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.

Design and performance of a microchip electrophoresis instrument with sensitive variable-wavelength fluorescence detection.

A modular instrument for high-speed microchip electrophoresis (MCE) equipped with a sensitive variable-wavelength fluorescence detection system was developed and evaluated. The experimental setup consists mainly of a lamp-based epifluorescence microscope for variable-wavelength fluorescence detection and imaging and a programmable four-channel bipolar high-voltage source capable of delivering up to +/- 10 kV per channel. The optical unit was equipped with a high-sensitivity photomultiplier tube and an adjustable aperture. The system was applied to MCE separations of flurescein isothiocyanate (FITC)-labelled amines utilizing blue light (450-480 nm) for excitation as well as for the separation of rhodamines utilizing excitation light in the green spectral region (531-560 nm). At optimized conditions baseline separation of four FITC-labelled amines could be obtained in less than 50 s at a detection limit of 460 ppt (1 nM) with a signal-to-noise ratio of 3:1. Three rhodamines could be baseline-separated in less than 6 s at a detection limit of 240 ppt (500 pM). The relative standard deviations of absolute migration times determined in repetitive MCE separations of FITC-labelled amines were below 2.5% (n= 25). By the application of cyclodextrin-modified electrolytes, chiral separation of FITC-labelled amines could be performed in seconds demonstrating the potential of microchip electrophoresis for chiral high-throughput screening.