| 1. |
- Mosbach, M., et al.
(författare)
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A miniaturised electrochemical affinity assay based on a wall-free sample droplet and micro-dispensing of the redox-labelled binding partner
- 2001
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Ingår i: Biosensors & Bioelectronics. - : Elsevier BV. - 1873-4235 .- 0956-5663. ; 16:9-12, s. 611-620
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Tidskriftsartikel (refereegranskat)abstract
- An affinity-assay was developed that is based on the modulation of the diffusion coefficient of a redox-labelled hapten upon complementary recognition of the analyte leading to an increase of molecular weight and hence to a decrease of the diffusion coefficient. The slower diffusion is monitored by means of cyclic voltammetry. In order to demonstrate the feasibility of this assay format, recognition of biotin by streptavidin has been chosen as a model system. Labelling of biotin was achieved by covalent binding of a ferrocene derivative to the biotin unit. To reduce the consumption of expensive compounds and to allow automatisation of the assay a novel miniaturised set-up was developed based on a wall-free sample droplet which forms the electrochemical cell with typical volumes of up to 10 mul. This droplet is dispensed by means of a step-motor driven syringe pump through a specially designed electrode holder spanning the gap between a micro-working electrode and a macroscopic counter electrode. By means of a piezo-driven micro-dispenser a predefined number of nano-droplets (100 pl volume each) containing the redox-labelled hapten are shot into the sample droplet. By this, any physical contact and hence any cross-contamination between the sample and the reagent solution could be avoided. Signal amplification can be achieved by redox recycling between the micro-electrode and the perpendicular positioned macroscopic counter electrode. (C) 2001 Elsevier Science B.V. All rights reserved.
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| 2. |
- Mosbach, M, et al.
(författare)
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Picodroplet-deposition of enzymes on functionalized self-assembled monolayers as a basis for miniaturized multi-sensor structures
- 2001
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Ingår i: Biosensors & Bioelectronics. - : Elsevier BV. - 1873-4235 .- 0956-5663. ; 16:9-12, s. 827-837
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Tidskriftsartikel (refereegranskat)abstract
- We are reporting on a novel approach for structured immobilisation of enzymes on gold surfaces modified with monolayers of functionalised alkylthiols. The formation of enzyme spots is achieved by shooting very small volumes of an appropriate enzyme solution (down to 100 pl) onto a thiol-monolayer modified gold surface using a micro-dispenser. Formation of enzyme patterns is obtained by moving the micro-dispenser relative to the modified gold surface using a micro-positioning device. Enzyme spots with typical lateral dimensions of 100 ml are obtained, but also, more complex structures, e.g. lines or meander structures, can be achieved by multiple droplets dispensed during the concomitant movement of the micro-dispenser. The first enzyme layer on top of the functionalised thiol-monolayer is subsequently covalently immobilised using either carbodiimide activation of carboxilic headgroups at the enzyme or via already introduced activated ester functions at the monolayer. Immobilised enzyme activities of glucose oxidase and lactate oxidase patterns have been characterised by means of scanning electrochemical microscopy. The product of the enzyme-catalysed reaction, H2O2, is detected with an micro-electrode in the presence of either or both substrates, glucose and lactate, leading to a visualisation of the corresponding enzyme pattern and the lateral enzymatic activity. (C) 2001 Elsevier Science B.V. All rights reserved.
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| 3. |
- Tkac, Jan, et al.
(författare)
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Improved selectivity of microbial biosensor using membrane coating. Application to the analysis of ethanol during fermentation
- 2003
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Ingår i: Biosensors & bioelectronics. - 0956-5663 .- 1873-4235. ; 18:9, s. 1125-1134
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Tidskriftsartikel (refereegranskat)abstract
- A ferricyanide mediated microbial biosensor for ethanol detection was prepared by surface modification of a glassy carbon electrode. The selectivity of the whole Gluconobacter oxydans cell biosensor for ethanol determination was greatly enhanced by the size exclusion effect of a cellulose acetate (CA) membrane. The use of a CA membrane increased the ethanol to glucose sensitivity ratio by a factor of 58.2 and even the ethanol to glycerol sensitivity ratio by a factor of 7.5 compared with the use of a dialysis membrane. The biosensor provides rapid and sensitive detection of ethanol with a limit of detection of 0.85 µM (S/N=3). The selectivity of the biosensor toward alcohols was better compared to previously published enzyme biosensors based on alcohol oxidase or alcohol dehydrogenases. The biosensor was successfully used in an off-line monitoring of ethanol during batch fermentation by immobilized Saccharomyces cerevisiae cells with an initial glucose concentration of 200 g l-1. © 2002 Elsevier Science B.V. All rights reserved.
