Application of ultraviolet-visible spectroscopy coupled with support vector regression for the quantitative detection of thiamethoxam in tea.

A model combining UV-visible (UV-Vis) spectroscopy and support vector regression (SVR) for the quantitative detection of thiamethoxam in tea is proposed. First, each original UV-Vis spectrum in the sample set is decomposed into some intrinsic mode functions (IMFs) and a residual via ensemble empirical mode decomposition. Next, the decomposed IMFs are reconstructed into high-frequency and low-frequency matrices, and the residuals are combined into a trend matrix. Then, the SVR is used to build regression sub-models between each matrix and the content of thiamethoxam in tea. Finally, the combination model is established by a weighted average of the sub-models. The prediction results are compared with SVR and SVR coupled with several preprocessing methods, and the results demonstrate the superiority of the proposed approach in the quantitative detection of thiamethoxam in tea.

Numerical investigation of plasmon sensitivity and surface-enhanced Raman scattering enhancement of individual TiN nanosphere multimers.

Titanium nitride (TiN) nanoparticles have recently been considered as potential candidate plasmonic materials; such materials support localized surface plasmon resonances (LSPRs) and show excellent thermal stability with a high melting point. The electromagnetic (EM) field coupling and gap distance between components of individual TiN nanosphere multimers are critical parameters affecting their plasmonic sensitivity and surface-enhanced Raman scattering (SERS) performance, both of which are numerically investigated by the finite element method. It is demonstrated that the fractional shifts of both the dipolar LSPR wavelength [Formula: see text] and the refractive index sensitivity factor S follow the universal 'plasmon ruler' behavior, which is explained well in terms of EM field distribution. The response of the obtained S to [Formula: see text] is also presented and elucidated in terms of the optical response of the dielectric constants of TiN. The maximum S and SERS enhancement (excited by three normally available lasers in experiments) are also predicted; both are comparable to the values for Au dimeric nanoparticles. The present work holds great promise for the development of non-noble metal plasmonic materials in both SERS and plasmonic sensing applications.

Design of a hybrid on-chip waveguide with giant backward stimulated Brillouin scattering.

On-chip waveguides on insulator with high stimulated Brillouin gain have wide potential application prospects in the field of nanophotonic structures. We propose a new on-chip hybrid silicon-chalcogenide slot waveguide structure consisting of a chalcogenide As2S3 rectangle core with an air slot and a wrapping layer of silicon. In the new hybrid waveguide, the high radiation pressure and electrostriction force, determined by pump and Stokes optical waves, and the acoustic displacement, determined by acoustic wave, can be achieved by adjusting the dimensions of rectangle core, the thickness of wrapping layers and the width of air slot. Therefore, a strong optomechanical coupling between high radiation pressure and transverse acoustic displacement will be generated. In such a way, a nonlinear gain for backward stimulated Brillouin scattering can be theoretically achieved with a high gain coefficient of 2.88×104 W-1m-1. The enhanced gain coefficient in the proposed waveguide is around 2.4 times as that in an on-chip silicon-chalcogenide hybrid slot waveguide on insulator without the wrapping layer. The Stokes amplification reaches 85.7 dB with the waveguide length of 2.5 cm. Therefore, this method provides a new idea to design nanophotonic waveguides for giant backward stimulated Brillouin scattering.

Optimal geometry parameter for plasmonic sensitivities of individual Au nanopoarticle sensors.

The shape, aspect ratio and size are key parameters governing the plasmon sensitivities of individual Au nanoparticle bio/chemical sensors. It is crucial to unveil the general geometry parameters to optimize their corresponding sensitivity applications. In this work, the geometry-dependent refractive-index sensitivity factor (S) and figure of merit (FOM) of individual Au nanoparticle sensors (including a nanodisc, nanorod, nanoellipsoid and hexagonal nanoplate) are numerically investigated by discrete dipole approximation (DDA). S is revealed to increase quadratically/linearly with aspect ratio, while FOM reaches a maximum at an optimized aspect ratio of about 3.0/8.0 for the studied prolate/oblate nanoparticles, respectively, reflecting their shapes and aspect ratios and, hence, their size effects. However, their responses to shape factors are shown to follow nearly the same trend regardless of their different detailed geometries, demonstrating that their shape factors provide the general geometry parameters governing the plasmon sensitivities of the concerned individual Au nanoparticle sensors. This can be analytically explained well under dipolar localized surface plasmon resonance (LSPR) conditions. Their optimal FOM is predicted to be about 12.5 RIU-1 at a shape factor of 10.5; the underlying reason for this is analytically discussed as well. The obtained results in this work are believed to hold great promise for choosing appropriate nanoparticle geometry parameters for individual Au nanoparticle LSPR-based bio/chemical sensor design and applications as well as to access the corresponding optimal geometry parameters and FOM simultaneously.

Using silver nanowire antennas to enhance the conversion efficiency of photoresponsive DNA nanomotors.

