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A new approach for bioassays based on frequency- and time-domain measurements of magnetic nanoparticles

Journal article
Authors Fredrik Öisjöen
Justin F. Schneiderman
A. P. Astalan
Alexei Kalaboukhov
C. Johansson
Dag Winkler
Published in Biosensors & Bioelectronics
Volume 25
Issue 5
Pages 1008-1013
ISSN 0956-5663
Publication year 2010
Published at
Pages 1008-1013
Language en
Keywords Bioassay, SQUID, Magnetic nanoparticles, AC-susceptibility, Magnetorelaxometry, prostate-specific antigen, biological immunoassays, magnetorelaxometry, biomolecules, particles, cancer, assay
Subject categories Biophysics


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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