A glass nanopore electrode for single molecule detection

<正>We have developed a simple method for fabricating robust and low noise glass nanopore electrodes with pore size 10±5 nm to detect single molecules.β-Cyclodextrin was used as model compound for characterization.In 1.0 mol/L NaCl solution,the molecules generated current pulses of 2-5 pA with noise level less than 0.8 pA.A slide mode and a plug mode were suggested for the way ofβ-cyclodextrin single molecule moving into the glass nanopores.     

Monitoring disulfide bonds making and breaking in biological nanopore at single molecule level

Monitoring subtle changes in ionic current flow through a nanopore could be applied to observe single molecule reaction. Here,we introduced cysteine to substitute for lysine at position 238 constructing a mutant aerolysin K238 C. It could be regarded as a nanoreactor to efficiently visualize chemical bonds making and breaking. The compound 5,5′-dithiobis-(2-nitrobenzoic acid)(DTNB) was selected as a reactant coming into collisions on the interface of the pore to occur a reversible reaction. Our results showed that the mutant aerolysin could respond to three molecules of DTNB simultaneously and reflect corresponding levels with distinguishable current signals. Therefore, this method constitutes a simple, generic tool for monitoring single molecule reaction, which evokes a guidance for the mutant aerolysin towards the application of tracking other more reactions at single molecule level.     

Single‐molecule imaging of photodegradation reaction in a chiral helical π‐conjugated polymer chain

How does the chemical reaction of a single polymer chain progress? This question is not proven, as long as it is studied the data of the ensemble average from the large number of molecules. In this study, we succeeded for the first time in the direct measurement of when, where, and how the chemical reaction of a polymer chain proceeds on a nanometer scale. That is, single‐molecule imaging of the photodegradation reaction of a chiral helical π‐conjugated polymer following laser irradiation of 405 nm was conducted. Analysis of the chemical kinetics showed that the photodegradation of the single polymer chain proceeded stepwise as a quantum phenomenon. When the motility of the chain‐end increased, reactivity of the photodegradation increased. It was also discovered that the photodegradation of the polymer chain proceeded continuously in one direction, like the “domino effect.” Our method allowed dynamic imaging of single polymer chains at a solid/liquid interface, and hence can be applied to the study of many types of polymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4103–4107, 2010     

High-throughput single molecule screening of DNA and proteins

We report a novel imaging technology for real time comprehensive analysis of molecular alterations in cells and tissues appropriate for automation and adaptation to high-throughput applications. With these techniques it should eventually be possible to perform simultaneous analysis of the entire contents of individual biological cells with a sensitivity and selectivity sufficient to determine the presence or absence of a single copy of a targeted analyte (e.g., DNA region, RNA region, protein), and to do so at a relatively low cost. The technology is suitable for DNA and RNA through sizing or through fluorescent hybridization probes, and for proteins and small molecules through fluorescence immunoassays. This combination of the lowest possible detection limit and the broadest applicability to biomolecules represents the final frontier in bioanalysis. The general scheme is based on novel concepts for single molecule detection (SMD) and characterization recently demonstrated in our laboratory. Since minimal manipulation is involved, it should be possible to screen large numbers of cells in a short time to facilitate practical applications. This opens up the possibility of finding single copies of DNA or proteins within single biological cells for disease markers without performing polymerase chain reaction or other biological amplification.     

Studying single molecule electrochemistry with scanning tunneling microscope break-junction technique

The fundamental principle of molecular electronics is to comprehend electrical properties of single molecules connected between two probe electrodes. In recent years, substantial advances in this field have been made to underpin experimental and theoretical understanding of single molecule electrochemistry. By using scanning tunneling microscope (STM) break-junction technique, the switching events of electrical current from single molecule bridge tuning by electrochemical gating are investigated to uncover the relationship between electrochemical electron transfer and charge transport processes in chemical and biological molecule junctions. In this short review, we outline the latest works of single molecule electrochemistry studied with STM break-junction technique from Nongjian Tao's group, and share the insights on the opportunities and challenges for future research.     

