Engineering tertiary chirality in helical biopolymers.

Tertiary chirality describes the handedness of supramolecular assemblies and relies not only on the primary and secondary structures of the building blocks but also on topological driving forces that have been sparsely characterized. Helical biopolymers, especially DNA, have been extensively investigated as they possess intrinsic chirality that determines the optical, mechanical, and physical properties of the ensuing material. Here, we employ the DNA tensegrity triangle as a model system to locate the tipping points in chirality inversion at the tertiary level by X-ray diffraction. We engineer tensegrity triangle crystals with incremental rotational steps between immobile junctions from 3 to 28 base pairs (bp). We construct a mathematical model that accurately predicts and explains the molecular configurations in both this work and previous studies. Our design framework is extendable to other supramolecular assemblies of helical biopolymers and can be used in the design of chiral nanomaterials, optically active molecules, and mesoporous frameworks, all of which are of interest to physical, biological, and chemical nanoscience.

Development of a reliable probes in situ linear exchange module based on an environment control atomic force microscope.

In this work, a reliable atomic force microscope (AFM) probes in situ linear exchange module based on a scanned-sample environment control AFM was developed. The reliability and functionality of the module were experimentally verified through surface topography scanning tests and wear tests under different conditions. The module is able to install up to three AFM probes simultaneously, and in situ exchange different AFM probes inside the chamber so that different measurements in the designated environments can be carried out continuously as required. Without opening the chamber and breaking the atmosphere, contaminants from outside can be effectively avoided, and unpredictable physical/chemical change of the sample can be prevented. The module can be potentially used as a critical tool in studying nanotribology.