| 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. |
- 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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| 3. |
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| 4. |
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| 5. |
- 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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| 6. |
- Baresel, Christian, et al.
(författare)
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Functionalized magnetic particles for water treatment
- 2019
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Ingår i: Heliyon. - : Elsevier BV. - 2405-8440. ; 5:8
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we have taken the concept of water treatment by functionalized magnetic particles one step forward by integrating the technology into a complete proof of concept, which included the preparation of surface modified beads, their use as highly selective absorbents for heavy metals ions (Zinc, Nickel), and their performance in terms of magnetic separation. The separation characteristics were studied both through experiments and by simulations. The data gathered from these experimental works enabled the elaboration of various scenarios for Life Cycle Analysis (LCA). The LCA showed that the environmental impact of the system is highly dependent on the recovery rate of the magnetic particles. The absolute impact on climate change varied significantly among the scenarios studied and the recovery rates. The results support the hypothesis that chelation specificity, magnetic separation and bead recovery should be optimized to specific targets and applications.
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| 7. |
- Enoksson, Peter, 1957, et al.
(författare)
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Micro- and Nanosystems for Sensing in Medicine
- 2008
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Ingår i: Proceedings of Medicinteknikdagarna 2008, 14-15 October, Göteborg, Sweden. ; , s. 117-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Jonasson, Christian, et al.
(författare)
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Modelling the effect of different core sizes and magnetic interactions inside magnetic nanoparticles on hyperthermia performance
- 2019
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 477, s. 198-202
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Tidskriftsartikel (refereegranskat)abstract
- We present experimental intrinsic loss power (ILP) values, measured at an excitation frequency of 1 MHz and at relatively low field amplitudes of 3.4–9.9 kA/m, as a function of the mean core diameter, for selected magnetic nanoparticles (MNPs). The mean core sizes ranged from ca. 8 nm to 31 nm. Transmission electron microscopy indicated that those with smaller core sizes (less than ca. 22 nm) were single-core MNPs, while those with larger core sizes (ca. 29 nm to 31 nm) were multi-core MNPs. The ILP data showed a peak at core sizes of ca. 20 nm. We show here that this behaviour correlates well with the predicted ILP values obtained using either a non-interacting Debye model, or via dynamic Monte-Carlo simulations, the latter including core-core magnetic interactions for the multi-core particles. This alignment of the models is a consequence of the low field amplitudes used. We also present interesting results showing that the core-core interactions affect the ILP value differently depending on the mean core size.
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| 9. |
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| 10. |
- Schaller, Vincent, 1979, et al.
(författare)
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Determination of nanocrystal size distribution in magnetic multicore particles including dipole-dipole interactions and magnetic anisotropy: A Monte Carlo study
- 2010
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Ingår i: AIP Conference Proceedings. - : AIP. - 1551-7616 .- 0094-243X. - 9780735408661 ; 1311, s. 42-50
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Konferensbidrag (refereegranskat)abstract
- A correct estimate of the size distribution (i.e., median diameter D and geometric standard deviation σ) of the magnetic nanocrystals (MNCs) embedded in magnetic multicore particles is a necessity in most applications relying on the magnetic response of these particles. In this paper we use a Monte Carlo method to simulate the equilibrium magnetization of two types of multicore particles: (I) MNCs fused in a random compact cluster, and (II) MNCs distributed on the surface of a large carrier sphere. The simulated magnetization data are then fitted using a common method based on a Langevin equation weighted with a size distribution function. Finally, the fitting parameters Dm and σm are compared to the real parameters Dp and σp used to generate the MNCs. Our results show that fitting magnetization data with a Langevin model that neglects magnetic anisotropy and dipole-dipole interactions leads to an erroneous estimate of the size distribution of the MNCs in multicore particles. The magnitude of the error depends on the particle morphology, number of MNCs contained in the particle and magnetic properties of the MNCs.
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| 11. |
- Schaller, Vincent, 1979, et al.
(författare)
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Effective magnetic moment of magnetic multicore nanoparticles
- 2009
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 80:9, s. 092406-
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Tidskriftsartikel (refereegranskat)abstract
- We carry out Monte Carlo simulations to study the effective magnetic moment mu(eff) in the low-field region of magnetic multicore nanoparticles. Transmission electron microscopy and scanning electron microscopy images show that these particles contain a number of magnetic nanocrystals (MNCs) randomly packed in a single cluster of total volume V(tot). We illustrate how the initial magnetic susceptibility chi(0) of magnetic multicore nanoparticles can be straightforward derived from mu(eff) computed at zero magnetic field. We observe that dipolar interactions between MNCs and polydispersity of the MNCs contribute to increase and to decrease mu(eff)/V(tot), respectively, while magnetic anisotropy of the MNCs does not show any effect. In all three cases, mu(eff)/V(tot) can be described by a linear relation to (mu B/k(B)T)(2) that we analytically derived for low applied fields.
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| 12. |
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| 13. |
- Schaller, Vincent, 1979, et al.
