Hubert Brueckl

Multispectral microbolometers for the midinfrared

The spectral responsivity and the dynamic behavior of microbolometers with an integrated absorbing metamaterial are investigated. Wavelength tailoring and tuning in different microbolometers are achieved by varying the lateral extension of the absorber elements. Maximum sensitivity is tuned between 2.9 and 7.7 μm, with peak absorptions reaching up to 88%. The presence of a continuous metallic shielding layer affects heat conduction and leads to faster thermal response times.

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.

Thermal switching field distribution of a single domain particle for field-dependent attempt frequency

We present an analytical derivation of the switching field distribution (SFD) at finite temperature for a single domain particle from the Neel-Brown model in the presence of a linearly swept magnetic field. By considering the field dependence of the attempt frequency f0 in the rate equation, we find enhancement of coercivity compared to models using constant f0. The contribution of thermal fluctuations to the standard deviation of the switching field HC derived here reaches values of 10% HC. Considering this contribution, which has been neglected in previous work, is important for the correct interpretation of measurements of switching field distributions.

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.

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.

Microfluidic chips fabrication from UV curable adhesives for heterogeneous integration

Conventional fabrication of microfluidic chips is based on silicon, glass, PDMS and various other polymeric materials (COC, polycarbonate, PMMA etc). Silicon and glass processing technologies are highly developed and the chips can be fabricated with ease. Polymeric microfluidic chips have become very common in recent years due to the demand for the cheap and disposable devices. New entrants in to the field are UV curable adhesives which are gaining recognition as promising players in microfluidics. UV curable adhesives are generally used in various applications ranging from usage in the manufacture of parts of an aircraft to sealing/packaging of microfluidic chips. Unlike any other previously discussed materials UV curable adhesives have the flexibility in alignment and bonding during fabrication process. These adhesives can be applied in between two surfaces which are to be glued and can be left like that for hours to days without bonding them as long as the glue is not exposed to UV light. In this paper we explain the detailed fabrication of microfluidic chips (100μm wide and 3μm (NOA74), 22μm (NOA 68) deep) completely made from UV curable adhesives having better chemical resistance, permeability and flexible surface treatments compared to other known polymeric materials. Firstly the patterns were etched on silicon, followed by PDMS molding and subsequently UV curable adhesives were casted and cured on structured PDMS master. After unmolding the stamps were mounted on a glass substrate and permanent bonding was achieved by further UV treatment and/or oxygen plasma treatment. The final devices were successfully tested for any leakage. These microfluidic chips will be integrated with a sensor and antenna for further biological studies. UV curable adhesives are also used for permanent/temporary sealing of microfluidic channels. These adhesives, which are still new to the fluidics branch can functionally and economically, have a greater impact on microfluidics.

Fabrication of nanoparticles for biosensing using UV-NIL and lift-off

A novel technique to realize large quantities of stacked multifunctional anisotropic nanoparticles with narrow size distribution is presented. Through the combination of Ultraviolet Nano-Imprint Lithography (UV-NIL), physical vapor deposition and subsequent lift-off processes we fabricate and disperse these particles in solution for the use in biomolecular sensing applications. Compared to chemical nanoparticle synthesis our approach holds several advantages. First, one can control the nanoparticle shape by choosing an appropriate nanopattern for the UV-NIL process. Second, we can choose the composition of the nanoparticles as the materials are deposited layer-wise by sputter deposition. Third, we can fabricate nanoparticles with very small geometrical variations. This is in contrast to chemical synthesis methods where the layer thicknesses and particle size distribution are harder to control.

Vortex magnetization state in a GMR spin-valve type field sensor

Micromagnetic sensors, viz., Hall elements, fluxgate, magnetoresistance and magnetoimpedance sensors, play a major role towards the miniaturization in the industrial society.

A device model framework for magnetoresistive sensors based on the Stoner–Wohlfarth model

Abstract The Stoner–Wohlfarth (SW) model provides an efficient analytical model to describe the behavior of magnetic layers within magnetoresistive sensors. Combined with a proper description of magneto-resistivity an efficient device model can be derived, which is necessary for an optimal electric circuit design. Parameters of the model are determined by global optimization of an application specific cost function which contains measured resistances for different applied fields. Several application cases are examined and used for validation of the device model.