荧光相关光谱单分子检测系统的研究

基于激光共焦构型,构建了一套高灵敏度和高稳定性的荧光相关光谱单分子检测系统。采用高数值孔径物镜使激光束高度聚焦,并用同一物镜收集样品的荧光,单光子计数器用于实时记录荧光信号。优化系统保持物镜焦点、针孔以及单光子计数器光敏区高度同轴。采用60×1.2(NA)的水浸物镜及直径为160μm的针孔得到的检测系统结构参数为ω0和z0分别为0.42μm和1.33μm,照射微区的体积为1.3fL。单个RhodamineGreen分子可获得13倍的信噪比。用该系统获得了小分子和生物大分子(DNA片段和蛋白质)的高质量荧光相关图谱,成功实现了单个分子的检测。     

OCS分子的共振多光子电离光谱

OCS分子的真空紫外吸收光谱早有研究,但有关OCS分子的多光子电离光谱尚未见报导。我们利用可调脉冲激光器,研究了OCS分子的共振多光子电离光谱。首次观察到OCS分子在277—285nm波长范围内的多光子电离光谱。OCS由硫氰酸铵和硫酸反应制取,经多次低温蒸馏纯化。产物通过FT-IR红外光谱和     

含铅聚合物微凝胶与硫化氢反应前后在良溶剂中的分子扩散行为

用溶液聚合法制备出轻度交联的含铅微凝胶,用光子相关光谱技术测定其在良溶剂中与H2S反应前、后的扩散行为,由外推法得到在浓度无限稀时的分子扩散系数,给出微凝胶的流体力学半径。结果表明:相同量的含铅微凝胶在不同的初始浓度下与H2S反应,生成含PbS纳米微粒的凝胶；但其体积增大不同,这说明H2S与含铅微凝胶的反应既可以在分子内也可以在分子间进行,分子间的反应使含硫化铅微凝胶扩散系数随浓度的变化曲线的线性范围变小。     

含铅聚合物微凝胶与硫化氢反应前后在良溶剂中的分子扩散行为

用溶液聚合法制备出轻度交联的含铅微凝胶,用光子相关光谱技术测定其在良溶剂中与H₂S反应前、后的扩散行为,由外推法得到在浓度无限稀时的分子扩散系数,给出微凝胶的流体力学半径。结果表明:相同量的含铅微凝胶在不同的初始浓度下与H₂S反应,生成含PbS纳米微粒的凝胶;但其体积增大不同,这说明H₂S与含铅微凝胶的反应既可以在分子内也可以在分子间进行,分子间的反应使含硫化铅微凝胶扩散系数随浓度的变化曲线的线性范围变小。     

氧气在聚丙烯内吸附和扩散的分子模拟

采用巨正则Monte Carlo和分子动力学模拟相结合的方法研究了氧气在不同聚合度的聚丙烯内的吸附和扩散. 模拟结果表明, 随聚丙烯聚合度的增加, 聚丙烯对氧气的吸附量逐渐增加, 而氧气在聚丙烯内的扩散系数减小; 当聚合度增大到一定程度时, 吸附量和扩散系数都趋于一稳定值. 随温度的升高, 氧气在聚丙烯内的吸附量减少, 而扩散系数增大. 本文还应用自由体积理论探讨了氧气在聚合物内扩散的机理, 发现氧气在聚丙烯内以空穴形式存在的自由体积之间扩散, 即氧气先在一个空穴内不停振动, 然后通过聚丙烯链段运动形成的通道跳跃到下一个空穴来完成扩散. 结果表明, 较高聚合度的聚合物材料在常温及低温下使用对于其在食品包装材料中的应用是有利的, 这为食品包装材料行业相关产品的应用开发提供了一定的指导和依据.     

荧光相关光谱及其在单分子检测中的应用进展

单分子检测在生命科学、化学、物理学等领域具有重要的意义。荧光相关光谱是单分子检测的新技术,在生命科学领域有巨大的应用潜力。综述了荧光相关光谱单分子检测的原理、实验技术以及在生物分子相互作用、活细胞、核酸、疾病诊断、高通量筛选以及与毛细管电泳联用等领域的研究,并展望了其发展前景。     

动态光散射对良溶剂中酚醛型聚醚砜的研究

用动态光散射方法研究了酚酞型聚醚砜(PES-C)在良溶剂DMF中的稀溶液性质。在稀溶液中,PES-C分子由于内旋转发生链折叠,整体上表现出柔性链的性质,较好的符合球形模型;而分子链的局部刚性结构又使分子尺寸稳定;它的扩散行为随温度的变化符合Arrehnius方程。表征了PES-C分子在稀溶液中的形态结构,且给出了PES-C分子在DMF中的扩散系数、扩散活化能、无限稀时的扩散系数和流体力学半径等重要特征参数。     

利用混合溶剂消除ATRP反应制备多臂星形聚合物的凝胶现象

研究了带有苄氯基团的超支化聚苯乙烯引发苯乙烯和甲基丙烯酸甲酯的ATRP反应的动力学,在良溶剂氯苯中,该反应很容易发生凝胶.如果在氯苯溶剂中反应一段时间后,加入1,4-二氧六环作为不良溶剂,则能有效阻止凝胶反应,最终得到分子量超过百万的星形聚合物.     

ATRP法合成结构对称的双羧基聚苯乙烯及其超分子的形成

从二甲苯出发,经过溴甲基化反应、氧化反应、酯化反应和溴代反应,合成了一种四官能团的引发剂,4,6-二(溴甲基)-1,3-苯二甲酸二甲酯.用该引发剂引发苯乙烯进行原子转移自由基聚合,实验结果表明聚合反应具有活性自由基聚合的特征.通过苯乙烯的本体聚合反应获得了分子量可控、双酯基位于聚合物链中间的聚苯乙烯.经过水解反应,使聚合物中的双酯基被水解成双羧基,从而得到了结构对称的两亲性聚合物,双羧基聚苯乙烯.利用该聚合物具有分子识别的特性,与十二烷胺形成了离子键超分子化合物.此工作为超分子星形聚合物的设计合成提供了简便快捷的方法.     

