Younan Xia

Bio: Younan Xia is an academic researcher from The Wallace H. Coulter Department of Biomedical Engineering. The author has contributed to research in topics: Nanocages & Nanowire. The author has an hindex of 216, co-authored 943 publications receiving 175757 citations. Previous affiliations of Younan Xia include Washington University in St. Louis & University of Texas at Dallas.

Seed‐Mediated Synthesis of Truncated Gold Decahedrons with a AuCl/Oleylamine Complex as Precursor

Abstract: 2010 WILEY-VCH Verlag Gmb Controlling the shape of metallic nanostructures, and therefore the exposed crystal facets, has enabled one to tune the optical, electronic, magnetic, and catalytic properties associated with these nanostructures. Consequently, shape-controlled synthesis has been a subject of active research in recent years. A variety of different shapes have been successfully obtained for noble metal nanostructures, including plates, rods, wires, cubes, octahedrons, decahedrons, and icosahedrons. Of the polyhedral shapes, it is well known that the decahedron is very common among noble metals such as silver, gold, and palladium. Most of these decahedrons have the most common morphology, that is they do not have any truncation (regular decahedron) for particle sizes in the range of 35–250 nm. However, when the size is less than 5 nm, the regular decahedron is rarely observed for this type of particle. Instead, the most common shape is the truncated decahedron. Three variants of this shape have been reported in the literature, including the rounded decahedron, the Marks decahedron, and the star decahedron. While these variants all belong to the decahedron family, they vary by their degree of truncation relative to the regular decahedron. The rounded, Marks, and star decahedrons correspond to the minimum, intermediate, and maximum truncation, respectively. Compared with the regular decahedron, which is rather unstable at small sizes, the truncated decahedrons are stable on the length scale of only a few nanometers. However, there is essentially no report on the structures of truncated decahedrons. This indicates that it is still a challenge to synthesize well-defined truncated decahedrons in high yields and with a high degree of uniformity. Various methods, such as seed-mediated growth, photochemical reduction, template-directed synthesis and electrochemical deposition, have been developed for the synthesis of noble metal nanostructures. Among these synthetic approaches, special attention has been directed to the seedmediated growth as it is capable of generating metal nanostructures with simple or complex shapes and compositions, including bimetallic species. For example, it has been employed to produce metal nanostructures as diverse as nanorods, nanoprisms, nanodecahedrons, and branched structures. Compared with other methods, seed-mediated growth offers a number of advantages. First, it makes the growth conditions milder than those needed when seeds are absent. For example, it was found that Au seeds could increase the reducing ability of ascorbic acid, which would otherwise be unable to reduceHAuCl4 at room temperature. Second, it offers greater feasibility for shape-controlled-growth under the influence of additives. This is due to the separation of nucleation and growth steps in a seed-mediated process. Finally, the crystallinity of the resultant nanostructures (i.e., single crystal versus twinned crystals) can easily be controlled by using different types of seeds. In our previous work, we discovered that the Au(I) complex can be used as a precursor for the synthesis of Au nanostructures in both hydrophilic solution and hydrophobic solution. There are a number of advantages to using Au(I) as a precursor, including: i) It is easier to reduce Au(I) than Au(III). The standard reduction potential of the Auþ/Au pair (1.692V versus the standard hydrogen electrode (SHE)) is higher than Au3þ/Au pair (1.498V versus SHE). ii) The reaction with Au(I) is more economical given that only one electron is consumed for reduction compared to three electrons needed in the reduction of Au(III). This would save the amount of reducing agent necessary to reduce the same amount of gold and therefore decreases the overall cost of the synthesis. iii) It is possible to prepare Au nanostructures under relatively mild reaction conditions, sometimes even in the absence of a reducing agent, for a Au(I) precursor because of the low stability of Au(I) halides and their derivatives. iv) The aurophilic effect between Au(I) ions and the attraction between the complexing agents makes it easier to control the size and shape of the resultant nanostructures. v) The complexing agent can also act as a stabilizer, resulting in a capping process concurrent with the crystal growth. Additionally, oleylamine, with a C1⁄4C bond and an amine group, can serve as both a stabilizer and a weak reducing agent during the formation of Au nanoparticles. Herein we report our investigation on the use of AuCl/oleylamine as a precursor to produce Au seeds, which are then used in a seed-mediated synthesis to form truncated Au decahedrons in tetrahydrofuran (THF) at room temperature. Based on transmission electron microscopy (TEM) images obtained at different tilting angles and high-resolution TEM analysis, we could conclude that the truncated Au decahedrons have five twin

A Solution-Phase, Precursor Route to Polycrystalline SnO2 Nanowires That Can Be Used for Gas Sensing under Ambient Conditions.

Abstract: This paper describes a solution-based, precursor method for the facile synthesis of uniform nanowires containing rutile SnO2 nanocrystallites. In a typical procedure, nanowires of ∼50 nm in diamete...

Coupling to light, and transport and dissipation of energy in silver nanowires

Abstract: Transient absorption experiments with diffraction-limited spatial resolution have been used to study the optical absorption properties and dynamics of isolated, single silver nanowires. The images and polarization analysis show that the near-IR pump and near-UV probe beams couple to fundamentally different electron motions. The near-IR pump laser excites the propagating surface plasmon polariton (SPP) modes of the wires when focused at the ends, and multipolar plasmon modes (antenna modes) for medial excitation. The images show that these two modes have comparable optical absorption cross-sections. In contrast, the near-UV probe couples to the transverse plasmon resonance of the wire independent of the spatial position. For either end-on or medial excitation, pump laser absorption causes lattice heating and coherently excites the breathing vibrational mode of the nanowires. The vibrational quality factors depend on the acoustic impedance mismatch between the nanowire and the environment, and are similar to those recently measured for silver nanocubes. Experiments performed with spatially separated pump and probe beams, with the pump beam focused at one end to excite the propagating SPP modes, show that the amplitudes of the initial transient absorption signal and the breathing motion decrease with distance along the wire. This arises because the propagating SPP mode decays as it moves down the wire, which reduces the number of electronic excitations and, therefore, the signal level in the experiments. The measured length scale for the SPP decay is similar to that obtained in previous light scattering experiments.

An enzyme-sensitive probe for photoacoustic imaging and fluorescence detection of protease activity

Abstract: A gold nanocage and dye conjugate has been demonstrated for use with photoacoustic imaging and fluorescence detection of protease activity. The detection sensitivity could be maximized by using gold nanocages with a localized surface plasmon resonance peak away from the emission peak of the dye. These hybrids can be potentially used as multimodal contrast agents for molecular imaging.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

Abstract: Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346