Kamyar Rahimian

High-efficiency magnetic particle focusing using dielectrophoresis and magnetophoresis in a microfluidic device

We describe a novel technique that utilizes simultaneous implementation of dielectrophoresis (DEP) and magnetophoresis (MAP) to focus magnetic particles into streams for optical analysis of biological samples. This technique does not require sheath flow and utilizes a novel interdigitated electrode array chip that yields multiple streams of flowing magnetic particles in single-file columns. The MAP force placed particles in close proximity to the microelectrodes where they were subjected to a strong DEP force that generated the particle focusing effect. Particle focusing efficiency was improved using this combination DEP–MAP technique compared to DEP alone: particle stream widths were reduced ~47% and stream width variability was reduced 80% for focused streams of 8.5 µm diameter magnetic particles. 3 µm diameter magnetic particles were strongly focused with DEP–MAP (~4 µm wide streams with sub-µm variability in stream width) while DEP alone provided minimal focusing. Additional components of a prototype detection system were also demonstrated including an integrated magnetic pelleting component, a hand-held MHz frequency signal generator and a bench-top near-confocal microscope for optical analysis of flowing particles. Preliminary testing of a sandwich assay performed on the surface of magnetic particles showed 50 ppb detection levels of a surrogate biotoxin (ovalbumin) in a raw milk sample.

Magnetic Extraction, Detection, and Isotope Analysis of Metal Ions Using Surface Modified Microspheres for Lab-on-a-Chip Applications

Liquid–liquid extraction and ion-exchange chromatography are efficient methods for sequestration of metal ions, but these methods are poorly suitable for microfluidic miniaturization. Here we examine several methods for rapid extraction, fluorometric detection, and the subsequent isotope analysis of lanthanide ions sequestered on surface modified magnetic microspheres as a versatile platform for chemical manipulation. The assays involve immobilization of a mixed-ligand complex of luminescent lanthanide ions at the surface of polystyrene microspheres. Using the ion-exchange properties of these microspheres, this scheme can be extended to the detection of nonluminescent ions.

Sequestration, fluorometric detection, and mass spectroscopy analysis of lanthanide ions using surface modified magnetic microspheres for microfluidic manipulation.

Several methods for rapid sequestration, fluorometric detection, and the subsequent mass spectroscopic analysis of lanthanide ions using surface modified polystyrene magnetic microspheres are demonstrated. Mixed-ligand antenna complexes of Eu(3+) in which one of the ligands is attached to the surface of the microspheres have been used as a means for the sequestration, immobilization, and detection of these ions. Using the ion-exchange properties of these microspheres, this scheme has been extended to the detection of nonluminescent ions. The principles of these assays form the basis for operation of a portable microfluidic device for general analytical and nuclear forensics applications and indicate the manner in which the established methods of analytical chemistry, such as liquid-liquid extraction and ion-exchange chromatography, can be adapted for such miniature devices.

Patterned functional arrays by selective de-wetting

Using a micro-Contact Printing ({mu}-CP) technique, substrates are prepared with patterns of hydrophilic, hydroxyl-terminated SAMS and hydrophobic methyl-terminated SAMS. Beginning with a homogeneous solution of silica, surfactant, ethanol, water, and functional silane, preferential ethanol evaporation during dip-coating, causes water enrichment and selective de-wetting of the hydrophobic SAMS. Correspondingly, film deposition occurs exclusively on the patterned hydrophilic SAMS. In addition, by co-condensation of tetrafunctional silanes (Si(OR){sub 4}) with tri-functional organosilanes ((RO){sub 3}Si(CH{sub 2}){sub 3}NH{sub 2}), the authors have selectively derived the silica framework with functional amine NH{sub 2} groups. A pH sensitive, micro-fluidic system was formed by further conjugation reactions with pH sensitive dye molecules.

Phenylen‐verbrückte, cyclische Siloxane als Vorstufen nichtschrumpfender Sol‐Gel‐Systeme und deren Nutzung als Kapselmaterial

Eine neue Klasse thermisch widerstandsfahiger Sol-Gel-Polymere ist uber das Disilaoxacyclopentanderivat 1 zuganglich, da dessen Ringoffnungspolymerisation Polysiloxane ohne Schrumpfungsprobleme liefert. Damit kann diese Reaktion, bei der auf Wasser oder andere Losungsmittel verzichtet werden kann, unter anderem genutzt werden, um elektronische Bauteile einzukapseln.

