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Biomedical subjects

Andreas Manz

Publications and source records attributed to Andreas Manz.

33 records · Page 2Linked to original sources
PubMed2004

Cyclic electrophoretic and chromatographic separation methods.

A review is given of the application of cyclic analytical methods in capillary electroseparation (CE) and liquid chromatography (LC) systems. Cyclic methods have been used since the early sixties in chromatographic systems to overcome pressure limitations to resolution. From the early nineties on they have also been applied in capillary electroseparation systems to overcome voltage limitations. Some basic theory is given, outlining the temporal development of resolution in cyclic CE and LC systems and calculating the maximal resolution that can be obtained as a function of the operational parameters of pressure and electrical field. Simple equations are given for the temporal change in the peak capacity and the loss of peaks from the systems as it occurs in some cyclic systems. Finally, a circular open tubular chromatographic system is proposed using integrated pumping and continuous detection. The performance of such a system is discussed using magnetohydrodynamic and alternating current electroosmotic pumping as examples of integrated pumps and Shah Convolution Fourier transform detection as an example of a continuous detection method.

Chromatography, Liquid↗
PubMed2003

High-speed free-flow electrophoresis on chip.

A microfluidic device has been developed for continuous separation in free-flow electrophoresis (FFE) mode. A mixture of two fluorescent reagents is separated into two component streams in 75 ms using a sample flow rate of 2 nL/s. The residence time of sample in the whole separation compartment is 2 s. The separation bed volume is 0.2 microL. The chip has also been used for free-flow electrophoresis of fluorescein-5-isothiocyanate-labeled amino acids in both aqueous and binary media. The short residence time and small sample flow rate make the FFE chip feasible for on-line monitoring on production lines and other chemical or biochemical processes. The in-house-made chip was composed of a plain glass substrate of 1.5-mm thickness and a PDMS layer of 0.3-mm thickness with micromachined channels. The channel design presented in this paper is versatile. With the same kind of PDMS substrates, chips for various purposes can be made depending on the locations of the reservoirs, which are cut out on the PDMS substrate. The results presented verify the scaling laws and allow prediction of FFE performances comparable to what is now state of the art on capillary electrophoresis chips.

Journal Article↗
PubMed2003

Sub-second isoelectric focusing in free flow using a microfluidic device.

Using a microfabricated chip with a bed volume of 0.2 microL we demonstrate the validity of the scaling laws for molecular mass transport of isoelectric focusing (IEF) in free flow. Nano- or microlitre sample volumes can be concentrated within 430 ms by a factor of up to 400. These very fast performances make the chip applicable to proteomic analysis and for continuous monitoring of biochemical processes.

Angiotensin I↗
PubMed2003

A microfluidic device with an integrated waveguide beam splitter for velocity measurements of flowing particles by Fourier transformation.

A microfabricated capillary electrophoresis device for velocity measurements of flowing particles is presented. It consists of a 1 x 128 planar waveguide beam splitter monolithically integrated with an electrically insulated fluidic channel network for fluorescence excitation at multiple points. Stray light rejection structures are included in order to suppress unwanted light between the detection regions. The emission pattern of particles passing the detection region was collected by a photomultiplier tube that was placed in close proximity to the channel, thereby avoiding the use of transfer optics. The integrated planar waveguide beam splitter was, furthermore, permanently connected to the light source by a glued-on optical fiber, to achieve a robust and alignment-free operation of the system. The velocity was measured using a Fourier transformation with a Shah function, since the response of the light array was designed to approximate a square profile. Deviations from this response were observed as a result of the multimode nature of the integrated waveguides.

Journal Article↗
PubMed2003

Guiding DC glow discharge in microchannels.

This work describes the conditions, in terms of dimensions and geometry, to guide a dc glow discharge preferentially through a microchannel in simple networks. Two- and three-channel microfluidic structures were studied. A preference towards a wider channel, in a two-channel network, was observed when the difference in width was at least 18% and the length was at least 10 mm. In a three-channel structure, a change in glow discharge intensity was observed when the network was downscaled from a pathlength of 2 to 0.5 cm. While the intensity within the path with fewer turns decreased with a reduction in size, the intensity of the path with greater number of turns increased.

Journal Article↗
PubMed2003

Counting and sizing of particles and particle agglomerates in a microfluidic device using laser light scattering: application to a particle-enhanced immunoassay.

