Aramid nanofibers (ANFs), or nanoscale Kevlar fibers, are of interest for their high mechanical performance and functional nanostructure. The dispersible nature of ANFs opens up processing opportunities for creating mechanically robust and flexible nanocomposites, particularly for energy and power applications. The challenge is to manipulate ANFs into an electrode structure that balances mechanical and electrochemical performance to yield a robust and flexible electrode. Here, ANFs and graphene oxide (GO) sheets are blended using layer-by-layer (LbL) assembly to achieve mechanically flexible supercapacitor electrodes. After reduction, the resulting electrodes exhibit an ANF-rich structure where ANFs act as a polymer matrix that interfacially interacts with reduced graphene oxide sheets. It is shown that ANF/GO deposition proceeds by hydrogen bonding and π-π interactions, leading to linear growth (1.2 nm/layer pairs) and a composition of 75 wt % ANFs and 25 wt % GO sheets. Chemical reduction leads to a high areal capacitance of 221 μF/cm, corresponding to 78 F/cm. Nanomechanical testing shows that the electrodes have a modulus intermediate between those of the two native materials. No cracks or defects are observed upon flexing ANF/GO films 1000 times at a radius of 5 mm, whereas a GO control shows extensive cracking. These results demonstrate that electrodes containing ANFs and reduced GO sheets are promising for flexible, mechanically robust energy and power.

Driving and measuring chemical reactions at the nanoscale is crucial for developing safer, more efficient, and environment-friendly reactors and for surface engineering. Quantitative understanding of surface chemical reactions in real operating environments is challenging due to resolution and environmental limitations of existing techniques. Here we report an atomic force microscope technique that can measure reaction kinetics driven at the nanoscale by multiphysical stimuli in an ambient environment. We demonstrate the technique by measuring local reduction of graphene oxide as a function of both temperature and force at the sliding contact. Kinetic parameters measured with this technique reveal alternative reaction pathways of graphene oxide reduction previously unexplored with bulk processing techniques. This technique can be extended to understand and precisely tailor the nanoscale surface chemistry of any two-dimensional material in response to a wide range of external, multiphysical stimuli.

The genomic DNA of eukaryotic cells exists in the form of chromatin, the structure of which controls the biochemical accessibility of the underlying DNA to effector proteins. In order to gain an in depth molecular understanding of how chromatin structure regulates DNA repair, detailed in vitro biochemical and biophysical studies are required. However, because of challenges associated with reconstituting nucleosome arrays containing site-specifically positioned DNA modifications, such studies have been limited to the use of mono- and dinucleosomes as model in vitro substrates, which are incapable of folding into native chromatin structures. To address this issue, we developed a straightforward and general approach for assembling chemically defined oligonucleosome arrays (i.e., designer chromatin) containing site-specifically modified DNA. Our method takes advantage of nicking endonucleases to excise short fragments of unmodified DNA, which are subsequently replaced with synthetic oligonucleotides containing the desired modification. Using this approach, we prepared several oligonucleosome substrates containing precisely positioned 2'-deoxyuridine (dU) residues and examined the efficiency of base excision repair (BER) within several distinct chromatin architectures. We show that, depending on the translational position of the lesion, the combined catalytic activities of uracil DNA glycosylase (UDG) and apurinic/apyrimidinic endonuclease 1 (APE1) can be either inhibited by as much as 20-fold or accelerated by more than 5-fold within compact chromatin (i.e., the 30 nm fiber) relative to naked DNA. Moreover, we demonstrate that digestion of dU by UDG/APE1 proceeds much more rapidly in mononucleosomes than in compacted nucleosome arrays, thereby providing the first direct evidence that internucleosome interactions play an important role in regulating BER within higher-order chromatin structures. Overall, this work highlights the value of performing detailed biochemical studies on precisely modified chromatin substrates in vitro and provides a robust platform for investigating DNA modifications in chromatin biology.

The functional implementation of graphene as a solid boundary lubricant requires the ability to control its frictional response across a variety of interfaces. This is challenging, as being a single atomic layer thick, the nanotribological properties of graphene depend highly on the competing interaction strengths with the converse sides of the top and bottom contacts of the interfaces it is placed in between. One method to modulate these interactions is to tune the surface chemistry (of one or both counter-faces) with self-assembled monolayers (SAMs). To fully understand the effects on the graphene/SAM (G-SAM) composite interfaces formed, however, first necessitates a basic understanding of graphene–SAM interactions. To explore graphene–SAM adhesive and frictional interactions over a range of chemical functionalities, SAMs were used to functionalize atomic force microscopy (AFM) tips with varying terminal end-groups (−NH2, −CH3, and –phenyl, compared to unfunctionalized −OH terminated reference tips). AFM pull-off force measurements and thermal gravimetric analysis (TGA) were used to evaluate the work of adhesion (mJ/m2) and interaction energy (kcal/mol) of the functionalized tips with graphene. Friction force microscopy (FFM) measurements were performed with the same functionalized AFM tips to examine the graphene-molecule frictional response. Tip–graphene interaction strength was increased for hydrophobic and aromatic functional groups. The frictional response was found to depend on a balance of graphene-molecule adhesion and shear strain.

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