Highlights in 2020

We report that stray magnetic fields can code and decode a collection of hierarchically-assembled beads. By the microfluidic assembling of mesoscopic superparamagnetic cores, diverse and non-volatile stray magnetic field response can be built in the series of microscopic spheres, dumbbells, pears, chains and triangles. Remarkably, the set of stray magnetic field fingerprints are readily discerned by a compact giant magnetoresistance sensor for parallelised screening of multiple distinctive pathogenic DNAs. This opens up the magneto-multiplexing opportunity and could enable streamlined assays to incorporate magneto-mixing, washing, enrichment and separation of analytes. This strategy therefore suggests a potential point-of-care testing solution for efficient kinetic assays.

This work is a result of a fruitful cooperation between the Helmholtz-Zentrum Dresden-Rossendorf e.V., The University of Technology Sydney (group of Dr. Gungun Lin and Prof. Dayong Jin) and Minomic International Ltd. (group of Bradley J. Walsh).

Y. Liu, G. Lin, Y. Chen, I. Mönch, D. Makarov, B. J. Walsh, and D. Jin
Coding and decoding stray magnetic fields for multiplexing kinetic bioassay platform
Lab Chip 20, 4561 (2020). URL   

Droplet-based magnetofluidics emerged as a novel analytic tool encompassing integrated novel functionalities, e.g. analytics in a flow cytometry format, magnetic barcoding and sorting of magnetically encoded emulsion droplets. For these applications, high-performance magnetic field sensors have to be integrated in microfluidic geometries to enable real-time tracking of low concentrations of magnetic species in droplets as they flow by the sensor. To boost the limit of detection of droplet-based magnetofluidics, novel sensor solutions are needed. Here, we realize a droplet-based magnetofluidic platform based on planar Hall effect (PHE) sensors. We applied this platform for the detection and analysis of nanoliter-sized superparamagnetic droplets encapsulating a ferrofluid composed of 10 nm Fe3O4 nanoparticles at concentrations ranging from 0.04 to 5 mg/cm³. These concentrations are chosen due to their relevance for biological and medical applications like cancer thermotherapy and Magnetic Resonance Imaging (MRI). Our detection platform with geomagnetic field biasing (50 µT) outperforms by 10 times the state-of-the-art devices in droplet-based magnetofluidics with integrated GMR sensors yet biased to 1 mT fields. The detection limit of our platform can be pushed down to 0.04 mg/cm³ when biased with an external magnetic field of 5 mT, which constitutes 2 orders of magnitude enhancement over the state-of-the-art in droplet-based magnetofluidics. These results open the route for new strategies of the utilization of ferrofluids in microfluidic geometries in e.g. bio(-chemical) or medical applications.

This work is a result of a fruitful cooperation between the Helmholtz-Zentrum Dresden-Rossendorf e.V., Bar-Ilan University (group of Prof. Lior Klein), Ben-Gurion University of the Negev (group of Dr. Asaf Grosz) and Instituto Nacional de Technologia Industrial (group of Pablo N. Granell).

J. Schütt, R. Illing, O. Volkov, T. Kosub, P. N. Granell, H. Nhalil, J. Fassbender, L. Klein, A. Grosz, and D. Makarov
Two orders of magnitude boost in the detection limit of droplet-based micro-magnetofluidics with planar Hall Effect sensors
ACS Omega 5, 20609 (2020). URL PDF   

We introduced a novel strategy to fabricate Janus micromotors through a microfluidic method by adhering functional nanoparticles (NPs) onto microspheres functionalized with a photocurable hydrogel precursor. The proposed approach allows us to fabricate Janus particles with tunable coverage of a hydrogel sphere with functional NPs (including photocatalytic TiO2, magnetic Fe3O4 and catalytic MnO2), hence enabling a straightforward tailoring of physical and chemical responses of the capped spheres under external stimuli (UV light illumination, concentration of H2O2 and magnetic field). The method can be readily extended to prepare multifunctional Janus micromotors by using various kinds of functional NPs (e.g., catalytic MnO2 and magnetic Fe3O4) during the fabrication. In addition to the detailed study of the fundamentals of the complex motion dynamics of Janus spheres, we revealed the potential of our TiO2 Janus microspheres for performing useful tasks in environmental applications with the focus on water purification.

This work is a result of a fruitful cooperation between the HZDR and the group of Prof. Yongfeng Mei at the Fudan University in Shanghai, China.

X. Lin, H. Zhu, Z. Zhao, C. You, Y. Kong, Y. Zhao, J. Liu, H. Chen, X. Shi, D. Makarov, and Y. F. Mei
Hydrogel-based Janus Micromotors Capped with Functional Nanoparticles for Environmental Applications
Adv. Mater. Technol. 5, 2000279 (2020). URL PDF   

We studied the anisotropy in the interaction of visible light-driven Ag/AgCl-based spherical Janus particles embedded in a dense matrix of passive SiO2 beads in pure water. We observe an anisotropic profile of the repulsive interaction between immobile active Janus particles and passive beads and explain it as a result of an asymmetry in the chemical gradient around the Janus particle, triggered upon visible light illumination. This leads to the distortion in the initially isotropic surrounding electric potential and results in the asymmetric exclusion of passive beads around the Ag/AgCl cap. With this study, we provide new insights into the rotational dynamics of photocatalytically active Janus particles embedded in a dense matrix of passive beads. We anticipate that these phenomena, peculiar for electro-kinetic motors, can be observed only due to the confinement imposed by a dense environment.

This work is the result of a fruitful cooperation between the Helmholtz-Zentrum Dresden-Rossendorf e.V., Dresden University of Technology (group of Dr. Larysa Baraban), Vrije Universiteit Brussel (Dr. Vyacheslav R. Misko), RIKEN Cluster for Pioneering Research (Prof. Franco Nori).

T. Huang, S. Gobeil, X. Wang, V. Misko, F. Nori, W. De Malsche, J. Fassbender, D. Makarov, G. Cuniberti, and L. Baraban
Anisotropic exclusion effect between photocatalytic Ag/AgCl Janus particles and passive beads in a dense colloidal matrix
Langmuir 36, 7091 (2020). URL