| 1. |
- Burestedt, E., et al.
(författare)
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Optimisation and validation of an automated solid phase extraction technique coupled on-line to enzyme-based biosensor detection for the determination of phenolic compounds in surface water samples
- 1995
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Ingår i: Chromatographia. - Heidelberg : Springer Berlin/Heidelberg. - 0009-5893 .- 1612-1112. ; 41:3-4, s. 207-215
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Tidskriftsartikel (refereegranskat)abstract
- A fully integrated screening system for phenolic compounds was developed incorporating on-line solid phase extraction, fractionation and biosensor detection. Two different types of biosensors, solid graphite and carbon paste electrodes incorporating the enzyme tyrosinase, were compared and used in the screening system. Interfacing of the solid phase extraction and fractionation with the biosensor detection was given special attention since the biosensors were not compatible with the organic modifier used for desorption of phenols from the solid phase extraction step. The system was validated with conventional analytical techniques. Surface water samples from the Ebro river were spiked with 1,10, and 25μg L−1 of catechol, phenol,p-cresol, respectively. Three out of seven samples were spiked and the correct samples were identified, containing phenols equivalent to the spiked concentrations. © 1995 Friedr. Vieweg & Sohn Verlagsgesellschaft mbH.
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| 2. |
- Lutz, Mareike, 1967-, et al.
(författare)
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Applying hollow fibres for separating free and bound label in continuous-flow immunochemical detection
- 1996
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Ingår i: Journal of Chromatography A. - Amsterdam : Elsevier B.V. - 0021-9673 .- 1873-3778. ; 755:2, s. 179-187
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Tidskriftsartikel (refereegranskat)abstract
- On-line liquid chromatography-immunochemical detection (LC-ICD) provides the possibility to individually monitor cross-reactive compounds overcoming the need of tedious fraction collection. ICD is performed as a post-column reaction detection system and is based on a two-step immunoreaction. In the first step unlabelled antibodies are added to the LC effluent and allowed to react with antigens (analytes) eluting from the LC column. The amount of analytes bound to the antibodies is measured by adding, in a second step, labelled antigen to the reaction mixture. For quantitation, free and bound label need to be separated prior to detection. The present paper describes a hollow fibre module (HFM), which can be used for this purpose. Separation of free and bound label occurs on discrimination by size. Using biotin as a model compound, a detection limit of 30 nmol/l can be reached employing anti-biotin antibodies and a low-molecular-mass fluorescence label in the LC-ICD system. Additional to low-molecular-mass labels, the HFM allows the use of small enzyme labels. In this context, horseradish peroxidase-labelled biotin was used as a label in combination with antibodies in the immunochemical detection of biotin. This allows future implementation of commercially available enzyme immunoassay kits in continuous-flow immunochemical detection.
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| 3. |
- Lutz, Mareike, 1967-, et al.
(författare)
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Biochemical detection for direct bead surface analysis
- 1997
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Ingår i: Analytical Chemistry. - Washington : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 69:23, s. 4878-4884
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Tidskriftsartikel (refereegranskat)abstract
- A continuous-now biochemical detection system is presented which recognizes biologically active compounds immobilized to solid phases. This approach can be used to screen, for example, solid-phase combinatorial libraries for lead compounds. Biochemical detection is performed by mixing a plug of a solid-phase suspension with labeled affinity protein, During a short reaction time, the labeled affinity protein will only bind to ligands, i.e., compounds with biological activity. Hereafter, the free and bound labels are separated by means of a hollow fiber module, Quantitation of the free label is performed with a conventional now-through fluorescence detector, Total assay time amounts to less than 3 min. Biochemical detection for direct bead surface analysis was developed for two model systems. The first model system used fluorescence-labeled avidin as affinity protein and its ligands biotin and iminobiotin immobilized to agarose as analytes. The second model system used fluorescence-labeled antisheep (Fab)(2) fragments as affinity protein and different IgGs immobilized to agarose as analytes. The feasibility of this approach for recognition of solid-phase immobilized ligands was documented by screening 50 samples with a 100% hit rate.
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| 4. |
- Lutz, Mareike, 1967-, et al.
(författare)
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Development and Optimization of a Solid Composite Tyrosinase Biosensor for Phenol Detection in Flow Injection Systems
- 1996
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Ingår i: Electroanalysis. - Weinheim : Wiley-VCH Verlagsgesellschaft. - 1040-0397 .- 1521-4109. ; 8:2, s. 117-123
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Tidskriftsartikel (refereegranskat)abstract
- Bulk-modified epoxy-graphite tyrosinase biosensors were fabricated by four different procedures. The influence of these fabrication procedures on the analytical performance of the enzyme electrode in an amperometric wall-jet flow cell has been studied. The bioprobe performance is assessed by cyclic voltammetry. Higher current densities and narrower peaks were obtained when the enzyme was introduced in the dry state into the epoxy-graphite material, instead of introducing it previously dissolved in the buffer. In the FI system responses of 11.79 μA cm-2 and 1.43 μA cm-2 are then obtained for catechol and phenol respectively for 50 μL injections of 20 μM solutions. Moreover, if gold/palladium is introduced into the epoxy-graphite, a further increase in current is achieved resulting in 27.70 μA cm-2 and 4.90 μA cm-2 for catechol and phenol, respectively. This biosensor can operate in aqueous as well as in mixed aqueous-organic environments.
