Detecting CD20-Rituximab interaction forces using AFM single-molecule force spectroscopy

The invention of atomic force microscopy(AFM) has provided new technology for measuring specific molecular interaction forces.Using AFM single-molecule force spectroscopy(SMFS) techniques,CD20-Rimximab rupture forces were measured on purified CD20 proteins,Raji cells,and lymphoma patient B cells.Rimximab molecules were linked onto AFM tips using AFM probe functionalization technology,and purified CD20 proteins were attached to mica using substrate functionalization technology.Raji cells(a lymphoma cell line) or lymphoma patient cells were immobilized on a glass substrate via electrostatic adsorption and chemical fixation.The topography of the purified CD20 proteins,Raji cells,and patient lymphoma cells was visualized using AFM imaging and the differences in the rupture forces were analyzed and measured.The results showed that the rupture forces between the CD20 proteins on Raji cells and Rituximab were markedly smaller than those for purified CD20 proteins and CD20 proteins on lymphoma patient B cells.These findings provide an effective experimental method for investigating the mechanisms underlying the variable efficacy of Rituximab.     

Research progress in quantifying the mechanical properties of single living cells using atomic force microscopy

The advent of atomic force microscopy （AFM） provides a powerful tool for investigating the behaviors of single living cells under near physiological conditions. Besides acquiring the images of cellular ultra-microstruc- tures with nanometer resolution, the most remarkable advances are achieved on the use of AFM indenting tech- nique to quantify the mechanical properties of single living ceils. By indenting single living cells with AFM tip, we can obtain the mechanical properties of cells and monitor their dynamic changes during the biological processes （e.g., after the stimulation of drugs）. AFM indentation-based mechan- ical analysis of single cells provides a novel approach to characterize the behaviors of cells from the perspective of biomechanics, considerably complementing the traditional biological experimental methods. Now, AFM indentation technique has been widely used in the life sciences, yielding a large amount of novel information that is meaningful to our understanding of the underlying mechanisms that govern the cellular biological functions. Here, based on the authors＇ own researches on AFM measurement of cellular mechani- cal properties, the principle and method of AFM indentationtechnique was presented, the recent progress of measuring the cellular mechanical properties using AFM was summa- rized, and the challenges of AFM single-cell nanomechani- cal analysis were discussed.     

The asymmetric membrane structure of erythrocytes from Crucian carp studied by atomic force microscopy

Cell membranes play a key role in cellular activities. Fish erythrocytes, prototype of the nucleated erythrocytes of lower vertebrates, are predominantly oval, biconvex discs with elliptical nucleus and much larger in size than human erythrocytes. In attempts to disclose the correlation of membrane structure between fish and human erythrocytes, we used in situ atomic force microscope （AFM） combined with single-molecule force spectroscopy to study the membrane structure of Crucian carp erythrocytes under quasi-native conditions. Our results revealed the asymmetric distribution of proteins in Crucian carp erythrocyte membrane： the outer leaflet of membrane is rather smooth without any proteins, whereas the inner leaflet of membrane is very rough with dense proteins. The asymmetry of fish erythrocyte membrane structure fits well with the semi-mosaic model of human erythrocyte membrane structure. This similarity of membrane structure between human and fish erythrocytes extends the semimosaic model of erythrocytes membrane structure to a wider range of species.     

原子力显微术对人体腰椎间盘组织超微结构的研究

报道了采用原子力显微镜对腰椎间盘组织成分的观察结果，并对胶原组织从结构上进行了分类，为深入到生物分子层次的研究提供了非常有意义的依据。     

品质因数调控技术提高AFM横向分辨力的研究

液体中轻敲模式下微悬臂梁的低品质因数会限制原子力显微镜的力灵敏度和成像分辨率，品质因数调控技术可以提高品质因数．在分析品质因数调控技术机理的基础上，分别在一般轻敲模式下和有品质因数调控电路支持的轻敲模式下，利用琼脂糖凝胶作为样品，测得力曲线．分析比较这2种情况下的曲线，表明在无品质因数调控时，微悬臂梁的驱动信号的振幅是恒定的，而在有品质因数调控时，微悬臂梁驱动电压随着针尖样品间距的减小而衰减，从而导致针尖一样品间的相互作用力减小，横向分辨力提高．为了验证该分析结果，检测了液体中的蛋白质分子．在有品质因数调控时，很容易获得清晰的蛋白质分子图像，由此证明了上述结论．     

Direct measurement of compression spring constant of single DNA molecule with AFM

