| 1. |
- Spegel, Christer, et al.
(författare)
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On-chip determination of dopamine exocytosis using mercaptopropionic acid modified microelectrodes
- 2007
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Ingår i: Electroanalysis. - : Wiley. - 1040-0397 .- 1521-4109. ; 19:2-3, s. 263-271
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Tidskriftsartikel (refereegranskat)abstract
- Gold and platinum, which often are used for thin film metallization, are not suitable for the measurement of dopamine (DA), since the oxidation product of DA forms a non-conducting polymer on the electrode surface. In this work several thiols were screened for their ability to prevent this polymerization. It was found that mercaptopropionic acid (MPA) decreased the rate of DA polymerization. MPA, possessing a weak acidic functionality, had the greatest effect on the DA electrochemistry by decreasing electrode passivation, as well as improving reversibility and sensitivity. Modifications of microchip electrodes with MPA did not only improve DA electrochemistry but also significantly increased the storage stability of the transducers. The microchips were ultimately used to detect K+ stimulated quantal release of DA from PC12 cells.
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| 2. |
- Dock, Eva, et al.
(författare)
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A steady-state and flow-through cell for screen-printed eight-electrode arrays
- 2005
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Ingår i: Analytica Chimica Acta. - : Elsevier BV. - 1873-4324 .- 0003-2670. ; 531:2, s. 165-172
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Tidskriftsartikel (refereegranskat)abstract
- An electrochemical cell has been developed enabling amperometric steady-state- and flow-injection measurements with screen-printed arrays consisting of eight working electrodes (circle divide = 1 mm) arranged radially around a printed Ag/AgCl reference electrode in the centre. The cell contained a rotator, providing similar hydrodynamics over all the working electrodes in the array, which was manually centered under the rotator. The reproducibility of steady-state measurements with eight-electrode platinum or gold arrays in this cell was studied by measuring and comparing currents from ferricyanide reduction at each electrode in the array. It was found that the relative standard deviation (R.S.D.) for the currents at different electrodes on one array was below 5%. Similar R.S.D. was found if measurements were compared between several arrays. This indicates that manual insertion/positioning of the eight-electrode array in the cell and hydrodynamics at the electrodes provided measurement reproducibility similar to the reproducibility of manufacturing eight-electrode platinum or gold arrays by screen-printing. A comparative study was performed between screen-printed and through mask sprayed carbon arrays. It was found that the reproducibility of the sprayed arrays was similar to that of the platinum or gold screen-printed arrays, with R.S.D. values below 6% regarding the variation between electrodes within the same array and the variation between different arrays. To enable flow-injection measurements, a tube (0.4 mm inner diameter) was inserted into a hole drilled through the centre of the steady-state cell rotator. This construction made it possible to inject the solution into the cell through the tube (not rotating), while the rotator was spinning over the eight-electrode array. It was found that this combination of flow-injection and mixing by a rotator provided a uniform current response over the array electrodes and that, at optimum conditions, the R.S.D. values between the eight electrodes in the array were nearly the same as in case of the steady-state measurements, i.e., below 5%. (C) 2004 Elsevier B.V. All rights reserved.
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| 3. |
- Dock, Eva, et al.
(författare)
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Multivariate data analysis of dynamic amperometric biosensor responses from binary analyte mixtures - application of sensitivity correction algorithms
- 2005
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Ingår i: Talanta. - : Elsevier BV. - 1873-3573 .- 0039-9140. ; 65:2, s. 298-305
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, it is demonstrated that a single-receptor biosensor can be used to quantitatively determine each analyte in binary Mixtures LIS in multivariate data analysis tools based on the dynamic responses received from flow injection peaks. Mixtures with different concentrations of two phenolic compounds, catechol and 4-chlorophenol, were measured with a graphite electrode modified with tyrosinase enzyme at an applied potential of -50 mV versus Ag/AgCl. A correction algorithm based on measurements of references in-between samples was applied to compensate for biosensor ageing as well as differences caused by deviations between biosensor preparations. After correction, the relative prediction errors with partial least squares regression (PLS-R) for catechol and 4-chlorophenol were 7.4 and 5.5%, respectively, using an analysis sequence measured on one biosensor. Additional validation mixtures of the two phenols were measured with a new biosensor, prepared with the same procedure but with a different batch of tyrosinase enzyme. Using the mixture responses for the first sensor as a calibration set in PLS-R. the relative prediction errors of the validation mixtures, after applying correction procedures. were 7.0% for catechol and 16.0% for 4-chlorophenol. These preliminary results indicate that by applying correction algorithms it could be possible to use less stable biosensors in continuous on-line measurements together with multivariate data analysis without time-consuming calibration procedures. (C) 2004 Elsevier B.V. All rights reserved.
