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Volume-amplified magnetic bioassay integrated with microfluidic sample handling and high-Tc SQUID magnetic readout

Journal article
Authors Sobhan Sepehri
Emil Eriksson
Alexei Kalaboukhov
Teresa Zardán Gómez de la Torre
Kiryl Kustanovich
Aldo Jesorka
Justin F. Schneiderman
Jakob Blomgren
Christer Johansson
Maria Strømme
Dag Winkler
Published in APL Bioengineering
Volume 2
Issue 1
Publication year 2018
Published at Institute of Neuroscience and Physiology
Institute of Neuroscience and Physiology, Department of Clinical Neuroscience
Language en
Keywords bioassay, high-Tc superconducting sensor, SQUID, functionalized magnetic nanoparticles, MNPs, microfluidics
Subject categories Medical Engineering, Medical Equipment Engineering


A bioassay based on a high-Tc superconducting quantum interference device (SQUID) reading out functionalized magnetic nanoparticles (fMNPs) in a prototype microfluidic platform is presented. The target molecule recognition is based on volume amplification using padlock-probe-ligation followed by rolling circle amplification (RCA). The MNPs are functionalized with single-stranded oligonucleotides, which give a specific binding of the MNPs to the large RCA coil product, resulting in a large change in the amplitude of the imaginary part of the ac magnetic susceptibility. The RCA products from amplification of synthetic Vibrio cholera target DNA were investigated using our SQUID ac susceptibility system in microfluidic channel with an equivalent sample volume of 3 μl. From extrapolation of the linear dependence of the SQUID signal versus concentration of the RCA coils, it is found that the projected limit of detection for our system is about 1.0 × 105 RCA coils (0.2 × 10−18 mol), which is equivalent to 66 fM in the 3 μl sample volume. This ultra-high magnetic sensitivity and integration with microfluidic sample handling are critical steps towards magnetic bioassays for rapid detection of DNA and RNA targets at the point of care.

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