Extraction of electrokinetically separated analytes with on-demand encapsulation.

Area of Science:

• Microfluidics
• Analytical Chemistry
• Biotechnology

Background:

• Microchip electrokinetic methods enhance molecular assay sensitivity through analyte enrichment and purification.
• Current limitations restrict their use to high electric field conditions, as analyte focusing is lost without the field.

Purpose of the Study:

• To present a novel two-phase encapsulation method for overcoming the electric field dependency of microchip electrokinetic separations.
• To enable stable, long-term analyte concentration maintenance for on- or off-chip analysis.

Main Methods:

• Passive filling and pinning of an oil phase in hydrophobic channels to encapsulate analytes.
• Utilizing a brief pressure pulse to encapsulate electrokinetically separated and focused analytes.
• Demonstration with DNA oligonucleotides after isotachophoresis (ITP) focusing and PCR amplicon purification.

Main Results:

• Encapsulated DNA oligonucleotide concentration remained at 60% for tens of minutes, a 22-fold improvement over free diffusion.
• Demonstrated selective encapsulation of PCR amplicon after ITP purification.
• Showcased parallel off-chip detection reactions using single encapsulated droplets.

Conclusions:

• The two-phase encapsulation method provides stable, field-free analyte retention, significantly enhancing molecular assay sensitivity.
• This technique allows for robust manipulation and analysis of separated analytes, expanding the utility of microchip electrokinetics.
• The method is scalable for multiple analyte zones and applicable to various downstream detection strategies.