Multi-scale magnetic nanoparticle based optomagnetic bioassay for sensitive DNA and bacteria detection

Bo Tian, Teresa Zardán Gómez De La Torre, Marco Donolato, Mikkel Fougt Hansen, Peter Svedlindh, Mattias Strömberg

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    Benefiting from their rapid readout, highly flexible devices and low-cost portable systems, optomagnetic biosensors have drawn increased attention in recent years as bioassay technologies for small molecules, biomarkers, DNA, and bacteria. Herein, an optomagnetic bioassay strategy suitable for point-of-care diagnostics, utilizing functionalized magnetic nanoparticles (100 nm) with Brownian relaxation behavior is optimized in order to obtain higher detection sensitivity for DNA molecules and bacteria. Presence of target DNA sequences or bacteria changes the dynamic behavior of the magnetic nanoparticles (binding to the target) and thus the optomagnetic response of the sample, which is measured by an optomagnetic setup including a 405 nm laser and a photodetector. The limit of detection is mainly set by the lowest measurable concentration of magnetic nanoparticles. Herein, as new results compared to previous work, we systematically optimize the concentration of 100 nm magnetic nanoparticles to increase the assay sensitivity and lower the limit of detection. To enable biplex detection, we perform this optimization in the presence of larger 250 nm magnetic nanoparticles that do not interact with the target. We show that the optimization and lowering of the 100 nm magnetic nanoparticle concentration result in a limit of detection of 780 fM of DNA coils formed by rolling circle amplification (size of about 1 μm) and 105 CFU per mL Salmonella (for immunoassay). These values are 15 times lower than those reported previously for this readout principle. Finally, we show that the 250 nm magnetic nanoparticles can serve as a second detection label for qualitative biplex detection of DNA coils formed by rolling circle amplification from V. cholerae and E. coli DNA coils using 100 nm and 250 nm magnetic detection nanoparticles, respectively.
    Original languageEnglish
    JournalAnalytical Methods
    Issue number25
    Pages (from-to)5009-5016
    Number of pages8
    Publication statusPublished - 2016

    Bibliographical note

    This article is Open Access and licensed under a Creative Commons Attribution 3.0 Unported Licence.


    • Analytical Chemistry
    • Engineering (all)
    • Chemical Engineering (all)
    • Amplification
    • Bacteria
    • Bioassay
    • DNA
    • DNA sequences
    • Escherichia coli
    • Magnetism
    • Molecules
    • Nanoparticles
    • Bacteria detection
    • Brownian relaxations
    • Detection sensitivity
    • Limit of detection
    • Magnetic detection
    • Magnetic nano-particles
    • Point of care diagnostic
    • Rolling circle amplifications
    • Nanomagnetics


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