Tying a molecular knot with optical tweezers.

Filamentous structures are abundant in cells. Relatively rigid filaments, such as microtubules and actin, serve as intracellular scaffolds that support movement and force, and their mechanical properties are crucial to their function in the cell. Some aspects of the behaviour of DNA, meanwhile, depend critically on its flexibility-for example, DNA-binding proteins can induce sharp bends in the helix. The mechanical characterization of such filaments has generally been conducted without controlling the filament shape, by the observation of thermal motions or of the response to external forces or flows. Controlled buckling of a microtubule has been reported, but the analysis of the buckled shape was complicated. Here we report the continuous control of the radius of curvature of a molecular strand by tying a knot in it, using optical tweezers to manipulate the strand's ends. We find that actin filaments break at the knot when the knot diameter falls below 0.4 microm. The pulling force at breakage is around 1 pN, two orders of magnitude smaller than the tensile stress of a straight filament. The flexural rigidity of the filament remained unchanged down to this diameter. We have also knotted a single DNA molecule, opening up the possibility of studying curvature-dependent interactions with associated proteins. We find that the knotted DNA is stronger than actin.     

单光刀与单光镊激光微束系统

提出了构建一种用于细胞非接触操作的激光微束系统。该系统由 Nd:YAG激光束经声压、热膨胀、汽化等综合效应实现的光刀和 He- Ne激光束经光学动力学效应实现的光镊组成。将两激光束耦合到显微镜中 ,实现了生物细胞的捕获、移动、翻转、打孔等一系列操作。在此基础上 ,分析了形成光镊所必需产生梯度力场的条件和形成光刀对能量的要求 ,进行了系统的总体设计、关键部件设计和选择 ,构建了一套激光微束操作实验系统 ,得到了预期的试验结果。在该系统上成功地实现了非接触细胞操作 ,并对染色体进行了切割。     

Compliance of bacterial flagella measured with optical tweezers

The development of the gradient force optical particle trap ('optical tweezers') has made it possible to manipulate biological materials using a single beam of laser light. Optical traps can produce forces in the microdyne range on intact cells without causing overt damage: such forces are sufficient to arrest actively swimming bacteria and can overcome torque generated by the flagellar motor of a bacterium tethered to a glass surface by a flagellar filament. By calibrating the trapping force against Stokes' drag and measuring the twist that is sustained by this force, we determined the torsional compliance of flagella in tethered Escherichia coli and a motile Streptococcus. Flagella behaved as linear torsion springs for roughly half a revolution, but became much more rigid when turned beyond this point in either direction.     

Bead movement by single kinesin molecules studied with optical tweezers

Kinesin, a mechanoenzyme that couples ATP hydrolysis to movement along microtubules, is thought to power vesicle transport and other forms of microtubule-based motility. Here, microscopic silica beads were precoated with carrier protein, exposed to low concentrations of kinesin, and individually manipulated with a single-beam gradient-force optical particle trap ('optical tweezers') directly onto microtubules. Optical tweezers greatly improved the efficiency of the bead assay, particularly at the lowest kinesin concentrations (corresponding to approximately 1 molecule per bead). Beads incubated with excess kinesin moved smoothly along a microtubule for many micrometres, but beads carrying from 0.17-3 kinesin molecules per bead, moved, on average, only about 1.4 microns and then spontaneously released from the microtubule. Application of the optical trap directly behind such moving beads often pulled them off the microtubule and back into the centre of the trap. This did not occur when a bead was bound by an AMP.PNP-induced rigor linkage, or when beads were propelled by several kinesin molecules. Our results are consistent with a model in which kinesin detaches briefly from the microtubule during a part of each mechanochemical cycle, rather than a model in which kinesin remains bound at all times.     

Single-cell discrimination based on optical tweezers Raman spectroscopy

The ability to discriminate between single cells in a label-free and noninvasive fashion is important for the classification of cells, and for the identification of similar cells from different origins. In this paper, we present the Raman spectroscopy-based identifi- cation of different types of single cells in aqueous media, and discrimination between the same types of cells from different donors using a novel Laser Tweezers Raman Spectroscopy (LTRS) technique, which combines laser trapping and micro-Raman spectroscopy. First, we measured the spectra of individual living human erythrocytes, i.e. red blood cells, and leucocytes (U937 cancer cells). High-quality Raman spectra with low fluorescence were obtained using a home-LTRS apparatus and 20 cells were measured for each cell type. The smoothing, baseline subtraction, and normalization of the data were followed by a principal components analysis (PCA). The PCA loading plots showed that the two different types of cells could be completely separated based only on the first component (PC1) (i.e. the peaks at 1300 cm1 ); the discrimination accuracy could therefore reach 100%. More than 50 spectra were taken for each erythrocyte obtained from the four healthy volunteers. The average discrimination accuracy was 84.5% for two random individuals taken from the four volunteers, according to the first and second PCs. This work demonstrates that LTRS is a powerful tool for the accurate identification and discrimination of single cells, and it has the potential to be applied for the highly sensitive identification of cells in clinical diagnosis and medical jurisprudence.     