The understanding of mechanical responses of individ-ual macromolecules under a small external load (usually F<0.5 nN) is of profound importance because the induced conformational transition can result in the change of bio-logical functions[1?3]. The advent of new instrumentations, especially the development of Pico-Newton force tech-nology, has made it possible to investigate the dynamic behavior of single biomolecule and manipulate it to make direct measurements of its elastic properties[4?…     

Elimination of bistability in constant-phase mode in atomic force microscopy

By presenting the phase properties of bistability in amplitude-modulation atomic force microscopy, we put forward a technique, the constant-phase mode, which may eliminate bistability. Using this approach, we keep the phase shift between driving and oscillation constant, slightly above -90°. In addition to the adjustment of the free amplitude, we add to amplitude-modulation atomic force microscopy another feedback so that the tip always oscillates in the high-amplitude state. A numerical simulation is carried out to demonstrate that the algorithm prevents bistability effectively.     

Conformations and adsorption behavior of poly（allylamine hydrochloride） studied by single molecule force spectroscopy

Poly（allylamine hydrochloride） （PAH）, which is frequently used in fabricating polyelectrolyte multilayer films, was studied by single molecule force spectroscopy （SMFS）. Plenty of force-extension curves with a long plateau were obtained in water, indicating that train-like structure was predominant when PAH was adsorbed on the substrate. It was found that the peak-type force-extension curves of PAH in water were not able to be fitted by the modified freely-jointed chain model. Additionally, there was a flat region in the derivative of force-extension curves. Thus, it was inferred that PAH chain in water was in a special conformation and underwent a ＂conformational transition＂ under the stretching of an external force. This phenomenon did not appear in the SMFS experiment in 1 mol/L urea solution, which indicated that urea was able to break the special conformation.     

耳蜗毛细胞换能的生物物理特性

耳蜗的声感受是通过将大气压的微小波动转换成沿听神经传导的AP而实现的，HC在这-机-电换能过程中起关键作用。近二十年来，HC换能的生物物理特性研究取得许多重要突破，已在诸多方面从根本上改变了人们对听觉机制的传统认识。本文从HC换能模型、IHC与OHC的功能差异以及耳蜗声分析主动机制等三方面对这一领域进行了讨论与展望。     

摩擦力对测量活塞环切向弹力影响的研究

本文采用推广的Ｍａｘｗｅｌｌ－Ｍｏｈｒ定理分析了测量活塞环的弹力Ｆｔ、Ｆｄ及Ｆｓ与平均径向压力Ｐｍ之间的数学关系，并采用力的平衡原理推导出包含摩擦力的Ｆｔ与Ｐｍ间的函数式．     

Effects of heavy metal on dielectric properties of E. coli revealed by dielectric spectroscopy

Dielectric spectroscopy of E. coli cell before and after exposure to heavy metals Cd^2＋ , Cu^2＋ , Zn^2＋ and Ca^2＋ was investigated. The results indicate that changes in dielectric spectra reflect effects of heavy metal on the structure and function of E. coli cells. Heavy metal can change membrane capacitance as well as pennittivity and conductivity of the cytoplasm. Changes in volume fraction suggested that dielectric measurement could monitor the growth of E. coli cells. These results demonstrated that dielectric spectroscopy was a potential effective technique for studying electric properties of biological cells.     

Micro-friction of diazoresin/polyacrylic acid self-assembly films in water with atomic force microscopy

Ultrathin films composed of diazoresin（DR）and polyacrylic acid（PAA）were fabricated.The surface morphology of the films in water was measured using an atomic force microscopy（AFM）.The self-assembly technique makes the surface rather flat and uniform.The friction force and its dependence on the velocity differ from the surface charge of the thin films.The friction force of repulsive DR/PAA film increases linearly with velocity and has lower values than that of attractive DR film over the full range of velocity.As the velocity increases,the attractive friction of DR film first decreases to a minimum at a velocity of 2 line/s and then increases all the way.When the surface is repulsive to the friction substrate,the friction of thin films that is determined by hydrated lubrication of polymer chains that is ultralubricated;when it is adhesive to the friction substrate,the friction is mainly contributed from the elastic deformation of adsorbed polymer chains in the low velocity region and from viscous sliding in the presence of hydrated-layer lubrication of the polymer chains in the higher velocity region.     

