| 1. |
- Akhtar, Sultan, et al.
(författare)
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Real-Space Transmission Electron Microscopy Investigations of Attachment of Functionalized Magnetic Nanoparticles to DNA-Coils Acting as a Biosensor
- 2010
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 114:41, s. 13255-13262
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Tidskriftsartikel (refereegranskat)abstract
- The present work provides the first real-space analysis of nanobead-DNA coil interactions. Immobilization of oligonucleotide-functionalized magnetic nanobeads in rolling circle amplified DNA-coils was studied by complex magnetization measurements and transmission electron microscopy (TEM), and a statistical analysis of the number of beads hybridized to the DNA-coils was performed. The average number of beads per DNAcoil using the results from both methods was found to be around 6 and slightly above 2 for samples with 40 and 130 nm beads, respectively. The TEM analysis supported an earlier hypothesis that 40 nm beads are preferably immobilized in the interior of DNA-coils whereas 130 nm beads, to a larger extent, are immobilized closer to the exterior of the coils. The methodology demonstrated in the present work should open up new possibilities for characterization of interactions of a large variety of functionalized nanoparticles with macromolecules, useful for gaining more fundamental understanding of such interactions as well as for optimizing a number of biosensor applications.
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| 2. |
- de la Torre, Teresa Zardan Gomez, et al.
(författare)
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Molecular diagnostics using magnetic nanobeads
- 2010
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596.
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Konferensbidrag (refereegranskat)abstract
- In this paper, we investigate the volume-amplified magnetic nanobead detection assay with respect to bead size, bead concentration and bead oligonucleotide surface coverage in order to improve the understanding of the underlying microscopic mechanisms. It has been shown that: (i) the immobilization efficiency of the beads depends on the surface coverage of oligonucleotides, (ii) by using lower amounts of probe-tagged beads, detection sensitivity can be improved and (iii) using small enough beads enables both turn-off and turn-on detection. Finally, biplex detection was demonstrated.
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| 3. |
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| 4. |
- Donolato, Marco, et al.
(författare)
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Novel readout method for molecular diagnostic assays based on optical measurements of magnetic nanobead dynamics
- 2015
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 87:3, s. 1622-1629
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate detection of DNA coils formed from a Vibrio cholerae DNA target at picomolar concentrations using a novel optomagnetic approach exploiting the dynamic behavior and optical anisotropy of magnetic nanobead (MNB) assemblies. We establish that the complex second harmonic optical transmission spectra of MNB suspensions measured upon application of a weak uniaxial AC magnetic field correlate well with the rotation dynamics of the individual MNBs. Adding a target analyte to the solution leads to the formation of permanent MNB clusters, namely, to the suppression of the dynamic MNB behavior. We prove that the optical transmission spectra are highly sensitive to the formation of permanent MNB clusters and, thereby to the target analyte concentration. As a specific clinically relevant diagnostic case, we detect DNA coils formed via padlock probe recognition and isothermal rolling circle amplification and benchmark against a commercial equipment. The results demonstrate the fast optomagnetic readout of rolling circle products from bacterial DNA utilizing the dynamic properties of MNBs in a miniaturized and low-cost platform requiring only a transparent window in the chip.
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| 5. |
- Göransson, Jenny, et al.
(författare)
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Sensitive Detection of Bacterial DNA by Magnetic Nanoparticles
- 2010
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 82:22, s. 9138-9140
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Tidskriftsartikel (refereegranskat)abstract
- This work presents sensitive detection of bacterial genomic DNA using a magnetic nanoparticle-based substrate-free method. For the first time, such a method is employed for detection of a clinically relevant analyte by implementing a solid-phase-based molecular probing and amplification protocol that can be executed in 80 min. The molecular detection and amplification protocol is presented and verified on samples containing purified genomic DNA from Escherichia coli cells, showing that as few as 50 bacteria can be detected. This study moves the use of volume-amplified magnetic nanoparticles one step further toward rapid, sensitive, and selective infectious diagnostics.
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| 6. |
- Strömberg, Mattias, et al.
