Frequency-Selective Rotation of Two-Particle Nanoactuators for Rapid and Sensitive Detection of Biomolecules

Abstract

We describe an optomagnetic bionanotechnology for rapid and sensitive solution-based affinity assays. Nanoactuators made from bioactive magnetic nanoparticles undergo rotational motion in the volume of a fluid under frequency-controlled magnetic actuation. The nanoactuators show a time-dependent scattering cross-section to an incoming light beam. We demonstrate that the temporal behavior of the scattered light intensity relates to the number, the magnetic properties and the size distribution of the nanoactuators, independently revealing the average value and variation in the magnetic properties of the nanoparticles as well as the concentration of nanoactuators. The method is applied to detect biomolecules in fluid by interparticle binding. In a total assay time of less than 3 min, we demonstrate a limit of detection lower than 400 fM in buffer and 5 pM in human plasma.

Distance within colloidal dimers probed by rotation-induced oscillations of scattered light

“…The experiments presented in this paper have been performed with a setup similar to that used by Ranzoni et al [7], displayed schematically in Fig. 1(a).…”

“…Furthermore, macromolecules can play a key role in inducing the aggregation of colloidal particles. This is for example the case in aggregation assays where the formation of particle clusters reveals the presence of analyte in solution, for the sensitive and fast detection of diagnostic biomarkers [5][6][7][8][9].…”

“…In earlier work we have developed a technique to study superparamagnetic dimers by rotating them in a magnetic field while measuring the laser light scattered by the dimers [7,8]. Because of the rotation, the dimers are alternatingly aligned with the laser beam and perpendicular to the laser beam, which gives an oscillating light scattering cross section.…”

“…Ranzoni et al [7,8] focused on 500 nm particles and scattering at small angles (30°), which produced scattering signals with high similarity to the geometric cross-section of the dimers. In this paper, we demonstrate that the use of larger scattering angles (mainly 90°) and somewhat larger particles (1 micrometer) leads to rapidly oscillating scattering signals which can be used to reveal detailed information about the dimers.…”

Planar Hall effect bridge geometries optimized for magnetic bead detection

“…The hydrodynamic diameter of the magnetic beads can be determined by measuring the Brownian relaxation frequency. 8 For both surface-and volume-based sensing, the magnetic beads are traditionally detected by either superconducting quantum interference devices (SQUIDs), 9 inductive methods, 10 fluxgates, 11 magneto-optical methods, 12 or magnetoresistive sensors. 7,[13][14][15] All methods, except for magneto-optical detection, directly measure the magnetic field from the magnetic beads.…”