A magnetic nanobead‐based bioassay provides sensitive detection of single‐ and biplex bacterial DNA using a portable AC susceptometer

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.

Comparison of optomagnetic and AC susceptibility readouts in a magnetic nanoparticle agglutination assay for detection of C-reactive protein

“…Although measurements of the magnetic signal have continued to be of interest (Dieckhoff et al, 2014;Engström et al, 2013;Strömberg et al, 2014;Zardán Gómez de la Torre et al, 2011), optomagnetic readout strategies have attracted significant focus (Antunes et al, 2015;Bejhed et al, 2015;Donolato et al, 2015aDonolato et al, , 2015bMezger et al, 2015;Ranzoni et al, 2012;Tian et al, 2016;Yang et al, 2016).…”

“…The assay strategies for the optomagnetic and magnetic readouts are essentially identical, but the two techniques probe very different properties of an MNP suspension and therefore they may respond differently when employed for readout in bioassays. For example, detection of the binding of MNPs to ~1 m large coils of DNA formed by rolling circle amplification has been performed by both techniques (Donolato et al, 2015a;Strömberg et al, 2014). There, the optomagnetic signal was observed to display a sign change when the circumference of MNP agglomerates approached the wavelength of the laser light and the scattering entered the Mie regime (Bejhed et al, 2015;Donolato et al, 2015a).…”

Recent advances in biological detection with magnetic nanoparticles as a useful tool

“…Stromberg et al [65] demonstrated sensitive (1.5 pmol/L) singleplex detection of bacterial DNA sequence in a portable AC susceptometer by a magnetic nanobead-based bioassay principle. This was the first demonstration of biplex volume-amplified magnetic nanobead detection assay (VAM-NDA) in the susceptometer.…”

Magnetic nanobeads present during enzymatic amplification and labeling for a simplified DNA detection protocol based on AC susceptometry

“…16 By utilizing a commercial AC susceptometer as read-out unit, we have demonstrated the versatility of this bioassay in several earlier studies. [17][18][19] We are currently focusing on developing a device, including automated sample preparation, for infectious diagnostics based on the bioassay principle using either a miniaturized AC susceptometer or a chip-based high-temperature superconducting quantum interference device. In connection to this work it is highly relevant to strive towards automation of the molecular protocol by investigating the possibilities for protocol simplifications.…”