基于氧化还原循环信号放大技术的单分子电化学研究进展

现代分析科学的整体发展对分析方法的灵敏度、选择性以及快速响应等有了更高的要求。在单分子水平上实现对目标分子的检测及控制是化学家们长期以来梦寐以求的一项富有挑战性的前沿领域,也是近年来分析科学很重要的前沿发展方向。用电化学方法直接检测单分子面临的一项挑战是单个分子在氧化还原过程中得失电子产生的电流变化太小,现代仪器无法对如此小的电流进行识别。使电极表面氧化还原过程中的电子交换实现多次循环可以放大产生的电流,从而实现单分子水平的直接电化学分析。本文对近期通过循环电子交换过程放大电流信号的技术和装置进行了综述,将各类方法进行对比,并对单分子电化学未来的发展方向进行了展望。     

基于裂结技术的单分子尺度化学反应研究进展

分子电子学是研究单分子器件的构筑、性质以及功能调控的一门新兴学科。其中,金属/分子/金属结的构筑和表征是现阶段分子电子学的主要研究内容。裂结技术是当前分子电子学研究的主要实验方法,主要包括机械可控裂结技术和扫描隧道显微镜裂结技术。本文对裂结技术进行了介绍,并对近年来利用这些技术,在单分子尺度化学反应的检测和动力学研究,以及将这些技术与溶液环境、静电场、电化学门控等方法相结合,调控单分子器件的电输运性质等方面所取得的进展进行了概述。     

一氧化碳共吸附法确定叔丁胺分子在Cu(111)表面的吸附位

采用扫描隧道显微镜(STM)和密度泛函理论(DFT)研究了78 K时单个叔丁胺分子在Cu(111)表面的吸附位. 我们提出以共吸附的一氧化碳√3 ×√3 超结构为基底铜原子的标识方法, 确定了低覆盖度的叔丁胺分子在Cu(111)表面的吸附位为顶位. 而采用单个一氧化碳分子标识基底铜原子的位置, 同样得出了叔丁胺分子的吸附位为顶位. 此外, 还采用DFT计算叔丁胺分子在Cu(111)表面的优势吸附构型. 理论计算结果表明顶位吸附构型为能量最稳定的构型, 与实验结果相吻合.     

Nanosensors lost in space. A random walk study of single molecule detection with single-nanopore sensors

Nanopores by providing single molecule detection and manipulation are lately in the forefront of life science and nanotechnology research. While single nanopore sensors can detect the residence of even one molecule or nanoparticle within the nanopore, the analytical significance of this process is often misunderstood. A fundamental problem of nanosensors is that their sensing zone is generally infinitesimal with respect of the probed sample volume. Consequently, the probability to have in extremely diluted solutions target molecules or nanoparticles encountering the nanosensor is low. Thus, eventhough the sensor by itself has single molecule detection capability the average time frame in which this occurs is by far not irrelevant for the analysis. In this paper we report on random walk simulations to determine the average time (encounter time) needed by a single molecule to encounter a single nanopore sensor. By assigning the simulation environment with real space and time values a semi-empirical equation for expressing the average encounter time in purely diffusive systems is provided. We also show that random walk simulations can be adapted to evaluate the encounter time in the presence of an external force field acting on the target molecule. As practically relevant application the case of electrophoretically driving DNA strands towards the nanopore sensor is presented and a semi-empirical equation for the encounter time is provided.     

Bi-analyte single molecule SERS technique with simultaneous spatial resolution

The simultaneous combination on CCD detectors of both spectral and spatial information is used in the framework of the single molecule (SM) bi-analyte Surface-Enhanced Raman Scattering (SERS) technique, to provide a new level of understanding on the origins of SM-spectra, as well as reveal the advantages and limitations of the statistical identification of SM-events. A new and deeper interpretation of the roots of the inhomogeneous broadening of single molecule Raman peaks can be uncovered, as well as the origin of Surface-Enhanced Fluorescence (SEF) emission by single molecules. In this manner, subtler aspects of SM-SERS spectroscopy can be revealed by the additional presence of spatial information on the localization of single molecules producing the signal. The spatial information is normally lost through the standard binning of CCD cameras for spectroscopy, which only emphasizes the spectral dimension of the problem. This novel extension of the bi-analyte SM-SERS method should contribute to the furtherance of the technique, and several of its fundamental aspects are discussed in detail.     

