Ovadia Lev

Recent bio-applications of sol-gel materials

This review is devoted to the most recent developments (2000–2005) of sol–gel materials at the interface with biology. In the context of bioencapsulation in mineral hosts, novel synthetic approaches have been designed, allowing the immobilization of numerous proteins, enzymes and immune molecules as well as poly-saccharides, phospholipids and nucleic acids. These efforts have led to the development of new biosensors and bioreactors. A similar trend was also observed for whole cell encapsulation, survival periods over several weeks now being achieved. This has opened the possibility of designing hybrid hosts for cell-based biosensing and bioproduction, ultimately allowing the development of artificial organs. Indeed, applications of sol–gel processes are not restricted to bioencapsulation, as demonstrated by recent progress in drug release systems and bioactive materials. Finally, the considerable efforts devoted to the biomimetic elaboration of mineral structures suggest that they might be the key for future development of improved sol–gel materials for bio-applications.

High-capacity antimony sulphide nanoparticle-decorated graphene composite as anode for sodium-ion batteries

Sodium-ion batteries are an alternative to lithium-ion batteries for large-scale applications. However, low capacity and poor rate capability of existing anodes are the main bottlenecks to future developments. Here we report a uniform coating of antimony sulphide (stibnite) on graphene, fabricated by a solution-based synthesis technique, as the anode material for sodium-ion batteries. It gives a high capacity of 730 mAh g(-1) at 50 mA g(-1), an excellent rate capability up to 6C and a good cycle performance. The promising performance is attributed to fast sodium ion diffusion from the small nanoparticles, and good electrical transport from the intimate contact between the active material and graphene, which also provides a template for anchoring the nanoparticles. We also demonstrate a battery with the stibnite-graphene composite that is free from sodium metal, having energy density up to 80 Wh kg(-1). The energy density could exceed that of some lithium-ion batteries with further optimization.

Exciting new directions in the intersection of functionalized sol–gel materials with electrochemistry

The implications of organically-modified silica-based materials in electrochemical science is reviewed along with some selected recent trends in the field of functionalized and sol–gel silica electrochemistry. These recent trends include the electro-assisted generation of organosilica films on solid electrode surfaces, the preparation and applications of sol–gel derived composite (carbon, gold, nanotubes) electrodes, the electrochemical characterisation of mass transfer reactions in porous functionalized silicas, solid-state electrochemistry and gas sensors involving sol–gel materials, imprinted functionalized silica, and the electrochemical characterisation and applications of ordered mesoporous organosilicas.

Sol-gel derived renewable-surface biosensors

Abstract A new type of sol-gel derived, polishable, amperometric biosensor is introduced. These new biosensors comprise enzymes immobilized in organically modified silica-carbon matrices. The silica backbone contributes rigidity, and the organically modified surface guarantees that water will not penetrate into the bulk of the electrode; the percolating carbon powder provides electric conductivity and shields the enzyme from the hostile environment encountered during the sol-gel molding process, and the encapsulated enzyme provides biocatalysis and specificity. Redox dopants can also be incorporated into the porous matrix for charge mediation. An amperometric glucose biosensor is used as a demonstrative test case. The preparation of unmediated and tetrathiafulvalene-mediated biosensors is described, and their dynamic and steady-state responses are demonstrated.

Sol‐Gel Derived Composite Ceramic Carbon Electrodes

Sol-gel electrochemistry is gaining popularity as a versatile general method for the production of inorganic-organic electrodes and electrochemical sensors. Carbon-ceramic electrodes constitute a fine example that demonstrates the disadvantages, capabilities and promise of sol-gel electrochemistry. The compositions, configurations and chemistry of carbon ceramic electrodes are reviewed. Application for diverse fields of electrochemistry, including electrochemical sensing, biosensing and energy storage cells are reviewed.

