Dielectrophoretic Response of Condensed DNA Clusters in AC Fields

The use of insulator-based dielectrophoresis (iDEP) for size-dependent separation and fractionation of DNA fragments has been regularly applied to lap-on-a-chip devices. During the use of insulator-based dielectrophoresis, homogeneously dispersed DNA molecules have been known to reversibly associate into segregated clusters under the influence of strong AC electric fields at low frequencies. This recently observed clustering phenomena has since gained attention in the field of colloidal physics, however, the significance of this visible DNA clustering behavior for DNA dielectrophoresis has yet to be investigated. Under these conditions, clustering behavior is believed to influence dielectrophoretic sorting for DNA molecules. As a result, this phenomenon could be used to improve DNA sample preparation and pre-concentration using microdevices for Next-Generation Sequencing (NGS) applications. Research investigating cluster formation through modeling and computer simulations has shown that this phenomenon may be due to electrohydrodynamic instability resulting from dipole-dipole interactions between molecules. Clustering behavior has the potential to enhance the efficiency of DNA fractionation by exploiting strong AC electric fields to induce condensation and separation of DNA molecules. Here, we examined DNA cluster formation and migration characteristics using various electric field parameters. Various amplitudes and frequencies of applied potential were examined to determine the extent of correlation in DNA clustering. DNA clustering was largely observed with frequencies ranging from 10 to 100 Hz and electric field strengths above 800 V/cm. Similar electric field parameters have produced some of the highest-observed sorting efficiencies in an iDEP constriction sorter for DNA molecules ranging in size from 10 - 50 kbp. These clusters correspond to unique dielectrophoretic behaviors for large DNA fragments. Our work suggests that DNA clustering can be exploited using insulator-based dielectrophoresis for size-based separation and fractionation with extremely high efficiencies. Such high efficiencies will significantly advance sample preparation and concentration of DNA and other macromolecules for biosensing and bioanalysis.