Electron Transport through Single π‐Conjugated Molecules Bridging between Metal Electrodes

Understanding electron transport through a single molecule bridging between metal electrodes is a central issue in the field of molecular electronics. This review covers the fabrication and electron‐transport properties of single π‐conjugated molecule junctions, which include benzene, fullerene, and π‐stacked molecules. The metal/molecule interface plays a decisive role in determining the stability and conductivity of single‐molecule junctions. The effect of the metal–molecule contact on the conductance of the single π‐conjugated molecule junction is reviewed. The characterization of the single benzene molecule junction is also discussed using inelastic electron tunneling spectroscopy and shot noise. Finally, electron transport through the π‐stacked system using π‐stacked aromatic molecules enclosed within self‐assembled coordination cages is reviewed. The electron transport in the π‐stacked systems is found to be efficient at the single‐molecule level, thus providing insight into the design of conductive materials.     

Micelle-hosted palladium nanoparticles catalyze citral molecule hydrogenation in supercritical carbon dioxide

A new approach of employing metal particles in micelles for the hydrogenation of organic molecules in the presence of fluorinated surfactant and water in supercritical carbon dioxide has very recently been introduced. This is allegedly to deliver many advantages for carrying out catalysis including the use of supercritical carbon dioxide (scCO2) as a greener solvent. Following this preliminary account, the present work aims to provide direct visual evidence on the formation of metal microemulsions and to investigate whether metal located in the soft micellar assemblies could affect reaction selectivity. Synthesis of Pd nanoparticles in perfluorohydrocarboxylate anionic micelles in scCO2 is therefore carried out in a stainless steel batch reactor at 40 degrees C and in a 150 bar CO2/H2 mixture. Homogeneous dispersion of the microemulsion containing Pd nanoparticles in scCO2 is observed through a sapphire window reactor at W0 ratios (molar water-to-surfactant ratios) ranging from 2 to 30. It is also evidenced that the use of micelle assemblies as new metal catalyst nanocarriers could indeed exert a great influence on product selectivity. The hydrogenation of a citral molecule that contains three reducible groups (aldehyde, double bonds at the 2,3-position and the 6,7-position) is studied. An unusually high selectivity toward citronellal (a high regioselectivity toward the reduction of the 2,3-unsaturation) is observed in supercritical carbon dioxide. On the other hand, when the catalysis is carried out in the conventional liquid or vapor phase over the same reaction time, total hydrogenation of the two double bonds is achieved. It is thought that the high kinetic reluctance for double bond hydrogenation of the citral molecule at the hydrophobic end (the 6,7-position) is due to the unique micelle environment that is in close proximity to the metal surface in supercritical carbon dioxide that guides a head-on attack of the molecule toward the core metal particle.     

单分子检测进展

单分子检测做为针对有限可数的化学微观个体性质和行为的测量分析方法,能够提供用传统的宏观测量方法得不到的分子微环境中微观个体信息,受到广泛关注。本文综述了近年来单分子检测领域的进展和单分子检测的基本技术,重点介绍了用电化学方法进行单分子检测的发展状况,并展望了单分子检测的发展前景。     

Ag2O/SiO2纳米复合催化剂制备及其催化性能研究

由喷雾燃烧法制备含Ag2O质量分数为8%和12%的Ag2O/SiO2纳米复合催化剂,采用SEM、XRD和FT-IR技术对催化剂及其前驱体进行表征,考察样品焙烧、活化中形貌和微观结构的变化.表征结果显示了处理过程中样品粒径和活性中心等变化情况,且两个催化剂变化情形一致.以分子氧为氧化剂,采用气相环己烷一步环氧化生成环氧环己烷反应,对催化剂进行活性测试,考察Ag2O负载量、实验温度、O2和原料气流速对催化剂性能的影响,并将两个催化剂活性测试结果进行比较.结果表明,8%Ag2O/SiO2纳米复合催化剂催化性能优于12%Ag2O/SiO2纳米复合催化剂;一定实验条件下,用8%Ag2O/SiO2纳米复合催化剂进行催化,环己烷转化率低于9.2%时,环氧环己烷选择性最高可达95.2%.     

