title: Comparison of optomagnetic and AC susceptibility readouts in a magnetic nanoparticle agglutination assay for detection of C-reactive protein.
abstract: There is an increasing need to develop biosensor methods that are highly sensitive and that can be combined with low-cost consumables. The use of magnetic nanoparticles (MNPs) is attractive because their detection is compatible with low-cost disposables and because application of a magnetic field can be used to accelerate assay kinetics. We present the first study and comparison of the performance of magnetic susceptibility measurements and a newly proposed optomagnetic method. For the comparison we use the C-reactive protein (CRP) induced agglutination of identical samples of 100nm MNPs conjugated with CRP antibodies. Both methods detect agglutination as a shift to lower frequencies in measurements of the dynamics in response to an applied oscillating magnetic field. The magnetic susceptibility method probes the magnetic response whereas the optomagnetic technique probes the modulation of laser light transmitted through the sample. The two techniques provided highly correlated results upon agglutination when they measure the decrease of the signal from the individual MNPs (turn-off detection strategy), whereas the techniques provided different results, strongly depending on the read-out frequency, when detecting the signal due to MNP agglomerates (turn-on detection strategy). These observations are considered to be caused by differences in the volume-dependence of the magnetic and optical signals from agglomerates. The highest signal from agglomerates was found in the optomagnetic signal at low frequencies.
authors.affiliation: Department of Micro- and Nanotechnology, DTU Nanotech, Technical University of Denmark, Building 345C, Kgs. Lyngby, DK-2800 Denmark. Electronic address: JepF@nanotech.dtu.dk.
authors.forename: Jeppe
authors.initials: J
authors.lastname: Fock
authors.affiliation: Department of Micro- and Nanotechnology, DTU Nanotech, Technical University of Denmark, Building 345C, Kgs. Lyngby, DK-2800 Denmark. Electronic address: Mattias.parmvi@blusense-diagnostics.com.
authors.forename: Mattias
authors.initials: M
authors.lastname: Parmvi
authors.affiliation: Department of Engineering Sciences, Uppsala University, Box 534, Uppsala, SE-751 21 Sweden. Electronic address: Mattias.Stromberg@angstrom.uu.se.
authors.forename: Mattias
authors.initials: M
authors.lastname: Strömberg
authors.affiliation: Department of Engineering Sciences, Uppsala University, Box 534, Uppsala, SE-751 21 Sweden. Electronic address: Peter.Svedlindh@angstrom.uu.se.
authors.forename: Peter
authors.initials: P
authors.lastname: Svedlindh
authors.affiliation: Department of Micro- and Nanotechnology, DTU Nanotech, Technical University of Denmark, Building 345C, Kgs. Lyngby, DK-2800 Denmark. Electronic address: Marco@blusense-diagnostics.com.
authors.forename: Marco
authors.initials: M
authors.lastname: Donolato
authors.affiliation: Department of Micro- and Nanotechnology, DTU Nanotech, Technical University of Denmark, Building 345C, Kgs. Lyngby, DK-2800 Denmark. Electronic address: Mikkel.Hansen@nanotech.dtu.dk.
authors.forename: Mikkel Fougt
authors.initials: MF
authors.lastname: Hansen
mesh_terms: D000372:Agglutination Tests / Q000379:methods; D000818:Animals; D055910:Antibodies, Immobilized / Q000737:chemistry*; D015374:Biosensing Techniques / Q000379:methods*; D002097:C-Reactive Protein / Q000032:analysis*; D006041:Goats; D006801:Humans; D057230:Limit of Detection; D008280:Magnetics / Q000379:methods; D058185:Magnetite Nanoparticles / Q000737:chemistry*
chemical_list: D055910:Antibodies, Immobilized; D058185:Magnetite Nanoparticles; D002097:C-Reactive Protein
keywords: Agglutination assay; Biosensor; Brownian relaxation; CRP; Magnetic beads