| 1. |
- Lutz, Mareike, 1967-, et al.
(författare)
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Effects of different additives on a tyrosinase based carbon paste electrode
- 1995
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Ingår i: Analytica Chimica Acta. - Amsterdam : Elsevier. - 0003-2670 .- 1873-4324. ; 305:1-3, s. 8-17
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Tidskriftsartikel (refereegranskat)abstract
- The influence of a number of solid and chemical additives on the sensitivity and operational stability of a tyrosinase carbon paste electrode was studied. Cyclic voltammograms were run of the electrochemically active catechol/o-quinone couple on unmodified and additive modified carbon paste electrodes without tyrosinase. This was done in order to study the influence of these additives on the pure electrochemistry of the carbon paste. The influence on the total system (additive and enzyme modified carbon paste electrode) was studied in the flow injection mode. In some instances a dramatic improvement of the direct electron transfer of the catechol/o-quinone couple was obtained with both solid and chemical additives included in the carbon paste. A similar improvement of biosensor sensitivity in the flow injection mode was obtained with most chemical additives whereas the solid additives had a negative impact on biosensor sensitivity. The results obtained in this work indicate that these additives influence the purely electrochemical processes at the carbon paste and/or the performance of the enzyme in the carbon paste environment. How and why these additives can possibly influence the biosensor performance are discussed. © 1995.
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| 2. |
- Marko-Varga, György, et al.
(författare)
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Effect of HY-Zeolites on the Performance of Tyrosinase-Modified Carbon Paste Electrodes
- 1996
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Ingår i: Electroanalysis. - Weinheim : Wiley-VCH Verlagsgesellschaft. - 1040-0397 .- 1521-4109. ; 8:12, s. 1121-1126
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Tidskriftsartikel (refereegranskat)abstract
- The dependence of electrode response on additive properties in enzyme-modified carbon paste was studied. Four different HY-zeolite powders, dealuminated to different extents and characterized by both Si/Al ratio and hydrophilicity, were used as the carbon paste modifiers. The enzyme tyrosinase used in biosensors for the detection of catechol and other phenolic compounds was chosen as the model system for the construction of a composite carbon paste biosensor incorporating different HY-zeolites as additives. Tyrosinase was trapped on the HY-zeolite particles from a buffer solution, dried and mixed with graphite powder and a pasting oil. It was found that by incorporating HY-zeolites into the carbon paste the heterogeneous reaction rate of catechol redox conversion and the signal response for catechol were increased. In the latter case a higher response was observed for increased hydrophilicity, i.e., decreased Si/Al ratio of the HY-zeolite. The carbon paste/solution interface is considered to be an aqueous/organic phase and the characteristics of the enzyme-modified carbon paste electrode are related to theories, explaining enzymatic catalysis in organic solvents.
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| 3. |
- Torto, N, et al.
(författare)
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Monitoring of enzymatic hydrolysis of starch by microdialysis sampling coupled on-line to anion exchange chromatography and integrated pulsed electrochemical detection using post-column switching
- 1997
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Ingår i: Biotechnology and Bioengineering. - 1097-0290. ; 56:5, s. 546-554
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Tidskriftsartikel (refereegranskat)abstract
- A quantitative evaluation of the hydrolysis of wheat starch using Termamyl, a thermostable alpha-amylase (endo-l,4-alpha-D-glucan, glucanohydrolase; EC 3.2.1.78), is reported. Data from the monitoring of the hydrolysis of wheat starch indicated that, after 1 h, glucose and maltooligosaccharides up to DP 7 were the main hydrolysis products and thus enabled optimization of a liquefication step during the production of L-lactic acid. The monitoring system used, both in the on- and off-line mode, was based on continuous flow microdialysis sampling (CFMS) coupled to anion exchange chromatography and integrated pulsed electrochemical detection (IPED). A microdialysis probe equipped with a 5-mm polysulfone (SPS 4005) membrane, with a molecular-weight cut-off of 5 kDa, was used to sample the hydrolysis products of native wheat starch at 90 degrees C. Characteristic fingerprint separations were achieved by anion exchange chromatography after enzymatic hydrolysis. Post-column switching improved the detection and, consequently, also quantification of the hydrolysates as fouling of the electrode could be reduced. Maltooligosaccharide standards were used for quantification and to verify the elution of the hydrolysates by spiking the off-line samples. (C) 1997 John Wiley & Sons, Inc.
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| 4. |
- Önnerfjord, Patrik, et al.
