The surface-enhanced Raman scattering (SERS) effect was critically dependent on the shape of the plasmonic nanostructures. It still remains a significant challenge in exploring the correlation between the SERS effect and the shape of nanostructures. Here, the polarized SERS combined with finite difference time domain (FDTD) calculation was developed to elucidate the origination of the SERS effect on an anisotropic spindle-shaped Fe 2 O 3 @Au nanoparticle. The surface enhancement factor for spindle-shaped Fe 2 O 3 @Au nanoparticles was estimated to be about sixorders by using pyridine as model molecules. A dramatic variation in SERS effect was observed by changing the excitation polarization direction. The maximum SERS intensity was detected when the excitation polarization was parallel to the long axes of Fe 2 O 3 @Au nanoparticles, while the minimum intensity was observed at the perpendicular orientation. The remarkable polarization-dependent SERS effects can be attributed to the local enhanced electric field that strongly depends on the polarization direction. The theoretical simulation based on the FDTD method was performed to evaluate the distribution of a local electromagnetic field on Fe 2 O 3 @Au single nanoparticles. It was in good agreement with the experimental results. This strategy provided deeper insight into the distribution of the SERS effect on a single anisotropic nanoparticle.
The rapid recombination of carriers on plasmon metal nanoparticles leads to relatively low efficiency of traditional photocatalysts. The combination of a metal and a semiconductor allows to the separation of hot electrons and holes to improve photocatalytic efficiency. In this study, Au nanoparticles were integrated with semiconductor TiO2 nanoparticles of different sizes to improve the photocatalytic activity. Various techniques have been developed to study the mechanism of catalytic activity, the significance of band bending in the space-charge region within metal–semiconductor nanocomposites, and the built-in electric field. The results provide theoretical and experimental evidence for the design of a high-performance surface plasmon resonance (SPR) photocatalyst. To reveal the interface band structure, surface-enhanced Raman spectroscopy (SERS) was employed to analyze the band structure of the TiO2–metal composites. This approach was based on the electrochemical Stark effect and a molecular probe strategy, combined with X-ray photoelectron spectroscopy (XPS), Electrochemical impedance spectroscopy (EIS), and other techniques at the molecular level. The results demonstrated that charge transfer occurred spontaneously between the Au nanoparticles and TiO2, and that the TiO2–metal interface constitutes a Schottky barrier. Moreover, the size of the TiO2 nanoparticles affects the degree of band bending. Optimal state matching was achieved with TiO2 (60 nm)–Au, improving the photocatalytic activity of the nanocomposite. The photocatalytic coupling reaction of p-aminothiophenol (PATP) acted as a probe to study the catalytic performance of TiO2–metal nanocomposites. The results revealed that the introduction of TiO2 improves the SPR catalytic activity of Au, mainly through the efficient separation of electrons and holes at the TiO2–metal interface.
Astrocytes are the most common glial type in the central nervous system (CNS). They play pivotal roles in neurophysiological and neuropathological processes. Mounting evidence indicates that astrocytes may act as neural stem cells and contribute to adult neurogenesis. In previous reports, freshly isolated O-2A progenitors were shown to revert to neural stem-like cells (NSLCs) when cultured with a serum-containing glial medium or bone morphogenic proteins (BMPs) for 3 days and with basic fibroblast growth factor (bFGF) consecutively. NSLCs possess self-renewal and multipotential capacities that can give rise to neurons and glial cells, which suggests that they have stem cell-like properties. However, the underlying molecular mechanisms and cell fate commitment when exposed to a neural conditioned medium remain obscure. In this study, we demonstrated that NSLCs grown in the serum-containing neurobasal medium can differentiate into induced neural-like cells (iNLCs). It was noteworthy that astroglia mixed in these cells, particularly in iNLCs, were gradually replaced by neural phenotypes during this glia-neuron conversion. Remarkably, these glial cells can maintain high levels of proliferation and self-renewal ability by activating the NF-κB and MAPK signals. Finally, we found that Notch, STAT3, autophagy, bHLH and Wnt signals appear to be critical modulators of these intricate events. Altogether, these data demonstrate that O-2A lineage astroglia can function as neural stem cells and display neurogenic plasticity. Dissecting the regulatory pathways involved in these processes is essential to the understanding of glial cell fate and its precise functions. This finding may foster a better understanding of astrocytic heterogeneity and lead to innovative ways to readily apply stem-like astroglia cells as candidate cell sources for neural repair.
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