Single DNA Translocation and Electrical Characterization Based on Atomic Force Microscopy and Nanoelectrodes.

Precision DNA translocation control is critical for achieving high accuracy in single molecule-based DNA sequencing. In this report, we describe an atomic force microscopy (AFM) based method to linearize a double-stranded DNA strand during the translocation process and characterize the electrical properties of the moving DNA using a platinum (Pt) nanoelectrode gap. In this method, λ DNAs were first deposited on a charged mica substrate surface and topographically scanned. A single DNA suitable for translocation was then identified and electrostatically attached to an AFM probe by pressing the probe tip down onto one end of the DNA strand without chemical functionalizations. Next, the DNA strand was lifted off the mica surface by the probe tip. The pulling force required to completely lift off the DNA agreed well with the theoretical DNA adhesion force to a charged mica surface. After liftoff, the captured DNA was translocated at varied speeds across the substrate and ultimately across the Pt nanoelectrode gap for electrical characterizations. Finally, finite element analysis of the effect of the translocating DNA on the conductivity of the nanoelectrode gap was conducted, validating the range of the gap current measured experimentally during the DNA translocation process.