Sang Man Koo

Simple preparation of monodisperse hollow silica particles without using templatesElectronic supplementary information (ESI) available: TEM showing effects of hydrolysis time, reaction temperature and calcination on the particles. TGA of hollow particles, BET measurements of hollow and calcined hollow particles. See http://www.rsc.org/suppdata/cc/b3/b301521a/

Monodisperse hollow silica particles were prepared without using templates via a two-step method in an aqueous solution, were controlled in size and hollow diameter, and were selectively soluble in organic solvents, leading to usefulness in many applications such as coating technology, catalysis, delivery systems, nanoreactors, and composite materials.

Characterization of Hydrophobic SiO2 Powders Prepared by Surface Modification on Wet Gel

Hydrophobic porous silica has been prepared by surface modification of TEOS (tetraethylorthosilicate) wet gel with 6 and 12 vol.% of TMCS (trimethylchlorosilane). We characterized the products by using FT-IR, TGA, DTA, N2 adsorption/desorption, contact angle and SEM. Surface silanol groups of the gel were widely replaced by–Si(CH3)3 to result in a hydrophobic SiO2 powder as confirmed by contact angle measurements with H2O, 1-butanol and ethanol. The modified dried gels had a surface area of 950–1000 m2/g (average pore size 120 Å), compared to the non-modified surface which had a surface area of 690 m2/g (average pore size 36 Å). The adsorption/desorption isotherm curves indicated they had similar pore characteristics as aerogels prepared by the supercritical drying process.

Near infrared luminescent oxygen nanosensors with nanoparticle matrix tailored sensitivity.

The development of sensors for noninvasive determination of oxygen levels in live cells and tissues is critical for the understanding of cellular functions, as well as for monitoring the status of disease, such as cancer, and for predicting the efficacy of therapy. We describe such nontoxic, targeted, and ratiometric 30 nm oxygen nanosensors made of polyacrylamide hydrogel, near-infrared (NIR) luminescent dyes, and surface-conjugated tumor-specific peptides. They enabled noninvasive real-time monitoring of oxygen levels in live cancer cells under normal and hypoxic conditions. The required sensitivity, brightness, selectivity, and stability were achieved by tailoring the interaction between the nanomatrix and indicator dyes. The developed nanosensors may become useful for in vivo oxygen measurements.

Ratiometric Singlet Oxygen Nano‐optodes and Their Use for Monitoring Photodynamic Therapy Nanoplatforms

Abstract Ratiometric photonic explorers for bioanalysis with biologically localized embedding (PEBBLE) nanoprobes have been developed for singlet oxygen, using organically modified silicate (ORMOSIL) nanoparticles as the matrix. A crucial aspect of these ratiometric singlet-oxygen fluorescent probes is their minute size. The ORMOSIL nanoparticles are prepared via a sol-gel–based process and the average diameter of the resultant particles is about 160 nm. These sensors incorporate the singlet-oxygen–sensitive 9,10-dimethyl anthracene as an indicator dye and a singlet-oxygen–insensitive dye, octaethylporphine, as a reference dye for ratiometric fluorescence-based analysis. We have found experimentally that these nanoprobes have much better sensitivity than does the conventional singlet-oxygen–free dye probe, anthracene-9,10-dipropionic acid disodium salt. The much longer lifetime of singlet oxygen in the ORMOSIL matrix, compared to aqueous solutions, in addition to the relatively high singlet oxygen solubility because of the highly permeable structure and the hydrophobic nature of the outer shell of the ORMOSIL nanoparticles, results in an excellent overall response to singlet oxygen. These nanoprobes have been used to monitor the singlet oxygen produced by “dynamic nanoplatforms” that were developed for photodynamic therapy. The singlet oxygen nanoprobes could potentially be used to quantify the singlet oxygen produced by macrophages.

Preparation of Silver Nanoparticles through Alcohol Reduction with Organoalkoxysilanes

Silver nanoparticles of narrow size distribution were prepared through the chemical reduction in an alcohol solution with several organoalkoxysilanes. In this system, organoalkoxysilanes served as a stabilizer, protecting silver nanoparticles from aggregation. The changes in size and morphology of colloidal silver nanoparticles were investigated with the addition of organoalkoxysilanes such as 3-aminopropyltriethoxysilane (APS), methyltriethoxysilane (MTS), phenyltrimethoxysilane (PTS), vinyltriethoxysilane (VTS), and 3-glycidoxypropyltrimethoxysilane (GPS) as stabilizers. The organic functional groups of organoalkoxysilanes interact with silver ions and clusters, which stabilize silver nanoparticles in the system. The silver nanoparticles obtained were characterized with transmission electron microscopy (TEM), UV-vis spectroscopy, etc.

