Impact of polymer hydrophobicity on the properties and performance of DNA sequencing matrices for capillary electrophoresis

To elucidate the impact of matrix chemical and physical properties on DNA sequencing separations by capillary electrophoresis (CE), we have synthesized, characterized and tested a controlled set of different polymer formulations for this application. Homopolymers of acrylamide and N,N-dimethylacrylamide (DMA) and copolymers of DMA and N,N-diethylacrylamide (DEA) were synthesized by free radical polymerization and purified. Polymer molar mass distributions were characterized by tandem gel permeation chromatography - laser light scattering. Polymers with different chemical compositions and similar molar mass distributions were selected and employed at the same concentration so that the variables of comparison between them were hydrophobicity and average coil size in aqueous solution. We find that the low-shear viscosities of 7% w/v polymer solutions decrease by orders of magnitude with increasing polymer hydrophobicity, while hydrophilic polymers exhibit more pronounced reductions in viscosity with increased shear. The performance of the different matrices for DNA sequencing was compared with the same sample under identical CE conditions. The longest read length was produced with linear polyacrylamide (LPA) while linear poly-N,N-dimethylacrylamide (PDMA) gave similar to 100 fewer readable bases. Read lengths with DMA/DEA copolymers were lower, and decreased with increasing DEA content. This study highlights the importance of polymer hydrophilicity for high-performance DNA sequencing matrices, through the formation of robust, highly-entangled polymer networks and the minimization of hydrophobic interactions between polymers and fluorescently-labeled DNA molecules. However, the results also show that more hydrophobic matrices offer much lower viscosities, enabling easier microchannel loading at low applied pressures.