金属纳米粒子再分散法测定二氧化铈稳定的单原子的位点数

单原子催化剂由于能最大限度地利用贵金属以及其独特的催化性能而引起了人们的兴趣.基于其表面原子性质,CeO2是稳定单金属原子最常用的载体之一.一旦金属含量超过其负载的载体容量,就会形成金属纳米粒子,因而许多单原子催化剂的金属含量受限.目前,还没有直接的测量方法来确定载体稳定单个原子的容量.本文开发了一种基于纳米颗粒的技术,即通过将Ru纳米颗粒重新分散成单个原子,并利用Ru单原子和纳米颗粒在CO2加氢反应中的不同催化性能,从而确定该容量.该方法避免了湿浸初期反离子对金属负载的影响,最终可应用于多种不同的金属.结果表明,该技术可跟踪氧空位浓度和表面氧含量的变化趋势,有望成为一种定量测定载体单原子稳定容量的新方法.     

单细胞分析中的荧光标记化学*

细胞内组分复杂、含量低,因此测定单细胞内化学组分的分析方法必须具有灵敏度高、选择性好和分辨率高的特点。高灵敏度的荧光检测技术是单细胞分析中应用最多的检测方法之一。但是细胞内绝大部分物质其天然态是没有荧光的,且由于细胞膜的阻碍,衍生试剂不能自由地进入细胞内。为了使衍生试剂透过细胞膜标记细胞内待测物质而不引起显著的稀释效应,已进行了大量的研究工作。本文综述了在单细胞分析中常用的荧光标记方法,包括细胞作为微反应器的衍生法,借助于脂质体与聚乙二醇（PEG）等增加细胞膜通透性的衍生方法和在毛细管/芯片毛细管电泳分析单细胞时柱上衍生和柱后衍生法以及量子点的标记法等。对这些方法的原理、特点和在单细胞分析中的应用也做了较为详细的阐述。     

An integrated microfluidic device for long-term culture of isolated single mammalian cells

We developed an integrated microfluidic chip for long-term culture of isolated single cells. This polydimethylsiloxane (PDMS) based device could accurately seed each single cell into different culture chambers, and isolate one chamber from each other with monolithically integrated pneumatic valves. We optimized the culture conditions, including the frequency of medium replacement and the introduction of conditioned medium, to keep the single cells alive for 4 days. We cultured a few hundred cells in a separated chamber on the same chip to continuously supply the conditioned medium into the culture chambers for single cells. This approach greatly facilitated the growth of single cells, and created a suitable microenvironment for observing cells’ autonomous process in situ without the interference of other adjacent cells. This single cell colony assay is expandable to higher throughput, fitting the needs in the studies of drug screening and stem cell differentiation.     

Single‐Molecule Sensors: Challenges and Opportunities for Quantitative Analysis

Measurement science has been converging to smaller and smaller samples, such that it is now possible to detect single molecules. This Review focuses on the next generation of analytical tools that combine single‐molecule detection with the ability to measure many single molecules simultaneously and/or process larger and more complex samples. Such single‐molecule sensors constitute a new type of quantitative analytical tool, as they perform analysis by molecular counting and thus potentially capture the heterogeneity of the sample. This Review outlines the advantages and potential of these new, quantitative single‐molecule sensors, the measurement challenges in making single‐molecule devices suitable for analysis, the inspiration biology provides for overcoming these challenges, and some of the solutions currently being explored.     

Towards high-throughput single cell/clone cultivation and analysis

In order to better understand cellular processes and behavior, a controlled way of studying high numbers of single cells and their clone formation is greatly needed. Numerous ways of ordering single cells into arrays have previously been described, but platforms in which each cell/clone can be addressed to an exact position in the microplate, cultivated for weeks and treated separately in a high-throughput manner have until now been missing. Here, a novel microplate developed for high-throughput single cell/clone cultivation and analysis is presented. Rapid single cell seeding into microwells, using conventional flow cytometry, allows several thousands of single cells to be cultivated, short-term (72 h) or long-term (10-14 days), and analyzed individually. By controlled sorting of individual cells to predefined locations in the microplate, analysis of single cell heterogeneity and clonogenic properties related to drug sensitivity can be accomplished. Additionally, the platform requires remarkably low number of cells, a major advantage when screening limited amounts of patient cell samples. By seeding single cells into the microplate it is possible to analyze the cells for over 14 generations, ending up with more than 10 000 cells in each well. Described here is a proof-of-concept on compartmentalization and cultivation of thousands of individual cells enabling heterogeneity analysis of various cells/clones and their response to different drugs.     

