Biomedical subjects

Frank Kohler

Publications and source records attributed to Frank Kohler.

4 recordsLinked to original sources

PubMed2006

Coating of powder-blasted channels for high-performance microchip electrophoresis.

Channels in microfluidic glass chips manufactured with the alternative powder blasting technology were permanently coated with poly(vinyl alcohol) (PVA) in order to improve the performance in microchip electrophoresis. The performance of coated and uncoated powder-blasted (pb) devices as well as coated and uncoated wet chemical etched (wc) chips was compared in electrophoretic separations of fluorescently labeled test compounds. The limited electrophoretic resolution obtained in pb-chips could significantly be improved by coating the channels with PVA. The resolution of test compounds in such coated pb-devices was even higher than in uncoated wc-chips. PVA-coated pb-chips could also successfully be applied in chiral separations. While in an uncoated pb-chip using a cyclodextrins buffer only one broad signal was obtained, two well-resolved signals were obtained in a coated device.

Electrophoresis, Microchip↗

PubMed2005

Deep UV laser-induced fluorescence detection of unlabeled drugs and proteins in microchip electrophoresis.

Deep UV fluorescence detection at 266-nm excitation wavelength has been realized for sensitive detection in microchip electrophoresis. For this purpose, an epifluorescence setup was developed enabling the coupling of a deep UV laser into a commercial fluorescence microscope. Deep UV laser excitation utilizing a frequency quadrupled pulsed laser operating at 266 nm shows an impressive performance for native fluorescence detection of various compounds in fused-silica microfluidic devices. Aromatic low molecular weight compounds such as serotonin, propranolol, a diol, and tryptophan could be detected at low-micromolar concentrations. Deep UV fluorescence detection was also successfully employed for the detection of unlabeled basic proteins. For this purpose, fused-silica chips dynamically coated with hydroxypropylmethyl cellulose were employed to suppress analyte adsorption. Utilizing fused-silica chips permanently coated with poly(vinyl alcohol), it was also possible to separate and detect egg white chicken proteins. These data show that deep UV fluorescence detection significantly widens the application range of fluorescence detection in chip-based analysis techniques.

Chymotrypsinogen↗

PubMed2003

High-speed chiral separations on a microchip with UV detection.

Fast chiral separations of a variety of basic and acidic compounds could be realized on microfluidic quartz chips. A microchip electrophoresis instrument equipped with a linear imaging UV-detector was used. The usually applied but troublesome fluorescence tagging in order to enable fluorescence detection could be omitted. Using sulfated cyclodextrins as chiral selectors baseline separation of 19 compounds could be achieved in less than 1 min with high reproducibility. The relative standard deviation of migration time was below 7%. The fastest separation could be performed in 2.5 s which is to date the fastest separation of enantiomers reported. It was possible to apply microchip electrophoresis (MCE) for the determination of high enantiomeric excess (ee) values, as exemplarily shown for pseudoephedrin where 2% of the minor enantiomer could reliably be determined beside high amount of the other isomer. Successful separation of a mixture of 3 chiral drugs could be performed in a single run in less than 11 s utilizing a separation length of only 12 mm. These results show that MCE has great potential for fast chiral analysis and high-throughput screening.

Buffers↗

PubMed2002

Poly(vinyl alcohol)-coated microfluidic devices for high-performance microchip electrophoresis.

The channels of microfluidic glass chips have been coated with poly(vinyl alcohol) (PVA). Applied for microchip electrophoresis, the coated devices exhibited a suppressed electroosmotic flow and improved separation performance. The superior performance of PVA-coated channels could be demonstrated by electrophoretic separations of labeled amines and by video microscopy. While a distorted sample zone is injected using uncoated channels the application of PVA-coated channels results in an improved shape of the sample zone with less band broadening. Applying PVA-coated microchips for the separation of amines labeled with Alexa Fluor 350 even sub-second separations, utilizing a separation length of only 650 microm, could be obtained, while this was not possible using uncoated devices. By using PVA-coated devices rather than an uncoated chip a threefold increase in separation efficiencies could be observed. As the electroosmotic flow (EOF) was suppressed, the anionic compounds were detected at the anode whereas the dominant EOF in uncoated devices resulted in an effective mobility to the cathode. Besides improved separation performance another important feature of the PVA-coated channels was the suppressed adsorption of fluorescent compounds in repetitive runs which results in an improved robustness and detection sensitivity. Applying PVA-coated channels, rinsing or etching steps could be omitted while this was necessary for a reliable operation of uncoated devices.

Amines↗