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Aging phenomena in ferrofluids suitable for magnetic biosensor applications
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
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2007 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, no 2, 023911- p.Article in journal (Refereed) Published
Abstract [en]

Agingphenomena were investigated in three different ferrofluids containing submicron sizedmagnetic beads consisting of a cluster of iron oxide nanoparticlesembedded in a dextrane matrix with primary amine groups onthe surface (one fresh sample and one sample aged duringthree months) and with a plain surface (only dextrane onthe surface, aged for three months), suitable for magnetic biosensorapplications. The main characterization technique used was measurement of thefrequency dependent complex magnetization using a superconducting quantum interference device.The experimental factors considered were the effect of ultrasonication, temperature,dc bias magnetic field, and addition of sodium dodecyl sulphatesurfactant. The stability against aging was found to depend stronglyon the bead surface, and the reproducibility of a refreshingprocedure involving addition of surfactant in combination with ultrasonication wasshown to be low. Aggregation was shown to be stronglyaffected by the presence of even a small bias magneticfield. Applying a dc bias field caused the formation ofmore or less stable chainlike aggregates with various lengths.

Place, publisher, year, edition, pages
2007. Vol. 101, no 2, 023911- p.
Keyword [en]
magnetic fluids, ageing, magnetic particles, iron compounds, nanoparticles, magnetic sensors, magnetisation, surfactants, aggregation, nanobiotechnology
National Category
Engineering and Technology Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-98018DOI: 10.1063/1.2424522ISI: 000243890800083OAI: oai:DiVA.org:uu-98018DiVA: diva2:173175
Available from: 2009-02-13 Created: 2009-02-13 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Molecular Diagnostics Using Volume-Amplified Magnetic Nanobeads: Towards the Development of a Novel Biosensor System
Open this publication in new window or tab >>Molecular Diagnostics Using Volume-Amplified Magnetic Nanobeads: Towards the Development of a Novel Biosensor System
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Micro- or nanometer sized magnetic particles (beads) currently have a vast range of life science applications in, for example, bioseparation techniques, cancer therapy, development of contrast agents and biosensing techniques. In the latter field, magnetic beads offer several unique advantages, including minimal background signals, physical and chemical stability and low manufacturing costs. Because of these properties, magnetic biosensing techniques are potential candidates for low-cost, easy-to-use molecular diagnostic devices.

This doctoral thesis focuses mainly on the proof of principle and further development of a new magnetic biosensor platform for detection of DNA targets, a potential candidate for a new generation of low-cost, easy-to-use diagnostic devices: the Volume-Amplified Magnetic Nanobead Detection Assay (VAM-NDA). The VAM-NDA principle combines target recognition by padlock probe ligation followed by rolling circle amplification (RCA) of the reacted probes with changes in Brownian relaxation behaviour of magnetic nanobeads (typically ~100 nm in diameter) induced by a change in hydrodynamic bead volume. More specifically, the RCA products (coils, typically ~1 μm in diameter) are detected magnetically by adding magnetic beads tagged with detection probes complementary to part of the repeating RCA-coil sequence. Thus, depending on the target concentration, a certain quantity of beads binds to the coils by base-pair hybridisation (bead immobilisation), resulting in a dramatic bead volume increase, which is then detected by measuring the complex magnetisation spectrum. Use of a commercial SQUID magnetometer for measuring complex magnetisation resulted in a detection limit in the low pM range for DNA targets with excellent quantification accuracy. Simultaneous multiplexing was also evaluated.

The stability and aging of typical commercial ferrofluids (suspensions of magnetic beads) were investigated by measuring the complex magnetisation of and interbead interactions in oligonucleotide-functionalised ferrofluids. In summary, the bead surface characteristics were found to have a strong impact on the measured dynamic magnetic properties.

Place, publisher, year, edition, pages
Uppsala: Universitetsbiblioteket, 2009. 102 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 598
Keyword
Magnetic Biosensors, Ferrofluid, Biofunctionalisation, Ferrofluidic Aging, Interbead Interactions, Magnetic Nanobeads, Complex Magnetisation, Brownian Relaxation, Padlock Probes, Rolling Circle Amplification
National Category
Other Engineering and Technologies
Identifiers
urn:nbn:se:uu:diva-9542 (URN)978-91-554-7402-7 (ISBN)
Public defence
2009-03-06, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
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Supervisors
Available from: 2009-02-13 Created: 2009-02-13 Last updated: 2009-06-22Bibliographically approved

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Strömberg, MattiasGunnarsson, KlasSvedlindh, PeterStrömme, Maria

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