Molecular Recognition in Confined Space Elucidated with DNA Nanopores and Single-Molecule Force Microscopy

Vertical DNA Nanostructure Arrays: Facilitating Functionalization on Macro-Scale Surfaces

The capability for varied functionalization and precise control at the nanoscale are significant advantages of DNA nanostructures. In the assembly of DNA nanostructure, the surface-assisted growth method utilizing double-crossover (DX) tile structures facilitates nucleation at relatively low concentrations on the surface based on electrostatic interactions, thereby enabling crystal growth over large areas. However, in surface-assisted growth, the geometrical hindrance of vertical structures on the DX tile structure surface makes it challenging to conjugate DNA nanostructures into fabricated surfaces. Here, the surface-assisted growth method was employed to extend the DX tile growth for forming vertical structure arrays on the substrate, providing attachment sites for functionalization on uniformly covered substrates at the macroscopic scale. Additionally, the spacing of the vertical structure arrays was demonstrated to be controllable through the strategic design of the repeating unit tiles that construct the DX crystals.

AFM Imaging Reveals MicroRNA-132 to be a Positive Regulator of Synaptic Functions

The modification of synaptic and neural connections in adults, including the formation and removal of synapses, depends on activity-dependent synaptic and structural plasticity. MicroRNAs (miRNAs) play crucial roles in regulating these changes by targeting specific genes and regulating their expression. The fact that somatic and dendritic activity in neurons often occurs asynchronously highlights the need for spatial and dynamic regulation of protein synthesis in specific milieu and cellular loci. MicroRNAs, which can show distinct patterns of enrichment, help to establish the localized distribution of plasticity-related proteins. The recent study using atomic force microscopy (AFM)-based nanoscale imaging reveals that the abundance of miRNA(miR)-134 is inversely correlated with the functional activity of dendritic spine structures. However, the miRNAs that are selectively upregulated in potentiated synapses, and which can thereby support prospective changes in synaptic efficacy, remain largely unknown. Using AFM force imaging, significant increases in miR-132 in the dendritic regions abutting functionally-active spines is discovered. This study provides evidence for miR-132 as a novel positive miRNA regulator residing in dendritic shafts, and also suggests that activity-dependent miRNAs localized in distinct sub-compartments of neurons play bi-directional roles in controlling synaptic transmission and synaptic plasticity.

Single-Polymer Friction Force Microscopy of dsDNA Interacting with a Nanoporous Membrane

Surface-grafted polymers can reduce friction between solids in liquids by compensating the normal load with osmotic pressure, but they can also contribute to friction when fluctuating polymers entangle with the sliding counter face. We have measured forces acting on a single fluctuating double-stranded DNA polymer, which is attached to the tip of an atomic force microscope and interacts intermittently with nanometer-scale methylated pores of a self-assembled polystyrene-block-poly(4-vinylpyridine) membrane. Rare binding of the polymer into the pores is followed by a stretching of the polymer between the laterally moving tip and the surface and by a force-induced detachment. We present results for the velocity dependence of detachment forces and of attachment frequency and discuss them in terms of rare excursions of the polymer beyond its equilibrium configuration.