Directly Characterizing the Capture Radius of Tethered Double-Stranded DNA by Single-Molecule Nanopipette Manipulation

The tethered molecule exhibits characteristics of both free and fixed states, with the electrodynamics involved in its diffusion, electrophoresis, and stretching processes still not fully understood. We developed a Single-Molecule Manipulation, Identification, and Length Examination (SMILE) system by integrating piezoelectric devices with nanopipettes. This system enabled successful capture and stretching of tethered double-stranded DNA within the nanopore. Our research unveiled distinct capture (r_capture) and stretch radii (r_stretch) surrounding the DNA's anchor point. Notably, consistent ratios of capture radius for DNA of varying lengths (2k, 4k, and 6k base pairs) were observed across different capturing voltages, approximately 1:1.4:1.83, showing a resemblance to their gyration radius ratios. However, the ratios of stretch radius are consistent to their contour length (L₀), with the stretching ratio (r_stretch/L₀) increasing from 70 to 90% as the voltage rose from 100 to 1000 mV. Additionally, through numerical simulations, we identified the origin of capture and stretch radii, determined by the entropic elasticity-induced capture barrier and the electric field-dominant escape barrier. This research introduces an innovative methodology and outlines research perspectives for a comprehensive exploration of the conformational, electrical, and diffusion characteristics of tethered molecules.