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| 4. |
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| 5. |
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| 6. |
- Heiskanen, Arto, et al.
(författare)
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Mediator-assisted simultaneous probing of cytosolic and mitochondrial redox activity in living cells.
- 2009
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Ingår i: Analytical Biochemistry. - : Elsevier BV. - 1096-0309 .- 0003-2697. ; 384:1, s. 11-19
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Tidskriftsartikel (refereegranskat)abstract
- This work describes an electron transfer mediator-assisted amperometric flow injection method for assessing redox enzyme activity in different subcellular compartments of the phosphoglucose isomerase deletion mutant strain of Saccharomyces cerevisiae, EBY44. The method is demonstrated using the ferricyanide-menadione double mediator system to study the effect of dicoumarol, an inhibitor of cytosolic and mitochondrial oxidoreductases and an uncoupler of the electron transport chain. Evaluation of the role of NAD(P)H-producing pathways in mediating biological effects is facilitated by introducing either fructose or glucose as the carbon source, yielding either NADH or NADPH through the glycolytic or pentose phosphate pathway, respectively. Respiratory noncompetent cells show greater inhibition of cytosolic menadione-reducing enzymes when NADH rather than NADPH is produced. Spectrophotometric in vitro assays show no difference between the cofactors. Respiratory competent cells show cytosolic inhibition only when NADPH is produced, whereas production of NADH reveals uncoupling at low dicoumarol concentrations and inhibition of complexes III and IV at higher concentrations. Spectrophotometric assays only indicate the presence of cytosolic inhibition regardless of the reduced cofactor used. This article shows the applicability of the amperometric method and emphasizes the significance of determining biological effects of chemicals in living cells.
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| 7. |
- Heiskanen, Arto, et al.
(författare)
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Monitoring of Saccharomyces cerevisiae Cell Proliferation on Thiol-Modified Planar Gold Microelectrodes Using Impedance Spectroscopy.
- 2008
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:16, s. 9066-9073
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Tidskriftsartikel (refereegranskat)abstract
- An impedance spectroscopic study of the interaction between thiol-modified Au electrodes and Saccharomyces cerevisiae of strain EBY44 revealed that the cells formed an integral part of the interface, modulating the capacitive properties until a complete monolayer was obtained, whereas the charge transfer resistance ( R ct) to the redox process of [Fe(CN)6] (3-/4-) showed a linear relationship to the number of cells even beyond the monolayer coverage. R ct showed strong pH dependence upon increasing the pH of the utilized buffer to 7.2. Upon addition of S. cerevisiae cells at pH 7.2, the obtained value of R ct showed over 560% increase with respect to the value obtained on the same thiol-modified electrode without cells. It was demonstrated that real-time monitoring of S. cerevisiae proliferation, with frequency-normalized imaginary admittance (real capacitance) as the indicator, was possible using a miniaturized culture system, ECIS Cultureware, with integrated planar cysteamine-modified Au microelectrodes. A monolayer coverage was reached after 20-28 h of cultivation, observed as an approximately 15% decrease in the real capacitance of the system.
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| 8. |
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| 9. |
- Kostesha, Natalie, et al.
(författare)
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Real-time detection of cofactor availability in genetically modified living Saccharomyces cerevisiae cells - Simultaneous probing of different geno- and phenotypes.
- 2009
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Ingår i: Bioelectrochemistry. - : Elsevier BV. - 1878-562X .- 1567-5394. ; 76, s. 180-188
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Tidskriftsartikel (refereegranskat)abstract
- This work describes a mediated amperometric method for simultaneous real-time probing of the NAD(P)H availability in two different phenotypes, fermentative and respiratory, of the phosphoglucose isomerase deletion mutant strain of S. cerevisiae, EBY44 [ENY.WA-1A pgi1-1D::URA3], and its parental strain, ENY.WA-1A. The developed method is based on multichannel detection using microelectrode arrays. Its versatility was demonstrated by using four microelectrode arrays for simultaneously monitoring the NAD(P)H availability of both geno- and phenotypes under the influence of two different carbon sources, glucose and fructose, as well as the cytosolic and mitochondrial inhibitor and uncoupler, dicoumarol. The obtained results indicate that the method is capable of accurately and reproducibly (overall relative standard error of mean 3.2%) mapping the real-time responses of the cells with different genotype-phenotype combinations. The ENY.WA cells showed the same response to glucose and fructose when dicoumarol was used; fermentative cells indicated the presence of cytosolic inhibition and respiratory cells a net effect of mitochondrial uncoupling. EBY44 cells showed cytosolic inhibition with the exception of respiratory cells when fructose was used as carbon source.
