Droplet-Based Sample Injection for Chip-Based Analytical Separations

The advent of capillary and chip-based electrophoresis has opened up new possibilities for high-throughput analysis of a diversity of biological systems. The high-resolution separations typical of chip-based electrophoresis are in large part defined by the ability to introduce small sample volumes into the separation channel. This is not a trivial process and standard electrokinetic and hydrodynamic methods are far from ideal. Herein, we review recent studies that integrate droplet-based and continuous flow microfluidics to provide an alternative injection mechanism that is simple to implement and enables reproducible transport of defined sample volumes without bias.

Electrophoresis remains one of the most powerful tools in separation science. In recent years capillary and chip-based electrophoresis (CE/MCE) formats have been developed and refined to provide rapid, high-throughput and automated analysis of a broad range of targets, including nucleic acids, proteins and peptides, small molecules, enzymes and cells. [1-3] Indeed, benefits including reduced sample and reagent volumes, facile automation and integration with other analytical techniques (such as chromatography and mass spectrometry), improved efficiency and high analytical throughput are inherent to both formats.[4,5] Interestingly, however, whilst there have been extensive studies aimed at controlling separation conditions and
capillary/channel surface chemistries, sample injection techniques and post-separation fractionation vary little from the original formats reported over 20 years ago.