Single Molecule DNA Resensing Using a Two-Pore Device.

A nanofluidic device is presented that, enables independent sensing and resensing of a single DNA molecule translocating through two nanopores with sub-micrometer spacing. The device concept is based upon integrating a thin nitride membrane with microchannels etched in borosilicate glass. Pores, coupled to each microchannel, are connected via a fluid-filled half-space on the device backside, enabling translocation of molecules across each pore in sequence. Critically, this approach allows for independent application of control voltage and measurement of trans-pore ionic current at each of the two pores, leading to 1) controlled assessment of molecular time of flight, 2) voltage-tuned selective molecule recapture, and 3) ability to acquire two correlated translocation signatures for each molecule analyzed. Finally, the rare cocapture of a single chain threading simultaneously through each of the two pores is reported.

Silicon nanowires as efficient thermoelectric materials.

Thermoelectric materials interconvert thermal gradients and electric fields for power generation or for refrigeration. Thermoelectrics currently find only niche applications because of their limited efficiency, which is measured by the dimensionless parameter ZT-a function of the Seebeck coefficient or thermoelectric power, and of the electrical and thermal conductivities. Maximizing ZT is challenging because optimizing one physical parameter often adversely affects another. Several groups have achieved significant improvements in ZT through multi-component nanostructured thermoelectrics, such as Bi(2)Te(3)/Sb(2)Te(3) thin-film superlattices, or embedded PbSeTe quantum dot superlattices. Here we report efficient thermoelectric performance from the single-component system of silicon nanowires for cross-sectional areas of 10 nm x 20 nm and 20 nm x 20 nm. By varying the nanowire size and impurity doping levels, ZT values representing an approximately 100-fold improvement over bulk Si are achieved over a broad temperature range, including ZT approximately 1 at 200 K. Independent measurements of the Seebeck coefficient, the electrical conductivity and the thermal conductivity, combined with theory, indicate that the improved efficiency originates from phonon effects. These results are expected to apply to other classes of semiconductor nanomaterials.

Quantitating cell-cell interaction functions with applications to glioblastoma multiforme cancer cells.

We report on a method for quantitating the distance dependence of cell-cell interactions. We employ a microchip design that permits a multiplex, quantitative protein assay from statistical numbers of cell pairs, as a function of cell separation, with a 0.15 nL volume microchamber. We interrogate interactions between pairs of model brain cancer cells by assaying for six functional proteins associated with PI3k signaling. At short incubation times, cells do not appear to influence each other, regardless of cell separation. For 6 h incubation times, the cells exert an inhibiting influence on each other at short separations and a predominately activating influence at large separation. Protein-specific cell-cell interaction functions are extracted, and by assuming pairwise additivity of those interactions, the functions are shown to correctly predict the results from three-cell experiments carried out under the identical conditions.

Site-selective DNA photocleavage involving unusual photoinitiated tautomerization of chiral tridentate vanadyl(V) complexes derived from N-salicylidene alpha-amino acids.

The titled vanadyl(V) complexes serve as efficient reagents for cleaving supercoiled plasmid DNA by photoinitiation. Complex 3d, derived from 2-hydroxy-1-naphthaldehyde and l-phenylalanine, exhibits a unique wedge feature, inducing a site-selective photocleavage at the C22-T23 of the bulge backbone for a HIV-27 DNA system at 0.1-5 muM. Transient absorption experiments for 3d indicate the involvement of LMCT with concomitant tautomerization, leading to an o-quinone-methide V-bound hydroxyl species responsible for the cleavage profiles. [structure: see text]

Furan-containing oligoaryl cyclophanene.

[structure: see text] Furan-containing oligoaryl cyclophanene 1 and the corresponding cyclophane 2 were synthesized from propargylic dithioacetal 3. The electrochemical and photophysical properties and the fluxional behavior of these molecules have been examined. The emission of 1 appeared at 499 nm whereas that of 2 appeared at 389 nm.

Synthesis and characterization of luminescent osmium(II) carbonyl complexes based on chelating dibenzoylmethanate and halide ligands.

Octahedral Os(II) complexes 1-5 with formula [Os(CO)3X(dbm)] are prepared through utilization of both solid-state pyrolysis and ligand exchange reactions. These complexes exhibit prominent 3pi-pi* phosphorescence with unusually long lifetimes (29-64 micros) and high quantum yields (0.08-0.13).

Reduction of thermal conductivity in phononic nanomesh structures.

Controlling the thermal conductivity of a material independently of its electrical conductivity continues to be a goal for researchers working on thermoelectric materials for use in energy applications and in the cooling of integrated circuits. In principle, the thermal conductivity κ and the electrical conductivity σ may be independently optimized in semiconducting nanostructures because different length scales are associated with phonons (which carry heat) and electric charges (which carry current). Phonons are scattered at surfaces and interfaces, so κ generally decreases as the surface-to-volume ratio increases. In contrast, σ is less sensitive to a decrease in nanostructure size, although at sufficiently small sizes it will degrade through the scattering of charge carriers at interfaces. Here, we demonstrate an approach to independently controlling κ based on altering the phonon band structure of a semiconductor thin film through the formation of a phononic nanomesh film. These films are patterned with periodic spacings that are comparable to, or shorter than, the phonon mean free path. The nanomesh structure exhibits a substantially lower thermal conductivity than an equivalently prepared array of silicon nanowires, even though this array has a significantly higher surface-to-volume ratio. Bulk-like electrical conductivity is preserved. We suggest that this development is a step towards a coherent mechanism for lowering thermal conductivity.

A remarkable ligand orientational effect in osmium-atom-induced blue phosphorescence.

A new series of Os(II)-based carbonyl complexes cis(CO),trans(Npy,Npy),cis(Ntz,Ntz)-[Os(CO)2(bptz)2] (1), cis(CO),cis(Npy,Npy),trans(Ntz,Ntz)-[Os(bptz)2(CO)2] (2), and cis(CO),trans(Npy,Npy),cis(Ntz,Ntz)-[Os(CO)2(fptz)2] (3), where bptz and fptz denote 3-tert-butyl-5-(2-pyridyl)- and 3-trifluoromethyl-5-(2-pyridyl)-1,2,4-triazolate, respectively, have been designed and synthesized in an effort to achieve high efficiency, room-temperature blue phosphorescence. Although 1 and 2 are geometric isomers, remarkably different excited-state relaxation pathways were observed. Complex 1 exhibits strong phosphorescence in CH3CN (Phi(p) approximately 0.47) and as a single crystal at room temperature, whereas complex 2 is nearly nonemissive under similar conditions. The associated relaxation dynamics have been comprehensively investigated by spectroscopic and relaxation dynamics as well as by theoretical approaches. Our results lead us to the conclusion that for complex 2, the "loose bolt" effect of metal-ligand bonding interactions plays a crucial role in the fast radiationless deactivation of this type of geometrical isomer. Fine adjustment can also be achieved by functionalizing the ligands so that the electron-withdrawing nature of the CF3 group in 3 stabilizes the HOMO of the triazolate moiety, thus moving the emission further into the pure "blue" region; this results in highly efficient phosphorescence and renders 3 particularly attractive for application in blue OLED devices.