Single T4-DNA molecules were confined in rectangular-shaped channels with a depth of 300 nm and a width in the range 150-300 nm casted in a poly(dimethylsiloxane) nanofluidic chip. The extensions of the DNA molecules were measured with fluorescence microscopy as a function of the ionic strength and composition of the buffer as well as the DNA intercalation level by the YOYO-1 dye. The data were interpreted with scaling theory for a wormlike polymer in good solvent, including the effects of confinement, charge, and self-avoidance. It was found that the elongation of the DNA molecules with decreasing ionic strength can be interpreted in terms of an increase of the persistence length. Self-avoidance effects on the extension are moderate, due to the small correlation length imposed by the channel cross-sectional diameter.Intercalation of the dye results in an increase of the DNA contour length and a partial neutralization of the DNA charge, but besides effects of electrostatic origin it has no significant effect on the bare bending rigidity. In the presence of divalent cations, the DNA molecules were observed to contract, but they do not collapse into a condensed structure. It is proposed that this contraction results from a divalent counterion mediated attractive force between the segments of the DNA molecule.

The effect of dextran nanoparticles on the conformation and compaction of single DNA molecules confined in a nanochannel was investigated with fluorescence microscopy. It was observed that the DNA molecules elongate and eventually condense into a compact form with increasing volume fraction of the crowding agent. Under crowded conditions, the channel diameter is effectively reduced, which is interpreted in terms of depletion in DNA segment density in the interfacial region next to the channel wall. Confinement in a nanochannel also facilitates compaction with a neutral crowding agent at low ionic strength. The threshold volume fraction for condensation is proportional to the size of the nanoparticle, due to depletion induced attraction between DNA segments. We found that the effect of crowding is not only related to the colligative properties of the agent and that confinement is also important. It is the interplay between anisotropic confinement and osmotic pressure which gives the elongated conformation and the possibility for condensation at low ionic strength.A substantial fraction of the total volume of biological media is occupied by macromolecules, which do not directly participate in biochemical reactions. Nevertheless, it is now well established that these background species have an important effect on molecular transport, reaction rates, and chemical equilibrium (1). The steric repulsion between impenetrable macromolecules in a crowded medium is a major factor in determining the thermodynamic activities of the reactants. Crowding by an inert osmotic agent can also affect macromolecular structure. A well known example is the transition of DNA to a compact form (condensation) in the presence of overthreshold concentrations of simple neutral polymers and simple salts (2, 3, 4). It has been proposed that macromolecular crowding is the basis for phase separation in the cytoplasm (5) and condensation of DNA into the nucleoid of bacterial cells (6). The latter hypothesis is supported by the observation that DNA can be condensed by cytoplasmic extracts from Escherichia coli at extract concentrations corresponding to about 1 ⁄2 the cellular concentration (7). Besides background species, the cytoplasm of most eukaryotic cells contains stationary elements such as fiber lattices and membranes. These structures affect macromolecular conformation through confinement in 1D or 2D. Accordingly, macromolecular crowding and confinement are intimately related and deserve an integrated approach to understand their modes of operation and how they couple.DNA condensation can be assisted and directed by a surface. In surface directed condensation, DNA is first adsorbed onto an interface, after which it is condensed with an agent. Examples that have been reported in the literature are the condensation of single molecules into rods and toroidal structures with protamine or ethanol (8, 9). Single DNA molecules can be confined and visualized with f luorescence microscopy in quasi 1D nanochannels. The extension in the longitudinal ...

Highly concentrated electrolytes (HCEs) significantly improve the stability of lithium metal anodes, but applications are often impeded by their limitation of density, viscosity, and cost. Here, fluorobenzene (FB), an economical hydrocarbon with low density and low viscosity, is demonstrated as a bifunctional cosolvent to obtain a novel FB diluted highly concentrated electrolyte (FB‐DHCE). First, the addition of FB suppresses the decomposition of dimethoxyethane (DME) on the Li metal by strengthening the interactions of DME and FSI− around Li+. Second, FB efficiently elevates the content of LiF in the solid electrolyte interphase (SEI) based on its electrochemical reduction reaction. The unique solvation and interfacial chemistry of FB‐DHCE enable dendrite‐free deposition of lithium with high Coulombic efficiency (up to 99.3%) and prolong cycling life (over 500 cycles at 1 mA cm−2). The performance of FB‐DHCE is further demonstrated in full cells under practical conditions, including ambient to low temperature (–20 °C), high areal capacity (7.6 mAh cm−2), high current density (3 mA cm−2), limited excess Li (20 µm Li), and lean electrolyte (3 g Ah−1). Employing FB as a cosolvent not only opens a novel pathway to stabilize Li metal anodes, but also could greatly advance the development of Li metal batteries.

