Showing papers by "Bing Xu published in 2006"

Using a Kinase/Phosphatase Switch to Regulate a Supramolecular Hydrogel and Forming the Supramolecular Hydrogel in Vivo

Abstract: We have designed and synthesized a new hydrogelator Nap−FFGEY (1), which forms a supramolecular hydrogel. A kinase/phosphatase switch is used to control the phosphorylation and dephosphorylation of the hydrogelator and to regulate the formation of supramolecular hydrogels. Adding a kinase to the hydrogel induces a gel−sol phase transition in the presence of adenosine triphosphates (ATP) because the tyrosine residue is converted into tyrosine phosphate by the kinase to give a more hydrophilic molecule of Nap−FFGEY−P(O)(OH)2 (2); treating the resulting solution with a phosphatase transforms 2 back to 1 and restores the hydrogel. Electron micrographs of the hydrogels indicate that 1 self-assembles into nanofibers. Subcutaneous injection of 2 in mice shows that 80.5 ± 1.2% of 2 turns into 1 and results in the formation of the supramolecular hydrogel of 1 in vivo. This simple biomimetic approach for regulating the states of supramolecular hydrogels promises a new way to design and construct biomaterials.

A biocompatible method of decorporation: Bisphosphonate-modified magnetite nanoparticles to remove uranyl ions from blood

Abstract: We report on the use of bisphosphonate to functionalize Fe3O4 magnetic nanoparticles via dopamine (DA) linkage. Using tetraethyl-3-aminopropane-1,1-bisphosphonate (BP) as the functional molecule, we created a system with an Fe3O4-DA-BP nanostructure, which possesses high specificity for removing uranyl ions from water or blood. This work demonstrates that magnetic nanoparticles, combined with specific receptor-ligand interactions, promise a sensitive and rapid platform for the detection, recovery, and decorporation of metal toxins from biological environment.

Magnetic‐Dipolar‐Interaction‐Induced Self‐Assembly Affords Wires of Hollow Nanocrystals of Cobalt Selenide

Abstract: Self-assembly, an attractive and practical methodology, allows the formation of a wide range of nanostructures for promising applications—for example, nanoparticle arrays for new optical band-gap materials or high-density magnetic recording media, self-assembled monolayers (SAM) for nanometerthick films on a variety of substrates, and nanofibers of selforganized small molecules or oligopeptides for drug delivery and tissue engineering. Hydrogen bonding and/or van der Waals interactions are usually the driving forces that result in self-assembly at the nanoscale. Despite extensive investigation, it is still difficult to control and predict the nanostructures resulting from these two types of forces. Although several recent reports have shown that magnetic dipolar interactions induce rather predictable nanoassemblies, methods for maintaining these assemblies when the magnetic force decreases or vanishes have been less thoroughly investigated. Therefore, we decided to use the magnetic dipoles inherently associated with magnetic nanoparticles to form 1D assemblies of hollow nanocrystals of semiconductors. We chose to make wires of hollow nanocrystals of CoSe2 to demonstrate the concept, because 1) the isolation of a nanonecklace of cobalt nanocrystals on a substrate from a dispersion after removal of the solvent indicated that magnetic dipolar interactions are sufficient to maintain 1D assemblies of nanocrystals in solution; 2) the recently reported formation of hollow CoSe nanocrystals from cobalt nanocrystals through the Kirkendall effect suggested that a similar process could be used to generate hollow CoSe2 nanocrystals from 1D assemblies of cobalt nanocrystals; 3) hollow nanostructures have received considerable attention because they exhibit properties that differ from their solid counterparts; and 4) nanowires of hollow nanocrystals of CoSe2 are unknown. Herein, we show that when their sizes reach approximately 20 nm cobalt nanocrystals self-assemble into wires in solution at temperatures as high as 455 K. Through the nanoscale Kirkendall effect, wires of hollow CoSe2 nanocrystals form without loss of the preassembled nanostructure induced by the magnetic dipolar interactions of the cobalt nanocrystals. In control experiments, when the size of the cobalt nanocrystals is 6 nm, or when 20-nm cobalt nanocrystals are in an alternating magnetic field, no wires of hollow CoSe2 nanocrystals form. These observations confirm that the magnetic interaction plays a key role in the formation of the nanowires of hollow CoSe2 crystals. Several types of ferromagnetic metallic nanocrystals (iron, cobalt, nickel, FePt, or CoPt) can be prepared readily, and their selfassembly depends on the magnetic dipolar interactions of particles of a certain size. Therefore, the method shown herein should be a general route to 1D assemblies of hollow nanocrystals. The synthesis of wires of hollow CoSe2 nanocrystals is easy and straightforward. Cobalt nanocrystals of approximately 20 nm in diameter were prepared according to a modified literature procedure and then dispersed in a solvent (for example, 1,2-dichlorobenzene) by using trioctylphosphine oxide (TOPO) as a surfactant. The injection of a dichlorobenzene solution of selenium into the dispersion of cobalt nanocrystals under reflux at 455 K resulted in a black dispersion of CoSe2 nanocrystals after approximately 30 min. Transmission electron microscope (TEM) images reveal that the CoSe2 nanocrystals form wires of intercon[*] J. Gao, Prof. B. Xu Department of Chemistry The Hong Kong University of Science & Technology Clear Water Bay, Hong Kong (China) Fax: (+852)2358-1594 E-mail: chbingxu@ust.hk

