We describe plasmonic interactions in suspended gold bowtie nanoantenna leading to strong electromagnetic field (E) enhancements. Surface-enhanced Raman scattering (SERS) was used to demonstrate the performance of the nanoantenna. In addition to the well-known gap size dependence, up to 2 orders of magnitude additional enhancement is observed with elevated bowties. The overall behavior is described by a SERS enhancement factor exceeding 10(11) along with an anomalously weak power law dependence of E on the gap size in a range from 8 to 50 nm that is attributed to a plasmonic nanocavity effect occurring when the plasmonic interactions enter a strongly coupled regime.

Hydrazone derivatives possess potential antitumor activities based on modulation of the iron metabolism in cancer cell. A novel hydrazone, N'-(2,4-dimethoxybenzylidene)-2-hydroxybenzohydrazide (DBH), has been synthesized and characterized, which is an analogue of 311 possessing potent anticancer activity. The interactions between DBH and bovine serum albumin (BSA) have been investigated systematically by fluorescence, molecular docking, circular dichroism (CD), UV-vis absorption, and electrochemical impedance spectroscopy (EIS) methods under physiological conditions. The fluorescence quenching observed is attributed to the formation of a complex between BSA and DBH, and the reverse temperature effect of the fluorescence quenching has been found and discussed. The primary binding pattern is determined by hydrophobic interaction occurring in Sudlow's site I of BSA. DBH could slightly change the secondary structure and induce unfolding of the polypeptides of protein. An average binding distance of ~4.0 nm has been determined on the basis of the Förster resonance energy theory (FRET). The effects of iron on the system of DBH-BSA have also been investigated. It is found that iron could compete against BSA to bind DBH. All of these results are supported by a docking study using a BSA crystal model. It is shown that DBH can efficiently bind with BSA and be transported to the focuses needed. Subsequent antitumor test and detailed anticancer mechanism are undergoing in our lab.

The surface plasmon resonances of gold contour bowtie nanostructures were simulated in the present study. The local electromagnetic field enhancement and the resonance wavelength for different dimensions of contour bowtie antennas with various contour thicknesses were investigated to find the critical conditions to induce additional enhancement compared to the solid bowtie antenna. Both the phase of the electric field and the bound surface charge distribution on the surface of the contour bowtie were studied to characterize the coupled plasmon configurations of the contour bowtie antenna. Also, a model was proposed to explain the resonance and hybridization behavior in the contour bowtie nanoantenna, and it was verified by examining the phase of the electric field in the polarization direction.

The aim of this study was to investigate the effect of gold nanoparticle (Au NP)-induced surface plasmons on the performance of organic photovoltaics (OPVs) that consist of copper phthalocyanine and fullerene as the active materials. The photon absorption can be enhanced by immobilization of surfactant-stabilized Au NPs on a self-assembled monolayer-modified indium tin oxide (ITO) electrode, and thus, the photocurrent as well as the power conversion efficiency (PCE) of these OPVs can be improved. Varying the density of the immobilized Au NPs in the devices provided no significant variation in the charge mobility but it did enhance the photocurrent. In addition, device simulation results demonstrated that the improvement in photocurrent was due to the enhancement of light absorption and the increase in charge separation, which was facilitated by the Au NPs. Overall, we attributed the improvement in PCE of OPVs to a localized surface plasmon resonance effect generated by the Au NPs.

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In this study, we developed a facile technique to fabricate a surface-enhanced Raman scattering (SERS) substrate. The technique involves self-assembling monodispersive SiO 2 spheres on silicon wafer, then coating with a thin Ag film to form a SERS substrate comprised of a Ag coated monolayer array of SiO 2 spheres. The substrate can detect minute amounts of organic dye. By optimizing the fabrication process, including controlling the size of the SiO 2 spheres, the distribution of the SiO 2 spheres on the silicon wafer, and the thickness of the Ag film, a dramatic increase in the enhancement of Raman scattering signals by surface plasmon resonance can be achieved. The enhancement of Raman scattering is closely correlated to the absorption peak of the organic dye and the excitation wavelength of the Raman system. A 40 000-fold enhancement has been observed for a substrate prepared with 350 nm SiO 2 spheres self-assembled on silicon wafer and coated with a 150 nm Ag layer. Through experimental and theoretical calculations (FDTD), such a strong signal intensity originates from the closeness between the absorption peak of the organic dye and the Raman excitation wavelength occurring at the hot spots of the SERS substrate. The high sensitivity, low cost and quick response provided by this type of SERS substrate are useful for the design and fabrication of functional devices and sensors.

The discovery of single-molecule sensitivity via surface-enhanced Raman scattering on resonantly excited noble metal nanoparticles has brought an increasing interest in its applications to the molecule detection and identification. Periodic gold bowtie nanostructures have recently been shown to give a large enhancement factor sufficient for single molecule detection. In this work, we simulate the plasmon resonance for periodic gold bowtie nanostructures. The difference between the dipole and the quadrupole resonances is described by examining the magnitude and phase of electric field, the bound surface charge, and the polarization. The gap size dependence of the field enhancement can be interpreted by considering cavity field enhancement. Also, additional enhancement is obtained through the long-range collective photonic effect when the bowtie array periodicity matches the resonance wavelength.

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