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| 10. |
- Mie, Axel, et al.
(författare)
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Analysis of triazines and associated metabolites with electrospray ionization field-asymmetric ion mobility spectrometry/mass spectrometry.
- 2008
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Ingår i: Analytical Sciences. - 0910-6340. ; 24:8, s. 973-978
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Tidskriftsartikel (refereegranskat)abstract
- Triazines comprise an important pollutant class owing to continued use in certain countries, and owing to strong environmental persistence that leads to problems even in countries like Sweden where the use of triazines has been prohibited for some years. We investigated mass-selective detection for analysis of triazines. More specifically, we studied the background reduction and sensitivity enhancement that result from the use of a new interface technique, field-asymmetric ion mobility spectrometry (FAIMS), in conjunction with electrospray ionization ion-trap mass spectrometry. This technique allows for ion sorting and discrimination against the considerable "chemical noise", nonspecific cluster and fragment ions, which are typically generated in electrospray ionization. This paper presents results of a pilot study of triazines and some metabolites in ideal solvents. Our long-range goal is automated analysis with mass-selective detection coupled to membrane-based sample cleanup and enrichment for additional enhancement in sensitivity.
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| 11. |
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| 12. |
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| 13. |
- Skjolding, Lars Henrik, et al.
(författare)
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Characterisation of nano-interdigitated electrodes
- 2008
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 100, s. 052045-052045
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Konferensbidrag (refereegranskat)abstract
- Interdigitated electrodes made up of two individually addressable interdigitated comb-like electrode structures have frequently been suggested as ultra sensitive electrochemical biosensors. Since the signal enhancement effects due to cycling of the reduced and oxidized species are strongly dependent on the inter electrode distances, since the nature of the enhancement is due to overlying diffusion layers, inter digitated electrodes with an electrode separation of less the non emicrometer a redesired for maximum signal amplification. Fabrication of submicron structures can only be made by advanced lithography techniques. By use of electron be amlithography we have fabricated arrays of interdigitated electrodes with an electrode separation distance of 200nm and an electrode finger width of likewise 200nm. The entire electrode structure is 100 micrometre times 100 micrometre, and the active electrode area is dictated by the opening in the passivation layer, that is defined by UV lithography. Here we report measurements of redox cycling of ferrocyanide by coupled cyclic voltammograms, where the potential atone of the working electrodes are varied and either an oxidising or reducing potential is applied to the complimentary interdigitated electrode. The measurements show fast conversion and high collection efficiency round 87% as expected for nano-interdigitated electrodes.
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| 14. |
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| 15. |
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| 16. |
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| 17. |
- Skjolding, Lars Henrik, et al.
(författare)
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Negative UV–NIL (NUV–NIL) – A mix-and-match NIL and UV strategy for realisation of nano- and micrometre structures
- 2009
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Ingår i: Microelectronic Engineering. - : Elsevier BV. - 1873-5568 .- 0167-9317. ; 86:4-6, s. 654-656
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Konferensbidrag (refereegranskat)abstract
- This paper presents a novel strategy for aligning patterns created with nano-imprint lithography (NIL) and UV lithography, similar to a mix-and-match process, which allows for the fabrication of large and small features in a single layer of resist. The resin used to demonstrate this new imprinting scheme is SU-8, a very widely used negative photoresist. Rapid stamp manufacturing using ma-N 2405 photoresist is also demonstrated. The processing scheme is a promising candidate for patterning of sensors featuring nanometre sized electrodes.
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| 18. |
- Solna, R, et al.
