Silica electroactive

Audebert, P. and Sanches, C. (1994) Modified electrodes from hydrophobic alkoxide silica gels — insertion of electroactive compounds as glucose oxidase. Journal of Sol-Gel Science and Technology, 2, 809-812. 

J. Wang, G. Liu, and Y. Lin, Bioassay label based on electroactive silica beads. Small 2, 1134-1138... 

The concept of using the functional groups of electrode surfaces themselves to attach reagents by means of covalent bonding offers synthetic diversity and has been developed for mono- and multi-layer modifications. The electrode surface can be activated by reagents such as organosilanes [5] which can be used to covalently bond electroactive species to the activated electrode surface. Recently, thermally induced free-radical polymerization reactions at the surfaces of silica gel have been demonstrated [21]. This procedure has been applied to Pt and carbon electrode surfaces. These thermally initiated polymer macromolecules have the surface Of the electrode as one of their terminal groups. Preliminary studies indicate that the... 

Iodide in vitamin tablets can be found by amperometric detection [88]. Nonaqueous eluents of methanol-containing ammonium perchlorate, which are relatively oxidant resistant, have been used in conjunction with a silica column to detect a wide range of drugs [89]. The use of higher potentials not possible in totally aqueous mobile phases allows for the detection of secondary and tertiary aliphatic amines 462 drugs have been detected in this manner. For compounds that are not electroactive, a procedure using a postcolumn photolysis can generate electroactive species [90] for penicillins [91], proteins [92], and barbiturates [93]. 

For electrochemical detection, the particles used are composed of doped silica (Co(bpy)33+ as the doping agent) [35], iron/gold [36], polystyrene beads internally loaded with electroactive markers (ferrocene) [37] or gold [38],... 

Doped silica particles are used directly as electroactive labels whereas metal- or marker-loaded particles are usually dissolved prior to the electrochemical measurements. Target detection could thus be as low as 5 x 1CT21 moles [37] and more usually in the pmole range [35,38]. 

Researchers turned their attention to applications of silica gel as a new electrode material. Silica gel, which has a three-dimensional structure with high specific surface area and is electroinactive in an aqueous medimn can be used as a support for electroactive species during their formation and/or enzymes by adsorption or entrapment [92,93]. Patel et al. recently reported application of poljwinyl ferrocene immobilized on silica gel particles to construct glucose sensors. Efficiency of carbon paste electrodes prepared with these polymeric electron mediators and GOx was comparable to electrodes constructed with other ferrocene based polymeric electron transfer systems. The fact that 70% of initial anodic current was retained after a month when electrodes were kept in the buffer at room temperature shows that polymerization of monomer vinylferrocene in the pores of silica gel and entrapping GOx in the matrix of poljwinyl ferrocene appears to have added stability to the sensors [94]. 

Recently, we (82) and others (82-84) have shown that similar hetero-structures can be prepared by using two-dimensional inorganic sheets (made by exfoliation of various lamellar solids) in place of the organic polyanion. This technique offers a potentially powerful alternative to the construction of multi-component electron transfer systems, because it can, in principle, be used to stack up an arbitrary number of redox-active polymers without interpenetration (85). This chapter describes the preparation and photochemistry of simple multilayer composites on high-surface-area silica. Specifically, the synthesis and electron transfer kinetics of systems containing a polycationic sensitizer, poly-[Ru(bpy)2(vbpy)(Cl)2] (1), (abbreviated [Ru(bpy)3 ]n bpy = 2,2 -bipytidine and vbpy = 4-vinyl-4 -methyl-2,2 -bipyridine), and an electron-acceptor polycation poly[(styrene-co-]V-vinylbenzyl-N -methyl-4,4 -bipyridine)(Cl)2] (2), (PS-MV ) are presented. Using a solution-phase electron donor, 3, as the third electroactive component, it was possible to prepare and study the photoinduced electron transfer reactions of several different diad and triad combinations. 

Silica nanoparticles (Si NPs) have been successfully used for electrochemical DNA detection. As silica is inherently inactive electrochemically, these particles are either loaded with electroactive molecules and used as labels, or employed as scaffolds... 

F. F. Fang, H. J. Choi, W. S. Ahn, Electroactive Response of Mesoporous Silica and Its Nanocomposites with Conducting Polymers. Compos. Sci. Technol. 2009,69,2088-2092. 

EE Eang, H.J. Choi, W.S. Ahn, Electroactive response of mesoporous silica and its nanocomposites with conducting polymers. Compos. Sci. Tech., 2009, 69, 2088. 

ECL response of allopurinol in aqueous media over a wide pH range (pH 2-13) was studied by Chi et al. [97] They found that allopurinol itself does not have ECL activity but could generate the ECL of Ru(bpy)3 in alkaline media giving rise to a sensitive Fl-ECL response. Humic acid (HA) was used as modifier to prepare the organic-inorganic hybrid modified glassy carbon electrode based on HA-silica-PVA (poly(vinyl alcohol)) sol-gel composite. Electroactive species of Ru(bpy)3 interact with the HA-sUica-PVA films to form Ru(bpy)3 modified electrodes [98]. 

NPA and its potential pro-drug, / -10,11-methylenedioxy-A/-propylnorapomor-phine, have been measured in monkey plasma. Samples were prepared by SPE on ODS-modified columns and the residue divided so that the electroactive catechol could be separated (nitrile-modified silica HPLC column) and detected at a GCE (+0.7 V vs Ag/AgCl). The pro-drug was analysed on an octyl-modified HPLC column with detection at 280 nm. The LoDs were 0.5 and lOpgL for NPA and the methylenedioxy derivative, respectively. The corresponding /V-methyl homo-logues were used as internal standards. 

Inert, inorganic materials (2) Redox-active metal oxides Electroinactive (silica, alumina, and zirconia) Electroactive (vanadium pentoxide, manganese oxide, tungsten oxide, etc.)... 

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