Monitoring of the Viability of Cells Immobilized by Sol-Gel Process

Three different types of cells, Pseudomonas fluorescens HK44, Saccharomyces cerevisiae strain SP4 and plant cells Nicotiana tabacum L. BY-2, were immobilized by entrapment in tetramethoxysilane prepolymer (TMOS) gel or in composite gel containing prepolymer TMOS and alginate in various ratios. Their growth and viability were monitored by bioluminescence and 2-D fluorescence spectra, which are fast and do not need the dissolution of a matrix. The resulting biocomposite gels were obtained by gelation of the mixtures of TMOS prep. or TMOS/alginate sols and the particular cells in proper media on glass supports to provide films ～1 mm thick. The effect of the following parameters on the growth and viability of the cells was studied: (a) the composition of the biocomposites, (b) the preparation conditions of TMOS and (c) the conditions of the procedure of entrapment. All three types of cells were tested in TMOS gel and the composite TMOS/alginate = 1:1 (v/v). The sensitivity of the cells to the changes of conditions increased in the sequence: P. fluorescence HK44 < S. cerevisiae strain SP4 < N. tabacum L. BY-2. Cell viability decreased with the increasing content of Si in biocomposites. The entrapment into alginate–silica composites resulted in the leakage of microbial and yeast cells. However, it had positive effects on the growth and metabolic activity of plant cells.     

Catalysis in Organic Solvents with Lipase Immobilized by Sol-Gel Technique

A series of immobilized lipases were obtained by sol-gel process, using silica prepolymers prepared from tetramethoxysilane, methyltrimethoxysilane, propyltrimethoxysilane and (3-aminopropyl)triethoxysilane. The activities of these biocatalysts were compared with the lipase adsorbed on poly(methylhydroxysiloxane) and encapsulated into a silicone rubber, lipase entrapped in nanoporous silica matrix and commercial sol-gel lipase. Model reactions were the esterification of stearic acid and Corey lactone bisalcohol (an intermediate of prostaglandin synthesis). The positive effect of hydrophobic-hydrophilic interface, created by the addition of organosilanes, on the activity of biocatalysts was partially reduced by decreasing specific surface of mesopores. Hydrophobic solvents increased the activity of the lipase entrapped in tetramethoxysilane–methyltrimethoxysilane prepolymer in the sequence acetone < toluene < benzene < decane < hexane. The activity of silicone rubber-encapsulated biocatalysts was proportional to polymer swelling in organic solvents (hexane > toluene > acetone).     

Two-stage weighted PROMETHEE II with results’ visualization

Central European Journal of Operations Research - Multicriteria decision-making methods are widely spread and used to assist the decision-makers to resolve problems. Many of the methods are simple...     

Biocompatible titania hydrogels with chemically triggered release of a photosensitive dye

5,10,15,20-Tetrakis(4-sulfonatophenyl)porphyrin was entrapped into biocompatible hydrogels formed by self-assembling micelles of the titanium dioxide prepared by hydrolysis of titanium ethoxide modified with triethanolamine (TEA). The materials were characterized by their optical and photosensitive properties. The immobilization led to changes of the absorption spectra of the dye and decreased its molar absorption coefficient. The TiO₂ matrix did not degrade the entrapped porphyrin upon u.v. irradiation. The formation of TEA–titanium(IV) chelates facilitated a controlled and triggered release of the immobilized dye from the hydrogels in lactate and citrate buffers. The released dye prolonged the sterility of citrate–phosphate buffer and its illumination with visible light inhibited growth of Aspergillus niger.     