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| 5. |
- 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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| 6. |
- Lutz, Mareike, 1967-, et al.
(författare)
-
Implementation of affinity solid-phases in continuous-flow biochemical detection
- 1997
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Ingår i: Journal of Chromatography A. - Amsterdam : Elsevier B.V. - 0021-9673 .- 1873-3778. ; 776:2, s. 169-178
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Tidskriftsartikel (refereegranskat)abstract
- A continuous-flow biochemical detection system is presented which allows the use of solid-phase immobilised affinity proteins. The biochemical detection is performed by mixing analyte with a labelled ligand followed by the addition of solid-phase immobilised affinity protein. After a reaction time of 85 s, free and bound label are separated by means of a hollow fibre module. Quantitation of the free label is performed with a conventional flow-through fluorescence detector. Total assay time amounts to less than 2 min. Biotin was chosen as the model compound using a range of streptavidin-coated solid-phases and an antibody-coated solid-phase as affinity material, and fluorescein–biotin as low-molecular-mass label. The relative standard deviation for twenty repetitive injections was 10.9%. A calibration curve was constructed in the concentration range between 20 and 400 nmol l−1 leading to a correlation coefficient of 0.994. A limit of detection of 8 nmol l−1 was obtained. © 1997 Elsevier Science B.V.
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| 7. |
- Lutz, Mareike, 1967-, et al.
(författare)
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On-line Coupling of Liquid Chromatography to Biological Assays
- 1997
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Ingår i: Chimica oggi. - Milan : Tekno Scienze. - 0392-839X .- 1973-8250. ; 15:1-2, s. 11-15
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Tidskriftsartikel (refereegranskat)abstract
- Combining two powerful technologies - liquid chromatography and bioassays results in analytical methodologies which are characterised by high selectivity and sensitivity. In contrast to microtitre-type bioassays, biochemical reactions proceed in a closed, continuous-flow reaction detection system coupled directly to the outlet of the chromatographic separation column. The interaction of substances eluting from the separation column with molecular targets such as antibodies or receptors is monitored directly overcoming tedious fraction collection and manual operations required to prepare the functions for batch immunoassays. important application areas are bioanalysis and drug discovery.
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| 8. |
- Lutz, Mareike, 1967-, et al.
(författare)
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On-Line Microdialysis-Electrospray Mass Spectrometry for Automated Desalting of Small-Volume Peptide Samples
- 1999
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Ingår i: Chromatographia. - Wiesbaden : Vieweg. - 0009-5893 .- 1612-1112. ; 49:Suppl. 1, s. S28-S34
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Tidskriftsartikel (refereegranskat)abstract
- Electrospray ionization mass spectrometry (ESI-MS) is an important tool for biomolecule analysis. Because the salt content of small-volume peptide samples can hamper analyte ionization, such samples require treatment before ESI-MS.The approach described here consists in interfacing ESI-MS with on-line microdialysis which affords rapid desalting and buffer-exchange. On-line microdialysis was performed by means of a hollow fiber (i.d. 200 μm) coupled to fused silica capillaries. Peptide samples were introduced into the capillary flow system as plugs and transferred to the dialysis cell and the electrospray by means of hydrodynamic pressure. As a result, the ionization efficiency of peptidic analytes was increased and adduct formation with, e.g., sodium, was reduced owing to reduced levels of nonvolatile salts. The feasibility of on-line microdialysis-ESI-MS is shown with a proteolytic digest originating from two-dimensional gel electrophoresis.
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| 9. |
- 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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| 10. |
- Owens, Paul K., et al.
(författare)
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Molecular imprinting for bio- and pharmaceutical analysis
- 1999
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Ingår i: TrAC. Trends in analytical chemistry. - Amsterdam : Elsevier. - 0165-9936 .- 1879-3142. ; 18:3, s. 146-154
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Tidskriftsartikel (refereegranskat)abstract
- The potential of analytical techniques based on molecular imprinting is reviewed from the viewpoint of bio- and pharmaceutical analysis. A literature study shows that molecularly imprinted polymers (MIPs) have been implemented predominantly in three areas of interest to pharmaceutical industry laboratories. First, in sample preparation, imprinted polymers are used as the sorbent for solid phase extraction purposes. Secondly, MIPs serve as the stationary phase for analytical chromatographic and electrophoretic separations. Thirdly, imprinted polymers are utilised as analyte recognition materials in affinity assays. The advantages of MIPs, e.g., physical robustness, high strength, resistance to elevated temperatures and pressures, and inertness towards acids, bases, metal ions and organic solvents, have been well exploited in a large number of applications. This article focuses on how these benefits may be used for improving the quality of analytical procedures. Some key MIP disadvantages are also highlighted, especially in relation to other analytical techniques. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
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