Silica particles, binding

The use of silica particles in bioapplications began with the publication by Stober et al. in 1968 on the preparation of monodisperse nanoparticles and microparticles from a silica alkoxide monomer (e.g., tetraethyl orthosilicate or TEOS). Subsequently, in the 1970s, silane modification techniques provided silica surface treatments that eliminated the nonspecific binding potential of raw silica for biomolecules (Regnier and Noel, 1976). Derivatization of silica with hydrophilic, hydroxylic silane compounds thoroughly passivated the surface and made possible the use of both porous and nonporous silica particles in all areas of bioapplications (Schiel et al., 2006). 

Add a blocking agent, such as a non-relevant protein (e.g., BSA) to a final concentration of 1 percent to mask any nonspecific binding sites and to couple with any remaining reactive groups on the silica particle surface. This is important especially if a limiting amount of antibody was initially reacted with the particles in step 5. React for 30 minutes to 1 hour at room temperature. 

Siroc [Silicate rock] Also known as the one-shot system. A chemical grouting system for hardening ground formations. Aqueous solutions of sodium silicate and formamide are mixed and injected into the ground the formamide slowly reacts with the silicate, precipitating hydrated silica, which binds the soil particles together. Invented in 1961 by the Diamond Alkali Company. See also Joosten. 

Silica particles surface-imprinted with a TSA of a-chymotrypsin were applied for the enantio-selective hydrolyzation of amides. Surprisingly, the particles showed reverse enantio-selectivity, i. e., the sol-gel imprinted with the L-isomer of the enzyme s TSA showed a higher selectivity for the D-isomer of the substrate [125]. Also Ti02 gels have been imprinted, e.g., with 4-(4-propyloxypheny-lazo)benzoic acid. QCM coated with ultrathin films of this gel were prepared by an immersion process and showed selective binding of the template [ 126]. These examples demonstrate once more the broad applicability of the concept of molecular imprinting. 

At pH 7 33% of the plutonium was not readily desorbed from particles. However, it is possible that complexing agents could alter the affinity of silicates for different cations. The natural affinity of kaolins is Th > La > Ca > K, but in the presence of citrate or fluoride the order is reversed (156). Presumably these complexing agents will also alter the binding of plutonium to the silica particles. 

This method is the simplest approach for simultaneous carotenoid, retinol, and tocopherol analysis. Both the column and mobile phase have been chosen to provide efficiency and selectivity for the analysis of these components without the use of a gradient. The method uses the Spherisorb ODS2 column, in which the Cl8 chain is monomerically bound to the silica particles (i.e., the C18 chain binds at one site to the silica particles). 

Binding and Elution from Glass or Silica Particles... 

RuII) and Cu" " should show quenching of (Rull) that is more rapid than that in water. This is the case for NaLS micelles but the rates on silica are actually lower than those observed in water. This is due to a lower mobility of Cu+" around a silica particle compared to an NaLS micelle, a fact already indicated by the strong binding of ions such as Rull to silica particles. 

The lifetime of PN++ is much enhanced on the anionic NaLS and silica particles compared to water. An interesting feature of the silica particles is that PN++ is easily observed, hut unlike micelles or water e-g n is not observed. This is not due to the fact that e g reacts with silica, as e aq produced in the water bulk by photo-ionization of pyrene sulfonic acid (this molecule does not well bind to silica), has a long lifetime,... 

Other signiflcant complexes of this type, containing one or more lanthanides, are formed by calixarenes (see Calixarenes) Much of this work has been prompted by their potential in separating lanthanides from uranium and other metals. A calixarene ligand with two amide substituents has been synthesised as an extractant for lanthanides dimeric Sm and Eu and monomeric Eu complexes have been prepared. Another calixarene, with four phosphine oxides attached, has been fixed to silica particles and the resulting system has been found to give very efficient extraction of Eu + and Ce + from simulated waste. A calix[4]arene complex of Gd + binds... 

Burow and Minoura performed a similar kind of investigation to prepare protein imprinted polymers [48]. They used methacrylate modified silica particles as the carrier matrix on which imprinted sites were created. Using acrylic acid as the functional monomer and A,TV -1,2-diethylene bisacrylamide as the cross-linker, template polymerisation was carried out in the presence of glucose oxidase. This approach led to formation of a thin layer of cross-linked polymer film on the silica surface. After removing the template protein, substrate selectivity of the polymer was tested. Preferential affinity of the polymer for its template suggests the formation of substrate-selective binding sites in the polymer matrix. 

Substantial efforts have been devoted to the development of molecular sensors for dopamine. Raymo et al.70 reported a two-step procedure to coat silica particles with fluorescent 2,7-diazapyrenium dications sensing toward dopamine. The analysis of the fluorescence decay with multiple-equilibria binding model revealed that the electron deficient dications and the electron-rich analytes form 1 1 and 1 2 complexes at the particle/water interface. The interfacial dissociation constants of the 1 1 complexes were 5.6mM and 3.6mM for dopamine and catechol, respectively. Dopamine was dominated by the interaction of its electron-rich dioxyarene fragment with the electron-deficient fluorophore in neutral aqueous environments. Ahn et al.71 reported tripodal oxazoline-based artificial receptors, capable of providing a preorganized hydrophobic environment by rational design, which mimics a hydrophobic pocket predicted for a human D2 receptor. A moderate binding affinity, a dissociation constant of 8.2 mM was obtained by NMR titrations of tripodal oxazoline-based artificial receptor with dopamine in a phosphate buffer solution (pH 7.0). Structurally related ammonium ions, norepinephrine, 2-phenylethylamine,... 

Several kits are commercially available for the extraction of RNA from plant, bacteria, or mammalian sources. We have used the RNeasy Mini Kit (Qiagen, Valencia, CA) for the extraction of RNA from bacteria following the procedure recommended by the manufacturer (92). This kit relies on guanidine thiocyanate-silica isolation of RNA. Here, guanidine thiocyanate serves as a chaotropic agent, which both lyses cells and inactivates nucleases. In its presence, the released nucleic acids bind to silica particles, which provide a solid phase from which the collected RNA can later be eluted using water (93). This kit is suitable for the isolation and purification of up to 100 pg RNA molecules >200... 

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