(författare)
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Amperometric screen-printed biosensor arrays with co-immobilised oxidoreductases and cholinesterases
- 2005
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Ingår i: Analytica Chimica Acta. - : Elsevier BV. - 1873-4324 .- 0003-2670. ; 528:1, s. 9-19
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Tidskriftsartikel (refereegranskat)abstract
- 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 10 min. 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 created with multivariate analysis-principal component analysis (PCA). (C) 2004 Elsevier B.V. All rights reserved.
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| 19. |
- Solna, R, et al.
(författare)
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Multienzyme electrochemical array sensor for determination of phenols and pesticides
- 2005
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Ingår i: Talanta. - : Elsevier BV. - 1873-3573 .- 0039-9140. ; 65:2, s. 349-357
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Tidskriftsartikel (refereegranskat)abstract
- The screen-printed four-electrode system was used as the amperometric transducer for determination of phenols and pesticides using immobilised tyrosinase. peroxidase. acetylcholinesterase and butyrylcholinesterase. Acetylthiocholine chloride was chosen as substrate for cholinesterases to measure inhibition by pesticides, hydrogen peroxide served as co-substrate for peroxidase to measure phenols. The compatibility of hydrolases and oxidoreductases working in the same array was studied. The detection of p-cresol, catechol and phenol as well as of pesticides including carbaryl, heptenophos and fenitrothion was carried out in flow-through and steady state arrangements. In addition. the effects of heavy metals (CL2+, Cd2+, Fe3+), fluoride (NaF), benzene and dimethylsulphoxide on cholinesterase activities ere evaluated. It was demonstrated that electrodes modified with hydrolases and oxidoreductases can function in the same array. The achieved R.S.D. values obtained for the flow system were below 4% for the same sensor and less than 10% within a group of five sensors. For the steady state system, R.S.D.s were approximately twice higher. One assay was completed in less than 6 min. The limit of detection for catechol Using tyrosinase was equal to 0.35 and 1.7 muM in the flow and steady state systems, respectively. On the contrary, lower limits of detection for pesticides were achieved in the steady state system-carbaryl 26 W, heptenophos 14 nM and fenitrothion 0.58 muM. (C) 2004 Elsevier B.V. All rights reserved.
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| 20. |
- Spegel, Christer, et al.
(författare)
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Chip Based Electroanalytical Systems for Cell Analysis
- 2008
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Ingår i: Electroanalysis. - : Wiley. - 1040-0397 .- 1521-4109. ; 20:6, s. 680-702
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Forskningsöversikt (refereegranskat)abstract
- This review with 239 references has as its aim to give the reader an introduction to the kinds of methods used for developing microchip based electrode systems as well as to cover the existing literature on electroanalytical systems where microchips play a crucial role for “none-destructive” measurements of processes related to living cells, i.e., systems without lysing the cells. The focus is on chip based amperometric and impedimetric cell analysis systems where measurements utilizing solely carbon fibre microelectrodes (CFME) and other non-chip electrode formats, such as CFME for exocytosis studies and scanning electrochemical microscopy (SECM) studies of living cells have been omitted. Included is also a discussion about some future and emerging nano tools and considerations that might have an impact on the future of “non-destructive” chip based electroanalysis of living cells.
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| 21. |
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| 22. |
- Spegel, Christer, et al.
(författare)
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Fully automated microchip system for the detection of quantal exocytosis from single and small ensembles of cells
- 2008
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Ingår i: Lab on a Chip. - : Royal Society of Chemistry (RSC). - 1473-0189. ; 2:8, s. 323-329
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Tidskriftsartikel (refereegranskat)abstract
- A lab-on-a-chip device that enables positioning of single or small ensembles of cells on an aperture in close proximity to a mercaptopropionic acid (MPA) modified sensing electrode has been developed and characterized. The microchip was used for the detection of Ca(2+)-dependent quantal catecholamine exocytosis from single as well as small assemblies of rat pheochromocytoma (PC12) cells. The frequency of events increased considerably upon depolarization of the PC12 cell membrane using a high extracelluar concentration of potassium. The number of recorded events could be correlated with the number of cells immobilized on the electrode. Quantal characteristics, such as the number of released molecules per recorded event, are equivalent to data obtained using conventional carbon fiber microelectrodes. The detection sensitivity of the device allows for the detection of less than 10 000 dopamine molecules in a quantal release. The distribution of peak rise-time and full width at half maximum was constant during measurement periods of several minutes demonstrating the stability of the MPA modified surface.
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| 23. |
- Tonning, E, et al.
