Dielectrophoretic Response of Condensed DNA Clusters in AC Fields

Insulator-based dielectrophoresis (iDEP) has been applied in analytical research as a method to separate and fractionate DNA in lab-on-a-chip devices. The development of similar continuous-flow, size-based separation techniques for DNA Next-Generation Sequencing (NGS) could advance the speed, efficiency, and accuracy of in situ analysis of genomic/biological data. When low-frequency and high-amplitude AC potentials are applied to homogeneously disperse λ-DNA, reversible segregated clusters are observed in high frame rate imaging. However, the fundamental physics of such cluster phenomena are poorly understood and limited studies have been published referencing the aggregation formation realized under these conditions. This recently observed clustering phenomenon has gained the attention of colloidal physicists who wish to understand the physical parameters that influence clustering of λ-DNA. We believe applied low-frequency potentials generate this clustering behavior, which influences the dielectrophoretic response of DNA molecules. As a result, this phenomenon could be used to improve DNA sample preparation and pre-concentration using microdevices for future NGS applications. Research investigating cluster formation through modeling and computer simulations has shown that this phenomenon may be due to electrohydrodynamic instability including by not limited to dipole-dipole interactions between molecules. However, these models often address simpler DNA systems and fail to predict the unexpected switch we observe from positive to negative DEP in DNA clustering. 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, thus it is important that we understand the physics behind this phenomenon. Our recent work examines DNA cluster formation and migration characteristics using various electric field parameters in order to quantify the movement of DNA particles in solution. Preliminary evidence suggests that the electrokinetic mobility of DNA clusters changes negligibly with changes in frequency. 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 to 50 kbp. Future work will aim to enhance techniques capable of automatically tracking DNA clusters throughout high-frame rate imaging to further understand clustering and transport mechanisms. Such techniques will significantly reduce biosensing and bioanalytical processing times.