Optimization of turn geometries for microchip electrophoresis

Chip-based microcolumn separation systems often require serpentine channels to achieve longer separation lengths within a compact are;a. However, analyte bands traveling through curved channels experience an increased dispersion that can reduce the benefit of increased channel length. This paper presents analytical solutions for dispersions, numerical models for minimizing dispersion in microchannel turns, and experiments used to validate numerical models and to demonstrate the effectiveness of dispersion-reduction schemes. An analytical solution for the geometric dispersion caused by a constant radius turn is presented. We also propose metrics for characterizing the performance of miniaturized electrophoresis systems that utilize dispersion-introducing turns. The analytical solution and metrics can be used to determine when compensating turns should be used and when these turns are either not necessary or ineffective. For situations where a constant radius turn introduces significant geometric dispersion, numerical shape optimization routines were used to determine optimal geometries that minimize geometric dispersion while limiting reductions in channel width. Experiments using photobleached-fluorescence and caged-fluorescence visualization were conducted to validate the employed numerical models and to verify the turn designs proposed here.