Creation and recovery of a W(111) single atom gas field ion source

Tungsten single atom tips have been prepared from a single crystal W(111) oriented wire using the chemical assisted field evaporation and etching method. Etching to a single atom tip occurs through a symmetric structure and leads to a predictable last atom unlike etching with polycrystalline tips. The single atom tip formation procedure is shown in an atom by atom removal process. Rebuilds of single atom tips occur on the same crystalline axis as the original tip such that ion emission emanates along a fixed direction for all tip rebuilds. This preparation method could be utilized and developed to prepare single atom tips for ion source development.     

Single Pt–Pd Bimetallic Nanoparticle Electrode: Controllable Fabrication and Unique Electrocatalytic Performance for the Methanol Oxidation Reaction

Understanding the electrocatalytic activity at single nanoparticles/nanoclusters level is extremely important. In this work, a method for the electro-deposition of single Pt–Pd nanoparticles (NPs) is described using a single nanopore electrode as a template. The electro-deposition process was investigated carefully and the results show that the process is controlled by diffusion and electro-crystallization process, simultaneously, and the glass sheath property around the nanopore has a large impact on the formation of single Pt–Pd NPs due to the “edge effect”. The prepared single Pt–Pd NPs exhibit excellent electrocatalytic activity in the methanol oxidation reaction, which can be used to screen electrocatalysts with high efficiency for utility in the energy field.     

Confined Nanopipette Sensing: From Single Molecules,Single Nanoparticles,to Single Cells

Nanopipettes provide a promising confined space that enables advances in electrochemical, optical, and mass spectrometric measurements at the nanoscale. They have been employed to reveal the hidden population properties and dynamics of single molecules and single particles. Moreover, new detection mechanisms based on nanopipettes have led to detailed information on single cells at high spatial and temporal resolution. In this Minireview, we focus on the fabrication and characterization of nanopipettes, summarize their wide applications for the analysis of single entities, and conclude with an outlook for advanced practical sensing.     

Aerolysin单分子界面的构建及高选择性单分子检测

提出了一种基于Aerolysin膜蛋白质分子构建单分子界面的方法, 运用蛋白质工程技术对单分子界面进行定点修饰, 所建立方法灵活、 可控且重复性好. 采用Poly(dA)₄为探针分子对修饰后的单分子界面进行了表征, 结果表明, 在孔口处的Arginine修饰影响了寡聚核苷酸的选择性. 为进一步理解Aerolysin单分子界面及合理设计功能性单分子界面提供了参考.     

Non‐hybridization single nucleotide polymorphism detection and genotyping assay through direct discrimination of single base mutation by capillary electrophoretic separation of single‐stranded DNA

The significant demands for single nucleotide polymorphism detection and genotyping assays have grown. Most common assays are based on the recognition of the target sequence by the hybridization with its specific probe having the complementary sequence of the target. Herein, a simple, label‐free, and economical non‐hybridization assay was developed for single nucleotide polymorphism detection and genotyping, based on the direct discrimination of single base mutation by simple capillary electrophoresis separation for single‐stranded DNA in an acidic electrophoretic buffer solution containing urea. Capillary electrophoresis separation of single‐base sequential isomers of DNA was achieved due to charge differences resulting from the different protonation properties of the DNA bases. Single nucleotide polymorphism detection and genotyping were achieved by discriminating the electropherogram pattern change, that is, peak number in the electropherogram, obtained by the proposed method. The successful practical application of the proposed method was demonstrated through single nucleotide polymorphism detection and genotyping on a known gene region of 84‐mer, in which guanine to adenine single‐base mutation is commonly observed, using a human hair sample in combination with genomic DNA extraction, polymerase chain reaction amplification, DNA purification from polymerase chain reaction products, and capillary electrophoresis separation.     