Plasmonic near-field coupling can induce the enhancement of photoresponsive processes by metal nanoparticles. Advances in nanostructured metal synthesis and theoretical modeling have kept surface plasmons in the spotlight. Previous efforts have resulted in significant intensity enhancement of organic dyes and quantum dots and increased absorption efficiency of optical materials used in solar cells. Here, we report that silver nanostructures can enhance the conversion efficiency of an interesting type of photosensitive DNA nanomotor through coupling with incorporated azobenzene moieties. Spectral overlap between the azobenzene absorption band and plasmonic resonances of silver nanowires increases light absorption of photon-sensitive DNA motor molecules, leading to 85% close-open conversion efficiency. The experimental results are consistent with our theoretical calculations of the electric field distribution. This enhanced conversion of DNA nanomotors holds promise for the development of new types of molecular nanodevices for light manipulative processes and solar energy harvesting.

Diaqua-bis-(hydrogen tartrato)cobalt(II) dihydrate.

The title complex, [Co(C(4)H(5)O(6))(2)(H(2)O)(2)]·2H(2)O, contains a Co(II) ion, two single deprotonated tartrate anions, two coordinated water mol-ecules and two lattice water mol-ecules. The coordination geometry of the Co(II) ion is a distorted octa-hedron with two O atoms from two coordinated water mol-ecules occupying cis positions in the equatorial plane and four O atoms from two hydrogen tartrate ions occupying the remaining positions. In the crystal, inter-molecular O-H⋯O hydrogen bonds link the mol-ecules into a three-dimensional network.

Diaqua-bis-(5-carb-oxy-1H-imidazole-4-carboxyl-ato-κN,O)iron(II).

In the title compound, [Fe(C(5)H(3)N(2)O(4))(2)(H(2)O)(2)], the Fe(II) ion lies on an inversion centre and is coordinated by two N and two O atoms from two 5-carb-oxy-1H-imidazole-4-carboxyl-ate ligands and two water mol-ecules in a distorted octa-hedral geometry. An intra-molecular O-H⋯O hydrogen bond occurs. In the crystal, inter-molecular N-H⋯O and O-H⋯O hydrogen bonds form a three-dimensional network, which consolidates the packing.

5-Carb-oxy-2-isopropyl-1H-imidazol-3-ium-4-carboxyl-ate monohydrate.

In the title compound, C(8)H(10)N(2)O(4)·H(2)O, the imidazole N atom is protonated and one of the carboxyl-ate groups is deprotoned, forming a zwitterion. An intra-molecular O-H⋯O hydrogen bond occurs. The crystal structure is stabilized by inter-molecular N-H⋯O and O-H⋯O hydrogen bonds. In addition, inter-molecular N-H⋯O and O-H⋯O hydrogen bonds link the mol-ecules into two-dimensional networks parallel to (10[Formula: see text]).

Improved optical properties of perovskite solar cells by introducing Ag nanopartices and ITO AR layers.

Embedded noble metal nanostructures and surface anti-reflection (AR) layers affect the optical properties of methylammonium lead iodide (CH3NH3PbI3) perovskite solar cells significantly. Herein, by employing a combined finite element method and genetic algorithm approach, we report five different types of CH3NH3PbI3 perovskite solar cells by introducing embedded Ag nanoparticles within the CH3NH3PbI3 layer and/or top ITO cylinder grating as an AR layer. The maximum photocurrent was optimized to reach 23.56 mA/cm2, which was 1.09/1.17 times higher than Tran's report/ flat cases. It is also comparable with values (23.6 mA/cm2) reported in the literature. The calculations of the electric field and charge carrier generation rate of the optimized solar cell further confirms this improvement than flat cases. It attributes to the synergistic effect of the embedded Ag nanoparticles and ITO AR layer. The results obtained herein hold great promise for future boosting the optical efficiency of perovskite solar cells.

Site-selective localization of analytes on gold nanorod surface for investigating field enhancement distribution in surface-enhanced Raman scattering.

Understanding detailed electric near-field distributions around noble metal nanostructures is crucial to the rational design of metallic substrates for maximizing surface-enhanced Raman scattering (SERS) efficiency. We obtain SERS signals from specific regions such as the ends, the sides and the entire surfaces of gold nanorod by chemisorbing analytes on the respective areas. Different SERS intensities from designated surfaces reflect their electric near-field intensities and thus the distributions. Our experimental results show that approximately 65% of the SERS enhancement emanated from the ends of gold nanorods which occupies only 28% of the total surface area, quantitatively exhibiting the strongly localized electric field around the ends. The reliability and generality of the investigation is confirmed by employing analytes with different chemical characteristics: positively and negatively charged, neutral, hydrophobic and hydrophilic ligands, which are selectively adsorbed on the different sites. Numerical simulations of the electric near-field distributions around the nanorod are in well agreement with our experimental results. In addition, we observed that the SERS intensities of colloidal gold nanospheres are independent of surface areas being functionalized by analytes, indicating a homogenous electric near-field distribution around gold nanospheres.

Effect of near-field coupling on far-field inelastic scattering imaging of gold nanoparticles.

The optical near-field enhancement induced by coupling between noble nanoparticles and the substrate has been studied by a far-field imaging method. The longitudinal mode of the incident laser is revealed to contribute to the coupling. The far-field images of individual gold nanoparticles exhibit a peanut-shaped pattern; these were constructed by the intensity of inelastically scattered light. The coupling between gold nanoparticles and the silicon substrate leads to the patterned image. By tuning the separation between the gold nanoparticles and substrate using SiO(2) layers of different thickness, the coupling efficiency decreases with the thickness of the SiO(2) layer.