共查询到20条相似文献，搜索用时 182 毫秒
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利用扫描隧道显微镜对单分子表征与控制的研究进展 总被引：1，自引：0，他引：1
扫描隧道显微镜能探测材料表面局域的原子级分辨率的空间和电子结
构，可操作性强，极大地增强了科学家表征单分子结构，研究单分子物理、化学特性，和操
纵单原子、单分子并构造纳米器件的能力。本文介绍了近年来利用扫描隧道显微镜进行单分
子表征和操纵的最新研究进展，讨论了在单分子尺度下若干特殊的物理现象和效应，说明了
单分子研究对物理学和其他学科发展所提供的机遇和挑战。 相似文献
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分子操纵是当前物理学发展的一个前沿领域。在微米、亚微米和纳米尺度上对分子的直接操纵和探测是ＤＮＡ芯片的物理、化学基础。文章在纳米科技研究工作的基础上对分子操纵和与之相关的交叉技术ＤＮＡ芯片的发展和应用作一概述。 相似文献
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化学通过化学键的剪裁和重组,以及超越分子层次的非共价作用和组装,创造和构建了一个全新的物质世界,为其它学科的创新研究和快速发展提供了不竭的知识基础和物质保障。纵观化学科学近年来的发展,化学正在不断走向＂精准＂化。本文结合国内外化学学科发展的现状,从合成化学,单分子单原子操纵和自组装三个方面对化学走向精准化的趋势进行了评述。首先,从官能团化学键种类转化控制的区域选择性到反应产物空间构型控制的立体选择性,两个方面论述了合成化学在反应选择性控制上走向精准化;其次探讨了利用单分子和单原子的操纵来实现分子和原子层次上对化学反应进行精确控制的策略;第三,则对利用自组装这一新一代的方法来实现分子层次以上有序结构的精准构建进行了讨论和展望。 相似文献
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中国科大制成新型单分子整流器 总被引：1，自引：0，他引：1
《科学中国人》2005,(8):46-46
日前，中国科学技术大学微尺度物质科学国家实验室在富勒烯单分子研究中又获重要进展。他们成功将富勒烯单分子中的一个碳原子用氮原子取代，并利用单电子隧穿效应，成功研制成仅由一个分子组成的新型单分子整流器。该分子器件有着和传统单分子整流器不同的工作原理，在重复性和可控性方面有着明显的优势。这是他们继用单分子操纵手段实现由两个富勒烯分子构成负微分电导二极管后，所取得的又一重要研究进展。 相似文献
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对于纳米技术,科学家们认为:它“将引起一场产业革命,其深远的意义堪与18世纪的工业革命相媲美”。基本概念纳米科学究竟研究什么?它是研究在千万分之一米到十亿分之一米范围内,原子、分子等的运动和变化的学问。在这一尺度范围内对原子、分子进行操纵和加工的技术称为纳米技术(“纳米技术”这个术语来自“纳米”一词,1纳米即1米的十亿分之一)。在这仅有一微米的千分之一的微小长。至于什么是纳米技术,不同的研究领域和研究人员的看法大相径庭。从迄今为止的研究状况来看,大体上分为三种概念。一是德雷克斯勒博士提出的“分子纳米技术”的概… 相似文献
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AC Faradaic reactions have been reported as a mechanism inducing non-ideal phenomena such as flow reversal and cell deformation in electrokinetic microfluidic systems. Prior published work described experiments in parallel electrode arrays below the electrode charging frequency (fc), the frequency for electrical double layer charging at the electrode. However, 2D spatially non-uniform AC electric fields are required for applications such as in plane AC electroosmosis, AC electrothermal pumps, and dielectrophoresis. Many microscale experimental applications utilize AC frequencies around or above fc. In this work, a pH sensitive fluorescein sodium salt dye was used to detect [H+] as an indicator of Faradaic reactions in aqueous solutions within non-uniform AC electric fields. Comparison experiments with (a) parallel (2D uniform fields) electrodes and (b) organic media were employed to deduce the electrode charging mechanism at 5 kHz (1.5fc). Time dependency analysis illustrated that Faradaic reactions exist above the theoretically predicted electrode charging frequency. Spatial analysis showed [H+] varied spatially due to electric field non-uniformities and local pH changed at length scales greater than 50 μm away from the electrode surface. Thus, non-uniform AC fields yielded spatially varied pH gradients as a direct consequence of ion path length differences while uniform fields did not yield pH gradients; the latter is consistent with prior published data. Frequency dependence was examined from 5 kHz to 12 kHz at 5.5 Vpp potential, and voltage dependency was explored from 3.5 to 7.5 Vpp at 5 kHz. Results suggest that Faradaic reactions can still proceed within electrochemical systems in the absence of well-established electrical double layers. This work also illustrates that in microfluidic systems, spatial medium variations must be considered as a function of experiment time, initial medium conditions, electric signal potential, frequency, and spatial position. 相似文献
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Thermodynamic systems with variable mass, like liquid/vapor equilibria and chemical reactions, are represented as networks having discrete elements and connections using bond graph symbols. The mass bond has special properties which are explained by entropy and volume stripping and indicate the reason why the derivative of the free enthalpy, not the internal energy, is the driving effort of chemical reactions. Chemical friction is represented by RS-fields that dissipate power which is different from the observed heat rate of chemical reactions. Different reticulations apply to reactions near and far from chemical equilibrium; their relation to experimental reaction kinetics and order of reaction is discussed. 相似文献
