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Göran Stemme

Publications and source records attributed to Göran Stemme.

14 recordsLinked to original sources
PubMed2007

A disposable lab-on-a-chip platform with embedded fluid actuators for active nanoliter liquid handling.

In this work we present the development of a disposable liquid handling lab-on-a-chip (LOC) platform with embedded actuators for applications in analytical chemistry. The proposed platform for nanoliter liquid handling is based on a thermally responsive silicone elastomer composite, consisting of PDMS and expandable microspheres. In our LOC platform, we integrate active dosing, transportation and merging of nanoliter liquid volumes. The disposable platform successfully demonstrates precise sample volume control with smart microfluidic manipulation and on-chip active microfluidic components. It is entirely fabricated from low-cost materials using wafer-level processing. Moreover, an enzymatic reaction and real-time detection was successfully conducted to exemplify its applicability as an LOC.

Chemistry Techniques, Analytical↗
PubMed2006

A micromachined interface for airborne sample-to-liquid transfer and its application in a biosensor system.

A novel micromachined interface for airborne sample-to-liquid adsorption and droplet-to-liquid transfer was designed and fabricated. It enables a robust sheet liquid flow serving as an adsorption site. The interface was characterised for flow and pressure properties and tested successfully for the transfer/adsorption of different samples. A qualitative theoretical model of the device characteristics is presented. We also used the interface to introduce a novel method and system for fast detection of dust- and vapour-based narcotics and explosives traces. The microfluidic vapour-to-liquid adsorption interface was coupled to a set of downstream QCM sensors. The system was tested successfully, with 50 ng cocaine samples rendering 15 Hz frequency shifts and with 100 ng heroine samples rendering 50 Hz frequency shifts. Gravitation invariance of the open liquid interface was demonstrated successfully, with the interface mounted upside down as well as vertically. The detection time was reduced to half of the time needed in previous systems. Machine size, weight and cost were reduced.

Adsorption↗
PubMed2006

Rapid melting curve analysis on monolayered beads for high-throughput genotyping of single-nucleotide polymorphisms.

This report describes a rapid solid-phase melting curve analysis method for single-nucleotide polymorphism (SNP) genotyping. The melting curve analysis is based on dynamic allele-specific hybridization (DASH). The DNA duplexes are conjugated on beads that are immobilized on the surface of a microheater chip with integrated heaters and temperature sensors. SNP on PCR products were scored, illustrating the sensitivity and robustness of the system. The method is based on random bead immobilization by microcontact printing. Single-bead detection and multiplexing were performed with a heating rate more than 20 times faster than conventional DASH. Analyses that took more than 15 min could be performed in less that 1 min, enabling ultrarapid SNP analysis. In addition, an array version of the chip was implemented enabling the preparation of an array of bead arrays for high-throughput and rapid SNP genotyping.

Alleles↗
PubMed2005

Pyrosequencing in a microfluidic flow-through device.

To explore genome variation meaningfully, there is a critical need for a high-throughput and inexpensive platform for DNA analysis. Pyrosequencing is a nonelectrophoretic bioluminometric DNA sequencing method that uses a four-enzyme mixture reaction to monitor nucleotide incorporation in real time. Currently, the commercialized pyrosequencing technique is limited to a 96-microtiter plate format. However, high throughput and inexpensive pyrosequencing is required to meet the need of screening large numbers of samples. We present here DNA pyrosequencing on a nanoliter-volume microfluidic platform. The microfluidic approach involves the trapping of the DNA on microbeads in an on-chip filter chamber and flow-through of the pyrosequencing reagents to monitor the reaction in real time. Two single-nucleotide polymorphisms were successfully scored to evaluate the microfluidic platform. In addition to significantly reducing reagent costs, microfluidic systems promise to improve the read length by eliminating intermediate product accumulation by constant removal of unincorporated nucleotides and elimination of dilution effects at each reaction cycle in the current plate format. Although only one filter chamber was used in this study, the platform should be readily adaptable to parallel analyses of nanoliter samples using filter chamber arrays to obtain high-throughput DNA analysis.

Base Sequence↗
PubMed2005

Behaviour and design considerations for continuous flow closed-open-closed liquid microchannels.

