In situ identification of crystal facet-mediated chemical reactions on tetrahexahedral gold nanocrystals using surface-enhanced Raman spectroscopy

National Basic Research Program of China [2010CB934700]; National Science Foundation of China [50725208, 20973019, 51002007, 21303006]Direct monitoring of a metal-catalyzed reaction by surface-enhanced Raman scattering (SERS) is always a challenging issue as it needs bifunctional metal structures that have plasmonic properties and also act as catalysts. Here we demonstrate that the tetrahexahedral (THH) gold nanocrystals (Au NCs) with exposed {520} facets give highly enhanced Raman signals from molecules at the interface, permitting in situ observation of chemical transformation from para-aminothiophenol (PATP) to 4,4'-dimercaptoazobenzene (DMAB). The origin of the intense SERS signals of DMAB is carefully investigated based on the comparison of the SERS spectra of PATP obtained with both the THH Au NCs and the Au nanospheres with the exposed {111} facets. It is elucidated that the high-index {520} facet rather than the localized surface plasmons of the THH Au NCs plays a key role in producing a high yield of the product DMAB which is accompanied by the selective enhancement of the characteristic Raman signals

Internal Noise-Sustained Circadian Rhythms in a Drosophila Model

AbstractCircadian rhythmic processes, mainly regulated by gene expression at the molecular level, have inherent stochasticity. Their robustness or resistance to internal noise has been extensively investigated by most of the previous studies. This work focuses on the constructive roles of internal noise in a reduced Drosophila model, which incorporates negative and positive feedback loops, each with a time delay. It is shown that internal noise sustains reliable oscillations with periods close to 24h in a region of parameter space, where the deterministic kinetics would evolve to a stable steady state. The amplitudes of noise-sustained oscillations are significantly affected by the variation of internal noise level, and the best performance of the oscillations could be found at an optimal noise intensity, indicating the occurrence of intrinsic coherence resonance. In the oscillatory region of the deterministic model, the coherence of noisy circadian oscillations is suppressed by internal noise, while the period remains nearly constant over a large range of noise intensity, demonstrating robustness of the Drosophila model for circadian rhythms to intrinsic noise. In addition, the effects of time delay in the positive feedback on the oscillations are also investigated. It is found that the time delay could efficiently tune the performance of the noise-sustained oscillations. These results might aid understanding of the exploitation of intracellular noise in biochemical and genetic regulatory systems

SYNCHRONIZATION AND ANTICOHERENCE RESONANCE OF BURSTING NEURONS WITH SPATIALLY CORRELATED NOISE

We investigate synchronization of bursting neurons, caused by spatially correlated noise, consisting of a common Guassian noise and a local one. It is found that the degree of noise-induced synchronization between identical neurons increases with both the noise intensity and noise correlation. As for non-identical neurons, it is demonstrated that the degree of phase synchronization decreases monotonously with the noise intensity for partially correlated noise, but the degree undergoes a minimum with the common noise intensity increasing. An interpretation is provided for the noise-induced synchronization between identical neurons by investigating noise-modulated spike train pattern in a single neuron. In addition, the coherence of spike train is minimized at some noise intensities. </jats:p