Transport Efficiency of Biofunctionalized Magnetic Particles Tailored by Surfactant Concentration

Abstract

Controlled transport of surface-functionalized magnetic beads in a liquid medium is a central requirement for the handling of captured biomolecular targets in microfluidic lab-onchip biosensors. Here, the influence of the physiological liquid medium on the transport characteristics of functionalized magnetic particles and on the functionality of the coupled protein is studied. These aspects are theoretically modeled and experimentally investigated for prototype superparamagnetic beads, surfacefunctionalized with green fluorescent protein immersed in buffer solution with different concentrations of a surfactant. The model reports on the tunability of the steady-state particle substrate separation distance to prevent their surface sticking via the choice of surfactant concentration. Experimental and theoretical average velocities are discussed for a ratchet-like particle motion induced by a dynamic external field superposed on a static locally varying magnetic field landscape. The developed model and experiment may serve as a basis for quantitative forecasts on the functionality of magnetic particle transport-based lab-on-chip devices.

Polycrystalline exchange-biased bilayers: magnetically effective vs. structural antiferromagnetic grain volume distribution

“…With the effect arising from exchange interaction across the common interface, the phenomenon has been named exchange bias (EB) and is a key effect for of the development of data storage and magnetic sensor technology [4][5][6][7]. Further, domain engineering of polycrystalline EB thin films [8][9][10][11][12][13] has proven to be an important ingredient of lab-ona-chip devices [14] enabling the actuation of magnetic particles in liquid media [15][16][17].…”

Three-dimensional close-to-substrate trajectories of magnetic microparticles in dynamically changing magnetic field landscapes

“…In the latter case, the domains either form naturally (e.g., in magnetic garnet films) 18 or are artificially imprinted into the thin film 21 , 22 . An outstanding advantage of the use of MFLs is a comparably large magnetic field gradient within a small volume (over small distances), allowing for rapid MP transport 19 with local steady-state velocities of more than 100 µm/s 23 , 24 . It is important to note, that the motion of MPs in these transport concepts occurs close to the substrate surface.…”

“…The MP motion dynamics are mainly governed by the magnetic gradient forces, the hydrodynamic drag exerted by the surrounding liquid, and the electrostatic and electrodynamic interactions with the underlying substrate 25 . If gravitation and buoyancy are neglected, the balance of magnetic, electrostatic, and van der Waals forces determines the equilibrium distance between particle and substrate, i.e., their interplay defines the position of the particles within the magnetic field landscape 23 , 25 , which in turn influences strongly the lateral MP motion. The experimental determination of this vertical distance would therefore be, besides the two-dimensional MP trajectories, an important additional observable for the understanding of the MP motion over a flat substrate.…”

“…The experimental determination of this vertical distance would therefore be, besides the two-dimensional MP trajectories, an important additional observable for the understanding of the MP motion over a flat substrate. Moreover, resolving vertical MP positions along the lateral trajectories creates an alternative access for bio-sensing applications: The electrostatic and electrodynamic interactions between MP and substrate change upon analyte binding 23 either on the particle’s or on the substrate’s surface when the opposing surface remains unchanged. Therefore, determining a change in the separation distance between MP and substrate upon analyte binding possesses a large potential as a bio-detection technique.…”

Translatory and rotatory motion of exchange-bias capped Janus particles controlled by dynamic magnetic field landscapes

“…MJPs with vortex and out-of-plane magnetic states within the caps were introduced in previous works to demonstrate a controlled steering of the MJP’s movement direction whilst being transported by different propulsion mechanisms in a liquid environment 18 – 24 . What is missing to date is an investigation of the translational and rotational dynamics of micron-sized MJP with in-plane magnetized caps especially towards their capability for a transport to and a controlled particle rotation over specific substrate surface positions in physiological liquids 25 .…”