Multiple sensor systems are designed by varying aza-crown ether moiety in silicon quantum dots (SiQDs) for detecting individual Mg2+, Ca2+, and Mn2+ metal ions with significant selectivity and sensitivity. The detection limit of Mg2+, Ca2+, and Mn2+ can reach 1.81, 3.15, and 0.47 μM, respectively. Upon excitation of the SiQDs which are coordinated with aza-crown ethers, the photoinduced electron transfer (PET) takes place from aza-crown ether moiety to the valence band of SiQDs core such that the reduced probability of electron-hole recombination may diminish the subsequent fluorescence. The fluorescence suppression caused by such PET effect will be relieved after selective metal ion is added. The charge-electron binding force between the metal ion and aza-crown ether hinders the PET and thereby restores the fluorescence of SiQDs. The design of sensor system is based on the fluorescence "turn-on" of SiQDs while in search of the appropriate metal ion. For practical application, the sensing capabilities of metal ions in the live cells are performed and the confocal image results reveal their promising applicability as an effective and nontoxic metal ion sensor. © 2016 American Chemical Society.

Hexapole oriented 2-bromobutane is photodissociated and detected by a slice-ion-imaging technique at 234 nm. The laser wavelength corresponds to the C - Br bond breaking with emission of a Br atom fragment in two accessible fine-structure states: the ground state Br (2P3/2) and the excited state Br (2P1/2), both observable separately by resonance-enhanced multiphoton ionization (REMPI). Orientation is evaluated by time-of-flight measurements combined with slice-ion-imaging. © 2016 Author(s).

This paper aims at discussing new facets on stereodynamical behaviors in chemical reactions, i.e. the effects of molecular orientation and alignment on reactive processes. Further topics on macroscopic processes involving deviations from Arrhenius behavior in the temperature dependence of chemical reactions and chirality effects in collisions are also discussed. © 2015 AIP Publishing LLC.

n/a

Self-assembly of atoms or molecules on a crystal surface is considered one of the most promising methods to create molecular devices. Here we report a stepwise self-assembly of C60 molecules into islands with unusual shapes and preferred sizes on a gold–indium-covered Si(111) surface. Specifically, 19-mer islands prefer a non-compact boomerang shape, whereas hexagonal 37-mer islands exhibit extraordinarily enhanced stability and abundance. The stepwise self-assembly is mediated by the moiré interference between an island with its underlying lattice, which essentially maps out the adsorption-energy landscape of a C60 on different positions of the surface with a lateral magnification factor and dictates the probability for the subsequent attachment of C60 to an island’s periphery. Our discovery suggests a new method for exploiting the moiré interference to dynamically assist the self-assembly of particles and provides an unexplored tactic of engineering atomic scale moiré magnifiers to facilitate the growth of monodispersed mesoscopic structures.

Various surface passivations for silicon nanowires have previously been investigated to extend their stability and utility. However, the fundamental mechanisms by which such passivations alter the electronic properties of silicon nanowires have not been clearly understood thus far. In this work, we address this issue through first-principles calculations on fluorine, methyl and hydrogen passivated [110] and [111] silicon nanowires. Comparing these results, we explain how passivations may alter the electronic structure through quantum confinement and strain and demonstrate how silicon nanowires may be modelled by an infinite circular quantum well. We also discuss why [110] nanowires are more strongly influenced by their surface passivation than [111] nanowires.

n/a

n/a

ABSTRACT. The importance of guanine-quadruplex (G4) is not only in protecting the ends of chromosomes for human telomeres but also in regulating gene expression for several gene promoters. However, the existence of G4 structures in living cells is still in debate. A fluorescent probe, 3,6-bis(1-methyl-2-vinylpyridinium) carbazole diiodide (o-BMVC), for differentiating G4 structures from duplexes is characterized. o-BMVC has a large contrast in fluorescence decay time, binding affinity, and fluorescent intensity between G4 structures and duplexes, which makes it a good candidate for probing G4 DNA structures. The fluorescence decay time of o-BMVC upon interaction with G4 structures of telomeric G-rich sequences is ∼2.8  ns and that of interaction with the duplex structure of a calf thymus is ∼1.2  ns. By analyzing its fluorescence decay time and histogram, we were able to detect one G4 out of 1000 duplexes in vitro. Furthermore, by using fluorescence lifetime imaging microscopy, we demonstrated an innovative methodology for visualizing the localization of G4 structures as well as mapping the localization of different G4 structures in living cells.