Hydrolysis of haloacetonitriles: LINEAR FREE ENERGY RELATIONSHIP, kinetics and products

Abstract The hydrolysis rates of mono-, di- and trihaloacetonitriles were studied in aqueous buffer solutions at different pH. The stability of haloacetonitriles decreases and the hydrolysis rate increases with increasing pH and number of halogen atoms in the molecule: The monochloroacetonitriles are the most stable and are also less affected by pH-changes, while the trihaloacetonitriles are the least stable and most sensitive to pH changes. The stability of haloacetonitriles also increases by substitution of chlorine atoms with bromine atoms. The hydrolysis rates in different buffer solutions follow first order kinetics with a minimum hydrolysis rate at intermediate pH. Thus, haloacetonitriles have to be preserved in weakly acid solutions between sampling and analysis. The corresponding haloacetamides are formed during hydrolysis and in basic solutions they can hydrolyze further to give haloacetic acids. Linear free energy relationship can be used for prediction of degradation of haloacetonitriles during hydrolysis in water solutions.

Voltammetric studies of composite ceramic carbon working electrodes

Abstract Sol-gel derived indicator ceramic carbon electrodes (CCEs) made of graphite powder entrapped in hydrophobically modified silica gel are presented. Voltammetric characteristics of the electrodes are compared with other classes of graphite electrodes. Background current, double layer capacitance and metrological characteristics, including renewal repeatability, interelectrode reproducibility and operational stability for various solvents are presented. The indicator CCEs exhibit better stability than carbon paste electrodes and their renewal is easier and more reproducible than that of glassy carbon electrodes.

Sol-gel luminescence biosensors: Encapsulation of recombinant E. coli reporters in thick silicate films

A class of sensing elements based on the encapsulation of genetically engineered bioluminescent Escherichia coli(E. coli) reporter strains in sol–gel derived silicates is described. We demonstrate the concept by the immobilization of these bacterial cells in thick silicate films. Heat shock, oxidative stress, fatty acids, peroxides, and genotoxicity reporting bacteria were incorporated in the sol–gel silicates and their luminescence response was compared to that of the non-immobilized culture. All the immobilized bacteria maintained viability and luminescence activity for several months. The bacteria–silicate hybrids can be used either as disposable sensors or in multiple use sensing test-kits, and they can be also integrated in early warning devices operated in continuous flow conditions.

Doped sol-gel glasses as pH sensors

Abstract A series of pH indicators were trapped in sol-gel porous glasses by polymerization of tetramethoxysilane in the presence of a surface active agent. The properties of these novel sensing materials including spectral shifts, shifts in the pH-sensing range, cycle repeatability, leachability, rates of response and isosbestic points are described. A prototype of a pH meter based on a pH-sensing glass was constructed.

Fluorescence and bioluminescence reporter functions in genetically modified bacterial sensor strains

Genetically modified bacteria, engineered to generate a quantifiable signal in response to pre-determined sets of environmental conditions, may serve as combined sensing/reporting elements in whole-cell biosensors. We have compared two of the several available reporter genes in such cells: green fluorescent proteins (GFPs) (Aquorea victoria gfp) and bioluminescence (Vibrio fischeri luxCDABE) genes, fused to either SOS (recA) or heat shock (grpE) promoters. In both cases, bacterial bioluminescence allowed faster and more sensitive detection of the model toxicants; the fluorescent reporter proteins were much more stable, and following long-term exposure allowed detection at levels similar to that of the bioluminescent sensors. From the two green fluorescent proteins tested, enhanced GFP (EGFP) displayed a more rapid response and higher signal intensity than GFPuv. To combine the advantages of both reporter functions, representatives of both types were jointly encapsulated in a sol‐gel matrix and immobilized onto a glass surface, to generate a bioluminescent toxicity and a fluorescent genotoxicity sensor. The dual-function sensor detected both toxic and genotoxic model compounds with no interference from the co-immobilized member. # 2003 Elsevier Science B.V. All rights reserved.