Biomedical subjects

Karin M Balss

Publications and source records attributed to Karin M Balss.

5 recordsLinked to original sources

PubMed2006

Scanning temperature gradient focusing.

Temperature gradient focusing (TGF) is a recently developed technique for the simultaneous concentration and electrophoretic separation of ionic analytes in microfluidic channels. One drawback to TGF as it has previously been described is the limited peak capacity; only a small number of analyte peaks (approximately 2-3) can be simultaneously focused and separated. In this paper, we report on a variation of the TGF method whereby the bulk flow rate is varied over time so that a large number of analytes can be sequentially focused, moved past a fixed detection point, and flushed to waste. In addition to improved peak capacity, the detection limits of the scanning TGF method can be adjusted on-the-fly, as needed for different samples. Finally, scanning TGF provides a technique by which high-resolution, high-peak-capacity electrophoretic separations can be performed in simple, straight, and short microfluidic channels.

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PubMed2005

Nanosecond imaging of microboiling behavior on pulsed-heated au films modified with hydrophilic and hydrophobic self-assembled monolayers.

Fast transient microboiling has been characterized on modified gold microheaters using a novel laser strobe microscopy technique. Microheater surfaces of different hydrophobicity were prepared using self-assembled monolayers of hexadecane thiol (hydrophobic) and 16-mercaptohexadecanol (hydrophilic) as well as the naturally hydrophilic bare gold surface. The microheater was immersed in a pool of water, and a 5-micros voltage pulse to the heater was applied, causing superheating of the water and nucleation of a vapor bubble on the heater surface. Light from a pulsed Nd:Yag laser was configured to illuminate and image the sample through a microscope assembly. The timing of the short duration (7.5 ns) laser flash was varied with respect to the voltage pulse applied to the heater to create a series of images illuminated by the flash of the laser. These images were correlated with the transient resistance change of the heater both during and after the voltage pulse. It was found that hydrophobic surfaces produced a bubble that nucleated at an earlier time, grew more slowly to a smaller maximum size, and collapsed more rapidly than bubbles formed on hydrophilic surfaces.

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PubMed2004

Simultaneous concentration and separation of enantiomers with chiral temperature gradient focusing.

A new technique is demonstrated for the simultaneous concentration and high-resolution separation of chiral compounds. With temperature gradient focusing, a combination of a temperature gradient, an applied electric field, and a buffer with a temperature-dependent ionic strength is used to cause analytes to move to equilibrium, zero-velocity points along a microchannel or capillary. Different analytes are thus separated spatially and concentrated in a manner that resembles isoelectric focusing but that is applicable to a greater variety of analytes including small chiral drug molecules. Chiral separations are accomplished by the addition of a chiral selector, which causes the different enantiomers of an analyte to focus at different positions along a microchannel or capillary. This new technique is demonstrated to provide high performance in a number of areas desirable for chiral separations including rapid separation optimization and method development, facile reversal of peak order (desirable for analysis of trace enantiomeric impurities), and high resolving power (comparable to capillary electrophoresis) in combination with greater than 1000-fold concentration enhancement enabling improved detection limits. In addition, chiral temperature gradient focusing allows for real-time monitoring of the interaction of chiral analyte molecules with chiral selectors that could potentially be applied to the study of other molecular interactions. Finally, unlike CE, which requires long channels or capillaries for high-resolution separations, separations of equivalent resolution can be performed with TGF in very short microchannels (mm); thus, TGF is inherently much more suited to miniaturization and integration into lab-on-a-chip-devices.

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PubMed2004

DNA hybridization assays using temperature gradient focusing and peptide nucleic acids.

Two types of DNA hybridization assays are demonstrated with temperature gradient focusing (TGF) and peptide nucleic acids (PNAs). In TGF, the application of a controlled temperature gradient along the length of a microchannel filled with an appropriate temperature-dependent buffer results in the formation of a gradient in both the electric field and electrophoretic velocity. Ionic species move in this gradient and concentrate at a unique point where the total velocity sums to zero. The first assay is a mixing assay in which PNA is allowed to flow through spatially focused DNA targets within a capillary. The second assay detects single base pair mutations (SBPM) by monitoring the fluorescence intensity of PNA/DNA duplexes as a function of temperature within the capillary. The SBPM analysis can be performed in less than 5 min with 100-fold more dilute analyte compared to conventional UV melting measurements.

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PubMed2004

Micellar affinity gradient focusing: a new method for electrokinetic focusing.

This report describes a new method for the concentration and separation of neutral and/or hydrophobic analytes based on a combination of the analytes' electrophoretic mobility, and affinity for partitioning into a micellar phase. Micellar affinity gradient focusing (MAGF) works by creating a gradient in the micellar retention factor. An electric field is applied along the channel to cause the (negatively charged) micelles to move from the region of high retention to the region of low retention, and the mobile phase is forced to move from the region of low retention to the region of high retention. Consequently, the analyte moves into the gradient region from both directions where it is concentrated at a point where its total velocity is zero. Different analytes, which interact differently with the micelles, will have zero total velocity at different points along the gradient, and will thereby be simultaneously concentrated and separated.

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