| 1. |
- Chang, S, et al.
(författare)
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An electrowetting-based microfluidic platform for magnetic bioassays
- 2010
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Ingår i: The 14th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2010, 3-7 Oktober, Groningen, Neterlands. - 9781618390622 ; 2, s. 1331-1333
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Konferensbidrag (refereegranskat)abstract
- Here we present our recent work on a droplet-based microfluidic device for manipulating microliter-sized droplets. By replacing the formerly used common dielectric SiO2 with Si3N4 and applying a 33 nm thick Teflon top layer to create a hydrophobic surface, we successfully lowered the actuation voltage from 450 V to 50 Vdc/40 Vac. Sputtered HfO2 with high dielectric constant was also investigated as an insulator, which could reproducibly yield thin defect-free insulation layers and lower the actuation voltage to less than 40 V.
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| 2. |
- Eberbeck, Dietmar, et al.
(författare)
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AC susceptometry and magnetorelaxometry for magnetic nanoparticle based biomolecule detection
- 2009
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Functionalized magnetic nanoparticles are increasingly used as probes in biomolecule detection. We compared two different techniques, which provide information on the state of the magnetic particle system. The dynamics of an ensemble of magnetic nanoparticles was probed measuring the response its magnetisation both on an alternating magnetic field by AC-susceptometry and on a jump of external magnetic field by magnetorelaxometry. In order to compare both techniques, we studied the binding of streptavidin functionalized nanoparticles (fluidMAG/BC-SAV) to biotin-agarose beads and to biotinylated prostate specific antigens (PSA-10). By both techniques we observed specific changes in shape and amplitude of the characteristic signals due the binding of the particles. Therewith the signals of bound and unbound probes can be discriminated and a homogeneous assay without time-comsuming washing steps is realized. The AC susceptometry method provides a robust and sensitive measurement technology. Magnetorelaxometry, utilizing superconducting quantum interference devices (SQUIDs) as magnetic field sensors, owns a much shorter measurement time and has the potential of an even higher sensitivity, at the expense of a considerably increased technological effort.
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| 3. |
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| 4. |
- Prieto Astalan, Andrea
(författare)
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Brownian Relaxation Measurements of Magnetic Nanoparticles: Towards the Development of a Novel Biosensor System
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Magnetic measurements of the Brownian relaxation time of thermally blocked magnetic nanoparticles dispersed in a solution have been performed in order to determine the hydrodynamic size distribution of the particles. By measuring changes in the hydrodynamic size of the particles, the ammount of analytes attached to the surface of particles can be determined. Thereby a biosensor can be developed for detection of analytes in solution. The in-house developed instrumental measurement technique that has been used is based on an induction coil system. The coil system consists of two detection coils that form a first order gradiometer coupling and are placed symmetrically in the centre of an excitation coil.We have been able to show that it is possible to develop a biosensor system that enables quantitative determination of analytes in solution. Prostate specific antigen (PSA) has been used as analyte in a model assay system. PSA in solution has been detected using magnetic nanoparticles coated with a specific monoclonal PSA antibody. When PSA molecules became attached to the particle surface they caused a small change in the hydrodynamic radius of the particle and thereby induced a small change in the particle’s Brownian relaxation time which has been determined by magnetic measurements. The assay procedure described above enables homogeneous detection (in solution and not on a bulk surface) of analytes without any need for label molecules or washing steps. Thereby a cost effective immunoassay with few steps can be developed. Two different approaches using either frequency or time domain measurements have been applied when measuring the Brownian relaxation times for determination of the amount of analyte in solution. In the first method the frequency dependent complex susceptibility of the particles was measured. Such a measurement is very sensitive to small changes in Brownian relaxation times of the magnetic particles induced by analyte adsorption onto the particle surface. A theoretical model has been developed for quantitative determination of analyte concentrations. The second method is based on the measurement of the time dependent induced differential voltage of the particle system when subjected to pulsed magnetic fields. This method enables real-time monitoring of fast processes, such as for instance, cluster formation. Analytes were used as links between magnetic particles coated with two different complementary antibodies in order to induce particle clustering. The development of a biosensor involves many steps, such as: assay procedure development, instrumental measurement method development, optimization of magnetic characteristics of the magnetic particles and others. Examples will be given regarding PSA detection, using both frequency domain and time domain measurements. Detailed descriptions of the two measurement methods will be given, as well as a comparison of them. The sensitivity of the developed biosensor system for detection of PSA is at the moment ten times lower than the sensitivity of conventional immuno-assay systems. The sensitivity can and will be further increased by optimization of the biosensor system.
