Biomedical subjects

Roland Zengerle

Publications and source records attributed to Roland Zengerle.

9 recordsLinked to original sources

PubMed2006

Localized functional chemical stimulation of TE 671 cells cultured on nanoporous membrane by calcein and acetylcholine.

Acetylcholine sensitive TE 671 cells were cultured on nanoporous membranes and chemically stimulated by localized application of i), calcein-AM and ii), acetylcholine, respectively, onto the bottom face of the membrane employing an ink jet print head. Stimulus correlated response of cells was recorded by fluorescence microscopy with temporal and spatial resolution. Calcein fluorescence develops as a result of intracellular enzymatic conversion of calcein-AM, whereas Ca(2+) imaging using fluo-4 dye was employed to visualize cellular response to acetylcholine stimulation. Using 25 pl droplets and substance concentration ranging from 10 microM to 1 mM on Nucleopore membranes with pore diameters between 50 nm and 1 microm, a resolution on the order of 50 microm was achieved.

Acetylcholine↗

PubMed2006

Centrifugal extraction of plasma from whole blood on a rotating disk.

We present a centrifugal process for the extraction of plasma from sediment by a decanting structure, terminating with metered plasma which is readily available for subsequent on-disk processing. Our technique supplies 2 microl plasma from 5 microl of whole blood at moderate spinning frequencies of 40 Hz within 20 s, only. The residual cell concentration in the purified plasma amounts to less than 0.11%, independent of the frequency of rotation. A capillary duct connects the extracted plasma to subsequent on-disk processing units.

Blood↗

PubMed2005

Modification of micronozzle surfaces using fluorinated polymeric nanofilms for enhanced dispensing of polar and nonpolar fluids.

In this work, we report on the surface modification of a micronozzle surface to enhance fluid dispensing in the nanoliter range. Unmodified dispensing chips usually suffer from lateral wetting of the nozzle surfaces by low surface tension liquids resulting in poor control of the volume of the dispensed fluid. Covalent attachment of a fluorinated acrylate polymer to the outer surface of the micronozzle using a novel UV irradiation process helps to overcome capillary and adhesive forces and results in an enhancement of the control on fluid dispensing in the nanoliter range. The modified nozzles have been tested with a variety of fluids having a wide range of surface tensions. The surface modification allows precise control of the dispensing of nanoliter droplets with a high degree of reproducibility.

Fluorine Compounds↗

PubMed2005

Fast and reliable protein microarray production by a new drop-in-drop technique.

In contrast to DNA microarrays, production of protein microarrays is an immense technological challenge due to high complexity and diversity of proteins. In this paper we investigate three essential aspects of protein microarray fabrication based on the highly parallel and non-contact TopSpot technology: evaporation of probes during long lasting production times, optimization of protein immobilization and improvement of protein microarray reproducibility. Evaporation out of the printhead reservoirs was reduced to a minimum by sealing the reservoirs with gas permeable foils or PDMS frames. This led to dramatically lowered setup times through the possibility of long-term, ready-to-print storage of filled printheads. To optimize immobilization efficiency 128 printing buffers were tested by printing two different proteins onto seven different microarray slide types. This way we were able to reduce the CV of spot diameter on the microarray slide below 1.14%. To remarkably increase protein immobilization efficiency on microarray slides the commonly used EDC-NHS system (a laboratory method for immobilization of proteins) was miniaturized by using a new drop-in-drop printing technique. Additionally the very fast UV cross-linking was used to immobilize antibodies. The optimized system was used to produce antibody microarrays and with it microarray ELISA experiments were performed successfully.

Animals↗

PubMed2004

Frequency-dependent transversal flow control in centrifugal microfluidics.

This work presents a novel flow switch for centrifugal microfluidic platforms which is solely controlled by the Coriolis pseudo force. This Coriolis switch consists of an inverse Y-structure with one common upstream channel and two symmetric outlets on a rotating disk. Above a certain threshold frequency, the Coriolis force becomes dominant that the entire flow is diverted into one of the outlets which is selected by the direction of rotation. The threshold frequency has been measured to be 350 rad s(-1)(approximately 55.7 Hz) for a channel width of 360 microm and a depth of 125 microm. The results are supported by extensive CFD simulations.