This paper introduces a method of combining open and closed microchannels in a single component in a novel way which couples the benefits of both open and closed microfluidic systems and introduces interesting on-chip microfluidic behaviour. Fluid behaviour in such a component, based on continuous pressure driven flow and surface tension, is discussed in terms of cross sectional flow behaviour, robustness, flow-pressure performance, and its application to microfluidic interfacing. The closed-open-closed microchannel possesses the versatility of upstream and downstream closed microfluidics along with open fluidic direct access. The device has the advantage of eliminating gas bubbles present upstream when these enter the open channel section. The unique behaviour of this device opens the door to applications including direct liquid sample interfacing without the need for additional and bulky sample tubing.

Equipment Design↗
PubMed2005

A concept for miniaturized 3-D cell culture using an extracellular matrix gel.

This paper presents a novel method to embed, anchor, and cultivate cells in a controlled 3-D flow-through microenvironment. This is realized using an etched silicon pillar flow chamber filled with extracellular matrix (ECM) gel mixed with cells. At 4 degrees C, while in liquid form, ECM gel is mixed with cells and injected into the chamber. Raising the temperature to 37 degrees C results in a gel, with cells embedded. The silicon pillars both stabilize and increase the surface to volume ratio of the gel. During polymerization the gel shrinks, thus creating channels, which enables perfusion through the chip. The pillars increase the mechanical stability of the gel permitting high surface flow rates without surface modifications. Within the structure cells were still viable and proliferating after 6 days of cultivation. Our method thus makes it possible to perform medium- to long-term cultivation of cells in a controlled 3-D environment. This concept opens possibilities to perform studies of cells in a more physiological environment compared to traditional 2-D cultures on flat substrates.

Animals↗
PubMed2004

A fast passive and planar liquid sample micromixer.

A novel microdevice for passively mixing liquid samples based on surface tension and a geometrical mixing chamber is presented. Due to the laminar flow regime on the microscale, mixing becomes difficult if not impossible. We present a micromixer where a constantly changing time dependent flow pattern inside a two sample liquid plug is created as the plug simply passes through the planar mixer chamber. The device requires no actuation during mixing and is fabricated using a single etch process. The effective mixing of two coloured liquid samples is demonstrated.

Journal Article↗
PubMed2004

Genotyping by dynamic heating of monolayered beads on a microheated surface.

A miniaturized bead-based dynamic allele-specific hybridization (DASH) approach for single-nucleotide polymorphism analysis is presented. Chips with integrated heater and temperature sensors for open-surface DNA analysis were microfabricated. Microcontact printing using a poly(dimethylsiloxane) (PDMS) stamp was employed to create monolayers of immobilized beads on the surface of the chip. This chip allows fast, well-controllable temperature ramping. The temperature distribution was homogeneous over the entire heater area. All three possible variants of an SNP site of a synthesized oligonucleotide were accurately scored using the bead-based DASH approach. Our assay has a nonoptimized temperature ramping rate of 4 degrees C-6 degrees C/min compared to earlier reported values of 2 degrees C-3 degrees C/min, thereby reducing the total analysis time by a factor of 2. Reliable DASH measurement data from areas as small as 12 x 13 microm was achieved. Our bead-based DASH approach has enabled a dramatic volume reduction and is a step towards developing a cost-effective high-throughput DASH method on arrays of single beads.

Alleles↗
PubMed2003

Single nucleotide polymorphism analysis by allele-specific primer extension with real-time bioluminescence detection in a microfluidic device.

A microfluidic approach for rapid bioluminescent real-time detection of single nucleotide polymorphism (SNP) is presented. The method is based on single-step primer extension using pyrosequencing chemistry to monitor nucleotide incorporations in real-time. The method takes advantage of the fact that the reaction kinetics differ between matched and mismatched primer-template configurations. We show here that monitoring the initial reaction in real time accurately scores SNPs by comparing the initial reaction kinetics between matched and mismatched configurations. Thus, no additional treatment is required to improve the sequence specificity of the extension, which has been the case for many allele-specific extension assays. The microfluidic approach was evaluated using four SNPs. Three of the SNPs included primer-template configurations that have been previously reported to be difficult to resolve by allele-specific primer extension. All SNPs investigated were successfully scored. Using the microfluidic device, the volume for the bioluminescent assay was reduced dramatically, thus offering a cost-effective and fast SNP analysis method.

Alleles↗
PubMed2003

Single-nucleotide polymorphism analysis by allele-specific extension of fluorescently labeled nucleotides in a microfluidic flow-through device.

