Discrete DNA Three-dimensional Nanostructures： the Synthesis and Applications

Structural DNA nanotechnology, an emerging technique that utilizes the nucleic acid molecule as generic polymer to programmably assemble well-defined and nano-sized architectures, holds great promise for new material synthesis and constructing functional nanodevices for different purposes. In the past three decades, rapid development of this technique has enabled the syntheses of hundreds and thousands of DNA nanostructures with various morphologies at different scales and dimensions. Among them, discrete three-dimensional （3D） DNA nanostructures not only represent the most advances in new material design, but also can serve as an excellent platform for many important applications. With precise spatial addressability and capability of arbitrary control over size, shape, and function, these nanostructures have drawn particular interests to scientists in different research fields. In this review article, we will briefly summarize the development regarding the synthesis of discrete DNA 3D nanostructures with various size, shape, geometry, and topology, including our previous work and recent progress by other groups. In detail, three methods majorly used to synthesize the DNA 3D objects will be introduced accordingly. Additionally, the principle, design rule, as well as pros and cons of each method will be highlighted. As functions of these discrete 3D nanostructures have drawn great interests to researchers, we will further discuss their cutting-edge applications in different areas, ranging from novel material synthesis, new device fabrication, and biomedical applications, etc. Lastly, challenges and outlook of these promising nanostructures will be given based on our point of view.

Electrically injected GeSn lasers with peak wavelength up to 2.7 μm

GeSn lasers enable the monolithic integration of lasers on the Si platform using all-group-Ⅳ direct-bandgap material.The GeSn laser study recently moved from optical pumping into electrical injection.In this work,we present explorative investigations of GeSn heterostructure laser diodes with various layer thicknesses and material compositions.Cap layer material was studied by using Si_(0.03)Ge_(0.89)Sn_(0.08) and Ge_(0.95)Sn_(0.05),and cap layer total thickness was also compared.The 190 nm SiGeSn-cap device had threshold of 0.6 kA/cm^(2) at 10 K and a maximum operating temperature(T_(max)) of 100 K,compared to 1.4 kA/cm^(2) and 50 K from 150 nm SiGeSn-cap device,respectively.Furthermore,the 220 nm GeSn-cap device had 10 K threshold at 2.4 kA/cm^(2) and T_(max) at 90 K,i.e.,higher threshold and lower maximal operation temperature compared to the SiGeSn cap layer,indicating that enhanced electron confinement using SiGeSn can reduce the threshold considerably.The study of the active region material showed that device gain region using Ge_(0.87)Sn_(0.13) had a higher threshold and lower T_(max),compared to Ge_(0.89)Sn_(0.11).The performance was affected by the metal absorption,free carrier absorption,and possibly defect density level.The maximum peak wavelength was measured as 2682 nm at 90 K by using Ge_(0.87)Sn_(0.13) in gain regions.The investigations provide directions to the future GeSn laser diode designs toward the full integration of group-Ⅳ photonics on a Si platform.

Binary self-assembly of highly symmetric DNA nanocages via sticky-end engineering

Discrete and symmetric three-dimensional（3D） DNA nanocages have been revoked as excellent candidates for various applications,such as guest component encapsulation and organization（e.g.dye molecules,proteins,inorganic nanoparticles,etc.） to construct new materials and devices.To date,a large variety of DNA nanocages has been synthesized through assembling small individual DNA motifs into predesigned structures in a bottom-up fashion.Most of them rely on the assembly using multiple copies of single type of motifs and a few sophisticated nanostructures have been engineered by co-assembling multi-types of DNA tiles simultaneously.However,the availability of complex DNA nanocages is still limited.Herein,we demonstrate that highly symmetric DNA nanocages consisted of binary DNA pointstar motifs can be easily assembled by deliberately engineering the sticky-end interaction between the component building blocks.As such,DNA nanocages with new geometries,including elongated tetrahedron（E-TET）,rhombic dodecahedron（R-DOD）,and rhombic triacontahedron（R-TRI） are successfully synthesized.Moreover,their design principle,assembly process,and structural features are revealed by polyacryalmide gel electrophoresis（PAGE）,atomic force microscope（AFM） imaging,and cryogenic transmission electron microscope imaging（cryo-TEM） associated with single particle reconstruction.