Multichannel Conductance of Folded Single‐Molecule Wires Aided by Through‐Space Conjugation

Deciphering charge transport through multichannel pathways in single‐molecule junctions is of high importance to construct nanoscale electronic devices and deepen insight into biological redox processes. Herein, we report two tailor‐made folded single‐molecule wires featuring intramolecular π–π stacking interactions. The scanning tunneling microscope (STM) based break‐junction technique and theoretical calculations show that through‐bond and through‐space conjugations are integrated into one single‐molecule wire, allowing for two simultaneous conducting channels in a single‐molecule junction. These folded molecules with stable π–π stacking interaction offer conceptual advances in single‐molecule multichannel conductance, and are perfect models for conductance studies in biological systems, organic thin films, and π‐stacked columnar aggregates.     

Nanoelectrochemical analysis inside a single living cell

This critical opinion reviews the methods to construct and apply electrodes for analysis inside single cells and of single organelles. Nanoelectrochemical methodology, with an emphasis on nanoelectrode construction and analysis of metabolites, neurotransmitters, reactive oxygen and nitrogen species, glucose, oxygen, hydrogen peroxide, and ions in cells are discussed for measurements from cytoplasm to single organelles.     

Tracking the optical mass centroid of single electroactive nanoparticles reveals the electrochemically inactive zone

The inevitable microstructural defects, including cracks, grain boundaries and cavities, make a portion of the material inaccessible to electrons and ions, becoming the incentives for electrochemically inactive zones in single entity. Herein, we introduced dark field microscopy to study the variation of scattering spectrum and optical mass centroid (OMC) of single Prussian blue nanoparticles during electrochemical reaction. The “dark zone” embedded in a single electroactive nanoparticle resulted in the incomplete reaction, and consequently led to the misalignment of OMC for different electrochemical intermediate states. We further revealed the dark zones such as lattice defects in the same entity, which were externally manifested as the fixed pathway for OMC for the migration of potassium ions. This method opens up enormous potentiality to optically access the heterogeneous intraparticle dark zones, with implications for evaluating the crystallinity and electrochemical recyclability of single electroactive nano-objects.

The schematic of single cubic-shaped Prussian blue (PB) mesocrystals formed by the oriented aggregation of small nanocrystals. The dark-field images of single PB nanoparticle at PB and Prussian white (PW) states, respectively.     

Atomic Force Microscopy Investigation of Poly[(R)‐3‐hydroxybutyrate] Lamellar Single Crystals: Relationship between Molecular Weight and Enzymatic Degradation Behavior

Enzymatic degradation behavior of a lamella of single crystals of poly(R)‐3‐hydroxybutyrate (P(3HB)) with an extracellular polyhydroxybutyrate (PHB) depolymerase purified from Alcaligenes faecalis T1 has been investigated by atomic force microscopy (AFM) in order to obtain further information for the chain packing state of P(3HB) in a lamellar single crystal. Two kinds of P(3HB) single crystals with different molecular weights, denoted respectively as H‐ and L‐P(3HB) for high and low molecular weights, respectively, were prepared. The enzymatic treatment was conducted for P(3HB) single crystals adsorbed on a surface of highly ordered pyrolytic graphite. The enzymatic degradation of both P(3HB) single crystals generates several crevices crosswise across the crystal at an early stage. Subsequently, the enzymatic degradation yields numbers of cracks lengthwise along the crystal. In addition to these common features, the interval between cracks crosswise across a lamella in H‐P(3HB) single crystal is longer than that in L‐P(3HB) single crystal, and each crack has V‐shaped and rectangular shaped morphology for H‐ and L‐P(3HB) single crystals, respectively. Based on these results, it is concluded that a lamella of P(3HB) single crystal has straight degradation pathways, that may correspond to a switchboard region, along the long axis of the crystal, independent of molecular weight of P(3HB) samples, and that a H‐P(3HB) single crystal has broader degradation pathways with longer intervals crosswise across the crystal than a L‐P(3HB) single crystal.     