Biofunctional Magnetic Nanoparticles for Protein Separation and Pathogen Detection

Abstract: Recent successful syntheses of monodispersed magnetic nanoparticles have offered a unique opportunity to control and probe biological interactions using magnetic force. This paper highlights a general strategy to generate biofunctional magnetic nanoparticles, illustrates applications for these nanoparticles in protein separation and pathogen detection, and analyzes the high sensitivity and high selectivity achieved by this system.

Using Enzymes to Control Molecular Hydrogelation

Abstract: The expression and distribution of enzymes differ by the types and states of cells, tissues, and organs, thus leading to diverse extracellular and intracellular environments. Using an enzymatic reaction to convert a precursor into a hydrogelator or vice versa, one can control the delivery, functions, and responses of a hydrogel according to a specific biological condition or environment, thus providing an accessible route to creating sophisticated soft materials for potential biomedical applications.

Self-assembly and self-orientation of truncated octahedral magnetite nanocrystals

Abstract: Monodispersed magnetite (Fe3O4) nanoparticles were synthesized. Transmission electron microscopy study shows that the nanoparticles are in the shape of Wagner-Seitz crystals. The magnetite nanoparticles self-assemble into body-centered cubic superlattice, in which the nanoparticles have the same crystallographic orientations. Shape plays a very critical role in controlling the orientation of the nanoparticles in the superlattice. Both the self-assembly and self-orientation of nanoparticles are important for technical applications. This can also act as a complement to conventional lithography techniques.

The origin of the non-monotonic field dependence of the blocking temperature in magnetic nanoparticles.

Abstract: The dependence of the peak temperature (TP) of the zero-field-cooled (ZFC) magnetization curves on the field in a magnetic nanoparticle system was studied using a diluted magnetic fluid composed of FePt nanoparticles. We found that the peak temperature increases with increasing applied field below 3 kOe; it then decreases when the applied field is increased further. We attribute the non-monotonic field dependence of the peak temperature to the anisotropic energy barrier distribution of the particles and to the slow decrease of high-field magnetization above the blocking temperature. Numerical simulations, based on magnetic dynamics, agree well with our experimental results.

