Dirk Herrmann

High-voltage contactless conductivity-detection for lab-on-chip devices using external electrodes on the holder

The detection of ionic species in a polymeric planar electrophoresis device by contactless conductivity measurement is described. To our knowledge this is the first report of such measurements carried out with external electrodes which are part of the holder rather than the separation chip itself. The approach allows the use of bare devices as used for optical measurements, which greatly simplifies the method. The use of a sine wave of 100 kHz of a high amplitude of 500 V for cell excitation assures high sensitivity which is demonstrated with electropherograms for alkali and heavy metal ions as well as inorganic anions and carboxylates at concentrations between 10 and 50 µM. The determination of underivatized amino acids was also possible by using a buffer in the alkaline region where these species are present in anionic form. Detection limits were found to be in the order of 1–5 µM for the inorganic ions and between about 5 and 50 µM for the organic species.

Further development of microstructured culture systems and their use in tissue engineering.

The Forschungszentrum Karlsruhe aims at improving its CellChip. Its main feature is the 1 cm2 core, subdivided into 900 cubic microcontainers (300 x 300 x 300 microns). It is manufactured by injection molding using biodegradable (polylactide) as well as non-degradable (PMMA or PC) polymers. The CellChips will be modified such that membranes will be mounted at the bottom of the CellChip, thus facilitating backend processing. Furthermore, the membranes can be adapted ideally to the assay system of interest by various surface modification techniques.

SmartHEALTH: a microfluidic multisensor platform for POC cancer diagnostics

A universal microfluidic platform as a multisensor device for cancer diagnostics, developed within the framework of the EU project SmartHEALTH [1], will be presented. Based on a standardization concept, a microfluidic platform was realized that contains various functional modules in order to allow in its final setup to run a complete diagnostic assay on a chip starting with sample preparation to a final detection via a sensor array. A twofold concept was pursued for the development and standardization: On the one hand, a standard footprint with defined areas for special functional elements was chosen, on the other hand a toolbox-approach [2] was used whereas in a first instance different functional fluidic modules were realized, evaluated and afterwards integrated into the microfluidic multisensor platform. One main characteristic of the platform is that different kind of sensors can be used with the same fluidic chip. For the read-out and fluidic control of the chip, common fluidic interfaces to the instrument were defined. This microfluidic consumable is a hybrid system consisting of a polymer component with an integrated sensor, reagent storage on chip, integrated valves and metering elements.

Polymer Micro Needles with Through-Going Capillaries

Removal or exact transfer of minimum substance volumes from reservoirs or micro fluidic systems (e.g. lab-on-a-chip systems) may be accomplished by using miniaturized tips with integrated through-going capillaries. A method to fabricate polymer micro needles with through-going capillaries by double-sided hot embossing has been developed.

Microfluidic polycarbonate chip for long-term cell analyses

Differentiation of stem cells to more specific tissue like heart, skin or nerve cells is influenced by long-range signaling molecules (morphogens). We designed a three-stacked microfluidic chip for long-term cultivation of cells to be probed with morphogen gradients to analyze this influence. We chose polycarbonate as material, which is commonly used in cytology. The microfluidic chip is made of two microstructured polycarbonate parts by hot embossing in a commercial polycarbonate foil. Each part contains one fluidic circuit: (1) the cell chamber part to cultivate and continuously supply the cells in and (2) the mixer part to form and provide a morphogen step gradient to these cells. A nanoperforated polycarbonate membrane embedded in-between the two parts allows exposing the cells to the provided step gradient. The two parts and the nanoperforated polycarbonate membrane of the microfluidic chip are assembled by a two-step thermal bonding process. We observed living and proliferating HeLa cells in the cell chamber part after six days of long-term cultivation. The activation of the Wnt/beta-catenin signaling pathway of HeLa cells in the cell chamber part was shown by applying a gradient of the Wnt pathway activator 6-bromoindirubin-3’-oxime (BIO) to the mixer part. We monitored the expected endogenous nuclear beta-catenin accumulation by fluorescence microscopy for those HeLa cells being exposed to a BIO concentration above the threshold. The presented microfluidic chips showed in a reproducible manner an adequate mechanical and chemical stability during the experiments. Polycarbonate is a material allowing for industrial mass production. Due to the three-stack design of the microfluidic chip, cells can be cultured under shear stress-free conditions and supplied continuously with culture medium, allowing for long-term experiments, while they are exposed to varying morphogen step gradients. We are convinced, that the differentiation of stem cells can be analyzed in a likewise microfluidic chip. Biomed Tech 2012; 57 (Suppl. 1)

MIKROSPITZEN AUS KUNSTSTOFF FÜR DIE MEDIKAMENTENAPPLIKATION

: Removal or exact transfer of minimum substance volumes from reservoirs or microfluidic systems may be accomplished by means of miniaturized tips with integrated through-going capillaries. Applications in biomedical engineering, e.g. for the application of drugs, or in life sciences, e.g. equipping of microarrays, require the use of disposable plastic products for hygienic reasons and reasons of costs. For this purpose, a method to fabricate microtips out of plastic by doublesided molding has been developed at the Forschungszentrum Karlsruhe.

LAB-ON-A-CHIP - SYSTEME FÜR DIE BIOMEDIZINISCHE FORSCHUNG UND DIAGNOSTIK

: In todays biomedical research and diagnosis, a number of substances and agents have to be checked. Frequently, plastic micro titer plates are used for this purpose as large-area test platforms. For the first time, plastic micro titer plates with 96 identical microfluidic labon-a-chip structures for simultaneous capillary electrophoresis (CE) have now been produced using microtechnical fabrication methods. Such structures are suited for e.g. the separation of biomolecules. In completely sealed microfluidic channel systems, smallest sample volumes can be processed, separated, mixed with other substances, or detected. Due to the small channel dimensions, these microfluidic systems are characterized by very small sample volumes needed.

Fabrication of Disposable Plastic Microplates with 96 Integrated Microfluidic Capillary Electrophoresis (CE) Structures for High Throughput Screening (HTS)

A novel microfluidic platform based on a standard microtiter plate has been developed by the Greiner Bio-One company and the Forschungszentrum Karlsruhe in Strategic cooperation. Instead of 96 wells, this novel platform accommodates 96 identical microfluidic CE structures on the same surface area (approx. 128 mm x 85 mm). The metal mold insert generated by micromilling possesses 96 inversely shaped CE structures that are molded into positive structures of PMMA or COC by vacuum hot embossing. In a further fabrication step, the obtained filigree microchannel structures are covered by an adapted, large-area cover plate to obtain real microcapillary structures. First tests demonstrated that these microcapillary structures have a good filling behavior. It may therefore be concluded that the channel geometry is accurate and homogeneous.