On the Mechanism of Negative Differential Resistance in Ferrocenylundecanethiol Self-Assembled Monolayers

Negative differential resistance (NDR) peaks in the current−voltage characteristics of ferrocenylundecanethiol self-assembled monolayers are not reversible. The peaks turn to smoothly increasing currents as oxygen is removed from the system, indicating that NDR arises from the reaction of an energetic charged species with ambient oxygen

In Vitro Selection of Histone H4 Aptamers for Recognition Imaging Microscopy

Recognition imaging microscopy is an analytical technique used to map the topography and chemical identity of specific protein molecules present in complex biological samples. The technique relies on the use of antibodies tethered to the cantilever tip of an AFM probe to detect cognate antigens deposited onto a mica surface. Despite the power of this technique to resolve single molecules with nanometer-scale spacing, the recognition step remains limited by the availability of suitable quality antibodies. Here we report the in vitro selection and recognition imaging of anti-histone H4 aptamers. In addition to identifying aptamers to highly basic proteins, these results suggest that aptamers provide an efficient, cost-effective route to highly selective affinity reagents for recognition imaging microscopy

Evolution of a Histone H4-K16 Acetyl-Specific DNA Aptamer

Evolution of a Histone H4-K16 Acetyl-Specific DNA Aptame

Solution Synthesis of Ultrathin Single-Crystalline SnS Nanoribbons for Photodetectors <i>via</i> Phase Transition and Surface Processing

We report the solution-phase synthesis and surface processing of ∼2–5 μm long single-crystalline IV–VI tin(II) sulfide (SnS) ultrathin nanoribbons, with thicknesses down to 10 nm, and their use in single nanoribbon based photodetectors. The SnS nanoribbons grow <i>via</i> a metastable-to-stable phase transition from zinc blende (ZB) nanospheres to orthorhombic nanoribbons; dual-phase intermediate heterostructures with zinc blende nanosphere heads and orthorhombic nanoribbon tails were observed. Exchange of long, insulating organic oleylamine ligands by short, inorganic HS^– ligands converts the organic SnS nanoribbons into completely inorganic, hydrophilic structures. Field-effect transistor (FET) devices were made from single SnS nanoribbons, both before and after ligand exchange, which exhibit p-type semiconductor behavior. The SnS single nanoribbon based photodetector devices showed highly sensitive and rapid photocurrent responses to illumination by blue, green, and red light. The switching behavior of photocurrent generation and annihilation is complete within approximately 1 ms and exhibits high photoconductivity gains (up to 2.3 × 10⁴) and good stability. The ON/OFF ratio of the photodetector can be engineered to 80 (4 nA/50 pA) using a small drain current (10 mV) for the all inorganic SnS nanoribbons. This work paves the way for the colloidal growth of low-cost, environmentally benign, single-crystalline narrow band gap semiconductor nanostructures from abundant elements for applications in photodetectors and other nanoscale devices

Electrophoretic Deformation of Individual Transfer RNA Molecules Reveals Their Identity

It has been hypothesized that the ribosome gains additional fidelity during protein translation by probing structural differences in tRNA species. We measure the translocation kinetics of different tRNA species through ∼3 nm diameter synthetic nanopores. Each tRNA species varies in the time scale with which it is deformed from equilibrium, as in the translocation step of protein translation. Using machine-learning algorithms, we can differentiate among five tRNA species, analyze the ratios of tRNA binary mixtures, and distinguish tRNA isoacceptors

Electronic Decay Constant of Carotenoid Polyenes from Single-Molecule Measurements

The conductance of carotenoid polyenes chemically bound at each end to gold contacts has been measured for single molecules containing 5, 7, 9, and 11 carbon−carbon double bonds in conjugation. The electronic decay constant, β, is determined to be 0.22 ± 0.04 Å-1, in close agreement with the value obtained from first principles simulations (0.22 ± 0.01 Å-1). The absolute values of the molecular conductance are within a factor of 3 of those calculated from first principles. The small value of β demonstrates that conductivity drops off only slowly with chain length, confirming that carotenoid conjugated chains are relatively good molecular “wires”