Solventless sol-gel chemistry through ring-opening polymerization of bridged disilaoxacyclopentanes

Hybrid magnetic composites made up of calibrated maghemite nanoparticles well dispersed in an epoxide resin were obtained by polymerization of the resin inside stable organosols of maghemite. The sol stability was ensured by ligand adsorption onto the particle surface. Studies of phenylphosphonic acid adsorption are presented. They show a strong interaction between PPA ions and hydroxyl groups of particle surface and through bridging ≡Fe 2 O 2 POΦ species. Infrared and Mossbauer spectroscopies as well as quasi- elastic light scattering and transmission electron microscopy were used to characterize the materials.Organic/inorganic hybrid films exhibiting ordered mesophases were prepared by a simple dip-coating procedure. Beginning with a homogeneous solution of tetraethyl orthosilicate, organoalkoxysilane ((R Si(OR)3, R is a non-hydrolyzable functional ligand) surfactant, we relied on solvent evaporation to induce micellization and continuous self-assembly into hybrid silica-surfactant thin film mesophases. Surface acoustic wave (SAW)-based nitrogen sorption measurements indicate that the films have high surface areas and unimodal pore diameters after removal of surfactants. INTRODUCTION Organic-inorganic hybrid mesoporous silica (with controlled pore structure and tailored pore chemistry) could find many applications in new types of catalysis and separation, environmental and industrial processes, electronics, and sensors.[ 1Al A route to fi.mctionalized amorphous silica materials that has been widely investigated in sol-gel chemistry involves the co-condensation of organosilanes with silicate to produce hybrid organic-inorganic networks[5~ 61.In these materials, an organic fictional group, R, is covalently bound to siloxane that is hydrolyzed to form silica copolymer. Mann et al. [’71first used this concept in direct synthesis of ordered organic-inorganic mesoporous powders containing octyland phenylgroups in 1996, later extending to mesoporous materials containing mercapto-, amino-, epoxylgroups.[8J 91 At the same time, several other studies were reported about direct synthesis of hybrid functional mesoporous silica[2~ 10-121. A solvent extraction procedure was used to remove the surfactant, resulting in a functionalized mesoporous product with a hexagonal MCM-41-type architecture. In each case mentioned above, the hybrid mesoporous silica was in the form of powder, precluding its use in such promising applications as membranes and optically-based sensors that generally require transparent, defect-freed supported thin films. We recently reported on a rapid and continuous approach to form thin silica films with ordered mesoporous structures131. Films with 2-dimensional hexagonal, 3-dimensional hexagonal, cubic, or lamellar structures were prepared from initially homogeneous silica SOISby evaporation-induced surfactant enrichment during sol-gel dip-coating. In this paper, we extended our work to the preparation of hybrid organic/inorganic thin films with tailored pore surface chemistries. EXPERIMENTAL Precursor solutions were prepared by addition of surfactants (cationic, CTAB; C133(CH2)15~(CHJ3Bror non-ionic, Brij-56; CH3(CH2)15-(OCH2CH2) 10-OH ), organosilanes (R Si(OR)3, see Table 1), or organic molecules (see Table 1) to an acidic silica sol prepared from TEOS [Si(OCH2CH3 )4] (A2**). The acid concentration employed in the A2** synthesis procedure was chosen to minimize the siloxane condensation rate, thereby promoting facile selfassembly during printing. In a typical preparation, TEOS [Si(OCH2CH3 ) ethanol, water andDisilaoxacyclopentanes have proven to be excellent precursors to sol-gel type materials. These materials have shown promise as precursors for encapsulation and microelectronics applications. The polymers are highly crosslinked and are structurally similar to traditional sol-gels, but unlike typical sol-gels they are prepared without the use of solvents and water, they have low VOCs and show little shrinkage during processing.

Sol-gel chemistry by ring-opening polymerization

Sol-gel processing of materials is plagued by shrinkage during polymerization of the alkoxide monomers and processing (aging and drying) of the resulting gels. The authors have developed a new class of hybrid organic-inorganic materials based on the solventless ring-opening polymerization (ROP) of monomers bearing the 2,2,5,5-tetramethyl-2,5-disilaoxacyclopentyl group, which permits them to drastically reduce shrinkage in sol-gel processed materials. Because the monomers are polymerized through a chain growth mechanism catalyzed by base rather than the step growth mechanism normally used in sol-gel systems, hydrolysis and condensation products are entirely eliminated. Furthermore, since water is not required for hydrolysis, an alcohol solvent is not necessary. Monomers with two disilaoxacyclopentyl groups, separated by a rigid phenylene group or a more flexible alkylene group, were prepared through disilylation of the corresponding diacetylenes, followed by ring closure and hydrogenation. Anionic polymerization of these materials, either neat or with 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane as a copolymer, affords thermally stable transparent gels with no visible shrinkage. These materials provide an easy route to the introduction of sol-gel type materials in encapsulation of microelectronics, which they have successfully demonstrated.

Porosity in Polysilsesquioxane Xerogels

Polymerization of organotrialkoxysilanes is a convenient method for introducing organic functionality into hybrid organic-inorganic materials. However, not much is known about the effects of the organic substituent on the porosity of the resulting xerogels. In this study, we prepared a series of polysilsesquioxane xerogels from organotrialkoxysilanes, RSi(OR′) 3 , with different organic groups (R = H, Me, Et, dodecyl, hexadecyl, octadecyl, vinyl, chloromethyl, cyanoethyl). Polymerizations of the monomers were carried out under a variety of conditions, varying monomer concentration, type of catalyst, and alkoxide substituent. The effect of the organic substituent on the sol-gel process was often dramatic. In many cases, gels were formed only at very high monomer concentration and/or with only one type of catalyst. All of the gels were processed as xerogels and characterized by scanning electron microscopy and nitrogen sorption porosimetry to evaluate their pore structure.