immobilised

Amperometric screen-printed biosensor arrays with co-immobilised oxidoreductases and cholinesterases [An article from: Analytica Chimica Acta]
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This digital document is a journal article from Analytica Chimica Acta, published by Elsevier in 2005. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.

Description:
Amperometric screen-printed biosensor arrays for detection of pesticides (organophosphates and carbamates) and phenols have been developed. Cholinesterases (AChE and BChE), tyrosinase (TYR), peroxidases (SBP, soybean and HRP, horseradish) and cellobiose dehydrogenase (CDH) were combined on the same array consisting of one Ag/AgCl reference electrode surrounded by eight radially distributed working electrodes of either carbon or platinum. Mainly cross-linking with glutaraldehyde was employed for enzyme immobilisation. The substrates for the enzymes were acetylthiocholine for cholinesterases (ChEs), cellobiose for CDH and hydrogen peroxide for peroxidases. Hydrogen peroxide was generated in the presence of glucose by co-immobilised glucose oxidase (GOx). All measurements were performed in an electrochemical steady state system specially constructed for eight channel screen-printed electrode arrays. The achieved relative standard deviation values calculated for different enzyme substrates (10 measurements) were typically below 7% and one assay was completed within less than 10min. The detection limits for pesticides and phenols were in the nanomolar and micromolar ranges, respectively. The developed biosensor array was evaluated on wastewater samples. To simplify interpretation of results, the measured data were treated with multivariate analysis-principal component analysis (PCA).

Luminol chemiluminescence induced by immobilised xanthine oxidase [An article from: Analytica Chimica Acta]
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This digital document is a journal article from Analytica Chimica Acta, published by Elsevier in 2005. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.

Description:
The properties of xanthine oxidase, immobilised on controlled-pore glass, were investigated and applied in assays for hypoxanthine and superoxide dismutase. Phosphate buffer (pH 7.8) was passed through a glass reactor packed with immobilised enzyme, immediately mixed with 1.0x10^-^4M luminol in carbonate buffer at pH 10.0 and CL measured. CL was enhanced 14-fold by EDTA and 57-fold by Fe(II)-EDTA. For soluble enzyme, injected into a similar FIA manifold, CL was enhanced to a lesser extent either by iron(II) or EDTA or iron(II)-EDTA. CL is enhanced more using dialysed enzyme than with crude enzyme. CL signals are initially high due to rapid reaction between iron(II) and oxygen, but the steady emission used for measurement results from the superoxide-driven Fenton reaction, generating hydroxyl radicals that oxidise luminol which then reacts with enzymatically produced superoxide. The calibration for hypoxanthine was linear (r^2=0.9834, n=7) up to 17@mM: CL/mV=0.0371[HX]/@mM-0.0142. The R.S.D. (n=4) was 1.69% at 8.24@mM and the apparent K"m>=16@mM, >=12x greater for immobilised enzyme than for the soluble xanthine oxidase. The chemiluminescence decreased with increased superoxide dismutase (SOD) concentration (IC"5"0=1.2@mgml^-^1 and detection limit=0.25@mgml^-^1) and it was shown to decrease to a lesser extent for catalase.

Bioremediation of diesel-contaminated soil by microorganisms immobilised in polyvinyl alcohol [An article from: International Biodeterioration & Biodegradation]
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This digital document is a journal article from International Biodeterioration & Biodegradation, published by Elsevier in 2004. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.

Description:
It is argued that bioaugmentation is best reserved for particularly recalcitrant contaminants where an autochthonous population may be missing, and that selection has produced the microbial diversity required for clean-up of less recalcitrant contaminants. However, biodegradable contaminants may persist as a result of sub-optimal environmental conditions such as temperature, pH, electron acceptor availability and biotic factors such as predation by protozoa. A role for immobilised-cell bioaugmentation may therefore still be envisaged for the bioremediation of, say, persistent fuel spills under such conditions, or in extreme environments. In this laboratory-scale study we examined the potential of immobilised hydrocarbon-degrading microorganisms for the clean up of diesel-contaminated soil. We used polyvinyl alcohol (PVA) cryogelation as an entrapment technique and microorganisms indigenous to the site. We constructed laboratory biopiles to compare immobilised bioaugmentation with liquid culture bioaugmentation and biostimulation. In terms of percentage removal of diesel after 32 days, the immobilised systems were found to be the most successful, with greatest removal in a co-immobilisation system containing PVA-entrapped microorganisms and a synthetic oil absorbent. Least success was achieved with a commercial liquid bioaugmentation agent containing surfactants and having a low pH, which also produced significant phytotoxicity. Other advantages of PVA cryogelation are discussed.

Phosphate-selective electrodes containing immobilised ionophores [An article from: Analytica Chimica Acta]
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This digital document is a journal article from Analytica Chimica Acta, published by Elsevier in 2004. The article is delivered in HTML format and is available in your Amazon.com Media Library immediately after purchase. You can view it with any web browser.

Description:
Phosphate selective electrodes have been produced based upon rubbery membranes containing heterocylic macrocycles as sensors covalently bound to a cross-linked polystyrene-block-polybutadiene-block-polystyrene (SBS) polymer. The membranes were robust and the best HPO"4^2^--selective membrane fabricated was composed of 7.1% (m/m) dicumyl peroxide, 28.3% (m/m) 2-nitrophenyloctylether, 9.8% (m/m) 3-(10-undecenyl)-1,5,8-triazacyclodecane-2,4-dione, 31.0% (m/m) SBS and 23.8% (m/m) PoleStar(TM) 200R (clay-based filler). The characteristics of this electrode were a linear Nernstian range of 3.9x10^-^3 to 1x10^-^6moldm^-^3 HPO"4^2^- with a limit of detection of 1.0x10^-^6moldm^-^3 HPO"4^2^-, a slope of -29.7+/-0.9mV per activity decade and a pH range from 6 to 8. Selectivity coefficients for phosphate against various interfering anions (chloride, sulfate and nitrate) were determined. Response times were 2min or under, stability of response and electrode lifetime in continuous use were also very satisfactory. The response behavior of HPO"4^2^--ISEs based upon mobile and bound ionophores was comparable and suggests that mobility of the ionophore is not necessary to obtain a working ISE and that covalent binding of ionophores can be used to produce ISEs of increased stability and robustness.