Magnetic susceptibility reduction method for magnetically labeled immunoassay

Abstract

In addition to synthesizing biofunctionalized magnetic nanopaticles for the purpose of magnetically labeling biomolecules, a system to measure the ac magnetic susceptibility of the labeled sample was developed. When a targeted biomolecule was mixed with magnetic fluid possessing biofunctionalized magnetic nanoparticles, portions of magnetic nanoparticles agglomerated to form clusters due to the association with the targeted biomolecule. Due to the formation of magnetic clusters, the measured ac magnetic susceptibility reduced. The relationship between the mixed-frequency ac magnetic susceptibility reduction and the amount of the detected biomolecule was established.

Highly stable monodisperse PEGylated iron oxide nanoparticle aqueous suspensions: a nontoxic tracer for homogeneous magnetic bioassays

“…alternating and rotating) has recently become a potent tool for detection of proteins and molecules bound to the NPs. [1][2][3][4][5][6] To conduct a successful homogeneous magnetic bioassay, particularly in a rotating magnetic field (RMF), the iron oxide NP aqueous suspensions relaxing via the Brownian mechanism (d core > 24 nm) are required.…”

“…In the last two decades, there has been a growing trend to employ high temperature decomposition of various iron precursors, such as iron acetylacetonate Fe(acac) 3 , 7 iron-oleate, 8 iron pentacarbonyl Fe(CO) 5 , 9 and hydrated iron(III) oxide FeO(OH) 10 to fabricate iron oxide NPs. By having a precise control over the synthesis parameters, these methods offer crystallized monodisperse particles with appropriate magnetic properties but, solely dispersible in non-polar solvents.…”

Planar Hall effect bridge geometries optimized for magnetic bead detection

“…Table I summarizes the nominal in-phase and out-of-phase 1st and 2nd harmonic signals for the three sensor designs calculated by inserting the sensor signals in Eqs. (16) and (17). Note that the in-phase 2nd harmonic sensor signal V 0 2 is proportional to the out-of-phase magnetic susceptibility v 00 and that the out-of-phase 2nd harmonic sensor signal V 00 2 is linearly related to the in-phase magnetic susceptibility v 0 for the PHEB and pPHEB designs and proportional to v 0 for the dPHEB design.…”

“…Moreover, to further simplify the treatment, we will only consider a DC external magnetic field applied in the y-direction H app y . These effects have been central for the use of frequency mixing detection schemes [16][17][18] that are, hence, not considered in the present work. We generally allow the magnetic bead susceptibility to be complex such that v ¼ v 0 À iv 00 , where v 0 and v 00 are the in-phase and out-of-phase magnetic susceptibilities, respectively.…”

“…This implies that these methods will also to some extent be affected by external magnetic fields. Lock-in techniques and various frequency mixing techniques [16][17][18] are often used to filter away the signal not due to the magnetic beads. However, it is still desired to minimize the signal due to externally applied magnetic fields.…”