Photobleaching in Two‐Photon Scanning Fluorescence Correlation Spectroscopy

Two‐photon excitation in fluorescence correlation spectroscopy (FCS) is often preferred to one‐photon excitation because of reduced bulk photobleaching and photodamage, and deeper penetration into scattering media, such as thick biological specimens. Two‐photon FCS, however, suffers from lower signal‐to‐noise ratios which are directly related to the lower molecular brightness achieved. We compare standard FCS with a fixed measurement volume with scanning FCS, where the measurement volume is scanned along a circular path. The experimental results show that photobleaching is the dominant cause of the effects observed at the high excitation powers necessary for good signal‐to‐noise ratios. Theoretical calculations assuming a nonuniform excitation intensity profile, and using the concept of generalized volume contrast, provide an explanation for the photobleaching effects commonly observed in two‐photon FCS at high excitation intensities, without having to assume optical saturation. Scanning alleviates these effects by spreading the photobleaching dose over a larger area, thereby reducing the depletion of fluorescent molecules in the measurement volume. These results, which facilitate understanding of the photobleaching in FCS and of the positive effects of scanning, are particularly important in studies involving the autocorrelation amplitude g(0), such as concentration measurements or binding studies using fluorescence cross‐correlation between two labeled species.     

Fluorescence Correlation Spectroscopy Study of Probe Diffusion in Poly(vinyl alcohol) Solutions and Gels

In this study, we demonstrate how the diffusion of probe particles in aqueous poly(vinyl alcohol) (PVA) solutions and gels is affected by: (i) the presence of cross-links, (ii) the cross-link density, (iii) the polymer concentration. We apply fluorescence correlation spectroscopy (FCS) to measure the diffusion time of a rhodamine-based fluorescent particle (TAMRA) and TAMRA-labeled dextran in PVA solutions and gels prepared at various polymer concentrations (1% to 8.6% w/v) and cross-link densities (1/400 to 1/50 cross-link monomers per PVA monomers). The measurements indicate that the probe particles are slowed down with increasing polymer concentration and with increasing cross-link density. Also, FCS can detect differences in the diffusion times measured in “fresh” and “aged” PVA solutions. We find that FCS provides a quantitative measure of network inhomogeneities.     

The Aggregation of Cyclodextrins as Studied by Photon Correlation Spectroscopy

Photon correlation spectroscopy has been used to study theaggregation processes of natural and some modified cyclodextrins (CDs) in diluted aqueoussolutions. -, -, and -CD form large, polydisperse aggregatesin water, although the aggregation capability is different depending on the macrocycle considered. -CD solutions filtered through 0.2~m give a single-modaldistribution of aggregates of 224 nm in size. The monomeric -CD can be isolated by filtering through 0.1 m. -CD displays a bimodaldistribution (monomer + aggregates) with both pore sizes. At the concentrations studied (0.012 M) the contribution in mass of the aggregates with both CDs isnegligible. -CD is much more persistent in its aggregation, even after sievingits solutions through 0.02 m filters, and time dependent. The aggregation displayed byCDs with partial substitution of the OH groups (Methyl--CD and Hydroxypropyl--CD) is much weaker, indicating the implication of the hydrophilic rims ofthe CDs in the process. High temperatures, addition of urea or electrolytes andionisation of the OH groups by raising the pH, prevent the aggregation.     

Transport of Propylene Carbonate-LiTFSI Electrolytes in P(VDF-HFP) Using Time-resolved ATR-FTIR Spectroscopy: Diffusion Coefficients and Molecular Interactions

The time-resolved attenuated total reflectance-Fourier transform infrared(ATR-FTIR) spectroscopy is employed to investigate the transport mechanism of gel electrolytes by monitoring the diffusion behavior of propylene carbonate-lithium bis(trifluoromethylsulfonyl)imide(PC-LiTFSI) solution through poly(vinylidene fluoride-co-hexafluoropropylene)(P(VDF-HFP)) films. Fickian behavior has been observed for both TFSI-and PC. Higher temperature leads to faster diffusion of TFSI~-and PC, which could be related to the increased free volume in P(VDF-HFP)matrix and rapid molecular movements upon heating. Various molecular interactions among LiTFSI, PC and P(VDF-HFP) have been recognized.During the diffusion process, PC molecules, in the form of small clusters, can firstly diffuse through the P(VDF-HFP) film and interact with P(VDFHFP) by dipole-dipole interaction, acting as the plasticizer. Then, Li~+ diffuses into P(VDF-HFP) with the help of ion-dipole interactions between Li~+and C=O of PC. Meanwhile, TFSI-diffuses through the polymer matrix in solvation states. In addition, slight ion-dipole interactions between Li~+and P(VDF-HFP) have been observed as well. Results in this work contribute to a better understanding of transport process in gel polymer electrolytes for lithium-ion batteries and support the development of improved gel polymer electrolytes by rationally regulating molecular interactions.     

Accelerating Diffusion‐Ordered NMR Spectroscopy by Joint Sparse Sampling of Diffusion and Time Dimensions

Diffusion‐ordered multidimensional NMR spectroscopy is a valuable technique for the analysis of complex chemical mixtures. However, this method is very time‐consuming because of the costly sampling of a multidimensional signal. Various sparse sampling techniques have been proposed to accelerate such measurements, but they have always been limited to frequency dimensions of NMR spectra. It is now revealed how sparse sampling can be extended to diffusion dimensions.