Hfq is a bacterial pleiotropic regulator that mediates several aspects of nucleic acids metabolism. The protein notably influences translation and turnover of cellular RNAs. Although most previous contributions concentrated on Hfq's interaction with RNA, its association to DNA has also been observed in vitro and in vivo. Here, we focus on DNA-compacting properties of Hfq. Various experimental technologies, including fluorescence microscopy imaging of single DNA molecules confined inside nanofluidic channels, atomic force microscopy and small angle neutron scattering have been used to follow the assembly of Hfq on DNA. Our results show that Hfq forms a nucleoprotein complex, changes the mechanical properties of the double helix and compacts DNA into a condensed form. We propose a compaction mechanism based on protein-mediated bridging of DNA segments. The propensity for bridging is presumably related to multi-arm functionality of the Hfq hexamer, resulting from binding of the C-terminal domains to the duplex. Results are discussed in regard to previous results obtained for H-NS, with important implications for protein binding related gene regulation.

Lithium sulfide (Li2S) as a cathodic material in Li-S batteries can not only deliver a high theoretical specific capacity of 1166 mA h g(-1), but also is essential for batteries using Li-free anode materials such as silicon and graphite. Various efforts have been made to synthesize a highly efficient Li2S-carbon composite; however, the electronically and ionically insulating nature and high melting point of Li2S strongly complicate the synthetic procedures, making it difficult to realize the expected capacity. Herein, a very simple method is proposed to prepare Li2S/graphene composites by one-pot pyrolysis of a mixture of graphene nanoplatelet aggregates (GNAs) and low-cost lithium sulfate (Li2SO4). For the first time, the entire pyrolysis process is clarified by thermogravimetry-mass spectrometry, wherein GNAs were found to partly serve as a carbon source to reduce Li2SO4 to Li2S, while the remaining GNAs formed thin graphene sheets as a result of this in situ etching, as a highly conductive host can immobilize the generated Li2S by intimate contact. Consequently, the obtained Li2S/graphene composite, combined with a Li2Sx-insoluble (x = 4-8) electrolyte developed by our group, exhibits excellent electrochemical behavior for Li-S batteries.

Increasing evidence supports the contribution of local inflammation to the development of Alzheimer's disease (AD) pathology, although the precise mechanisms are not clear. In this study, we demonstrate that the pro-inflammatory protein S100A9 interacts with the A1–40 peptide and promotes the formation of fibrillar -amyloid structures. This interaction also results in reduced S100A9 cytotoxicity by the binding of S100A9 toxic species to A1–40 amyloid structures. These results suggest that secretion of S100A9 during inflammation promotes the formation of amyloid plaques. By acting as a sink for toxic species, plaque formation may be the result of a protective response within the brain of AD patients, in part mediated by S100A9.

The effect of the bacterial heat-stable nucleoid-structuring protein (H-NS) on the conformation of single DNA molecules confined in a nanochannel was investigated with fluorescence microscopy. With increasing concentration of H-NS, the DNA molecules either elongate or contract. The conformational response is related to filamentation of H-NS on DNA through oligomerization and H-NS mediated bridging of distal DNA segments and is controlled by the concentration and ionic composition of the buffer. Confinement in a nanochannel also facilitates compaction of DNA into a condensed form for over-threshold concentrations of H-NS. Divalent ions such as magnesium facilitate but are not required for bridging nor condensation. The time scale of the collapse after exposure to H-NS was determined to be on the order of minutes, which is much shorter than the measured time required for filamentation of around one hour. We found that the effect of H-NS is not only related to its binding properties but also the confinement is of paramount importance. The interplay between confinement, H-NS-mediated attraction, and filamentation controls the conformation and compaction of DNA. This finding might have implications for gene silencing and chromosome organisation, because the cross-sectional dimensions of the channels are comparable to those of the bacterial nucleoid.

Dynamical control of cellular microenvironments is highly desirable to study complex processes such as stem cell differentiation and immune signaling. We present an ultra-multiplexed microfluidic system for high-throughput single-cell analysis in precisely defined dynamic signaling environments. Our system delivers combinatorial and time-varying signals to 1500 independently programmable culture chambers in week-long live-cell experiments by performing nearly 106 pipetting steps, where single cells, two-dimensional (2D) populations, or 3D neurospheres are chemically stimulated and tracked. Using our system and statistical analysis, we investigated the signaling landscape of neural stem cell differentiation and discovered “cellular logic rules” that revealed the critical role of signal timing and sequence in cell fate decisions. We find synergistic and antagonistic signal interactions and show that differentiation pathways are highly redundant. Our system allows dissection of hidden aspects of cellular dynamics and enables accelerated biological discovery.