Micropreparative fraction collection in microfluidic devices.

Micropreparative fraction collection following microchip-based electrophoretic analysis of biomolecules is of major importance for a variety of biomedical applications. In this paper, we present a microfabricated device-based fraction collection system. Various size DNA fragments were separated and collected by simply redirecting the desired portions of the detected sample zones to corresponding collection wells using appropriate voltage manipulations. The efficiency of sampling and collection of the fractions was enhanced by placing a cross channel at or downstream of the detection point. Following the detection of the band of interest, the potentials were reconfigured to sampling/collection mode, so that the selected sample zone migrated to the appropriate collection well of the microdevice. The potential distribution assured that the rest of the analyte components in the separation column was retarded, stopped, or reversed, increasing in this way the spacing between the sample zone being collected and the immediately following one. By this means, a precise collection of spatially close consecutive bands could be facilitated. Once the target sample fraction reached the corresponding collection well, the potentials were switched back to separation mode. Alternation of the separation/detection and sampling/collection cycles was repeated until all required sample zones were physically isolated. The integrated device consists of a sample introduction, separation, fraction sampling, and fraction collection compartments. The feasibility of the fraction collection technique was tested on a mixture of dsDNA fragments. The amounts of DNA collected in this way were enough for further downstream sample processing, such as conventional PCR-based analysis.