A New Approach in Measuring Cu–EMC Adhesion Strength by AFM

Abstract: Copper-epoxy molding compound (Cu-EMC) interface is known to be one of the weakest interfaces in an electronic package exhibiting delamination during reliability test. Thiol compound which bonds readily and forms a self-assembly monolayer (SAM) with copper is proposed to improve interfacial adhesion between copper and EMC. Conventional adhesion evaluation involves force measurement in macro-scale. However, inconclusive or even contradictive results are common in those tests because of uncontrollable surface conditions such as contamination and, in particular, roughness. To eliminate the roughness effect and reflect the true chemical bonding condition, an Si wafer was used as a substrate in the experiments. This study involves the use of an atomic force microscope (AFM) in characterizing the nanoscale adhesion force in a Cu-SAM-EMC system. Findings were used as the criteria in selecting a SAM candidate. A thiol compound having a carbonyl group is shown to be the best adhesion promoter from the measurement. The nanoscale AFM results are shown to be consistent with the result of macroscopic shear tests. It has been demonstrated, with SAM treatment on a cleaned copper surface, that the fracture force between Cu-EMC samples is improved from 119 to 195N

Therapeutic uses of artificial nanostructures

Abstract: The present invention provides a method for controlling the fate of mammalian cells or microorganisms by the enzymatic formation of intracellular nanostructures. Enzymatic reactions trigger the intracellular self-assembly to convert a proper precursor into another molecule or nanoobject that will aggregate inside cells or inside or between tissues or organs. Further, this invention provides a method for making artificial nanostructures inside or between tissues or organs, by injecting a proper designed precursor into tissues or organs, and enzymatic reaction converting the precursor to a hydrogelator to form artificial nanostructures and inducing hydrogelation and at the state of a disease, another enzyme converts the hydrogelator back to precursor to induce gel-to-sol transition to release a drug. The present invention can be applied to treat diseases caused by the malfunction of cells, infection caused by microorganisms and provides a novel route for controlled drug releases, formation of new therapeutic agents, and in-situ formation of hydrogel to treat degenerative diseases such as osteoarthritis.

Photosensitizer decorated iron oxide nanoparticles : bimodal agent for combined hyperthermia and photodynamic therapy

Abstract: As the PDT effect may be enhanced by localized hyperthermia (HT), it would be logical to find a single agent that could bring about these two modalities at precisely the target site for synergism. Since highly localized HT can be induced by magnetic field excitation of superparamagnetic nanoparticles, we report here the design and synthesis of photosensitizer-decorated iron oxide nanoparticles and their tumoricidal effect. Thus, a porphyrin is covalently anchored on the iron oxide nanoparticle via dihydroxybenzene which binds tightly on the surface of the nanoparticle by M-O bond. The morphology of the resultant nanoparticle was studied to show that the crystallinality is not changed and the nanoparticle remains superparamagnetic at room temperature. The conjugate is also strongly fluorescent indicating that the iron oxide hardly affects the optical properties of the surface bound porphyrin moieties. The conjugate is readily taken by cancer cell (Hela cell line) and is able to trigger apoptosis after excitation by light.

Kinetics study of disulfide self assembly monolayer (SAM) deposition for Cu-EMC adhesion

Abstract: This paper presents a study of disulfide self assembly monolayer (SAM) onto sputtered Cu substrate. Extrinsic parameter includes substrate roughness, solution concentration, deposition time and agitation has been investigated. Ellipsometer was used to measure the SAM thickness to investigate impact of process parameter on homogenous film quality. 50 A sputtered Cu on Si wafer having roughness of around 10 A is recommended to be used as substrate in the process. It has been discovered that agitation which prevents local concentration of disulfide solution, is crucial for success of film deposition. Without agitation, larger thickness variation has been attained (36plusmn22 A comparing with 30plusmn16 A). Furthermore, relatively uniform film (37plusmn10 A for DS-A, 30plusmn8 A for DS-C) can be realized from low concentration (0.5 muM) ethanol in 1 hr. Atomic force microscope (AFM) has been used to probe topography images of deposited film. No significant aggregates but few pinholes have been found on disulfide treated surface. An experiment procedure in obtaining uniform thin film from disulfide solution on Cu substrate has been investigated.

