Publications

Externally controlled microswimmers offer prospects for transport in biological research and medical applications. This requires biocompatibility of the swimmers and the possibility to tailor their propulsion mechanisms to the respective low Reynolds number environment. Here, we incorporate low amounts of the biocompatible alloy of iron and platinum (FePt) in its L10 phase in microstructures by a versatile one-step physical vapor deposition process. We show that the hard magnetic properties of L10 FePt are beneficial for the propulsion of helical micropropellers with rotating magnetic fields. Finally, we find that the FePt coatings are catalytically active and also make for Janus microswimmers that can be light-actuated and magnetically guided.

The presence of a metallic layer can influence the properties of high-temperature superconductors underneath. We investigate the influence of metallic structures deposited in form of nanoparticles or continuous layers by electron beam evaporation or ion beam sputtering on the properties of Y1Ba2Cu3O7-x (YBCO) thin films. To generally avoid diffusion of metal atoms an additional barrier layer is introduced. Detailed measurements of the magnetic moment of the superconductor as a function of temperature and magnetic field have been performed using SQUID magnetometry. It is found that the modification of the superconducting properties of coated YBCO strongly depends on the deposition method of the metal on top rather than the type of metal (Ni or Ag), its magnetic properties (ferromagnetic or paramagnetic) or its morphology (nanoparticles or thin film). The main result is a transient increase of the critical temperature Tc and critical current density Jc that was observed for samples prepared by electron beam evaporation.

The application of nanoparticles for drug or gene delivery promises benefits in the form of single‐cell‐specific therapeutic and diagnostic capabilities. Many methods of cell transfection rely on unspecific means to increase the transport of genetic material into cells. Targeted transport is in principle possible with magnetically propelled micromotors, which allow responsive nanoscale actuation and delivery. However, many commonly used magnetic materials (e.g., Ni and Co) are not biocompatible, possess weak magnetic remanence (Fe3O4), or cannot be implemented in nanofabrication schemes (NdFeB). Here, it is demonstrated that co‐depositing iron (Fe) and platinum (Pt) followed by one single annealing step, without the need for solution processing, yields ferromagnetic FePt nanomotors that are noncytotoxic, biocompatible, and possess a remanence and magnetization that rival those of permanent NdFeB micromagnets. Active cell targeting and magnetic transfection of lung carcinoma cells are demonstrated using gradient‐free rotating millitesla fields to drive the FePt nanopropellers. The carcinoma cells express enhanced green fluorescent protein after internalization and cell viability is unaffected by the presence of the FePt nanopropellers. The results establish FePt, prepared in the L10 phase, as a promising magnetic material for biomedical applications with superior magnetic performance, especially for micro‐ and nanodevices.