DNA-based machines that walk by converting chemical energy into controlled motion could be of use in applications such as next generation sensors, drug delivery platforms, and biological computing. Despite their exquisite programmability, DNA-based walkers are, however, challenging to work with due to their low fidelity and slow rates (~1 nm/min). Here, we report DNA-based machines that roll rather than walk, and consequently have a maximum speed and processivity that is three-orders of magnitude greater than conventional DNA motors. The motors are made from DNA-coated spherical particles that hybridise to a surface modified with complementary RNA; motion is achieved through the addition of RNase H, which selectively hydrolyses hybridised RNA. Spherical motors move in a self-avoiding manner, whereas anisotropic particles, such as dimerised particles or rod-shaped particles travel linearly without a track or external force. Finally, we demonstrate detection of single nucleotide polymorphism by measuring particle displacement using a smartphone camera.

Phase transitions significantly differ between 2D and 3D systems, but the influence of dimensionality on the glass transition is unresolved. We use microscopy to study colloidal systems as they approach their glass transitions at high concentrations and find differences between two dimensions and three dimensions. We find that, in two dimensions, particles can undergo large displacements without changing their position relative to their neighbors, in contrast with three dimensions. This is related to Mermin-Wagner long-wavelength fluctuations that influence phase transitions in two dimensions. However, when measuring particle motion only relative to their neighbors, two dimensions and three dimensions have similar behavior as the glass transition is approached, showing that the long-wavelength fluctuations do not cause a fundamental distinction between 2D and 3D glass transitions.colloidal glass transition | dimensionality | long-wavelength fluctuations | phase transition | two-dimensional physics I f a liquid can be cooled rapidly to avoid crystallization, it can form into a glass: an amorphous solid. The underlying cause of the glass transition is far from clear, although there are a variety of theories (1-3). One recent method of understanding the glass transition has been to simulate the glass transition in a variety of dimensions (including four dimensions or higher) (4-8). Indeed, the glass transition is often thought to be similar in two and three dimensions (9, 10), and in simple simulation cases such as hard particles, one might expect that dimensionality plays no role. As a counterargument, 2D and 3D fluid mechanics are qualitatively quite different (11). Likewise, melting is also known to be qualitatively different in two and three dimensions (12-15).Recent simulations give evidence that the glass transition is also quite different in two and three dimensions (4, 5). In particular, Flenner and Szamel (4) simulated several different glassforming systems in two and three dimensions and found that the dynamics of these systems were fundamentally different in two and three dimensions. They examined translational particle motion (motion relative to a particle's initial position) and bond-orientational motion (topological changes of neighboring particles). They found that, in two dimensions, these two types of motion became decoupled near the glass transition. In these cases, particles could move appreciable distances but did so with their neighbors, so that their local structure changed slowly. In three dimensions, this was not the case; translational and bondorientational motions were coupled. They additionally observed that the transient localization of particles well known in three dimensions was absent in the 2D data. To quote Flenner and Szamel, "these results strongly suggest that the glass transition in two dimensions is different from in three dimensions."In this work, we use colloidal experiments to test dimensiondependent dynamics approaching the glass transition. Colloidal samples at high concen...

Mechanical forces transmitted through integrin transmembrane receptors play important roles in a variety of cellular processes ranging from cell development to tumorigenesis. Despite the importance of mechanics in integrin function, the magnitude of integrin forces within adhesions remains unclear. Literature suggests a range from 1 to 50 pN, but the upper limit of integrin forces remains unknown. Herein we challenge integrins with the most mechanically stable molecular tension probe, which is comprised of the immunoglobulin 27th (I27) domain of cardiac titin flanked with a fluorophore and gold nanoparticle. Cell experiments show that integrin forces unfold the I27 domain, suggesting that integrin forces exceed 80 pN. The introduction of a disulfide bridge within I27 “clamps” the probe and resists mechanical unfolding. Importantly, the addition of a reducing agent initiates SH exchange, thus unclamping I27 at a rate that is dependent on the applied force. By recording the rate of S-S reduction in clamped I27 we infer that integrins apply 110+/−15 pN within focal adhesions. The rates of S-S exchange are heterogeneous and integrin subtype-dependent. Nanoparticle titin tension sensors along with kinetic analysis of unfolding demonstrate that a subset of integrins apply tension many fold greater than previously reported.

Hydrogels are important in biological and medical applications, such as drug delivery and tissue engineering. DNA hydrogels have attracted significant attention due to the programmability and biocompatibility of the material. We developed a series of low-cost one-strand DNA hydrogels self-assembled from single-stranded DNA monomers containing multiple palindromic domains. This new hydrogel design is simple and programmable. Thermal stability, mechanical properties, and loading capacity of these one-strand DNA hydrogels can be readily regulated by simply adjusting the DNA domains.

We report the synthesis and characterization of a new class of organic/inorganic hybrid polymers composed of covalently-bound 1,3,5-benzenetricarboxamide linkers and anionic polyoxovanadate clusters with varying counter-cations. These materials form gels within seconds upon contact with polar aprotic organic liquids and catalyze the degradation of odorants and toxic molecules under mild conditions including aerobic oxidation of thiols, hydrogen peroxide-catalyzed oxidation of sulfides, and hydrolysis of organophosphate chemical warfare agent analogues.