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利用低温超高真空扫描隧道显微镜,对吸附于金表面的单个钴酞菁分子进行单分子选键化学"手术",成功"剪裁"了分子外围的氢原子,并使其与金属表面形成稳定的化学键.该成果发表在Science上,审稿人给予高度评价,并邀请美国专家撰写专文介绍和评述该成果. 相似文献
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Fei Xie Baojun Wang Wei Wang Tian Dong Jianhua Tong Shanhong Xia Wengang Wu Zhihong Li 《Biomicrofluidics》2013,7(3)
Some aqueous reactions in biological or chemical fields are accomplished at a high temperature. When the reaction temperature is higher than 100 °C, an autoclave reactor is usually required to elevate the boiling point of the water by creating a high-pressure environment in a closed system. This work presented an alternative continuous flowing microfluidic solution for aqueous reaction with a reaction temperature higher than 100 °C. The pressure regulating function was successfully fulfilled by a small microchannel based on a delicate hydrodynamic design. Combined with micro heater and temperature sensor that integrated in a single chip by utilizing silicon-based microfabrication techniques, this pressure regulating microchannel generated a high-pressure/high-temperature environment in the upstream reaction zone when the reagents continuously flow through the chip. As a preliminary demonstration, thermal digestion of aqueous total phosphorus sample was achieved in this continuous flowing micro-reactor at a working pressure of 990 kPa (under the working flow rate of 20 nl/s) along with a reaction temperature of 145 °C. This continuous flowing microfluidic solution for high-temperature reaction may find applications in various micro total analysis systems. 相似文献
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In order to fully explore and utilize the advantages of droplet-based microfluidics, fast, sensitive, and quantitative measurements are indispensable for the diagnosis of biochemical reactions in microdroplets. Here, we report an optical detection technique using two-photon fluorescence lifetime imaging microscopy, with an aligning-summing and non-fitting division method, to depict two-dimensional (2D) maps of mixing dynamics by chaotic advection in microdroplets with high temporal and spatial resolution. The mixing patterns of two dye solutions inside droplets were quantitatively and accurately measured. The mixing efficiency in a serpentine droplet mixer was also quantified and compared with the simulation data. The mapped chaotic mixing dynamics agree well with the numerical simulation and theoretical prediction. This quantitative characterization is potentially applicable to the real-time kinetic study of biological and chemical reactions in droplet-based microfluidic systems. 相似文献
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Roger A. Grey Author Vitae 《Journal of The Franklin Institute》2004,341(3):197-205
Throughout his distinguished career of over 40 years, Robin Hochstrasser has made significant contributions to several areas of science in the fields of chemical and biochemical physics. He has been at the forefront and made fundamental contributions to the fields of photochemistry, solid-state chemistry, ultra-fast laser spectroscopies, and protein dynamics. He has been a prolific researcher, producing over 560 publications. His work has been characterized by experts in the fields as “a constant stream of experiments of lasting significance” (J. Phys. Chem. 100 (1996) 11791).Robin began his career in the 1960s using a variety of magnetic and electric field measurements to study crystals at low temperatures to understand spin quantization in solids and electron exchanged-mediated energy transfer. This work, described as a “classic contribution” (J. Phys. Chem. 100 (1996) 11791) was the basis for much of the subsequent experimental and theoretical work on the effect of magnetic fields on molecular spectra and on the measurements of dipole moments.In the late 1970s, Robin recognized the power of laser technology for the study of molecules and soon became a leader in the field investigating solid, gas phase, and condensed phase systems. He developed and applied various ultra-fast laser techniques to study the structure and dynamics of complex molecules in liquid phase, chemical, and biochemical reactions. He made seminal contributions to the development of