Ulrike Lehmann

Microfluidic applications of magnetic particles for biological analysis and catalysis

Keywords: Spin-Valve Sensors ; Cell Tracking Velocimetry ; On-A-Chip ; Polymerase-Chain-Reaction ; Total Analysis Systems ; Iron-Oxide Nanoparticles ; Field-Flow Fractionation ; Cross-Coupling Reactions ; Circulating Tumor-Cells ; Mode Magnetophoretic Microseparator Reference LMIS2-ARTICLE-2010-004doi:10.1021/cr9001929View record in Web of Science Record created on 2010-01-20, modified on 2016-08-08

Monolithic Silicon Chip for Immunofluorescence Detection on Single Magnetic Beads

While fluorescence detection is widely used for bioassays owing to its high sensitivity, a complete fluorescent microscopy setup, comprised of a light source, optical filters, a microscope body, and a camera, still is bulky equipment, compromising its use in a point-of-care environment. Here we propose an integrated monolithic silicon chip for integrated magnetic manipulation and optical detection of fluorescently labeled magnetic beads. Our approach permits microscopeless measurement of the fluorescence of a single microparticle. We demonstrate the viability of this approach by the detection of cancer biomarker 5D10 monoclonal antibodies (mAbs) in a noncompetitive sandwich immunoassay performed on the surface of magnetic beads, in a phosphate buffered saline-bovine serum albumin (PBS-BSA) solution, with a detection limit of 1 ng mL(-1).

Highly sensitive SnO2 sensor via reactive laser-induced transfer.

Gas sensors based on tin oxide (SnO2) and palladium doped SnO2 (Pd:SnO2) active materials are fabricated by a laser printing method, i.e. reactive laser-induced forward transfer (rLIFT). Thin films from tin based metal-complex precursors are prepared by spin coating and then laser transferred with high resolution onto sensor structures. The devices fabricated by rLIFT exhibit low ppm sensitivity towards ethanol and methane as well as good stability with respect to air, moisture, and time. Promising results are obtained by applying rLIFT to transfer metal-complex precursors onto uncoated commercial gas sensors. We could show that rLIFT onto commercial sensors is possible if the sensor structures are reinforced prior to printing. The rLIFT fabricated sensors show up to 4 times higher sensitivities then the commercial sensors (with inkjet printed SnO2). In addition, the selectivity towards CH4 of the Pd:SnO2 sensors is significantly enhanced compared to the pure SnO2 sensors. Our results indicate that the reactive laser transfer technique applied here represents an important technical step for the realization of improved gas detection systems with wide-ranging applications in environmental and health monitoring control.

A Cmos Microsystem Combining Magnetic Actuation and In-Situ Optical Detection of Microparticles

We present a CMOS-based hybrid microfluidic system that combines the manipulation of magnetic microparticles through a magnetic field with in situ optical detection via single photon avalanche diodes (SPADs). Magnetic particles are actuated within a glass micro-capillary and are detected upon passage over the SPAD, where they block incident light and thus lower the photon count. The optical sensors, which are not influenced by the magnetic actuation forces, allow detecting the presence of magnetic particles of 30, 5 and 1 mum diameter, while being able to distinguish between different sizes.

Actuation and Detection of Magnetic Microparticles in a Bio- analytical Microsystem with Integrated CMOS Chip

In this chapter, we present a hybrid microsystem that combines magnetic actuation with in situ optical detection. The chosen detection mechanism allows the observation and measurement of single magnetic microparticles of different sizes, as well as the detection of fluorescent labels attached to the particles’ surface. We are able to detect mouse IgG as target antigen in a sandwich immunoassay down to a concentration of 0.1 ng/ml. Our work represents a first step toward a full diagnostic LOC system for detection of specific antigens.

Two-dimensional magnetic droplet manipulation platform for miniaturized bioanalytical applications

We present a new approach for the manipulation of small liquid samples for the miniaturization of bioanalytical systems. In our system, minute liquid volumes are manipulated via the interaction of a changeable magnetic field and magnetic microparticles contained within aqueous droplets. Our setup enables the easy conversion of macroscopic bioanalytical protocols into the lab-on-a-chip format. Here we present the implementation of a DNA extraction and purification protocol as well as the on-chip optical detection of bioactive molecules. In both cases the miniaturization results in a decrease of the reaction and detection time as well as an increase in sensitivity.