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.

Alloying and Dealloying Processes Involved in the Preparation of Metal Nanoshells through a Galvanic Replacement Reaction

Abstract: The galvanic replacement reaction between Ag nanoparticles and an aqueous HAuCl4 solution has recently been demonstrated as a simple and convenient route to metal nanostructures with hollow interiors and highly crystalline walls (see, for example, Sun, Y.; Mayers, B. T.; Xia, Y. Nano Lett. 2002, 2, 481. Sun, Y.; Xia, Y. Science, 2002, 298, 2176). However, the details of morphological, compositional, structural, and spectral changes involved in the entire process of this template-engaged reaction is yet to be elucidated. The experimental results described in this letter indicate that the templating process proceeded through two distinctive steps: (i) formation of pinhole-free nanoshells with homogeneous, uniform walls of Au/Ag alloys via a combination of the replacement reaction and alloying; and (ii) formation of porous nanoshells (nanocages) through a dealloying process, in which Ag was selectively dissolved from the walls made of Au/Ag alloys. As alloying and dealloying proceeded, the surface plasmon r...

On the polyol synthesis of silver nanostructures: glycolaldehyde as a reducing agent.

Abstract: The polyol synthesis is a popular method of preparing metal nanostructures, yet the mechanism by which metal ions are reduced is poorly understood. Using a spectrophotometric method, we show, for the first time, that heating ethylene glycol (EG) in air results in its oxidation to glycolaldehyde (GA), a reductant capable of reducing most noble metal ions. The dependence of reducing power on temperature for EG can be explained by this temperature-dependent oxidation, and the factors influencing GA production can have a profound impact on the nucleation and growth kinetics. These new findings provide critical insight into how the polyol synthesis can be used to generate metal nanostructures with well-controlled shapes. For example, with the primary reductant identified, it becomes possible to evaluate and understand its explicit role in generating nanostructures of a specific shape to the exclusion of others.

Nanofiber Scaffolds with Gradations in Mineral Content for Mimicking the Tendon-to-Bone Insertion Site

Abstract: We have demonstrated a simple and versatile method for generating a continuously graded, bonelike calcium phosphate coating on a nonwoven mat of electrospun nanofibers. A linear gradient in calcium phosphate content could be achieved across the surface of the nanofiber mat. The gradient had functional consequences with regard to stiffness and biological activity. Specifically, the gradient in mineral content resulted in a gradient in the stiffness of the scaffold and further influenced the activity of mouse preosteoblast MC3T3 cells. This new class of nanofiber-based scaffolds can potentially be employed for repairing the tendon-to-bone insertion site via a tissue engineering approach.

Colloidal Crystals with Tunable Colors and Their Use as Photonic Papers

Abstract: This article describes the fabrication and characterization of colloidal crystals whose stop bands could be varied through the application of a liquid. Such a colloidal crystal was generated by infiltrating the voids within an opaline lattice of polystyrene beads with a liquid prepolymer to poly(dimethylsiloxane), followed by thermal curing. When a liquid (e.g., a silicone fluid, hexane, or octane) capable of swelling the elastomer matrix was applied to the surface of this crystal, the lattice constant and thus the wavelength of Bragg-diffracted light was increased. For instance, the color of light diffracted from a colloidal crystal made of 175 nm polystyrene beads could be varied from violet to green, orange, and red simply by swelling it with different solvents. On the basis of this mechanism, we further demonstrated a photonic paper/ink system where color patterns could be conveniently generated on the surface of a thin film of colloidal crystal by writing with a Pilot pen, by screen printing, or by m...

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