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| 4. |
- Bachinger, T., et al.
(författare)
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Gas sensor arrays for early detection of infection in mammalian cell culture
- 2002
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Ingår i: Biosensors & bioelectronics. - 0956-5663 .- 1873-4235. ; 17:5, s. 395-403
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Tidskriftsartikel (refereegranskat)abstract
- The detection of bacterial infections in a mammalian cell culture process is realised using a gas sensor array. In production-scale and laboratory-scale cultivations of a perfused recombinant CHO-cell culture producing human blood coagulation Factor VIII, we show that the gas sensor array identifies bacterial contamination earlier than conventional methods. The sensitivity of the instrument is verified by inoculation of a blank cell culture medium with defined bacterial cell counts. © 2002 Elsevier Science B.V. All rights reserved.
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| 5. |
- Filippini, Daniel, et al.
(författare)
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Microplate based biosensing with a computer screen aided technique
- 2003
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Ingår i: Biosensors & bioelectronics. - 0956-5663 .- 1873-4235. ; 19:1, s. 35-41
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Tidskriftsartikel (refereegranskat)abstract
- Melanophores, dark pigment cells from the frog Xenopus laevis, have the ability to change light absorbance upon stimulation by different biological agents. Hormone exposure (e.g. melatonin or α-melanocyte stimulating hormone) has been used here as a reversible stimulus to test a new compact microplate reading platform. As an application, the detection of the asthma drug formoterol in blood plasma samples is demonstrated. The present system utilizes a computer screen as a (programmable) large area light source, and a standard web camera as recording media enabling even kinetic microplate reading with a versatile and broadly available platform, which suffices to evaluate numerous bioassays. Especially in the context of point of care testing or self testing applications these possibilities become advantageous compared with highly dedicated comparatively expensive commercial systems.
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| 6. |
- Gabig-Ciminska, Magdalena, et al.
(författare)
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Electric chips for rapid detection and quantification of nucleic acids
- 2004
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Ingår i: Biosensors & bioelectronics. - : Elsevier BV. - 0956-5663 .- 1873-4235. ; 19:6, s. 537-546
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Tidskriftsartikel (refereegranskat)abstract
- A silicon chip-based electric detector coupled to bead-based sandwich hybridization (BBSH) is presented as an approach to perform rapid analysis of specific nucleic acids. A microfluidic platform incorporating paramagnetic beads with immobilized capture probes is used for the biorecognition steps. The protocol involves simultaneous sandwich hybridization of a single-stranded nucleic acid target with the capture probe on the beads and with a detection probe in the reaction solution, followed by enzyme labeling of the detection probe, enzymatic reaction, and finally, potentiometric measurement of the enzyme product at the chip surface. Anti-DIG-alkaline phosphatase conjugate was used for the enzyme labeling of the DIG-labeled detection probe. p-Aminophenol phosphate (pAPP) was used as a substrate. The enzyme reaction product, p-aminophenol (pAP), is oxidized at the anode of the chip to quinoneimine that is reduced back to pAP at the cathode. The cycling oxidation and reduction of these compounds result in a current producing a characteristic signal that can be related to the concentration of the analyte. The performance of the different steps in the assay was characterized using in vitro synthesized RNA oligonucleotides and then the instrument was used for analysis of 16S rRNA in Escherichia coli extract. The assay time depends on the sensitivity required. Artificial RNA target and 16S rRNA, in amounts ranging from 10(11) to 10(10) molecules, were assayed within 25 min and 4 h, respectively.