A microfluidic device for counting and sizing particles and particle agglomerates based on laser light scattering is demonstrated. The particles were confined hydrodynamically and passed through a focused laser beam. Scattering at two different angles, 15 degree and 45 degree, was detected. At an acquisition rate of 10 kHz, a throughput of 150 particles s(-1) was achieved. Scattering intensity was found to depend on particle volume for 2 to 9 microm diameter particles. Size discrimination of particles with a diameter ratio of 1: 2 was accomplished. In addition, the scattering signals of particle agglomerates formed in a particle-enhanced immunoassay for C-reactive protein (CRP) were measured. Scattering intensity was found to be dependent on the CRP concentration, 100 ng CRP per mL could be detected. The particle counting method presented is generic and can be employed in a wide variety of assays as well as for cell counting and particle counting.

C-Reactive Protein↗
PubMed2003

Time-resolved Fourier transform infrared spectrometry using a microfabricated continuous flow mixer: application to protein conformation study using the example of ubiquitin.

We report on the use of time-resolved Fourier transform infrared spectroscopy (FT-IR) to study chemically induced conformational changes of proteins using the example of ubiquitin. For this purpose a micromachined mixer is coupled to a conventional IR transmission cell with a pathlength of 25 microm and operated in both the continuous and the stopped-flow mode. This experimental set-up allows the elucidation of reaction pathways in the time frame of about 500 milliseconds to seconds with little reagent consumption and low pressure. For continuous flow measurements employed in the time frame from 0.5 to 1.4 s the reaction time is determined by the flow rate used as the connection between the point of confluence in the micromixer and the flow cell was kept constant in all experiments. For stopped-flow experiments (>1.4 s) the time is determined by data acquisition of the rapid scanning infrared spectrometer. Ubiquitin, a small well-known protein with 76 amino acid residues, changes its conformation from native to A-state with the addition of methanol under low pH conditions. We investigated the conformational change in the time frame from 0.5 to 10 s by mixing ubiquitin (20% methanol-d(4)) with an 80% methanol-d(4) solution at pD 2 by evaluating the time dependent changes in the amide I band of the protein.

Amides↗
PubMed2003

Micromixer-based time-resolved NMR: applications to ubiquitin protein conformation.

Time-resolved NMR spectroscopy is used to studychanges in protein conformation based on the elapsed time after a change in the solvent composition of a protein solution. The use of a micromixer and a continuous-flow method is described where the contents of two capillary flows are mixed rapidly, and then the NMR spectra of the combined flow are recorded at precise time points. The distance after mixing the two fluids and flow rates define the solvent-protein interaction time; this method allows the measurement of NMR spectra at precise mixing time points independent of spectral acquisition time. Integration of a micromixer and a microcoil NMR probe enables low-microliter volumes to be used without losing significant sensitivity in the NMR measurement. Ubiquitin, the model compound, changes its conformation from native to A-state at low pH and in 40% or higher methanol/water solvents. Proton NMR resonances of the His-68 and the Tyr-59 of ubiquitin are used to probe the conformational changes. Mixing ubiquitin and methanol solutions under low pH at microliter per minute flow rates yields both native and A-states. As the flow rate decreases, yielding longer reaction times, the population of the A-state increases. The micromixer-NMR system can probe reaction kinetics on a time scale of seconds.

Kinetics↗
PubMed2003

Advances in capillary electrochromatography and micro-high performance liquid chromatography monolithic columns for separation science.

Over the last decade, monoliths or continuous beds have emerged as an alternative to traditional packed-bed columns for use in capillary electrochromatography (CEC) and micro-high performance liquid chromatography (micro-HPLC). Monolithic columns can be divided into two categories: silica-based monolithic columns and rigid organic polymer-based monolithic columns resulting from the polymerization of acrylamide, styrene, acrylate or methacrylate monomers. In this paper, the chemistry and most recent applications of these various types of monoliths in both CEC and micro-HPLC are presented.

Acrylates↗
PubMed2002

Three-dimensional microfluidic confinement for efficient sample delivery to biosensor surfaces. application to immunoassays on planar optical waveguides.

