Joerg Schotter

Homogeneous Biosensing Based on Magnetic Particle Labels.

The growing availability of biomarker panels for molecular diagnostics is leading to an increasing need for fast and sensitive biosensing technologies that are applicable to point-of-care testing. In that regard, homogeneous measurement principles are especially relevant as they usually do not require extensive sample preparation procedures, thus reducing the total analysis time and maximizing ease-of-use. In this review, we focus on homogeneous biosensors for the in vitro detection of biomarkers. Within this broad range of biosensors, we concentrate on methods that apply magnetic particle labels. The advantage of such methods lies in the added possibility to manipulate the particle labels by applied magnetic fields, which can be exploited, for example, to decrease incubation times or to enhance the signal-to-noise-ratio of the measurement signal by applying frequency-selective detection. In our review, we discriminate the corresponding methods based on the nature of the acquired measurement signal, which can either be based on magnetic or optical detection. The underlying measurement principles of the different techniques are discussed, and biosensing examples for all techniques are reported, thereby demonstrating the broad applicability of homogeneous in vitro biosensing based on magnetic particle label actuation.

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.

Air- and Water-Resistant Noble Metal Coated Ferromagnetic Cobalt Nanorods

Cobalt nanorods possess ideal magnetic properties for applications requiring magnetically hard nanoparticles. However, their exploitation is undermined by their sensitivity toward oxygen and water, which deteriorates their magnetic properties. The development of a continuous metal shell inert to oxidation could render them stable, opening perspectives not only for already identified applications but also for uses in which contact with air and/or aqueous media is inevitable. However, the direct growth of a conformal noble metal shell on magnetic metals is a challenge. Here, we show that prior treatment of Co nanorods with a tin coordination compound is the crucial step that enables the subsequent growth of a continuous noble metal shell on their surface, rendering them air- and water-resistant, while conserving the monocrystallity, metallicity and the magnetic properties of the Co core. Thus, the as-synthesized core-shell ferromagnetic nanorods combine high magnetization and strong uniaxial magnetic anisotropy, even after exposure to air and water, and hold promise for successful implementation in in vitro biodiagnostics requiring probes of high magnetization and anisotropic shape.

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.

Recognition of biomolecular interactions by plasmon resonance shifts in single- and multicomponent magnetic nanoparticles

Composite biomarkers open prospects to combine the targeting advantages of magnetic nanoparticles with direct plasmon-based optical detection of biomolecular interactions. Although nanoparticles from ferromagnetic 3d-transition metals could be suitable for such a task, they are shown to be rather large, thus tending to agglomerate in aqueous suspensions. A superior alternative uses composite nanoparticles consisting of a superparamagnetic core and a noble metal shell. Systematic Mie-theory based calculations of their plasmon peak shifts and sensitivity against biomolecular binding events on their surfaces are presented for this hybrid particle class.