Measurements of leucocyte membrane elasticity based on the optical tweezers

A 1-μm in diameter polystyrene bead coated with lectin is trapped by optical tweezers whics is formed by a focused laser beam (740nm).A leucocyte adhered to the bottom of sample cell is chosen to close to the trapped bead.When their stable combination is confirmed,the leucocyte is displaced by moving the sample stage.A“tether”is then formed between the trapped bead and the membrane.The force acting on the tether is measured by a detector equipped on the optical tweezers system.The deformation of the membrane is diverse in different contact conditions.When the contact area is small,the tether is very thin and the force on it is 7.4pN(10^-12N),while the tether is much thicker under a larger contact area and its corresponding force is about 14pN.It is presumed that the latter is related to the deformation of cytoskeleton.     

光镊技术在生命科学研究中的发展与应用

介绍了光镊技术的原理和系统结构,追踪了光镊操作和探测技术从微米到纳米的进展,最后给出了纳米光镊在生物技术领域的应用.     

基于FDTD对尖端为轴锥体的光纤光镊的模拟分析

基于动量守恒,采用时域有限差分法(FDTD),仿真模拟了光纤光镊轴锥角和工作距离关系及捕获力大小和轴锥角的关系.结果表明工作距离和捕获力的大小和轴锥角度的大小有着密切的关系.模拟结果与其它相关文件报道的实验结果基本相符合.     

光纤中脉冲传输的稳定性数值分析

光脉冲在光纤中传输的稳定性是光通信及其相关领域的一个关键问题.针对包含高阶色散的光脉冲传输方程,通过数值方法分析了其稳态的稳定性,得出了稳定性条件,给出了部分仿真实验结果.研究结果表明,若考虑光纤的损耗以及高阶色散因素,其稳定性范围逐渐变小.     

基于多波长SRP的分布式WDM光网络光路建立研究

针对WDM光网络的单波长预留协议中经常出现多个连接请求竞争同一波长而产生冲突的问题,提出将多波长预留概念扩展到分离预留协议以及基于马尔可夫的分离预留协议(MSRP)中。首先,讨论了三种多波长方案,利用多波长进行可能选择和进一步分离,从而减少请求的整体阻塞;然后,将它们与对应的单波长协议进行比较,发现单波长协议的性能得到了明显改善;最后,仿真实验使用三种多波长协议建立光路,比较结果表明,多波长MSRP执行效果最好。     

自聚焦光导纤维中光的传播

推导了自聚焦光导纤维中光线传播的路径方程,阐明了自聚焦作用的物理实质。     

光栅光阀MEMS光开关系统设计

分析了光栅光阀(grating light valve,GLV)的光学特性,对GLV结构进行了计算机仿真。利用GLV在静电力驱动下具有较高的光学效率、快速的调制速率等优点,基于平行平板电容模型的GLV模拟算法,设计了光栅光阀1×2 MEMS(micro-electro-mechanical systems,微机电系统)光开关,经CoventorWare仿真表明,在1.55μm光波长正入射及给定GLV参数时,所设计的光开关1级衍射效率达到50%,开关时间为微秒级,并具有耐磨损、时间快、寿命长等特点。     

基于Tellurite光纤的受激布里渊散射慢光数值模拟

利用受激布里渊散射对Tellurite光纤实现慢光进行数值研究.通过数值模拟得到在小信号以及增益饱和情况下,斯托克斯脉冲的时间延迟和脉冲展宽随增益的变化关系;同时模拟了在固定的增益参数下,时间延迟及脉冲展宽随斯托克斯峰值功率的变化关系.结果表明由于Tellurite光纤具有较高的增益系数,可以有效减少增益饱和对斯托克斯脉冲的时间延迟的限制并且具有较大的延迟时间,同时表明较高的斯托克斯峰值功率也是造成增益饱和的重要原因.     

基于光场调控的光学图像相关处理:原理与技术进展

光学图像识别以信息处理容量大、运算速度快(基本上接近光速)和高度并行处理能力等特点得到研究人员的广泛关注,在成像、生物医疗、国防军事等领域均具有广阔的应用前景.近年来,随着空间光场调控技术的发展,人们对结构光场的认识愈加深入,使得光学图像识别这一领域焕发出新的生命力.本文从范德·拉格特相关器(Vander Lugt Correlator, VLC)和联合变换相关器(Joint Transform Correlator, JTC)这两大主要光学图像识别相关器的基本原理出发,介绍了光场调控在光学图像相关识别及处理应用中的物理原理与技术进展.从线性光学、非线性光学以及量子光学这三个角度分别介绍不同领域如何通过光场调控实现全光型的光学图像相关处理.     

啁啾高斯光脉冲和群速度色散对带前置放大器光接收机灵敏度的影响研究

研究了啁啾高斯光脉冲信号对带前置放大器光接收机灵敏度的影响,以及群速度色散对光接收机灵敏度恶化量的影响.发现适当选取高斯光脉冲信号的占空比、啁啾分量、光接收机均衡滤波器输出的升余弦频谱波形滚降因子的值可以提高光接收机灵敏度;群速度色散存在时光脉冲的宽度并非越小越好.结果对实际光接收机的分析和设计有一定指导意义.     

基于光学游标测量原理的平行光入射角度测量方法

为解决平行光入射角度精确测量时,很难同时实现高精度和大量程两方面的测量性能要求的问题,提出了一种基于光学游标测量原理的大量程条件下的高精度平行光入射角度测量方法及测量装置。基于该方法设计的测量装置,在±64°测量范围内,全量程测量精度优于0.02°。对测量装置的实验结果表明,实验结果与理论分析相吻合。该装置可以在航天、精密计量测试以及自动控制等领域实现对平行光入射角度的精密测量。