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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 mu m 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 27.7 h. Moreover, reference phagocytosis experiments at 4 degrees 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. (C) 2012 Elsevier B.V. All rights reserved.

In this work we study the magnetic properties of 4-nm-thick permalloy films deposited into flat elliptical holes with an aspect ratio of 2:1 and short axis ranging from 2000 down to 70 nm. The holes are patterned into 50- and 200-nm-thick SiO 2 dielectric by e-beam lithography. The magnetization switching characteristics of the embedded magnetic elements were probed by localized magneto-optical Kerr effect and magnetic force microscopy measurements. It is shown that the switching mode, field and distribution depend on the hole depth and very strongly on the element's size, especially when the short axis shrinks below 100 nm. The results are compared with micromagnetic simulations.

In classical DNA chip analysis, the target DNA moves by diffusion and Brownian motion only. We introduce a system for enhancing the signals and reducing the hybridization times of bio chips. It allows active agitation within the hybridization buffer by controlled movement of magnetic particles within the analyte solution. First results show that the system easily achieves specific fluorescent signals about four times higher than the ones obtained by a referencing standard procedure within the same hybridization time, while unspecific signals remain unchanged. The device can easily be applied to existing bio chip applications and allows universal operation in the field of molecular diagnostics.

Ballistic electron emission microscopy (BEEM) is a three terminal extension of scanning tunneling microscopy and yields topographic and spectroscopic information on high-energy electron transport in semiconductors at nm-resolution. In BEEM on GaAs–AlGaAs double barrier resonant tunneling diodes (DBRTDs) ballistic electrons which tunnel through a resonant state inside the DBRTD result in a characteristic linear behavior in the BEEM spectrum. On DBRTDs nanostructured into narrow quantum wires, however, this tunneling is quenched for electron energies below the AlGaAs barrier heights. This quenching of the ballistic current can be explained in terms of a transfer Hamiltonian formalism applied to tunneling processes between electron systems of different dimensionality. We measured BEEM spectra on InAs self-assembled quantum dots (SAQDs) for positions on the dots and for “off-dot” regions on the so-called InAs wetting layer. From these data, we determined the local InAs–GaAs band offsets on the dots and on the wetting layer and investigated the temperature dependence of the InAs–GaAs barrier height.

This paper reports the well-controlled replication of nanostructures with features sizes as small as 50nm on the surface of polymethylpentene (PMP) substrates by injection molding. A 2'' silicon wafer carrying the nanostructures served as exchangeable mold insert. This PMP injection molding process is aimed at developing a planar optical polymer waveguide platform for evanescent wave sensing. In particular we focus on disposable polymer optical biochips for the label-free detection of bio-molecules.

In ballistic electron emission microscopy on Au–GaAs double barrier resonant tunneling diodes, electrons are transferred across an interface between an area of high and low effective mass and subsequently through a low-dimensional state. Experimentally, the resonant level in the double barrier structure becomes evident as clear step in the ballistic current measured as a function of sample bias. To analyze the spectrum, an extended transfer matrix method, together with the commonly accepted Bell Kaiser model is used. In terms of this model we show that only electrons with zero wave vector parallel to the barriers can be transmitted resonantly.

Ballistic electron emission microscopy (BEEM) has been used to study MBE grown Al 0.4 Ga 0.6 As/GaAs superlattice structures at variable temperature. The influence of the superlattice miniband manifests itself even at 300 K by a considerable lowering of the collector current threshold voltage compared to the threshold measured on samples with a thick Al 0.4 Ga 0.6 As barrier. On the other hand, reference samples with neither a superlattice nor a barrier give low thresholds, as expected for a Au/GaAs Schottky barrier. The temperature dependence of the threshold for the superlattice sample agrees excellently with self-consistent Schrodinger–Poisson calculations of the structure.

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 2.2 h 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. (C) 2012 Elsevier B.V. All rights reserved.

In ballistic electron emission microscopy on Au–GaAs double barrier resonant tunneling diodes, electrons are transferred across an interface between an area of high and low effective mass and subsequently through a low-dimensional state. Using an extended transfer matrix method, we show that in this situation only electrons with zero wave vector parallel to the barriers can be transmitted resonantly.

In Ballistic Electron Emission Microscopy, ballistic electrons are injected from a metallic base contact into a semiconductor. In the this experiment, the miniband of a GaAsAlGaAs superlattice is employed as energy filter in order to study the energetic distribution of the ballistic electrons injected into the semiconductor. It is found, that due to the large difference in electron mass between Au and GaAs, parallel momentum conservation leads to considerable electron refraction at the AuGaAs interface. Moreover, a resonant tunneling structure directly at the sample surface can act as momentum filter for electrons injected at k // =0.