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| 7. |
- Hansson, Kenny, 1972-, et al.
(författare)
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Comparative studies with surface plasmon resonance and free oscillation rheometry on the inhibition of platelets with cytochalasin E and monoclonal antibodies towards GPIIb/IIIa
- 2002
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Ingår i: Biosensors & bioelectronics. - 0956-5663 .- 1873-4235. ; 17:9, s. 761-771
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Tidskriftsartikel (refereegranskat)abstract
- In the haemostatic system a multitude of processes are intertwined in fine-tuned interactions that arrest bleeding, keep the circulatory system open, and the blood flowing. The occurrence of both surface and bulk interactions adds an additional dimension of complexity. These insights have led to the belief that global overall procedures can inform on the likely behaviour of the system in health and disease. Two sensing procedures: surface plasmon resonance (SPR), which senses surface interactions, and free oscillation rheometry (FOR), which senses interactions within the bulk, have been combined and evaluated. The contribution of blood cells, mainly platelets, to the SPR and FOR signals was explored by simultaneous SPR and FOR measurement during native whole blood coagulation, accelerated via the platelets through addition of SFLLRN peptide and inhibition of platelet aggregation with abciximab (ReoPro®) and of shape change with cytochalasin E. The SPR technique was found to be sensitive to inhibition of blood cell functions such as adhesion to and spreading on surfaces, as well as platelet aggregation. SPR seemed not to be directly sensitive to fibrin polymerisation in coagulating whole blood. The FOR technique detected the coagulation as a bulk phenomenon, i.e. the gelation of the blood due to fibrin formation was detected. The combination of SPR and FOR may therefore be suitable for studies on blood cell functions during coagulation.
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| 8. |
- Hansson, Kenny, 1972-, et al.
(författare)
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Surface plasmon resonance and free oscillation rheometry in combination : a useful approach for studies on haemostasis and interactions between whole blood and artificial surfaces
- 2002
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Ingår i: Biosensors & bioelectronics. - 0956-5663 .- 1873-4235. ; 17:9, s. 747-759
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Tidskriftsartikel (refereegranskat)abstract
- In haemostatic and biomaterial research biological processes at surfaces and in the bulk phase of the surface-contacting medium are important. The present work demonstrates the usefulness of the combination of surface plasmon resonance (SPR), sensitive to changes in refractive index at surfaces, and free oscillation rheometry (FOR), sensitive to rheological properties of the bulk, for simultaneous real-time measurements on coagulation and fibrinolysis of blood plasma and coagulation of whole blood. SFLLRN stimulated coagulation of native whole blood presented a higher SPR signal with different appearance than plasma coagulation, while the FOR signals corresponding to plasma and whole blood coagulation were similar. This indicated that the SPR technique was more sensitive to cell-surface interactions than to fibrin formation in whole blood during coagulation, while the FOR technique were equally sensitive to coagulation in whole blood and plasma. Spontaneous coagulation of native whole blood in contact with methyl- and hydroxyl-terminated self-assembled monolayers (SAM) on gold and gold surfaces regenerated after coagulation were also studied. The regenerated gold surfaces displayed the shortest coagulation times, although the contact-activation of blood coagulation for these surfaces was low. The methylated and hydroxylated surfaces were comparable in terms of coagulation activation, while the hydroxylated surfaces presented FOR signals that indicated detaching of the coagulum from the surface. The combination of SPR and FOR is well suited for studies of cell– and protein–surface interactions and simultaneous bulk processes. Possible applications are investigations of blood cell defects in patients and monitoring of native whole blood interactions with artificial surfaces.
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| 9. |
- Johansen, Knut, et al.
