A Method for Measuring the Three-Dimensional Refractive-Index Distribution of Single Cells Using Proximal Two-Beam Optical Tweezers and a Phase-Shifting Mach—Zehnder Interferometer

This paper describes a method for measuring the three-dimensional (3D) refractive-index distribution in a single cell. The method can be used to observe the distribution of cell components without fluorescence staining. The two-dimensional optical path length distributions from multiple directions are obtained by non-contact rotation of the cell. These optical path lengths are converted into the line integrals of the refractive index, and the 3D refractive-index distribution is reconstructed by means of computed tomography. The refractive-index distribution in a breast cancer cell can be measured using a phase-shifting Mach—Zehnder interferometer in conjunction with proximal two-beam optical tweezers.     

阵列光镊的发展与应用

在生命科学研究中和在微量液体环境下分离液体中的细胞、生物大分子或胶体颗粒一直是一项具有挑战性的工作。"光镊"技术自20世纪80年代被提出到现在,在生命科学研究领域已经得到了日益广泛的运用。激光对细胞捕获的作用已得到进一步扩展,二维"光镊阵列"技术是近年来"光镊"技术中最重要的发展之一。讨论了阵列光镊的发展现状及基本原理,分析了它在生命科学中的应用,并对其发展趋势进行了展望。     

Coherent Activation of DNA Tweezers: A “SET–RESET” Logic System

Open sesame : Aptamer–substrate complexes activate the coherent operation of two tweezers that act as a “SET–RESET” logic system. Each tweezer cycles between a fluorescent open state and a closed quenched state (Q=quencher, F=fluorophore) when triggered by adenosine monophosphate (AMP) and adenosine deaminase (AD).

     

Mechanical properties of single motor molecules studied by three-dimensional thermal force probing in optical tweezers.

A new method combining three-dimensional (3D) force measurements in an optical trap with the analysis of thermally induced (Brownian) position fluctuations of a trapped probe was used to investigate the mechanical properties of a single molecule, the molecular motor kinesin. One kinesin molecule attached to the probe was bound in a rigorlike state to one microtubule. The optical trap was kept weak to measure the thermal forces acting on the probe, which were mainly counterbalanced by the kinesin tether. The stiffness of kinesin during stretching and compression with respect to its backbone axis were measured. Our results indicate that a section of kinesin close to the motor domain is the dominating element in the flexibility of the motor structure. The experiments demonstrate the power of 3D thermal fluctuation analysis to characterize mechanical properties of individual motor proteins and indicate its usefulness to study single molecule in general     

酯键型鹅去氧胆酸分子钳对氨基酸甲酯的手性识别

利用紫外可见光谱差光谱滴定法考察了新型鹅去氧胆酸分子钳1～6对D／L氨基酸甲酯的对映选择性识别性能。结果表明,分子钳1～6对所考察的氨基酸甲酯均具有识别能力,其对D-氨基酸甲酯的识别优于对L-氨基酸甲酯的识别。受体与底物间的大小、形状匹配,微环境效应等对识别性能均有重要影响。识别作用的主要推动力来自受体与底物之间的互补氢键,受体与底物芳环之间的π-π堆叠作用等非共价键作用力的协同作用。     

Label‐Free Biosensing over a Wide Concentration Range with Photonic Force Microscopy

We present a label‐free biosensor that measures molecular interactions between biomolecules on the surface of a probe bead and substrate over a wide concentration range. This system is capable of detecting target biomolecules with concentrations varying from 10 nM to 0.1 pM , with high selectivity and sensitivity.     

Metalla‐Assembled Electron‐Rich Tweezers: Redox‐Controlled Guest Release Through Supramolecular Dimerization

Developing methodologies for on‐demand control of the release of a molecular guest requires the rational design of stimuli‐responsive hosts with functional cavities. While a substantial number of responsive metallacages have already been described, the case of coordination‐tweezers has been less explored. Herein, we report the first example of a redox‐triggered guest release from a metalla‐assembled tweezer. This tweezer incorporates two redox‐active panels constructed from the electron‐rich 9‐(1,3‐dithiol‐2‐ylidene)fluorene unit that are facing each other. It dimerizes spontaneously in solution and the resulting interpenetrated supramolecular structure can dissociate in the presence of an electron‐poor planar unit, forming a 1:1 host–guest complex. This complex dissociates upon tweezer oxidation/dimerization, offering an original redox‐triggered molecular delivery pathway.     

Determinants for Fusion Speed of Biomolecular Droplets

Biomolecular droplets formed through phase separation have a tendency to fuse. The speed with which fusion occurs is a direct indicator of condensate liquidity, which is key to both cellular functions and diseases. Using a dual-trap optical tweezers setup, we found the fusion speeds of four types of droplets to differ by two orders of magnitude. The order of fusion speed correlates with the fluorescence of thioflavin T, which in turn reflects the macromolecular packing density inside droplets. Unstructured protein or polymer chains pack loosely and readily rearrange, leading to fast fusion. In contrast, structured protein domains pack more closely and have to break extensive contacts before rearrangement, corresponding to slower fusion. This molecular interpretation for disparate fusion speeds provides mechanistic insight into the assembly and aging of biomolecular droplets.