(författare)
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Chemometric exploration of an amperometric biosensor array for fast determination of wastewater quality
- 2005
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Ingår i: Biosensors & Bioelectronics. - : Elsevier BV. - 1873-4235 .- 0956-5663. ; 21:4, s. 608-617
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Tidskriftsartikel (refereegranskat)abstract
- Four wastewater samples of different treatment qualities; untreated, alarm, alert and normal, from a Swedish chen-ti-thermo-mechanical pulp mill and pure water were investigated using an amperometric bioelectronic tongue in a batch cell. The aim was to explore enzymatically modified screen-printed amperometric sensors for the discrimination of wastewater quality and to counteract the inherent drift. Seven out of eight platinum electrodes on the array were modified with four different enzymes; tyrosinase, horseradish peroxidase, acetyl cholinesterase and butyryl cholinesterase. At a constant potential the current intensity on each sensor was measured for 200s, 100s before injection and 100s after injection of the sample. The dynamic biosensor response curves from the eight sensors were used for principal component analysis (PCA). A simple baseline and sensitivity correction equivalent to multiplicative drift correction (MDC), using steady state intensities of reference sample (catechol) recordings, was employed. A clear pattern emerged in perfect agreement with prior knowledge of the samples explaining 97% of the variation in the data by two principal components (PCs). The first PC described the treatment quality of the samples and the second PC described the difference between treated and untreated samples. Horseradish peroxidase and pure platinum sensors were found to be the determinant sensors, while the rest did not contribute much to the discrimination. The wastewater samples were characterized by the chemical oxygen demand (COD), biological oxygen demand (BOD), total organic carbon (TOC), inhibition of nitrification, inhibition of respiration and toxicity towards Vibrio fischeri using Microtox (R), the freshwater alga Pseudokirchneriella subcapita and the freshwater crustacean Daphnia magna. (c) 2005 Elsevier B.V. All rights reserved.
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| 24. |
- Tudorache, Madalina, et al.
(författare)
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Evaluation of progesterone content in saliva using magnetic particle-based immuno supported liquid membrane assay (m-ISLMA)
- 2006
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Ingår i: Biosensors & Bioelectronics. - : Elsevier BV. - 1873-4235 .- 0956-5663. ; 22:2, s. 241-246
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Tidskriftsartikel (refereegranskat)abstract
- Progesterone in saliva was monitored using a new method called magnetic particle-based immuno supported liquid membrane assay (m-ISLMA) in a sequential injection (SI) setup, allowing automatic sample cleanup, analyte enrichment, and detection in a single analysis unit. Progesterone (Ag) diffuses from a continuous flowing sample - the donor - into a supported organic liquid membrane (SLM), based on analyte partitioning (solubility) between the aqueous donor and the organic phase. The Ag is re-extracted from the SLM into a second stagnant aqueous acceptor, containing antibodies (Ab) immobilized on magnetic beads, held at the bottom of the acceptor by a magnet. Due to the formation of strong Ag-Ab-bead complexes and a large excess of Ab-beads, the Ag is accumulated and selectively enriched in the acceptor. The extracted progesterone was quantified by injecting into the acceptor a horseradish peroxidase (HRP) labeled analyte tracer, the substrate (luminol, H2O2, and p-iodophenol), and finally detection of the generated chemiluminescence by a photomultiplier tube. After optimization of experimental parameters (e.g., sample flow rate, extraction time, type of organic solvent and antibody-bead concentration in the acceptor), a detection limit of 8.50 +/- 0.17 fg L-1 and a dynamic range between 35 fg L-1 and 10 pg L-1 was reached. The progesterone level of saliva for three subjects (women in different period of ovarian cycle) was investigated, and the corresponding progesterone concentrations detected with m-ISLMA coincided well with the expected values. (c) 2006 Elsevier B.V. All rights reserved.
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| 25. |
- Tudorache, Madalina, et al.