Magnetic particles–based biosensor for biogenic amines using an optical oxygen sensor as a transducer

We have developed a fibre optic biosensor with incorporated magnetic microparticles for the determination of biogenic amines. The enzyme diamine oxidase from Pisum sativum was immobilized either on chitosan-coated magnetic microparticles or on commercial microbeads modified with a ferrofluid. Both the immobilized enzyme and the ruthenium complex were incorporated into a UV-cured inorganic–organic polymer composite and deposited on a lens that was connected, by optical fibres, to an electro-optical detector. The enzyme catalyzes the oxidation of amines under consumption of oxygen. The latter was determined by measuring the quenched fluorescence lifetime of the ruthenium complex. The limits of detection for the biogenic amines putrescine and cadaverine are 25–30 μmol?L^?1, and responses are linear up to a concentration of 1 mmol L^?1.

Composites with photosensitive 5,10,15,20-tetrakis(<Emphasis Type="Italic">N</Emphasis>-methylpyridinium-4-yl)porphyrin entrapped into silica gels

Photosensitive cationic 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin (TMPyP) was entrapped into microporous silica gels prepared by sol–gel method from tetrakis(2-hydroxyethoxy)silane (THES) and tetramethoxysilane (TMOS), resp., using different water and PEG 600 contents in the initial mixture. The absorption spectra of both composites showed that incorporation of TMPyP has led to a bathochomic shift (ca. 8 nm) of the Soret band and to a decrease in their molar absorption coefficient compared to TMPyP in solution. The TMPyP encapsulation kept the molecular state of the porphyrin in the free-base monomer form. In comparison to TMOS analogs, THES composites showed prolonged shape stability at least for 3 months, one-order higher rate of chemical substrate photooxidation and higher photobiocidal activity against E. coli.     

Effect of Doping Silica Gel Layers with TiOTi-Chains and Cu2+-Ephedrine on the Sensitivity of the Layers to Gases

In this paper the interaction of polysiloxane and TiOTi-doped polysiloxane gel layers containing Cu²⁺-ephedrine (CuEP) with carbon dioxide, nitrogen and water is investigated. This interaction is studied through changes of the output optical power from an optical fiber coated with the investigated gel layer. The layers are prepared with sols based on tetraethoxysilane and titanium isopropoxide, isopropanol, acetylacetone and Cu²⁺-ephedrine by the repeated dip-coating method. The applied gel layers are dried at 70°C.Spectral and temporal changes of the output optical power due to effect of the tested gases are measured. The measurements show big changes of the output optical power of fibers coated with CuEP-doped silica gel layers in a wavelength range from 400 to 700 nm, which is in relation with spectral effects of CuEP in alcoholic solutions. Relatively lower changes of the attenuation spectra without any attenuation band are found in the spectra of TiOTi-doped siloxane gel layers containing CuEP. The angular distributions of the output optical power of the coated fibers indicate high optical losses of the layers.     

Whole-cell optical biosensor for mercury — operational conditions in saline water

The present study demonstrates the influences of chlorides, fluorides and bromides of potassium and sodium on the growth and Hg²⁺-induced bioluminescence of bioreporter Escherichia coli ARL1. In a Luria-Bertani medium (LB), cell growth was inhibited by concentrations of sodium and potassium fluorides above 0.2 mol L^?1. The addition of NaCl increased cell tolerance to the toxic effects of fluorides and bromides. Lag periods of 10 h and more were observed for cultivations in LB without NaCl and with halides (NaCl, KCl, NaBr, KBr, NaF and KF) at concentrations lower than 0.06 mol L^?1. In a phosphate buffer (PB), the bioluminescence of E. coli ARL1, induced with HgCl₂, was increased by the addition of NaCl, KCl, NaBr, KBr, NaF and KF (concentration of 0–0.25 mol L^?1). In a saline phosphate buffer (PBS), the maxima of induced bioluminescence declined to 50 %, in the case of NaF (0.12 mol L^?1), and to zero for KF. An addition of tryptone to the induction medium increased induced light emission ten-fold. Concentrated artificial sea water (ASW) (70–100 % ASW) inhibited bioluminescence induction. The new detection assay with E. coli ARL1 made possible the detection of 0.57 µL^?1 of HgCl₂ in double-diluted artificial sea water (25 % ASW).