Showing papers by "Gerald Urban published in 2006"

Read-out concepts for multiplexed bead-based fluorescence immunoassays on centrifugal microfluidic platforms

Abstract: We present novel concepts to process and read out multiplexed, bead-based fluorescence immunoassays. At the start of the read-out process, a statistically arranged monolayer of color-encoded beads is aggregated in a detection chamber. Each bead is first identified by incorporated color tags which are either dyes or luminescing quantum dots (QDs). Subsequently, the reaction-specific fluorescence signal is quantified. The read-out process is accelerated by an in-house-developed image-processing algorithm. The optical read-out device consists of standard components, e.g. a color CCD-camera as detection unit, an LED as light source, optical filters, and a drive to spin the polymer disk. The liquid handling along the complete assay protocol is realized on a centrifugal lab-on-a-disk platform. We successfully demonstrate the performance of this device by the implementation of a hepatitis A and a tetanus assay. © 2005 Elsevier B.V. All rights reserved.

Sensitivity enhancement for colorimetric glucose assays on whole blood by on-chip beam-guidance.

Abstract: In this paper, we present a novel concept for optical beam-guidance to significantly enhance the sensitivity of colorimetric assays by extending the optical path length through the detection cell which linearly impacts the resulting attenuation of a probe beam according to the law of Beer-Lambert. In our setup, the incident probe beam is deflected by 90( composite function) into the chip plane at monolithically integrated V-grooves to pass a flat detection cell at its full width (i.e., with a path length of 10 mm) instead of its usually much smaller height. Afterwards, the attenuated beam is redirected by another V-groove towards an external detector. The general beam-guidance concept is demonstrated by a glucose assay on human whole blood on a centrifugal microfluidic "lab-on-a-disk" platform made of COC. We achieve an excellent linearity with a correlation coefficient (R (2)) of 0.997 paired with a lower limit of detection (200 microM) and a good reproducibility with a coefficient of variation (CV) of 4.0% over nearly three orders of magnitude. With an accelerated sedimentation of cellular constituents by centrifugal forces, the sample of whole blood can be analyzed in a fully integrated fashion within 210 s. This time-to-result can even be improved by the numerical extrapolation of the saturation value. Additionally, the direct assay on whole blood also shows a negligible correlation with the hematocrit of the blood sample.

Selective sample recovery of DEP-separated cells and particles by phaseguide-controlled laminar flow

Abstract: The selective recovery of particles is demonstrated after separation with dielectrophoretic (DEP) forces. Particles are separated based on their size using the so-called cage-speed separation protocol. A two-lane laminar flow enables the selective recovery of the particles. In order to prevent hydrostatic pressure flow, liquid reservoirs are absent. The sample liquid is thus replaced with air during recovery. Phaseguides are introduced in the system to control the liquid–air interface, so that the two-lane laminar flow profile is preserved.

A sensitive microsystem as biosensor for cell growth monitoring and antibiotic testing

Abstract: Standard bacterial tests such as growth inhibition tests are the only convenient investigation method to detect the impacts of water soluble drugs, e.g. antibiotics, on bacteria. State of the art methods for determining the inhibiting effect of toxic components are cumbersome, because they are for parallelization not feasible. The principle of these inhibition tests is the detection of cell numbers by measuring the optical density. With this time-consuming and complicate method only endpoint detection and no monitoring of cell growth is possible, which is obviously a drawback. Furthermore, colored and turbid components cannot be tested. A new microsystem is introduced in this paper overcoming the mention problems. A continuously working conductivity sensor system for high throughput application is developed. With this miniaturized system a reduction of sample volume from 50 ml down to 12 μl becomes possible. An additional advantage is the possibility of online monitoring during biological tests and cell growth detection in high turbid or colored samples, which could not be investigated before. The sensor system is calibrated for growth inhibition of Pseudomonas putida, tested with antibiotics.

A microsystem for growth inhibition test of Enterococcus faecalis based on impedance measurement

Abstract: Bacterial tests such as growth inhibition tests are the only convenient investigation method to detect the impacts of toxic water soluble materials, eg antibiotics, on bacteria The principle of these inhibition tests is the detection of cell numbers by measuring the optical density With this time consuming cumbersome and complicate method only endpoint detection and no monitoring of cell growth is possible In this paper we present a conductivity measurement system based on the theory of Maxwell–Fricke The intention of this work was to reduce the sample volume and have a standard screening platform, therefore we choose the 1536 microtiter plate format without a bottom foil as screening system for the growth inhibition test The equivalent circuit models of the electrode–electrolyte interface and their influence to biological species were discussed The presented sensor system in this paper can distinguish living and death cells during the continuous biomass monitoring

BioMEMS for the electrochemical detection of troponin I

Abstract: In this paper, a foil-based BioMEMS for the electrochemical detection of troponin I, a marker for myocardial infarction is presented.