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| 5. |
- Schaller, Vincent, 1979, et al.
(författare)
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Development of an electrowetting-based microfluidic platform for magnetic immunoassays
- 2009
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Ingår i: 13th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2009; Jeju; South Korea; 1 November 2009 through 5 November 2009. - 9780979806421 ; , s. 85-87
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Konferensbidrag (refereegranskat)abstract
- We report the transport of magnetic nanoparticles (MNPs) in suspension in a 2 μl de-ionized water droplet (DIWD) using ElectroWetting-On-Dielectic (EWOD) actuation, and the detection of the MNPs by magnetic AC-susceptibility measurements using a highly sensitive high-Tc dc Superconducting Quantum Interference Device (SQUID) gradiometer. These results constitute the first development step towards a MNP-based magnetic immunoassay platform with SQUID-readout and sample droplet handling.
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| 6. |
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| 7. |
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| 8. |
- Schaller, Vincent, 1979, et al.
(författare)
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Towards an electrowetting-based digital microfluidic platform for magnetic immunoassays
- 2009
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Ingår i: Lab on a Chip - Miniaturisation for Chemistry and Biology. - : Royal Society of Chemistry (RSC). - 1473-0189 .- 1473-0197. ; 9:23, s. 3433-3436
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate ElectroWetting-On-Dielectric (EWOD) transport and SQUID gradiometer detection of magnetic nanoparticles (MNPs) suspended in a 2 mu l de-ionized water droplet. This proof-of-concept methodology constitutes the first development step towards a highly sensitive magnetic immunoassay platform with SQUID readout and droplet-based sample handling. Magnetic AC-susceptibility measurements were performed on MNPs with a hydrodynamic diameter of 100 nm using a high-Tc dc Superconducting Quantum Interference Device (SQUID) gradiometer as detector. We observed that the signal amplitude per unit volume is 2.5 times higher for a 2 ml sample droplet compared to a 30 ml sample volume.
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| 9. |
- Youahri, Yassine, et al.
(författare)
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Micro cooling of squid sensor
- 2008
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Ingår i: Proceedings of Micro System Workshop 2008 (MSW08) 6-7 May, Göteborg, Sweden. ; , s. S1-12
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 10. |
- Öisjöen, Fredrik, 1982, et al.
(författare)
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A new approach for bioassays based on frequency- and time-domain measurements of magnetic nanoparticles
- 2010
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Ingår i: Biosensors and Bioelectronics. - : Elsevier BV. - 0956-5663 .- 1873-4235. ; 25:5, s. 1008-1013
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a one-step wash-free bioassay measurement system capable of tracking biochemical binding events. Our approach combines the high resolution of frequency- and high speed of time-domain measurements in a single device in combination with a fast one-step bioassay. The one-step nature of our magnetic nanoparticle (MNP) based assay reduces the time between sample extraction and quantitative results while mitigating the risks of contamination related to washing steps. Our method also enables tracking of binding events, providing the possibility of, for example, investigation of how chemical/biological environments affect the rate of a binding process or study of the action of certain drugs. We detect specific biological binding events occurring on the surfaces of fluid-suspended MNPs that modify their magnetic relaxation behavior. Herein. we extrapolate a modest sensitivity to analyte of 100 ng/ml with the present setup using our rapid one-step bioassay. More importantly, we determine the size-distributions of the MNP systems with theoretical fits to our data obtained from the two complementary measurement modalities and demonstrate quantitative agreement between them. (
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