(författare)
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Micro-immuno supported liquid membrane assay (mu-ISLMA)
- 2006
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Ingår i: Biosensors & Bioelectronics. - : Elsevier BV. - 1873-4235 .- 0956-5663. ; 21:8, s. 1513-1520
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Tidskriftsartikel (refereegranskat)abstract
- A chemiluminescent (CL) based micro-immuno supported liquid membrane assay (mu-ISLMA) has been developed that enables clean up, enrichment and detection of simazine in a single miniaturised cartridge system. The mu-ISLM cartridge contains a supported liquid membrane (SLM) sandwiched between a donor and an acceptor plate (channel volumes 1.65 mu L), the latter being covered by a thin layer of gold on to which anti-simazine antibodies were covalently immobilised via a self assembled monolayer (SAM) of either dithiobis(11-aminoundecane, hydrochloride) (DTAU) or beta-mercaptoethylamine (beta-MEA). The mu-ISLMA based on DTAU was characterised by both a high apparent extraction efficiency (E-app = 136%) and high apparent enrichment factor (E-e(app) = 544), which resulted in a very high sensitivity for simazine (LOD = 0.1 ng L-1). The paper discusses the influence of the different SAMs and three different anti-simazine-antibody preparations (polyclonal, affinity purified polyclonal and monoclonal) on the extraction parameters and assay sensitivity. The influence of the sample matrix (e.g. mineral water, orange juice and milk) on the simazine mu-ISLMA was also investigated. (c) 2005 Elsevier B.V. All rights reserved.
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| 26. |
- Tudorache, Madalina, et al.
(författare)
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Micro immuno supported liquid membrane (mu-ISLM) extraction
- 2005
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Ingår i: Micro Total Analysis Systems 2004, Vol 1. - 0260-6291. ; :296, s. 512-514
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Konferensbidrag (refereegranskat)abstract
- A mu-ISLM (micro Immuno Supported Liquid Membrane) extraction system coupled in a sequential injection analysis (SIA) configuration, capable of simultaneous sample cleanup and enrichment was developed. The capacity of the extraction channels - donor and acceptor, respectively - were reduced from originally 10 to 1.65 mu L. The acceptor channel surface was covered with a gold layer enabling immobilisation of antibodies via an alkanthiol self-assembled monolayer. The mu-ISLM-SIA system resulted in very high extraction efficiency and enrichment factor (Extraction efficiency (E): 136%; Enrichment factor (E-e): 544) and a subsequent low detection limit for the model analyte simazine of 0.1 ng/L.
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| 27. |
- Tudorache, Madalina, et al.
(författare)
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Selective immuno-supported liquid membrane (ISLM) extraction, enrichment and analysis of 2,4,6-trichlorophenol
- 2005
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388. ; 256:1-2, s. 143-149
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Tidskriftsartikel (refereegranskat)abstract
- 2,4,6-Trichlorophenol (2,4,6-TCP) was extracted from liquid samples (standards and spiked river water) using immuno-supported liquid membrane (ISLM) extraction followed by fluorescence flow immunoassay (FFIA) detection of the immuno-extracted analyte. ISLM-FFIA involves simultaneous on-line sample clean-up, enrichment and detection of analytes. The analyte is transported from a continuously flowing aqueous sample phase (donor) through a supported liquid membrane (SLM), containing an immobilised organic solvent, to a stagnant aqueous phase (acceptor), containing excess anti-analyte antibody, where it is trapped as analyte-anti body complex. The acceptor content is then dispensed and mixed on-line with a fluorescent analyte tracer (2,4,6-TCP/NH/(CH2)(3)/CO/EDF) and the resulting labelled fraction, separated from the mixture by restricted access column, is an indirect measure of the analyte amount extracted in the acceptor. The performance of ISLM-FFIA was compared with a similar FFIA (without the extraction step) with the following results: the ISLM-FFIA configuration leads to improved assay sensitivity (LOD 27.92 +/- 2.44 and 224 +/- 15.86 mu g L-1 for ISLM-FFIA and FFIA, respectively) and improved selectivity and recovery for 2,4,6-TCP in presence of other chlorophenols (e.g. 2,4,5-trichlorophenol and 4-chlorophenol) compared to FFIA alone. (c) 2005 Elsevier B.V. All rights reserved.
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| 28. |
- Tudorache, Madalina, et al.