Theoretical Studies of Single Molecule Spectroscopy at Room Temperature

This talk is motivated by recent room-temperature single molecule experiments, which measure the optical spectrum along single molecular trajectories and monitor the molecular dynamics and chemical kinetics of individual reactive systems. These experiments contain new information that requires theoretical models and interpretations. Several aspects of single molecule spectroscopy are analyzed:(1) Event-averaged single molecule quantities are calculated, with the prediction of the echo signal in the joint event probability distribution function^[1]. Similar to the photon echo phenomenon, the single molecule echo signal measures solvent effects on chemical kinetics. (2) The statistics of single molecule blinking events are often correlated to underlying quantum mechanisms. The distribution functions of waiting-time sequences are examined for several quantum processes, including electron transfer, solvent relaxation, laser-induced emission, and single quantum-dot blinking^[2]. (3) Single molecule measurements of heterogeneous diffusion reveal deviations from the Gaussian distribution of Brownian motion. As a quantitative measure, the non-Gaussian indicator decays asymptotically to zero according to 1/t for finite time correlation, but saturates at a plateau value for power-law correlation.     

Review: Applications of single-shot laser-induced breakdown spectroscopy

As applications for laser-induced breakdown spectroscopy (LIBS) become more varied with a greater number of field and industrial LIBS systems developed and as the technique evolves to be more quantitative that qualitative, there is a more significant need for LIBS systems capable of analysis with the use of a single laser shot. In single-shot LIBS, a single laser pulse is used to form a single plasma for spectral analysis. In typical LIBS measurements, multiple laser pulses are formed and collected and an ensemble-averaged method is applied to the spectra. For some applications there is a need for rapid chemical analysis and/or non-destructive measurements; therefore, LIBS is performed using a single laser shot. This article reviews in brief several applications that demonstrate the applicability and need for single-shot LIBS.     

Insulator-based dielectrophoretic single particle and single cancer cell trapping

Trapping of individual cells at specific locations in a microfluidic lab-on-a-chip platform is essential for single cell studies, especially those requiring individual stimulation followed by downstream analysis. To this aim, we have designed microdevices based on direct current (DC) insulator-based dielectrophoresis (iDEP) acting as individual single cell traps. We present both the design of a negative iDEP trap and a positive iDEP trap using insulating posts integrated at microchannel intersections. We obtained electric field distributions via numerical simulations adapted to the intersection and trap geometry with which we predict single particle pathlines. With polystyrene particles of 10?μm diameter, we demonstrated an effective design for a single particle trap in the case of negative dielectrophoresis. The onset trapping voltage shows an inverse relation to the buffer conductivity, thus indicating the influence of electrokinetic effects on the trapping behavior. Additionally, we demonstrated the proof-of-principle of single MCF-7 breast cancer cell trapping in a positive iDEP trap. Our single particle trapping experiments were further in very good agreement with numerical simulations. To ensure that no significant damage occurred to the cells during the experiment, we further optimized medium conditions to ensure viability of the cells for at least 1?h, more than sufficient for microfluidic trapping experiments. Our results thus indicated the successful design of DC iDEP traps, which can easily be integrated into a variety of microchip operations for single cell analysis.     

高分子单链的研究进展

随着纳米科技在高分子领域的不断升温,高分子单链凝聚态的研究引起了人们的广泛重视。高分子单链以纳米尺度的微粒孤立存在,不存在分子链之间的几何缠结。本文综述了近年来国内外高分子单链的研究进展。首先介绍了高分子单链的主要制备方法如喷雾法、冷冻干燥法、微乳液聚合法、反向沉淀法以及表面扩展膜法,接着详细介绍了高分子单链的表征技术及高分子链构象的计算机模拟技术,最后介绍了高分子单链及单分子胶束在制备金属纳米粒子领域的应用,并展望了高分子单链的研究领域和方向。     

A Self‐Digitization Dielectrophoretic (SD‐DEP) Chip for High‐Efficiency Single‐Cell Capture,On‐Demand Compartmentalization,and Downstream Nucleic Acid Analysis

The design and fabrication of a self‐digitization dielectrophoretic (SD‐DEP) chip with simple components for single‐cell manipulation and downstream nucleic acid analysis is presented. The device employed the traditional DEP and insulator DEP to create the local electric field that is tailored to approximately the size of single cells, enabling highly efficient single‐cell capture. The multistep procedures of cell manipulation, compartmentalization, lysis, and analysis were performed in the integrated microdevice, consuming minimal reagents, minimizing contamination, decreasing lysate dilution, and increasing assay sensitivity. The platform developed here could be a promising and powerful tool in single‐cell research for precise medicine.