Understanding spin-selective interactions between electrons and chiral molecules is critical to elucidating the significance of electron spin in biological processes and to assessing the potential of chiral assemblies for organic spintronics applications. Here, we use fluorescence microscopy to visualize the effects of spin-dependent charge transport in self-assembled monolayers of double-stranded DNA on ferromagnetic substrates. Patterned DNA arrays provide background regions for every measurement to enable quantification of substrate magnetization-dependent fluorescence due to the chiral-induced spin selectivity effect. Fluorescence quenching of photoexcited dye molecules bound within DNA duplexes is dependent upon the rate of charge separation/recombination upon photoexcitation and the efficiency of DNA-mediated charge transfer to the surface. The latter process is modulated using an external magnetic field to switch the magnetization orientation of the underlying ferromagnetic substrates. We discuss our results in the context of the current literature on the chiral-induced spin selectivity effect across various systems.

Nanoparticle assembly is a complex and versatile method of generating new materials, capable of using thousands of different combinations of particle size, shape, composition, and ligand chemistry to generate a library of unique structures. Here, a history of particle self-assembly as a strategy for materials discovery is presented, focusing on key advances in both synthesis and measurement of emergent properties to describe the current state of the field. Several key challenges for further advancement of nanoparticle assembly are also outlined, establishing a roadmap of critical research areas to enable the next generation of nanoparticle-based materials synthesis.

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Liquid-crystal-based biomaterials provide promising platforms for the development of dynamic and responsive interfaces for tissue engineering. Cholesteryl ester liquid crystals (CLCs) are particularly well suited for these applications, due to their roles in cellular homeostasis and their intrinsic ability to organize into supramolecular helicoidal structures on the mesoscale. Here, we developed a nonwoven CLC electrospun scaffold by dispersing three cholesteryl esterbased mesogens within polycaprolactone (PCL). We tuned the ratio of our mesogens so that the CLC would be in the mesophase at the cell culture incubator temperature of 37 °C. In these scaffolds, the PCL polymer provided an elastic bulk matrix while the homogeneously dispersed CLC established a viscoelastic fluidlike interface. Atomic force microscopy revealed that the 50% (w/v) cholesteryl ester liquid crystal scaffold (CLC-S) exhibited a mesophase with topographic striations typical of liquid crystals. Additionally, the CLC-S favorable wettability and ultrasoft fiber mechanics enhanced cellular attachment and proliferation. Increasing the CLC concentration within the composites enhanced myoblast adhesion strength promoted myofibril formation in vitro with mouse myoblast cell lines.

Spin-dependent and enantioselective electron-molecule scattering occurs in photoelectron transmission through chiral molecular films. This spin selectivity leads to electron spin filtering by molecular helices, with increasing magnitude, concomitant with increasing numbers of helical turns. Using ultraviolet photoelectron spectroscopy, we measured spin-selective surface charging accompanying photoemission from ferromagnetic substrates functionalized with monolayers of mercurated DNA hairpins that constitute only one helical turn. Mercury ions bind specifically at thymine-thymine mismatches within self-hybridized single-stranded DNA, enabling precise control over the number and position of Hg 2+ along the helical axis. Differential charging of the organic layers, manifested as substrate magnetization-dependent photoionization energies, was observed for DNA hairpins containing Hg 2+ ; no differences were measured for hairpin monolayers in the absence of Hg 2+ . Inversion of the DNA helical secondary structure at increased metal loading led to complementary inversion in spin selectivity. We attribute these results to increased scattering probabilities from relativistic enhancement of spin-orbit interactions in mercurated DNA.