Structural Modification of DNA Studied by Scanning Tunneling Microscopy

Full Width at Half Maximum of Nanopore Current Blockage Controlled by a Single-Biomolecule Interface

A biological nanopore is one of the predominant single-molecule approaches as a result of its controllable single-biomolecule interface, which could reflect the "intrinsic" information on an individual molecule in a label-free way. Because the current blockage is normally treated as the most important parameter for nanopore identification of every single molecule, the fluctuation of current blockage for certain types of molecules, defined as full width at half maximum (fwhm) of current blockage, actually owns a dominant influence on nanopore resolution. Therefore, controlling the fwhm of current blockage of molecules is critical for the sensing capability of the nanopore. Here, taking an aerolysin nanopore as a model, by precisely controlling the functional group in this single-biomolecule interface, we could narrow the fwhm of nanopore current blockage for DNA identification and prolong the duration inside the nanopore. Moreover, a substantial correlation between fwhm of current blockage and duration is established, showing a non-monotonic variation. Besides, the mechanism is also clarified with studying the detailed current blockage events. This proposed correlation is further demonstrated to be applied uniformly across different mutant aerolysins for a certain DNA. This study proposes a new strategy for regulating molecular sensing from the duration of the analyte, which could guide the resolution of heterogeneity analysis using nanopores.

Synthesis of Metallopolymers and Direct Visualization of the Single Polymer Chain

During the past few decades, the study of the single polymer chain has attracted considerable attention with the goal of exploring the structure-property relationship of polymers. It still, however, remains challenging due to the variability and low atomic resolution of the amorphous single polymer chain. Here, we demonstrated a new strategy to visualize the single metallopolymer chain with a hexameric or trimeric supramolecule as a repeat unit, in which Ru(II) with strong coordination and Fe(II) with weak coordination were combined together in a stepwise manner. With the help of ultrahigh-vacuum, low-temperature scanning tunneling microscopy (UHV-LT-STM) and scanning tunneling spectroscopy (STS), we were able to directly visualize both Ru(II) and Fe(II), which act as staining reagents on the repeat units, thus providing detailed structural information for the single polymer chain. As such, the direct visualization of the single random polymer chain is realized to enhance the characterization of polymers at the single-molecule level.