(författare)
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A flow immunoassay for studies of human exposure and toxicity in biological samples
- 1998
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Ingår i: Journal of Molecular Recognition. - 0952-3499. ; 11:1-6, s. 182-184
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes a heterogeneous competitive flow immunoassay with a high sample throughput which can be used for the screening of smaller analytes in various samples. The method is based on off-line incubation of the analyte (Ag), a fluorescent labelled tracer (Ag*) and the corresponding antibody (Ab). The separation of bound (Ab-Ag*) and free tracer (Ag*) is based on a size exclusion and reversed phase mechanism utilizing a restricted access (RA) column. The column traps the free unbound tracer (Ag*) in its hydrophobic (C18) inner cavity but excludes the large Ab-Ag* complex, which is passed on and measured by the fluorescence detector. The flow immunoassay was developed using the triazine herbicide atrazine as a model compound owing to its human toxicity and widespread use. A sample throughput of 80 samples per hour and a detection limit of 300 pg ml-1 in water were obtained. Urine samples were successfully applied for direct injections into the flow system, while for human plasma samples an additional clean-up step using solid phase extraction was efficiently included where pure extract is obtained with the highly stable and biocompatible extracting column material. The resulting detection limits for atrazine in plasma and water samples using this clean-up and trace enrichment procedure were found to be 2 ng ml-1 and 20 pg ml-1 respectively.
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| 5. |
- Önnerfjord, Patrik, et al.
(författare)
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High sample throughput flow immunoassay utilising restricted access columns for the separation of bound and free label
- 1998
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Ingår i: Journal of Chromatography A. - 0021-9673. ; 800:2, s. 219-230
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Tidskriftsartikel (refereegranskat)abstract
- A flow immunodetection system with high sample throughput capacity is described for the screening of various analytes. The immunochemical detection principle is based on the chromatographic separation of the formed immunocomplex (AbAg or AbAg*) and the free antigen (Ag) by a restricted access (RA) column, utilising size-exclusion and reversed-phase mechanism. A fluorescein labelled analyte (Ag*) was used in the competitive assay format with fluorescence detection. The speed and simplicity of the assay were the greatest advantages, allowing measurement of the analyte to be carried out in less than 1 min. The biocompatibility and capacity of the restricted access material allowed multiple injections of up to 5000, without any breakthrough of the fluorescent tracer molecule and thus need for regeneration. The flow immunoassay was developed using the well-known atrazine herbicide and some transformation products as model compounds, due to their human toxicity and widespread use. The sample throughput was 80 samples per hour and the detection limits were 1.4 nM (300 pg/ml) for atrazine (Ab I) and 2.3 nM (500 pg/ml) for the sum of triazines (Ab II-III). Different sample matrices, PBS buffer, creek water, and urine were successfully applied in the flow system without the need for any sample handling step. For plasma samples an additional clean-up step using solid-phase extraction had to be included. The resulting detection limits for atrazine in plasma and water samples using this clean-up and trace enrichment procedure were found to be 2 ng/ml and 20 pg/ml, respectively. The analysis could be performed at a sample throughput rate of 400 per 6-h working shift.
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| 6. |
- Önnerfjord, Patrik, et al.
(författare)
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Tyrosinase graphite-epoxy based composite electrodes for detection of phenols
- 1995
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Ingår i: Biosensors and Bioelectronics. - 0956-5663. ; 10:6-7, s. 607-619
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Tidskriftsartikel (refereegranskat)abstract
- The characterization and analytical performance of a tyrosinase graphite-epoxy electrode for the detection of phenolic compounds are described. The biocomposite configuration is based on the entrapment of commercially available tyrosinase in a graphite-epoxy matrix, and the mixing of the resulting conductive epoxy resin with a hardener. The enzyme electrode is mounted as a working electrode in an amperometric flow cell of the confined wall-jet type and studied in the flow injection mode. The bioprobe is electrochemically characterized by hydrodynamic and cyclic voltammetry for catechol and phenol. An applied potential of -100 mV vs. Ag/AgCl is found to be optimal for electrochemical reduction of the enzyme products (quinone forms) for the biocomposite electrode. The dependence of the response of the biocomposite on the flow rate, the amount of loaded enzyme, the buffer composition, pH, and oxygen is investigated. The response of the biosensor to different phenolic compounds is also evaluated. The limits of detection (S/N = 3) for phenol and catechol were 1·0 μM and 0·04 μM, respectively. No loss in response could be detected after 100 injections of catechol (R.S.D. <2%). Stability of the biocomposite depends on storage conditions. Theoretical advantages described in the literature for biocomposite electrodes, for example, repolishing and bulk modification, are empirically studied in this work.
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