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In this work we studied the influence of light emitting diode (LED) generated light on living cells which were cultivated in common cell culture microtiter plates. In detail we investigated signaling side effects including apoptosis by the use of a cell permeable peroxide activatable fluorescent dye (5,6-Chloromethyl-2′,7′-dichlorodihydrofluorescein diacetate). A high level production of peroxides in UV and blue light exposed cells was measured while the light of longer wavelengths caused only minor effects on the cells.

For most electrochemical impedance spectroscopy measurements Ferro-/Ferricyanide is used as redox-probe, but it has limitations in its application for biosensors based on gold electrodes because of chemical degradation induced by the Ferro-/Ferricyanide. The in-situ reduction of [Ru(NH3)6]3+ to [Ru(NH3)6]2+ by means of a direct current during EIS measurements is introduced to generate a stable redox-probe for biosensors. This method of enhanced EIS measurement has been applied to determine the charge transfer resistance of a human-IgG biosensor with a linear range from 0.9 to 50 mg/L IgG.

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 order to enable local functionalisation of label-free optical waveguide biosensors in a cost effective mass-fabrication compatible manner, we investigate surface modification employing inkjet printing of a) functional polymers (biotin-modified polyethyleneimine (PEI-B)) to implement high receptor densities at the surface and b) UV-curable benzophenone dextran (benzo-dextran) to form a voluminous porous hydrogel matrix. The combination of these approaches on a single chip is promising for the detection of biomolecules. We evaluate these functional polymers and hydrogels on an integrated four-channel silicon nitride (Si3N4) waveguide based Mach-Zehnder interferometric (MZI) sensor platform operating at a wavelength of 850nm (TM-Mode).

Inkjet printing is a versatile method to apply surface modification procedures in a spatially controlled, cost-effective and mass-fabrication compatible manner. Utilizing this technology, we investigate two different approaches for functionalizing label-free optical waveguide based biosensors: a) surface modification with amine-based functional polymers (biotin-modified polyethylenimine (PEI-B)) employing active ester chemistry and b) modification with dextran based hydrogel thin films employing photoactive benzophenone crosslinker moieties. Whereas the modification with PEI-B ensures high receptor density at the surface, the hydrogel films can serve both as a voluminous matrix binding matrix and as a semipermeable separation layer between the sensor surface and the sample. We use the two surface modification strategies both individually and in combination for binding studies towards the detection of the protein inflammation biomarker, C-reactive protein (CRP). For the specific detection of CRP, we compare two kinds of capture molecules, namely biotinylated antibodies and biotinylated CRP-specific DNA based aptamers. Both kinds of capture molecules were immobilized on the PEI-B by means of streptavidin-biotin affinity binding. As transducer, we use an integrated four-channel silicon nitride (Si3N4) waveguide based Mach-Zehnder interferometric (MZI) photonic sensing platform operating at a wavelength of 850nm (TM-mode).