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Biomedical subjects

Qihui Shi

Publications and source records attributed to Qihui Shi.

7 recordsLinked to original sources
PubMed2006

Growth of gold nanorods and bipyramids using CTEAB surfactant.

Gold nanorods and bipyramids have been synthesized using the seed-mediated approach in aqueous cetyltriethylammonium bromide (CTEAB) solutions in the presence of silver nitrate. Gold nanoparticle seeds that are stabilized with either CTEAB or sodium citrate have been used. The use of the CTEAB-stabilized seeds gives gold nanorods in high yield in one step with the longitudinal plasmon wavelength ranging from 750 to 1030 nm, depending on the amount of the seeds. The longitudinal plasmon wavelength can be extended to 1100 nm by the use of a two-step growth method. The growth of gold nanorods in CTEAB solutions takes 5-10 h, more than 5 times slower than that in cetyltrimethylammonium bromide solutions at the same concentration of surfactants. The use of the citrate-stabilized seeds gives both gold bipyramids and a small percentage of gold nanorods. The longitudinal plasmon wavelength of the bipyramids is tunable from 700 to 1100 nm by varying the amount of the citrate-stabilized seeds. The growth of gold bipyramids takes more than 1 day. Transmission electron microscopy characterizations reveal that the gold nanorods grown from both types of gold nanoparticle seeds are single-crystalline and that the gold bipyramids are penta-twinned.

Journal Article↗
PubMed2006

Oxide hemostatic activity.

The tunable in vitro blood clotting activity of high-surface-area hemostatic bioactive glass is evaluated by Thromboelastograph, a clinical instrument for quantifying changes in blood during coagulation. The hemostatic trends associated with hemostatic bioactive glass and a new preparation of spherical hemostatic bioactive glass, along with similar Si- and Ca-containing oxides, are described and related to Si:Ca ratios, Ca2+ availability and coordination environment, porosity, DeltaHHydration, and surface area. Hemostatic bioactive glass is a new material with an excellent efficacy for inducing hemostasis and is chemically distinct from the traditional bioglass employed for bone growth.

Blood Coagulation↗
PubMed2006

Selective shortening of single-crystalline gold nanorods by mild oxidation.

Gold nanorods (NRs) have received much attention due to their size-dependent surface plasmon-related optical properties. A seed-mediated approach has recently been developed for the synthesis of Au NRs with varying length-to-diameter aspect ratios. With the introduction of silver ions in the growth solution, Au NRs of narrow size distributions can be produced in high yields. Herein we describe an approach for the continuous and selective shortening of Au NRs synthesized by the silver ion-assisted seed-mediated method through oxidation with environmentally benign oxygen at slightly elevated temperatures. UV-visible extinction measurements indicate that the longitudinal surface plasmon band of Au NRs decreases in intensity and blue-shifts as a function of the oxidation time. Transmission electron microscopy (TEM) imaging shows that the length of Au NRs decreases with oxidation and their diameter stays almost constant, which suggests that oxidation starts at the ends of Au NRs. The size distributions of shortened Au NRs are similar to those of starting NRs. Further oxidation transforms Au NRs into nanospheres, which become smaller in diameter and finally completely disappear. It has been found that the oxidation rate of Au NRs can be controlled by temperature and acid concentration. Furthermore, high-resolution TEM studies reveal that Au NRs synthesized by the silver ion-assisted seed-mediated method are single crystalline and they stay single crystalline during oxidation. It is expected that Au NRs of any aspect ratio with narrow size distributions within the limit of that possessed by starting NRs can be produced by this mild oxidation approach.

Crystallization↗
PubMed2005

Vesicle array-templated large-area silica surface patterns.

Micropatterning has important applications in a wide range of areas, including microelectronics, optics, information displays, and biotechnology. Herein, we describe a vesicle-array templating approach for the generation of surface patterns of micrometer-sized silica features on the surfaces of silica monoliths. The approach makes use of tetraethyl orthosilicate as silica precursor, a poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) triblock copolymer, EO2PO16EO2, as surfactants, and water, ethanol, and dimethylformamide as solvents. The morphological shapes of produced silica features are synthetically controlled through varying the sequence of silica precursor hydrolysis, vesicle formation, and silica condensation. Prehydrolysis of the silica precursor, before being mixed with the copolymer, gives hollow convex protrusions. Direct mixing of the silica precursor and the copolymer produces concave depressions. An increase in the amount of water in the mixture solution without prehydrolysis of the silica precursor results in hierarchical patterns of larger concave depressions attached with smaller convex protrusions. It has further been demonstrated that concave surface patterns can function as microlens arrays that are capable of producing numerous optical images from a common object.

Journal Article↗
PubMed2003

One-step nanocasting synthesis of highly ordered single crystalline indium oxide nanowire arrays from mesostructured frameworks.

A one-step nanocasting route has been demonstrated to prepare highly ordered single-crystal indium oxide nanowire (IONW) arrays with mesostructured frameworks. Unlike the reported multistep nanocasting process (synthesis of mesoporous materials, and then incorporation of precursors and formation of inorganic frameworks), a highly ordered mesostructured surfactant-silica monolith with low external surface serves as both the template and the reducing agent and makes the formation of single-crystal IONWs in its channels easily in one step by using normal In(NO(3))(3) as an inorganic precursor. After silica is removed, highly ordered uniform single-crystal IONW arrays with hexagonal (p6mm) or cubic (Ia3d) mesostructures are derived. These new materials are studied by XRD, SEM, TEM, N(2) adsoption, and UV spectrum. Furthermore, this one-step nanocasting synthesis route is a generalized method and can be used to synthesized a highly ordered mesoporous silica monolith with metal oxide nanocrystals in its channels. To the best of our knowledge, this is the first report of a single crystalline mesostructured In(2)O(3) framework.

Journal Article↗