(författare)
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A magnetic nanobead-based bioassay provides sensitive detection of single- and biplex bacterial DNA using a portable AC susceptometer
- 2014
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Ingår i: Biotechnology Journal. - : Wiley. - 1860-6768 .- 1860-7314. ; 9:1, s. 137-145
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Tidskriftsartikel (refereegranskat)abstract
- Bioassays relying on magnetic read-out using probe-tagged magnetic nanobeads are potential platforms for low-cost biodiagnostic devices for pathogen detection. For optimal assay performance it is crucial to apply an easy, efficient and robust bead-probe conjugation protocol. In this paper, sensitive (1.5 pM) singleplex detection of bacterial DNA sequences is demonstrated in a portable AC susceptometer by a magnetic nanobead-based bioassay principle; the volume-amplified magnetic nanobead detection assay (VAM-NDA). Two bead sizes, 100 and 250 nm, are investigated along with a highly efficient, rapid, robust, and stable conjugation chemistry relying on the avidin-biotin interaction for bead-probe attachment. Avidin-biotin conjugation gives easy control of the number of detection probes per bead; thus allowing for systematic investigation of the impact of varying the detection probe surface coverage upon bead immobilization in rolling circle amplified DNA-coils. The existence of an optimal surface coverage is discussed. Biplex VAM-NDA detection is for the first time demonstrated in the susceptometer: Semi-quantitative results are obtained and it is concluded that the concentration of DNA-coils in the incubation volume is of crucial importance for target quantification. The present findings bring the development of commercial biodiagnostic devices relying on the VAM-NDA further towards implementation in point-of-care and outpatient settings.
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| 7. |
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| 8. |
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| 9. |
- Strömberg, Mattias, et al.
(författare)
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Immobilization of oligonucleotide-functionalized magnetic nanobeads in DNA-coils studied by electron microscopy and atomic force microscopy
- 2011
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Ingår i: MRS Online Proceedings Library. - : Springer Science and Business Media LLC.
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Konferensbidrag (refereegranskat)abstract
- Immobilization of oligonucleotide-functionalized magnetic nanobeads by hybridization in DNA-coils formed by rolling circle amplification has been investigated using transmission electron microscopy (TEM) and atomic force microscopy (AFM). The TEM results supported earlier made observations that small beads with low oligonucleotide surface coverage preferably immobilize in the interior of the DNA-coils and do not tend to link several DNA-coils together whereas large beads with high surface coverage to a larger extent connect several DNA-coils together to clusters of several DNA-coils with beads. AFM provided direct visualization of the DNA-coils as thread-like objects. DNA-coils with immobilized beads appeared as a collection of beads with thread-like features in their near vicinity.
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| 10. |
- Strömberg, Mattias, et al.
(författare)
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Interbead interactions within oligonucleotide functionalized ferrofluids suitable for magnetic biosensor applications
- 2007
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 40:5, s. 1320-1330
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Tidskriftsartikel (refereegranskat)abstract
- Interactions in oligonucleotide functionalized ferrofluids were investigated by measurements of frequency dependent complex magnetization in a superconducting quantum interference device. The ferrofluids consisted of aqueous suspensions of single-stranded oligonucleotide functionalized 130 nm sized magnetic beads, suitable for further use in magnetic biosensor applications based on changes in the Brownian relaxation behaviour of oligonucleotide-coated beads. The interbead interactions were found to depend strongly on the surface coverage by oligonucleotide molecules. At low surface coverage, aggregates of beads within the ferrofluid were formed, most likely due to interbead SS-crosslinking reactions. When the surface coverage increased, the entropic interbead repulsion arising from the thermal motion of oligonucleotide molecules began to stabilize the ferrofluid by preventing aggregation, and the crosslinking probability decreased. At a surface coverage, of ~40 oligonucleotides per bead, determined by a radioactive labelling analysis, an optimal configuration was obtained for which the ferrofluid behaved as consisting of almost non-interacting beads. At higher oligonucleotide functionalization degrees, the high coverage induced less thermal motion flexibility of the oligonucleotide chains which decreased the entropic repulsion effect. This in turn led to a higher crosslinking probability, as well as an increase in the hydrodynamic size of the beads. Thus, the ferrofluid sample of nearly non-interacting nature, in which an optimal degree of stabilization and the highest Brownian relaxation frequency are achieved in the low surface coverage region, may be considered as the most appropriate one for further use in magnetic biosensor applications, from both a functional and an economic point of view.
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