Deposition of Titania Nanoparticles on Spherical Silica

Titania coated silica nanoparticles were prepared through a sol-gel process using peptized TiO2 nano-sols. The TiO2 sols were obtained by peptization, the process of redispersing a coagulated colloid, and were coated on SiO2 particles by the control of the weight ratio of TiO2/SiO2 and the pH of the mixture in aqueous solution. At pH 4.5 the difference of zeta-potential between SiO2 and TiO2 maximized and then the TiO2-coated SiO2 particles with highest TiO2 contents (∼20%) were obtained without the self-aggregation of TiO2 sols. The morphologies of particles were characterized with field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) and the isoelectric points (IEP) of particles were measured by zeta potential. The nature of exposed titanium ions on the surface of titania-coated silica nanoparticles was elucidated by X-ray photoelectron spectroscopy (XPS).

One-Step Synthesis of Structurally Controlled Silicate Particles from Sodium Silicates using a Simple Precipitation Process

Silicate particles with various types of internal structures were prepared via one-pot synthesis. Spherical particles with sizes of 50-100 nm could be obtained by a simple precipitation process with the addition of alcohol to an aqueous sodium silicate solution. By controlling the reaction conditions such as the precipitating solvent (different types of alcohols), reaction time, temperature, and addition rate, spherical silicate particles with hollow, porous, dense internal structures were synthesized without using an external template. In addition, the amount of Na in the silicate particles was effectively reduced by washing with hot water, acid, or ion-exchange resins. Spherical particles maintained their morphologies after heat treatment at 500 degrees C. Electron microscopy, N(2) adsorption/desorption measurements, ICP-OES, XRD analysis, and IR and (29)Si NMR spectrometry were performed to elucidate the chemical and physical properties of the obtained silicate particles. This method of synthesis could provide a commercial route to the simple, economical mass production of silica particles.

Strontium β-diketonate complexes with polyamine donor ligands: the synthesis and structural characterization of [Sr(thd)2(L)]n (n=2; L=diethylenetriamine, n=1; L=triethylenetetramine, tetraethylenepentamine and tris(2-aminoethyl)amine) complex

Abstract Four novel [Sr(thd)2(L)]n (n=2; L=diethylenetriamine (I), n=1; L=triethylenetetramine (II), tetraethylenepentamine (III), and tris(2-aminoethyl)amine (IV)) complexes were synthesized by the reaction of Sr(thd)2 with corresponding polyamines in THF and characterized by FTIR, 1H NMR and single-crystal X-ray crystallography. Complex I exists as a dimmer in the solid state in which two strontium atoms are bridged by two thd ligands. Complexes II and III exist as monomers in the solid state and in both complexes, the polyamine ligands are coordinated to the central strontium atom in a meridional fashion, with the two thd ligands on opposite sides of the neutral ligand plane. Complex IV also exist as a monomer in the solid state. In this molecule, strontium atom is eight-coordinate with all of the nitrogens of the amine ligand and all oxygens of the thd ligand binding to the metal atom. The amine ligand is coordinated to one side of the metal atom and resulting in a cis-relationship. Thermogravimetric analysis shows that complexes I, II, III and IV are sufficiently volatile and sublimed without residue.

Encapsulation of Water-Soluble Dye in Spherical Sol-Gel Silica Matrices

The water-soluble, Lithol rubine B, dye was encapsulated into silica microspheres matrices. Encapsulation has been carried out by sol-gel process of W/O microemulsions formed from sodium silicate and dye aqueous solution in cyclohexane medium. The average particle size could be tailored from 1–10 μm, depending on the processing parameter such as homogenizing speed in the formation of W/O emulsion, the weight ratio of water to oil, and concentration of sodium silicate solution, etc. The pore size of dye-doped silica microspheres was measured by nitrogen adsorption-desorption isotherms. The leaching behavior of dye entrapped in silica matrices was investigated by UV/VIS and UV diffuse reflectance spectroscopy for the extract and solid powders after immersion for 24 h in water. The doping of GPTS (3-glycidoxypropyltrimethoxysilane) in sodium silicate and dye mixture solution greatly enhanced the stability against leaching of the dye. It was ascribed that GPTS serves simultaneously as an intermediate for the chemical bonding between the dye and silica, and as an agent for the formation of hybrid sol responsible for the shrinkage of pore size.

New synthetic route for preparing rattle-type silica particles with metal cores

Rattle-type silica particles with metal cores, applicable to catalysts and metal/inorganic composite coating materials, were prepared by the pre-shell/post-core method that can control the size of metal cores inside silica capsules and exchange from metal cores into different ones with a metal displacement reaction.