We describe a microfluidic approach for allele-specific extension of fluorescently labeled nucleotides for scoring of single-nucleotide polymorphism (SNP). The method takes advantage of the fact that the reaction kinetics differs between matched and mismatched configurations of allele-specific primers hybridized to DNA template. A microfluidic flow-through device for biochemical reactions on beads was used to take advantage of the reaction kinetics to increase the sequence specificity of the DNA polymerase, discriminating mismatched configurations from matched. The volume of the reaction chamber was 12.5 nL. All three possible variants of an SNP site at codon 72 of the p53 gene were scored using our approach. This work demonstrates the possibility of scoring SNP by allele-specific extension of fluorescently labeled nucleotides in a microfluidic flow-through device. The sensitive detection system and easy microfabrication of the microfluidic device enable further miniaturization and production of an array format of microfluidic devices for high-throughput SNP analysis.

Alleles↗
PubMed2003

Characterization of micromachined hollow tips for two-dimensional nanoelectrospray mass spectrometry.

In this work an improved design of chip-based nanoelectrospray nozzles is reported. Two-dimensional matrices of out-of-plane 10 microm i.d. silicon dioxide tips with a tapered shape were manufactured using deep reactive ion etching technology. Using a peptide sample, six micromachined tips and six commercially pulled silica capillary tips were compared employing an ion trap mass spectrometer. At a flow rate of 100 nL/min, the detectability obtained was approximately the same for the two types of tips. The relative standard deviation of the signal-to-noise ratio for the peptides between six different tips was on average 22% for the micromachined tips and 45% for the pulled capillary tips. The usefulness of the micromachined tips for analysis of non-covalent protein-ligand complexes was demonstrated by the analysis of a sample of RNase A and cytidine 2'-monophosphate. In another test, analyzing a tryptic digest of 1 pmol/microL cytochrome C, 18 peptides corresponding to a 82% sequence coverage were detected. Using MS/MS, the whole sequence of an 11 amino acid cytochrome C fragment was obtained. Computer simulations were performed on the shape and magnitude of the electrical field around micromachined and pulled capillary tips. To reach the threshold electric field density at the tip apex required to initiate an electrospray, a higher electrospray voltage was needed for the chip-based tips compared with pulled capillary tips. This is due to the influence of the chip base.

Animals↗
PubMed2002

Expandable microspheres for the handling of liquids.

Two novel concepts for controlled handling of liquids in microfluidic systems are presented: a one-shot micropump and a normally open one-shot valve based on thermo-expanding Expancel microspheres. Expancel microspheres are small spherical plastic particles that, when heated, increase their volume considerably. We show that liquid volumes in the nanoliter range can be actuated against a counter pressure of at least 100 kPa and fluid flow can be inhibited in a microchannel against pressures of at least 100 kPa.

Journal Article↗
PubMed2002

Characterization of micromachined spiked biopotential electrodes.

We present the characterization of dry spiked biopotential electrodes and test their suitability to be used in anesthesia monitoring systems based on the measurement of electroencephalographic signals. The spiked electrode consists of an array of microneedles penetrating the outer skin layers. We found a significant dependency of the electrode-skin-electrode impedance (ESEI) on the electrode size (i.e., the number of spikes) and the coating material of the spikes. Electrodes larger than 3 x 3 mm2 coated with Ag-AgCl have sufficiently low ESEI to be well suited for electroencephalograph (EEG) recordings. The maximum measured ESEI was 4.24 k(omega) and 87 k(omega), at 1 kHz and 0.6 Hz, respectively. The minimum ESEI was 0.65 k(omega) an 16 k(omega), at the same frequencies. The ESEI of spiked electrodes is stable over an extended period of time. The arithmetic mean of the generated dc offset voltage is 11.8 mV immediately after application on the skin and 9.8 mV after 20-30 min. A spectral study of the generated potential difference revealed that the ac part was unstable at frequencies below approximately 0.8 Hz. Thus, the signal does not interfere with a number of clinical applications using real-time EEG. Comparing raw EEG recordings of the spiked electrode with commercial Zipprep electrodes showed that both signals were similar. Due to the mechanical strength of the silicon microneedles and the fact that neither skin preparation nor electrolytic gel is required, use of the spiked electrode is convenient. The spiked electrode is very comfortable for the patient.

Anesthesia, General↗