, with a lifetime of 0.200 ± 0.020 ns. About 10% of the emitted fluorescence transits through channel 2 with a lifetime of 1.7 ± 0.2 ns. These results do not agree with previously published decay data obtained when tetracene is excited by means of powerful lasers. Thus there is experimental evidence to believe that the decay properties of condensed materials can be very dependent on the excitation density. Because synchrotron radiation compared to lasers is a very weak source, and therefore secondary effects are minimized in our experimental conditions, the decay values reported in the present work are the true lifetimes of the tetracene single crystal.     

Fluorescence lifetime distributions in membrane systems

Membranes are complex biological systems that display heterogeneity at all spatial scales. At a molecular level, the heterogeneity arises from lipid and protein composition. At the cellular level, heterogeneity is due to membrane organization and large scale morphology. A quantitative evaluation of membrane heterogeneity at a microscopic level is very important for several fields of membrane studies. We have developed a method for the analysis of the decay of fluorescent membrane probes that can provide a quantity sensitive to membrane heterogeneity. This method is based on the analysis of the fluorescence decay using continuous lifetime distributions. The major challenge in the interpretation of the analysis results is in the identification, at a molecular level, of the mechanisms that influence the fluorescence decay. In this review we illustrate the principles of data analysis and we show examples of identification of the measured parameters with specific variables that affect membrane heterogeneity.     

用时间分辨光谱研究红细胞悬液的荧光发射

实验获得了激光照射红细胞悬液的荧光光谱,并分别监测不同荧光峰值波长处强度随时间的衰变过程,测试了其相应的荧光寿命。结果表明,在波长为407nm的激光照射下,红细胞悬液向外发射中心波长分别位于596,628,692nm的荧光光谱,各荧光峰对应衰变过程的平均荧光寿命分别为1.97,13.31,14.58ns。利用荧光强度和吸收率的加和性表示了混合物的总吸收率和总荧光发射强度,通过理论计算获得了红细胞悬液中锌卟啉、原卟啉和其他游离物参与荧光发射的相对含量和相对强度在不同荧光峰位的变化关系,进一步解释了不同峰位处荧光发射强度和平均荧光寿命的变化原因。     

Dependence of the refractive power of Nd:YAG rods on the intracavity intensity

The refractive power of two flashlamp-pumped Nd:YAG rods was measured as being dependent on the output coupling of the resonator. With laser oscillation, the refractive power or thermal heat is decreased by up to 15% and a minimum occurs at a specific output coupling. The experimental results could be explained by a theoretical model assuming a non-radiative transition from the upper laser level to the ground state. The lifetime of this non-radiative transition decreases with increasing pumping power per pulse and, for pumping power higher than 100 kW, saturation at a value of 0.63 times the fluorescence lifetime occurs. The results indicate that the non-radiative process is caused by energy migration to flashlamp-induced transient quenching centres.     

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。     

基于皮秒时间分辨的癌细胞荧光寿命研究

研究了用于癌症诊断与治疗的光敏剂血卟啉(hematoporphyrin derivative,HPD)的超快光动力学过程,采用超短脉冲激光光谱技术和皮秒时间相关单光子计数系统,测量了经血卟啉培养的活体癌细胞与正常细胞的皮秒时间分辨荧光光谱及荧光峰值强度随时间衰变曲线,观测到：癌细胞与正常细胞样品荧光寿命的快成分分别为150和300 ps;癌细胞与正常细胞的荧光峰值强度经12 h分别衰减10%和55%。经对测量所得的荧光衰减曲线进行分析,计算出癌细胞与正常细胞的荧光寿命分别为824和1798 ps;血卟啉在癌细胞与正常细胞样品中滞留时间分别为17天和6天。结果表明癌细胞与正常细胞对血卟啉亲和性及对血卟啉滞留的稳定性有显著差异,测量结果确认了荧光光谱技术诊断与治疗癌症的可行性,并对实时监测生物样品微弱超快荧光具有重要的指导意义和临床应用价值。     

激光诱导叶绿素荧光寿命的测量及其特性分析

提出了一种用于评估植物生长状况及环境监测的激光诱导叶绿素荧光寿命测量方法. 采用波长355 nm的激光作为光源激发叶绿素荧光, 由光电倍增管接收其荧光信号, 由于被测叶绿素荧光衰减函数与激光脉冲、仪器响应函数卷积在一起, 根据它们的特性, 运用时间分辨测量法分别测得叶绿素荧光及其背景信号, 并结合一种新型解卷积算法可分离出真实的叶绿素荧光衰减函数, 从而获取叶绿素的荧光寿命. 测试结果表明: 该方法能够实现叶绿素荧光寿命的高精度实时监测, 对不同叶绿素含量的溶液荧光寿命进行了测试, 证明叶绿素含量与其荧光寿命具有相关性, 并且拟合了叶绿素含量与荧光寿命的标定曲线. 关键词： 荧光寿命 激光诱导荧光 时间分辨测量法 叶绿素含量     

拟威布尔分布密度函数在荧光寿命成像数据分析中的应用

荧光寿命法成像技术(FLIM)是一种非常有效、功能强大且能用来分析复杂生物组织和细胞分子的成像技术。传统的荧光寿命成像的数据分析,按某些具有不同寿命、离散的单参量指数模型来描述荧光衰减过程。在生物组织这样既复杂又不均匀的样品中,虽然多参量指数模型能提供比单参量指数模型对实验数据更好的拟合效果,但是离散多参量的假定往往是随意的。提出了拟威布尔分布密度函数可能是生物荧光分子团衰减动力过程的真实再现,并且通过计算证明,对于某些生化感兴趣的荧光分子团的多槽基面效价测定样品的数据,相对于单参量指数与多参量指数衰减函数有更好的一致性。同时讨论了将该荧光衰减模型应用于荧光寿命成像的前景。     

A new estimate of the proton lifetime

We find a theoretical upper limit of 10³² years for the proton decay lifetime in the SU(5) grand unified theory of Georgi and Glashow based on a calculation at the two-loop level.     

Exciton emission dynamics in single InAs/GaAs quantum dots due to the existence of plasmon-field-induced metastable states in the wetting layer

A very long lifetime exciton emission with non-single exponential decay characteristics has been reported for single InA-s/GaAs quantum dot(QD) samples,in which there exists a long-lived metastable state in the wetting layer(WL)through radiative field coupling between the exciton emissions in the WL and the dipole field of metal islands.In this article we have proposed a new three-level model to simulate the exciton emission decay curve.In this model,assuming that the excitons in a metastable state will diffuse and be trapped by QDs,and then emit fluorescence in QDs,a stretchedlike exponential decay formula is derived as I(t)=At~(β-1)e~(-(rt)β),which can describe well the long lifetime decay curve with an analytical expression of average lifetime