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Lab-on-chip Systems Carrying Artificial Motors for Multiplexed and Multiparametric Biochemical Assays

Subject Area Microsystems
Analytical Chemistry
Biological Process Engineering
Term from 2019 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 413655771
 
Final Report Year 2023

Final Report Abstract

In this project, we focused on understanding of fuel-free visible light driven photocatalytic and electrokinetic Janus micromotors. In particular, we investigated the interaction of these motors with a complex fluidic microenvironment. This know-how is necessary for further development of novel bio- or chemosensory assays on a chip. An important aspect, which should be taken into consideration for these developments, is that Janus particles, driven by ionic selfdiffusiophoresis, are highly influenced by their own surface charges as well as the charge distribution at and electric potentials of nearby surfaces, e.g. substrate and/or surrounding active and passive particles. For instance, electrokinetic properties of active Janus particles enabled us to understand dynamics and develop design rules for new types of geometrically flat walls characterized by a soft-potential. We demonstrate that microchannels and fluidic circuits constructed based on soft-potential walls obey different rules for the objects passing through. In particular, such systems may offer efficient way to transport species through narrow channels and constrictions without clogging. This result is of high relevance for microfluidic systems, where the clogging of the channels is a frequent problem. Next important achievement is the understanding of the interaction of light driven Janus particles with surrounding passive beads. Particularly, we reported on the anisotropy of active-passive particle interaction in a soft matter system containing an immobile yet photochemical Ag/AgClbased Janus particle embedded in a dense matrix of passive beads in water. The asymmetry in the chemical gradient around the Janus particle, triggered upon visible light illumination, distorts the isotropy of the surrounding electric potential and results in the repulsion of adjacent passive beads to a certain distance away from the Janus particle. This exclusion effect is found to be anisotropic with larger distances to passive beads in front of the Ag/AgCl cap of the Janus particle. When the colloidal matrix and the density of micromotors become higher, the unusual processes of the colloidal ensemble solidification is observed. This defect-induced solidification occurs under non-equilibrium conditions: the resulting colloidal solid exists as long as a constant supply of energy in the form of ion flow is provided by the catalytic photochemical reaction at the surface of active Janus particle. The findings could be useful for the understanding of the phase transitions of matter under extreme conditions far from thermodynamic equilibrium. In addition to the fundamental activities on active soft matter, in the frame of the project we put much efforts on understanding of magnetic properties of magnetic thin films, which are deposited on curved surfaces of Janus particles. These activities led to unexpected fundamental discoveries in the area of magnetism of geometrically curved nanoobjects. We observed experimentally peculiar twist of the magnetic vortex string in thin films of permalloy prepared on curved surfaces of SiOx spherical particles. This effect was not reported before. This lack in fundamental knowledge in magnetism stimulated us to develop a micromagnetic theory of curvilinear micromagnetism accounting for local and nonlocal effects. Physically, this theory helped us to discover a novel non-local chiral symmetry breaking effect, which does not exist in planar magnets: it is essentially non-local and manifests itself even in static spin textures living in curvilinear magnetic nanoshells. These results made major contribution to the establishing the new research topic of “curvilinear micromagnetism”, which is actively explored by numerous groups worldwide. The results obtained in the frame of this DFG project provided a solid base in the understanding of active soft matter systems, such as light driven micromotors and their utility in microfluidic systems for bioanalytic purposes as well as curvature effects in magnetic geometrically curved architectures. This know-how resulted in new ideas, which allowed postdoctoral researchers contributing to the project as well as PIs of the project attracting third party funding from national (DFG) and European (RIA, ERC) funding agencies.

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