位置扰动型电液力控制系统多余力的抑制

在位置扰动下,电液力控制系统中液压缸被动运动引起强迫流量,导致多余力的产生。为了减少多余力对系统跟踪性能的影响,首先建立位置扰动下的电液力控制系统数学模型,分解出多余力表达式,在此基础上提出采用一个与系统中电液伺服阀主阀芯运动方向相反的补偿用电液伺服阀来消除多余力的方案,然后以一个典型的液压系统为例,借助Simulink软件进行数值仿真分析。结果表明,补偿阀能够及时、有效地排出强迫流量并大幅减少多余力,位置扰动下多余力减少量最多达93.5%,输出力跟踪幅值误差不大于2%,稳态误差不大于1.8%。     

Imaging surface structure of purple membrane partly dissolved by CHAPS with atomic force microscope

Atomic force microscope was employed to study the surface structure of purple membrane (PM) using contact mode in liquid. The surface structures of native PM and PM partly dissolved by detergent CHAPS were com- pared. Results show that 6 mmol/L CHAPS could induce some cracks and holes in PM. While Bateriorhodopsin (BR) was still presented as trimers in the two-dimensional hex- agonal structure. We assume that it was caused by the inter- action between CHAPS micellar and PM. Both absorption spectra and flash photolysis kinetic spectra indicated that BR抯 biochemical functions have been changed.     

井下钻柱受力实测接头研究

为了进一步了解钻进过程中钻柱在井下的实际受力状况 ,研制了井下钻柱受力实测接头。介绍了该接头的数据采集与处理方法、测量的参数、总体结构和基本工作特性。用所研制的测力接头在胜利油田进行了井下实际测量 ,得到了各参数的实测曲线。对实测结果的初步分析表明 ,下钻过程中钻柱轴向加速度的最大值可达到 98m/s2 ,由动载荷引起的钻柱轴向力的附加值最大可达到悬重的 5 %。     

Change of proton motive force across thylakoid membrane in soybean leaf during state transitions

Change of proton gradient across thylakoid membrane in soybean leaves was studied with millisecond delayed light emission(ms-DLE) during the coures of state transitions which were indicated by the cholrophyll fluores-cence at room temperature and 77K.When dark-adapted leaves were induced to state Ⅰ with far-red light,Fm/F0,F685/F735 and the intensity of fast phase of ms-DLE were af-fected slightly.However,during the induction to state Ⅱ with red light,both Fm/F0 and F685/F735 decreased immedi-ately and the former were quicker than the latter.In this interval,the intesity of fast phase of ms-DLE increased to a maximum and then decreased to a lower valus during the transition to stateⅡ.Nigericin,an uncoupler which elimi-nates the proton gradient across thylakoid membrane,inhib-ited the increase in the intensity of fast phase of ms-DLE during the transition to state Ⅱ.Another uncoupler,valino-mycin,which eliminates the membrane potential,did not affect the changes of the intensity of fast phase.These results suggest that the prompt increase in the intensity of fast phase of ms-DLE at the beginning of transitions to state Ⅱ is cor-related mainly with the proton gradient released from water oxidation in photosystemⅡ.     

Effect of Si on austenite stabilization,martensite morphology,and magnetic properties in Fe-26%Ni-x%Si alloys

The effect of Si on the austenite stabilization, martensite morphology, and magnetic properties in Fe-26%Ni-x%Si (x=3.5, 5, and 6) alloys have been studied by means of transmission electron microscopy (TEM) and M?ssbauer spectroscopy techniques. TEM observations reveal that the martensite morphology is closely dependent on the Si content. The volume fraction changes of martensite and austenite phases, the hyperfine magnetic field, and isomer shift values have been determined by Mssbauer spectroscopy. The M?ssbauer study reveals that the hyperfine magnetic field, the isomer shift values and the volume fraction of martensite decrease with increasing Si content.     

透微波AlN-BN复合陶瓷介电性能研究进展

简述了透微波材料的介电性能要求,综述了AlN-BN复合陶瓷材料介电性能的研究进展,分析讨论了AlN-BN复合材料的制备工艺、极化机理、影响因素,最后对改进AlN-BN复合材料的介电性能的研究方向提出了展望.     

页岩有机质纳米力学性质研究进展

页岩有机质纳米尺度下的力学行为目前不够明确且利用常规实验仪器无法准确获得,表征其纳米尺度下的力学性质,对于搭建微观-宏观岩石力学模型和实现高效水力压裂是极具现实意义的。基于近年国内外关于页岩有机质纳米力学性质表征等方面所取得的研究进展,总结了目前常用的表征技术、力学性质主要特征及主控因素。综合结果表明,纳米压痕和原子力显微镜是目前表征纳米力学性质常用的技术与方法,两者在精度、分辨率、设备技术等方面都存在各自的优势或缺陷;目前有机质纳米力学性质的测定主要集中在弹性模量和硬度,成熟度和温度在不同程度上改变着有机质的内部结构,从而改变其力学性质;提出了"多尺度""多技术""多角度""多学科"等工作设想与建议。