Enhancing the Sensitivity of DNA and Aptamer Probes in the Dextran/PEG Aqueous Two-Phase System

Increasing the local concentration of DNA-based probes is a convenient way to improve the sensitivity of biosensors. Instead of using organic solvents or ionic liquids that phase-separate with water based on hydrophobic interactions, we herein studied a classic aqueous two-phase system (ATPS) comprising polyethylene glycol (PEG) and dextran. Polymers of higher molecular weights and higher concentrations favored phase separation. DNA oligonucleotides are selectively enriched in the dextran-rich phase unless the pH was increased to 12. A higher volume ratio of PEG-to-dextran and a higher concentration of PEG also enrich more DNA probes in the dextran-rich phase. The partition efficiency of the T15 DNA was enriched around seven times in the dextran phase when the volume ratio of dextran and PEG reached 1:10. The detection of limit improved by 3.6-fold in a molecular beacon-based DNA detection system with the ATPS. The ATPS also increased the sensitivity for the detection of Hg2+ and adenosine triphosphate, although these target molecules alone distributed equally in the two phases. This work demonstrates a simple method using water soluble polymers to improve biosensors.