Probing DNA mechanical characteristics by dielectrophoresis

Microfabricated electrode systems have recently become useful for immobilization and stretching biopolymers to precise locations in microfluidic devices. In this paper we discuss the modeling, fabrication and characterization of such a platform to investigate the elongation and orientation of different-sized deoxyribose nucleic acid (DNA) molecules, tethered onto aluminum electrodes, by a distributed force applied along the DNA backbone under the influence of high frequency non-uniform ac electric fields. The DNA molecules are elongated from a random coil into an extended conformation and orientated along the electric field lines as a result of the forces acting on the molecules during the application of the ac electric fields. Stable elongation is observed in the frequency range 0.1–1 MHz, with field strengths of 0.3–1.9 MV/m. Maximum elongation for two different DNA fragments, irrespective of size, is found for frequencies about 100 kHz. With a model that incorporates dielectrophoresis directly, we show that electric field experimental results can be used for detecting some characteristics of the DNA elasticity which manifest themselves clearly at higher extensions but cannot be observed at lower ones. The entropic elasticity and highly extensibility of DNA are all closely related to this account. By the elastic DNA model presented and by considering the base–stacking interactions between DNA adjacent nucleotide base pairs, we find an underlying scaling relation between the DNA extension and the applied voltage of the form 〈 δ 〉 ∼ V p − p 1 − 1.15 , which emphasizes the significance of the electric fields.