Drop-to-drop liquid-liquid extraction of DNA in an electrowetting-on-dielectric digital microfluidics

Recent advancements in microfluidics and lab-on-a-chip technologies enabled miniaturization and automation of many downstream nucleic acid analysis steps such as PCR. However, DNA extraction/isolation protocol remains a stand-alone sample preparation step. For a quick sample-to-result solution, downstream protocols and sample preparation protocols need to be seamlessly integrated into a single lab-on-a-chip platform. As a step toward such integration, this paper introduces microfluidic DNA isolation using the liquid-liquid extraction (LLE) method in the drop-to-drop (DTD) format. The electrowetting-on-dielectric digital microfluidic platform is capable of handling a two-phase liquid system easily, which enables DTD LLE. In this study, the extraction of plasmid DNA (pDNA) from an aqueous sample to an ionic liquid is demonstrated. Prior to pDNA extraction study, the DTD LLE protocol was developed and optimized using organic dyes as solutes. The selective extraction of pDNA in the presence of proteins as interfering molecules is also demonstrated. This work implies that DTD LLE can substitute for magnetic beads steps in standard DNA isolation protocols.