Moritz Eggeling

Magnetoresistive-based real-time cell phagocytosis monitoring.

The uptake of large particles by cells (phagocytosis) is an important factor in cell biology and also plays a major role in biomedical applications. So far, most methods for determining the phagocytic properties rely on cell-culture incubation and end-point detection schemes. Here, we present a lab-on-a-chip system for real-time monitoring of magnetic particle uptake by human fibroblast (NHDF) cells. It is based on recording the time evolution of the average position and distribution of magnetic particles during phagocytosis by giant-magnetoresistive (GMR) type sensors. We employ particles with a mean diameter of 1.2 μm and characterize their phagocytosis-relevant properties. Our experiments at physiological conditions reveal a cellular uptake rate of 45 particles per hour and show that phagocytosis reaches saturation after an average uptake time of 27.7h. Moreover, reference phagocytosis experiments at 4°C are carried out to mimic environmental or disease related inhibition of the phagocytic behavior, and our measurements clearly show that we are able to distinguish between cell-membrane adherent and phagocytosed magnetic particles. Besides the demonstrated real-time monitoring of phagocytosis mechanisms, additional nano-biointerface studies can be realized, including on-chip cell adhesion/spreading as well as cell migration, attachment and detachment dynamics. This versatility shows the potential of our approach for providing a multifunctional platform for on-chip cell analysis.

Artificial cilia of magnetically tagged polymer nanowires for biomimetic mechanosensing

Polymeric nanowires of polypyrrole have been implemented as artificial cilia on giant-magneto-resistive multilayer sensors for a biomimetic sensing approach. The arrays were tagged with a magnetic material, the stray field of which changes relative to the underlying sensor as a consequence of mechanical stimuli which are delivered by a piezoactuator. The principle resembles balance sensing in mammals. Measurements of the sensor output voltage suggest a proof of concept at frequencies of around 190 kHz and a tag thickness of ∼300 nm. Characterization was performed by scanning electron microscopy and magnetic force microscopy. Micromagnetic and finite-element simulations were conducted to assess basic sensing aspects.

The Dependence of Vortex Oscillation Frequency on Small In-Plane Magnetic Fields in Spin-Valve Nanocontacts

In this work we investigate the magnetic field dependence of the precession frequency of vortex states in spin-valve nanocontacts with an amorphous CoFeB free layer and an artificial antiferromagnet as polarizer. The nanocontacts have radii between 70 and 90 nm. We show that the excitation frequency in these devices responds to small, in-plane magnetic fields along the easy and hard axis directions. The characteristics of the frequency response depend on the generated magnetic configuration under the nanocontact. This, in turn, results from the combined effect of the applied magnetic field and the current-generated Oersted field. Taking also into account the relative large nanocontact radii, a variety of vortex excitation modes can arise with distinctive frequency versus field responses, some of which could be considered for magnetic field sensing applications.

Low spin current-driven dynamic excitations and metastability in spin-valve nanocontacts with unpinned artificial antiferromagnet

This work investigates the spin-torque-related dynamics of nonuniform magnetic vortexlike states in spin-valve nanocontacts, employing an unpinned artificial antiferromagnet as polarizer and amorphous CoFeB as free layer. Subgigahertz spectra are obtained for contacts of 150–200 nm in diameter. Low critical current density and reversibility of the dynamic spectra with respect to the current are obtained. The spectral power and linewidth depend on the in-plane magnetic field, assuming maximum, respectively minimum, values within the free layer’s magnetization switching. For certain field and current windows metastable dynamic states are clearly demonstrated.

Silicon nitride waveguide integration platform for medical diagnostic applications

The impressive progress of silicon photonic integrated device technology during the past fifteen years has been primarily driven by the requirements of optical data- and telecommunication. Research and development in silicon photonics has therefore been focused on the telecom wavelengths in the 1.55 μm and 1.31 μm regions and on silicon-on-insulator (SOI) material as waveguide integration platform. The rising cost burden of the traditional healthcare system as well as the increasing health consciousness among people is stimulating the decentralization of healthcare and is creating a strong demand for novel medical diagnostic devices suitable for point-of-care testing. This opens up new possibilities for integrated nanophotonic sensing devices operating in the visible and <; 1.1 μm near infrared region. In this talk, we will present our ongoing research activities on the development of a CMOS-compatible photonic integrated circuit technology platform. This platform relies on silicon nitride waveguides fabricated by low-temperature plasma enhanced chemical vapor deposition (PECVD), which allows their monolithic co-integration with silicon photodiodes and CMOS based electronic read-out circuitry. We have achieved propagation losses of less than 1 dB/cm at a wavelength of 850nm in silicon nitride waveguides processed directly on an optoelectronic CMOS chip employing chemical-mechanical planarization (CMP). We will present the design and experimental validation of various nanophotonic building blocks required for the implementation of medical diagnostic sensing devices. We will show results of optical biosensing experiments based on integrated Mach-Zehnder interferometers and demonstrate how inkjet material printing technology can be effectively used to locally functionalize the optical waveguide transducer components. Moreover, we will discuss the potential of this silicon nitride waveguide based nanophotonic integration platform for the miniaturization of optical coherence tomography systems.

Progress in Using Magnetic Nanoobjects for Biomedical Diagnostics

A magnetic biochip using the combination of both magnetic nanoobjects as markers and magnetoresistive sensors has proven to be competitive to standard fluorescent DNA‐detection at low concentrations. Magnetic nanoobjects additionally provide the unique possibility to actively manipulate biomolecules, on‐chip, which paves the way to an integrated ‘magnetic lab‐on‐a‐chip’ containing detection and manipulation. It is shown that the hybridization process can be accelerated on a biochip. Looking forward, a paradigm change from the ‘magnetic lab‐on‐a‐chip’ to a ‘magnetic lab‐on‐a‐bead’ is discussed as a future device solution. The ferromagnetic nanoobjects themselves are thereby directly used both as molecular recognition site and as detection unit.