Kinetic study of disulfide molecular film deposition for Cu-EMC adhesion promotion

Abstract: This paper presents a study of disulfide thin film onto sputtered Cu substrate. Extrinsic parameter includes solution concentration, deposition time and agitation has been investigated. Ellipsometer was used to measure the molecular film thickness. It has been discovered that agitation which prevents local concentration of disulfide solution, is crucial for success of film deposition. Without agitation, larger thickness variation has been attained (36plusmn22 Aring comparing with 30plusmn16 Aring). Furthermore, relatively uniform film (37plusmn10 Aring for DS-A, 30plusmn8 Aring for DS-C) can be realized from low concentration (0.5 muM) ethanol in 1 hr. No significant aggregates but few pinholes have been found on disulfide treated surface. An experiment procedure in obtaining uniform thin film from disulfide solution on Cu substrate has been investigated.

Kinetics Study of Disulfide Self Assembly Monolayer (SAM) Deposition for Cu-EMC Adhesion Promotion

Abstract: This paper presents a study of disulfide self assembly monolayer (SAM) onto sputtered Cu substrate Extrinsic parameter includes substrate roughness, solution concentration, deposition time and agitation has been investigated Ellipsometer was used to measure the SAM thickness to investigate impact of process parameter on homogenous film quality 50 A sputtered Cu on Si wafer having roughness of around 10 A is recommended to be used as substrate in the process It has been discovered that agitation which prevents local concentration of disulfide solution, is crucial for success of film deposition Without agitation, larger thickness variation has been attained (36plusmn22 A comparing with 30plusmn16 A) Furthermore, relatively uniform film (37plusmn10 A for DS-A, 30plusmn8 A for DS-C) can be realized from low concentration (05 muM) ethanol in 1 hr Atomic force microscope (AFM) has been used to probe topography images of deposited film No significant aggregates but few pinholes have been found on disulfide treated surface An experiment procedure in obtaining uniform thin film from disulfide solution on Cu substrate has been investigated

Interfacial strength assessment of Cu-epoxy system by atomic force microscope

Abstract: This paper presents a novel nano-scale interfacial covalent bond measurement method by atomic force microscopy (AFM) with reference to the adhesion of self-assembly monolayer on epoxy/copper systems. Covalent bond strength measurements were conducted using AFM for self assembly monolayer (SAM) coated copper (Cu) tips on epoxy after epoxy has been cured at its curing temperature. In-situ curing of Cu-epoxy force measurement simulates situation of epoxy molding compound (EMC) curing inside conventional transfer molding process. The Cu-SAM-epoxy system testing provides a good testing platform for evaluating the performance of various SAM materials as an adhesion promoter. Adhesion enhancement at the interface has been achieved by surface modification of Cu surface with thiol solution. Normalized adhesion strength was reported as measured adhesion force divided by tip epoxy contact area. It illustrated that with thiol treatment, Cu-epoxy interfacial adhesion strength has been enhanced from 2.83/spl plusmn/0.07/spl times/ 10-5 nN/nm/sup 2/ and 5.38/spl plusmn/2.48/spl times/10-5 nN/nm/sup 2/.

Kinetic Study of Disulfide Molecular Film Deposition for Cu-EMC Adhesion Promotion

Abstract: This paper presents a study of disulfide thin film onto sputtered Cu substrate Extrinsic parameter includes solution concentration, deposition time and agitation has been investigated Ellipsometer was used to measure the molecular film thickness It has been discovered that agitation which prevents local concentration of disulfide solution, is crucial for success of film deposition Without agitation, larger thickness variation has been attained (36plusmn22 Aring comparing with 30plusmn16 Aring) Furthermore, relatively uniform film (37plusmn10 Aring for DS-A, 30plusmn8 Aring for DS-C) can be realized from low concentration (05 muM) ethanol in 1 hr No significant aggregates but few pinholes have been found on disulfide treated surface An experiment procedure in obtaining uniform thin film from disulfide solution on Cu substrate has been investigated