Damascene Process for Controlled Positioning of Magnetic Colloidal Nanocrystals

2010 WILEY-VCH Verlag Gmb Size and composition of nanocrystals (NCs) allow tailoring their optical, magnetic or electronic properties. Incorporated at specific positions on a chip, they might offer specific functions, i.e., the construction of devices that could not be achieved with the host material only. Therefore magnetic and fluorescent colloidal nanoparticles have attracted a lot of interest owing to their potential in diverse fields ranging for example from biomedical, plasmonic, and photonic applications to nano-electromagnetic devices. Data storage devices, and lab-on-a-chip concepts are among the most promising applications for NCs. Singleferromagnetic-NC-based magnetic media are promoted as a candidate to replace conventional storagemedia due to their small dimensions and single-domain magnetism. Meanwhile, due to their low toxicity, magnetic NCs have exhibited great suitability in biomedical applications, such as DNA incubation, molecular detection, cell separation, etc. Towards these aims, significant progress has been made in the synthesis of magnetic NCs with well-defined compositions, shapes, structures, and sizes. Nevertheless, one major challenge remains, namely, to produce assemblies of colloidal magnetic NCs on well-controlled sites, which is essential to enable separate identification and addressability for single-magnetic nanoparticle units. The accurate positioning of a few, or even single NCs at well-defined sites of a patterned template is thus a precondition for many applications. Throughout the last decade a wide range of positioning methods have been investigated, involving, for example magnetic or electrostatic forces, sedimentation, layer-by-layer growth, lithography, and selective wetting. Although these early attempts were successful to some extent, the preparation of large-area ordered assemblies of single NCs with low defect density and a size down to or less than 20 nm still presents problems. Other methods taking advantage of selective adhesive host–guest interactions have been also reported but they cannot be regarded as generally applicable solutions since they are only effective for a specific type of NCs and substrate materials. Another strategy combines patterned templates and capillary forces or convective flow to assemble monodispersed spherical colloidal nanoparticles with sub-100-nm diameter into uniform aggregates with controlled sizes, shapes, and structures on a large area. The quality of structures prepared by using capillary forces, inevitably depends upon the flow speed, contact angle, temperature, density, etc. In this Communication, we report a straight-forward approach for large-scale nanofabrication with high accuracy following the same strategy as the well-established Damascene process in integrated circuit (IC) manufacturing. In the latter, metal interconnects are produced by depositing a thin Cu film on prepatterned Si wafers and constriction of the Cu film to connecting lines is achieved via a chemical–mechanical back polishing. In our work, the basic idea of this technique is utilized for controlled positioning of NCs by means of deposition on a prepatterned template and subsequent NC removal by polishing, which is practically independent of temperature and suspension conditions. Mechanical polishing generally refers to the use of cloth-covered plates and suitable polishing abrasives. The present work demonstrates the potential of such techniques to prepare assemblies of ordered NCs with a size down to 18 nm at low cost and great convenience. Another advantage of this approach is the absence of suspensions or any other solvent during the final processing step, which is an advantage with respect to environment-friendly production. This method allows arranging specific numbers of NCs down to single ones per pit. The structures produced were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), as well as magnetic force microscopy (MFM) at room temperature. Si (001) wafers were chosen as substrates. Patterning was achieved by twomethods: (i) by electron beam lithography using a LEO Supra 35 SEM system with a Raith Elphy electron beam writing unit and (ii) by direct structuring via a charged-particle nanopatterning (CHARPAN) technique, which features a programmable aperture plate system to achieve more than 40000 ion beams with <20 nm spot size. For (i) an electron resist

Homogeneous Protein Analysis by Magnetic Core-Shell Nanorod Probes.

Studying protein interactions is of vital importance both to fundamental biology research and to medical applications. Here, we report on the experimental proof of a universally applicable label-free homogeneous platform for rapid protein analysis. It is based on optically detecting changes in the rotational dynamics of magnetically agitated core-shell nanorods upon their specific interaction with proteins. By adjusting the excitation frequency, we are able to optimize the measurement signal for each analyte protein size. In addition, due to the locking of the optical signal to the magnetic excitation frequency, background signals are suppressed, thus allowing exclusive studies of processes at the nanoprobe surface only. We study target proteins (soluble domain of the human epidermal growth factor receptor 2 - sHER2) specifically binding to antibodies (trastuzumab) immobilized on the surface of our nanoprobes and demonstrate direct deduction of their respective sizes. Additionally, we examine the dependence of our measurement signal on the concentration of the analyte protein, and deduce a minimally detectable sHER2 concentration of 440 pM. For our homogeneous measurement platform, good dispersion stability of the applied nanoprobes under physiological conditions is of vital importance. To that end, we support our measurement data by theoretical modeling of the total particle-particle interaction energies. The successful implementation of our platform offers scope for applications in biomarker-based diagnostics as well as for answering basic biology questions.

Contemporaneous cell spreading and phagocytosis: magneto-resistive real-time monitoring of membrane competing processes.

