Reaction pathway and free-energy barrier for reactivation of dimethylphosphoryl-inhibited human acetylcholinesterase

Ag-decorated TiO₂ nanograss for 3D SERS-active substrate with visible light self-cleaning and reactivation

The production of SERS-active substrates which are uniform, sensitive, reproducibile and durable still remains an important issue. Here, we report a strategy for the fabrication of a large-area Ag-decorated TiO₂ nanograss SERS-active substrate by a simple solvothermal approach combined with Ag evaporation. The nanograss consists of dense rutile TiO₂ nanorods of about 5 nm in diameter and the decorated Ag nanoparticles are an average of 8 nm in diameter. The Ag protrusions and gaps between them contribute to three dimensional SERS "hot spots" which can be modulated by simply controlling the Ag evaporating parameters. The Ag-decorated TiO₂ substrate is highly efficient in detecting rhodamine 6G (R6G) and 4-aminothiophenol (4-ATP) molecules and has good homogeneity. An obvious red shift and even high enhancement of b₂ vibration mode were observed in detecting 4-ATP due to the effective charge transfer from the Ag atoms to sulfur atoms. The Ag-decorated TiO₂ substrate can be easily self-cleaned and reactivated by visible light irradiation without obvious degeneration of SERS signals. Our results demonstrate that the Ag-decorated TiO₂ substrate with high and homogeneous SERS activity has potential feasibility as a sensitive SERS probe.

Ordered array of gold semishells on TiO2 spheres: an ultrasensitive and recyclable SERS substrate

Ordered array of Au semishells on TiO(2) spheres with controlled size are prepared by combining the nanosphere self-assembly and atomic layer deposition (ALD). This ordered 2-D structure with designed array of metal nanogaps can be used as an ultrasensitive surface-enhanced Raman scattering (SERS) substrate with high reproducibility and stability. More importantly, the SERS substrates are recyclable, as enabled by their self-cleaning function due to the TiO(2) photocatalytic degradation of the target molecules. The high SERS sensitivity and recyclability are demonstrated by the detection of Rhodamine 6G (R6G) and brilliant cresyl blue (BCB) molecules. As both the nanosphere lithography and ALD are scalable processes, such 2-D ordered substrates may find applications in chemical sensing.

Intra-particle coupling and plasmon tuning of multilayer Au/dielectric/Au nanocrescents adhered to a dielectric cylinder

A 3D numerical study on surface plasmon resonance is presented for a multilayer Au/dielectric/Au nanocrescent structure adhered to a dielectric cylinder. Investigations are carried out on the structure’s coupling modes, local field enhancement (LFE) and plasmon tuning capability. The cavity coupling via the cylinder is found to be dominant in tuning the plasmon wavelength. This provides the possibility of tailoring the device's plasmon band by adjusting the cylinder’s size and material. By using a cylinder with higher permittivity, the plasmon peak significantly shifts to the near- or mid-infrared regime without increasing the size of the crescents, thus increase of radiation loss can be fully avoided. Extra crescent layers can also be added to the structure to induce intra-particle couplings among Au crescents and enlarge the areas of the hot-spots, without shifting the plasmon band. The LFE of the multiple-layer structure is shown to be dramatically increased through the intra-particle coupling among the Au crescents, compared with a single layer Au nanocrescent structure. Further increase of LFE can be achieved by substituting semiconductors for the dielectrics in the structure due to the charge transport at metal-semiconductor interfaces.

Photodeposition of Ag or Pt onto TiO2 nanoparticles decorated on step edges of HOPG

Ordered linear arrays of titanium dioxide nanoparticles were fabricated on highly oriented pyrolytic graphite utilizing a step edge decoration method. Ag- or Pt-based nanoparticles were then photodeposited onto the titanium dioxide nanoparticles (∼18 nm) to simultaneously verify photocatalytic activity and to demonstrate a viable route to load the titanium dioxide nanoparticles with metals. Scanning electron microscopy and atomic force microscopy determined the morphology, size, and distribution of the particles. X-ray photoelectron spectroscopy confirmed the identity of the titanium dioxide nanoparticles, and transmission electron microscopy showed that some of the particles were rutile single crystals. Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy determined the chemical composition of the metal-based nanoparticles selectively loaded on the linear arrays of titanium dioxide nanoparticles.

Surface-enhanced Raman spectroscopy and homeland security: a perfect match?

This Nano Focus article reviews recent developments in surface-enhanced Raman spectroscopy (SERS) and its application to homeland security. It is based on invited talks given at the "Nanorods and Microparticles for Homeland Security" symposium, which was organized by one of the authors and presented at the 238th ACS National Meeting and Exhibition in Washington, DC. The three-day symposium included approximately 25 experts from academia, industry, and national laboratories and included both SERS and non-SERS approaches to detection of chemical and biological substances relevant to homeland security, as well as fundamental advances. Here, we focus on SERS and how it is uniquely positioned to have an impact in a field whose importance is increasing rapidly. We describe some technical challenges that remain and offer a glimpse of what form solutions might take.