Recent progress in two-photon small molecule fluorescent probes for enzymes

This review aims to provide a summary of the progress in TP small molecule fluorescent probes for enzymes in recent years and displays the main fluorescent mechanisms that have been applied to design probes.     

A quantum chemical study of the catalysis for cytidine deaminase: contribution of the extra water molecule

Cytidine deaminase is known as an important enzyme responsible for the hydrolytic deamination of cytidine, which is applied as a key step to the conversion of the precursor of the cancer drug to an active form in the living body. Cytidine with water is efficiently converted to uridine with ammonia in the cleft of cytidine deaminase. In this work, the catalysis of cytidine deaminase for the hydrolytic deamination was examined using cytosine as a model of cytidine and the model molecules for the active site of cytidine deaminase by means of the quantum chemical method. We especially investigated the contribution of the water molecule from the solvent to the catalysis, because the X-ray diffraction analysis of a crystal structure has revealed the existence of the water molecule in the vicinity of the substrate bound to the active site inside the cleft. Our computations showed that the extra water molecule from the solvent has a possibility to support the catalysis of cytidine deaminase.     

Small organic molecule catalyzed enantioselective direct aldol reaction in water

Protonated pyrrolidine based small organic molecules have been designed and evaluated for the asymmetric direct aldol reaction in water. The designed organocatalysts are multifunctional in nature and exploit the combined effect of hydrogen bonding and hydrophobic interactions for enantioselective catalysis in water. As a result a unique direct asymmetric aldol reaction in water catalyzed by a small organic molecule having an amide linkage has been developed. The developed catalyst affords chiral β-hydroxyketones in good yields (93%) and enantioselectivities (upto 62%) in water.     

Reorientation and translation of individual dye molecules in a polymer matrix

The orientational and translational motion of individual dye molecules embedded in a polymer matrix is studied in the temperature regime above the glass transition. The rotational diffusion close to the glass transition is heterogeneous on the single molecule level and few sudden changes in the reorientational speed of single molecules are found. The exchange between these reorientational speeds is found to be one order of magnitude slower than the reorientational time constant of the molecules. Translational motion can be clearly identified at about 1.2 T_g. However, the translational diffusion shows no signs of heterogeneity on the timescale of our experiments, from which we conclude, that the timescale of the exchange process between microenvironments has become too fast or that no heterogeneity exists at the temperatures above 1.2 T_g.     

Efficient light harvesting in dye-endcapped conjugated polymers probed by single molecule spectroscopy

The development of sophisticated microscopic models of energy transfer in linear multichromophoric systems such as conjugated polymers is rarely matched by suitable experimental studies on the microscopic level. To assess the roles of structural, temporal, and energetic disorder in energy transfer, single molecule spectroscopic investigations of the elementary processes leading to energetic relaxation in conjugated polymers are desirable. We present a detailed study of energy transfer processes occurring in dye-endcapped conjugated polymer molecules on the single molecule level. These processes are mostly masked in ensemble investigations. Highly efficient intramolecular energy transfer along a single polyindenofluorene chain to a perylene endcap occurs in many instances and is resolved in real time. We further consider the spectral emission characteristics of the single molecule, the polarization anisotropy which reveals the chain conformation, the fluorescence intermittency, and the temperature dependence and conclude that the efficiency of energy transfer in the ensemble is controlled by the statistics of the individual molecules. The weak thermal activation of energy transfer indicates the involvement of vibrational modes in interchromophoric coupling. Whereas backbone-endcap coupling is strong, the rate-limiting step for intramolecular energy transfer is the migration along the backbone. The results are particularly relevant to understanding undesired exciton trapping on fluorenone defects in polyfluorenes.