Journal Article↗

PubMed2004

Non-contact production of oligonucleotide microarrays using the highly integrated TopSpot nanoliter dispenser.

For the first time we report on the production of oligonucleotide microarrays using a highly parallel and highly integrated, pressure driven TopSpot nanoliter dispenser. The system enables non-contact printing of different media like oligonucleotides, DNA or protein solutions. We optimized the printing buffer needed for oligonucleotides microarrays production with respect to two major aspects: microfluidical optimum for droplet dispensing and biochemical coupling efficiency on different commercially available microarray slides. Coefficient of variations (CVs) of generated spot diameters were measured to be smaller than 1% within one single dispensing nozzle and smaller than 1.5% within all 24 parallel nozzles of the printhead for all printing buffers used. No carry-over and no cross-talk was found, in extensive experiments with oligonucleotides. Optimized printing buffer compositions and concentrations for oligonucleotide microarrays were found, as well as optimized coupling protocols. Furthermore, buffers and protocols were adapted to a host of different microarray slides used. With this system, prime critical points of microarray production are solved, leading to high quality high throughput microarray fabrication.

Nanotechnology↗

PubMed2004

Aggregation of bead-monolayers in flat microfluidic chambers - simulation by the model of porous media.

In this paper, we for the first time simulate the process of hydrodynamic bead aggregation in a flat micro-fluidic chamber by a porous-media model in an iterative routine. This allows us to optimize the chamber design of our recently developed experimental method to form periodical monolayers from the flow of bead suspension. Periodical monolayers are advantageous for parallel assay formats since they enhance the mechanical rigidity of the aggregated pattern. This is important to avoid a spatial rearrangement along various steps of a read-out procedure which would impair the correlation between measurements. Furthermore, the monolayer formation guarantees the individual optical accessibility of all probe beads. By modelling the monolayers with porous media, we can drastically reduce the degrees of freedom in a two-phase, multi-particle problem. This way, we are able to compute stationary hydrodynamic flow patterns in the chamber. In order to simulate the complete filling process from these stationary solutions, we developed an iterative master routine which takes the transient aggregation pattern as the initial condition, then evaluates the placement of the newly introduced beads, and finally converts the points of aggregation into porous media.

Journal Article↗

PubMed2004

A highly parallel nanoliter dispenser for microarray fabrication.

We report about the correlation between satellite free droplet release and liquid viscosity in a highly parallel, pressure driven nanoliter dispenser. In extensive studies, we found that for liquids of different viscosities the duration of the pressure pulse is the predominant effect compared to pressure amplitude. This result is of essential importance when actuation parameters have to be adopted for different media like oligonucleotide, DNA or protein solutions as it is the case for the non-contact high throughput fabrication of microarrays (Ducree et al., 2000). Experiments with oligonucleotides as well as with different proteins showed ascertained carry-over and cross-contamination free printing of DNA and protein microarrays. With it a prime critical point of microarray production is solved, leading to high quality whilst high throughput microarray fabrication. For oligonucleotides printing, we found CVs to be better than 1% within one single dispensing channel and 1.5% within all 24 channels of a 24 channel printhead for each used printing buffer. By optimizing the protein printing buffer the CVs for protein printing were reduced to about 1% within all 24 channels. As a serious practical application test oligonucleotides microarrays were produced using our nanoliter dispenser system. With it a full DNA hybridization experiment was performed. Clear positive signals one hand and no signals in the negative controls on the other hand showed that our system is suited for microarray production.

Adsorption↗

PubMed2003

Highly parallel dispensing of chemical and biological reagents.

We present a technology for the highly parallel dispensing of a multitude of reagents. It allows one to dispense up to 96 different reagents simultaneously in a fixed array, in a volume range of 100 pL up to several nL. The pitch of the dispensed droplets can be as small as 500 microm. All channels are fired simultaneously, giving an unprecedented throughput. The system was originally developed for the high-throughput fabrication of microarrays, but can easily be adopted for other applications such as highly parallel filling of nanotiterplates. Based on our standard configuration we achieved droplets with 125- micro m in-flight diameter (1.2 nL) with a CV of <1%.

Buffers↗