Magnetophoretic lensing by concentric topographic cylinders of perpendicular magnetic anisotropy multilayers

Abstract

Colloidal magnetophoretic lensing of water suspended micrometer-sized superparamagnetic beads (SPBs) above a topographically patterned magnetic thin film system with perpendicular magnetic anisotropy is demonstrated. The magnetic pattern consisting of concentric annuli of micron-sized widths has been superimposed with a rotating external magnetic field, and it is shown that the trajectories of the SPBs above this structure are similar to light rays in an optical focusing lens. SPB trajectories converge towards the central region and have divergent trajectories while passing the center. The experimental findings are corroborated by a quantitative model for the SPB trajectories. The magnetophoretic lensing effect leads to a high SPB concentration in the center of the pattern and may be useful for applications where SPBs have to approach each other in a controlled way.

Transport Efficiency of Biofunctionalized Magnetic Particles Tailored by Surfactant Concentration

“…In the following, we only inspect the average steady-state velocity for one motion step since the time interval for the bead’s acceleration is with 1 μs much smaller than all relevant timescales for the presented experiments and can therefore be neglected . By balancing F d ( x , z b ′ ) and F m ( x , z b ) at a given time t , the spatial dependence of the BSPB’s momentary steady-state velocity can be calculated. , When applying this approach to transport concepts with acceleration phases in the temporal resolution of the experiment, the equation of motion has to be solved rather than utilizing this force balancing approach . Due to the position-dependent energy landscape, v⃗ b ( x , z ′, t ) varies along the bead’s path.…”

“…13,22 When applying this approach to transport concepts with acceleration phases in the temporal resolution of the experiment, the equation of motion has to be solved rather than utilizing this force balancing approach. 40 Due to the position-dependent energy landscape, v⃗ b (x,z′,t) varies along the bead's path. Performing the calculation of v⃗ b (x,z′,t) for each time interval Δt = 10 μs during the transport experiment, we can construct the step-like particle trajectory…”

Transport efficiency of biofunctionalized magnetic particles tailored by surfactant concentration

“…12,20 When applying this approach to transport concepts with acceleration phases in the temporal resolution of the experiment the equation of motion has to be solved rather than utilizing this force balancing approach. 38 Due to the position dependent energy landscape, v b (x, z , t) varies along the bead's path. Performing the calculation of v b (x, z , t) for each time interval ∆t = 10 µs during the transport experiment we can construct the step like particle trajectory…”

Combined Funnel, Concentrator, and Particle Valve Functional Element for Magnetophoretic Bead Transport Based on Engineered Magnetic Domain Patterns

“…[12,18,27] An important functionality of dynamic MFLs suitable for LOC devices is their ability to guide SPBs toward a sensing position in order to increase analyte detection sensitivity, [28] thus, emphasizing the need for a matching micromagnetic pattern within the underlying substrate. For instance, conducting micro-loops, [29,30] spiderweb-like, [28] concentric cylinder [31] as well as periodic circular micromagnetic structures [32] have been utilized to controllably focus SPBs toward a designated on-chip area, either with the goal of detecting the particles [28,29,32] or reducing the interparticle distance for a potential analyte-induced particle aggregation. [31] However, lacking control over the number of SPBs arriving at the focus position is oftentimes a drawback: Typically, all particles subjected to the MFL above the micromagnetic pattern will be focused, resulting in a broad distribution for the number of assembled particles.…”