Manipulation of Superparamagnetic Beads on Patterned Exchange-Bias Layer Systems for Biosensing Applications

Abstract

A technology platform based on a remotely controlled and stepwise transport of an array arrangement of superparamagnetic beads (SPB) for efficient molecular uptake, delivery and accumulation in the context of highly specific and sensitive analyte molecule detection for the application in lab-on-a-chip devices is presented. The near-surface transport of SPBs is realized via the dynamic transformation of the SPBs’ magnetic potential energy landscape above a magnetically stripe patterned Exchange-Bias (EB) thin film layer systems due to the application of sub-mT external magnetic field pulses. In this concept, the SPB velocity is dramatically influenced by the magnitude and gradient of the magnetic field landscape (MFL) above the magnetically stripe patterned EB substrate, the SPB to substrate distance, the magnetic properties of both the SPBs and the EB layer system, respectively, as well as by the properties of the external magnetic field pulses and the surrounding fluid. The focus of this review is laid on the specific MFL design in EB layer systems via light-ion bombardment induced magnetic patterning (IBMP). A numerical approach is introduced for the theoretical description of the MFL in comparison to experimental characterization via scanning Hall probe microscopy. The SPB transport mechanism will be outlined in terms of the dynamic interplay between the EB substrate’s MFL and the pulse scheme of the external magnetic field.

Smart Surfaces: Magnetically Switchable Light Diffraction through Actuation of Superparamagnetic Plate‐Like Microrods by Dynamic Magnetic Stray Field Landscapes

“…For domains of remanent in‐plane magnetizations, the magnetic charges are created within the domain walls between adjacent magnetic domains . For the current work, a periodic parallel‐stripe magnetic domain pattern with in‐plane magnetizations has been fabricated, where the neighboring domains' magnetizations are set either parallel or antiparallel with respect to the short stripe axis (head‐to‐head (hh)/tail‐to‐tail (tt) magnetization configuration in adjacent domains; see Experimental Section) . In this system, Néel‐type domain walls between adjacent domains serve as local sources for magnetic stray fields (see Figure b) …”

“…The experimentally observed maximum frequency at which a restoration of the rainbow color pattern without remarkable losses in brightness could still be observed was found to be in the range of 25–30 Hz (see Videos S3 and S4). In analogy to the concept described for spherical superparamagnetic beads in the present MFL, the superimposed external field dynamically controls the rods' effective magnetic potential energy landscape and, therefore, their spatial positioning and alignment.…”

“…Assuming a homogeneous distribution of rods in the fluid container at the beginning of the experiment, the average time τ the microrods need to travel to the substrate surface corresponds to the time they need to travel half the container height h , i.e., approximately τ = 100 min for h /2 = 50 µm. For distances z ≤ 1 µm between the rod centers and the substrate surface, the attractive magnetic force originating from the magnetic stray fields above the domain walls becomes relevant . Here, the magnetic moments of the microrods are oriented parallel to the stray fields above the domain walls and are strongest over the domain wall center.…”

“…Here, the magnetic moments of the microrods are oriented parallel to the stray fields above the domain walls and are strongest over the domain wall center. The magnetic stray fields were calculated according to the model described in refs . and are scaled by the thickness of the ferromagnetic layer in the present experiment (see Experimental Section for details).…”

Magnetic domain propagation in Pt/Co/Pt micro wires with engineered coercivity gradients along and across the wire

“…In electronics DWs can be used to store bits of information [14], to non-volatile register the magnetic fields [15], and to perform logic operations [16]. In medicine and biochemistry DWs can be used for transport of superparamagnetic particles (e.g., beads) functionalized with capture molecules for specific biomolecular sensing [17][18][19]. In these applications it is important to control the position of the DWs.…”