A microchip-based flow confinement method for rapid delivery of small sample volumes to sensor surfaces is described. For flow confinement, a sample flow is joined with a perpendicular makeup flow of water or sample medium. Under laminar flow conditions, the makeup flow confines the sample into a thin layer above the sensing area and increases its velocity. This can benefit mass transport limited processes such as DNA hybridization or heterogeneous immunoassays. For proof of concept, this method was applied to a high-affinity immunoassay with excess capture antibody. Rabbit IgG was immobilized onto a silicon nitride waveguide. Cy5-labeled anti-rabbit IgG was hydrodynamically pumped over the immobilized zone through an attached 3D-PDMS flow cell with 20-microm-deep microchannels. The degree of confinement was adjusted through the volume flow rate of the confining flow. Evanescent field-based fluorescence detection enabled monitoring of the binding event. Assays were allowed to reach equilibrium to enable sensorgram normalization for inter-run comparison. The corresponding assay completion times could be reduced from 55 min for static drop conditions to 13 min for 25:1 flow confinement (ratio of confining to sample flow). For typical analytical applications, where equilibrium formation is not required, the faster response should translate to very short analysis times. Concurrently with the faster binding, sample consumption was reduced by 96% compared to conventional whole-channel sample delivery. Diffusional loss of analyte into the confining layer was identified as the main limitation of flow confinement, particularly for long sensing pads.

Biosensing Techniques↗
PubMed2002

Evaporation driven pumping for chromatography application.

A continuous transport process for liquids in micro-channels is reported. Flow was generated by evaporation at the channel end plus capillary forces. The micro-channels integrated into a two-glass-layer device were 110 microm wide, 28 microm deep and 4 or 10 cm long. A continuous liquid transport velocity of up to 2.25 mm s(-1) was observed for aqueous solutions. The flow velocity is shown to increase when an air stream is guided over the evaporation zone.

Journal Article↗
PubMed2002

Glow discharge in microfluidic chips for visible analog computing.

Here we present a novel visible analog computing approach for solving a wide class of shortest path problems. Using a microfluidic chip for computation, based on the lighting up of a glow discharge, the solution to maze search problems, the solution of a network shortest path and k-shortest paths problems and the practical application of finding the shortest paths between several landmarks from a street map are presented. The solution and visible display (in real time) for these problems shows only a small difference in practical problem solving time among problems with varying differences in size.

Journal Article↗
PubMed2002

On-line on-chip post-column derivatisation reactions for pre-ionisation of analytes and cluster analysis in gradient micro-liquid chromatography/electrospray mass spectrometry.

A system is presented that demonstrates the principle of on-line and on-chip post-column derivatisation reactions in micro-high-performance liquid chromatography (micro-HPLC) hyphenated to electrospray time-of-flight mass spectrometry (ESI-TOFMS). In this micro-HPLC-chip-MS set-up, the analytes are separated using gradient micro-HPLC and subsequently derivatised on-chip and detected. One of the major limitations of MS detection is its dependency on the degree of ionisation, which is widely variable and compound-specific. Optimising and controlling the degree of ionisation in a simple manner would allow MS detection to be truly generic. One way of achieving this is by pre-ionisation of analytes using simple derivatisation procedures that are both rapid and quantitative. Performing this in situ on the system described here overcomes issues of sample handling and efficiency losses when time-consuming "bench chemistry" is necessary prior to analysis. The power of the system is demonstrated by the separation of primary and secondary amines, which are subsequently derivatised with a positively charged phosphonium complex and detected in an enhanced manner. Typically, molecular cations (M(+)) are detected showing that the ionisation process is dominated by the phosphonium species, leading to more constant ionisation for a variety of compounds. In addition, stable isotopically labelled ((12)C/(13)C)-phosphonium reagent is used for the reactions, allowing for inherent signal/noise (S/N) improvement and automated data processing using cluster analysis. A similar reaction scheme is used for the derivatisation of ketones and aldehydes, also demonstrating dramatic increases in sensitivity, especially with increasing temperature. Minimal loss in chromatographic fidelity in terms of retention times is observed by the introduction of the micromixer chip into the system. Optimal flow rates in micro-HPLC and ESI-MS are compatible with flow rates for the chip as well as a multitude of in-line optical detectors including UV and fluorescence. In addition, the micromixer chip can be positioned pre-column if preferred. The system is robust, easily fully automated and applicable to a wide variety of reactions. The system has a major advantage in its simple robust connection to the "normal scale" outside world.

Journal Article↗