(författare)
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Monte Carlo simulation of magnetic multi-core nanoparticles
- 2009
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 321:10, s. 1400-1403
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a Monte Carlo simulation is carried out to evaluate the equilibrium magnetization of magnetic multi-core nanoparticles in a liquid and subjected to a static magnetic field. The particles contain a magnetic multi-core consisting of a cluster of magnetic single-domains of magnetite. We show that the magnetization of multi-core nanoparticles cannot be fully described by a Langevin model. Inter-domain dipolar interactions and domain magnetic anisotropy contribute to decrease the magnetization of the particles, whereas the single-domain size distribution yields an increase in magnetization. Also, we show that the interactions affect the effective magnetic moment of the multicore nanoparticles.
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| 14. |
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| 15. |
- Schaller, Vincent, 1979, et al.
(författare)
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Motion of nanometer sized magnetic particles in a magnetic field gradient
- 2008
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 104:9, s. no:093918-
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Tidskriftsartikel (refereegranskat)abstract
- Using magnetic particles with sizes in the nanometer range in biomedical magnetic separation has gained much interest recently due to their higher surface area to particle volume and lower sedimentation rates. In this paper, we report our both theoretical and experimental investigation of the motion of magnetic particles in a magnetic field gradient with particle sizes from 425 nm down to 50 nm. In the experimental measurements, we monitor the absorbance change of the sample volume as the particle concentration varies over time. We also implement a Brownian dynamics algorithm to investigate the influence of particle interactions during the separation and compare it to the experimental results for validation. The simulation agrees well with the measurements for particle sizes around 425 nm. Some discrepancies remain for smaller particle sizes, which may indicate that additional factors also influence the separation for the smaller size range. We observe that the separation process includes the formation of chainlike particle aggregates due to the magnetic dipole-dipole interactions between particles when subjected to an external magnetic field. We can also see that the hydrodynamic interaction between these chains contributes to reducing the separation time. In conclusion, we show that the formation of these particle aggregates, and to a less extent the hydrodynamic interactions between them contributes to significantly enhancing the particle separation process. © 2008 American Institute of Physics.
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| 16. |
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| 17. |
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| 18. |
- Schaller, Vincent, 1979
(författare)
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Studies of magnetic multi-core nanoparticles for biomedical applications
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent years, there has been growing interest in using magnetic multi-core nanoparticles in biomedical applications, and particularly in bioseparation and biosensing. In this thesis, two computer simulation techniques have been implemented to study the magnetic response of these particles, and a microfluidic platform has been fabricated to manipulate bio-functionalized magnetic particles in suspension for immunoassays.The motion of the magnetic multi-core nanoparticles subjected to a magnetic field gradient, such as when used in magnetic bioseparation, was investigated using a Brownian dynamics algorithm. Optical measurements based on absorbance change as a function of particle concentration have been carried out as well. Both simulations and experiments indicate that particle aggregation is an essential factor to accelerate the separation process.A Monte Carlo method based on the Metropolis algorithm has been used to simulate the equilibrium magnetic properties of the magnetic multi-core nanoparticles. Results show that the Langevin model, even when including the size distribution of the magnetic nanocrystals (MNCs) contained in the nanoparticles, is not sufficient to fully describe the magnetization of this type of particles. Other intrinsic properties, such as the magnetic anisotropy of the MNCs and the magnetic dipole-dipole interactions between MNCs, must also be taken into account. The effective magnetic moment μ_eff and initial magnetic susceptibility χ_0 were studied both at zero magnetic field and in the low field region. We show that the true value of χ_0 can easily be derived in a single step from the value of μ_eff computed at zero field and including all additional factors (e.g. size distribution, magnetic anisotropy, and dipolar interactions). These findings are particularly relevant for biosensing systems relying on the low-field magnetic response of bio-functionalized magnetic multi-core nanoparticles.Finally, a digital microfluidic chip based on electrowetting-on-dielectric (EWOD) was fabricated to manipulate microliter-sized water droplets containing a suspension of bio-functionalized magnetic multi-core nanoparticles. AC-susceptibility measurements were performed using a Superconducting Quantum Interference Device (SQUID) sensor.
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| 19. |
- Schaller, Vincent, 1979, et al.
(författare)
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The effect of dipolar interactions in clusters of magnetic nanocrystals
- 2010
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 200:SECTION 7
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Konferensbidrag (refereegranskat)abstract
- Monte Carlo simulations are carried out to evaluate the effective magnetic moment µeff of clusters containing 100 magnetic nanocrystals (MNCs) in a low magnetic field. The true value of the initial magnetic susceptibility, i.e. x0=∂M/∂H at zero field, can be assesed from µeff. Resuslts show that the dipolar interaction contribute to reduce the efeective magnetic moment. Below a threshold value near the low-field region, clusters of MNCs with smaller diameters possess a larger effective magnetic moment per unit volume compared to clusters with larger MNCs. This is of particular interest for bio-sensing systems relying on the magnetic responce of magnetic multi-core nanoparticles in the low-field region.
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| 20. |
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| 21. |
- 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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