(författare)
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Ultrasensitive magnetic particle-based immunosupported liquid membrane assay
- 2005
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 1520-6882 .- 0003-2700. ; 77:22, s. 7156-7162
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Tidskriftsartikel (refereegranskat)abstract
- A magnetic particle-based immuno-supported liquid membrane assay (m-ISLMA) based on chemiluminescence detection of a horseradish peroxidase-labeled hapten tracer that allows sample cleanup, analyte enrichment, and detection in a single analysis unit has been developed. Antibodies were immobilized on magnetic beads, and their position in the acceptor was controlled by two alternating opposing electromagnetic fields generated by a voltage applied to either of two electromagnets placed below and above the acceptor channel of the supported liquid membrane unit. The influence of antibody bead dilution in the acceptor was investigated and found to follow the ISLM theory, that is improved enrichment and sensitivity with increasing antibody concentration. Two different extraction procedures were investigated: procedure 1 (m-ISLMA-P1), which keeps the antibody beads trapped at the bottom of the acceptor during the entire analysis process; and procedure 2 (m-ISLMA-P2), which keeps the antibody beads dispersed and in motion in the acceptor phase during the extraction process. m-ISLMAP2 resulted in 2000 times improved enrichment of simazine and a more than 3 orders of magnitude better limit of detection (LOD10%) (1.29 x 10(-5) mu g L-1) than for m-ISLMA-P1 (2.00 x 10(-2) mu g L-1) and corresponding microtiter plate magnetic particle-based ELISA (m-ELISA, LOD10% 1.30 x 10(-1) mu g L-1). m-ISLMA-P2 and m-ELISA were further applied for the extraction and analysis of simazine-spiked surface water and fruit juice, finding no evidence for matrix influence for the former method; however, indications that trace amounts (nanograms per liter) of simazine or specific cross-reactants were present in both samples.
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| 29. |
- Yaropolov, A., et al.
(författare)
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Electroenzymatic reactions with oxygen on laccase-modified electrodes in anhydrous (pure) organic solvent
- 2007
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Ingår i: Bioelectrochemistry. - : Elsevier BV. - 1878-562X .- 1567-5394. ; 70:2, s. 199-204
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Tidskriftsartikel (refereegranskat)abstract
- The electroenzymatic reactions of Trametes hirsuta laccase in the pure organic solvent dimethyl sulfoxide (DMSO) have been investigated within the framework for potential use as a catalytic reaction scheme for oxygen reduction. The bioelectrochemical characteristics of laccase were investigated in two different ways: (i) by studying the electroreduction of oxygen in anhydrous DMSO via a direct electron transfer mechanism without proton donors and (ii) by doing the same experiments in the presence of laccase substrates, which display in pure organic solvents both the properties of electron donors as well as the properties of weak acids. The results obtained with laccase in anhydrous DMSO were compared with those obtained previously in aqueous buffer. It was shown that in the absence of proton donors under oxygenated conditions, formation of superoxide anion radicals is prevented at bare glassy carbon and graphite electrodes with adsorbed laccase. The influence of the time for drying the laccase solution at the electrode surface on the electroreduction of oxygen was studied. Investigating the electroenzymatic oxidation reaction of catechol and hydroquinone in DMSO reveals the formation of various intermediates of the substrates with different electrochemical activity under oxygenated conditions. The influence of the content of aqueous buffer in the organic solvent on the electrochemical behaviour of hydroquinone/1,4-benzoquinone couple was also studied. (C) 2006 Elsevier B.V. All fights reserved.
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| 30. |
- Yaropolov, A I, et al.
(författare)
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An amperometric biosensor based on laccase immobilized in polymer matrices for determining phenolic compounds
- 2005
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Ingår i: Journal of Analytical Chemistry. - : Springer Science and Business Media LLC. - 1608-3199 .- 1061-9348. ; 60:6, s. 553-557
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Tidskriftsartikel (refereegranskat)abstract
- An amperometric enzyme electrode based on laccase for determining phenolic compounds is proposed. The following three types of polymer materials were used for enzyme immobilization on the surface of a glassy-carbon electrode: positively charged cetyl ethyl poly (ethyleneimine) (CEPEI) and negatively charged commercial Nafion and Eastman AQ 29D polymers. The advantages and disadvantages of each of the above polymers for enzyme immobilization are discussed. The detection limits of the model phenolic compounds hydroquinone and pyrocatechol in a buffer solution on laccase immobilization in a Nation membrane were 3.5 x 10(-8) and 5.0 x 10(-8) M, respectively, at a signal-to-noise ratio of 3. Electrodes with laccase immobilized in Nation and Eastman AQ 29D membranes exhibited the shortest response time. The operating stability and the stability in storage can be significantly improved by the additional incorporation of gelatin in the polymer matrices. Gelatin prevents enzyme inactivation as a result of enzyme modification by the free-radical oxidation products of phenolic compounds.
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