Biomedical subjects

Steffen Hardt

Publications and source records attributed to Steffen Hardt.

3 recordsLinked to original sources

PubMed2005

Automated chip-based device for simple and fast nucleic acid amplification.

A chip-based PCR device is presented that is capable of rapid temperature ramping and handling sample volumes in the microliter range. The PCR chip comprises a microchannel thermally connected to three temperature zones. Inside this microchannel, the PCR sample plug is driven and precisely positioned by a ferrofluidic actuator for more than 40 cycles within 5 min. Computer simulations predict that the sample plugs are thermally equilibrated on a time scale of some 10 ms when transported to a different temperature zone. Hence, the thermal limitations on the cycle speed of the system are considerably reduced compared with conventional cyclers. The system was developed on a modular platform suitable for handling further microfluidic tasks such as DNA extraction and preparation of the PCR mix. Thus, the aspired chip-based platform represents not only a PCR system but a complete analysis system, from the injection of a patient's blood sample to its final appraisal.

Automation↗

PubMed2003

Integrated polymer chip for two-dimensional capillary gel electrophoresis.

Two-dimensional (2D) gel electrophoresis (GE) is one of the most powerful methods for nucleic acid and protein separation, but generally suffers from high laboratory efforts connected with high analysis costs. Therefore, we herein present the development of a miniaturized 2D capillary GE (CGE) device which allows for an efficient protein separation in analysis times of about 1.5 h. This integrated 2D-CGE chip comprises a first channel for isoelectric focussing (IEF), a second specially designed transfer channel, 300 parallel micro channels, each having a cross section of 50 microm x 50 microm, and buffer reservoirs. The present work discusses fabrication aspects, in particular the combination of different microfabrication technologies, experimental separation performances of isoelectric focussing (IEF) and CGE, and presents computer simulations and first experimental results of protein transfer from the first to the second dimension.

Animals↗

PubMed2002

Contactless conductivity detector for microchip capillary electrophoresis.

A microfabricated electrophoresis chip with an integrated contactless conductivity detection system is described. The new contactless conductivity microchip detector is based on placing two planar sensing aluminum film electrodes on the outer side of a poly(methyl methacrylate) (PMMA) microchip (without contacting the solution) and measuring the impedance of the solution in the separation channel. The contactless route obviates problems (e.g., fouling, unwanted reactions) associated with the electrode-solution contact, offers isolation of the detection system from high separation fields, does not compromise the separation efficiency, and greatly simplifies the detector fabrication. Relevant experimental variables, such as the frequency and amplitude of the applied ac voltage or the separation voltage, were examined and optimized. The detector performance was illustrated by the separation of potassium, sodium, barium, and lithium cations and the chloride, sulfate, fluoride, acetate, and phosphate anions. The response was linear (over the 20 microM-7 mM range) and reproducible (RSD = 3.4-4.9%; n = 10), with detection limits of 2.8 and 6.4 microM (for potassium and chloride, respectively). The advantages associated with the contactless conductivity detection, along with the low cost of the integrated PMMA chip/detection system, should enhance the power and scope of microfluidic analytical devices.

Anions↗