Showing papers by "Bing Xu published in 2004"

Dopamine as a robust anchor to immobilize functional molecules on the iron oxide shell of magnetic nanoparticles

Abstract: We report on the use of dopamine (DA) as a robust molecular anchor to link functional molecules to the iron oxide shell of magnetic nanoparticles. Using nitrilotriacetic acid (NTA) as the functional molecule, we created a system with an M/Fe2O3-DA-NTA (M = Co or SmCo5.2) nanostructure, which possesses high stability and specificity for separating histidine-tagged proteins. The well-established biocompatibility of iron oxide and the robust covalent bonds between DA and Fe2O3 render this strategy attractive for constructing biofunctional magnetic nanoparticles containing iron oxide.

Facile one-pot synthesis of bifunctional heterodimers of nanoparticles: a conjugate of quantum dot and magnetic nanoparticles.

Abstract: Sequential addition of sulfur and Cd(acac)2 into the colloid solution of FePt nanoparticles (∼2.5 nm) under a reductive environment generates heterodimers of CdS and FePt with sizes of ∼7 nm. The heterodimers exhibit both superparamagnetism and fluorescence, indicating that the discrete properties of the individual parts of the dimers are preserved. This simple methodology may lead to the production of large quantities of various heterostructures with tailored properties on the nanoscale.

Nitrilotriacetic acid-modified magnetic nanoparticles as a general agent to bind histidine-tagged proteins.

Abstract: Using Nα,Nα-bis(carboxymethyl)lysine to react with FePt magnetic nanoparticles, we synthesized the FePt−NTA conjugate, which immobilizes Ni2+ ions and selectively binds to histidine-tagged proteins...

Molecular recognition remolds the self-assembly of hydrogelators and increases the elasticity of the hydrogel by 10(6)-fold.

Abstract: Addition of vancomycin (1, the receptor) to the supramolecular hydrogel of self-assembled pyrene-d-Ala-d-Ala (2, the ligand) increases the storage modulus of the hydrogel of 2 by about 106-fold. Rheology, microscopy, and spectroscopy investigations suggest that the two-dimensional polymers, formed by the ligand-receptor interaction between 1 and 2, and the self-dimerization of 1, are mainly responsible for the observed dramatic increase in elasticity.

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 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 condition such as contamination and, in particular, roughness. To eliminate roughness effect and reflect the true chemical bonding condition, Si wafer was used as substrate in the experiments. This study involves the use of atomic force microscope (AFM) in characterizing the nano-scale adhesion force in Cu-SAM-EMC system. Findings were used as the criteria in selecting SAM candidate. Thiol compound having carbonyl group is shown to be the best adhesion promoter from the measurement. The nano-scale AFM results are shown to be consistent with the result of macro scale shear tests. It has been demonstrated, with SAM treatment on a cleaned Cu surface, the fracture force between Cu-EMC samples is improved from 119N to 195N.

Solventless Polymerization to Grow Thin Films on Solid Substrates

Abstract: We report on the formation of polymeric thin films on a solid surface using gaseous monomers. The process consists of adding catalysts on the surface of a solid substrate and polymerizing volatile monomers at the gas/solid interface, or directly using the vapors of the catalyst and the monomers to selectively form polymers inside the microchannels. The morphology and properties of these thin films depend on the concentration of catalysts, the time of exposure to the monomers, and the type of the monomers, which can be easily controlled at the molecular level. This solventless process can be used for a range of applications.