two-dimensional infrared spectroscopy (2D IR) on a time scale of a picosecond or less. This 2D IR spectroscopy measures coupling between two functional groups in a large molecule and can thus be used to measure distances, as for example, two amide carbonyl groups in a peptide molecule. On the ultra-fast timescale, one application of 2D IR is to gain information on the rate of protein folding and unfolding in solution. Some of Robin's greatest contributions to understanding biomolecules are said to be in the experimental studies on the picosecond and femtosecond dynamics of heme proteins. Using techniques he developed he was able to observe the interactions of oxygen, carbon monoxide, and nitric oxide with hemoglobin inside the protein. 相似文献
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Models for chemical reaction kinetics typically assume well-mixed conditions, in which chemical compositions change in time but are uniform in space. In contrast, many biological and microfluidic systems of interest involve non-uniform flows where gradients in flow velocity dynamically alter the effective reaction volume. Here, we present a theoretical framework for characterizing multi-step reactions that occur when an enzyme or enzymatic substrate is released from a flat solid surface into a linear shear flow. Similarity solutions are developed for situations where the reactions are sufficiently slow compared to a convective time scale, allowing a regular perturbation approach to be employed. For the specific case of Michaelis-Menten reactions, we establish that the transversally averaged concentration of product scales with the distance x downstream as x(5/3). We generalize the analysis to n-step reactions, and we discuss the implications for designing new microfluidic kinetic assays to probe the effect of flow on biochemical processes. 相似文献
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【目的/意义】爆发式增长的文献资源为传统的阅读活动带来了困难,也给STM图书的组织与服务提出了
新的要求。图书标注框架是图书内容与形式的规范化表示,对于解决图书的深度标引和知识关联具有重要意义。
【方法/过程】首先从用户需求出发明确了STM图书资源标注框架的构建原则,而后从图书的物理特征、内容特征、
增强特征和使用特征4个维度设计了本文框架包含的实体对象及其语义关系,最后展现了利用该框架进行STM图
书知识建模表示的过程,并通过应用案例验证了本文框架的可用性。【结果/结论】该标注框架具有需求驱动、多维
揭示、深度描述和语义关联等特征,对于支持STM图书资源的上层服务具有参考价值。【创新/局限】本文设计了
STM图书资源的标注框架,并选取应用实例探究其知识揭示与表达能力,但未能从知识服务视角对标注结果开展
进一步的应用研究。 相似文献
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Yu-Chiu Kao Meng-Hua Hsieh Chung-Chun Liu Huei-Jyuan Pan Wei-Yu Liao Ji-Yen Cheng Po-Ling Kuo Chau-Hwang Lee 《Biomicrofluidics》2014,8(2)
We employed direct-current electric fields (dcEFs) to modulate the chemotaxis of lung cancer cells in a microfluidic cell culture device that incorporates both stable concentration gradients and dcEFs. We found that the chemotaxis induced by a 0.5 μM/mm concentration gradient of epidermal growth factor can be nearly compensated by a 360 mV/mm dcEF. When the effect of chemical stimulation was balanced by the electrical drive, the cells migrated randomly, and the path lengths were largely reduced. We also demonstrated electrically modulated chemotaxis of two types of lung cancer cells with opposite directions of electrotaxis in this device. 相似文献
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Yao Zhang Ben Yang Atif Ghafoor Yang Zhang Yu-Fan Zhang Rui-Pu Wang Jin-Long Yang Yi Luo Zhen-Chao Dong J G Hou 《国家科学评论(英文版)》2019,6(6):1169
The strong spatial confinement of a nanocavity plasmonic field has made it possible to visualize the inner structure of a single molecule and even to distinguish its vibrational modes in real space. With such ever-improved spatial resolution, it is anticipated that full vibrational imaging of a molecule could be achieved to reveal molecular structural details. Here we demonstrate full Raman images of individual vibrational modes at the ångström level for a single Mg-porphine molecule, revealing distinct characteristics of each vibrational mode in real space. Furthermore, by exploiting the underlying interference effect and Raman fingerprint database, we propose a new methodology for structural determination, which we have called ‘scanning Raman picoscopy’, to show how such ultrahigh-resolution spectromicroscopic vibrational images can be used to visually assemble the chemical structure of a single molecule through a simple Lego-like building process. 相似文献