Adhesion and spreading of cells strongly depend on the properties of the underlying surface, which has significant consequences in long-term cell behavior adaption. This relationship is important for the understanding of both biological functions and their bioactivity in disease-related applications. Employing our magnetic lab-on-a-chip system, we present magnetoresistive-based real-time and label-free detection of cellular phagocytosis behavior during their spreading process on particle-immobilized sensor surfaces. Cell spreading experiments carried out on particle-free and particle-modified surfaces reveal a delay in spreading rate after an elapsed time of about 2.2h for particle-modified surfaces due to contemporaneous cell membrane loss by particle phagocytosis. Our associated magnetoresistive measurements show a high uptake rate at early stages of cell spreading, which decreases steadily until it reaches saturation after an average elapsed time of about 100 min. The corresponding cellular average uptake rate during the entire cell spreading process accounts for three particles per minute. This result represents a four times higher phagocytosis efficiency compared to uptake experiments carried out for confluently grown cells, in which case cell spreading is already finished and, thus, excluded. Furthermore, other dynamic cell-surface interactions at nano-scale level such as cell migration or the dynamics of cell attachment and detachment are also addressable by our magnetic lab-on-a-chip approach.

Applications, Surface Modification and Functionalization of Nickel Nanorods

The growing number of nanoparticle applications in science and industry is leading to increasingly complex nanostructures that fulfill certain tasks in a specific environment. Nickel nanorods already possess promising properties due to their magnetic behavior and their elongated shape. The relevance of this kind of nanorod in a complex measurement setting can be further improved by suitable surface modification and functionalization procedures, so that customized nanostructures for a specific application become available. In this review, we focus on nickel nanorods that are synthesized by electrodeposition into porous templates, as this is the most common type of nickel nanorod fabrication method. Moreover, it is a facile synthesis approach that can be easily established in a laboratory environment. Firstly, we will discuss possible applications of nickel nanorods ranging from data storage to catalysis, biosensing and cancer treatment. Secondly, we will focus on nickel nanorod surface modification strategies, which represent a crucial step for the successful application of nanorods in all medical and biological settings. Here, the immobilization of antibodies or peptides onto the nanorod surface adds another functionality in order to yield highly promising nanostructures.

Next-Generation Magnetic Nanocomposites: Cytotoxic and Genotoxic Effects of Coated and Uncoated Ferric Cobalt Boron (FeCoB) Nanoparticles In Vitro

Metal nanoparticles (NPs) have unique physicochemical properties and a widespread application scope depending on their composition and surface characteristics. Potential biomedical applications and the growing diversity of novel nanocomposites highlight the need for toxicological hazard assessment of next‐generation magnetic nanomaterials. Our study aimed to evaluate the cytotoxic and genotoxic properties of coated and uncoated ferric cobalt boron (FeCoB) NPs (5–15 nm particle size) in cultured normal human dermal fibroblasts. Cell proliferation was assessed via ATP bioluminescence kit, and DNA breakage and chromosomal damage were measured by alkaline comet assay and micronucleus test. Polyacryl acid‐coated FeCoB NPs [polyacrylic acid (PAA)‐FeCoB NPs) and uncoated FeCoB NPs inhibited cell proliferation at 10 μg/ml. DNA strand breaks were significantly increased by PAA‐coated FeCoB NPs, uncoated FeCoB NPs and l‐cysteine‐coated FeCoB NPs (Cys‐FeCoB NPs), although high concentrations (10 μg/ml) of coated NPs (Cys‐ and PAA‐FeCoB NPs) showed significantly more DNA breakage when compared to uncoated ones. Uncoated FeCoB NPs and coated NPs (PAA‐FeCoB NPs) also induced the formation of micronuclei. Additionally, PAA‐coated NPs and uncoated FeCoB NPs showed a negative correlation between cell proliferation and DNA strand breaks, suggesting a common pathomechanism, possibly by oxidation‐induced DNA damage. We conclude that uncoated FeCoB NPs are cytotoxic and genotoxic at in vitro conditions. Surface coating of FeCoB NPs with Cys and PAA does not prevent but rather aggravates DNA damage. Further safety assessment and a well‐considered choice of surface coating are needed prior to application of FeCoB nanocomposites in biomedicine.