(författare)
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Sensitivity deviation : Instrumental linearity errors that influence concentration analyses and kinetic evaluation of biomolecular interactions
- 2000
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Ingår i: Biosensors & bioelectronics. - 0956-5663 .- 1873-4235. ; 15:9-10, s. 503-509
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Tidskriftsartikel (refereegranskat)abstract
- Many scientific instruments utilise multiple element detectors, e.g. CCD's or photodiode arrays, to monitor the change in a position of an optical pattern. For example, instruments for affinity biosensing based on surface plasmon resonance (SPR) or resonant mirror are equipped with such detectors. An important and desired property of these bioanalytical instruments is that the calculation of the movement or change in shape follows the true change. This is often not the case and it may lead to linearity errors, and to sensitivity errors. The sensitivity is normally defined as the slope of the calibration curve. A new parameter is introduced to account for the linearity errors, the sensitivity deviation, defined as the deviation from the undistorted slope of the calibration curve. The linearity error and the sensitivity deviation are intimately related and the sensitivity deviation may lead to misinterpretation of kinetic data, mass transport limitations and concentration analyses. Because the linearity errors are small (e.g. 10 pg/mm2 of biomolecules on the sensor surface) with regard to the dynamic range (e.g. 30 000 pg/mm2), they can be difficult to discover. However, the linearity errors are often not negligible with regard to a typical response (e.g. 0-100 pg/mm2), and may therefore cause serious problems. A method for detecting linearity errors is outlined. Further on, this paper demonstrates how integral linearity errors of less than 1% can result in a sensitivity deviation of 10%, a value that in our opinion cannot be ignored in biospecific interaction analysis (BIA). It should also be stressed out that this phenomenon also occurs in other instruments using array detectors. (C) 2000 Elsevier Science S.A.Many scientific instruments utilize multiple element detectors, e.g. CCD's or photodiode arrays, to monitor the change in a position of an optical pattern. For example, instruments for affinity biosensing based on surface plasmon resonance (SPR) or resonant mirror are equipped with such detectors. An important and desired property of these bioanalytical instruments is that the calculation of the movement or change in shape follows the true change. This is often not the case and it may lead to linearity errors, and to sensitivity errors. The sensitivity is normally defined as the slope of the calibration curve. A new parameter is introduced to account for the linearity errors, the sensitivity deviation, defined as the deviation from the undistorted slope of the calibration curve. The linearity error and the sensitivity deviation are intimately related and the sensitivity deviation may lead to misinterpretation of kinetic data, mass transport limitations and concentration analyses. Because the linearity errors are small (e.g. 10 pg/mm2 of biomolecules on the sensor surface) with regard to the dynamic range (e.g. 30 000 pg/mm2), they can be difficult to discover. However, the linearity errors are often not negligible with regard to a typical response (e.g. 0-100 pg/mm2), and may therefore cause serious problems. A method for detecting linearity errors is outlined. Further on, this paper demonstrates how integral linearity errors of less than 1% can result in a sensitivity deviation of 10%, a value that in our opinion cannot be ignored in biospecific interaction analysis (BIA). It should also be stressed out that this phenomenon also occurs in other instruments using array detectors.
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| 10. |
- Liljeblad, Mathias, et al.
(författare)
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Analysis of glycoproteins in cell culture supernatants using a lectin immunosensor technique
- 2002
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Ingår i: Biosensors & bioelectronics. - 0956-5663 .- 1873-4235. ; 17:10, s. 883-891
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Tidskriftsartikel (refereegranskat)abstract
- A method based on a surface plasmon resonance technique for detection of changes in concentration and glycosylation of proteins in cell culture supernatant is described. The method was used to analyze α1-acid glycoprotein (AGP) produced by a human hepatoma cell line (HepG2). Cell culture supernatant was injected to a BIACORE 2000 instrument and AGP was captured on the sensor chip by immobilized antibodies. The captured glycoprotein was then analyzed for content of carbohydrate epitopes using three different lectins, Aleuria aurantia lectin (AAL), Sambucus nigra agglutinin (SNA), and Triticum vulgaris agglutinin (wheat germ agglutinin, WGA). The method was used to analyze changes in concentration and glycosylation of AGP produced by HepG2 cells grown with or without three different cytokines, interleukin-1β (IL-1β), interleukin-6 (IL-6), and transforming growth factor β-1 (TGFβ1). Using the described method it was shown that when HepG2 cells were grown in the presence of IL-6 both AGP concentration and fucosylation increased. When HepG2 cells instead were grown in the presence of TGFβ1 AGP fucosylation increased whereas AGP concentration decreased.
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